S.A. Vanalakar

Farming of maize-like zinc oxide via a modified SILAR technique as a selective and sensitive nitrogen dioxide gas sensor

Novel hierarchical nanostructures of metal oxides have enormous potential in various applications. In this report, novel nanostructured maize-like ZnO was synthesized via a facile and economical modified successive ionic layer adsorption and reaction (M-SILAR) method and subsequent heat treatment at 300 °C for 30 min as a highly-sensitive NO2 gas sensor. The M-SILAR technique described uses two bath solutions instead of the conventionally used four bath solutions. Their structural, morphological, and optical properties have been thoroughly characterized using advanced techniques such as X-ray diffraction, field-emission scanning electron microscopy and photoluminescence spectroscopy. The obtained hexagonal wurtzite ZnO structure appears as the hierarchical maize corn-like morphology with nano-granules. The ZnO maize based sensor contains numerous active sites, which afford beneficial conditions for gas adsorption and diffusion. Moreover, the synthesized sensor was proven to be an excellent NO2 sensing material with high selectivity, superior sensitivity, and good response/recovery at relatively a low operating temperature. The peculiar structure of our sample, the preparation method and its nitrogen dioxide detection have wide application prospects.

Investigations on Chemo-Mechano Stabilities of the Molybdenum Thin Films Deposited by DC-Sputter Technique

Abstract This paper reports the chemical and mechanical stability of Molybdenum (Mo) thin films deposited by direct current magnetron sputtering technique onto soda lime glass substrates. Mo thin films were deposited at various Ar (working) gas pressures to get optimized structural, morphological, adhesive and electrical properties. Mo thin films were further characterized by field emission scanning electron microscope (FE-SEM), X-ray diffraction, Hall measurements and the cross hatch tape test. To study their chemical stability the prepared Mo thin films were further dipped in acetic acid and ammonia solution for 6 h. Mechanical stability of Mo thin films was tested by high speed ultrasonication for an hour. Both the chemical and mechanical stability studies showed that Mo thin films were highly stable since morphology, adhesion and electrical properties did not alter significantly. FE-SEM results showed that the grain size of the chemo-mechano stability tested Mo thin films remained significantly similar with an unimportant effect on the film thickness. Electrical properties showed that electrical resistivity and hall mobility for as-deposited Mo thin films were 2.7 · 10–5 Ω cm and 5.1 cm2/Vs, respectively and remained nearly stable regardless of chemical and mechanical treatment. All of the films passed the cross hatch tape test and showed an excellent adhesion with glass substrates. The wettability investigations showed that all the Mo thin films were hydrophilic in nature and having contact angles in the range of 35○ to 40○.

Structural, Optical, Surface Morphological and Electrical Properties of Cu2ZnSnS4 Thin Film Synthesized by Drop Casting Technique

Abstract Quaternary Cu2ZnSnS4 (CZTS) thin films have been receiving an excessive technological interest in the solar cell industry due to its outstanding opto-electronics properties. This study report the deposition of CZTS thin films on the soda lime glass substrate using simple and cost effective drop casting route. In this route, CZTS ink was prepared using CuCl2, SnCl2, ZnCl2, Na2S as a precursors, and polyvinylpyrrolidone as a binder with de-ionized water as a solvent. The CZTS ink was then drop-cast onto the clean glass substrate at 110 ℃ and sintered at 550 ℃ for 1.30 h in sulfur vapor. Amorphous thin films of CZTS were deposited, and thermally converted to polycrystalline, semiconducting CZTS. Films were studied using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, field-emission scanning electron microscopy, energy dispersive spectrometer, and UV–Vis spectroscopy. A polycrystalline CZTS thin films were obtained with a ratio of Zn/Sn = 1.0, S / metal = 1.07. The films had a band gap of about 1.56 eV. The films were p-type with a hall mobility of 32 cm2/Vs. These drop cast CZTS thin films can be applied as the absorber layers in solar cells. We expect that the method and idea presented in this work will provide a new way for the construction of highly efficient photo-absorber not only for CZTS, but also for other semiconductor materials.

Rapid synthesis of CdS nanowire mesh via a simplistic wet chemical route and its NO2 gas sensing properties

In this report, 1-D interconnected CdS nanowires were prepared rapidly via a wet chemical route at relatively low temperature, using cadmium sulphate, thiourea and ammonia as raw materials. The formation of a CdS nanowire mesh (CdS NW mesh) and its structural, optical, surface morphological properties and elemental composition were studied by various characterization techniques. The cubic crystal structure of the CdS interconnected nanowire mesh was confirmed via X-ray diffraction and field emission scanning electron microscopy analysis. The photoluminescence spectroscopy measurements reveal the presence of defects in the as synthesized CdS NW mesh. However, the defect states are beneficial for the gas sensing behavior. Therefore, the gas sensing properties of the CdS NW mesh were studied using NO2 as an analyte gas at moderate operating temperature. The nanowire mesh and inter-wire space were observed to play a crucial role in determining the gas sensing performance of the devices. The as synthesized CdS NW mesh shows a gas response of about 1850% to 100 ppm NO2 gas. In particular, our CdS based gas sensor showed a fifty fold better gas response towards NO2 gas than the earlier reports in the literature. Due to the high value of gas sensitivity, the reported CdS NW mesh could be a suitable candidate for NO2 sensing.

Thickness dependent photoelectrochemical performance of chemo-synthesized nanostructured CdS thin films

Abstract Thin films of cadmium sulfide (CdS) with different film thicknesses were chemo-synthesized onto soda lime glass and fluorine doped tin oxide (FTO) coated glass substrates. The synthesized CdS films were characterized by using UV-vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The XRD patterns revealed the formation of CdS with a cubic crystal structure. The variation in band gap energies was found to be in the range of 2.42–2.85 eV. An increase of 0.43 eV over the bulk band gap energy of CdS was found due to the quantum size effect in CdS thin films. The atomic force microscopy study depicted a novel egg-like morphology of CdS nanoparticles. Further, photoelectrochemical (PEC) performance of as grown CdS thin films was investigated using two electrode configurations in polysulfide electrolyte. The sample with film thickness 1389 Å showed the best PEC performance compared to other samples.

Gas sensing properties of 3D mesoporous nanostructured ZnO thin films

Advancing the properties of selective and sensitive metal oxide based gas sensors is a challenging research topic for the detection of toxic, and pollutant gases. In the present research, we successfully deposited a three dimensional (3D) mesoporous ZnO nanostructure on a glass substrate by using a hydrothermal method, and tested the material for its gas sensing performance. These 3D mesoporous ZnO nanostructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and photoluminescence techniques. Gas sensing performance analysis was carried out for nitrogen dioxide (NO2) gas at different temperatures and concentrations. The 3D mesoporous ZnO nanostructure revealed excellent gas sensing performance for NO2 gas because of its large surface area. The larger surface area led to an increase in the gas sensitivity. In addition, the sensor based on the 3D mesoporous ZnO nanostructure could be used at a low operating temperature of 150 °C. This work suggests that the 3D mesoporous ZnO nanostructure is a versatile material for NO2 gas sensing applications.