Room temperature ammonia gas sensing characteristics of Co3O4

Room temperature ammonia gas-sensing characteristics of Co3O4 pellet sensor are reported in this paper. For this purpose, Co3O4 powder is prepared by a route of simple precipitation + heating at 800° C/2 hr. The as-prepared powder is characterized by using X-ray diffraction and scanning electron microscopy. The ammonia gas-sensing properties of Co3O4 pellets made at various loads of 3, 5, 7 & 9 ton and at constant time 4 min. are measured using home-built static gas sensing system. The characterization studies revealed that the cobalt oxide particles formed are cubic spinel Co3O4, highly pure and spherical in shape. The particle size distribution is found to be nearly uniform with average particle size ~ 1 μm. The ammonia gas sensing properties of Co3O4 pellet sensor are found to be good. The highest sensitivities – S.F. 175 and 358 are found at ~ 25 ppm and 250 ppm concentrations of ammonia gas respectively for the Co3O4 pellet sensor made at the load 3 ton. Further, an admirable repeatability and reversibility in the ammonia gas sensing characteristics are observed for all the Co3O4 pellet sensors. The average response time of 4.0 min. and recovery time of 3.0 min. are obtained for all the Co3O4 pellet sensors. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2785

Inter-electrode separation induced amorphous-to-nanocrystalline transition of hydrogenated silicon prepared by capacitively coupled RF PE-CVD technique

Role of inter-electrode spacing in capacitively coupled radio frequency plasma enhanced chemical vapor deposition deposition (PE-CVD) system was studied. The influence of inter-electrode separation on the structural, optical and electrical properties of the deposited films was carefully invesigated keeping all other deposition parameters constant. The results indicate that the film growth rate critically depends up on the plasma chemistry/gas phase chemistry altered by variation of interelectrode separation. Structure and optical properties are strongly influenced by interelectrode separation. The nanocrystallization in the material was observed for smaller inter-electrode separation, whereas higher inter-electrode separation favors amorphous structure of the deposited material. The band gap of the material was found to decrease from ~2 eV to 1.8 eV when inter-electrode separation was varied from 15 mm to 40 mm. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2200

Hot-wire CVD growth simulation for thickness uniformity

Obtaining thickness uniformity over a large substrate area seems to be a bottleneck as far as the industrial applications of the hot-wire CVD (Cat-CVD) process is concerned. In order to address the different issues in this respect, we have simulated the hot-wire CVD growth process and proposed a proper filament geometry for maximum thickness uniformity. The hot filament was assumed as a one-dimensional assembly of point sources. Five types of commonly used filament geometries were considered for their performance to identify the best filament geometry for maximum thickness uniformity. Here, the chamber pressure was assumed to be low enough so that the Knudsen number Kn>1. Based on our results, we propose a parallel filament geometry for maximum thickness uniformity over large substrate areas. By applying the model further to the parallel filament geometry, the relations between substrate–filament distance and minimum filament length, as well as the number of parallel filaments and the separation between them, which are necessary for the required thickness uniformity over the given substrate area, were determined. The validity of the model was checked using the ‘Matched-Pair t-test’. The effect of chamber pressure on thickness uniformity and growth rate, when it is sufficiently high to make the Knudsen number Kn<1, was also simulated. The thickness uniformity was observed to increase with an increase in chamber pressure

Fabrication of ZnO Scaffolded CdS Nanostructured Photoanodes with Enhanced Photoelectrochemical Water Splitting Activity under Visible Light

