Design and development of the growth-process for the production of wafer-scale spatially homogeneous thickness controlled atomically thin transition metal dichalcogenides (TMDs) is one of the key challenges to realize modern electronic devices. Here, we demonstrate rapid and scalable synthesis of MoS2 films with precise thickness control via gas-phase chemical vapor deposition approach. We show that a monolayer MoS2 can be synthesized over a 2-in. sapphire wafer in a growth time as low as 4 min. With a linear growth rate of 1-layer per 4 min, MoS2 films with thicknesses varying from 1- to 5-layers with monolayer precision are produced. We propose that, in addition to Raman spectroscopy, the energy splitting of exciton bands in optical-absorbance spectra may be another choice for layer thickness identification. With suitable precursor selection, our approach can facilitate the rapid synthesis of spatially homogeneous atomically thin TMDs on a large scale.

Anomalous magnetoresistance in wet chemical synthesized bulk polycrystalline Ca2Fe2O5 and its comparative magnetic features with nanostructured Ca2Fe2O5.

A viable solution for the large-scale production of MoS2 thin films directly on SiO2/Si with relatively larger growth rates is demonstrated via a gas-phase precursor-assisted chemical vapor deposition approach. Comprehensive Raman and photoluminescence measurements reveal the excellent spatial homogeneity and high optical quality of the MoS2 thin films. The electrical properties of the MoS2 layers were tested by fabricating arrays of back-gated monolayer MoS2 field-effect transistors. Our findings suggest that the electrical properties are influenced by the grain size of the MoS2 monolayers.

The need for improved UV emitting luminescent materials underscored by applications in optical communications, sterilization and medical technologies is often addressed by wide bandgap semiconducting oxides. Among these, the Mg-doped ZnO system is of particular interest as it offers the opportunity to tune the UV emission by engineering its bandgap via doping control. However, both the doped system and its pristine congener, ZnO, suffer from being highly prone to parasitic defect level emissions, compromising their efficiency as light emitters in the ultraviolet region. Here, employing the process of femtosecond pulsed laser ablation in a liquid (fs-PLAL), we demonstrate the systematic control of enhanced UV-only emission in Mg-doped ZnO nanoparticles using both photoluminescence and cathodoluminescence spectroscopies. The ratio of luminescence intensities corresponding to near band edge emission to defect level emission was found to be six-times higher in Mg-doped ZnO nanoparticles as compared to pristine ZnO. Insights from UV-visible absorption and Raman analysis also reaffirm this defect suppression. This work provides a simple and effective single-step methodology to achieve UV-emission and mitigation of defect emissions in the Mg-doped ZnO system. This is a significant step forward in its deployment for UV emitting optoelectronic devices.

No abstract