Nipin Kohli

Deposition, characterization and gas sensors application of RF magnetron-sputtered terbium-doped ZnO films

Influence of terbium (Tb) doping on structural, optical and morphological properties of radio frequency magnetron-sputtered ZnO films has been investigated using various characterization techniques. Investigations revealed the formation of hexagonal wurtzite structure of ZnO with preferential c-axis orientation, presence of oxygen vacancies, modification of surface morphology and surface roughness, and confirmation of oxidation states of elements present in ZnO and Tb-doped ZnO films. Subsequently, films deposited with varied Tb concentrations have been tested for ethanol vapor sensing. Doped films exhibited reduction in optimum operable temperature, enhancement in ethanol sensing response and improvement in response/recovery time in comparison with pristine ZnO. The observed improvement in doped samples has been attributed to modifications in surface properties such as morphology, surface roughness, basicity, structural disorder and oxygen vacancies introduced due to dopant incorporation.

Sensitive and selective ethanol sensor based on Zn-doped SnO2 nanostructures

Influence of Zn doping on the structural, optical and gas sensing properties of SnO2 nanoparticles has been examined in this work. Formation of tetragonal rutile structure of synthesized samples of undoped and Zn-doped SnO2 has been confirmed by X-ray diffraction (XRD) and Raman results. Decrease in particle size with increase in dopant concentration has been observed from transmission electron microscope and XRD analysis. Energy dispersive X-ray analysis confirmed presence of dopant in doped nanoparticles. It has been observed that doping also induced increase in specific surface area. Photoluminescence results indicated large number of oxygen vacancies in Zn-doped SnO2 nanoparticles. The sensor based on Zn-doped SnO2 displayed an enhanced sensing performance towards ethanol which is attributed to large surface area and huge number of oxygen vacancies. In addition, fabricated sensor showed good selectivity towards ethanol and exhibited reproducibility as well.

Gas sensing behaviour of Cr2O3 and W6+: Cr2O3 nanoparticles towards acetone

This paper reports the acetone gas sensing properties of Cr2O3 and 2% W6+ doped Cr2O3 nanoparticles. The simple cost-effective hydrolysis assisted co-precipitation method was adopted. Synthesized samples were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. XRD revealed that synthesized nanoparticles have corundum structure. The lattice parameters have been calculated by Rietveld refinement; and strain and crystallite size have been calculated by using the Williamson-Hall plots. For acetone gas sensing properties, the nanoparticles were applied as thick film onto alumina substrate and tested at different operating temperatures. The results showed that the optimum operating temperature of both the gas sensors is 250°C. At optimum operating temperature, the response of Cr2O3 and 2% W6+ doped Cr2O3 gas sensor towards 100 ppm acetone was found to be 25.5 and 35.6 respectively. The investigations revealed that the addition of W6+ as a dopant enhanced ...

Optical studies of reduced graphene oxide thin films

We report here a simple and efficient method for fabrication of reduced graphene oxide (rGO) thin films. Graphite oxide can be completely exfoliated to produce aqueous colloidal suspensions of graphene oxide (GO) sheets by simple ultra-sonication. Graphene oxide thin films were reduced towards graphene by exposure to hydrazine vapor, ammonia vapor and microwaves. The samples were characterized using X-ray diffraction (XRD) and UV-Visible spectroscopy (UV-Vis).

Effect of Sn doping on morphology and ethanol sensing response of ZnO nanorods

In this work we are reporting the effect of doping of tin on the morphology and sensing response ZnO nanorods. We adopted chemical route to synthesize nanorods of ZnO and then 2% of Sn by weight was added at the time of reaction. To understand the structure we subjected the synthesized materials to XRD and FESEM. The addition of dopant has altered the morphology of ZnO, moreover it has also enhanced the sensing response for ethanol appreciably.

P1.4.11 Fabrication of LPG Sensors Based upon Chemically Tailored Sizes of Chromium Oxide Nanoparticles

In this work, an attempt has been made to alter the particle size of chromium oxide and then to investigate sensing behaviour of these Cr2O3 samples towards LPG. We have followed chemical route for synthesizing nanoparticles of chromium oxide. To tailor nanoparticles of chromium oxide, synthesis was carried out at various reaction temperatures namely, 5, 27 and 65 o C. In order to understand the structure and morphology of synthesized materials; they were subjected to X-ray diffraction and field emission scanning electron microscope. The obtained results have endorsed our prejudice and we found that reaction temperature has played a pivotal role in tailoring particle sizes. Interestingly, we observed that Cr2O3 nanoparticles synthesized at 27°C were smaller as compared to those synthesized at 5 and 65°C. Thick film gas sensors of thus-prepared Cr2O3 powders were obtained by depositing them on alumina substrates. These fabricated sensors were studied for their optimum operating temperatures for LPG and we found that all the sensors exhibited best response at 250°C. The investigation revealed that sensing response of Cr2O3 nanoparticles synthesized at 27°C was exceptionally higher than that of Cr2O3 nanoparticles synthesized at 5 and 65°C.

