Prashant K. Bankar

Ultra-thin V2O5 nanosheet based humidity sensor, photodetector and its enhanced field emission properties

We report the synthesis of V2O5 nanosheets by a simple hydrothermal method. The as synthesized V2O5 nanosheets were characterized by 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% 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 nanosheet based sensor. We also demonstrated the V2O5 nanosheets as an ultra-violet photodetector with a sensing response time of ∼65 s and recovery time of ∼75 s with a maximum photoresponsivity of ∼6.2%. Further, we have also carried out field emission (FE) investigations of V2O5 nanosheets under a planar “Diode” assembly in an ultrahigh vacuum (UHV) chamber at a base pressure of ∼1 × 10−8 mbar. The turn on fields required to draw field emission current densities of 1 μA cm−2 and 10 μA cm−2 are found to be 1.15 V μm−1 and 1.72 V μm−1, respectively. We achieved a maximum field emission current density of 1.532 mA cm−2 at an applied electric field of 3.2 V μm−1. The field enhancement factors calculated from the slope of the Fowler–Nordheim (F–N) plot are found to be 8530 and 3530 at low field and high field regions, respectively. Our results open up several avenues towards the successful utilization of V2O5 nanosheets and other metal oxide nanosheets for various nanoelectronics device applications including sensors, photodetector and flat panel displays.

Vapour–liquid–solid growth of one-dimensional In2Se3 nanostructures and their promising field emission behaviour

Single crystalline ultra long In2Se3 nanowires have been grown by employing a single step facile thermal evaporation route under optimized conditions on Au/Si wafers, and morphology dependent field emission investigations on the In2Se3 nanostructure at the base pressure ∼1 × 10−8 mbar are explored. In addition, structural and morphological analysis of as-synthesized In2Se3 nanostructures has been carried out using XRD, SEM and TEM. A plausible explanation of the vapor–solid–liquid (VLS) growth mechanism based on the experimental results and reported literature has been presented. Furthermore, field emission measurements demonstrate remarkably enhanced emission behaviour, which is explained on the basis of the field enhancement factor and aspect ratio of the nanostructures. The synthesized In2Se3 nanowire emitter delivers a very high current density of ∼1.2 mA cm−2 at an applied electric field of ∼6.33 V μm−1. The present results demonstrate In2Se3 as an important candidate for potential applications in nano/micro-electronic devices.

Synthesis of Ni-doped ZnO nanostructures by low-temperature wet chemical method and their enhanced field emission properties

In this study, we report an enhancement in the field emission (FE) properties of ZnO nanostructures obtained by doping with Ni at a base pressure of ∼1 × 10−8 mbar, which were grown by a simple wet chemical process. The ZnO nanostructures exhibited a single-crystalline wurtzite structure up to a Ni doping level of 10%. FESEM showed a change in the morphology of the nanostructures from thick nanoneedles to nanoflakes via thin nanorods with an increase in the Ni doping level in ZnO. The turn-on field required to generate a field emission (FE) current density of 1 μA cm−2 was found to be 2.5, 2.3, 1.8 and 1.7 V μm−1 for ZnO (Ni0%), ZnO (Ni5%), ZnO (Ni7.5%) and ZnO (Ni10%), respectively. A maximum current density of ∼872 μA cm−2 was achievable, which was generated at an applied field of 3.1 V μm−1 for a Ni doping level of 10% in ZnO. Long-term operational current stability was recorded at a preset value of 5 μA for a duration of 3 h and was found to be very high. The experimental results indicate that Ni-doped ZnO-based field emitters can open up many opportunities for their potential use as an electron source in flat panel displays, transmission electron microscopy, and the generation of X-rays. Thus, the simple low-temperature (∼80 °C) wet chemical synthesis approach and the robust nature of the ZnO nanostructure field emitter can provide prospects for the future development of cost-effective electron sources.

Nanostructured BiOI–GO composite: facile room temperature synthesis with enhanced multifunctionality in field emission and photocatalytic activity

Coupling of layered semiconductors with graphene-based materials could enable enhanced performance as compared to the pristine counterparts. Herein, we report enhanced multifunctional behaviour of a bismuth oxyiodide–graphene oxide (BiOI–GO) composite regarding its field emission and photocatalytic characteristics. The layered bismuth oxyiodide (BiOI) nanodiscs and nanostructured BiOI–GO composite were synthesized at room temperature employing a facile, single step precipitation method. The as-synthesized products were characterized using XRD, SEM, TEM, and a Raman spectrophotometer so as to reveal their phase, morphological and structural properties. Field emission (FE) studies of pristine layered BiOI nanodiscs and BiOI–GO nanocomposite emitters were carried out at the base pressure of ∼1 × 10−8 mbar. The values of turn on field required to draw an emission current density of 10 μA cm−2 are found to be 2.7 and 1.2 V μm−1 for BiOI nanodiscs and BiOI–GO nanocomposite emitters, respectively. Extraction of an emission current density of ∼1150 μA cm−2 from the BiOI–GO nanocomposite emitter at the remarkably low applied field of 2.8 V μm−1 signifies its enhanced FE performance. The superior FE characteristics of the BiOI–GO nanocomposite emitter are attributed to modulation of the electronic properties due to composite formation, and the high aspect ratio of the nanosheets/nanodiscs. Furthermore, the BiOI–GO nanocomposite exhibits enhanced photocatalytic activity towards degradation of methyl orange (MO) dye.

