Research articles

2019


  • GHz nanomechanical resonator in an ultraclean suspended graphene p-n junction
    Minkyung Jung, P. Rickhaus, S. Zihlmann, A. Eichler, P. Makk, and C. Schönenberger.
    Nanoscale, 11:4355, feb 2019. [DOI] arXiv:1812.06412
    [Abstract]

    We demonstrate high-frequency mechanical resonators in ballistic graphene p–n junctions. Fully suspended graphene devices with two bottom gates exhibit ballistic bipolar behavior after current annealing. We determine the graphene mass density and built-in tension for different current annealing steps by comparing the measured mechanical resonant response to a simplified membrane model. We consistently find that after the last annealing step the mass density compares well with the expected density of pure graphene. In a graphene membrane with high built-in tension, but still of macroscopic size with dimensions 3 × 1 micrometer^2, a record resonance frequency of 1.17 GHz is observed after the final current annealing step. We further compare the resonance response measured in the unipolar with the one in the bipolar regime. Remarkably, the resonant signals are strongly enhanced in the bipolar regime. This enhancement is caused in part by the Fabry-Pérot resonances that appear in the bipolar regime and possibly also by the photothermoelectric effect that can be very pronounced in graphene p–n junctions under microwave irradiation.


  • New generation of Moiré superlattices in doubly aligned hBN/graphene/hBN heterostructures
    L. Wang, S. Zihlmann, Ming-Hao Liu, P. Makk, K. Watanabe, T. Taniguchi, A. Baumgartner, and C. Schönenberger.
    Nano Letters, feb 2019. [DOI] arXiv:1812.10031
    [Abstract]

    The specific rotational alignment of two-dimensional lattices results in a moiré superlattice with a larger period than the original lattices and allows one to engineer the electronic band structure of such materials. So far, transport signatures of such superlattices have been reported for graphene/hBN and graphene/graphene systems. Here we report moiré superlattices in fully hBN encapsulated graphene with both the top and the bottom hBN aligned to the graphene. In the graphene, two different moiré superlattices form with the top and the bottom hBN, respectively. The overlay of the two superlattices can result in a third superlattice with a period larger than the maximum period (\SI{14}{nm}) in the graphene/hBN system, which we explain in a simple model. This new type of band structure engineering allows one to artificially create an even wider spectrum of electronic properties in two-dimensional materials.


  • Non-equilibrium properties of graphene probed by superconducting tunnel spectroscopy
    S. Zihlmann, P. Makk, S. Castillas, J. Gramich, K. Thodkar, S. Caneva, R. Wang, S. Hofmann, and C. Schönenberger.
    Phys. Rev. B, 99:75419, feb 2019. [DOI] arXiv:1811.08746
    [Abstract]

    We report on non-equilibrium properties of graphene probed by superconducting tunnel spectroscopy. A hexagonal boron nitride (hBN) tunnel barrier in combination with a superconducting Pb contact is used to extract the local energy distribution function of the quasiparticles in graphene samples in different transport regimes. In the cases where the energy distribution function resembles a Fermi-Dirac distribution, the local electron temperature can directly be accessed. This allows us to study the cooling mechanisms of hot electrons in graphene. In the case of long samples (device length L much larger than the electron-phonon scattering length le−ph), cooling through acoustic phonons is dominant. We find a cross-over from the dirty limit with a power law T3 at low temperature to the clean limit at higher temperatures with a power law T4 and a deformation potential of 13..3 eV. For shorter samples, where L is smaller than le−ph but larger than the electron-electron scattering length le−e, the well-known cooling through electron out-diffusion is found. Interestingly, we find strong indications of an enhanced Lorenz number in graphene. We also find evidence of a non-Fermi-Dirac distribution function, which is a result of non-interacting quasiparticles in very short samples

2018


  • Spectroscopy of the superconducting proximity effect in nanowires using integrated quantum dots
    C. Jünger, A. Baumgartner, R. Delagrange, D. Chevallier, S. Lehmann, M. Nilsson, K. A. Dick, C. Thelander, and C. Schönenberger.
    submitted, dec 2018. arXiv:1812.06850
    [Abstract]

    The superconducting proximity effect has been the focus of significant research efforts over many YEARs and has recently attracted renewed interest as the basis of topologically non-trivial states in materials with a large spin orbit interaction, with protected boundary states useful for quantum information technologies. However, spectroscopy of these states is challenging because of the limited spatial and energetic control of conventional tunnel barriers. Here, we report electronic spectroscopy measurements of the proximity gap in a semiconducting indium arsenide (InAs) nanowire (NW) segment coupled to a superconductor (SC), using a spatially separated quantum dot (QD) formed deterministically during the crystal growth. We extract the characteristic parameters describing the proximity gap which is suppressed for lower electron densities and fully developed for larger ones. This gate-tunable transition of the proximity effect can be understood as a transition from the long to the short junction regime of subgap bound states in the NW segment. Our device architecture opens up the way to systematic, unambiguous spectroscopy studies of subgap bound states, such as Majorana bound states.


  • Wideband and on-chip excitation for dynamical spin injection into graphene
    D. I. Indolese, S. Zihlmann, P. Makk, C. Jünger, K. Thodkar, and C. Schönenberger.
    Phys. Rev. Appl., 10:44053, oct 2018. [DOI] arXiv:1806.09356
    [Abstract]

    Graphene is an ideal material for spin transport as very long spin relaxation times and lengths can be achieved even at room temperature. However, electrical spin injection is challenging due to the conductivity mismatch problem. Spin pumping driven by ferromagnetic resonance is a neat way to circumvent this problem as it produces a pure spin current in the absence of a charge current. Here, we show spin pumping into single layer graphene in micron scale devices. A broadband on-chip RF current line is used to bring micron scale permalloy (Ni80Fe20) pads to ferromagnetic resonance with a magnetic eld tunable resonance condition. At resonance, a spin current is emitted into graphene, which is detected by the inverse spin hall voltage in a close-by platinum electrode. Clear spin current signals are detected down to a power of a few milliwatts over a frequency range of 2 GHz to 8 GHz. This compact device scheme paves the way for more complex device structures and allows the investigation of novel materials.


  • Signatures of van Hove singularities probed by the supercurrent in a graphene – hBN superlattice
    D. I. Indolese, R. Delagrange, P. Makk, J. R. Wallbank, K. Wanatabe, T. Taniguchi, and C. Schönenberger.
    Phys. Rev. Lett., 121:137701, sep 2018. [DOI] arXiv:1805.10184
    [Abstract]

    The bandstructure of graphene can be strongly modified when it is aligned with its Boron Nitride substrate. A moiré superlattice forms, which manifests itself by the appearance of new Dirac points, accompanied by van Hove singularities. In this work, we present supercurrent measurements in a Josephson junction made from such a graphene superlattice in the long and diffusive transport regime, where the supercurrent depends on the Thouless energy. We can then estimate the specific density of states of the graphene superlattice from the combined measurement of the critical current and the normal state resistance. The result matches with theoretical predictions and highlights the strong increase of the density of states at the van Hove singularities. By measuring the magnetic field dependence of the supercurrent, we find the presence of edge currents at these singularities. We explain it by the reduction of the Fermi velocity associated with the flat band at the van Hove singularity, which suppresses the supercurrent in the bulk while the electrons at the edge remain less localized, resulting in an edge supercurrent. We attribute this different behavior of the edges to defects or chemical doping.


  • Co-existence of classical snake states and Aharanov-Bohm oscillations along graphene p-n junctions
    Peter Makk, Clevin Handschin, Endre Tovari, Kenji Watanabe, Takashi Taniguchi, Klaus Richter, Ming-Hao Liu, and Christian Schönenberger.
    Phys. Rev. B, 98:35413, july 2018. [DOI] arXiv:1804.02590
    [Abstract]

    Snake states and Aharonov-Bohm interferences are examples of magnetoconductance oscillations that can be observed in a graphene p-n junction. Even though they have already been reported in suspended and encapsulated devices including different geometries, a direct comparison remains challenging as they were observed in separate measurements. Due to the similar experimental signatures of these effects a consistent assignment is difficult, leaving us with an incomplete picture. Here we present measurements on p-n junctions in encapsulated graphene revealing several sets of magnetoconductance oscillations allowing for their direct comparison. We analysed them with respect to their charge carrier density, magnetic field, temperature and bias dependence in order to assign them to either snake states or Aharonov-Bohm oscillations. Furthermore we were able to consistently assign the various Aharonov-Bohm interferences to the corresponding area which the edge states enclose. Surprisingly, we find that snake states and Aharonov-Bohm interferences can co-exist within a limited parameter range


  • Cooper-pair splitting in two parallel InAs nanowires
    Shoji Baba, Christian Jünger, Sadashige Matsuo, Andreas Baumgartner, Yosuke Sato, Hiroshi Kamata, Kan Li, Sören Jeppesen, Lars Samuelson, Hongqi Xu, Christian Schönenberger, and Seigo Tarucha.
    New Journal of Physics, 20:63021, june 2018. [DOI] arXiv:1802.08059
    [Abstract]

    We report on the fabrication and electrical characterization of an InAs double – nanowire (NW) device consisting of two closely placed parallel NWs coupled to a common superconducting electrode on one side and individual normal metal leads on the other. In this new type of device we detect Cooper-pair splitting (CPS) with a sizeable efficiency of correlated currents in both NWs. In contrast to earlier experiments, where CPS was realized in a single NW, demonstrating an intrawire electron pairing mediated by the superconductor (SC), our experiment demonstrates an inter- wire interaction mediated by the common SC. The latter is the key for the realization of zero-magnetic field Majorana bound states, or Parafermions; in NWs and therefore constitutes a milestone towards topological superconductivity. In addition, we observe transport resonances that occur only in the superconducting state, which we tentatively attribute to Andreev Bound states and/or Yu-Shiba resonances that form in the proximitized section of one NW.


  • Blocking-state influence on shot noise and conductance in quantum dots
    M. -C. Harabula, V. Ranjan, R. Haller, G. Fülöp, and C. Schönenberger.
    Phys. Rev. B, 97:115403, mar 2018. [DOI] arXiv:1801.00286
    [Abstract]

    Quantum dots (QDs) investigated through electron transport measurements often exhibit varying, state-dependent tunnel couplings to the leads. Under speci c conditions, weakly coupled states can result in a strong suppression of the electrical current and they are correspondingly called blocking states. Using the combination of conductance and shot noise measurements, we investigate blocking states in carbon nanotube (CNT) QDs. We report negative di erential conductance and super- Poissonian noise. The enhanced noise is the signature of electron bunching, which originates from random switches between the strongly and weakly conducting states of the QD. Negative differential conductance appears here when the blocking state is an excited state. In this case, at the threshold voltage where the blocking state becomes populated, the current is reduced. Using a master equation approach, we provide numerical simulations reproducing both the conductance and the shot noise pattern observed in our measurements.


  • Large spin relaxation anisotropy and valley-Zeeman spin-orbit coupling in WSe2/Gr/hBN heterostructures
    S. Zihlmann, A. W. Cummings, J. H. Garcia, M. Kedves, K. Watanabe, T. Taniguchi, C. Schönenberger, and P. Makk.
    Phys. Rev. B, 97:75434, feb 2018. [DOI] arXiv:1712.05678
    [Abstract]

    Large spin-orbital proximity effects have been predicted in graphene interfaced with a transition metal dichalcogenide layer. Whereas clear evidence for an enhanced spin-orbit coupling has been found at large carrier densities, the type of spin-orbit coupling and its relaxation mechanism remained unknown. We show for the first time an increased spin-orbit coupling close to the charge neutrality point in graphene, where topological states are expected to appear. Single layer graphene encapsulated between the transition metal dichalcogenide WSe2 and hBN is found to exhibit exceptional quality with mobilities as high as 100 000 cm2/Vs. At the same time clear weak anti-localization indicates strong spin-orbit coupling and a large spin relaxation anisotropy due to the presence of a dominating symmetric spin-orbit coupling is found. Doping dependent measurements show that the spin relaxation of the in-plane spins is largely dominated by a valley-Zeeman spin-orbit coupling and that the intrinsic spin-orbit coupling plays a minor role in spin relaxation. The strong spin-valley coupling opens new possibilities in exploring spin and valley degree of freedoms in graphene with the realization of new concepts in spin manipulation.


  • Charge transport in a single molecule transistor probed by scanning tunneling microscopy
    S. Bouvron, R. Maurand, A. Graf, P. Erler, L. Gragnaniello, M. Skripnik, D. Wiedmann, C. Engesser, C. Nef, W. Fu, C. Schönenberger, F. Paulya, and M. Fonin.
    Nanoscale, 10:1487-1493, jan 2018. [DOI]
    [Abstract]

    We report on the scanning tunneling microscopy/spectroscopy (STM/STS) study of cobalt phthalocyanine (CoPc) molecules deposited onto a back-gated graphene device. We observe a clear gate voltage (Vg) dependence of the energy position of the features originating from the molecular states. Based on the analysis of the energy shifts of the molecular features upon tuning Vg, we are able to determine the nature of the electronic states that lead to a gapped differential conductance. Our measurements show that capacitive couplings of comparable strengths exist between the CoPc molecule and the STM tip as well as between CoPc and graphene, thus facilitating electronic transport involving only unoccupied molecular states for both tunneling bias polarities. These findings provide novel information on the interaction between graphene and organic molecules and are of importance for further studies, which envisage the realization of single molecule transistors with non-metallic electrodes.


  • High-detection efficiency and low-timing jitter with amorphous superconducting nanowire single-photon detectors
    M. Caloz, M. Perrenoud, C. Autebert, B. Korzh, M. Weiss, C. Schönenberger, R. J. Warburton, H. Zbinden, and F. Bussières.
    Appl. Phys. Lett., 112:61103, jan 2018. [DOI] arXiv:1710.06740
    [Abstract]

    Recent progress in the development of superconducting nanowire single-photon detectors (SNSPDs) made of amorphous material has delivered excellent performances, and has had a great impact on a range of research fields. Despite showing the highest system detection effciency (SDE) ever reported with SNSPDs, amorphous materials typically lead to lower critical currents, which impacts on their jitter performance. Combining a very low jitter and a high SDE remains a challenge. Here, we report on highly effcient superconducting nanowire single-photon detectors based on amorphous MoSi, combining system jitters as low as 26 ps and a SDE of 80\% at 1550 nm. We also report detailed observations on the jitter behaviour, which hints at intrinsic limitations and leads to practical implications for SNSPD performance.


  • Quantum-Confined Stark Effect in a MoS2 Monolayer van der Waals Heterostructure
    J. G. Roch, N. Leisgang, G. Froehlicher, P. Makk, K. Watanabe, T. Taniguchi, C. Schönenberger, and R. J. Warburton.
    Nano Letters, 18:1070−1074, jan 2018. [DOI] arXiv:1710.09750
    [Abstract]

    The optics of dangling-bond-free van der Waals heterostructures containing transition metal dichalcogenides are dominated by excitons. A crucial property of a confined exciton is the quantum confined Stark effect (QCSE). Here, such a heterostructure is used to probe the QCSE by applying a uniform vertical electric field across a molybdenum disulfide (MoS2) monolayer. The photoluminescence emission energies of the neutral and charged excitons shift quadratically with the applied electric field, provided that the electron density remains constant, demonstrating that the exciton can be polarized. Stark shifts corresponding to about half the homogeneous linewidth were achieved. Neutral and charged exciton polarizabilities of (7.8 ± 1.0) × 10−10 and (6.4 ± 0.9) × 10−10 D m V−1 at relatively low electron density (~10^12 cm−2) have been extracted, respectively. These values are one order of magnitude lower than the previously reported values but in line with theoretical calculations. The methodology presented here is versatile and can be applied to other semiconducting layered materials.