CdS, characterized by its comparatively narrow energy band gap (∼2.4 eV), is an appropriate material for prospective use as a photoanode in photoelectrochemical water splitting. Regrettably, it encounters several obstacles for practical and large-scale applications, including issues such as bulk carrier recombination and diminished conductivity. Here, we have tried to address these challenges by fabricating a novel photoelectrode (ZnO/CdS) composed of one-dimensional ZnO nanorods (NRs) decorated with two-dimensional CdS nanosheets (NSs). A facile two-step chemical method comprising electrodeposition along with chemical bath deposition is employed to synthesize the ZnO NRs, CdS NSs, and ZnO/CdS nanostructures. The prepared nanostructures have been investigated by UV–visible absorption spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy. The fabricated ZnO/CdS nanostructures have shown enhanced photoelectrochemical properties due to the improvement of the semiconductor junction surface area and thereby enhanced visible light absorption. The incorporation of CdS NSs has been further found to promote the rate of the charge separation and transfer process. Subsequently, the fabricated ZnO/CdS photoelectrodes achieved a photocurrent conversion efficiency 3 times higher than that of a planar ZnO NR photoanode and showed excellent performance under visible light irradiation. The highest applied bias photon-to-current conversion efficiency (% ABPE) of about ∼0.63% has been obtained for the sample with thicker CdS NSs on ZnO NRs with a photocurrent density of ∼1.87 mA/cm2 under AM 1.5 G illumination. The newly synthesized nanostructures further demonstrate that the full photovoltaic capacity of nanomaterials is yet to be exhausted

Evolution of structural and optical properties of rutile TiO2 thin films synthesized at room temperature by chemical bath deposition method

Nanocrystalline thin films of TiO2 were prepared on glass substrates from an aqueous solution of TiCl3 and NH4OH at room temperature using the simple and cost-effective chemical bath deposition (CBD) method. The influence of deposition time on structural, morphological and optical properties was systematically investigated. TiO2 transition from a mixed anatase–rutile phase to a pure rutile phase was revealed by low-angle XRD and Raman spectroscopy. Rutile phase formation was confirmed by FTIR spectroscopy. Scanning electron micrographs revealed that the multigrain structure of as-deposited TiO2 thin films was completely converted into semi-spherical nanoparticles. Optical studies showed that rutile thin films had a high absorption coefficient and a direct bandgap. The optical bandgap decreased slightly (3.29–3.07 eV) with increasing deposition time. The ease of deposition of rutile thin films at low temperature is useful for the fabrication of extremely thin absorber (ETA) solar cells, dye-sensitized solar cells, and gas sensors

Evolution of microstructure and opto-electrical properties in boron doped nc-Si:H films deposited by HW-CVD method

Demand for an efficient window layer for a-Si:H based solar cells in terms of electrical conductivity and optical band gap is ever increasing since the inception of single junction and tandem solar cells. In this paper, we report synthesis of highly conducting boron doped p-type nc-Si:H films by HW-CVD using the mixture of silane (SiH4) and diborane (B2H6) without hydrogen (H2) dilution. Variation in film characteristics with B2H6 gas-phase ratio was studied, and revealed that the boron doping induces amorphization in nc-Si:H film structure. The AFM analysis show increase in rms surface roughness and micro-void density while FTIR spectroscopy analysis show shift of hydrogen bonding from Si–H2 and (Si–H2)n complexes to Si–H configuration on boron doping. The hydrogen content was found <2.66 at.% while the band gap remain as high as 1.8 eV or more. At optimized B2H6 gas-phase ratio, we have obtained p-type nc-Si:H films having high band gap (∼2.0 eV), high dark conductivity (∼1.2 S/cm) with low hydrogen content (∼1.78 at.%) at reasonably high deposition rate (∼9.2 Å/s). The obtained films can be used as a window layer in a-Si:H based p–i–n and tandem solar cells and color light detectors

Evolution of structural and optical properties of rutile TiO2 thin films synthesized at room temperature by chemical bath deposition method

Nanocrystalline thin films of TiO2 were prepared on glass substrates from an aqueous solution of TiCl3 and NH4OH at room temperature using the simple and cost-effective chemical bath deposition (CBD) method. The influence of deposition time on structural, morphological and optical properties was systematically investigated. TiO2 transition from a mixed anatase–rutile phase to a pure rutile phase was revealed by low-angle XRD and Raman spectroscopy. Rutile phase formation was confirmed by FTIR spectroscopy. Scanning electron micrographs revealed that the multigrain structure of as-deposited TiO2 thin films was completely converted into semi-spherical nanoparticles. Optical studies showed that rutile thin films had a high absorption coefficient and a direct bandgap. The optical bandgap decreased slightly (3.29–3.07 eV) with increasing deposition time. The ease of deposition of rutile thin films at low temperature is useful for the fabrication of extremely thin absorber (ETA) solar cells, dye-sensitized solar cells, and gas sensors