Nanocrystalline TiO2 Films: Heat Treatment and Structural Stability

Nanotubular titanium dioxide (TiO2) films have been fabricated by chemical anodic oxidation on a titanium substrate. The initial amorphous oxide films have been subjected to heat treatment at 400, 450, and 500°C. The effect of the annealing temperature on the structural and I–V characteristics has been comprehensively studied. It has been shown that annealing at 400°C for 30 min leads to the formation of the anatase (TiO2) phase with a fraction of up to ~98%. The sample microstructure exhibits a high degree of ordering and uniformity of the TiO2 array vertically aligned relative to the substrate. The average nanotube inner diameter is approximately 50–60 nm and the nanotube wall thickness is 10–15 nm. Raman spectra of the samples have revealed the main vibrational modes Eg, Eg, B1g, A1g, and Eg corresponding to the anatase (TiO2) phase. The calculated O–Ti–O bond lengths ranging from 1.89 to 2.85 Å are typical of a distorted TiO $$_{6}^{{8 - }}$$ octahedron. The I–V characteristics of the films are nonlinear and typical of oxide materials with the resistance switching effect. The results obtained confirm that the heat treatment enables the targeted modification of the structure and properties of TiO2 nanotubes.