  • Spin transport in two-layer-CVD-hBN/graphene/hBN heterostructures
    M. Gurram, S. Omar, S. Zihlmann, P. Makk, Q. C. Li, Y. F. Zhang, C. Schönenberger, and B. J. van Wees.
    Phys. Rev. B, 97:45411, jan 2018. [DOI] arXiv:1712.00815
    [Abstract]

    We study room-temperature spin transport in graphene devices encapsulated between a layer-by-layer-stacked two-layer-thick chemical vapor deposition (CVD) grown hexagonal boron nitride (hBN) tunnel barrier, and a few-layer-thick exfoliated-hBN substrate. We find mobilities and spin-relaxation times comparable to that of SiO2 substrate-based graphene devices, and we obtain a similar order of magnitude of spin relaxation rates for both the Elliott-Yafet and D’Yakonov-Perel’ mechanisms. The behavior of ferromagnet/two-layer-CVDhBN/ graphene/hBN contacts ranges from transparent to tunneling due to inhomogeneities in the CVD-hBN barriers. Surprisingly, we find both positive and negative spin polarizations for high-resistance two-layer-CVDhBN barrier contacts with respect to the low-resistance contacts. Furthermore, we find that the differential spininjection polarization of the high-resistance contacts can be modulated by dc bias from −0.3 to +0.3 V with no change in its sign, while its magnitude increases at higher negative bias. These features point to the distinctive spin-injection nature of the two-layer-CVD-hBN compared to the bilayer-exfoliated-hBN tunnel barriers.

2017


  • Andreev bound states probed in three-terminal quantum dots
    J. Gramich, A. Baumgartner, and C. Schönenberger.
    Phys. Rev. B, 96:195418, nov 2017. [DOI] arXiv:1612.01201
    [Abstract]

    Andreev bound states (ABSs) are well-de ned many-body quantum states that emerge from the hybridization of individual quantum dot (QD) states with a superconductor and exhibit very rich and fundamental phenomena. We demonstrate several new electron transport phenomena mediated by ABSs that form on three-terminal carbon nanotube (CNT) QDs, with one superconducting (S) contact in the center and two adjacent normal metal (N) contacts. Three-terminal spectroscopy allows us to identify the coupling to the N contacts as the origin of the Andreev resonance (AR) linewidths and to determine the critical coupling strengths to S, for which a ground state (or quantum phase) transition in such S-QD systems can occur. In addition, we ascribe replicas of the lowest-energy ABS resonance to transitions between the ABS and odd-parity excited QD states, a process we call excited state ABS resonances. In the conductance between the two N contacts we find a characteristic pattern of positive and negative differential subgap conductance, which we explain by considering two nonlocal processes, the creation of Cooper pairs in S by electrons from both N terminals, and a novel transport mechanism called resonant ABS tunneling, possible only in multi-terminal QD devices. In the latter process, electrons are transferred via the ABS without effectively creating Cooper pairs in S. The three-terminal geometry also allows spectroscopy experiments with different boundary conditions, for example by leaving S floating. Surprisingly, we find that, depending on the boundary conditions and the device parameters, the experiments either show single-particle Coulomb blockade resonances, ABS characteristics, or both in the same measurements, seemingly contradicting the notion of ABSs replacing the single particle states as eigenstates of the QD. We qualitatively explain these results as originating from the nite time scale required for the coherent oscillations between the superposition states after a single electron tunneling event. These experiments demonstrate that three-terminal experiments on a single complex quantum object can also be useful to investigate charge dynamics otherwise not accessible due to the very high frequencies.


  • Measuring a Quantum Dot with an Impedance-Matching On-Chip Superconducting LC Resonator at Gigahertz Frequencies
    M. -C. Harabula, T. Hasler, G. Fülöp, M. Jung, V. Ranjan, and C. Schönenberger.
    Phys. Rev. Appl., 8:54006, nov 2017. [DOI] arXiv:1707.09061
    [Abstract]

    We report on the realization of a bonded-bridge on-chip superconducting coil and its use in impedance matching a highly ohmic quantum dot (QD) to a 3-GHz measurement setup. The coil, modeled as a lumped-element LC resonator, is more compact and has a wider bandwidth than resonators based on coplanar transmission lines (e.g., λ/4 impedance transformers and stub tuners), at potentially better signal-to-noise ratios. Specifically, for measurements of radiation emitted by the device, such as shot noise, the 50 × larger bandwidth reduces the time to acquire the spectral density. The resonance frequency, close to 3.25 GHz, is 3 times higher than that of the one previously reported, a wire-bonded coil. As a proof of principle, we fabricate an LC circuit that achieves impedance matching to an approximately 15 kOhm load and validate it with a load defined by a carbon nanotube QD, whose shot noise we measure in the Coulomb-blockade regime.


  • Giant Valley-Isospin Conductance Oscillations in Ballistic Graphene
    C. Handschin, P.Makk, P. Rickhaus, R. Maurand, K. Watanabe, T. Taniguchi, K. Richter, Ming-Hao Liu, and C. Schönenberger.
    Nano Letters, 17:5389-5393, aug 2017. [DOI] arXiv:1708.09614
    [Abstract]

    At high magnetic fields the conductance of graphene is governed by the half-integer quantum Hall effect. By local electrostatic gating a p−n junction perpendicular to the graphene edges can be formed, along which quantum Hall channels copropagate. It has been predicted by Tworzidło and co-workers that if only the lowest Landau level is filled on both sides of the junction, the conductance is determined by the valley (isospin) polarization at the edges and by the width of the flake. This effect remained hidden so far due to scattering between the channels copropagating along the p−n interface (equilibration). Here we investigate p−n junctions in encapsulated graphene with a movable p−n interface with which we are able to probe the edge configuration of graphene flakes. We observe large quantum conductance oscillations on the order of e2/h which solely depend on the p−n junction position providing the first signature of isospin-defined conductance. Our experiments are underlined by quantum transport calculations.


  • Restoring the Electrical Properties of CVD Graphene via Physisorption of Molecular Adsorbates
    K. Thodkar, D-. Thompson, F. Lüönd, L. Moser, F. Overney, L. Marot, C. Schönenberger, B. Jeanneret, and M. Calame.
    ACS Appl. Mater. Interfaces, 9(29):25014-25022, july 2017. [DOI]
    [Abstract]

    Chemical vapor deposition (CVD) is a powerful technique to produce graphene for large-scale applications. Polymer-assisted wet transfer is commonly used to move the graphene onto silicon substrates, but the resulting devices tend to exhibit p-doping, which decreases the device quality and reproducibility. In an effort to better understand the origin of this effect, we coated graphene with n-methyl-2-pyrrolidone (NMP) and hexamethyldisilazane (HMDS) molecules that exhibit negligible charge transfer to graphene but bind more strongly to graphene than ambient adsorbents. Using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), electrical transport measurements, and quantum mechanical computer simulations, we show that the molecules help in the removal of p-doping, and our data indicate that the molecules do this by replacing ambient adsorbents (typically O2 and water) on the graphene surface. This very simple method of improving the electronic properties of CVD graphene by passivating its surface with common solvent molecules will accelerate the development of CVD graphene-based devices


  • Contactless Microwave Characterization of Encapsulated Graphene p-n Junctions
    V. Ranjan, S. Zihlmann, P. Makk, K. Watanabe, T. Taniguchi, and C. Schönenberger.
    Phys. Rev. Appl., 7(5):54015, may 2017. [DOI] arXiv:1702.02071
    [Abstract]

    Accessing intrinsic properties of a graphene device can be hindered by the influence of contact electrodes. Here, we capacitively couple graphene devices to superconducting resonant circuits and observe clear changes in the resonance-frequency and -widths originating from the internal charge dynamics of graphene. This allows us to extract the density of states and charge relaxation resistance in graphene p-n junctions without the need of electrical contacts. The presented characterizations pave a fast, sensitive and non-invasive measurement of graphene nanocircuits.


  • Optically probing the detection mechanism in a molybdenum silicide superconducting nanowire single-photon detector
    M. Caloz, B. Korzh, N. Timoney, M. Weiss, S. Gariglio, R. J. Warburton, C. Schönenberger, J. Renema, H. Zbinden, and F. Bussieres.
    Applied Physics Letters, 110(8):83106, feb 2017. [DOI] arXiv:1611.08238
    [Abstract]

    We experimentally investigate the detection mechanism in a meandered molybdenum silicide superconducting nanowire single-photon detector by characterising the detection probability as a function of bias current in the wavelength range of 750–2050 Onm. Contrary to some previous observations on niobium nitride or tungsten silicide detectors, we find that the energy-current relation is nonlinear in this range. Furthermore, thanks to the presence of a saturated detection efficiency over the whole range of wavelengths, we precisely quantify the shape of the curves. This allows a detailed study of their features, which are indicative of both Fano fluctuations and position-dependent effects.


  • Fabry-Pérot Resonances in a Graphene/hBN Moiré Superlattice
    C. Handschin, P.Makk, P. Rickhaus, M. -H. Liu, K. Watanabe, T. Taniguchi, K. Richter, and C. Schönenberger.
    Nano Letters, 17:328-333, jan 2017. [DOI] arXiv:1701.09141
    [Abstract]

    While Fabry-Pérot (FP) resonances and Moiré superlattices are intensively studied in graphene on hexagonal boron nitride (hBN), the two effects have not been discussed in their coexistence. Here we investigate the FP oscillations in a ballistic pnp-junctions in the presence and absence of a Moiré superlattice. First, we address the effect of the smoothness of the confining potential on the visibility of the FP resonances and carefully map the evolution of the FP cavity size as a function of densities inside and outside the cavity in the absence of a superlattice, when the cavity is bound by regular pn-junctions. Using a sample with a Moiré superlattice, we next show that an FP cavity can also be formed by interfaces that mimic a pn-junction but are defined through a satellite Dirac point due to the superlattice. We carefully analyze the FP resonances, which can provide insight into the band-reconstruction due to the superlattice.


  • Charge Noise in Organic Electrochemical Transistors
    R. L. Stoop, K. Thodkar, M. Sessolo, H. J. Bolink, and Calame M. C. Schönenberger.
    Phys. Rev. Appl., 7(1):14009, jan 2017. [DOI]
    [Abstract]

    Organic electrochemical transistors (OECTs) are increasingly studied as transducers in sensing applications. While much emphasis has been placed on analyzing and maximizing the OECT signal, noise has been mostly ignored, although it determines the resolution of the sensor. The major contribution to the noise in sensing devices is the 1/f noise, dominant at low frequency. In this work, we demonstrate that the 1/f noise in OECTs follows a charge-noise model, which reveals that the noise is due to charge fuctuations in proximity or within the bulk of the channel material. We present the noise scaling behavior with gate voltage, channel dimensions and polymer thickness. Our results suggest the use of large area channels in order to maximize the signal-to-noise-ratio (SNR) for biochemical and electrostatic sensing applications. Comparison with literature shows that the magnitude of the noise in OECTs is similar to that observed in graphene transistors, and only slightly higher compared to Carbon nanotubes and Silicon nanowire devices. In a model ion-sensing experiment with OECTs, we estimate crucial parameters such as the characteristic SNR and corresponding limit of detection.

2016


  • Gate-controlled conductance enhancement from quantum Hall channels along graphene p-n junctions
    E. Tovari, P. Makk, Ming-Hao Liu, P. Rickhaus, Z. Kovas-Krausz, C. Schönenberger, and S. Csonka.
    Nanoscale, 8(47):19910-19916, Dec. 2016. [DOI] arXiv:1606.08007
    [Abstract]

    The formation of quantum Hall channels inside the bulk of graphene is studied using various contact and gate geometries. p-n junctions are created along the longitudinal direction of samples, and enhanced conductance is observed in the case of bipolar doping due to the new conducting channels formed in the bulk, whose position, propagating direction and, in one geometry, coupling to electrodes are determined by the gate-controlled filling factor across the device. This effect could be exploited to probe the behavior and interaction of quantum Hall channels protected against uncontrolled scattering at the edges.


  • Magnetoresistence engineering and singlet/triplet switching in InAs nanowire quantum dots with ferromagnetic sidegates
    G. Fábián, P. Makk, M. H. Madsen, J. Nygård, C. Schönenberger, and A. Baumgartner.
    Phy. Rev. B, 94:195415, Nov. 2016. [DOI] arXiv:1608.07143
    [Abstract]

    We present magnetoresistance (MR) experiments on an InAs nanowire quantum dot device with two ferromagnetic sidegates (FSGs) in a split-gate geometry. The wire segment can be electrically tuned to a single dot or to a double dot regime using the FSGs and a backgate. In both regimes we find a strong MR and a sharp MR switching of up to 25\% at the field at which the magnetizations of the FSGs are inverted by the external field. The sign and amplitude of the MR and the MR switching can both be tuned electrically by the FSGs. In a double dot regime close to pinch-off we find {\it two} sharp transitions in the conductance, reminiscent of tunneling MR (TMR) between two ferromagnetic contacts, with one transition near zero and one at the FSG switching fields. These surprisingly rich characteristics we explain in several simple resonant tunneling models. For example, the TMR-like MR can be understood as a stray-field controlled transition between singlet and a triplet double dot states. Such local magnetic fields are the key elements in various proposals to engineer novel states of matter and may be used for testing electron spin-based Bell inequalities.


  • A success story
    Christel Möller and Christian Schönenberger.
    Nature Nanotechnology, 11:908, Oct. 2016. [DOI] arXiv:…

  • Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices
    J. Gramich, A. Baumgartner, and C. Schönenberger.
    Appl. Phys. Lett., 108(17):172604, April 2016. [DOI] arXiv:1601.00672
    [Abstract]

    We report thermally activated transport resonances for biases below the superconducting energy gap in a carbon nanotube quantum dot (QD) device with a superconducting Pb and a normal metal contact. These resonances are due to the superconductor’s finite quasi-particle population at elevated temperatures and can only be observed when the QD life-time broadening is considerably smaller than the gap. This condition is fulfilled in our QD devices with optimized Pd/Pb/In multi-layer contacts, which result in reproducibly large and “clean” superconducting transport gaps with a strong conductance suppression for subgap biases. We show that these gaps close monotonically with increasing magnetic field and temperature. The accurate description of the subgap resonances by a simple resonant tunneling model illustrates the ideal characteristics of the reported Pb contacts and gives an alternative access to the tunnel coupling strengths in a QD.


  • Cooper-Paare tunneln durch einen Quantenpunkt
    Andreas Baumgartner, Jörg Gramich, and Christian Schönenberger.
    Physik in unserer Zeit, 47(2):62, March 2016. [DOI] arXiv:…
    [Abstract]

    Elektronische Bauteile aus Supraleitern und Quantenpunkten zeigen eine Vielzahl von neuen und fundamentalen physikalischen Eigenschaften und stellen neue quantentechnologische Anwendungen in Aussicht. Kuerzlich ist es gelungen, den wohl grundlegendsten Transportprozess in einer solchen Struktur in Experimenten zu identifizieren, naemlich den direkten Transport von Elektronen aus einem Supraleiter durch einen Quantenpunkt, das sogenannte Andreev-Tunneln. Das Verstaendnis dieses Prozesses liefert die Grundlage fuer zukuenftige Anwendungen, die quantenmechanische Phaenomene in elektronischen Bauteilen ausnutzen werden.


  • Role of hexagonal boron nitride in protecting ferromagnetic anostructures from oxidation
    S. Zihlmann, P. Makk, C. A. F. Vaz, and C. Schönenberger.
    2D Materials, 3(1):11008, Feb 2016. [DOI] arXiv:1509.03087
    [Abstract]

    Ferromagnetic contacts are widely used to inject spin polarized currents into non-magnetic materials such as semiconductors or 2-dimensional materials like graphene. In these systems, oxidation of the ferromagnetic materials poses an intrinsic limitation on device performance. Here we investigate the role of ex situ transferred chemical vapour deposited hexagonal boron nitride (hBN) as an oxidation barrier for nanostructured cobalt and permalloy electrodes. The chemical state of the ferromagnets was investigated using x-ray photoemission electron microscopy because of its high sensitivity and lateral resolution. We have compared the oxide thickness formed on ferromagnetic nanostructures covered by hBN to uncovered reference structures. Our results show that hBN reduces the oxidation rate of ferromagnetic nanostructures suggesting that it could be used as an ultra-thin protection layer in future spintronic devices.


  • Full characterization of a carbon nanotube parallel double quantum dot
    G. Abulizi, A. Baumgartner, and C. Schönenberger.
    Physica Status Solidi B, 253(12):2428, 2016. [DOI] arXiv:1605.02300v1
    [Abstract]

    We have measured the differential conductance of a parallel carbon nanotube (CNT) double quantum dot (DQD) with strong inter-dot capacitance and inter-dot tunnel coupling. Nominally, the device consists of a single CNT with two contacts. However, we identify two sets of Coulomb blockade (CB) diamonds that do not block transport individually, which suggests that two quantum dots (QDs) are contacted in parallel. We find strong and periodic anti-crossings in the gate and bias dependence, which are only possible if the QDs have similar characteristics. We discuss qualitatively the level spectrum and the involved transport processes in this device and extract the DQD coupling parameters. These results lead us to believe that clean and undoped QDs are formed parallel to the CNT axis, possibly on the outer and inner shells of a multi-wall CNT, or in a double-stranded CNT bundle.


