Kashmira Harpale

Morphology tuning and electron emission properties of a carbonaceous LaB6 system obtained using a thermal plasma route

In the present study, we report the morphological tuning of carbonaceous nanocrystalline lanthanum hexaboride (LaB6) using an arc plasma route. It was possible to obtain different morphologies, namely: pebbles, rods and sheets, on a nano-scale by means of plasma assisted vapour phase growth and by varying the plasma current. At elevated plasma currents, as a consequence of graphite electrodes being used in the arc geometry, the synthesized product was obtained in the form of carbonaceous LaB6 having a high degree of crystallinity. Detailed morphological analysis using electron microscopy has revealed that nanorods and nanosheets of carbonaceous LaB6 can be grown by elevating the plasma currents. The field emission (FE) current was found to be enhanced from 200 μA cm−2 to 660 μA cm−2 for the hierarchical structure of nanosheets as compared to that of nanopebbles at a much reduced turn-on potential. A stable FE current is an important feature exhibited by all these LaB6 nanostructures.

Facile, single step synthesis of CdS—RGO heterostructure and its photo enhanced field emission investigations

CdS–RGO heterostructure was synthesized by a thermal evaporation method and characterized using x-ray diffraction, SEM, TEM, photoluminescence spectroscopy (PL) and Raman spectroscopy so as to reveal its structural, compositional and electronic properties, prior to field emission (FE) investigations. The FE characteristics with and without visible illumination of the CdS–RGO heterostructure planar emitter were measured at base pressure 1 × 10−8 mbar. The values of turn-on field, corresponding to emission current density of 1 μA/cm2 without and with illumination, are found to be 2.3 and 2.0 V μm−1, respectively. Furthermore, under pulsating illumination, the emitter exhibits emission current pulses depicting nearly four times enhancement in the emission current, with rise and fall time constants as 4.4 and 6.4 s, respectively. The photoenhanced FE behaviour is attributed to the modulation of electronic properties due to the CdS nanostructures. The results obtained herein propose the CdS–RGO heterostructure emitter as a photo-sensitive field emission switch in next generation optoelectronic nanodevices.

Morphological, structural and field emission characterization of hydrothermally synthesized MoS2-RGO nanocomposite

A few layered MoS2-RGO nanocomposite has been synthesized employing a facile hydrothermal synthesis route. The morphological and structural analysis performed using SEM, TEM, HRTEM and Raman spectroscopy clearly reveal formation of vertically aligned a few layer thick MoS2 sheets on RGO surface. Attempts have been made to reveal the influence of graphite oxide (GO) percentage on morphology of the nanocomposite. Furthermore, field emission (FE) investigations of as-synthesied MoS2-RGO nanocomposite are observed to be superior to the pristine MoS2 emitter. The values of turn-on field, defined at emission current density of 10 μA cm−2, are found to be 2.6 and 4.7 V μm−1 for the MoS2-RGO (5%) nanocomposite and pristine MoS2 emitters, respectively. The value of threshold field, defined at emission current density of 100 μA cm−2, is found to be 3.1 V μm−1 for MoS2-RGO nanocomposite. The emission current stability at the pre-set value of 1 μA over 3 h duration is found to be fairly good, characterized by current fluctuation within ±18% of the average value. The enhanced FE behavior for MoS2-RGO nanocomposite is attributed to a high enhancement factor (β) of 4128 and modulation of the electronic properties. The facile approach adopted herein can be extended to enhance various functionalities of other nanocomposites.

Direct synthesis of Cu2O-RGO nanocomposite on Cu foil by thermal evaporation method and its field emission study

In this work, a facile one step thermal evaporation method for deposition of Cu2O nanoparticles on RGO sheets to form Cu2O-RGO nanocomposite is discussed. To the best of our knowledge, this is the first report on Cu2O-RGO nanocomposite, directly grown on Cu foil by a simple thermal evaporation route. The as –prepared nanocomposite exhibits well dispersed Cu2O nanoparticles distributed all over the graphene sheet. Field emission properties of the nanocomposite were investigated at a base pressure of 1*10−8 torr. The turn on field, required to draw emission current density of 0.1µA/cm2, was found to be 3.8V/µm with a maximum emission current density of 80 µA/cm2 at an applied field of 6.8 V/µm. Moreover, the nanocomposite shows fairly good emission stability without significant degradation of emission current. The FE results seem to be encouraging, indicative of potential candidature of the Cu2O-RGO nanocomposite emitter as an electron source for practical applications in vacuum nanoelectronic devices

Polypyrrole nanostructures and their field emission investigations

Polypyrrole (PPy) nanostructures have been synthesized on indium doped tin oxide (ITO) substrates by a facile electrochemical route employing cyclic voltammetry (CV) mode. The morphology of the PPy thin films was observed to be influenced by the monomer concentration. Furthermore, FTIR revealed formation of electrically conducting state of PPy. Field emission investigations of the PPy nanostructures were carried out at base pressure of 1×10-8mbar. The values of turn-on field, corresponding to emission current density of 1 μA/cm2 were observed to be 0.6, 1.0 and 1.2 V/μm for the PPy films characterized with rod-like, cauliflower and granular morphology, respectively. In case of PPy nanorods maximum current density of 1.2 mA/cm2 has been drawn at electric field of 1 V/μm. The low turn on field, extraction of very high emission current density at relatively lower applied field and good emission stability propose the PPy nanorods as a promising material for field emission based devices.

Morphology dependent field emission characteristics of polypyrrole thin film emitters

Polypyrrole (PPy) nanostructures have been synthesized on indium doped tin oxide (ITO) substrates by a facile electrochemical route employing cyclic voltammetry (CV) mode. The morphology of the PPy thin films was observed to be influenced by the monomer concentration and formation of rod-like, cauliflower and granular structures were obtained with monomer concentrations of 0.1, 0.3, and 0.5 M, respectively. Furthermore spectroscopic analysis (UV-visible and FTIR) revealed formation of electrically conducting state of PPy under the prevailing experimental conditions. The field emission investigations of the PPy nanostructures have been carried out at base pressure of 1 × 10-8 mbar. The values of turn-on field, corresponding to emission current density of 1 μA/cm2 were observed to be 0.6, 1.0 and 1.2 V/μm for the PPy films characterized with rod-like, cauliflower and granular morphology, respectively. Interestingly, in case of PPy nanorods maximum current density of 1.2 mA/cm2 has been observed at electric field of 1 V/μm, which is higher than PPy cauliflower (0.4 mA/cm2 at 2.4 V/μm) and granular (0.5 mA/cm2 at 2.68 V/μm) morphology. The observed values of turn on and threshold field in case of PPy nanorods are comparative to earlier reported values for different conducting polymer nanostructures and nanocomposites. The observation of relatively lower turn-on field for rod-like morphology is attributed to the high aspect ratio of the PPy nanostructures. The emission current was found to be stable around the preset value for more than 2 hrs. The low turn on field, extraction of very high emission current density at relatively lower applied field and good emission stability propose the PPy nanorods as a promising material for field emission based devices.