Papers by Keyword: Epitaxial Film

Abstract: Infrared (IR) absorption and polarized Raman spectra were measured in BaSi₂ epitaxial films to investigate the vibrational modes and the symmetry of Si₄ cluster in BaSi₂. By an analysis based on Raman and/or IR activity in the spectra, the symmetry of Si₄ cluster was determined as T_h-symmetry and the observed Raman lines and IR peaks were assigned to A_g, E_g, F_g, and F_u, respectively. In the three Raman lines of F_g-mode, one LO phonon line and two TO phonon lines were classified by the depolarization ratio of polarized Raman intensities.

Abstract: 4H-silicon carbide epitaxial film was etched using chlorine trifluoride gas. The etch rate of C-face at 2-100 % and at various temperatures was 0.8 – 10 μm min^-1, which was comparable to those of the silicon carbide substrates. The surface morphology observed after the etching was very smooth, in contrast to that of the substrate showing many pits.

Abstract: The in situ cleaning process of a silicon carbide epitaxial reactor was developed using chlorine trifluoride gas for removing the film-type silicon carbide deposition formed on a susceptor. By adjusting the etching temperature to less than 330 °C, the formed silicon carbide films could be removed without significant damage to the susceptor.

Abstract: To investigate the epitaxial strain effect on local electronic structure of FeO₆ octahedron of BiFeO₃ epitaxial film, polarization-dependent Fe L₂₃-edge x-ray absorption spectroscopy studies were performed on both tetragonal (T)-like BFO/LAO and rhombohedral (R)-like BFO/STO epitaxial films. Charge transfer multiplet theory based fittings were also performed to reveal the local electronic structure difference. Due to dramatic structural difference caused by epitaxial strain between these two samples, significant electronic structure differences were observed between these two specimens. For BFO/LAO, anisotropic electronic structure appears in vertically-elongated FeO₆ octahedron and an additional shift of Fe ion off the central position is suggested. For BFO/STO, electronic structure is almost isotropic.

Abstract: We report the growth of Cu₂O thin films on glass and MgO(100) substrates by molecular beam epitaxy. Crystal orientation of Cu₂O thin films on glass substrate were changed from (100) to (111) with increasing the deposition rate. The Cu₂O thin films were epitaxially grown on MgO(100) substrate with an orientation relationship of Cu₂O(110) // MgO(100). The film quality and electrical properties of Cu₂O thin films were changed with deposition rate. The slow deposition rate resulted in high conductivity and mobility, as well as good crystallinity and orientation.

Abstract: Landau-Ginzburg free energy expression with the normalized coefficients is used to elucidate the phase transition properties of strained ferroelectric films. In particular, we investigate the need to include higher order free energy terms for epitaxial strained BaTiO3 thin films. Our study reveals that the inclusion of eighth-order expression into the free energy is crucial in determining the phase transition of highly-strained BaTiO3 epitaxial films normally grown on thick cubic substrates. The phase transition is found to be second order but the unstrained film undergoes the first order phase transition. On the order hand, the calculation based on the usual sixth-order Landau-Ginzburg expression show that the films have no phase transition, which is contrary to the experimental observations.

Abstract: It has been widely accepted that wide-band-gap semiconductor SiC can provide low-loss semiconductor switches and diodes for the power electronics applications. The SiC devices enable the low-loss and compact converters and inverters.

Abstract: La_0.7Sr_0.3MnO₃(LSMO) films 35-350nm thick have been grown on (001)LaAlO₃ (LAO) substrates. The strain state evolution was examined fully by x-ray reciprocal space maps, in order to clarify its impact on the thickness-dependent properties of the films. It was found that LSMO epitaxial films have properties which is from partially strained to fully relaxed with film thickness increasing on the same substrate. Resistivity measurement shows that the relaxed film has higher resistivity than that of the strained film, because the relaxed film contains the high deficiency density. In this paper, however, the relaxed property of the same thickness LSMO epitaxial film grown on the different substrates is also discussed.

Abstract: Thin films of hematite find extensive applications in photoelectrochemistry, photocatalysis, and gas sensors. c-axis oriented hematite films have been directly grown on c-plane sapphire substrate using chemical method via hydrolysis of ferric cations. X-ray diffraction (XRD) reveals that the crystalline phases of the films and corresponding sediment produced in the solution were α-Fe₂O₃ and pure β-FeOOH, demonstrating the promotion of nucleation of hematite on sapphire substrate as a result of lowered interface energy. Phi-scan results indicate that the hematite films are grown with (0001) planes parallel to c-plane of Al₂O₃. Scanning electron microscopic observation shows that the hematite films are composed of pyramid-shaped nanocrystals with smooth surface facets.

Abstract: Y3Fe5O12 (YIG) films were pulsed laser deposited onto the Gd3Ga5O12(111) substrates. Processing conditions were optimized to obtain films with a narrow ferromagnetic resonance (FMR) linewidth: 0.9 Oe in 1.22 μm thick YIG at 9 GHz. Due to sharp film-to-substrate interface YIG films remain strained hence possess unusually high lattice mismatch induced uniaxial anisotropy Hu = - 880 Oe. We fabricated and tested magnetostatic surface wave (MSSW) band pass hybrid-type filters with YIG film lain on transducers alumina board. MSSW filter with antennas areal size of 2 mm2 at 7.5 GHz shows insertion loss – 9 dB and a resonant 3 dB bandwidth as narrow as 12.5 MHz.