  • Additional peak appearing in the one-photon luminescence of single gold nanorods
    T. Fröhlich, C. Schönenberger, and M. Calame.
    Optics Letters, 7:1325, 2016. [DOI]
    [Abstract]

    We used a confocal laser microscope to investigate the one photon photoluminescence (PL) of gold antennas. The PL spectra can be precisely fitted to a plasmon-enhanced PL model. For increasing the antenna length, the energy peak position decreases continuously until it reaches a value of 1.7–1.8 eV. For longer antennas and smaller plasmon energies, we observe an additional, persistent shoulder in the PL spectra, which we explain by a Gaussian-shaped peak at ΔX ≈ 1.78–1.79 eV. We attribute this behavior to the opening of an additional decay path for electrons at the gold interband transition edge, which we observe only for long antennas.


  • Wet etch methods for InAs nanowire patterning and self-aligned electrical contacts
    G. Fülöp, S. d’Hollosy, L. Hofstetter, A. Baumgartner, J. Nygard, C. Schönenberger, and S. Csonka.
    Nanotechnology, 27(19):195303, 2016. [DOI] arXiv:1601.01562
    [Abstract]

    Advanced synthesis of semiconductor nanowires (NWs) enables their application in diverse fields, notably in chemical and electrical sensing, photovoltaics, or quantum electronic devices. In particular, indium arsenide (InAs) NWs are an ideal platform for quantum devices, e.g. they may host topological Majorana states. While the synthesis has been continously perfected, only a few techniques have been developed to tailor individual NWs after growth. Here we present three wet chemical etch methods for the post-growth morphological engineering of InAs NWs on the sub-100 nm scale. The first two methods allow the formation of self-aligned electrical contacts to etched NWs, while the third method results in conical shaped NW profiles ideal for creating smooth electrical potential gradients and shallow barriers. Low temperature experiments show that NWs with etched segments have stable transport characteristics and can serve as building blocks of quantum electronic devices. As an example we report the formation of a single electrically stable quantum dot between two etched NW segments.


  • Microwave Photodetection in an Ultraclean Suspended Bilayer Graphene p–n Junction
    M. Jung, P. Rickhaus, S. Zihlmann, and C. Schönenberger.
    Nano Letters, 16:6988, xxx 2016. [DOI]
    [Abstract]

    We explore the potential of bilayer graphene as a cryogenic microwave photodetector by studying the microwave absorption in fully suspended clean bilayer graphene p–n junctions in the frequency range of 1–5 GHz at a temperature of 8 K. We observe a distinct photocurrent signal if the device is gated into the p–n regime, while there is almost no signal for unipolar doping in either the n–n or p–p regimes. Most surprisingly, the photocurrent strongly peaks when one side of the junction is gated to the Dirac point (charge-neutrality point CNP), while the other remains in a highly doped state. This is different to previous results where optical radiation was used. We propose a new mechanism based on the phototermal effect explaining the large signal. It requires contact doping and a distinctly different transport mechanism on both sides: one side of graphene is ballistic and the other diffusive. By engineering partially diffusive and partially ballistic devices, the photocurrent can drastically be enhanced.


  • Spin transport in fully hexagonal boron nitride encapsulated graphene
    M. Gurram, S. Omar, S. Zihlmann, P. Makk, C. Schönenberger, and B. J. van Wees.
    Physical Review B, 93(11):115441, 2016. [DOI] arXiv:1603.04357
    [Abstract]

    We study fully hexagonal boron nitride (hBN) encapsulated graphene spin valve devices at room temperature. The device consists of a graphene channel encapsulated between two crystalline hBN flakes: thick-hBN flake as a bottom gate dielectric substrate which masks the charge impurities from Si_{O2}/Si substrate and single-layer thin-hBN flake as a tunnel barrier. Full encapsulation prevents the graphene from coming in contact with any polymer/chemical during the lithography and thus gives homogeneous charge and spin transport properties across different regions of the encapsulated graphene. Further, even with the multiple electrodes in-between the injection and the detection electrodes which are in conductivity mismatch regime, we observe spin transport over 12.5 $\mu$m-long distance under the thin-hBN encapsulated graphene channel, demonstrating the clean interface and the pinhole-free nature of the thin hBN as an efficient tunnel barrier.


  • Implementing Silicon Nanoribbon Field-Effect Transistors as Arrays for Multiple Ion Detection
    R. Stoop, M. Wipf, S. Müller, K. Bedner, I. A. Wright, C. J. Martin, E. C. Constable, A. Fanget, C. Schönenberger, and M. Calame.
    Biosensors, 6:21, 2016. [DOI]
    [Abstract]

    Ionic gradients play a crucial role in the physiology of the human body, ranging from metabolism in cells to muscle contractions or brain activities. To monitor these ions, inexpensive, label-free chemical sensing devices are needed. Field-effect transistors (FETs) based on silicon (Si) nanowires or nanoribbons (NRs) have a great potential as future biochemical sensors as they allow for the integration in microscopic devices at low production costs. Integrating NRs in dense arrays on a single chip expands the field of applications to implantable electrodes or multifunctional chemical sensing platforms. Ideally, such a platform is capable of detecting numerous species in a complex analyte. Here, we demonstrate the basis for simultaneous sodium and fluoride ion detection with a single sensor chip consisting of arrays of gold-coated SiNR FETs. A microfluidic system with individual channels allows modifying the NR surfaces with self-assembled monolayers of two types of ion receptors sensitive to sodium and fluoride ions. The functionalization procedure results in a differential setup having active fluoride- and sodium-sensitive NRs together with bare gold control NRs on the same chip. Comparing functionalized NRs with control NRs allows the compensation of non-specific contributions from changes in the background electrolyte concentration and reveals the response to the targeted species.


  • Signatures of single quantum dots in graphene nanoribbons within the quantum Hall regime
    E. Tovari, P. Makk, P. Rickhaus, C. Schönenberger, and S. Csonka.
    Nanoscale, 8:11480, 2016. [DOI] arXiv:1601.01628
    [Abstract]

    We report on the observation of periodic conductance oscillations near quantum Hall plateaus in suspended graphene nanoribbons. They are attributed to single quantum dots that form in the narrowest part of the ribbon, in the valleys and hills of a disorder potential. In a wide flake with two gates, a double-dot system’s signature has been observed. Electrostatic confinement is enabled in single-layer graphene due to the gaps that form between Landau levels, suggesting a way to create gate-defined quantum dots that can be accessed with quantum Hall edge states.


  • Label-Free FimH Protein Interaction Analysis Using Silicon Nanoribbon BioFETs
    M. Wipf, R. L. Stoop, G. Navarra, S. Rabbani, B. Ernst, K. Bedner, C. Schönenberger, and M. Calame.
    ACS Sens., 1:781-788, 2016. [DOI]
    [Abstract]

    The detection of biomarkers at very low concentration and low cost is increasingly important for clinical diagnosis. Moreover, monitoring affinities for receptorantagonist interactions by time-resolved measurements is crucial for drug discovery and development. Biosensors based on ion-sensitive field-effect transistors (BioFETs) are promising candidates for being integrated into CMOS structures and cost-effective production. The detection of DNA and proteins with silicon nanowires has been successfully demonstrated using high affinity systems such as the biotin−streptavidin interaction. Here, we show the time-resolved label-free detection of the interaction of the bacterial FimH lectin with an immobilized mannose ligand on gold-coated silicon nanoribbon BioFETs. By comparing our results with a commercial state of the art surface plasmon resonance system, additional surface effects become visible when using this charge based detection method. Furthermore, we demonstrate the effect of sensor area on signal-to-noise ratio and estimate the theoretical limit of detection.


  • Comparative study of single and multi domain CVD graphene using large-area Raman mapping and electrical transport characterization
    K. Thodkar, El M. Abbassi, F. Lüönd, F. Overney, Sch C. ", B. Jeanneret, and M. Calame.
    physica status solidi (RRL) – Rapid Research Letters, 10(11):807, 2016. [DOI]
    [Abstract]

    We systematically investigate the impact of granularity in CVD graphene films by performing Raman mapping and electrical characterization of single (SD) and multi domain (MD) graphene. In order to elucidate the quality of the graphene film, we study its regional variations using large-area Raman mapping and compare the G and 2D peak positions of as-transferred chemical vapor deposited (CVD) graphene on SiO2 substrate. We find a similar upshift in wavenumber in both SD and MD graphene in comparison to freshly exfoliated graphene. In our case, doping could play the dominant role behind the observation of such upshifts rather than the influence due to strain. Interestingly, the impact of the polymer-assisted wet transfer process is the same in both the CVD graphene types. The electrical characterization shows that SD graphene exhibits a substantially higher (a factor 5) field-effect mobility when compared to MD graphene. We attribute the low sheet resistance and mobility enhancement to a decrease in charge carrier scattering thanks to a reduction of the number of grain boundaries and defects in SD graphene.

2015


  • Competing surface reactions limiting the performance of ion-sensitive field-effect transistors
    R. L. Stoop, M. Wipf, S. Müller, K. Bedner, I. A. Wright, C. J. Martin, E. C. Constable, Wangyang Fu, A. Tarasova, M. Calame, and C. Schönenberger.
    Sensors and Actuators B, 220:500-507, Dec. 2015. [DOI]
    [Abstract]

    Ion-sensitive field-effect transistors based on silicon nanowires are promising candidates for the detection of chemical and biochemical species. These devices have been established as pH sensors thanks to the large number of surface hydroxyl groups at the gate dielectrics which makes them intrinsically sensitive to protons. To specifically detect species other than protons, the sensor surface needs to be modified. However, the remaining hydroxyl groups after functionalization may still limit the sensor response to the targeted species. Here, we describe the influence of competing reactions on the measured response using a general site-binding model. We investigate the key features of the model with a real sensing example based on gold-coated nanoribbons functionalized with a self-assembled monolayer of calcium-sensitive molecules. We identify the residual pH response as the key parameter limiting the sensor response. The competing effect of pH or any other relevant reaction at the sensor surface has therefore to be included to quantitatively understand the sensor response and prevent misleading interpretations.


  • Gate tuneable beamsplitter in ballistic graphene
    P. Makk.
    Nature Physics, 11:894-895, Dec 2015. [DOI]

  • Gate tuneable beamsplitter in ballistic graphene
    P. Rickhaus, P. Makk, M. -H. Liu, K. Richter, and C. Schönenberger.
    Applied Physics Letters, 107:251901, Dec 2015. [DOI] arXiv:1511.03044
    [Abstract]

    We present a beam splitter in a suspended, ballistic, multiterminal, bilayer graphene device. By using local bottomgates, a p-n interface tilted with respect to the current direction can be formed. We show that the p-n interface acts as a semi-transparent mirror in the bipolar regime and that the reflectance and transmittance of the p-n interface can be tuned by the gate voltages. Moreover, by studying the conductance features appearing in magnetic field, we demonstrate that the position of the p-n interface can be moved by 1μm. The herein presented beamsplitter device can form the basis of electron-optic interferometers in graphene


  • Shot Noise of a Quantum Dot Measured with Gigahertz Impedance Matching
    T. Hasler, M. Jung, V. Ranjan, G. Puebla-Hellmann, A. Wallraff, and C. Schönenberger.
    Physical Review Applied, 4(5):54002, Nov 2015. [DOI] arXiv:1507.04884.pdf
    [Abstract]

    The demand for a fast high-frequency read-out of high-impedance devices, such as quantum dots, necessitates impedance matching. Here we use a resonant impedance-matching circuit (a stub tuner) realized by on-chip superconducting transmission lines to measure the electronic shot noise of a carbonnanotube quantum dot at a frequency close to 3 GHz in an efficient way. As compared to wideband detection without impedance matching, the signal-to-noise ratio can be enhanced by as much as a factor of 800 for a device with an impedance of 100 kOmega. The advantage of the stub resonator concept is the ease with which the response of the circuit can be predicted, designed, and fabricated. We further demonstrate that all relevant matching circuit parameters can reliably be deduced from power-reflectance measurements and then used to predict the power-transmission function from the device through the circuit. The shot noise of the carbon-nanotube quantum dot in the Coulomb blockade regime shows an oscillating suppression below the Schottky value of 2eI, as well as an enhancement in specific regions


  • Ordered nanoparticle arrays interconnected by molecular linkers: electronic and optoelectronic properties
    J. Liao, S. Blok, S. J. van der Molen, S. Diefenbach, A. W. Holleitner, C. Schönenberger, A. Vladyka, and M. Calame.
    Chem. Soc. Rev., 44:999-1014, Nov 2015. [DOI]
    [Abstract]

    Arrays of metal nanoparticles in an organic matrix have attracted a lot of interest due to their diverse electronic and optoelectronic properties. Recent work demonstrates that nanoparticle arrays can be utilized as a template structure to incorporate single molecules. In this arrangement, the nanoparticles act as electronic contacts to the molecules. By varying parameters such as the nanoparticle material, the matrix material, the nanoparticle size, and the interparticle distance, the electronic behavior of the nanoparticle arrays can be substantially tuned and controlled. Furthermore, via the excitation of surface plasmon polaritons, the nanoparticles can be optically excited and electronically read-out. The versatility and possible applications of well-ordered nanoparticle arrays has been demonstrated by the realization of switching devices triggered optically or chemically and by the demonstration of chemical and mechanical sensing. Interestingly, hexagonal nanoparticle arrays may also become a useful platform to study the physics of collective plasmon resonances that can be described as Dirac-like bosonic excitations.


  • Fork stamping of pristine carbon nanotubes onto ferromagnetic contacts for spin-valve devices
    J. Gramich, A. Baumgartner, M. Muoth, C. Hierold, and C. Schönenberger.
    Physica status solidi (b), 252(11):2496-2502, November 2015. [DOI] arXiv:1504.05693
    [Abstract]

    We present a fabrication scheme called ‘fork stamping’ optimized for the dry transfer of individual pristine carbon nanotubes (CNTs) onto ferromagnetic contact electrodes fabricated by standard lithography. We demonstrate the detailed recipes for a residue-free device fabrication and in-situ current annealing on suspended CNT spin-valve devices with ferromagnetic Permalloy (Py) contacts and report preliminary transport characterization and magnetoresistance experiments at cryogenic temperatures. This scheme can directly be used to implement more complex device structures, including multiple gates or superconducting contacts.


  • Formation Mechanism of Metal–Molecule–Metal Junctions: Molecule-Assisted Migration on Metal Defects
    D. Thompson, J. Liao, M. Nolan, A. J. Quinn, C. A. Nijhuis, C. O’Dwyer, P. N. Nirmalraj, C. Schönenberger, and M. Calame.
    J. Phys. Chem. C, 119(33):19438–19451, Aug 2015. [DOI]
    [Abstract]

    Activation energies, Ea, measured from molecular exchange experiments are combined with atomic-scale calculations to describe the migration of bare Au atoms and Au–alkanethiolate species on gold nanoparticle surfaces during ligand exchange for the creation of metal–molecule–metal junctions. It is well-known that Au atoms and alkanethiol–Au species can diffuse on gold with sub-1 eV barriers, and surface restructuring is crucial for self-assembled monolayer (SAM) formation for interlinking nanoparticles and in contacting nanoparticles to electrodes. In the present work, computer simulations reveal that naturally occurring ridges and adlayers on Au(111) are etched and resculpted by migration of alkanethiolate–Au species toward high coordination kink sites at surface step edges. The calculated energy barrier, Eb, for diffusion via step edges is 0.4–0.7 eV, close to the experimentally measured Ea of 0.5–0.7 eV. By contrast, putative migration from isolated nine-coordinated terrace sites and complete Au unbinding from the surface incur significantly larger barriers of +1 and +3 eV, respectively. Molecular van der Waals packing energies are calculated to have negligible effect on migration barriers for typically used molecules (length < 2.5 nm), indicating that migration inside SAMs does not change the size of the migration barrier. We use the computational methodology to propose a means of creating Au nanoparticle arrays via selective replacement of citrate protector molecules by thiocyanate linker molecules on surface step sites. This work also outlines the possibility of using Au/Pt alloys as possible candidates for creation of contacts that are well-formed and long-lived because of the superior stability of Pt interfaces against atomic migration.


