Enhancement of optical absorption by modulation of the oxygen flow of TiO{sub 2} films deposited by reactive sputtering

Journal Article · Fri Jun 01 00:00:00 EDT 2012 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4724334· OSTI ID:22089228

Pereira, Andre L. J. ^[1]; Lisboa Filho, Paulo N.; Dias da Silva, Jose H. ^[1]; Acuna, Javier; Brandt, Iuri S.; Pasa, Andre A. ^[2]; Zanatta, Antonio R. ^[3]; Vilcarromero, Johnny ^[4]; Beltran, Armando ^[5]

---

1. Universidade Estadual Paulista, UNESP, Bauru SP (Brazil)
2. Universidade Federal de Santa Catarina, UFSC, Florianopolis SC (Brazil)
3. Universidade de Sao Paulo, USP, Sao Carlos SP (Brazil)
4. Universidade Federal de Sao Carlos, UFSCar, Sorocaba SP (Brazil)
5. Universitat Jaume I, Castellon (Spain)

Oxygen-deficient TiO{sub 2} films with enhanced visible and near-infrared optical absorption have been deposited by reactive sputtering using a planar diode radio frequency magnetron configuration. It is observed that the increase in the absorption coefficient is more effective when the O{sub 2} gas supply is periodically interrupted rather than by a decrease of the partial O{sub 2} gas pressure in the deposition plasma. The optical absorption coefficient at 1.5 eV increases from about 1 Multiplication-Sign 10{sup 2} cm{sup -1} to more than 4 Multiplication-Sign 10{sup 3} cm{sup -1} as a result of the gas flow discontinuity. A red-shift of {approx}0.24 eV in the optical absorption edge is also observed. High resolution transmission electron microscopy with composition analysis shows that the films present a dense columnar morphology, with estimated mean column width of 40 nm. Moreover, the interruptions of the O{sub 2} gas flow do not produce detectable variations in the film composition along its growing direction. X-ray diffraction and micro-Raman experiments indicate the presence of the TiO{sub 2} anatase, rutile, and brookite phases. The anatase phase is dominant, with a slight increment of the rutile and brookite phases in films deposited under discontinued O{sub 2} gas flow. The increase of optical absorption in the visible and near-infrared regions has been attributed to a high density of defects in the TiO{sub 2} films, which is consistent with density functional theory calculations that place oxygen-related vacancy states in the upper third of the optical bandgap. The electronic structure calculation results, along with the adopted deposition method and experimental data, have been used to propose a mechanism to explain the formation of the observed oxygen-related defects in TiO{sub 2} thin films. The observed increase in sub-bandgap absorption and the modeling of the corresponding changes in the electronic structure are potentially useful concerning the optimization of efficiency of the photocatalytic activity and the magnetic doping of TiO{sub 2} films.

• OSTI ID: 22089228
• Journal Information: Journal of Applied Physics, Vol. 111, Issue 11; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION
CRYSTAL DEFECTS
DENSITY FUNCTIONAL METHOD
DEPOSITION
ELECTRONIC STRUCTURE
ENERGY GAP
PERIODICITY
PHOTOCATALYSIS
RAMAN SPECTRA
RED SHIFT
SEMICONDUCTOR MATERIALS
SIMULATION
THIN FILMS
TITANIUM OXIDES
TRANSMISSION ELECTRON MICROSCOPY
VACANCIES
X-RAY DIFFRACTION