One of the most frequently used methods for characterizing thin films is UV–Vis absorption. The near-edge region can be fitted to a simple expression in which the intercept gives the band-gap and the fitting exponent identifies the electronic transition as direct or indirect (see Tauc et al., Phys. Status Solidi 15, 627 (1966); these are often called “Tauc” plots). While the technique is powerful and simple, the accuracy of the fitted band-gap result is seldom stated or known. We tackle this question by refitting a large number of Tauc plots from the literature and look for trends. Nominally pure zinc oxide (ZnO) was chosen as a material with limited intrinsic deviation from stoichiometry and which has been widely studied. Our examination of the band gap values and their distribution leads to a discussion of some experimental factors that can bias the data and lead to either smaller or larger apparent values than would be expected. Finally, an easily evaluated figure-of-merit is defined that may help guide more accurate Tauc fitting. For samples with relatively sharper Tauc plot shapes, the population yields Eg(ZnO) as 3.276 ± 0.033 eV, in good agreement with data for single crystalline material.

Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system

https://repositorio.uchile.cl/bitstream/handle/2250/132554/ZnOAgCdO-nanocomposite-for-visible-light-induced%20photocatalytic.pdf?sequence=1

ZnO/Ag/CdO nanocomposite for visible light-induced photocatalytic degradation of industrial textile effluents.

http://cgcri.csircentral.net/815/1/815.pdf

Sol–gel electrochromic coatings and devices: A review

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The Basics of Crystallography and Diffraction

Transparent thin film coatings of sol-gel derived titanium dioxide were produced on cotton fabrics at a low temperature of 150°C. The photocatalytic activity of the formed layers was studied by means of their antibacterial property. SEM images show the formation of continuous layers of titanium dioxide with grains of about 20 nm in diameter. The UV-blocking effect of titania coatings was also studied. XRD patterns revealed the existence of anatase phase in a small scale within the titania layers.

Low Temperature Sol-Gel Processed Photocatalytic Titania Coating

Growth, characterization and studying of sol–gel derived CdS nanoscrystalline thin films incorporated in polyethyleneglycol: Effects of post-heat treatment

Optoelectronic studies of sol–gel derived nanostructured CdO–ZnO composite films

Synthesis and characterization of vanadium doped SnO2 diluted magnetic semiconductor nanoparticles with enhanced photocatalytic activities

The ZnO thin films were prepared from zinc acetate dihydrate as main precursor by using sol-gel method and deposited by drainage and dip coating technique. Four different routes and coating techniques were used for the preparation of samples. The morphology, optical, and structural properties of the sol-gel made ZnO thin films were studied with respect to the preparation of sol-gel route, drainage and dip coating technique. The microstructure of the ZnO thin films and the powders were analyzed by X-ray diffraction. The ZnO thin films prepared in this study were amorphous while its powders were polycrystalline with various diffraction peaks in the X-ray diffraction patterns. The morphology of the film was examined by using scanning electron microscopy. The surface morphology of the ZnO thin films strongly depends on preparation route and deposition technique. The optical characteristics of the samples were obtained by using UV-Visible spectrophotometer at 200–900 nm wavelength. The optical constants (refractive index, extinction coefficient etc.) of the ZnO thin films depend on preparation conditions. The photoluminescence spectra of the ZnO films show the band-edge and sub-band transitions.

/pdf/comparative-study-of-zno-thin-films-prepared-by-different-3hhoy5jh8p.pdf

Farhad E. Ghodsi

Papers

Growth, characterization and studying of sol–gel derived CdS nanoscrystalline thin films incorporated in polyethyleneglycol: Effects of post-heat treatment

Optoelectronic studies of sol–gel derived nanostructured CdO–ZnO composite films

Synthesis and characterization of vanadium doped SnO2 diluted magnetic semiconductor nanoparticles with enhanced photocatalytic activities

Comparative Study of ZnO Thin Films Prepared by Different Sol-Gel Route

Fiber-like stripe ATO (SnO2:Sb) nanostructured thin films grown by sol–gel method: Optical, topographical and electrical properties