College of Natural and Computational Sciences

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The College of Natural and Computational Sciences advances education, research, and innovation in natural sciences, mathematics, statistics, and computational disciplines.

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    EFFECT OF CADMIUM ION CONCENTRATION ON THESTRUCTURALAND OPTICAL PROPRTIES OF CdS THIN FILMS BYCHEMICALBATHDEPOSITION METHOD
    (HAWASSA UNIVERSITY, 2024-11) TESFALEM BEREHANU AYELE
    Cadmium Sulfide (CdS) thin films were successfully deposited on glass substrates at four different concentration of cadmium ion (Cd 2+ ) by chemical bath deposition technique at a bath temperatureof80 0c for 50 minutes. The reagents used for the deposition were cadmium sulphate (CdSO4) for Cd2+source, thiourea (CS(NH2)2) for S 2- source and ammonia (NH3) as complexing agent. Thesynthesized thin films were characterized by XRD and UV-Vis Spectrophotometer. TheXRDanalysis of CdS thin films revealed that cubic crystal structure with preferred orientationalongthe(111) plane and the crystalline size increases in the range of 8.78nm to 18.98nmwith increasingcadmium ion (Cd 2+ ) concentration in the solution. Moreover, after the increase of Cd2+ionconcentration one peak of CdO with cubic structure appeared. Also the dislocation density(δ) andstrain (ε) were calculated. From VU-Vis Spectrophotometer study, the optical band gap valuesofCdS thin films decreased in the range of 2.0eV to 1.85eV with increasing the cadmiumion(Cd2+)concentration.
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    EFFECT OF THIOUREA CONCENTRATION ON THE STRUCTURAL AND OPTICAL PROPERTIES OF PbS THIN FILMS SYNTHESIZED BY CHEMICAL BATH DEPOSITION METHOD
    (HAWASSA UNIVERSITY, 2024-11) ADDISU MINAYEHU ENGIDA
    In the present work lead sulfide (PbS) thin films were synthesized on glass substrate by chemical bath deposition method as material employing lead acetate as a source of Pb2+ and thiourea as a source of precursor S2- and sodium hydroxide as complexing agent in the solution of distilled water. The thin film have been deposited at constant bath temperature of 800c and the deposition time was 20 minute for different samples in the various 0.2M thiourea concentrations of 8, 9, 10, 11 and 12 mL respectively. The thin films were characterized by using X – ray diffraction and UV – Vis spectrophotometer. X-ray diffraction analyses revealed that all the films were polycrystalline in nature with the diffraction peaks indices to the face centred cubic structure. For as the deposited thin films, it revealed that PbS nanocrystalline with preferred orientation along the (111) for 8 mL which changes to (200) for 9 – 12 mL in per set of 1 mL for various thiourea concentration due to the change of the total system free energy during the film growth. The structural parameters, such as the lattice constant (a), crystallite size (D), dislocation density (ρ) and micro strain (ε) were evaluated from the XRD spectra. The average crystalline size was calculated using the Debye – Scherer’s formula and found to decrease from 35.71 to 29.64 nm with an increase thiourea concentration in the case of increasing the growth rate, at fast deposition rate and growing species has no enough time to be organized. The dislocation density and micro strain were found to vary inversely with the crystallite size, whereas the lattice constant was found to decrease with a decrease of in crystallite size. The UV – Vis spectroscopy characterization of the sample revealed that the optical band gap of energy was increased from 1.55 to 1.61 eV with increasing thiouera concentration due to the quantum size effect of polycrystalline PbS thin film. Keywords: Chemical bath deposition, Lead sulphide, thin films