Spatially branched CdS–Bi2S3 heteroarchitecture: single step hydrothermal synthesis approach with enhanced field emission performance and highly responsive broadband photodetection

This report explores the controlled hierarchical synthesis of CdS nanostructure branches on Bi2S3 nanorod cores via a facile single step hydrothermal route. Morphological and structural studies reveal the formation of CdS–Bi2S3 heteroarchitecture with excellent stoichiometry between the constituent elements. The growth of CdS over Bi2S3 strongly depends on optimization of the reaction conditions, especially low PVP concentration. Furthermore, the as-synthesized CdS–Bi2S3 heteroarchitecture demonstrates multifunctionality in field emission and photoresponse. Interestingly, the CdS–Bi2S3 heteroarchitecture shows enhanced field emission properties such as low turn-on field (∼1.8 V μm−1 for 10 μA cm2), high emission current density and better current stability in comparison to Bi2S3 and other nanostructures. The as-synthesized CdS–Bi2S3 heteroarchitecture exhibits considerable response and recovery times, ∼207 ms and 315 ms, respectively in comparison to bare Bi2S3 nanostructures (∼655 ms and 678 ms). The present results demonstrate CdS–Bi2S3 heteroarchitecture as a potential candidate for future optoelectronic device applications.

Spitzer shaped ZnO nanostructures for enhancement of field electron emission behaviors

We observed enhanced field emission (FE) behavior for spitzer shaped ZnO nanowires synthesized via a hydrothermal approach. The spitzer shaped and pointed tipped 1D ZnO nanowires of average diameter 120 nm and length ∼5–6 μm were randomly grown over an ITO coated glass substrate. The turn-on field (Eon) of 1.56 V μm−1 required to draw a current density of 10 μA cm−2 from these spitzer shaped ZnO nanowires is significantly lower than that of pristine and doped ZnO nanostructures, and MoS2@TiO2 heterostructure based FE devices. The orthodoxy test that was performed confirms the feasibility of a field enhancement factor (βFE) of 3924 for ZnO/ITO emitters. The enhancement in FE behavior can be attributed to the spitzer shaped nanotips, sharply pointed nanotips and individual dispersion of the ZnO nanowires. The ZnO/ITO emitters exhibited very stable electron emission with average current fluctuations of ±5%. Our investigations suggest that the spitzer shaped ZnO nanowires have potential for further improving in electron emission and other functionalities after forming tunable nano-hetero-architectures with metal or conducting materials.

Effect of synthesis parameters on morphology of polyaniline (PANI) and field emission investigation of PANI nanotubes

Polyaniline (PANI) nanostructures have been synthesized by simple chemical oxidation route at different monomer concentration along with variation in synthesis temperature. The effect of variation of synthesis parameters has been revealed using different characterization techniques. The structural and morphological characterization of the synthesized PANI nanostructures was carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), whereas Fourier Transform Infrared spectroscopy (FTIR) has been used to reveal the chemical properties. With the variation in the synthesis temperature and monomer concentration, various morphologies characterized by formation of PANI nanoparticles, nanofibres, nanotubes and nanospheres, are revealed from the SEM analysis. The FTIR analysis reveals the formation of conducting state of PANI under prevailing experimental conditions. The field emission investigation of the conducting PANI nanotubes was performed in all metal UHV system at base press...

Efficient field emission from graphene nanosheets decorated with platinum nanoparticles

Graphene and its derivatives are expected to be efficient field emitters due to their unique geometry and electrical properties. In this work we have decorated Graphene nanosheets with noble metal nanoparticles specifically Platinum by simple chemical route which produces high density of protrusions. The assynthesized Graphene nanosheets were characterized using XRD and TEM. The values of turn-on and threshold fields, required to draw an emission current density ~ 1 and ~10 μA/cm2, are found to be ~ 1.55 and ~1.70 V/μm, for anode-cathode separation of ~ 2 mm. Interestingly, very high emission current density of ~ 496.5 μA/cm2 has been drawn from the emitter at relatively lower applied electric field of ~ 3.1 V/μm. The observed field emission characteristics can be attributed to the enhancement of the applied electric field at these local protrusions, thus increasing the number of emission sites. The emission current stability studied at the preset value of ~1 μA over the period of more than 3 hrs is found to be good, characterized with fewer fluctuations. The observed results indicate that field emission behaviour of Graphene can be improved by decorating it with Pt nanoparticles.