Gas sensing properties of zinc oxide thin films prepared by spray pyrolysis

Metal oxide semiconductors are widely employed as potential materials for the development of sensing devices for poisonous and inflammable gases. The change in resistivity of active material is exploited as a sensing parameter. A large volume of research work has been carried out in the last few decades on sensors and potential sensor materials. The advent of nanostructured materials has given a new impetus to the sensor research. Preparation and sensing response of zinc oxide thin films towards alcohol has been reported in this paper. Zinc oxide thin film has been prepared by using spray pyrolysis, using zinc acetate and methanol as the starting materials. The thin film was characterized for morphology and structure by using x-ray diffractometer (XRD) and field emission scanning electron microscope (FESEM) techniques. The results indicated that the ZnO particles are crystallized in the wurtzite hexagonal phase, which were well distributed in the films. Prepared zinc oxide thin film was exposed to different alcohols to check its gas sensing behaviour at different temperatures.Metal oxide semiconductors are widely employed as potential materials for the development of sensing devices for poisonous and inflammable gases. The change in resistivity of active material is exploited as a sensing parameter. A large volume of research work has been carried out in the last few decades on sensors and potential sensor materials. The advent of nanostructured materials has given a new impetus to the sensor research. Preparation and sensing response of zinc oxide thin films towards alcohol has been reported in this paper. Zinc oxide thin film has been prepared by using spray pyrolysis, using zinc acetate and methanol as the starting materials. The thin film was characterized for morphology and structure by using x-ray diffractometer (XRD) and field emission scanning electron microscope (FESEM) techniques. The results indicated that the ZnO particles are crystallized in the wurtzite hexagonal phase, which were well distributed in the films. Prepared zinc oxide thin film was exposed to differe...

Influence of Dy doping on structural, morphological and gas sensing properties of ZnO

Effect of dysprosium (Dy) as a dopant on structural, morphological and gas sensing properties of zinc oxide has been studied in the present work. A chemical route was adopted for synthesis of pure and Dy doped zinc oxide. Synthesized samples were characterized using X-ray diffraction, field emission scanning electron microscope, Branneur Emmet Teller and X-ray photoelectron spectroscopy. XRD studies confirmed the hexagonal wurtzite structure of pure and doped samples and the lattice constants and unit cell volume were calculated using Rietveld refinement. Gas sensors were fabricated from synthesized samples and it has been found that Dy doping has significantly improved sensor response towards ethanol. In addition, reduction in optimum operating temperature has been achieved from 400 to 300°C because of doping. The improved sensor properties in doped sensor have been attributed to reduction in particle size, increase in surface area and high surface basicity.

Improvement in LPG sensing response by surface activation of ZnO thick films with Cr2O3

Liquefied Petroleum Gas (LPG) sensing response of pure and Cr2O3 activated ZnO has been investigated in this study. Zinc oxide was synthesized by co-precipitation route and deposited as a thick film on an alumina substrate. The surface of ZnO sensor was activated by chromium oxide on surface oxidation by chromium chloride. The concentration of chromium chloride solution used to activate the ZnO sensor surface has been varied from 0 to 5 %. It is observed that response to LPG has improved as compared to pure ZnO.

Structural, optical and ethanol gas sensing properties of In2O3 and Dy3+:In2O3 nanoparticles

This paper reports the structural, optical and ethanol gas sensing properties of In2O3 and 5% Dy3+doped In2O3 nanoparticles. The simple cost-effective hydrolysis assisted co-precipitation method was adopted. Synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible spectroscopy (UV-vis) techniques. XRD revealed that synthesized nanoparticles have cubic bixbyite phase. The lattice parameter, strain and crystallite size have been calculated by using the Williamson-Hall plots. UV-vis spectroscopy showed the red shift in the optical band gap due to Dy3+ doping in In2O3 nanoparticles. For ethanol gas sensing properties, the nanoparticles were applied as thick film onto alumina substrate and tested at different operating temperatures. The results showed that the optimum operating temperature of both the gas sensors is 300°C. At optimum operating temperature, the response of In2O3 and Dy3+:In2O3 gas sensor towards 250 ppm ethanol was found to be 9.65 and...