  • Gigahertz Quantized Charge Pumping in Bottom-Gate-Defined InAs Nanowire Quantum Dots
    S. d’Hollosy, M. Jung, A. Baumgartner, V. A. Guzenko, M. H. Madsen, J. Nygård, and C. Schönenberger.
    Nano Letters, 15:4585, June 2015. [DOI] arXiv:1509.01574
    [Abstract]

    Semiconducting nanowires (NWs) are a versatile, highly tunable material platform at the heart of many new developments in nanoscale and quantum physics. Here, we demonstrate charge pumping, that is, the controlled transport of individual electrons through an InAs NW quantum dot (QD) device at frequencies up to 1.3 GHz. The QD is induced electrostatically in the NW by a series of local bottom gates in a state of the art device geometry. A periodic modulation of a single gate is enough to obtain a dc current proportional to the frequency of the modulation. The dc bias, the modulation amplitude and the gate voltages on the local gates can be used to control the number of charges conveyed per cycle. Charge pumping in InAs NWs is relevant not only in metrology as a current standard, but also opens up the opportunity to investigate a variety of exotic states of matter, for example, Majorana modes, by single electron spectroscopy and correlation experiments.


  • Snake trajectories in ultraclean graphene p–n junctions
    P. Rickhaus, P. Makk, Ming-Hao Liu, E. Tovari, M. Weiss, R. Maurand, and C. Schönenberger.
    Nature Communications, 6:6470, 3 March 2015. [DOI] arXiv:1502.01935
    [Abstract]

    Snake states are trajectories of charge carriers curving back and forth along an interface. There are two types of snake states, formed by either inverting the magnetic field direction or the charge carrier type at an interface. The former has been demonstrated in GaAs–AlGaAs heterostructures, whereas the latter has become conceivable only with the advance of ballistic graphene where a gap-less p–n interface governed by Klein tunnelling can be formed. Such snake states were hidden in previous experiments due to limited sample quality. Here we report on magneto-conductance oscillations due to snake states in a ballistic suspended graphene p–n junction, which occur already at a very small magnetic field of 20 mT. The visibility of 30 percent is enabled by Klein collimation. Our finding is firmly supported by quantum transport simulations. We demonstrate the high tunability of the device and operate it in different magnetic field regimes.


  • Sensing with Advanced Computing Technology: Fin Field Effect Transistors with High-K Gate Stack on Bulk Silicon
    S. Rigante, P. Scarbolo, M. Wipf, R. L. Stoop, K. Bedner, E. Buitrago, A. Bazigos, D. Bouvet, M. Calame, C. Schönenberger, and A. M. Ionescu..
    ACS Nano, 9(5):4972, March 2015. [DOI]
    [Abstract]

    Field-effect transistors (FETs) form an established technology for sensing applications. However, recent advancements and use of high-performance multigate metal–oxide semiconductor FETs (double-gate, FinFET, trigate, gate-all-around) in computing technology, instead of bulk MOSFETs, raise new opportunities and questions about the most suitable device architectures for sensing integrated circuits. In this work, we propose pH and ion sensors exploiting FinFETs fabricated on bulk silicon by a fully CMOS compatible approach, as an alternative to the widely investigated silicon nanowires on silicon-on-insulator substrates. We also provide an analytical insight of the concept of sensitivity for the electronic integration of sensors. N-channel fully depleted FinFETs with critical dimensions on the order of 20 nm and HfO2 as a high-k gate insulator have been developed and characterized, showing excellent electrical properties, subthreshold swing, SS ~ 70 mV/dec, and on-to-off current ratio, Ion/Ioff ~ 10^6, at room temperature. The same FinFET architecture is validated as a highly sensitive, stable, and reproducible pH sensor. An intrinsic sensitivity close to the Nernst limi


  • Scalable Tight-Binding Model for Graphene
    Ming-Hao Liu, P. Rickhaus, P. Makk, E. Tovari, R. Maurand, F. Tkatschenko, M. Weiss, C. Schönenberger, and K. Richter.
    Phys. Rev. Lett., 114:36601, 22 Jan. 2015. [DOI] arXiv:1407.5620
    [Abstract]

    Artificial graphene consisting of honeycomb lattices other than the atomic layer of carbon has been shown to exhibit electronic properties similar to real graphene. Here, we reverse the argument to show that transport properties of real graphene can be captured by simulations using “theoretical artificial graphene.” To prove this, we first derive a simple condition, along with its restrictions, to achieve band structure invariance for a scalable graphene lattice. We then present transport measurements for an ultraclean suspended single-layer graphene pn junction device, where ballistic transport features from complex Fabry-Pérot interference (at zero magnetic field) to the quantum Hall effect (at unusually low field) are observed and are well reproduced by transport simulations based on properly scaled single-particle tight-binding models. Our findings indicate that transport simulations for graphene can be efficiently performed with a strongly reduced number of atomic sites, allowing for reliable predictions for electric properties of complex graphene devices. We demonstrate the capability of the model by applying it to predict so-far unexplored gate-defined conductance quantization in single-layer graphene.


  • Point contacts in encapsulated graphene
    C. Handschin, B. Fülöp, P. Makk, S. Blanter, M. Weiss, K. Watanabe, T. Taniguchi, S. Csonka, and C. Schönenberger.
    Applied Physics Letters, 107(18):183108, 2015. [DOI] arXiv:1509.04137v1.pdf
    [Abstract]

    We present a method to establish inner point contacts on hexagonal boron nitride (hBN) encapsulated graphene heterostructures with dimensions as small as 100 nm by pre-patterning the top-hBN in a separate step prior to dry-stacking. 2 and 4-terminal field effect measurements between different lead combinations are in qualitative agreement with an electrostatic model assuming point-like contacts. The measured contact resistances are 0.5-1.5 k$\Omega$ per contact, which is quite low for such small contacts. By applying a perpendicular magnetic fields, an insulating behaviour in the quantum Hall regime was observed, as expected for inner contacts. The fabricated contacts are compatible with high mobility graphene structures and open up the field for the realization of several electron optical proposals.


  • Resonant and Inelastic Andreev Tunneling Observed on a Carbon Nanotube Quantum Dot
    J. Gramich, A. Baumgartner, and C. Schönenberger.
    Physical Review Letters, 115:216801, 2015. [DOI] arXiv:1507.00526
    [Abstract]

    We report the observation of two fundamental sub-gap transport processes through a quantum dot (QD) with a superconducting contact. The device consists of a carbon nanotube contacted by a Nb superconducting and a normal metal contact. First, we find a single resonance with position, shape and amplitude consistent with the theoretically predicted resonant Andreev tunneling (AT) through a single QD level. Second, we observe a series of discrete replicas of resonant AT at a separation of ∼145μeV, with a gate, bias and temperature dependence characteristic for boson-assisted, inelastic AT, in which energy is exchanged between a bosonic bath and the electrons. The magnetic field dependence of the replica’s amplitudes and energies suggest that two different bosons couple to the tunnel process.


  • Entanglement Detection with Non-Ideal Ferromagnetic Detectors
    P. Rozek, P. Busz, W. Klobus, D. Tomaszewski, A. Grudka, A. Baumgartner, C. Schönenberger, and J. Martinek.
    Acta Physica Polonica A, 127(2):493, 2015. [DOI]
    [Abstract]

    Entangled states are essential in basics quantum communication protocols and quantum cryptography. Ferromagnetic contacts can work as a spin detector, giving possibility of converting information about electron spin to the electric charge, and therefore, detection of entangled states with the electric current measurements is possible. Method of conrming entanglement with non-ideal detectors is presented, the impact of decoherence and noise on states and quality of entanglement is discussed. Entanglement witness (EW) operator method is compared with the CHSH inequalities approach. Required spin polarization for the EW is lower than for the CHSH inequalities. System with asymmetric spin polarizations of detectors was analyzed, including the CHSH inequalities and the EW method.


  • Magnetic field tuning and quantum interference in a Cooper pair splitter
    G. Fülöp, F. Domínguez, S. d’Hollosy, A. Baumgartner, P. Makk, M. H. Madsen, V. A. Guzenko, J. Nygard, C. Schönenberger, Levy A. Yeyati, Csonka S. -. in cooperation with the Csonka(Budapest), and Levi Yeyati group (Madrid).
    Physical Review Letters, 115:227003, 2015. [DOI] arXiv:1507.01036
    [Abstract]

    Cooper pair splitting (CPS) is a process in which the electrons of naturally occurring spin-singlet pairs in a superconductor are spatially separated using two quantum dots. Here we investigate the evolution of the conductance correlations in an InAs CPS device in the presence of an external magnetic field. In our experiments the gate dependence of the signal that depends on both quantum dots continuously evolves from a slightly asymmetric Lorentzian to a strongly asymmetric Fano-type resonance with increasing field. These experiments can be understood in a simple three – site model, which shows that the nonlocal CPS leads to symmetric line shapes, while the local transport processes can exhibit an asymmetric shape due to quantum interference. These findings demonstrate that the electrons from a Cooper pair splitter can propagate coherently after their emission from the superconductor and how a magnetic field can be used to optimize the performance of a CPS device. In addition, the model calculations suggest that the estimate of the CPS efficiency in the experiments is a lower bound for the actual efficiency.


  • Ordered nanoparticle arrays interconnected by molecular linkers: electronic and optoelectronic properties
    J. Liao, S. Blok, S. J. van der Molen, S. Diefenbach, A. W. Holleitner, C. Schönenberger, A. Vladykae, and M. Calame.
    Chem. Soc. Rev., 44(1):382, 2015. [DOI]

  • Clean carbon nanotubes coupled to superconducting impedance-matching circuits
    V. Ranjan, G. Puebla-Hellmann, M. Jung, T. Hasler, A. Nunnenkamp, M. Muoth, C. Hierold, A. Wallraff, and C. Schönenberger.
    Nature Communications, 6:7165, 2015. [DOI] arXiv:1505.04681
    [Abstract]

    Coupling carbon nanotube devices to microwave circuits offers a significant increase in bandwidth and signal-to-noise ratio. These facilitate fast non-invasive readouts important for quantum information processing, shot noise and correlation measurements. However, creation of a device that unites a low-disorder nanotube with a low-loss microwave resonator has so far remained a challenge, due to fabrication incompatibility of one with the other. Employing a mechanical transfer method, we successfully couple a nanotube to a gigahertz superconducting matching circuit and thereby retain pristine transport characteristics such as the control over formation of, and coupling strengths between, the quantum dots. Resonance response to changes in conductance and susceptance further enables quantitative parameter extraction. The achieved near matching is a step forward promising high-bandwidth noise correlation measurements on high impedance devices such as quantum dot circuits.


  • Guiding of Electrons in a Few-Mode Ballistic Graphene Channel
    P. Rickhaus, M. -H. Liu, P. Makk, R. Maurand, S. Hess, S. Zihlmann, M. Weiss, K. Richter, and Schönenberger Richter (Uni. C. -. in cooperation with group Regensburg).
    Nano Letters, 15(5819), 2015. arXiv:1509.02653
    [Abstract]

    In graphene, the extremely fast charge carriers can be controlled by electron-optical elements, such as waveguides, in which the transmissivity is tuned by the wavelength. In this work, charge carriers are guided in a suspended ballistic few-mode graphene channel, defined by electrostatic gating. By depleting the channel, a reduction of mode number and steps in the conductance are observed, until the channel is completely emptied. The measurements are supported by tight-binding transport calculations including the full electrostatics of the sample.


  • Graphene spintronics: the European Flagship perspective
    S. Roche, J. Akerman, B. Beschoten, J. -C. Charlier, M. Chshiev, S. P. Dash, B. Dlubak, J. Fabian, A. Fert, M. Guimaraes, F. Guinea, I. Grigorieva, C. Schönenberger, P. Seneor, C. Stampfer, S. O.Valenzuela, X. Waintal, and B. van Wees.
    2D Materials, 2:30202, 2015. [DOI]

2014


  • Local electrical tuning of the nonlocal signals in a Cooper pair splitter
    G. Fülöp, S. d’Hollosy, A. Baumgartner, P. Makk, V. A. Guzenko, M. H. Madsen, J. Nygård, C. Schönenberger, and S. Csonka.
    Physical Review B, 90:235412, Dec 2014. arXiv:http://arxiv.org/abs/1409.0818
    [Abstract]

    A Cooper pair splitter consists of a central superconducting contact, S, from which electrons are injected into two parallel, spatially separated quantum dots (QDs). This geometry and electron interactions can lead to correlated electrical currents due to the spatial separation of spin-singlet Cooper pairs from S. We present experiments on such a device with a series of bottom gates, which allows for spatially resolved tuning of the tunnel couplings between the QDs and the electrical contacts and between the QDs. Our main findings are gate-induced transitions between positive conductance correlation in the QDs due to Cooper pair splitting and negative correlations due to QD dynamics. Using a semi-classical rate equation model we show that the experimental findings are consistent with in-situ electrical tuning of the local and nonlocal quantum transport processes. In particular, we illustrate how the competition between Cooper pair splitting and local processes can be optimized in such hybrid nanostructures.


  • CVD Graphene Electrical Quantum Metrology
    K. Thodkar, C. Nef, W. Fu, C. Schönenberger, M. Calame, F. Lüönd, F. Overney, B. Jeckelmann, and B. Jeanneret.
    IEEE Proceedings of the Conference on Precision Electromagnetic Measurements (CPEM 2014), pages 540-541, October 2014. [DOI] arXiv:http://
    [Abstract]

    Graphene, a two dimensional material with sp2 hybridized carbon atoms arranged in honey comb lattice, is known for its unique electronic and mechanical properties. Soon after the isolation of 2D graphene crystals Quantum Hall effect (QHE) has been observed in this material at room temperature. The Quantum Hall plateaus in graphene have large spacing between the Landau levels in comparison to other 2DEGs, which makes it an ideal material for a quantum resistance standard defined by the electron charge and Planck s constant. We will present results for graphene by Chemical Vapor Deposition (CVD) and transferred to SiO2/Si using different techniques. The transferred graphene films were patterned into millimeter scale Hall bar geometry and characterized using confocal Raman spectroscopy. First electrical transport measurements will be presented.


  • Large-scale fabrication of BN tunnel barriers for graphene spintronics
    W. Fu, P. Makk, R. Maurand, M. Bräuninger, and C. Schönenberger.
    Journal of Applied Physics, 116(20):74306, August 2014.

  • Sensor system including silicon nanowire ion sensitive FET arrays and CMOS readout
    P. Livi, A. Shadmani, M. Wipf, R. L. Stoop, J. Rothe, Y. Chen, M. Calame, and C. Schönenberger.
    Sensors and Actuators B, 204:568577, Aug 2014. [DOI]

  • Fabrication of ballistic suspended graphene with local-gating
    R. Maurand, P. Rickhaus, P. Makk, S. Hess, E. Tovari, C. Handschin, M. Weiss, and C. Schönenberger.
    Carbon, 79:486-492, Aug 2014. [DOI]

  • Carbon nanotube quantum dots on hexagonal boron nitride
    A. Baumgartner, G. Abulizi, K. Watanabe, T. Taniguchi, J. Gramich, and C. Schönenberger.
    Appl. Phys. Lett., 105:23111, June 2014. [DOI] arXiv:1406.0897
    [Abstract]

    We report the fabrication details and low-temperature characteristics of the first carbon nanotube (CNT) quantum dots on flakes of hexagonal boron nitride (hBN) as substrate. We demonstrate that CNTs can be grown on hBN by standard chemical vapor deposition and that standard scanning electron microscopy imaging and lithography can be employed to fabricate nanoelectronic structures when using optimized parameters. This proof of concept paves the way to more complex devices on hBN, with more predictable and reproducible characteristics and electronic stability.


  • Regulating a Benzodifuran Single Molecule Redox Switch via Electrochemical Gating and Optimization of Molecule/Electrode Coupling
    Zhihai Li, Hui Li, Songjie Chen, Toni Fröhlich, Chenyi Yi, Christian Schönenberger, Michel Calame, Silvio Decurtins, Shi-Xia Liu, and Eric Borguet.
    J. Am. Chem. Soc., 136:8867-8870, June 2014.

  • High-yield fabrication of nm-sized gaps in monolayer CVD graphene
    C. Nef, L. Pósa, P. Makk, W. Fu, A. Halbritter, C. Schönenberger, and M. Calame.
    Nanoscale, 6:7249-7254, May 2014.
    [Abstract]

    Herein we demonstrate the controlled and reproducible fabrication of sub-5 nm wide gaps in single-layer graphene electrodes. The process is implemented for graphene grown via chemical vapor deposition using an electroburning process at room temperature and in vacuum. A yield of over 95 percent for the gap formation is obtained. This approach allows producing single-layer graphene electrodes for molecular electronics at a large scale. Additionally, from Raman spectroscopy and electroburning carried out simultaneously, we can follow the heating process and infer the temperature at which the gap formation happens.


