Hardness of Nanocrystalline TiO 2 Thin Films Danuta Kaczmarek 1,a , Jaroslaw Domaradzki 1,a , Damian Wojcieszak 1,a , Eugeniusz Prociow 1,a , Michal Mazur 1,a , Frank Placido 2,a , Steffen Lapp 2,a 1 Faculty of Microsystem Electronics and Photonics, Wroclaw University of Technology, Janiszewskiego 11/17, 50-372 Wroclaw, Poland 2 University of the West of Scotland, High Street, Paisley, PA1 2BE, and SUPA, Scottish Universities Physics Alliance, United Kingdom a damian.wojcieszak@pwr.wroc.pl (corresponding author) Keywords: hardness, nanocrystalline, TiO 2 , thin film, nanoindentation Abstract. In this work results of hardness investigations of nanocrystalline TiO 2 thin films are presented. Thin films were prepared by low pressure hot target reactive sputtering (LPHTRS) and high energy reactive magnetron sputtering (HERMS). In both processes a metallic Ti target was sputtered under low pressure of oxygen working gas. After deposition by LPHTRS TiO 2 thin films with anatase structure were obtained and after additional post-process annealing at 1070 K, these films recrystallized into the rutile structure. Annealing also resulted in an increase of average crystallite size from 33 nm (for anatase) to 74 nm (for rutile). The HERMS process is a modification of the LPHTRS process with the addition of an increased amplitude of unipolar voltage pulses, powering the magnetron. This effectively increases the total energy of the depositing particles at the substrate and allows dense, nanocrystalline (8.7 nm crystallites in size) TiO 2 thin film with the rutile structure to be formed directly. The hardness of the films was determined by nanoindentation. The results showed that the nanocrystalline TiO 2 -rutile thin film as-deposited using HERMS had high hardness (14.3 GPa), while the TiO 2 -anatase films as-deposited by LPHTRS, were 4-times lower (3.5 GPa). For LPHTRS films recrystallized by additional annealing, the change in thin film structure from anatase to rutile resulted in an increase of film hardness from 3.5 GPa to only 7.9 GPa. The HERMS process can therefore produce the TiO 2 rutile structure directly, with hardness that is 2 times greater than rutile films produced by LPHTRS with additional annealing step. Introduction Nowadays, for many commercial products high resistance against external hazards is often required. Especially, hardness is one of the most important parameters, resulting in many devices being coated with different so called hard coatings. Recent research has shown that coatings with nanocrystalline structures have greatly increased hardness compared to the non-crystalline coatings that are usually applied in the coating industry [1]. Such coatings, besides their protective function, are often required to satisfy many other requirements, for example: excellent transparency in the visible range [2], high photocatalytic activity [3], wettability (hydrophobic or hydrophilic properties) [4, 5]. For these reasons, well known optical coatings such as SnO 2 [6], ZrO 2 [7], SiO 2 [8] and TiO 2 [9] are good candidates for hard coatings. Apart from the intrinsic material differences, in practise the application of different process parameters [10], additional post-process treatment (e.g. annealing) [11] or doping with different elements [12] also allow the properties of thin film coatings to be varied. Of these, modification of the film structure during thin film deposition seems to be the most desirable and important route since it allows significantly new structural properties that can not readily be achieved by post-deposition treatments. In this work the influence of deposition process parameters on the hardness of nanocrystalline TiO 2 thin films have been investigated. Thin films were manufactured by two so called hot-target reactive magnetron sputtering processes. The main difference between the two was the amplitude of the magnetron power supply [13, 14]. While films prepared by the low pressure hot target reactive Journal of Nano Research Vols. 18-19 (2012) pp 195-200 Online available since 2012/Jul/26 at www.scientific.net © (2012) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/JNanoR.18-19.195 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 188.121.13.86-19/08/12,21:21:39)