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We explore solid electrolytes for electrostatic gating using field-effect transistors (FETs) in which thin WSe2 crystals are exfoliated and transferred onto a lithium-ion conducting glass ceramic substrate. For negative gate voltages (VG < 0), the devices work equally well as ionic liquid gated FETs while offering specific advantages, whereas no transistor action is seen for VG > 0. For VG < 0, the devices can nevertheless be driven into the ambipolar injection regime by applying a large source-drain bias and strong electroluminescence is observed when direct band-gap WSe2 monolayers are used. Detecting and imaging the emitted light is much simpler in these FETs as compared to ionic liquid gated transistors, because the semiconductor surface is exposed (i.e., not covered by another material). Our results show that solid electrolytes are complementary to the existing liquid gates, as they enable experiments that are not possible when the semiconductor is buried under the liquid itself. [ABSTRACT FROM AUTHOR]

We perform scanning photocurrent microscopy on WS2 ionic liquid-gated field effect transistors exhibiting high-quality ambipolar transport. By properly biasing the gate electrode, we can invert the sign of the photocurrent showing that the minority photocarriers are either electrons or holes. Both in the electron- and hole-doping regimes the photocurrent decays exponentially as a function of the distance between the illumination spot and the nearest contact, in agreement with a two-terminal Schottky-barrier device model. This allows us to compare the value and the doping dependence of the diffusion length of the minority electrons and holes on a same sample. Interestingly, the diffusion length of the minority carriers is several times larger in the hole accumulation regime than in the electron accumulation regime, pointing out an electron-hole asymmetry in WS2. [ABSTRACT FROM AUTHOR]

We have developed a process to fabricate suspended graphene devices with local bottom gates, and tested it by realizing electrostatically controlled pn junctions on a suspended graphene mono-layer nearly 2 μm long. Measurements as a function of gate voltage, magnetic field, bias, and temperature exhibit characteristic Fabry-Perot oscillations in the cavities formed by the pn junction and each of the contacts, with transport occurring in ballistic regime. Our results demonstrate the possibility to achieve a high degree of control on the local electronic properties of ultra-clean suspended graphene layers, a key aspect for the realization of high quality graphene nanostructures. [ABSTRACT FROM AUTHOR]

The authors report a systematic study of the bias-dependent contact resistance in rubrene single-crystal field-effect transistors with Ni, Co, Cu, Au, and Pt electrodes. They show that the reproducibility in the values of contact resistance strongly depends on the metal, ranging from a factor of 2 for Ni to more than three orders of magnitude for Au. Surprisingly, field-effect transistors with Ni, Co, and Cu contacts exhibit an unexpected reproducibility of the bias-dependent differential conductance of the contacts once this has been normalized to the value measured at zero bias. This reproducibility may enable the study of microscopic carrier injection processes into organic semiconductors. [ABSTRACT FROM AUTHOR]

We have investigated the contact resistance of rubrene single-crystal field-effect transistors (FETs) with nickel electrodes by performing scaling experiments on devices with channel length ranging from 200 nm up to 300 μm. We find that the contact resistance can be as low as 100 Ω cm with narrowly spread fluctuations. For comparison, we have also performed scaling experiments on similar gold-contacted devices, and found that the reproducibility of FETs with nickel electrodes is largely superior. These results indicate that nickel is a very promising electrode material for the reproducible fabrication of low resistance contacts in organic FETs. [ABSTRACT FROM AUTHOR]

Discusses the synthesis of single-walled carbon nanotubes by chemical vapor deposition of methane at controlled locations on a substrate using patterned catalytic islands. Allowing of a large number of ohmically contacted nanotube devices with controllable length to be placed on a single substrate; Demonstration of ohmic contacting.