Bismuth trioxide (Bi 2 O 3 ) ultrathin films were successfully synthesized on silicon substrates by means of atomic layer deposition (ALD) using Bi(thd) 3 (thd: 2,2,6,6-tetramethyl-3,5heptanedionato) and H 2 O as precursors. The optimum ALD window was about 270−300 °C, and an ALD-type growth mechanism via surface saturation reaction was identified; the growth rate was about 0.1 Å/cycle. The X-ray diffraction and high-resolution transmission electron microscopy investigation revealed that Bi 2 O 3 films crystallized into a predominant alpha phase above 250 °C. The resistivity at room temperature was about 1.2 × 10 6 Ω•cm, which is also proof of the α-phase of as-deposited Bi 2 O 3 films. In addition, a new method to obtain γ-Bi 2 O 3 film was discovered. The α-Bi 2 O 3 films (synthesized by ALD) transformed into metastable γ-Bi 2 O 3 with preferred orientation (222) after annealing above 512 °C, and γ-phase could persist at room temperature.

Lattice vibrations of highly a-axis oriented CoFe 2 O 4 (CFO) films have been investigated by Raman scattering in the temperature range of 80-873 K. The five phonon modes T 1g (2), T 1g (3), E g , A 1g (1), A 1g (2), and their evolutions can be uniquely distinguished. It was found that an electron transfer between Co 2þ and Fe 3þ cations occurs in octahedral sites at about 173 K. The structure disorder in the CFO films appears with increasing the temperature, which indicates the cation migration between tetrahedral and octahedral sites. The phenomena suggest the structural transformation trend from inverse spinel to normal spinel at the elevated temperatures. V

Iron-doped titanium dioxide nanocrystalline (nc-TiO 2 :Fe) films with the a composition from 2 to 10% have been deposited on Si(100) substrates by a facile nonhydrolytic sol-gel route. X-ray diffraction analysis shows that the films are polycrystalline and exhibit the pure tetragonal rutile phase structure. The Fe dopant effects on the surface morphology, microstructure, phonon modes, and dielectric functions of the nc-TiO 2 :Fe films have been investigated by atomic force microscopy, ultraviolet Raman scattering, far-infrared reflectance, and spectroscopic ellipsometry at room temperature. With increasing Fe composition, the first-order Ramanactive phonon modes E g , A 1g , and B 2g are shifted toward a lower frequency side of 10, 6, and 7 cm -1 , respectively. The four additional vibrations, which are strongly related to the surface structure of the films, can be observed due to the two-phonon scattering process. Moreover, the three infrared-active transverseoptic (TO) phonon modes E u (TO) can be located at about 183, 382, and 500 cm -1 , respectively. The dielectric functions of the films have been uniquely extracted by fitting the measured ellipsometric spectra with a fourphase layered model (air/surface rough layer/film/Si) in the photon energy range 0.73-4 eV (310-1700 nm). Adachi's dielectric function model has been successfully applied and reasonably describes the optical response behavior of the nc-TiO 2 :Fe films from the near-infrared to ultraviolet photon energy region. It is found that the real part of dielectric functions in the transparent region slightly decreases with increasing Fe composition. Furthermore, the optical band gap linearly decreases from 3.43 to 3.39 eV with increasing Fe composition due to the energy level of Fe t 2g , which is closer to the valence band. It is believed that the decrease of the optical constants and optical band gap for the nc-TiO 2 :Fe films with the Fe composition is mainly ascribed to the differences of the crystallinity and the electronic band structure, which can be perturbed by the transition metal introduction.

Transparent p-type conductive CuGaO 2 films have been fabricated on sapphire substrates by sol-gel method. The stable sol solution for CuGaO 2 were formed by copper(II) acetate monohydrate and gallium(III) nitrate hydrate, and the c-axis orientation of CuGaO 2 films were strengthened with increasing annealing temperature. The pure phase CuGaO 2 film was obtained at 900 o C for 30 min in N 2 atmosphere, and its microstructure, compositions, optical and electrical properties were analyzed. It was found that the sol-gel derived CuGaO 2 films show a high optical transparency (60-80%) in the visible region, the direct and indirect band gaps were approximately 3.56 and 3.24 eV, respectively. It shows a crossover from the thermal activation behavior to that of three-dimensional variable range hopping from the temperature-dependent electrical conductivity at about 160 K.

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