X-ray characterization of sol-gel TiO2 thin films

MIGUEL ANGEL ALTERACH; MARIO ROBERTO ROSENBERGER; DIEGO GERMÁN LAMAS; CARLOS ENRIQUE SCHVEZOV; ALICIA ESTHER ARES

Madrid

Congreso; XXII IUCr Congress; 2011

IUCr

TiO2 thin films deposited on a Ti-6Al-4V alloy by means of the sol–gel dip-coating technique were characterized using X-ray synchrotron radiation. The crystalline structure and thickness of the films were obtained and related to the parameters of the sol-gel process. The process involves immersing the substrate (Ti-6Al-4V) in a colloidal dispersion (sol), withdrawing the substrate at constant low velocity, drying of the coating and heat treatment. For the dispersion preparations, titanium butoxide, isopropanol, ethyl acetoacetate, HCl and distilled H2O were used. Several withdrawing velocities and number of layer were used, these ranged from 1 to 3 cm/min and from 1 to 3, respectively. Two values of titanium butoxide/isopropanol molar ratio were used in the dispersions: 1/20 and 1/10. Dispersions with aging times ranged from 1 to 10 days were used. The samples received a heat treatment for 1 h at a fixed temperature of 500 C to each layer of coating and heated to 10 C/min and cooling inside the furnace. The morphology of the coatings was observed by optical microscopy and SEM. The crystalline structure was determined by X-ray diffraction with a glancing incidence angle of 1º and the thickness was determined by the X-ray reflectometry technique. These experiments were carried out at the D12A-XRD1 beamline of the LNLS (Campinas, Brazil). The coatings were homogeneous, compact and smooth to the optical microscope, and of different colors according to their thickness. With increase of the withdrawing velocity, the number of layers, the titanium butoxide/isopropanol ratio or the aging time of the dispersions, the thicknesses of the coatings increased, all in a range from 25 nm to 142 nm. Cracks were observed on films with thicknesses thicker than 100 nm. By X-ray diffraction of the monolayer and multilayer coatings was determined the presence of anatase and rutile. The results show a relation between thickness and structure. In the thinnest films no crystal structure was detected, while for films with intermediate thickness rutile phase was detected, and for the thickest films both rutile and anatase phases were detected. The brookite structure was not detected in any film.