Evaluation of structural and mechanical properties of aluminum oxide thin films deposited by a sol–gel process: Comparison of microwave to conventional anneal A.R. Phani * , S. Santucci Department of Physics, University of L’Aquila and INFM-CASTI Regional Laboratory Via Vetoio 10, Coppito, L’Aquila 67010, Italy Received 8 July 2005; received in revised form 12 June 2006 Available online 7 September 2006 Abstract Thin films of Al 2 O 3 have been deposited on polished silica glass substrates at room temperature by sol–gel dip coating technique fol- lowed by two different exposure methods. One set was annealed at different temperatures ranging from 200 °C to 800 °C for 10 h and a second set was exposed to microwave (2.45 MHz) radiation at different powers for 10 min. The lower temperature and shorter time with microwave irradiation might be ascribed to the activating and facilitating effect of microwaves on solid phase diffusion. Unlike other preparation methods, microwave heating is generally quite faster, and energy efficient. X-ray diffraction (XRD) and scanning electron microscopy (SEM), energy dispersive X-ray analysis techniques have been employed to characterize structural, morphological and ele- mental compositions of the films. Adhesion strength failure measurements on films performed by scratch test in progressive loading sequence have shown critical loads up to 25 N (partial perforation) for both annealed films and films exposed to microwave irradiation. Nanohardness indentation tests of the films exposed (800 W) to microwave have shown hardness of 8.3 GPa with elastic modulus of 120 GPa compared to the conventional annealed film (800°) of 4.5 GPa with elastic modulus of 90 GPa. Ó 2006 Elsevier B.V. All rights reserved. PACS: 47.54.Jk; 47.20.Hw; 81.07.b; 81.16.Be Keywords: X-ray diffraction; Spin coating; SEM S100; Mechanical properties; Hardness; Atomic force and scanning tunneling microscopy; Scanning electron microscopy; Sintering; Sol–gels (xerogels); X-ray diffraction 1. Introduction There have been many investigations of oxide films syn- thesized from the sol–gel method because of several advan- tages, such as low processing temperature, homogeneity, possibility of coating on large area substrates, and most important cost effective. Unlike PVD or CVD coating tech- nologies it does not require any high vacuum equipment. Sol–gel oxide films have many wide applications as func- tional materials in optical, microelectronics and photoelec- tronics industries, and also for the purpose of corrosion, scratch, abrasion resistance materials as well. It is known that tribological and mechanical properties of the films coated on the substrate will influence their function, life- time, and productivity. Therefore in recent times, there has been a lot of research focused on the physical, mechan- ical and tribological properties of the oxide films. Unfortu- nately, less attention has been focused on the mechanical and tribological properties of the films deposited by sol– gel technique. Ceramic oxides such as Al 2 O 3 , ZrO 2 are widely used in many mechanical, optical, and microelec- tronic applications because of their excellent properties such as chemical resistance, good mechanical strength, and high hardness, transparency, high abrasive and corro- sion resistance as well as being insulating materials. Usually these oxides are prepared by techniques such as chemical 0022-3093/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.06.013 * Corresponding author. Tel.: +39 862 433037; fax: +39 862 433033. E-mail address: phani_ayala@yahoo.com (A.R. Phani). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 352 (2006) 4093–4100