Thin film deposition of metal sulfide and metal oxide layers with and without polymer intercalation by using chemical bath deposition technique

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Chiloane, Mothepane Happy
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Vaal University of Technology
A well adherent single layer thin film of zinc oxide (ZnO), zinc sulfide (ZnS), cadmium oxide (CdO) and cadmium sulfide (CdS) has been deposited on silica glass substrates from basic baths containing zinc acetate, cadmium acetate, ammonium hydroxide, triethanolamine, thiourea, and sodium hydroxide as precursors by chemical bath deposition (CBD), followed by multilayer deposition of metal oxide/metal sulfide and metal sulfide/metal oxide then intercalated by polyvinyl alcohol (PVA). CBD was used for the deposition of the metal sulfide/oxide thin films under acidic and basic conditions for single layer thin film by varying temperature and pH. SEM micrograph of the as-deposited ZnS, ZnO, CdO, and CdS thin film, show the film to be uniform, dense, homogeneous at lower temperatures and composed of large irregular shaped grains that are scattered at higher temperatures. These large grains are comprised of smaller spherical grains. Star shapes were observed for ZnO and ZnS thin films while spherical shapes were observed for CdO and CdS thin films. The effect of temperature on the optical properties was studied by varying the deposited films at different temperatures of 60˚C, 70˚C, and 90˚C. The increase in temperature on the single layer depositions caused the decrease in %T which was in support with the large SEM results which in higher absorbance. Films of different thickness of (114.4 nm, 107.7 nm, 100.4 nm, and 99.67 nm) respectively were obtained for single layer deposition. The XRD study of the ZnS, ZnO, CdO, and CdS monolayer films deposited does not reveal any well-defined peak, indicating a highly disordered material. The XRD of CdO thin films showed one broad peak around 2θ value 26.37° corresponding to (111) plane. The structural studies had similar behavior of CdS, ZnO, and ZnS was similar with CdO with one broad peak at 2θ ~ 26˚. To enhance the property of MO, MS thin film was formed on the interfaces of MO thin film as a passivation and a substrate layer at 60°C with a pH value of 11 for 60 minutes deposition time and vice versa for enhancing the property of MS. The structural, morphological and optical properties of CBD deposited thin films have been studied by varying the processing parameters and the MO/MS multilayer ratio of the starting precursors to provide a better understanding of the growth conditions by studying the MO/MS and MS/MO multilayer thin film materials with further intercalation of polyvinyl alcohol (PVA). Multilayer thin films show different physical properties other than the conventional monolayer thin films. The films were deposited as the matrix of MO/MS and MS/MO of respectively at temperatures of 60˚C at alkaline medium for 60 minutes deposition time. SEM micrograph of CdO/CdS was observed to be spherical shapes which show the film to be uniform, dense, and homogeneous. Large spherical particles that appear to be increasing in size and non-homogeneous were observed in the deposition of CdS/CdO. The deposited ZnO/ZnS thin films show large conglomerate of snowflake structures and that of ZnS/ZnO thin film were polycrystalline in structure. The optical properties and band-gap energy were studied by depositing the films at 60˚C for 60 minutes. Transparent multilayer thin films were successfully deposited on the silica glass substrate. The %T was relative ~89% in the visible the region, and some oscillations due to thin film interference effects. The optical %T of the multilayer deposition showed slight changes from the monolayer. The multilayer film thickness was increased for deposition of CdO/CdS, CdS/CdO, ZnO/ZnS and ZnS/ZnO series (145.47, 131.O, 128.8, 148.38 nm) illustrating that an increase in layer increases the thickness of the material deposited. The increase in thickness showed that CBD deposition technique does not wash away the pre-deposited layer of the thin film material and hence the structure should be enhanced. XRD measurements are performed to investigate the change in the crystal structure of the film, as the number of layers deposited was increased, and the composition of the growth solution is varied the deposited CdO/CdS and CdS/CdO thin film has a monocrystalline and hexagonal structure which is (θ= 8.2˚ and 11.878˚) with one large broad peak at ~ θ= 27˚ which was due to the amorphous glass substrate that was detected. The presence of diffraction peaks of ZnO/ZnS indicates that the film is polycrystalline with cubic structure is detected at 2θ= 26.79°. It is revealed that the films have peaks corresponding to (111), (220) and (311). There was only one peak that occurred in XRD pattern at 2θ of 12.488˚ at (002) for deposition of ZnS/ZnO thin film was polycrystalline. To enhance the structure and study the effect of thickness intercalation of MO and MS with polyvinyl alcohol (PVA) was deposited to create the layers of MO/PVA/MS. Intercalated MO and MS thin films were successfully deposited on the glass substrate by chemical bath deposition (CBD) using PVA as the intercalation polymer by varying the effect the polymer on the inorganic layers. The intercalation by polymers followed multiple layer deposition of the metal chalcogenide in which MO becomes the first layer and the polymer as the second layer followed by the MS as the third layer respectively at temperatures of 60˚C at alkaline medium for 60 minutes deposition time. The thin film composition materials of the intercalated growth are composed of CdO/PVA/CdS, CdS/PVA/CdO, ZnO/PVA/ZnS and ZnS/PVA/ZnO. The intercalated SEM imaging was more smooth, homogeneous and spherical shape. The optical properties of the intercalated thin films are transparent at %T of ~88 % showing a more transparent material. The film thickness of the intercalated MO/PVA/MS and MS/PVA/MO was decreased to (52.67, 37.15, 102.45 and 116.6 nm) respectively, illustrating that the PVA has a huge impact on the thickness as well as the structure of the deposited material by use of CBD technique. The XRD patterns showed the formation of the polycrystalline and monocrystalline structure of CdS/PVA/CdO and ZnO/PVA/ZnS multilayer thin film. The pattern of ZnS/PVA/ZnO and CdO/PVA/CdS was amorphous in structure. The intercalated PVA reduced the crystallinity of the deposited material.
M. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology.
Thin film, Metal sulfide, Metal, Polymer