  • Entanglement witnessing and quantum cryptography with nonideal ferromagnetic detectors
    W. Kobus, A. Grudka, A. Baumgartner, D. Tomaszewski, C. Schönenberger, and Jan Martinek.
    Phys. Rev. B, 89:125404, March 2014.

  • Investigation of the dominant 1/f Noise Source in Silicon Nanowire Sensors
    K. Bedner, V. A. Guzenko, A. Tarasov, M. Wipf, L. Stoop, S. Rigante, J. Brunner, W. Fu, C. David, M. Calame, J. Gobrecht, and C. Schönenberger.
    Sensor & Actuators B, 191:270-275, 2014.

  • Random telegraph signals in molecular junctions
    J. Brunner, M. T. Gonzalez, C. Schönenberger, and M. Calame.
    J. Phys.: Condens. Matter, 26:474202, 2014.

  • Electrolyte gate dependent high-frequency measurement of graphene field-effect transistor for sensing applications
    W. Fu, El M. Abbassi, T. Hasler, M. Jung, M. Steinacher, M. Calame, C. Schönenberger, G. Puebla-Hellmann, S. Hellmüller, T. Ihn, and A. Wallraff.
    Appl. Phys. Lett., 104:13102, 2014.
    [Abstract]

    We performed radiofrequency (RF) reflectometry measurements at 2�4 GHz on electrolyte-gated graphene field-effect transistors, utilizing a tunable stub-matching circuit for impedance matching. We demonstrate that the gate voltage dependent RF resistivity of graphene can be deduced, even in the presence of the electrolyte which is in direct contact with the graphene layer. The RF resistivity is found to be consistent with its DC counterpart in the full gate voltage range. Furthermore, in order to access the potential of high-frequency sensing for applications, we demonstrate time-dependent gating in solution with nanosecond time resolution.


  • Rendering graphene supports hydrophilic with non-covalent aromatic functionalization for transmission electron microscopy
    R. S. Pantelic, W. Fu, C. Schönenberger, and H. Stahlberg.
    Appl. Phys. Lett., 104:134103, 2014.
    [Abstract]

    Amorphous carbon films have been routinely used to enhance the preparation of frozen-hydrated transmission electron microscopy (TEM) samples, either in retaining protein concentration, providing mechanical stability or dissipating sample charge. However, strong background signal from the amorphous carbon support obstructs that of the sample, and the insulating properties of amorphous carbon films preclude any efficiency in dispersing charge. Graphene addresses the limitations of amorphous carbon. Graphene is a crystalline material with virtually no phase or amplitude contrast and unparalleled, high electrical carrier mobility. However, the hydrophobic properties of graphene have prevented its routine application in Cryo-TEM. This letter reports a method for rendering graphene TEM supports hydrophilic – a convenient approach maintaining graphene’s structural and electrical properties based on non-covalent, aromatic functionalization.


  • Optimized fabrication and characterization of carbon nanotube spin valves
    J. Samm, J. Gramich, A. Baumgartner, M. Weiss, and C. Schönenberger.
    J. Appl. Phys., 115:174309, 2014.
    [Abstract]

    We report an improved fabrication scheme for carbon based nanospintronic devices and demonstrate the necessity for a careful data analysis to investigate the fundamental physical mechanisms leading to magnetoresistance. The processing with a low-density polymer and an optimised recipe allows us to improve the electrical, magnetic, and structural quality of ferromagnetic Permalloy contacts on lateral carbon nanotube (CNT) quantum dot spin valve devices, with comparable results for thermal and sputter deposition of the material. We show that spintronic nanostructures require an extended data analysis, since the magnetization can affect all characteristic parameters of the conductance features and lead to seemingly anomalous spin transport. In addition, we report measurements on CNT quantum dot spin valves that seem not to be compatible with the orthodox theories for spin transport in such structures.


  • Nonlocal spectroscopy of Andreev bound states
    J. Schindele, A. Baumgartner, R. Maurand, M. Weiss, and C. Schönenberger.
    Phys. Rev. B, 89:45422, 2014.

2013


  • Viewpoint: To Screen or Not to Screen, That is the Question
    R. Maurand and C. Schönenberger.
    APS Physics Viewpoints, 6:75, July 2013. [DOI]

  • pH Response of Silicon Nano\-wire Sensors: Impact of Nano\-wire Width and Gate Oxide
    K. Bedner, V. A. Guzenko, A. Tarasov, M. Wipf, R. L. Stoop, D. Just, S. Rigante, W. Fu, R. A. Minamisawa, C. David, M. Calame, J. Gobrecht, and C. Schönenberger.
    Sensors and Materials, 25(8):567-576, 05 2013.
    [Abstract]

    We present a systematic study of the performance of silicon nanowires (SiNWs) with different widths when they are used as ion-sensitive field-effect transistors (ISFETs) in pH-sensing experiments. The SiNW widths ranged from 100 nm to 1 �m. The SiNW-ISFETs were successfully fabricated from silicon-on-insulator (SOI) wafers with Al2O3 or HfO2 as gate dielectric. All the SiNWs showed a pH Response close to the Nernstian limit of 59.5 mV/pH at 300 K, independent of their width, or the investigated gate dielectric or operating mode. Even nanowires (NWs) in the 100 nm range operated reliably without degradation of their functionality. This result is of importance for a broad research field using SiNW sensors as a candidate for future applications.


  • pH Response of Silicon Nanowire Sensors: Impact of Nanowire Width and Gate Oxide
    K. Bedner, V. A. Guzenko, A. Tarasov, M. Wipf, L. Stoop, D. Just, S. Rigante, W. Fu, R. A. Minamisawa, C. David, M. Calame, J. Gobrecht, and C. Schönenberger.
    Sensors and Materials, 25(8):567, 2013.

  • g-factor anisotropy in nanowire-based InAs quantum dots
    S. d’Hollosy, G. Fabian, A. Baumgartner, J. Nygard, and C. and Schönenberger.
    AIP Conference Proceedings, 1566:359, 2013.
    [Abstract]

    The determination and control of the electron g-factor in semiconductor quantum dots (QDs) are fundamental prerequisites in modern concepts of spintronics and spin-based quantum computation. We study the dependence of the g-factor on the orientation of an external magnetic field in quantum dots (QDs) formed between two metallic contacts on stacking fault free InAs nanowires. We extract the g-factor from the splitting of Kondo resonances and find that it varies continuously in the range between |g| = 5 and 15.


  • Hydrogen plasma microlithography of graphene supported on a Si/SiO2 substrate
    B. Eren, T. Glatzel, M. Kisiel, W. Fu, R. Pawlak, U. Gysin, C. Nef, L. Marot, M. Calame, C. Schönenberger, and E. Meyer.
    Appl. Phys. Lett., 102:71601, 2013.
    [Abstract]

    In this work, a silicon stencil mask with a periodic pattern is used for hydrogen plasma microlithography of single layer graphene supported on a Si/SiO2 substrate. Obtained patterns are imaged with Raman microscopy and Kelvin probe force microscopy, thanks to the changes in the vibrational modes and the contact potential difference (CPD) of graphene after treatment. A decrease of 60 meV in CPD as well as a significant change of the D/G ratio in the Raman spectra can be associated with a local hydrogenation of graphene, while the topography remains invariant to the plasma exposure.


  • Natural channel protein inserts and functions in a completely artificial, solid-supported bilayer membrane
    Xiaoyan Zhang, Wangyang Fu, Cornelia Palivan, and Wolfgang Meier.
    Scientific Report, 3:2196, 2013.

  • High mobility graphene ion-sensitive field-effect transistors by noncovalent functionalization
    W. Fu, C. Nef, A. Tarasov, M. Wipf, R. Stoop, O. Knopfmacher, M. Weiss, M. Calame, and C. Schönenberger.
    Nanoscale, 5:12104, 2013.
    [Abstract]

    Noncovalent functionalization is a well-known nondestructive process for property engineering of carbon nanostructures, including carbon nanotubes and graphene. However, it is not clear to what extend the extraordinary electrical properties of these carbon materials can be preserved during the process. Here, we demonstrated that noncovalent functionalization can indeed delivery graphene field-effect transistors (FET) with fully preserved mobility. In addition, these high-mobility graphene transistors can serve as a promising platform for biochemical sensing applications.


  • Entanglement witnessing in superconducting beamsplitters
    H. Soller, L. Hofstetter, and D. Reeb.
    EPL, 102(5):7, 2013. [DOI]

  • Ultraclean Single, Double, and Triple Carbon Nanotube Quantum Dots with Recessed Re Bottom Gates
    M. Jung, J. Schindele, S. Nau, M. Weiss, A. Baumgartner, and C. Schönenberger.
    Nano Lett., 13:4522-4526, 2013.

  • Silicon Nanowire Ion-Sensitive Field-Effect Transistor Array Integrated with a CMOS-based Readout Chip
    P. Livi, M. Wipf, A. Tarasov, R. Stoop, K. Bedner, J. Rothe, Y. Chen, A. Stettler, C. Schönenberger, and A. Hierlemann.
    Proc. Of IEEE Transducers, Barcelona, SPAIN, 16-20 June 2013, pages 1751-1754, 2013.

  • Ballistic interferences in suspended graphene
    P. Rickhaus, R. Maurand, M. Weiss, C. Schönenberger, Ming-Hao Liu, and K. Richter.
    Nature communications, 4(2342):1-6, 2013. [DOI]
    [Abstract]

    Graphene is the 2-dimensional (2D) carbon allotrope with the atoms arranged in a honeycomb lattice [1]. The low-energy electronic excitations in this 2D crystal are described by massless Dirac fermions that have a linear dispersion relation similar to photons [2, 3]. Taking advantage of this optics-like electron dynamics, generic optical elements like lenses, beam splitters and wave guides have been proposed for electrons in engineered and ballistic graphene [4, 5]. Tuning of these elements rely on the ability to adjust the carrier concentration in defined areas, including the possibility to create bipolar regions of opposite charge (p-n regions). However, the combination of ballistic transport and complex electrostatic gating remain challenging. Here, we report on the fabrication and characterization of fully suspended graphene p-n junctions. By local electrostatic gating, resonant cavities can be defined, leading to complex Fabry-Perot interference patterns in the unipolar and the bipolar regime. The amplitude of the observed conductance oscillations account for quantum interference of electrons that propagate ballistically over long distances exceeding 1 micrometer. We also demonstrate that the visibility of the interference pattern is enhanced by Klein collimation at the p-n interface [6, 7]. This finding paves the way to more complex gate controlled ballistic graphene devices and brings electron optics in graphene closer to reality.


  • Two Indistinguishable Electrons Interfere in an Electronic Device
    C. Schönenberger.
    Science, 339:1041, 2013.

  • Low-bias active control of TeraHertz-waves by coupling large-area CVD-graphene to a TeraHertz-Metamaterial
    F. Valmorra, G. Scalari, C. Maissen, W. Fu, C. Schönenberger, J. W. Choi, H. G. Park, Hyung Gyu, M. Beck, and J. Faist.
    Nano Lett., 13:3193-3198, 2013.

  • Spin Symmetry of the Bilayer Graphene Groundstate
    F. Freitag, M. Weiss, R. Maurand, J. Trbovic, and C. Schönenberger.
    Phys. Rev. B, 87:161402, 2013.
    [Abstract]

    We show nonlinear transport experiments on clean, suspended bilayer graphene that reveal a gap in the density of states. Looking at the evolution of the gap in magnetic fields of different orientation, we find that the groundstate is a spin-ordered phase. Of the three possible gapped groundstates that are predicted by theory for equal charge distribution between the layers, we can therefore exclude the quantum anomalous Hall phase, leaving the layer antiferromagnet and the quantum spin Hall phase as the only possible gapped groundstates for bilayer graphene


  • Selective Sodium Sensing with Gold-Coated Silicon Nanowire Field-Effect Transistors in a Differential Setup
    M. Wipf, R. L. Stoop, A. Tarasov, K. Bedner, W. Fu, I. A. Wright, C. J. Martin, E. C. Constable, M. Calame, and C. Schönenberger.
    ACS Nano, 7(7):5978-5983, 2013.

2012


  • A Verilog-A Model for Silicon Nanowire Biosensors: From Theory to Verification
    P. Livi, K. Bedner, A. Tarasov, Mathias Wipf, Y. Chen, C. Schönenberger, and A. Hierlemann.
    Sensors and Actuators B, 186(doi:10.1016/j.snb.2012.09.026):789-795, Dec. 2012.
    [Abstract]

    Silicon nanowires offer great potential as highly sensitive biosensors. Since the signals they produce are quite weak and noisy, the use of integrated circuits is preferable to read out and digitize these signals as quickly as possible following the sensing event to take full advantage of the properties of the nanowires. In order to design optimized and tailored circuits, simulations involving the sensor itself in the design phase are needed. We propose here a Verilog-A model for silicon nanowire-based biosensors. The model can easily be applied using commercially available Electronic Design Automation (EDA) tools that are commonly used for integrated circuit design and simulations. The model is quite general and comprehensive; it can be used to simulate different types of sensing events, while still being quite simple and undemanding in terms of computational power. The model is described in detail and verified with measurements from two different nanowire sensors featuring aluminum-oxide and hafnium-oxide coatings. Good agreement has been achieved in all cases, with errors never exceeding 21 percent. The complete Verilog-A code is made available in the Appendix.


  • Silicon-Based Ion-Sensitive Field-Effect Transistor Shows Negligible Dependence on Salt Concentration at Constant pH
    O. Knopfmacher, A. Tarasov, M. Wipf, W. Fu, M. Calame, and C. Schönenberger.
    ChemPhysChem, 6:9291-9298, Sept. 2012.

  • Understanding the Electrolyte Background for Biochemical Sensing with Ion-Sensitive Field-Effect Transistors
    A. Tarasov, M. Wipf, R. L. Stoop, K. Bedner, W. Fu, V. A. Guzenko, O. Knopfmacher, M. Calame, and C. Schönenberger.
    ACS Nano, 6:9291-9298, Sept. 2012.
    [Abstract]

    Silicon nanowire field-effect transistors have attracted substantial interest for various biochemical sensing applications, yet there remains uncertainty concerning their response to changes in the supporting electrolyte concentration. In this study, we use silicon nanowires coated with highly pH-sensitive hafnium oxide (HfO2) and aluminum oxide (Al2O3) to determine their response to variations in KCl concentration at several constant pH values. We observe a nonlinear sensor response as a function of ionic strength, which is independent of the pH value. Our results suggest that the signal is caused by the adsorption of anions (Cl-) rather than cations (K+) on both oxide surfaces. By comparing the data to three well established models, we have found that none of those can explain the present data set. Finally, we propose a new model which gives excellent quantitative agreement with the data.


  • Homogeneity of Bilayer Graphene
    F. Freitag, M. Weiss, R. Maurand, J. Trbovic, and C. Schönenberger.
    Solid State Communications, 152:2053-2057, Sept. 2012.
    [Abstract]

    We present non-linear transport measurements on suspended, current annealed bilayer graphene devices. Using a multi-terminal geometry we demonstrate that devices tend to be inhomogeneous and host two different electronic phases next to each other. Both of these phases show gap-like features of different magnitude in non-linear transport at low charge carrier densities, as already observed in previous studies. Here, we investigate the magnetic field dependence and find that both features grow with increasing field, the smaller one with 0.6meV/T, the larger one with a 5�10 times higher field dependence. We attribute the larger of the two gaps to an interaction induced broken symmetry state and the smaller one to localization in the more disordered parts of the device.


  • Sensing with liquid-gated graphene field-effect transistors
    W. Fu, C. Nef, A. Tarasov, M. Wipf, R. Stoop, O. Knopfmacher, M. Weiss, M. Calame, and C. Schönenberger.
    Proceedings of the IEEE conference on nanotechnology (IEEE-NANO), Aug. 2012.
    [Abstract]

    Liquid-gated graphene field-effect transistors (GFETs) with reliable performance are developed. It is revealed that ideal defect-free graphene should be inert to electrolyte composition changes in solution, whereas a defective one responses to electrolyte composition. This finding sheds light on the large variety of pH or ion-induced gate shifts that have been published for GFETs in the recent literature. As a next step to target graphene-based (bio-) chemical sensing platform, non-covalent functionalization of graphene has to be introduced.


