Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 13, Issue 28, Pages 13096-13105Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c0cp02924f
Keywords
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Funding
- Natural Science Foundation of China [60906046, 11074076]
- Major State Basic Research Development Program of China [2007CB924901, 2011CB922200]
- Program of New Century Excellent Talents, MOE [NCET-08-0192]
- PCSIRT
- Shanghai Municipal Commission of Science and Technology [10DJ1400201, 10SG28 10ZR1409800, 09ZZ42]
- Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning
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Iron (Fe)-doped (0 to 4%) TiO2 nano-crystalline (nc) films with the grain size of about 25 nm have been deposited on n-type Si (100) substrates by a facile nonhydrolytic sol-gel processing. X-ray diffraction measurements prove that the films are polycrystalline and present the pure anatase phase. X-ray photoelectron spectroscopy spectra indicate that the chemical valent state of Fe element is +3 and the Fe3+ ions replace the Ti4+ sites. The Fe dopant effects on the surface morphology, microstructure, and dielectric functions of the nc-Fe/TiO2 films have been studied by atomic force microscope, ultraviolet Raman scattering and spectroscopic ellipsometry. With increasing Fe composition, the intensity of Raman-active mode B-1g increases, while that of the A(1g) phonon mode decreases. The dielectric functions have been uniquely extracted by fitting ellipsometric spectra with the Adachi's dielectric function model and a four-phase layered model. It is found that the real part of dielectric functions in the transparent region and the optical band gap slightly decrease with the Fe composition due to the introduction of acceptor level Fe t(2g). Finally, the composition and temperature dependence of the surface and lattice defects in the Fe/TiO2 films have been investigated by photoluminescence spectra in detail. At room temperature, the emission intensities decrease with increasing Fe compositions since the Fe incorporation could prolong the radiative lifetime and/or shorten the non-radiative lifetime. By analyzing the low temperature photoluminescence spectra, the intensities and positions of five emission peaks and shoulder structure can be unambiguously assigned. The phenomena could be reasonably explained by the physical mechanisms such as oxygen vacancies, localized excitons, self-trapped excitons, and indirect transitions, which are strongly related to the electronic band structure perturbed by the Fe doping.
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