Effect of Target Sintering Temperature on the Morphological and Optical Properties of Pulsed Laser Deposited TiO2 Thin Films

Laid Kadri,Stoian George,Georgiana Bulai,Silviu Gurlui,Corneliu Doroftei,Mohamed Adnane,Liviu Leontie,Aurelian Carlescu

doi:10.3390/coatings11050561

Abstract

In this paper, we report on the effect of titanium dioxide (TiO2) target sintering temperature on the morphological and optical properties of amorphous titanium dioxide thin films synthesized by pulsed laser deposition (PLD) on indium tin oxide (ITO) glass substrate and subsequently heat-treated in air at low temperature (150 °C). Three types of targets were used, unsintered (pressed at room temperature), sintered at 500 °C and sintered at 1000 °C. The surface morphology of the samples was investigated by scanning electron microscopy (SEM), and profilometry was used for thickness measurements. The structural properties of the films were examined by X-ray diffraction (XRD), while their optical properties were studied by UV‒vis spectroscopy. The obtained TiO2 thin films have an amorphous nature, as shown by XRD analysis. Profilometer showed that sintered target samples have more reliable thicknesses than unsintered ones. The SEM studies revealed the sufficient structural homogeneity of sintered target nanosized TiO2 films and agglomerates in the case of unsintered target film. The UV‒vis transmittance spectra showed high transparency in the visible range of PLD films, proportional to the target sintering temperature. The optical band gaps of the films deposited using the 500 °C and 1000 °C sintered targets are closer to those of anatase and rutile phases, respectively, which provides a promising approach to the challenges of amorphous TiO2-based nanostructures.

Highlights

IntroductionPulsed laser deposition offers several benefits: the simple system operation, flexibility, a wide range of deposition conditions, rich choice of materials, the possibility to use in situ heating and reactive background gases, and a relatively high reproducibility [8,19,32,33]
We report the successful synthesis of nanosized amorphous TiO2 films by pulsed laser deposition (PLD) on indium tin oxide (ITO) glass substrate at room temperature (25 ◦ C), without reactive background gases, from two targets sintered at different temperatures
The lower thickness of the as 500-TiO2 and as 1000-TiO2 films compared to that of as 25-TiO2 one could be due to the greater density of sintered targets compared to that of the unsintered one.the films obtained from sintered targets had slight differences in the thickness

Summary

Introduction

Pulsed laser deposition offers several benefits: the simple system operation, flexibility, a wide range of deposition conditions, rich choice of materials, the possibility to use in situ heating and reactive background gases, and a relatively high reproducibility [8,19,32,33]. This technique allows the deposition of films with determined thickness, morphology, stoichiometry, grain size and composition by varying the deposition parameters (laser pulse geometry, laser fluence, wavelength or repetition frequency, target-substrate distance, substrate temperature, deposition time, etc.) [11,34,35]. The obtained thin films may display a satisfactory uniformity and highly transparent TiO2 nanostructures via low-temperature processing, and exhibit similar optical properties to those of crystalline TiO2

Experimental Details

Morphological Properties

Target sintering temperature influence on thin-film

Structural

Optical Properties

Conclusions