Gas Sensing with h-BN Capped MoS2 Heterostructure Thin Film Transistors

We have demonstrated selective gas sensing with molybdenum disulfide (MoS2) thin films transistors capped with a thin layer of hexagonal boron nitride (h-BN). The resistance change was used as a sensing parameter to detect chemical vapors such as ethanol, acetonitrile, toluene, chloroform and methanol. It was found that h-BN dielectric passivation layer does not prevent gas detection via changes in the source-drain current in the active MoS2 thin film channel. The use of h-BN cap layers (thickness H=10 nm) in the design of MoS2 thin film gas sensors improves device stability and prevents device degradation due to environmental and chemical exposure. The obtained results are important for applications of van der Waals materials in chemical and biological sensing.Comment: 3 pages; 4 figure

Ab initio Studies of the Possible Magnetism in BN Sheet by Non-magnetic Impurities and Vacancies

We performed first-principles calculations to investigate the possible magnetism induced by the different concentrations of non-magnetic impurities and vacancies in BN sheet. The atoms of Be, B, C, N, O, Al and Si are used to replace either B or N in the systems as impurities. We discussed the changes in density of states as well as the extent of the spatial distributions of the defect states, the possible formation of magnetic moments, the magnitude of the magnetization energies and finally the exchange energies due to the presence of these defects. It is shown that the magnetization energies tend to increase as the concentrations of the defects decreases in most of the defect systems which implies a definite preference of finite magnetic moments. The calculated exchange energies are in general tiny but not completely insignificant for two of the studied defect systems, i.e. one with O impurities for N and the other with B vacancies.Comment: 8 pages, 10 figures, submitted to Phys. Rev.

Current

and optical low-frequency noise of GaInN/GaN green light emitting diode

Low-Frequency 1/f Noise in MoS2 Thin-Film Transistors: Comparison of Single and Multilayer Structures

We report on the transport and low-frequency noise measurements of MoS2 thin-film transistors with "thin" (2-3 atomic layers) and "thick" (15-18 atomic layers) channels. The back-gated transistors made with the relatively thick MoS2 channels have advantages of the higher electron mobility and lower noise level. The normalized noise spectral density of the low-frequency 1/f noise in "thick" MoS2 transistors is of the same level as that in graphene. The MoS2 transistors with the atomically thin channels have substantially higher noise levels. It was established that, unlike in graphene devices, the noise characteristics of MoS2 transistors with "thick" channels (15-18 atomic planes) could be described by the McWhorter model. Our results indicate that the channel thickness optimization is crucial for practical applications of MoS2 thin-film transistors.Comment: 12 pages, 3 figure

One-loop radiative corrections to photon-pair production in polarized positron-electron annihilation

A theoretical description of photon-pair production in polarized positron-electron annihilation is presented. Complete one-loop electroweak radiative corrections are calculated taking into account the exact dependence on the electron mass. Analytical results are derived with the help of the SANC~system. The relevant contributions to the cross section are calculated analytically using the helicity amplitude approach. The cases of unpolarized and longitudinally polarized fermions in the initial state are investigated. Calculations are realized in the Monte Carlo integrator MCSANCee and generator ReneSANCe which allow one the implementation of any experimental cuts used in the analysis of $e^+e^-$ annihilation data of both low and high energies.Comment: 17 pages, 6 tables, 3 figure