  • Force-conductance correlation in individual molecular junctions
    C. Nef, P. L. T. M. Frederix, J. Brunner, M. Calame, and Schönenberger.
    Nanotechnology, 23:365201, August 2012.
    [Abstract]

    Conducting atomic force microscopy is an attractive approach enabling the correlation of mechanical and electrical properties in individual molecular junctions. Here we report on measurements of gold-gold and gold-octanedithiol-gold junctions. We introduce two-dimensional histograms in the form of scatter plots to better analyze the correlation between force and conductance. In this representation, the junction-forming octanedithiol compounds lead to a very clear step in the force-conductance data, which is not observed for control monothiol compounds. The conductance found for octanedithiols is in agreement with the idea that junction conductance is dominated by a single molecule.


  • True Reference Nanosensor Realized with Silicon Nanowires
    A. Tarasov, M. Wipf, K. Bedner, J. Kurz, W. Fu, V. A. Guzenko, O. Knopfmacher, L. Stoop, M. Calame, and C. Schönenberger.
    Langmuir, 28:9899-9905, May 2012.
    [Abstract]

    Conventional gate oxide layers (e.g., SiO2, Al2O3, or HfO2) in silicon field-effect transistors (FETs) provide highly active surfaces, which can be exploited for electronic pH sensing. Recently, great progress has been achieved in pH sensing using compact integrateable nanowire FETs. However, it has turned out to be much harder to realize a true reference electrode, which — while sensing the electrostatic potential — does not respond to the proton concentration. In this work, we demonstrate a highly effective reference sensor, a so-called reference FET, whose proton sensitivity is suppressed by as much as 2 orders of magnitude. To do so, the Al2O3 surface of a nanowire FET was passivated with a self-assembled monolayer of silanes with a long alkyl chain. We have found that a full passivation can be achieved only after an extended period of self-assembling lasting several days at 80 degC. We use this slow process to measure the number of active proton binding sites as a function of time by a quantitative comparison of the measured nonlinear pH-sensitivities to a theoretical model (site-binding model). Furthermore, we have found that a partially passivated surface can sense small changes in the number of active binding sites reaching a detection limit of delta Ns approx 170 1/micron^2 Hz^1/2 at 10 Hz and pH 3.


  • Near-Unity Cooper Pair Splitting Efficiency
    J. Schindele, A. Baumgartner, and C. Schönenberger.
    Phys. Rev. Lett., 109:157002, 2012.
    [Abstract]

    The two electrons of a Cooper pair in a conventional superconductor form a spin singlet and therefore a maximally entangled state. Recently, it was demonstrated that the two particles can be extracted from the superconductor into two spatially separated contacts via two quantum dots in a process called Cooper pair plitting (CPS). Competing transport processes, however, limit the efficiency of this process. Here we demonstrate efficiencies up to 90 percent, significantly larger than required to demonstrate interactiondominated CPS, and on the right order to test Bell�s inequality with electrons. We compare the CPS currents through both quantum dots, for which large apparent discrepancies are possible. The latter we explain intuitively and in a semiclassical master equation model. Large efficiencies are required to detect electron entanglement and for prospective electronics-based quantum information technologies.


  • Molecular electronics: functions and features arising from tailor-made molecules
    M. Mayor, M. Calame, and R. Waser.
    in Nanoelectronics and Information Technology, 3rd ed., Wiley-VCH, 2012.

  • Negative Differential Photoconductance in Gold Nanoparticle Arrays in the Coulomb Blockade Regime
    M. A. Mangold, M. Calame, M. Mayor, and A. W. Holleitner.
    ACS Nano, 6(5):4181, 2012.

  • Spontaneously Gapped Ground State in Suspended Bilayer Graphene
    F. Freitag, J. Trbovic, M. Weiss, and C. Schönenberger.
    Phys. Rev. Lett., 108:76602, 2012.

  • Quantum Hall Effect in Graphene with Superconducting Electrodes
    P. Rickhaus, M. Weiss, L. Marot, and C. Schönenberger.
    Nano Letters, 12:1942, 2012.

  • Cooper-Pair Splitter: towards a source of source of entangled electrons
    C. Schönenberger.
    SPS Communications, 36(Jan):17-18, 2012.

  • Kondo effect and spin-active scattering in ferromagnet-superconductor junctions
    H. Soller, L. Hofstetter, S. Csonka, Levy A. Yeyati, C. Schönenberger, and A. Komnik.
    Phys. Rev. B, 85:174512, 2012.

2011


  • Finite bias Cooper pair splitting
    L. Hofstetter, S. Csonka, A. Baumgartner, G. Fülöp, S. d�Hollosy, J. Nygård, and C. Schönenberger.
    Phys Rev. Lett., 107:136801, 2011.
    [Abstract]

    In a device with a superconductor coupled to two parallel quantum dots (QDs) the electrical tunability of the QD levels can be used to exploit nonclassical current correlations due to the splitting of Cooper pairs. We experimentally investigate the effect of a finite potential difference across one quantum dot on the conductance through the other completely grounded QD in a Cooper pair splitter fabricated on an InAs nanowire. We demonstrate that the nonlocal electrical transport through the device can be tuned by electrical means and that the energy dependence of the effective density of states in the QDs is relevant for the rates of Cooper pair splitting (CPS) and elastic cotunneling. Such experimental tools are necessary to understand and develop CPS-based sources of entangled electrons in solid-state devices.


  • Conductance fluctuations in graphene devices with superconducting contacts in different charge density regimes
    F. Freitag, J. Trbovic, and C. Schönenberger.
    Phys. Status Solidi B (arXiv:1108.4599), 248:2649, 2011.

  • Graphene Transistors Are Insensitive to pH Changes in Solution
    W. Fu, C. Nef, O. Knopfmacher, A. Tarasov, M. Weiss, M. Calame, and C. Schönenberger.
    Nano Letters, 11:3597, 2011.

  • Signal-to-noise ratio in dual-gated silicon nanotibbon field-effect sensors
    A. Tarasov, W. Fu, O. Knopfmacher, J. Brunner, M. Calame, and C. Schönenberger.
    Appl. Phys. Lett., 98:12114, 2011.

  • Gate-tunable split Kondo effect in a carbon nanotube quantum dot
    A. Eichler, M. Weiss, and C. Schönenberger.
    Nanotechnology, 22:265201, 2011.

2010


  • Sensitivity considerations in dual-gated Si-nanowire FET sensors
    O. Knopfmacher, A. Tarasov, W. Fu, M. Calame, and C. Schönenberger.
    European Cells and Materials, 20, Suppl. 3:140, November 2010.

  • Permalloy-based carbon nanotube spin-valve
    H. Aurich, A. Baumgartner, F. Freitag, A. Eichler, J. Trbovic, and C. Schönenberger.
    App. Phys. Lett, 97:153116, September 2010.

  • Molecular junctions: from tunneling to function
    M. Calame.
    Chimia Int. J. Chem, 64:391, 2010.

  • Quantitative Single-Molecule Detection at Ultralow Concentrations
    P. Haas, P. Then, A. Wild, W. Grange, S. Zorman, M. Hegner, M. Calame, U. Aebi, J. Flammer, and B. Hecht.
    Analytical Chemistry, 82 (14):6299�6302, 2010.

  • Hybrid superconductor – quantum dot devices
    De S. Franceschi, L. Kouwenhoven, C. Schönenberger, and W. Wernsdorfer.
    Nature Nanotechnology (invited), 5:703, 2010.

  • Novel Cruciform Structures as Model Compounds for Coordination Induced Single Molecule Switches
    S. Grunder, R. Huber, S. Wu, C. Schönenberger, M. Calame, and M. Mayor.
    Chimia Int. J. Chem, 64(3):140, 2010.

  • Ferromagnetic Proximity Effect in a Ferromagnet Quantum-Dot Superconductor Device
    L. Hofstetter, A. Geresdi, M. Aagesen, J. Nygård, C. Schönenberger, and S. Csonka.
    Phys. Rev. Lett., 104:246804, 2010.

  • Magnetic field and contact resistance dependence of non-local charge imbalance
    A. Kleine, A. Baumgartner, J. Trbovic, D. S. Golubev, A. D. Zaikin, and C. Schönenberger.
    Nanotechnology, 21:274002, 2010.

  • Cyclic conductance switching in networks of redox-active molecular junctions
    J. Liao, J. Agustsson, S. Wu, C. Schönenberger, M. Calame, Y. Leroux, M. Mayor, O. Jeannin, Y. -F. Ran, S. -X. Liu, and S. Decurtins.
    Nano Letters, 10:759�764, 2010.

  • Oligoaryl Cruciform Structures as Model Compounds for Coordination-Induced Single-Molecule Switches
    S. Grunder, R. Huber, S. Wu, C. Schönenberger, M. Calame, and M. Mayor.
    Eur. J. Org. Chem., page 833�845, 2010.

  • Eine Trenneinrichtung für Quantenpaare
    C. Schönenberger.
    Physik in unserer Zeit, 2:58, 2010.

  • Cooper Pair Splitter: Eine Trenneinrichtung für Quantenpaare
    C. Schönenberger.
    SSOM Bulletin 1+2 2010, 2010.

  • The Nernst limit in dual-gated Si nanowire FET sensors
    O. Knopfmacher, A. Tarasov, Wangyang Fu, M. Wipf, B. Niesen, M. Calame, and C. Schönenberger.
    Nano Letters, 10(6):2268-2274, 2010.

  • Superconductivity-enhanced conductance fluctuations in few layer graphene
    J. Trbovic, N. Minder, F. Freitag, and C. Schönenberger.
    Nanotechnology, 21:274005, 2010.

2009


  • Finite-bias visibility dependence in an electronic Mach-Zehnder interferometer
    E. Bieri, M. Weiss, O. Göktas, M. Hauser, C. Schönenberger, and S. Oberholzer.
    Phys. Rev. B, 79:245324, 2009.

  • Surface plasmon enhanced photoconductance of gold nanoparticle arrays with incorporated alkane linkers
    M. A. Mangold, C. Weiss, M. Calame, and A. W. Holleitner.
    Applied Physics Letters, 94(16):161104, 2009. [DOI]

  • Molecular junction based on aromatic coupling
    S. Wu, M. T. Gonzalez, R. Huber, S. Grunder, M. Mayor, C. Schönenberger, and M. Calame.
    Swiss Physical Society Communications, 26:10, 2009.

  • Tuning the Josephson current in carbon nanotubes with the Kondo effect
    A. Eichler, R. Deblock, M. Weiss, C. Schönenberger, H. Bouchiat, C. Karrasch, and V. Meden.
    Phys. Rev. B, 79:161407(R), 2009.

  • Cooper pair splitter realized in a two-quentum-dot Y-junction
    L. Hofstetter, S. Csonka, J. Nygård, and C. Schönenberger.
    Nature, 460:906, 2009.

  • Contact resistance dependence of crossed Andreev reflection
    A. Kleine, A. Baumgartner, J. Trbovic, and C. Schönenberger.
    Eur. Phys. Lett., 87:27011, 2009.
    [Abstract]

    We report experiments in nanometer-scaled superconductor/normal metal hybrid devices which show that in a small window of contact resistances, crossed Andreev reflection (CAR) can dominate the nonlocal transport for all energies below the superconducting gap. Besides crossed Andreev reflection, elastic cotunneling (EC) and nonlocal charge imbalance can be identified as competing subgap transport mechanisms in temperature-dependent four-terminal nonlocal measurements. We demonstrate a systematic change of the nonlocal resistance vs. bias characteristics with increasing contact resistances, which can be varied in the fabrication process. For samples with higher contact resistances, CAR is weakened relative to EC in the midgap regime, possibly due to dynamical Coulomb blockade. Gaining control of crossed Andreev reflection is an important step towards the realization of a solid-state entangler.


  • Gap opens in metallic nanotubes
    C. Schönenberger.
    Nature Nanotechnology, 4:147, 2009.

  • Light-controlled conductance switching of ordered metal-molecule-metal devices
    S. J. van der Molen, J. Lia, T. Kudernac, J. Agustsson, L. Bernard, M. Calame, B. van Wees, B. L. Fering, and C. Schönenberger.
    Nano Letters, 9:76-80, 2009.

  • Light-controlled conductance switching of ordered metal-molecule-metal devices
    S. J. van der Molen, J. Liao, T. Kudernac, J. Agustsson, L. Bernard, M. Calame, B. van Wees, B. L. Feringa, and C. Schönenberger.
    Nano Letters, 9(1):76-80, 2009.

2008


  • Detection of Transient Events in the Presence of Background Noise
    Wilfried Grange, Philippe Haas, Andreas Wild, Michael Andreas Lieb, Michel Calame, Martin Hegner, and Bert Hecht.
    J. Phys. Chem. B, 112(23):7140-7144, 2008. [DOI]

  • Giant g-factor fluctuations in InAs Nanowire Quantum Dots
    S. Csonka, L. Hofstetter, F. Freitag, S. Oberholzer, C. Schönenberger, T. S. Jespersen, M. Aagesen, and J. Nygård.
    Nano Letters, 8:3932, 2008.

  • Conductance values of alkanethiol molecular junctions
    M. T. Gonzalez, J. Brunner, R. Huber, S. Wu, C. Schönenberger, and M. Calame.
    New J. of Phys., 10:65018, 2008.

  • Large oscillating non-local voltage in multiterminal single-wall carbon nanotube devices
    G. Gunnarsson, J. Trbovic, and C. Schönenberger.
    Phys. Rev. B (rapid), 77:201405, 2008.

  • Electrical conductance of conjugated oligomers at the single molecule level
    R. Huber, M. -T. Gonzalez, S. Wu, M. Langer, S. Grunder, V. Horhoiu, M. Mayor, M. Bryce, C. Wang, R. Jitchati, C. Schönenberger, and M. Calame.
    J. Am. Chem. Soc., 130:1080-1084, 2008.

  • Interlinking Au nanoparticles in 2D arrays via conjugated dithiolated molecules
    J. Liao, Markus A. Mangold, S. Grunder, M. Mayor, C. Schönenberger, and M. Calame.
    New J. of Phys., 10:65019, 2008.

  • Molecular junctions based on aromatic coupling
    S. Wu, M. T. Gonzalez, R. Huber, S. Grunder, M. Mayor, C. Schönenberger, and M. Calame.
    Nature Nanotechnology, 3:569, 2008.

  • Scaling of 1/f nois ein tunable break-junctions
    ZhengMing Wu, SongMei Wu, S. Oberholzer, M. Steinacher, M. Calame, and C. Schönenberger.
    Phys. Rev. B, 78:235421, 2008.

2007


  • Controlled formation of metallic nanowires via Au nanoparticle ac trapping
    L. Bernard, M. Calame, S. J. van der Molen, J. Liao, and C. Schönenberger.
    Nanotechnology, 18:235202, May 2007.

  • Spectroscopy of Molecular Junction Networks Obtained by Place Exchange in 2D Nanoparticle Arrays
    L. Bernard, Y. Kamdzhilov, M. Calame, S. J. van der Molen, J. Liao, and C. Schönenberger.
    J. Phys. Chem. C, 111:18445-18450, 2007.

  • Even-Odd Effect in Andreev Transport through a Carbon Nanotube Quantum Dot
    A. Eichler, M. Weiss, S. Oberholzer, C. Schönenberger, Levy A. Yeyati, J. C. Cuevas, and A. Martin-Rodero.
    Phys. Rev. Lett., 99:126602, 2007.
    [Abstract]

    We have measured the current($I$)-voltage($V$) characteristics of a single-wall carbon nanotube quantum dot coupled to superconducting source and drain contacts in the intermediate coupling regime. Whereas the enhanced differential conductance $dI/dV$ due to the Kondo resonance is observed in the normal state, this feature around zero bias voltage is absent in the super\-conducting state. Nonetheless, a pronounced even-odd effect appears at finite bias in the $dI/dV$ sub-gap structure caused by Andreev reflection. The first-order Andreev peak appearing around $V=\Delta/e$ is markedly enhanced in gate-voltage regions, in which the charge state of the quantum dot is odd. This enhancement is explained by a `hidden’ Kondo resonance, pinned to one contact only. A comparison with a single-impurity Anderson model, which is solved numerically in a slave-boson mean\-field approach, yields good agreement with the experiment.


  • Mapping electron delocalization by charge transport spectroscopy in an artificial molecule
    M. R. Gräber, M. Weiss, D. Keller, S. Oberholzer, and C. Schönenberger.
    Annalen der Physik, 16(10-11):672-677, 2007.

