The effectiveness of five different anchor groups for non-covalent interfacing to graphene electrodes are compared. A family of six molecules is tested in single-molecule junctions: five consist of the same porphyrin core with different anchor groups, and the sixth is a reference molecule without anchor groups. The junction formation probability (JFP) has a strong dependence on the anchor group. Larger anchors give higher binding energies to the graphene surface, correlating with higher JFPs. The best anchor groups tested are 1,3,8-tridodecyloxypyrene and 2,5,8,11,14-pentadodecylhexa-peri-hexabenzocoronene, with JFPs of 36% and 38%, respectively. Many junctions are tested at 77 K for each molecule by measuring source-drain current as a function of bias and gate voltage. For each compound, there is wide variation in the strength of the electronic coupling to the electrodes and in the location of Coulomb peaks. In most cases, this device-to-device variability makes it impossible to observe trends between the anchor and the charge-transport characteristics. Tetrabenzofluorene anchors, which are not π-conjugated with the

Abstract. Effective electron mobilities are obtained by transport measurements on InAs nanowire field-effect transistors at temperatures ranging from 10 − 200 K. The mobility increases with temperature below ∼ 30 − 50 K, and then decreases with temperature above 50 K, consistent with other reports. The magnitude and temperature dependence of the observed mobility can be explained by Coulomb scattering from ionized surface states at typical densities. The behaviour above 50 K is ascribed to the thermally activated increase in the number of scatterers, although nanoscale confinement also plays a role as higher radial subbands are populated, leading to interband scattering and a shift of the carrier distribution closer to the surface. Scattering rate calculations using finite-element simulations of the nanowire transistor confirm that these mechanisms are able to explain the data.

The radial confining potential in a semiconductor nanowire plays a key role in determining its quantum transport properties. Previous reports have shown that an axial magnetic field induces flux-periodic conductance oscillations when the electronic states are confined to a shell. This effect is due to the coupling of orbital angular momentum to the magnetic flux. Here, we perform calculations of the energy level structure, and consequently the conductance, for more general cases ranging from a flat potential to strong surface band bending. The transverse states are not confined to a shell, but are distributed across the nanowire. It is found that, in general, the subband energy spectrum is aperiodic as a function of both gate voltage and magnetic field. In principle, this allows for precise identification of the occupied subbands from the magnetoconductance patterns of quasi-ballistic devices. The aperiodicity becomes more apparent as the potential flattens. A quantitative method is introduced for matching features in the conductance data to the subband structure resulting from a particular radial potential, where a functional form for the potential is used that depends on two free parameters. Finally, a short-channel InAs nanowire FET device is measured at low temperature in search of conductance features that reveal the subband structure. Features are identified and shown to be consistent with three specific subbands. The experiment is analyzed in the context of the weak localization regime, however, we find that the subband effects predicted for ballistic transport should remain visible when back scattering dominates over interband scattering, as is expected for this device.

The superconducting proximity effect is probed experimentally in Josephson junctions fabricated with InAs nanowires contacted by Nb leads. Contact transparencies [Formula: see text] are observed. The electronic phase coherence length at low temperatures exceeds the channel length. However, the elastic scattering length is a few times shorter than the channel length. Electrical measurements reveal two regimes of quantum transport: (i) the Josephson regime, characterised by a dissipationless current up to ∼100 nA, and (ii) the quantum dot (QD) regime, characterised by the formation of Andreev bound states (ABS) associated with spontaneous QDs inside the nanowire channel. In regime (i), the behaviour of the critical current I versus an axial magnetic field [Formula: see text] shows an unexpected modulation and persistence to fields [Formula: see text] T. In the QD regime, the ABS are modelled as the current-biased solutions of an Anderson-type model. The applicability of devices in both transport regimes to Majorana fermion experiments is discussed.

We study random telegraph noise in the conductance of InAs nanowire field-effect transistors due to single electron trapping in defects. The electron capture and emission times are measured as functions of temperature and gate voltage for individual traps, and are consistent with traps residing in the few-nanometer-thick native oxide, with a Coulomb barrier to trapping. These results suggest that oxide removal from the nanowire surface, with proper passivation to prevent regrowth, should lead to the reduction or elimination of random telegraph noise, an important obstacle for sensitive experiments at the single electron level.

