Mashudur Rahaman

Optical and Morphological Characterization of BaSeThinFilms Synthesized via Chemical Bath Deposition

Barium selinide (BaSe) thin films were deposited onto glass substrate via chemical bath deposition (CBD) method. The effect of deposition time on the thin film formation mechanism has been studied to understand the optimum conditions for synthesis process. The phase identification and surface morphology of thin coated films were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively while the optical characterizations were conducted by means of ultraviolet visible (UV- Vis) spectroscopy. XRD study confirms the polycrystalline hexagonal structure of the thin films. The XRD peaks at 2θ =23.84° and 2θ = 23.86 o showed the preferential orientation along the (021) and (201)plane with deposition time 20 hours and 22 hours respectively, whereas the major peak at (111) was obtained with a deposition time of 24 hours. With the increase in deposition time up to 24 hours, the film gradually grew thicker along with the fine increase in the grain size. The direct optical band gap of the films was measured to be varied from 1.33 to 3.37 eV.

Reduction of hydrogen sulfide (H 2 S) from poultry based biogas by aeration technique

Biogas, produced in anaerobic digestion (AD)-plants, primarily consists of methane (CH4) and carbon dioxide (CO2) with smaller amount of hydrogen sulfide (H2S) and ammonia (NH3). Trace amount of some other gases are occasionally present in biogas. For electricity generation from biogas needs reduction of H2S, because it forms a complex bond with iron hence damage the generator. Reduction of Hydrogen Sulfide (H2S) from poultry based biogas can be done by dosing air/oxygen to the main digester into the digestion process. For optimization there are two sets of aeration technique have been followed. Firstly two hour interval air injection and secondly air injection based on percentage of hourly gas production. The optimum air percentage to minimize H2S should be at least 3.00%. After aeration H2S level comes to the desired level (<50ppm) within 1.5–2 hours and remains constant up to 7–9 hours and biogas can be used for effective power generation. A complete aeration system has been developed which is simple and cost effective for H2S reduction to the desired level from poultry based biogas plant. This system can be applied for any size of poultry based biogas plant for effective power generation.

Experimental Study on Structural, Optical and Electrical Properties of Chemical Bath Deposited CdZnS Thin Films

CdZnS thin films have been prepared from an aqueous solution containing cadmium chloride, zinc acetate and thiourea by chemical bath deposition (CBD) method on a glass substrate at 82°C. Amount of cadmium chloride and zinc acetate were systematically varied as y=0.2, 0.4, 0.6, 0.8 (y=a/(a+b), a=volume of zinc acetate, b=volume of cadmium chloride) and subsequent effects on the films property were studied by diffractometer, scanning electron microscope, spectrophotometer, four point probe and hall effect measurement. X-ray diffraction result shows that an increase in the Zn-content decreases the crystalline quality of the films. Transmittance and absorbance data was obtained by using UV-Vis spectrometer. Transmittance of 85-90% is found beyond the 700 nm wavelength. Optical bandgaps calculated from these data show a gradual increase in value with a gradual increase in Zn content. The electrical resistance of the so prepared films were measured by four point probe method. The result indicates that the resistance increases with increasing Zn content.