Achieving tunability of two dimensional (2D) transition metal dichalcogenides (TMDs) functions calls for the introduction of hybrid 2D materials by means of localized interactions with zero dimensional (0D) materials. A metal-semiconductor interface, as in gold (Au) - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science as it constitutes an outstanding platform to investigate plasmonic-exciton interactions and charge transfer. The applied aspects of such systems introduce new options for electronics, photovoltaics, detectors, gas sensing, catalysis, and biosensing. Here we consider pristine MoS2 and study its interaction with Au nanoislands, resulting in local variations of photoluminescence (PL) in Au-MoS2 hybrid structures. By depositing monolayers of Au on MoS2, we investigate the electronic structure of the resulting hybrid systems. We present strong evidence of PL quenching of MoS2 as a result of charge transfer from MoS2 to Au: p-doping of MoS2. The results suggest new avenues for 2D nanoelectronics, active control of transport or catalytic properties.

We have demonstrated tuning of the electrical property of single layer MoS ₂ from semiconducting to the insulating regime by oxygen plasma.

We investigate the low-temperature electron transport properties of chemically reduced graphene oxide (RGO) sheets with different carbon $s{p}^2$ fractions of 55$\%$ to 80$\%$. We show that in the low-bias (Ohmic) regime, the temperature ($T$) dependent resistance ($R$) of all the devices follow Efros-Shklovskii variable range hopping (ES-VRH) $R\sim \exp \left[{(T_{\mathrm{ES}}/T)}^{1/2}\right]$ with $T_{\mathrm{ES}}$ decreasing from 3.1×10${}^4$ to 0.42×10${}^4$ K and electron localization length increasing from 0.46 to 3.21 nm with increasing $s{p}^2$ fraction. From our data, we predict that for the temperature range used in our study, Mott-VRH may not be observed even at 100$\%$ $s{p}^2$ fraction samples due to residual topological defects and structural disorders. From the localization length, we calculate a band-gap variation of our RGO from 1.43 to 0.21 eV with increasing $s{p}^2$ fraction from 55 to 80$\%$, which agrees remarkably well with theoretical predictions. We also show that, in the high bias non-Ohmic regime at low temperature, the hopping is field driven and the data follow $R\sim \exp \left[{(E_0/E)}^{1/2}\right]$ providing further evidence of ES-VRH.

The present study explores the structural, optical (photoluminescence (PL)), and electrical properties of lateral heterojunctions fabricated by selective exposure of mechanically exfoliated few layer two-dimensional (2D) molybdenum disulfide (MoS ₂ ) flakes under oxygen (O ₂ )-plasma. Raman spectra of the plasma exposed MoS ₂ flakes show a significant loss in the structural quality due to lattice distortion and creation of oxygen-containing domains in comparison to the pristine part of the same flake. The PL mapping evidences the complete quenching of peak A and B consistent with a change in the exciton states of MoS ₂ after the plasma treatment, indicating a significant change in its band gap properties. The electrical transport measurements performed across the pristine and the plasma-exposed MoS ₂ flake exhibit a gate tunable current rectification behavior with a rectification ratio up to 1.3 × 10 ³ due to the band-offset at the pristine and plasma-exposed MoS ₂ interface. Our Raman, PL, and electrical transport data confirm the formation of an excellent lateral heterojunction in 2D MoS ₂ through its bandgap modulation via oxygen plasma.

Reduced graphene oxide has certain unique qualities that make them versatile for a myriad of applications. Unlike graphene oxide, reduced graphene oxide is a conductive material and well suited for use in electrically conductive materials, such as solar cell devices. In this study, we report on the synthesis of graphene oxide as well as the fabrication and characterization of dye-sensitized solar cells with a photoanode which is an amalgam of reduced graphene oxide and titanium dioxide. The synthesized reduced graphene oxide and the corresponding photoanode were fully characterized using Ultraviolet-visible, Fourier transform infrared (FTIR), and Raman Spectrometry. The morphology of the sample was assessed using Atomic Force Microscopy, Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy, and Energy Dispersive X-ray Spectroscopy. The photovoltaic characteristics were determined by photocurrent and photo-voltage measurements of the fabricated solar cells. The electrical impedances of both sets of devices were also evaluated. Overall, the solar to electric power efficiency of the device with reduced graphene oxide was observed to be higher (2.02%) than the device without the reduced graphene oxide (1.61%).