Most of recent research on layered chalcogenides is understandably focused on single atomic layers. However, it is unclear if single-layer units are the most ideal structures for enhanced gas-solid interactions. To probe this issue further, we have prepared large-area MoS2 sheets ranging from single to multiple layers on 300 nm SiO2/Si substrates using the micromechanical exfoliation method. The thickness and layering of the sheets were identified by optical microscope, invoking recently reported specific optical color contrast, and further confirmed by AFM and Raman spectroscopy. The MoS2 transistors with different thicknesses were assessed for gas-sensing performances with exposure to NO2, NH3, and humidity in different conditions such as gate bias and light irradiation. The results show that, compared to the single-layer counterpart, transistors of few MoS2 layers exhibit excellent sensitivity, recovery, and ability to be manipulated by gate bias and green light. Further, our ab initio DFT calculations on single-layer and bilayer MoS2 show that the charge transfer is the reason for the decrease in resistance in the presence of applied field.

Room-temperature, bottom-gate, field-effect transistor characteristics of 2D ultrathin layer GaS and GaSe prepared from the bulk crystals using a micromechanical cleavage technique are reported. The transistors based on active GaS and GaSe ultrathin layers demonstrate typical n-and p-type conductance transistor operation along with a good ON/OFF ratio and electron differential mobility.

We investigated transient photoresponse and Hall effect in amorphous In-Ga-Zn-O thin films and observed a stretched exponential response which allows characterization of the activation energy spectrum with only three fit parameters. Measurements of as-grown films and 350 K annealed films were conducted at room temperature by recording conductivity, carrier density, and mobility over day-long time scales, both under illumination and in the dark. Hall measurements verify approximately constant mobility, even as the photoinduced carrier density changes by orders of magnitude. The transient photoconductivity data fit well to a stretched exponential during both illumination and dark relaxation, but with slower response in the dark. The inverse Laplace transforms of these stretched exponentials yield the density of activation energies responsible for transient photoconductivity. An empirical equation is introduced, which determines the linewidth of the activation energy band from the stretched exponential parameter b. Dry annealing at 350 K is observed to slow the transient photoresponse. V

Articles you may be interested inDiffusion length and junction spectroscopy analysis of low-temperature annealing of electron irradiation-induced deep levels in 4 H -Si C J. Appl. Phys. 99, 033701 (2006); 10.1063/1.2160708 Annealing behavior between room temperature and 2000°C of deep level defects in electron-irradiated n -type 4H silicon carbide J. Appl. Phys. 98, 043518 (2005); 10.1063/1.2009816 Deep levels created by low energy electron irradiation in 4 H -SiC A deep level transient spectroscopy study of electron irradiation induced deep levels in p-type 6H-SiCAl doped p-type 6H silicon carbide was irradiated by low energy electrons to create primary defects. Two deep levels at E V + 0.36 eV and E V + 0.81 eV were created by this irradiation. Isochronal annealing study was carried out on the electron irradiated sample to investigate the annealing out of the two primary defects and the creation of thermal annealing-induced secondary defects. Four more deep hole traps ͑0.45, 0.56, 0.74, and 0.71 eV above the valence band͒ were formed during the whole annealing process up to a temperature of 1600°C. All the electron irradiated deep level defects were annealed out after the 1600°C annealing.

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