Angle-resolved x-ray photoelectron spectroscopy study of GeO_x growth by plasma post-oxidation

The growth process of GeO_x films formed by plasma post-oxidation(PPO) at room temperature(RT) is investigated using angle-resolved x-ray photoelectron spectroscopy(AR-XPS). The experimental results show that the distributions of the Ge~(4+)states, a mixture of the Ge_(2+)and Ge~(3+)states, and the Ge~(1+)states are localized from the GeO_x surface to the GeO_x/Ge interface. Moreover, the Ge~(1+)states are predominant when the two outermost layers of Ge atoms are oxidized.These findings are helpful for establishing in-depth knowledge of the growth mechanism of the GeO_x layer and valuable for the optimization of Ge-based gate stacks for future complementary metal–oxide–semiconductor(MOS) field-effect transistor(CMOSFET) devices.     

Study of nanocrystalline V02 thin films prepared by magnetron sputtering and post-oxidation

Nanocrystalline VO2 thin films were deposited onto glass slides by direct current magnetron sputtering and postoxidation. These films undergo semiconductor-metal transition at 70 ℃, accompanied by a resistance drop of two magnitude orders. The crystal structures and surface morphologies of the VO2 films were characterized by x-ray diffraction （XRD） and atomic force microscope （AFM）, respectively. Results reveal that the average grain size of VO2 nanograins measured by XRD is smaller than those measured by AFM. In addition, Raman characterization indicates that stoichiometric VO2 and oxygen-rich VO2 phases coexist in the films, which is supported by x-ray photoelectron spectroscopy （XPS） results. Finally, the optical properties of the VO2 films in UV-visible range were also evaluated. The optical band gap corresponding to 2p-3d inter-band transition was deduced according to the transmission and reflection spectra. And the deduced value, Eopt2p-3d ： 1.81 eV, is in good agreement with that previously obtained by theoretical calculation.     

Study of nanocrystalline VO2 thin films prepared by magnetron sputtering and post-oxidation

Nanocrystalline VO2 thin films were deposited onto glass slides by direct current magnetron sputtering and postoxidation. These films undergo semiconductor-metal transition at 70°C, accompanied by a resistance drop of two magnitude orders. The crystal structures and surface morphologies of the VO2 films were characterized by x-ray diffraction (XRD) and atomic force microscope (AFM), respectively. Results reveal that the average grain size of VO2 nanograins measured by XRD is smaller than those measured by AFM. In addition, Raman characterization indicates that stoichiometric VO2 and oxygen-rich VO2 phases coexist in the films, which is supported by x-ray photoelectron spectroscopy (XPS) results. Finally, the optical properties of the VO2 films in UV-visible range were also evaluated. The optical band gap corresponding to 2p-3d inter-band transition was deduced according to the transmission and reflection spectra. And the deduced value, E opt2p-3d = 1.81 eV, is in good agreement with that previously obtained by theoretical calculation.