Effect of complexing agent and annealing atmosphere on properties of nanocrystalline ZnS thin films.

Department of Materials Science and Engineering, Chonnam National University, Gwangju 500-757, Korea.
Journal of Nanoscience and Nanotechnology (Impact Factor: 1.34). 05/2010; 10(5):3686-90. DOI: 10.1166/jnn.2010.2330
Source: PubMed

ABSTRACT The nanocrystalline Zinc Sulfide (ZnS) thin films were prepared on glass substrates by chemical bath deposition (CBD) method using aqueous solutions of zinc acetate, thiourea and tri-sodium citrate in alkaline medium at 80 degrees C. The tri-sodium citrate acts as a complexing agent. The effects of complexing agent and annealing atmosphere (95%N2 + 5%H2S) on structural, morphological and optical properties of ZnS thin films were studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and optical absorption. XRD study revealed that single phase ZnS powder was formed in the solution with tri-sodium citrate, however, ZnS and ZnO mixed phase powder was formed in the solution without tri-sodium citrate. The films deposited with trisodium citrate showed ZnS with hexagonal wurtzite phase. However, annealed film in (N2 + H2S) atmosphere showed cubic (zincblende) phase. FE-SEM images show that grain size of as-deposited and annealed ZnS films are about 20 nm and 50 nm, respectively. Optical absorption study showed that the films have moderate optical transmission from 65% to 75% in the visible region and the optical band gap energy of as-deposited ZnS film is 3.91 eV and it decreases to 3.73 eV after annealing.

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    ABSTRACT: Zinc sulfide (ZnS) thin films have been prepared by chemical bath deposition method with improving growth rate and morphology using the mixed complexing agents of ethylenediamine tetra-acetate disodium salt (Na2EDTA) and hexamethylenetetramine (HMTA). The effects of HMTA quantity on the morphological, compositional, optical, structural and electrical properties of ZnS thin films with fixed Na2EDTA concentration have been investigated. ZnS thin films were deposited on glass substrates using aqueous solutions containing zinc acetate dehydrate and thioacetamide in acidic medium (pH 4). Field emission scanning electron microscopy results show that the morphology of a deposited ZnS thin film using HMTA as a complexing agent is rough. However, very uniform and smooth ZnS thin films are obtained using mixed complexing agents of Na2EDTA and HMTA. The growth rate and root mean square of ZnS thin films are improved with increasing HMTA quantities. X-ray diffraction patterns show that all the ZnS thin films are grown as a hexagonal structure without secondary phase (ZnO) regardless of HMTA quantity. Optical band gap energy of ZnS thin films deposited using mixed complexing agents increase from 3.75 to 3.87eV with increasing quantity of HMTA.
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