Recent investigations on two-dimensional black phosphorus material mainly highlight work on few atomic layers and multilayers. It is still unknown if the black phosphorus atomically thin sheet is an ideal structure for the enhanced gas-solid interactions due to its large surface area. To further investigate this concern, we have synthesized few atomic layer thick nanosheets of black phosphorus using an electrochemical exfoliation method. The surface morphology and thickness of the nanosheet were identified using AFM, TEM, and Raman spectroscopy. The black phosphorus nanosheet thick film device was used for the gas sensing application with exposure to different humidites. Further, the few layer black phosphorus nanosheet based transistor shows good mobility and on/off ratio. The UV light irradiation on the black phosphorus nanosheet shows good response time. The overall results show that the few layer thick film of black phosphorus nanosheets sample exhibits creditable sensitivity and better recovery time to be used in humidity sensor and photodetector applications.

We investigate the growth mechanism and temperature dependent Raman spectroscopy of chemical vapor deposited large area monolayer of MoS2, MoSe2, WS2 and WSe2 nanosheets up to 70 μm in lateral size. Further, our temperature dependent Raman spectroscopy investigation shows that softening of Raman modes as temperature increases from 80 K to 593 K is due to the negative temperature coefficient and anharmonicity. The temperature dependent softening modes of chemical vapor deposited monolayers of all TMDCs were explained on the basis of a double resonance phonon process which is more active in an atomically thin sample. This process can also be fundamentally pertinent in other emerging two-dimensional layered and heterostructured materials.

Most of the recent research work on layered chalcogenides is understandably focused on single atomic layers. However, it is uncertain if the single layer units are most ideal structures for enhanced gas-solid interactions. To probe this concern, we have synthesized few layer thick SnSe 2 nanosheets ink using liquid exfoliation method. The morphology, thickness / layering and elemental analysis of the sheets were characterized by using SEM, TEM, AFM, Raman spectroscopy and by XPS. The two dimensional (2D) SnSe 2 nanosheets sensor device with different thicknesses was assessed for the humidity and gas sensing performances with exposure to humidity in different conditions. The results show that compared to the bulk / thicker counterpart, sensor device of few SnSe 2 layers exhibit excellent sensitivity, recovery and ability to be tune the sensing performance with thickness and can be used in lab on chip devices.

We report synthesis of V2O5 nanosheets by simple hydrothermal method. The as synthesized V2O5 nanosheets were characterized by using Raman Spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and UV-Vis Spectroscopy. The humidity sensing behaviors were investigated in the range of 11-97% of relative humidity (RH) at room temperature. The maximum sensitivity of 45.3%, response time of ~ 4 min. and recovery time of ~ 5 min. were observed for the V2O5 nanosheets based sensor. We also demonstrated the V2O5 nanosheets as Ultra-Violet photodetector with sensing response time of ~ 65 s and recovery time of ~ 75 s with maximum photoresponsivity of ~ 6.2% were observed. Further, We have also carried out field emission (FE) investigations of V2O5 nanosheets under planer "Diode" assembly in ultrahigh vacuum (UHV) chamber at a base pressure of ~1 x 10 -8 mbar. The turn on field required to draw field emission current density of 1 µA/cm 2 and 10 µA/cm 2 is found to be 1.15 V/µm and 1.72 V/µm respectively. We achieved maximum field emission current density of 1.532 mA/cm 2 at an applied electric field of 3.2 V/µm. The field enhancement factor calculated from the slope of Fowler -Northeim (F-N) plot is found to be 8530 and 3530 at low field and high field region respectively. Our results open up several avenues and key success towards the utilization of V2O5 nanosheets and other metal oxide nanosheets for various nanoelectronics device applications including sensors, photodetector and flat panel displays.Since the invention of graphene, atomically thin two dimensional (2D) materials have attracted enormous attention due to their potential applications in next generation nano-electronics and optoelectronics device 1,2 . The first 2D layered materials isolated were graphene followed by several inorganic layered such as MoS 2 , WS 2 , MoSe 2 , WSe 2 , Black Phosphorous 58 etc. and metal oxides materials such as MoO 3, WO 3 , MnO 2 were invented for various applications including humidity sensor 3-8 , photodetector 9-23 , transistor 24 , gas sensor 25,26 , solar cell 43-46 , supercapacitor 47-50 , catalyst for water splitting 51,52 etc. Humidity sensors have been developed to measure and monitor the environmental humidity that plays an important role in the agriculture, food as well as medical industry along with human activities 27 . The layered V 2 O 5 is most stable oxide as compared with other oxides of vanadium. The 2D form of V 2 O 5 has high surface to volume ratio and high oxidation state at nanoscale geometry. Recently nanostructure V 2 O 5 has been used in various application including field emission 29-30, 59-63 ,