Abnormal behavior of longitudinal optical phonon in silicon dioxide films on 4H-SiC bulk epitaxial substrate using Fourier transform infrared (FT-IR) spectroscopy.

We report the abnormal behavior of longitudinal optical (LO) phonon in a silicon dioxide (SiO2) film on a 4H-SiC bulk epitaxial substrate using an attenuated total reflection (ATR) technique. The peak frequency of the LO phonon in the ATR spectrum was observed at around 1165 cm(-1) and red-shifted by approximately 92 cm(-1) relative to that at the grazing incidence (40°), whereas the peak frequency of the transverse optical (TO) phonon in the ATR spectrum agreed well with that at the grazing incidence. Furthermore, the peak frequency of the TO phonon hardly depends on change in the incident angle and thickness, suggesting that the microstructure of the sample is homogeneous within a thickness of 100 nm. On the other hand, we found that the microstructure of the sample was inhomogeneous within a thickness less than 5 nm. Fourier transform infrared (FT-IR) spectroscopy provides us with a large amount of data on microstructures in the SiO2 films on a 4H-SiC substrate.

Characterization of silicon dioxide films on a 4H-SiC Si(0001) face by fourier transform infrared (FT-IR) spectroscopy and cathodoluminescence spectroscopy.

We used Fourier transform infrared (FT-IR) spectroscopy to characterize silicon dioxide (SiO(2)) films on a 4H-SiC(0001) Si face. We found that the peak frequency of the transverse optical (TO) phonon in SiO(2) films grown on a 4H-SiC substrate agrees well with that in SiO(2) films grown on a Si substrate, whereas the peak frequency of the longitudinal optical (LO) phonon in SiO(2) films on a 4H-SiC substrate is red-shifted by approximately 50 cm(-1) relative to that in SiO(2) films on a Si substrate. We concluded that this red-shift of the LO phonon is mainly caused by a change in inhomogeneity due to a decrease in density in the SiO(2) films. Furthermore, cathodoluminescence (CL) spectroscopy results indicated that the channel mobility of the SiC metal-oxide-semiconductor field-effect transistor (MOSFET) decreases roughly in proportion to the increase in the intensity of the CL peak at 460 and 490 nm, which is attributed to the increase in the number of oxygen vacancy centers (OVCs). FT-IR and CL spectroscopies provide us with a large amount of data on OVCs in the SiO(2) films on a 4H-SiC substrate.

Crucial role of the lipid part of lipopolysaccharide for conformational change of minor spike H protein of bacteriophage phiX174.

The contribution of the lipid part of lipopolysaccharide (LPS) to recognition by minor spike H protein of bacteriophage phiX174 was investigated by comparing the interactions of H protein with LPS and its deacylated derivatives. The fluorescence and circular dichroism (CD) spectra of H protein increased upon binding to intact LPS and a partially deacylated derivative. In contrast, completely deacylated derivatives showed lower affinities and almost no fluorescence or CD changes of H protein. These results demonstrate that the lipid part of LPS is responsible for the conformational change of minor spike H protein, which would function as a trigger for phage DNA ejection for infection of the host cell.

Different contributions of the outer and inner R-core residues of lipopolysaccharide to the recognition by spike H and G proteins of bacteriophage phiX174.

The binding of spike H and G proteins of bacteriophage phiX174 with lipopolysaccharides (LPSs) were evaluated by a competitive enzyme-linked plate assay using the biotin-labeled LPS of Escherichia coli C, one of a host strain, and the non-labeled LPSs having different R-core polysaccharide lengths. H protein promptly decreased its affinity when some saccharide residues were truncated from the outer R-core. However, G protein showed significant affinity to the LPSs lacking all the residues of the outer R-core and some of the inner R-core. Thus, G protein rather than H protein well recognized the residues of the inner R-core of LPS.

Contributions of polysaccharide and lipid regions of lipopolysaccharide to the recognition by spike G protein of bacteriophage phi X174.

A histidine-tagged G protein of bacteriophage phi X174 (HisG) bound strongly with lipopolysaccharide (LPS) of Escherichia coli C, one of a phi X174-sensitive Ra strain. The dissociation constant, Kd, was measured to be 0.16 +/- 0.04 microM by fluorometric titration. HisG showed slightly less affinity to LPSs of the insensitive Rc and Rd 2 strains having shorter R-core polysaccharide sequences than that of the sensitive Ra strains. The difference between the two types of LPS was demonstrated by CD spectra; LPSs of the sensitive strains increased the signal intensity for beta-sheet, while the insensitive strains decreased it. The chemically degraded LPS derivatives lacking a hydrophobic lipid region showed much less affinity to HisG, indicating the importance of the lipid region of LPS for strong binding with HisG. On the other hand, since the degraded derivatives increased the intensity of CD spectra, the polysaccharide region is thought to contribute to the conformation change of the protein.