Phase transformation of nanostructured titanium dioxide thin films grown by sol–gel method

Abstract

Nanostructured TiO 2 thin films were deposited on quartz glass at room temperature by sol-gel dip coating method. The effects of annealing temperature between 200 • C to 1100 • C were investigated on the structural, morphological, and optical properties of these films. The X-ray diffraction results showed that nanostructured TiO 2 thin film annealed at between 200 • C to 600 • C was amorphous transformed into the anatase phase at 700 • C, and further into rutile phase at 1000 • C. The crystallite size of TiO 2 thin films was increased with increasing annealing temperature. From atomic force microscopy images it was confirmed that the microstructure of annealed thin films changed from column to nubbly. Besides, surface roughness of the thin films increases from 1.82 to 5.20 nm, and at the same time, average grain size as well grows up from about 39 to 313 nm with increase of the annealing temperature. The transmittance of the thin films annealed at 1000 and 1100 • C was reduced significantly in the wavelength range of about 300-700 nm due to the change of crystallite phase. Refractive index and optical high dielectric constant of the n-TiO 2 thin films were increased with increasing annealing temperature, and the film thickness and the optical band gap of nanostructured TiO 2 thin films were decreased.

The formation of anatase TiO2 from TiO nanocrystals in sol–gel process

“…After annealing at 300 and 400 1C for 1 h anatase appears to grow rapidly. The formation of anatase after annealing is generally consistent with previous results [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. However, it is apparent that no TiO was detected by XRD.…”

“…Increasing the annealing temperatures further would cause anatase to transform to rutile, as shown in the references [9][10][11][17][18][19][20][21][22][23]. Because the anatase to rutile transformation has been extensively studied [27], it was not repeated here.…”

“…Further annealing or hydrothermal treatments of the amorphous TiO 2 specimens at higher temperatures, generally less than 600 1C, lead to the formation of anatase [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. At still higher annealing temperatures anatase starts to transform to rutile so that mixed anatase and rutile or single-phase rutile are formed [9][10][11][17][18][19][20][21][22][23]. Rutile can also be formed from anatase at lower temperatures of 180-300 1C by increasing the annealing time [7,13,19].…”

“…In the process amorphous TiO 2 powders [7][8][9][10][11][12][13][14][15][16][17][18][19][20] or films [21][22][23][24][25][26] were formed at low reacting temperatures, usually near the room temperature. Further annealing or hydrothermal treatments of the amorphous TiO 2 specimens at higher temperatures, generally less than 600 1C, lead to the formation of anatase [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. At still higher annealing temperatures anatase starts to transform to rutile so that mixed anatase and rutile or single-phase rutile are formed [9][10][11][17][18][19][20][21]…”

Titanium Dioxide Thin Films Containing Gold-Silver Nanoclusters by Sol–Gel Technique

“…The anatase phase has been reported to be enhanced at temperatures below 800 ∘ C, which at higher temperatures reverts to the more stable rutile phase [1][2][3]. The use of polycrystalline TiO 2 films are favored in a variety of applications such as optics [4], dye sensitized solar cells [5], dielectric applications [6], photocatalytic layers [7] and self cleaning purposes [8] due to its high refractive index, the high dielectric constant, the high transparency in the visible range, wide band gap and chemical stability.…”