Interactions between sintering, crystallization and chemical development of sol-gel and colloidal titanium dioxide thin films

Sol-gel and colloidal processing are attractive ways of depositing thin oxide films. This work focuses on the complex interplay between materials chemistry and microstructure during both isothermal and non-isothermal heat treatments when transforming an as-deposited titanium dioxide precursor film to a dense, crystalline film.; In sol-gel films, the densification, measured with Rutherford backscattering spectrometry and ellipsometry, increases with increasing heating rate. Densest films containing the lowest amount of hydroxyls are obtained using rapid thermal annealing. By measuring thin film densification as a function of temperature, in conjunction with a study of crystallization using electron and x-ray diffraction, it is shown that the densification halts when the films are partially crystallized. Faster heating rates which cause crystallization at higher temperatures therefore lead to greater film shrinkage. When very fast rates are achieved with RTA, however, the crystallization temperature drops to a lower value than is expected, probably because of a kinetic barrier to crosslinking via condensation. Chemical analysis indicates that loss of H occurs concurrently with densification so that H density decreases only slightly with temperature. Crystallization occurs concurrently with a substantial loss of C and H in the films.; The spin-deposition of colloidal anatase particles has the potential to produce films with good mechanical, chemical and optical stability. Films consisting of discrete, weakly-bonded anatase crystals (an average of 8 nm in diameter) were deposited from a colloidal sol synthesized from titanium (IV) isopropoxide. Using thermal analysis, ion-beam scattering and ellipsometry, the chemical and optical changes that occur during non-isothermal sintering were studied. Chemical and shrinkage rate analyses indicate that there are two primary causes of film densification: water loss and solid-state sintering. The loss of chemisorbed (Type II) water leads abruptly to 2.5% shrinkage at temperatures near 225{dollar}spcirc{dollar}C, whereas the loss of Type I water does not alter the particle configuration. At temperatures above about 450{dollar}spcirc{dollar}C, solid-state sintering (encouraged by the small particle size and {dollar}(-{dollar}OH) groups) causes further film shrinkage. The refractive index of the films is not stable because of adsorption of water from the atmosphere.