Stability and Surface Reactivity of Anatase TiO₂Films

Abstract

Atomic Layer Deposition has been used to deposit a series of TiO 2 films on native oxide Si(100) at temperatures ranging from 100 to 300 • C using tetrakis(dimethylamino) titanium and H 2 O. The films were subjected to post-deposition thermal treatment and their structure, morphology and composition was examined. As-deposited films were amorphous and began to crystallize after thermal treatment at 500 • C. The films deposited at 100 • C and treated thermally at temperatures up to 900 • C for 10 min crystallized exclusively in the anatase phase forming crystallites with lateral size in excess of 200 nm. The films deposited at higher temperatures formed rutile crystallites with no mixing of the two phases. The films containing anatase grains exhibited significantly higher surface activity as evidenced by the detection of surface bound species such as carbonates (CO), carbon-nitrogen (CN) and nitrosyls. Although 100 • C is not within the ALD window for optimal film growth, it appears that the poor film adhesion to the substrate as well as the low film density and possibly the presence of carbon containing impurities result in the stabilization of anatase crystallites with lateral size at least one order of magnitude higher than it is widely reported in the literature.

Engineering of Large Third-Order Nonlinearities in Atomic Layer Deposition Grown Nitrogen-Enriched TiO2

“…X-ray diffraction analysis of some of the ALD samples indicates that the as-grown films are amorphous and remain practically amorphous even after the thermal treatment (Figure ). The annealed 100 °C ALD film shows a couple of peaks compatible with the presence of anatase crystallites in agreement with earlier observations . A change in the sample degree of crystallization can thus be excluded as the source of the nonlinear properties.…”

“…Films deposited at 100 °C are known to contain a substantial amount of water and carbon. Films prepared at 200 and 250 °C have been shown to be the purest and with very similar composition . This difference in color is also mirrored in the difference in the film transmission (Figure c).…”

“…Films prepared at 200ºC and 250°C have been shown to be the purest and with very similar composition. 17 This difference in color is also mirrored in the difference in the film transmission (Figure 3(c)). Before annealing, the transmission for the as-grown 250°C TiO2 film was ALD films it appears that the onset of absorption is blue-shifted unlike nitrogen-containing TiO2 films produced by other techniques.…”

“…The annealed 100 °C ALD film shows a couple of peaks compatible with the presence of anatase crystallites in agreement with earlier observations. 17 A change in the sample degree of crystallization can thus be excluded as the source of the nonlinear properties.…”

“…TiO 2 ALD films with 60 nm nominal thickness were deposited at 100, 150, 200, 250, 275, and 300 °C on quartz and native oxide Si(100) concurrently using thermal ALD with tetrakis dimethylamino titanium (TDMAT) and H 2 O. , For our reactor configuration, 200 °C is the optimal ALD temperature. The nominal film thickness was based on the process growth rate per cycle derived by measuring the thickness of thinner films deposited on native oxide Si(100) using spectroscopic ellipsometry (Woollam alsphaSE).…”