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.

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The energy calibration and resolution of the electromagnetic calorimeter (ECAL) of the CMS detector have been determined using proton-proton collision data from LHC operation in 2010 and 2011 at a centre-of-mass energy of √ s = 7 TeV with integrated luminosities of about 5 fb −1 . Crucial aspects of detector operation, such as the environmental stability, alignment, and synchronization, are presented. The in-situ calibration procedures are discussed in detail and include the maintenance of the calibration in the challenging radiation environment inside the CMS detector. The energy resolution for electrons from Z-boson decays is better than 2% in the central region of the ECAL barrel (for pseudorapidity |η| < 0.8) and is 2-5% elsewhere. The derived energy resolution for photons from 125 GeV Higgs boson decays varies across the barrel from 1.1% to 2.6% and from 2.2% to 5% in the endcaps. The calibration of the absolute energy is determined from Z → e + e − decays to a precision of 0.4% in the barrel and 0.8% in the endcaps.

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.

2Light absorption in graphene causes a large change in electron temperature, due to low electronic heat capacity and weak electron phonon coupling, 1-3 making it very attractive as a hot-electron bolometer material. Unfortunately, the weak variation of electrical resistance with temperature has substantially limited the responsivity of graphene bolometers. Here we show that quantum dots of epitaxial graphene on SiC exhibit an extraordinarily high variation of resistance with temperature due to quantum confinement, higher than 430 M K -1 at 2.5 K, leading to responsivities for absorbed THz power above 1 × 10 10 V W -1 . This is five orders of magnitude higher than other types of graphene hot electron bolometers. The high responsivity combined with an extremely low noise-equivalent power, about 2 × 10 -16 W/√Hz at 2.5K, place the performance of graphene quantum dot bolometers well above commercial cooled bolometers. Additionally, these quantum dot bolometers have the potential for superior performance for operation above 77K.The electrical resistivity of pristine graphene shows a weak temperature dependence, varying by less than 30% (200% for suspended graphene) from 30 mK to room temperature 4,5 , because of the very weak electron-phonon scattering 6 . A stronger temperature dependence was obtained either by using dual-gated bilayer graphene 1,7 to create a tunable band gap 7 , or by introducing defects to induce strong localization 2 . Both schemes have successfully produced bolometric detection, with responsivities up to 2 × 10 5 V W -1 and temperature coefficient for the resistance as high as 22 kK -1 at 1.5K 1,2 . These devices required the use of multilayer structures adding complexity. In the case of bilayer graphene, top and bottom gates were needed to electrically induce a bandgap. In the case of disordered graphene, a boron nitride layer was used as a tunneling barrier between the graphene and the electrodes to reduce thermal conductance due to diffusion of the electrons to the electrodes. 3Here we demonstrate hot-electron bolometric detection using nano-patterned dots of epitaxial graphene. A bandgap is induced via quantum confinement, without the need of gates, using a simple single-layer structure. We study the THz response of dots with diameter varying from 30 nm to 700 nm, at 0.15 THz and at temperatures from 2.5K to 80K. These devices are extremely sensitive and the responsivity increases by decreasing the dot diameter, with the smaller dots still showing a clear response at liquid nitrogen temperature. Our fabrication process is fully scalable and easily provides multiple devices on the same chip, making it suitable for bolometer arrays. Moreover, its flexibility allows patterning of arrays of dots electrically connected in parallel, to control the device impedance while preserving the strong temperature dependence.We fabricated our dots using e-beam lithography and a process developed by Yang et al., 8 (see Methods). Fig. 1a shows an image of a typical quantum dot and the temperature dependenc...

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The transport characteristics of graphene devices with low n‐ or p‐type carrier density (∼1010–1011 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.