  • Tetrathiafulvalene-based molecular electrical wires
    F. Giacalome, M. A. Herranz, L. Grüter, M. T. Gonzalez, M. Calame, C. Schönenberger, C. R. Arroyo, G. Rubio-Bollinger, M. Vélez3, N. Agrait, and N. Martin.
    ChemComm, pages 4854-4856, 2007.

  • New Cruciform Structures: Toward Coordination Induced Single Molecule Switches
    S. Grunder, R. Huber, V. Horhoiu, M. -T. Gonzalez, C. Schönenberger, M. Calame, and M. Mayor.
    J. Org. Chem, 72:8337-8344, 2007.

  • Feedback controlled electromigration in four-terminal nanojunctions
    Z. -M. Wu, M. Steinacher, R. Huber, M. Calame, S. J. Molene, and C. Schönenberger.
    Appl. Phys. Lett., 91:53118, 2007.

2006


  • Schaltende Moleküle
    C. Schönenberger, M. Calame, and M. Mayor.
    UniNova, Wissenschaftsmagazin der Universität Basel, 103:22-24, July 2006.

  • Molecular Electronics
    M. Calame and C. Schönenberger.
    Imaging & Microscopy, 8:36, June 2006.

  • Controlling spin in an electronic interferometer with spin-active interfaces
    A. Cottet, T. Kontos, W. Belzig, C. Schönenberger, and C. Bruder.
    Europhys. Lett., 74:320-326, April 2006.

  • Electrical Conductance of Molecular Junctions by a Robust Statistical Analaysis
    M. T. González, S. Wu, R. Huber, S. J. vam der Molen, C. Schönenberger, and M. Calame.
    Nano Letters, 6(10):2238-2242, 2006.

  • Molecular States in Carbon Nanotube Double Quantum Dots
    M. R. Gräber, W. A. Coish, C. Hoffmann, M. Weiss, J. Furer, S. Oberholzer, D. Loss, and C. Schönenberger.
    Phys. Rev. B, 74:75427, 2006.

  • Defining and Controlling Double Quantum Dots in Single-Wall Carbon Nanotubes
    M. R. Gräber, M. Weiss, S. Oberholzer, and C. Schönenberger.
    Semicond. Sci. Technol., 21:S64-S68, 2006.

  • Nanospintronics with Carbon Nanotubes
    A. Cottet, T. Kontos, S. Sahoo, H. T. Man, M. -S. Choi, W. Belzig, C. Bruder, A. F. Morpurgo, and C. Scönenberger.
    Semicond. Sci. Technol., 21:S78-S95, 2006.

  • Reversible formation of molecular junctions in two-dimensional nanoparticle arrays
    J. Liao, L. Bernard, M. Langer, C. Schönenberger, and M. Calame.
    Adv. Mat., 18(8):2444, 2006.

  • Positive cross-correlations in a normal-conducting fermionic beam-splitter
    S. Oberholzer, E. Bieri, C. Schönenberger, M. Giovannini, and J. Faist.
    Phys. Rev. Lett., 96:46804, Feb.~2006 2006.

  • Charge and Spin Transport in Carbon Nanotubes
    C. Schönenberger.
    Semicond. Sci. Technol., 21:S1-S9, 2006.

  • Directional scrolling of hetero-films on Si (110) and Si (111) surfaces
    L. Zhang, E. Deckhardt, A. Weber, C. Schönenberger, and D. Grützmacher.
    Microelectronic Engineering, 83(4-9):1233-36, 2006.
    [Abstract]

    NOTE, this is work done at PSI, actually no real contribution from Basel


  • Anomalous Coiling of SiGe/Si and SiGe/Si/Cr Helical Nanobelts
    L. Zhang, E. Ruh, D. Grützmacher, L. Dong, D. J. Bell, B. J. Nelson, and C. Schönenberger.
    Nano Letters, 6(7):1311-1317, 2006.
    [Abstract]

    NOTE, this is work done at PSI, actually no real contribution from Basel


  • Fabrication and characterization of freestanding Si/Cr micro- and nanospirals
    L. Zhang, L. Dong, D. J. Bell, B. J. Nelson, C. Schönenberger, and D. Grützmacher.
    Microelectronic Engineering, 83(4-9):1237-40, 2006.
    [Abstract]

    NOTE, this is work done at PSI, actually no real contribution from Basel

2005


  • Electric field control of spin transport
    S. Sahoo, T. Kontos, J. Furer, C. Hoffmann, M. Gräber, A. Cottet, and C. Schönenberger.
    Nature Physics, 1:99-102, Nov 2005.

  • Electrical spin injection in multi-wall carbon nanotubes with transparent ferromagnetic contacts
    S. Sahoo, T. Kontos, C. Schönenberger, and C. Sürgers.
    Appl. Phys. Lett., 86:112109, March 2005.

  • Shot-noise and conductance measurements of transparent superconductor/two-dimensional electron gas junctions
    B. -R. Choi, A. E. Hansen, T. Kontos, C. Hoffmann, S. Oberholzer, W. Belzig, C. Schönenberger, T. Akazaki, and H. Takayanagi.
    Phys. Rev. B, 72:24501, 2005.

  • Resonant tunneling through a C$_{60}$ molecular junction in liquid environment
    L. Grüter, F. Cheng, T. T. Heikkilä, M. T. González, F. Diederich, C. Schönenberger, and M. Calame.
    Nanotechnology, 16:2143-2148, cond-mat/0507264 v1 2005.

  • Electrical conductance of atomic contacts in liquid envirnoments
    L. Grüter, M. T. González, R. Huber, Michel C., and C. Schönenberger.
    Small, 1(11):1067-1070, 2005.

  • Controllable fabrication of SiGe/si and SiGe/Si/Cr helical nanobelts
    L. Zhang, E. Deckhardt, A. Weber, C. Schönenberger, and D. Grützmacher.
    Nanotechnology, 16:655-663, 2005.
    [Abstract]

    NOTE, this is work done at PSI, actually no real contribution from Basel

2004


  • On the Kondo effect in carbon nanotubes at half-filling
    B. Babić, T. Kontos, and C. Schönenberger.
    Phys. Rev. B, 70:235419, 2004.

  • Observation of Fano-Resonances in Single-Wall Carbon Nanotubes
    B. Babić and C. Schönenberger.
    Phys. Rev. B, 70:195408, 2004.

  • Conductance properties of nanotubes coupled to superconducting leads: signatures of Andreev states dynamics
    E. Vecino, M. Buitelaar, A. Martín-Rodero, C. Schönenberger, and Levy A. Yeyati.
    Solid-State Communications 131, 625 (2004), 131:625, cond-mat/0406240 2004.

  • Quantum dot coupled to a normal and a superconducting lead
    M. R. Gräber, T. Nussbaumer, W. Belzig, and C. Schönenberger.
    Nanotechnology, 15:S479, 2004.

2003


  • Multiple Andreev Reflections in a Carbon Nanotube Quantum Dot
    M. R. Buitelaar, W. Belzig, T. Nussbaumer, B. Babić, B. Bruder, and C. Schönenberger.
    Phys. Rev. Lett., 91:57005, August 2003.

  • Quantum Shot Noise
    C. Beenakker and C. Schönenberger.
    Physics Today, 56(5):37-42, May 2003.

  • Intrinsic thermal vibrations of suspended doubly clamped singe-wall carbon nanotubes
    B. Babić, J. Furer, S. Sahoo, S. Farhangfar, and C. Schönenberger.
    Nano Letters, 3:1577, 2003.

  • Ambipolar field-effect transistor on as-grown single-wall carbon nanotube
    B. Babić, M. Iqbal, and C. Schönenberger.
    Nanotechnology, 14:327-331, 2003.

  • Sensitivity of Single Multiwalled Carbon Nanotubes to the Environment
    M. Krüger, I. Widmer, T. Nussbaumer, M. Buitelaar, and C. Schönenberger.
    New Journal of Physics, 5:138.1-138.11, 2003.

  • From Photon Bunching to Electron Antibunching
    Christian Schönenberger.
    Bulletin of the SSOM, 2003.

2002


  • Nanomechanics of Microtubules
    A. Kis, S. Kasas, B. Babić, A. J. Kulik, G. A. D. Briggs, C. Schönenberger, S. Cataicas, and L. Forró.
    Phys. Rev. Lett., 89(24):248101, Dec 2002.

  • Vortex motion in micrometer-sized thin films of amorphous Nb$_0.7$Ge$_0.3$ weak-pinning superconductors
    D. Babić, T. Nussbaumer, C. Strunk, C. Schönenberger, and C. Sürgers.
    Phys. Rev. B, 66:14537, July 2002.

  • Orientation and Positioning of DNA molecules with an electric field technique
    F. Dewarrat, M. Calame, and C. Schönenberger.
    Single Mol., 3(4):189-193, July 2002.

  • Multi-wall carbon nanotubes as quantum dots
    M. R. \. Buitelaar, A. \. Bachtold, T. \. Nussbaumer, M. \. Iqbal, and C. \. Schönenberger.
    Phys. Rev. Lett., 88(15):156801, April 2002.

  • A quantum dot in the Kondo regime coupled to superconductors
    M. \. R. \. Buitelaar, T. \. Nussbaumer, and C. \. Schönenberger.
    Phys. Rev. Lett., 89(25):256801, 2002.

  • UHV compatible nanostructuring technique for mesoscopic hybrid devices: application to superconductor/ferromagnet Josephson contacts
    T. Hoss, C. Strunk, C. Sürgers, and C.~Schönenberger.
    Physica E, 14:341-345, 2002.

  • Shot noise of series quantum point contacts intercalating chaotic cavities
    S. \. Oberholzer, E. \. V. \. Sukhorukov, C. \. Strunk, and C. \. Schönenberger.
    Phys. Rev. B, 66:233304, 2002.

  • Crossover between classical and quantum shot noise in chaotic cavities�
    S. \. Oberholzer, E. V. \. Sukhorukov, and C. \. Schönenberger.
    Nature, 415:765, 2002.

  • Fabrication and superconducting properties of nanostructured SFS contacts
    C. \. Sürgers, T. \. Hoss, C. \. Strunk, and C.~Schönenberger.
    Journal of Magnetism and Magnetic Materials, 240:598-600, 2002.

  • The amplitude of non-equilibrium quantum interference in metallic mesoscopic systems
    C. \. Terrier, D. Babić, C. Strunk, T. \. Nussbaumer, and C. \. Schönenberger.
    Europhys. Lett., 59(3):437-443, 2002.

2001


  • Suppression of tunneling into multi-walled carbon nanotubes
    M. Bachtold, M. de Jonge, K. Grove-Rasmussen, P. L. McEuen, M. Buitelaar, and C.~Schönenberger.
    Phys. Rev. Lett., 87(16):166801, Oct~15 2001.

  • Carbon nanotubes, materials for the future
    L. Forró and C.~Schönenberger.
    Europhysics news, 32(3):86-90, May/June 2001.

  • The Electrochemical Nanotube Field-Effect Transistor
    M. Krüger, M. Buitelaar, T. Nussbaumer, C.~Schönenberger, and L. \. Forró.
    App. Phys. Lett., 78(9):1291-1293, Feb.~2001 2001.

  • Shot Noise by Quantum Scattering in Chaotic Cavities
    S.~Oberholzer, E.~V.~Sukhorukov, C.~Strunk, C.~Schönenberger, T.~Heinzel, and M.~Holland.
    Phys. Rev. Lett., 86(10):2114-2117, 2001.

  • Shot Noise in Schottky’s Vacuum Tube is Classical
    C. \. Schönenberger, S. Oberholzer, E. V. Sukhorukov, and H. Grabert.
    cond-mat/0112504, pages 1-5, 2001.

  • Comment on `Magnetoresistance and differential conductance in multiwalled carbon nanotubes’
    C. Schönenberger and A. Bachtold.
    Phys. Rev. B, 64:157401, 2001.

  • Andreev reflection and excess noise in diffusive SNS junctions
    Christoph Strunk.
    Physica C, C 352:61-66, 2001.

2000


  • Physics of Multiwall-Carbon Nanotubes
    C. Schönenberger and L. Forró.
    Physics World, 13(6):37-41, June 2000.

  • Electric Properties of Multiwall Carbon Nanotubes
    Christian Schönenberger.
    Proceedings of the Int. School of Physics, Enrico Fermi, Nuovo Cimento, June 2000.

  • Ground State Superconducting Phase Fluctuations as a Precursor for Strong Critical Fluctuations in high-$T_c$ Superconductors
    J. R. Cooper, D. Babić, J. W. Loram, Wai Lo, and D. A. Cardwell.
    Fizika A, 2000.
    [Abstract]

    We analyse the reversible magnetisation and specific heat of YBa$_2$Cu$_3$O$_{7-\delta}$ in the vortex liquid state and find that both properties are reasonably well described by the 3D XY critical-fluctuation model. The free-energy density in the vortex liquid state has a particularly simple form over a wide range of fields ($H$) and temperatures ($T$). This leads us to a picture in which the presence of critical fluctuations in high-$T_c$ superconductors is directly linked to the remarkably small number of overlapping Cooper pairs at $T$=0 and $H$=0 rather than low dimensionality or high temperatures.


  • The Reversible Magnetisation of YBa$_2$Cu$_3$O$_{7-\delta}$: 3D XY Critical Fluctuations and a Field Dependent Correlation Volume
    D. Babić and J. R. Cooper.
    Physica B, 284-288:769-770, 2000.
    [Abstract]

    The reversible magnetisation of YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ crystals shows 3D XY scaling behaviour over a wide doping range ($0 \leq \delta \leq 0.35$). In an extended region the reversible magnetisation is proportional to $H^{-1/2}$, this corresponds to a free energy density of $k_{B} T$ in a correlation VOLUME $V_{c}(H,T)= \xi_{ab}(T) \xi_{c}(T) (\Phi_{0} / H)^{1/2}$. All the reversible magnetisation curves can be collapsed on to a single curve by taking into account changes of anisotropy and $\xi_{ab}$ with $\delta$. We discuss some possible implications of this new result.


  • Effect of the Normal State Gap on the Thermoelectric Power, Irreversibility line and $c$-axis Resistivity of YBa$_2$Cu$_3$O$_{7 – \delta}$
    J. R. Cooper, H. Minami, V. W. Wittorf, D. Babić, and J. W. Loram.
    Physica C, 341-348:855-858, 2000.
    [Abstract]

    We discuss the effects of the normal state gap (NSG or $E_G$) on two normal state properties, the thermoelectric power of Y$_{0.8}$Ca$_{0.2}$Ba$_2$Cu$_3$O$_{7 – \delta}$ and the $c$-axis resistivity of YBa$_2$Cu$_3$O$_{7 – \delta}$ and one superconducting property, the irreversibility or vortex lattice melting line of YBa$_2$Cu$_3$O$_{7 – \delta}$. Rather surprisingly a simple Giaver tunneling model seems to give a good description of the $c$-axis resistivity and the available $c$-axis magnetoresistance data for YBa$_2$Cu$_3$O$_{7-\delta}$.


  • Multiple Andreev reflection and giant excess noise in diffusive superconductor/normal-metal/superconductor junctions
    T.~Hoss, C.~Strunk, T.~Nussbaumer, R.~Huber, U.~Staufer, and C.~Schönenberger.
    Phys. Rev. B, 62(6):4079-4085, 2000.
    [Abstract]

    We have studied superconductor/normal-metal/superconductor (SNS) junctions consisting of short Au or Cu wires between Nb or Al banks. The Nb based junctions display inherent electron heating effects induced by the high thermal resistance of the NS boundaries. The Al based junctions show in addition subharmonic gap structures in the differential conductance $dI/dV$ and a pronounced peak in the excess noise at very low voltages $V$. We suggest that the noise peak is caused by fluctuations of the supercurrent at the onset of Josephson coupling between the superconducting banks. At intermediate temperatures where the supercurrent is suppressed a noise contribution $\propto 1/V$ remains, which suggests the presence of a long range proximity effect in the noise.


  • Universal conductance fluctuations and low temperature 1/f noise in mesoscopic AuFe Spin glasses
    G. Neuttiens, C. Strunk, Van C. Haesendonck, and Y. Bruynseraede.
    Phys. Rev. B, 2000.

  • The Hanbury Brown and Twiss Experiment with Fermions
    S. Oberholzer, M. Henny, C. Strunk, C. Schönenberger, T. Heinzel, K. Ensslin, and M. Holland.
    Physica E, 6:314-317, 2000.

