Atomic force microscopy study of TiO2 sol–gel films thermally treated under NH3 atmosphere

doi:10.1016/j.tsf.2009.02.070

Thin Solid Films

Volume 517, Issue 23, 1 October 2009, Pages 6243-6247

https://doi.org/10.1016/j.tsf.2009.02.070 Get rights and content

Abstract

Multilayered TiO₂ films were obtained by sol–gel and dipping deposition on quartz substrate followed by thermal treatment under NH₃ atmosphere. In an attempt to understand the close relationship between microstructural characteristics and the synthesis parameters, a systematic research of the structure and the morphology of NH₃ modified TiO₂ sol–gel films by XRD and Atomic Force Microscopy is reported. The surface morphology has been evaluated in terms of grains size, fractal dimension and surface roughness. For each surface, it was found a self-similar behavior (with mean fractal dimension in the range of 2.67–3.00) related to an optimum morphology favorable to maintain a nano-size distribution of the grains. The root mean square (RMS) roughness of the samples was found to be in the range of 0.72–6.02 nm.

Introduction

Titanium containing compounds, TiN_x and TiO_xN_y like, are widely used as multifunctional materials (e.g. sensors, electronic devices, hard coatings, etc) [1], [2], [3], [4], [5], [6]. The employment of TiO_xN_y as photocatalyst in the visible range is an important subject in scientific papers [7], [8], [9], [10]. Literature studies have shown that an optimum concentration of nitrogen incorporated into the TiO₂ matrix preserves the anatase phase required by the photocatalytic activity and, in the same time reduce the optical band gap down to the visible range [7], [8], [11], [12]. The versatility of preparation procedures has lead to a wide variety of structural, optical and electrical properties as well as a large variety of potential applications. Thus, the efficiency of TiO₂ has been substantially enhanced in photocatalitic reactions by dopping either with cations of the transitional metals (V, Cr, Mn, Fe) or with anions as N, C or F. The morphology of the titanium oxynitride films (TiO_xN_y), prepared by physical methods, has been intensively studied in the last years [2], [10], [13], [14], [15], [16].

In this study, three-layered TiO₂ films have been deposited by the sol–gel method on quartz substrate, followed by thermal treatment in ammonia atmosphere in the range of 400–1000 °C. In order to understand the close relation between the microstructural characteristics and the sol–gel chemical route of preparation, a systematic study on the morphology of the multilayered TiO₂ films has been performed by Atomic force microscopy (AFM). Surface properties of the films such as surface topography, grains analysis, roughness and self similarity in terms of correlation lengths and fractal dimensions have been investigated.

Section snippets

Film preparation

TiO₂ thin films have been prepared by sol–gel method and deposited by dip-coating technique on quartz substrates. Tetrabutyl orthotitanate (Ti[C₄H₉O]₄–TBOTi) from Aldrich has been used as titanium precursor. A quantity of 35.22 ml TBOTi was dissolved in 166.20 ml ethyl alcohol (Panreac) in a closed beaker at room temperature under continuous stirring. The pH of the sol was adjusted to 1.5 by addition of 2 ml nitric acid (HNO₃). Deionized water (1.36 ml) was added and the solution was refluxed

Structure and topography

The XRD analysis (Fig. 1) has revealed that the as prepared TiO₂ films (sample 1), as well as the samples treated in NH₃ at 400 and 500 °C (samples 2 and 3) consist of nanocrystalline TiO₂ in the anatase phase with (101) preferential orientation. The treatment at 800 °C resulted in development of a titanium oxynitride phase (TiO_xN_y) while at 1000 °C the arising of a titanium nitride in the form of TiN_0.9 (osbornite) could be noticed.

Fig. 2 shows the 3D topography of the TiO₂ films as obtained

Conclusions

Continuous and homogeneous multilayered ammonia treated TiO₂ thin films on quartz substrate were successfully prepared, as proved by XRD and AFM analysis. Structural and morphologic differences can be observed with the increase of temperature of the thermal treatment.

In the topography survey, three different morphologies could be identified: a defect-reach surface for the as-prepared sample, a common structure for mid temperatures (400–500 °C) attributed to anatase phase, which with some minor

Acknowledgements

One of the authors (M. Anastasescu) would like to thanks to Dr. Paolo Bariani (Schaefer South-East) for helpful discussions about SPIP. The financial support of CEEX (318/2006) and CNCSIS-Romania (grant No. 1247/2007) are gratefully acknowledged. The team of NCSR Demokritos thanks the financial support from GSRT under bilateral collaboration projects.

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Atomic force microscopy study of TiO2 sol–gel films thermally treated under NH3 atmosphere

Abstract

Introduction

Section snippets

Film preparation

Structure and topography

Conclusions

Acknowledgements

Thin Solid Films

Appl. Surf. Sci.

Thin Solid Films

Mater. Sci. Eng., A Struct.

J. Photochem. Photobiol., A Chem.

J. Mater. Process. Technol.

Thin Solid Films

Thin Solid Films

Atomic force microscopy study of TiO₂ sol–gel films thermally treated under NH₃ atmosphere