Highly luminescent MoS 2 nanocrystals (NCs) with controlled size distribution have been achieved using a simple yet inexpensive and impurity free sono-chemical exfoliation method followed by gradient centrifugation. The size of nanocrystals could be varied within the diameter range of ∼4 to 70 nm. Typical MoS 2 nanocrystal has exhibited high crystalline quality with 0.25 nm lattice fringe spacing for (002) planes for 2-H phase of MoS 2 . Raman spectra has revealed that both out-of-plane and in-plane vibrational modes are stiffen due to the edge effect of MoS 2 NCs. The size tunable optical properties of MoS 2 NCs have been investigated by optical absorption and photoluminescence spectroscopy. The coexistence of direct band gap emission from 2D MoS 2 nanosheets and quantum confined nanocrystals has been achieved. A strong and tunable photoluminescence (560−518 nm) emission due to the quantum size effect of tiny NCs below a critical dimension is reported for the first time. The photocurrent measurement of the Au/MoS 2 −NCs/Au junction has been performed at room temperature to investigate the optical responsivity and switching characteristics, demonstrating the potential of MoS 2 nanocrystals for next generation photonic devices.

Chemically reduced graphene oxide (RGO) has recently attracted growing interest in the area of chemical sensors because of its high electrical conductivity and chemically active defect sites. This paper reports the synthesis of chemically reduced GO using NaBH4 and its performance for ammonia detection at room temperature. The sensing layer was synthesized on a ceramic substrate containing platinum electrodes. The effect of the reduction time of graphene oxide (GO) was explored to optimize the response, recovery, and response time. The RGO film was characterized electrically and also with atomic force microscopy and X-ray photoelectron spectroscopy. The sensor response was found to lie between 5.5% at 200 ppm (parts per million) and 23% at 2800 ppm of ammonia, and also resistance recovered quickly without any application of heat (for lower concentrations of ammonia). The sensor was exposed to different vapors and found to be selective toward ammonia. We believe such chemically reduced GO could potentially be used to manufacture a new generation of low-power portable ammonia sensors.

Template-free, bottom-up synthesized, micron sized few layer 2H-MoS2for photodetector and photocatalytic applications.

Sonication induced vertical fragmentation of two-dimensional (2D) WS nanosheets into highly luminescent, monodispered, zero-dimensional (0D) quantum dots (QDs) is reported. The formation of 0D structures from 2D sheets and their surface/microstructure characterization are revealed from their microscopic and spectroscopic investigations. Size dependent optical properties of WS nanostructures have been explored by UV-vis absorption and photoluminescence spectroscopy. Interestingly, it is observed that, below a critical dimension (∼2 nm), comparable to the Bohr exciton radius, the tiny nanocrystals exhibit strong emission. Finally, the electroluminescence characteristics are demonstrated for the first time, by forming a heterojunction of stabilizer free WS QDs and ZnO thin films. The signature of white light emission in the light emitting device is attributed to the adequate intermixing of emission characteristics of WS QDs and ZnO. The observation of white electroluminescence may pave the way to fabricate prototype futuristic efficient light emitting devices.

We demonstrate a facile method for the Suzuki coupling of aryl molecules on the diamond surface. This is a more versatile alternative compared to previous coupling methods based on alkene linkers because it opens up possibilities for the application of diamond in molecular electronics and photovoltaics. The diamond surface is premodified with aryldiazonium salt in order to functionalize it with aryl halide or aryl boronic acid, and these are then used as synthons in the subsequent Suzuki coupling to aryl molecules. This method is highly specific and can be used for the uninterrupted molecular conjugation of diamond to a large class of organic molecules. As a proof of concept, we also demonstrate a diamond-fullerene photocurrent converter by using Suzuki coupled oligothiophene as the conjugated linker between diamond (electron donor) and fullerene (electron acceptor).