Paola Barbara

Electron-hole transport and photovoltaic effect in gated MoS2 Schottky junctions

Semiconducting molybdenum disulfphide has emerged as an attractive material for novel nanoscale optoelectronic devices due to its reduced dimensionality and large direct bandgap. Since optoelectronic devices require electron-hole generation/recombination, it is important to be able to fabricate ambipolar transistors to investigate charge transport both in the conduction band and in the valence band. Although n-type transistor operation for single-layer and few-layer MoS2 with gold source and drain contacts was recently demonstrated, transport in the valence band has been elusive for solid-state devices. Here we show that a multi-layer MoS2 channel can be hole-doped by palladium contacts, yielding MoS2 p-type transistors. When two different materials are used for the source and drain contacts, for example hole-doping Pd and electron-doping Au, the Schottky junctions formed at the MoS2 contacts produce a clear photovoltaic effect.

Mechanism of NO2 detection in carbon nanotube field effect transistor chemical sensors

We report an experimental method that clearly determines the sensing mechanism of carbon-nanotube field effect transistors. The nanotube/electrode contacts are covered with a thick and long passivation layer that hinders their exposure to chemicals in a controlled fashion, leaving only the midsection of the nanotube exposed. In the case of nitrogen dioxide, a considerably delayed response is fully consistent with the diffusion of the gas through the passivation layer. The results clearly indicate that nitrogen dioxide detection is due to changes at the interfaces between the nanotube and the electrodes and not to molecules adsorbed on the nanotube surface.

Low Carrier Density Epitaxial Graphene Devices On SiC

The transport characteristics of graphene devices with low n- or p-type carrier density (∼10(10) -10(11) cm(-2) ), fabricated using a new process that results in minimal organic surface residues, are reported. The p-type molecular doping responsible for the low carrier densities is initiated by aqua regia. The resulting devices exhibit highly developed ν = 2 quantized Hall resistance plateaus at magnetic field strengths of less than 4 T.

Electrical properties and memory effects of field-effect transistors from networks of single- and double-walled carbon nanotubes

We study field-effect transistors made of single- and double-walled carbon nanotube networks for applications as memory devices. The transfer characteristics of the transistors exhibit a reproducible hysteresis which enables their use as nano-sized memory cells with operations faster than 10 ms, endurance longer than 10(+4) cycles and charge retention of a few hours in air. We propose water enhanced charge trapping at the SiO(2)/air interface close to the nanotubes as the dominant mechanism for charge storage. We show that charge storage can be improved by limiting exposure of the device to air.

Reentrant ac magnetic susceptibility in Josephson-junction arrays: An alternative explanation for the paramagnetic Meissner effect

The paramagnetic Meissner effect (PME) measured in high-

Carbon nanotube quantum dots as highly sensitive terahertz-cooled spectrometers.

{T}_{C}

Epitaxial graphene quantum dots for high-performance terahertz bolometers.

granular superconductors has been attributed to the presence of \ensuremath{\pi} junctions between the grains. Here we present measurements of complex ac magnetic susceptibility from two-dimensional arrays of conventional (non-\ensuremath{\pi}) Nb/Al/AlOx/Nb Josephson junctions. We measured the susceptibility as a function of the temperature T, the ac amplitude of the excitation field

A photolithographic process for fabrication of devices with isolated single-walled carbon nanotubes

{h}_{\mathrm{ac}}

Paramagnetic Meissner effect in multiply-connected superconductors

and the external magnetic field

Josephson-junction arrays as high-efficiency sources of coherent millimeter-wave radiation

{H}_{\mathrm{dc}}.