Effect of Preheating Temperature on Microstructure and Optical Properties of ZnO Thin Films Prepared by Sol-Gel Spin Coating Technique

Abstract

Highly-oriented ZnO thin films prepared by using low-cost technique such as sol-gel technique are of much importance to ZnO-based white light-emitting diodes. The chose of proper preheating temperature in sol-gel technique is still critical for highly-oriented ZnO thin film so far. The mechanisms for the preheating in the formation of ZnO thin film and for the reactions involved in the sol solution have not been clearly stated yet. Thus, in this work, the highly-oriented ZnO thin films were prepared on glass substrates by using sol-gel spincoating technique. The sol solution was prepared by using the two-step method rather than usual one-step method, which facilitates the understanding of the mechanism for the reactions involved in the sol solution. The effect of the preheating temperature on the microstructure and the optical properties of the films were in particular investigated. The mechanisms for the preheating in the formation of the films and for the reactions involved in the sol solution prepared by the two-step method were also proposed in terms of the experimental results. The preheating not only enhances the volatilization of the solvent 2-methoxyethanol and the decomposition of the residual organic species, but also results into the formation of small number of ZnO particles. The preheating temperature of 300• C is most favorable for the highly-oriented ZnO thin film. Increasing the preheating temperature results into the blue shift of the absorption edges of the films. This can be explained by using the quantum-size effect. The photoluminescence spectra of the films show an UV emission at the near-band edge and a broad green-yellow emission at 470-620 nm. The former is closely related to the excitons, while the latter is to the intrinsic defect species in the film.

Study on NiO:Zn2+ films fabricated through dc magnetron reactive sputtering: substrate temperature-dependent microstructure pattern, optical and electrical properties

“…The absorption coefficient a near the absorption edge can be estimated by the formula a=1/t ln ((1-R) 2 /T), where t, R and T denotes thickness, reflectivity and transmissivity, respectively. Thanks to the quite small reflectivity near the absorption edge, the formula is usually simplified as a=1/t ln (1/T) near the absorption edge [20,28]. Figure 5 presents the Tauc curves (ahν) 2 versus hν of the NiO:Zn 2+ films at different T sub .…”

Photocatalytic Performance of Sol-Gel Prepared TiO2 Thin Films Annealed at Various Temperatures

“…All as-prepared samples were pre-baked on a hot plate in air at 200 • C immediately after the spin-coating process for one hour to promote solvent evaporation [91][92][93]. Afterwards, the samples were put into an oven (SnolTherm, UAB, Utena, Lithuania) with an Omron E5CC digital controller (OMRON ELECTRONICS GmbH, Langenfeld, Germany).…”

Preparation of Very Thin Zinc Oxide Films by Liquid Deposition Process: Review of Key Processing Parameters

“…The morphology of sol-gel ZnO thin films is generally granular [102][103][104][105][106] or columnar [106][107][108], by coarsening or maturation of smaller particles during the preheating [75,109,110] or heating [79,104] steps. Some more particular transformations can be observed: (i) from grains to more complex objects such as nanorods [111]; (ii) from a vertical to a lateral geometry [108,112,113] probably involving nuclei as a former layer for a self-template growth until coalescence [108]; (iii) from a granular to a columnar structure by the continuous growth of grains assisted by an enhanced diffusion process [80]; or (iv) from glassy plate surface to nano-grain or nano-needle shape by contraction of zinc acetate sheets to form polynucleous precursors [90].…”