  • Interference and interactions in multiwall nanotubes
    C.~Strunk, A.~Bachtold, T.~Nussbaumer, and C.~Schönenberger.
    Physica B, 280(1-4):384-385, 2000.
    [Abstract]

    The electrical properties of single multiwall nanotubes (NTs) have been investigated in parallel and perpendicular magnetic field. Quantum interference phenomena like weak localization, Aharonov-Bohm effect, UCF, and nonlocal resistance contributions prove that NTs are mesoscopic (phase-coherent) objects at low temperature. The relatively large elastic-scattering length, inferred from our data, suggests that our NTs are 1d quasi-ballistic conductors where long-range coulomb interactions should be important. This is further substantiated by the temperature dependence of the resistance and by tunneling spectroscopy displaying a pronounced zero-bias anomaly.


  • Synthesis of Gold Sols of Rod-Shaped Particles using porous Alumina as Template
    M. I. van der Zande, M. R. Böhmer, L. G. J. Fokkink, and C. Schönenberger.
    Langmuir, 16:451, 2000.

1999


  • Aharonov-Bohm Oscillations in Carbon Nanotubes
    A. Bachtold, C. Strunk, J. -P. Salvetat, J. -M. Bonard, L. Forró, T. Nussbaumer, and C. Schönenberger.
    Nature, 397:673, 1999.

  • Electrical conduction through DNA molecules
    H. -W. Fink and C. Schönenberger.
    Nature, 398:407, 1999.

  • The 1/3-shot noise suppression in diffusive nanowires
    M. Henny, S. Oberholzer, C. Strunk, and C. Schönenberger.
    Phys.\ Rev.\ B., 59:2871, 1999.

  • The Fermionic Hanbury-Brown & Twiss Experiment
    M. Henny, S. Oberholzer, C. Strunk, T. Heinzel, K. Ensslin, M. Holland, and C. Schönenberger.
    Science, 284:296, 1999.

  • Nonorganic evaporation mask for superconducting nanodevices
    T. Hoss, C. Strunk, and C. Schönenberger.
    Microelectronic Engineering, 46:149, 1999.

  • Interference and Interaction in Multiwall Carbon Nanotubes
    C. Schönenberger, A. Bachtold, C. Strunk, J. -P. Salvetat, and L. Forró.
    Appl. Phys. A, 69:283, 1999.

  • Amplitude of Aharonov-Bohm oscillations in mesoscopic metallic rings as a function of the DC bias voltage
    C. Terrier, T. Nussbaumer, C. Strunk, D. Babić, and C. Schönenberger.
    Fizika A, 8(3):157-164, 1999.
    [Abstract]

    We report measurements of the amplitude of the Aharonov-Bohm oscillations in a mesoscopic diffusive gold ring as a function of the DC bias voltage $V_{DC}$. The amplitude of the $h/e$ oscillations increases with $V_{DC}$ once the Thouless energy $E_c$ and thermal energy are exceeded, and decreases at higher values of $V_{DC}$. The increase of the amplitude is interpreted in terms of a superposition of the statistically independent contributions of $eV_{DC}/E_c$ energy intervals, whereas its decrease at high $V_{DC}$ could be attributed to enhanced inelastic scattering processes.

1998


  • Resistance anomalies in mesoscopic super\-conducting Al-structures
    C. Strunk, V. Bruyndoncx, Van C. Haesendonck, V. V. Moshchalkov, Y. Bruynseraede, C. -J. Chien, B. Burk, and V. Chandrasekhar.
    Phys. Rev. B, pages 10854-10866, 1998.

  • Contacting Single Template Sythesized Nanowires for Electric Measurements
    A. Bachtold, C. Terrier, M. Krüger, M. Henny, T. Hoss, C. Strunk, R. Huber, H. Birk, U. Staufer, and C. Schönenberger.
    Microelectronic Engineering, 41/42:571, 1998.

  • Contacting Carbon-Nanotubes selectively with Low-Ohmic Contacts for Four-Probe Electric Measurements
    A. Bachtold, J. -P. Salvetat, J. -M. Bonard, M. Henny, C. Terrier, C. Strunk, L. Forró, and C. Schönenberger.
    Appl. Phys. Lett., 73:274-276, 1998.

  • Thermoelectric Effects in Mesoscopic AuFe Spinglass Wires
    G. Neuttiens, J. Eom, C. Strunk, H. Pattyn, Van C. Haesendonck, Y. Bruynseraede, and V. Chandrasekhar.
    Europhysics Letters, 42:185-192, 1998.

  • Extrinsic origins of electrical transport anomalies near the superconducting transition in mesoscopic aluminum lines
    B. Burk, C. J. Chien, V. Chandrasekhar, Strunk V. C. Bruyndoncx, Van C. Haesendonck, V. V. Moshchalkov, and Y. Bruynseraede.
    Journal of Applied Physics, 83:1549-1553, 1998.

  • Size dependent thermopower in mesoscopic AuFe wires
    C. Strunk, M. Henny, C. Schönenberger, G. Neuttiens, and Van C. Haesendonck.
    Phys. Rev. Lett., 81:2982, 1998.

1997


  • Electron Holography of Individual DNA Molecules
    H. -W. Fink, H. Schmid, E. Ermantraut, and T. Schulz.
    J. Opt. Soc. Am. A, 14(9):2168, Sept. 1997.

  • Carbon Nanotubes are Coherent Electron Sources
    Heinz Schmid and Hans-Werner Fink.
    Appl. Phys. Lett., 70(20):2679, May 1997.

  • Electron Heating Effects in Diffusive Metal Wires
    M. Henny, H. Birk, R. Huber, C. Strunk, A. Bachtold, M. Krüger, and C. Schönenberger.
    Appl. Phys. Lett., 71:773, 1997.

  • Template-Synthesis of Nanowires in Porous Polycarbonate Membranes: Electrochemistry and Morphology
    C. Schönenberger, B. M. I. van der Zande, L. G. J. Fokkink, M. Henny, C. Schmid, M. Krüger, A. Bachtold, R. Huber, H. Birk, and U. Staufer.
    J. Phys. Chem. B, 101:5497-5506, 1997.

  • Microscopes images individual charges
    Christian Schönenberger.
    Physics World, 10:15, 1997.

  • Aqueous Gold Sols of Rod Shaped Particles
    M. I. van der Zande, Marcel R. Böhmer, Lambertus G. J. Fokkink, and C. Schönenberger.
    J. Phys. Chem. B, 101:852-854, 1997.

1996


  • Fabrication of a Silicon-Pyrex-Silicon Stack by AC Anodic Bonding
    M. Despont, H. Gross, F. Arrouy, C. Stebler, and U. Staufer.
    Sensors and Actuators, Dec. 1996.

  • Fabrication of an Integrated Silicon-Based Lens for Low-Energy Miniaturized Electron Columns
    M. Despont, G. Beljakovic, C. Stebler, U. Staufer, and P. Vettiger.
    Jap. J. Appl. Phys., Dec. 1996.

  • Preamplifier for Electrical Current Noise Measurements at Low Temperatures
    H. Birk, K. Oostveen, and C. Schönenberger.
    Rev. Sci. Instr., 67:2977, 1996.

  • Superconductor-semiconductor interaction effects in mesoscopic hybrid structures
    F. Rahman, T. J. Thornton, R. Huber, L. F. Cohen, W. T. Yuen, and R. A. Stradling.
    prb, 54:14026, 1996.

  • Nanometer Lithography on Hydrogen-Terminated Silicon by Scanning-Probe Microscopy
    Christian Schönenberger and Niels Kramer.
    Microelectronic Engineering, 32:203-217, 1996.

  • Secondary Electron Imaging by Means of a Microfabricated Electron Column
    C. Stebler, M. Despont, and U. Staufer.
    J. Phys. III France, 6:1435, 1996.

  • Microcolumn Based Low Energy E-Beam Writing
    C. Stebler, M. Despont, U. Staufer, T. H. P. Chang, K. Y. Lee, and S. A. Rishton.
    Microelectronic Engineering, 30:45, 1996.

  • Electron-Beam Microcolumn Fabrication and Testing
    M. Despont, U. Staufer, C. Stebler, H. Gross, and P. Vettiger.
    Microelectronic Engineering, 30:69, 1996.

  • Fluxiod Quantization Effects in Superconducting Mesoscopic Al Multiloop Structures
    V. Bruyndoncx, C. Strunk, V. V. Moshchalkov, Van C. Haesendonck, and Y. Bruynseraede.
    Europhysics Letters, 36:449-459, 1996.

  • Absence of Size Dependence in the Spin-Glass Resistivity of Mesoscopic AuFe Wires?
    C. Strunk, V. Bruyndoncx, Van C. Haesendonck, V. V. \. Moshchalkov, Y. Bruynseraede, B. Burk, C. J. Chien, and V. Chandrasekhar.
    Europhysics Letters, 34:617-622, 1996.

  • Nonmonotonic Superconducting Transitions in Mesoscopic Al Structures induced by Radiofrequency Radiation
    C. Strunk, V. Bruyndoncx, Van C. Haesendonck, V. V. \. Moshchalkov, Y. Bruynseraede, B. Burk, C. J. Chien, and V. Chandrasekhar.
    Phys. Rev. B, 53:11332-11335, 1996.

  • Asymmetric Nonlinear Differential Resistance of Mesoscopic AuFe Spin-Glass Wires
    J. Eom, G. Neuttiens, C. Strunk, Van C. Haesendonck, Y.~Bruynseraede, and V. Chandrasekhar.
    Phys. Rev. Lett., 77:2276-2279, 1996.

  • Nonlocal Effects in Mesoscopic Al Structures
    J. Eom, G. Neuttiens, C. Strunk, Van C. Haesendonck, C. Strunk, V. Bruyndoncx, V. V. Moshchalkov, Van C. Haesendonck, and Y. Bruynseraede.
    Phys. Rev. B, 54:R12701-R12704, 1996.

1995


  • Shot-noise suppression in the single-electron tunneling regime
    H. Birk, M. J. M. de Jong, and C. Schönenberger.
    Phys. Rev. Lett., 75:1610, 1995.

  • Nanolithografie: Nanolithografie op Silicium en gehydrogeneerd amorf Silicium met een Scanning Tunneling Microscoop
    J. Jorritsma, N. Kramer, H. Birk, M. R. vand der Berg, and C. Schönenberger.
    Nevacblad, 33(1):17-21, 1995.

  • Fabrication of large arrays of metallic nanowires on V-grooved substrates
    J. Jorritsma, M. A. M. Gijs, C. Schönenberger, and J. G. H. Stienen.
    Appl. Phys. Lett., 67:1489, 1995.

  • Nanometer Lithography on Silicon and Hydrogenated Amorphous Silicon with Low Energy Electrons
    N. Kramer, J. Jorritsma, H. Birk, and C. Schönenberger.
    J. Vac. Sci. Technol. B, 13:805, 1995.

  • Nanometer Lithography on Silicon and Hydrogenated Amorphous Silicon with Low Energy Electrons
    N. Kramer, J. Jorritsma, H. Birk, and C. Schönenberger.
    Microelectronic Engineering, 27:47-50, 1995.

  • Fabrication of metallic nanowires with a scanning tunneling microscope
    N. Kramer, J. Jorritsma, H. Birk, and C. Schönenberger.
    Appl. Phys. Lett., 66:1325, 1995.

  • Resistless High Resolution Optical Lithography on Silicon
    N. Kramer, M. Niesten, and C. Schönenberger.
    Appl. Phys. Lett., 67:2989, 1995.

  • Giant Magnetoresistance of Electrodeposited Co/Cu Multilayers
    S. K. J. Lenczowski, C. Schönenberger, M. A. M. Gijs, and W. J. M. de Jonge.
    J. Magn. Magn. Mater., 148:455, 1995.

  • Decapitation of tungsten field emitter tips during sputter sharpening
    C. Schiller, A. A. Koomans, T. L. van Rooy, C. Schönenberger, and H. B. Elswijk.
    Surface Science, L925:339, 1995.

  • Domain Structure of Self-Assembled Alkanethiol Monolayers on Gold
    C. Schönenberger, J. Jorritsma, J. A. M. Sondag-Huethorst, and L. G. J. Fokkink.
    J. Phys. Chem., 99:3259, 1995.

1994


  • What are the `holes’ in self-assembled monolayers of alkanethiols on Au
    C. Schönenberger, J. A. M. Sondag-Huethorst, J. Jorritsma, and L. G. J. Fokkink.
    Langmuir, 10:611, 1994.

  • Formation of Holes in Alkanethiol Monolayers on Gold
    J. \. A. \. M. \. Sondag-Huethorst, C. \. Schönenberger, and L. \. G. \. J. \. Fokkink.
    J.\ Phys.\ Chem., 98:6826, 1994.

1993


  • Single-electron tunneling in double-barrier junctions by scanning-tunneling microscopy
    C. Schönenberger, H. van Houten, J. M. Kerkhof, and H. C. Donkersloot.
    Appl. Surf. Sci., 67:222, 1993.

  • Polarization charge relaxation and the Coulomb staircase in ultra-small double-barrier tunnel junctions
    C. Schönenberger, C. W. J. Beenakker, and H. van Houten.
    Physica B, 189:218, 1993.

1992


  • Characterization of titanium nanoscopic wire by STM and SFM
    C. Joachim, B. Rousset, C. Schönenberger, A. Kerrien, E. Druet, and J. Chevalier.
    Nanotechnology, 2(96), 1992.

  • Single-electron tunneling observed at room temperature by scanning-tunneling microscopy
    C. Schönenberger, H. van Houten, and H. C. Donkersloot.
    Europhys. Lett., 20:249, 1992.

  • Charge flow during metal-insulator contact
    C. Schönenberger.
    Phys. Rev. B, 45:3861, 1992.

  • Single-electron tunneling up to room temperatures
    C. Schönenberger, H. van Houten, H. C. Donkersloot, A. M. T. van der Putten, and L. G. L. Fokkink.
    Physica Scripta, T45:289-291, 1992.

1991


  • Luminescence in scanning tunneling microscopy on III-V nanostructures
    S. F. Alvarado, Ph. Renaud, D. L. Abraham, C. Schönenberger, D. J. Arent, and H. P. Meier.
    J. Vac. Sci. Technol. B, 9:409, 1991.

  • Probing single charges by scanning force microscopy
    C. Schönenberger and S. F. Alvarado.
    Modern Phys. Lett. B, 5:871, 1991.

  • Magnetic force microscopy and its applications to longitudional thin films
    C. Schönenberger, S. F. Alvarado, S. E. Lambert, and I. L. Sanders.
    J. Mag. Mag. Mat., 93, 1991.

1990


  • STM and luminescence
    D. L. Abraham, A. Veider, C. Schönenberger, D. J. Arent, H. P. Meier, and S. F. Alvarado.
    Helv. Phys. Acta, 63:783, 1990.

  • Nanometer resolution in luminescence microscopy of III-V heterostructures
    D. L. Abraham, A. Veider, C. Schönenberger, H. P. Meier, D. J. Arent, and S. F. Alvarado.
    Appl. Phys. Lett., 56:1564, 1990.

  • Separation of magnetic and topographic effects in force microscopy
    C. Schönenberger, S. F. Alvarado, S. E. Lambert, and I. L. Sanders.
    J. Appl. Phys., 67:7278, 1990.

  • Understanding magnetic force microscopy
    C. Schönenberger and S. F. Alvarado.
    Z. Phys. B – Condensed Matter, 80:373, 1990.

  • Observation of single charge carriers by force microscopy
    C. Schönenberger and S. F. Alvarado.
    Phys. Rev. Lett., 65:3162, 1990.

1989


  • Scanning tunneling microscopy as a tool to study surface roughness of sputtered thin films
    C. Schönenberger, S. F. Alvarado, and C. Ortiz.
    J. Appl. Phys., 66:4258, 1989.

  • A differential interferometer for force microscopy
    C. Schönenberger and S. F. Alvarado.
    Rev. Sci. Instr., 60:3131, 1989.

1987


  • Hall-Effect and Resistivity Study of the Heavy Fermion System URu2Si2
    J. Schoenes, C. Schönenberger, J. J. M. Franse, and A. A. Menovsky.
    Phys. Rev. B, 55(10):5375-5378, 1987.

  • Transport Properties of the Heavy Fermion System URu2Si2
    C. Schönenberger, C. Schoenes, and J. J. M. Franse.
    Helvetica Physica Acta, 60(5-6):785-788, 1987.