Memristive systems are generalisations of memristors, which are resistors with memory. In this paper, we present a quantum description of quantum-dot memristive systems. Using this model we propose and experimentally demonstrate a simple and practical scheme for realising memristive systems with quantum dots. The approach harnesses a phenomenon that is commonly seen as a bane of nanoelectronics, i.e. switching of a trapped charge in the vicinity of the device. We show that quantum-dot memristive systems have hysteresis current-voltage characteristics and quantum jump induced stochastic behaviour. While our experiment requires low temperatures, the same setup could in principle be realised with a suitable single-molecule transistor and operated at or near room temperature.

The native oxide at the surface of III-V nanowires, such as InAs, can be a major source of charge noise and scattering in nanowire-based electronics, particularly for quantum devices operated at low temperatures. Surface passivation provides a means to remove the native oxide and prevent its regrowth. Here, we study the effects of surface passivation and conformal dielectric deposition by measuring electrical conductance through nanowire field effect transistors treated with a variety of surface preparations. By extracting field effect mobility, subthreshold swing, threshold shift with temperature, and the gate hysteresis for each device, we infer the relative effects of the different treatments on the factors influencing transport. It is found that a combination of chemical passivation followed by deposition of an aluminum oxide dielectric shell yields the best results compared to the other treatments, and comparable to untreated nanowires. Finally, it is shown that an entrenched, top-gated device using an optimally treated nanowire can successfully form a stable double quantum dot at low temperatures. The device has excellent electrostatic tunability owing to the conformal dielectric layer and the combination of local top gates and a global back gate.PACS numbers:

Evidence is given for the effectiveness of InAs surface passivation by the growth of an epitaxial In 0.8 Al 0.2 As shell. The electron mobility is measured as a function of temperature for both core-shell and unpassivated nanowires, with the core-shell nanowires showing a monotonic increase in mobility as temperature is lowered, in contrast to a turnover in mobility seen for the unpassivated nanowires. We argue that this signifies a reduction in low temperature ionized impurity scattering for the passivated nanowires, implying a reduction in surface states. Core-shell nanowires were grown in a gas source molecular beam epitaxy system using Au seed particles 16 . First, InAs cores were grown axially by the Au assisted vapour liquid solid mechanism on a p-GaAs (111)B substrate at a growth temperature of 420This was followed by the inclusion of Al to facilitate radial growth of the In 0.8 Al 0.2 As shell 17 .The nanowires were characterized using transmission electron microscopy (TEM).As-grown nanowires were sonicated and suspended in ethanol, dispersed onto TEM grids have an inner core and an outer shell structure. In general, the nanowires had a core diameter of 20-50 nm and a shell that was 12-15 nm thick, independent of core diameter. The chemical composition of the nanowires was analyzed by energy-dispersive x-ray spectroscopy (EDS). As shown in Figure 1a, the EDS line scan analysis along the radial direction showsIn and As in the core region and In, As and Al in the shell region. High-resolution TEM (HRTEM) image of a representative unetched nanowire in Figure 1b clearly shows lattice 3 fringes of a single-crystal nanowire along the [2110] zone axis. Both core and shell exhibit wurtzite crystal structure, evidenced by ABAB... stacking, and confirmed by selected area diffraction. HRTEM and electron diffraction data are both consistent with a dislocation-free core-shell interface for these nanowires. However, at higher Al concentrations, dislocations due to relaxation of the core-shell interface are observed 17 . The nanowires studied here had low stacking fault densities, achieved by using sufficiently low growth rates 17,18 . Below, we also show data from unpassivated InAs nanowires that were grown under nominally identical conditions to the growths of the nanowire cores mentioned previously, except that the axial growth rate was 0.25 µm/hr and 0.5 µm/hr for the core-shell and bare nanowires, respectively.FET devices were fabricated using a standard e-beam lithography technique. As-grown nanowires were mechanically deposited onto a 175 nm thick SiO 2 layer above a n ++ -Si substrate. Selected nanowires with diameters 40−80nm were located relative to pre-existing fiducial markers by scanning electron microscopy (SEM), with care taken to minimize the electron dose. The contact areas were etched with citric acid to remove the shell material, followed by room temperature sulfur passivation to prevent oxide regrowth 19 during the sample transfer to an e-beam metal evaporator. Ni/Au (30nm/50nm) metal contacts were...