Amit Kumar Rana

Sr- and Ni-doping in ZnO nanorods synthesized by a simple wet chemical method as excellent materials for CO and CO2 gas sensing

In this study, the effect of Sr- and Ni-doping on the microstructural, morphological and sensing properties of ZnO nanorods has been investigated. Nanorods with different Sr and Ni loadings were prepared using a simple wet chemical method and characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) analysis. XRD data confirmed that Sr- and Ni-doped samples maintain the wurtzite hexagonal structure of pure ZnO. However, unlike Sr, Ni doping modifies the nanorod morphology, increases the surface area (SA) and decreases the ratio of the IUV/Igreen photoluminescence peak to a greater extent. Sensing tests were performed on thick film resistive planar devices for monitoring CO and CO2, as indicators of indoor air quality. The effect of the operating temperature, nature and loading of the dopant on the sensibility and selectivity of the fabricated sensors towards these two harmful gases was investigated. The gas sensing characteristics of Ni- and Sr-doped ZnO based sensors showed a remarkable enhancement (i.e. the response increased and shifted towards a lower temperature for both gases) compared to the ZnO-based one, demonstrating that these ZnO nanostructures are promising for the fabrication of sensor devices for monitoring indoor air quality.

Controlling of ZnO nanostructures by solute concentration and its effect on growth, structural and optical properties

ZnO nanostructured films were prepared by a chemical bath deposition method on glass substrates without any assistance of either microwave or high pressure autoclaves. The effect of solute concentration on the pure wurtzite ZnO nanostructure morphologies is studied. The control of the solute concentration helps to control the nanostructure to form nano-needles, and -rods. X-ray diffraction (XRD) studies revealed highly c-axis oriented thin films. Scanning electron microscopy (SEM) confirms the modification of the nanostructure dependent on the concentration. Transmission electron microscopy (TEM) results show the single crystalline electron diffraction pattern, indicating high quality nano-material. UV–vis results show the variation in the band gap from 3.20 eV to 3.14 eV with increasing concentration as the nanostructures change from needle- to rod-like. Photoluminescence (PL) data indicate the existence of defects in the nanomaterials emitting light in the yellow–green region, with broad UV and visible spectra. A sharp and strong peak is observed at ~438 cm−1 by Raman spectroscopy, assigned to the optical mode of ZnO, the characteristic peak for the highly-crystalline wurtzite hexagonal phase. The solute concentration significantly affects the formation of defect states in the nanostructured films, and as a result, it alters the structural and optical properties. Current–voltage characteristics alter with the measurement environment, indicating potential sensor applications.

Search for Origin of Room Temperature Ferromagnetism Properties in Ni-Doped ZnO Nanostructure

The origin of room temperature (RT) ferromagnetism (FM) in Zn1-xNixO (0< x < 0.125) samples are systematically investigated through physical, optical, and magnetic properties of nanostructure, prepared by simple low-temperature wet chemical method. Reitveld refinement of X-ray diffraction pattern displays an increase in lattice parameters with strain relaxation and contraction in Zn/O occupancy ratio by means of Ni-doping. Similarly, scanning electron microscope demonstrates modification in the morphology from nanorods to nanoflakes with Ni doping, suggests incorporation of Ni ions in ZnO. More interestingly, XANES (X-ray absorption near edge spectroscopy) measurements confirm that Ni is being incorporated in ZnO as Ni2+. EXAFS (extended X-ray absorption fine structure) analysis reveals that structural disorders near the Zn sites in the ZnO samples upsurges with increasing Ni concentration. Raman spectroscopy exhibits additional defect driven vibrational mode (at 275 cm-1), appeared only in Ni-doped samples and the shift with broadening in 580 cm-1 peak, which manifests the presence of the oxygen vacancy (VO) related defects. Moreover, in photoluminescence (PL) spectra, we have observed a peak at 524 nm, indicating the presence of singly ionized VO+, which may be activating bound magnetic polarons (BMPs) in dilute magnetic semiconductors (DMSs). Magnetization measurements indicate weak ferromagnetism at RT, which rises with increasing Ni concentration. It is therefore proposed that the effect of the Ni ions as well as the inherent exchange interactions arising from VO+ assist to produce BMPs, which are accountable for the RT-FM in Zn1-xNixO (0< x < 0.125) system.

Studies on the control of ZnO nanostructures by wet chemical method and plausible mechanism

Most of the applications of the nano structures dependent on the morphology which affects the opto electronics properties. This research article provides a pathway of guiding optical properties like band-gap and fluorescence properties by controlled growth of nano-rods, -flowers, -needles or- tubes without external chemical doping, by simple hydro thermal method by controlling over synthesis parameter, temperature.This research article provides a pathway of controlled growth of ZnO nano-rods, -flowers, -needles or -tubes without external chemical catalysis, via a simple wet chemical method by control of synthesis temperature. Morphological effects on structural and optical properties are studied by Ultraviolet-visible (UV-vis) spectroscopy shows slight enhancement in the band gap, with increasing synthesis temperature. Photoluminescence (PL) data indicates the existence of defect in the nanomaterials, which is more elaborately explained by schematic band diagram. A sharp and strong peak in Raman spectroscopy is observed at ∼438cm−1 is assigned to the E2high optical mode of the ZnO, indicating the wurtzite hexagonal phase with high crystallinity.

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.

Controlled Zn1−xNixO nanostructures for an excellent humidity sensor and a plausible sensing mechanism

Here, we report on the chemi-resistive humidity sensing behavior of a Zn1−xNixO nanomaterial synthesized using a wet chemical method. At room temperature, the x = 0.10 sample shows excellent humidity sensitivity of 152% and a response/recovery time of 27/3 s within the 33–97% relative humidity (RH) range. The experimental data observed over the entire range of RH values can be well-fitted to a Freundlich adsorption isotherm model, which reveals two distinct water adsorption regimes. The obtained results suggest that the x = 0.10 sample has the highest adsorption strength. Theoretical humidity detection limits for the x = 0, 0.05 and 0.10 samples are found to be about 7.24% RH, 6.31% RH and 3.71% RH, respectively. The excellent humidity sensing observed using the ZnO and Ni doped ZnO nanostructures is attributed to a Grotthuss mechanism, considering the distribution of available adsorption sites. Therefore, Ni doped ZnO nanostructures synthesized via employing an economical wet chemical technique demonstrate promising capabilities to act as potential candidates for the fabrication of next-generation humidity sensors.