UV illumination enhanced desorption of oxygen molecules from monolayer MoS2 surface

The oxygen adsorption can drastically alter the electronic properties of the two-dimensional(2D)materials,which is usually dificult to be removed.In this work,we report the ultraviolet(UV)ilumination induced desorption of the O2 molecules from the monolayer MoS2 surface by using the atmosphere dependent transport measurement,Kelvin probe microscopy,photoluminescence spectroscopy and X-ray photoelectron spectroscopy.Obvious increasing of the conductivity,rising of the Fermi level,and red shift of the photoluminescence peaks of the MoS2 were observed after the UV ilumination in vacuum,indicating the elimination of the depletion effect from the oxygen adsorption.Such parameter changes can be reversibly recovered by the subsequent O2 exposure.Furthermore,obvious decreasing of the oxygen concentration after the UV ilumination was also observed by X-ray photoelectron spectroscopy.Thus the UV induced O2 photodesorption effect is evidenced.The photo-excited charge transfer mechanism is proposed to account for the photodesorption effect.These results provide a nondestructive way to clean the MoS2 surface and manipulate the performance of the MoS2 based devices.

Fabrication of large area hexagonal boron nitride thin films for bendable capacitors

Highly reliable and bendable dielectrics are desired in flexible or bendable electronic devices for future applications. Hexagonal boron nitride （h-BN） can be used as bendable dielectric due to its wide band gap. Here, we fabricate high quality h-BN films with controllable thickness by a low pressure chemical vapor deposition method. We demonstrate a parallel-plate capacitor using h-BN film as the dielectric. The h-BN capacitors are reliable with a high breakdown field strength of -9.0 MV/cm. Tunneling current across the h-BN film is inversely exponential to the thickness of dielectric, which makes the capacitance drop significantly. The h-BN capacitor shows a best specific capacitance of 6.8 F/cm^2, which is one order of magnitude higher than the calculated value.

Growth of large scale PtTe,PtTe_(2) and PtSe_(2) films on a wide range of substrates

1T phase of transition metal dichalcogenides(TMDCs)formed by group 10 transition metals(e.g.Pt,Pd)have attracted increasing interests due to their novel properties and potential device applications.Synthesis of large scale thin films with controlled phase is critical especially considering that these materials have relatively strong interlayer interaction and are difficult to exfoliate.Here we report the growth of centimeter-scale PtTe,1T-PtTe2 and 1T-PtSe2 films via direct deposition of Pt metals followed by tellurization or selenization.We find that by controlling the Te flux,a hitherto-unexplored PtTe phase can also be obtained,which can be further tuned into PtTe2 by high temperature annealing under Te flux.These films with different thickness can be grown on a wide range of substrates,including NaCl which can be further dissolved to obtain free-standing PtTe2 or PtSe2 films.Moreover,a systematic thickness dependent resistivity and Hall conductivity measurements show that distinguished from the semiconducting PtSe2 with hole carriers,PtTe2 and PtTe films are metallic.Our work opens new opportunities for investigating the physical properties and potential applications of group 10 TMDC films and the new monochalcogenide PtTe film.