GaN heteroepitaxial growth on sapphire (0001) substrates was carried out by radio-frequency plasma-assisted molecular beam epitaxy (rf-MBE). A Ga-polarity growth was achieved by using an AlN high-temperature buffer layer. The epilayer polarity was characterized directly by coaxial impact collision ion scattering spectra (CAICISS). It was found that the properties of the GaN films showing Ga-face polarity, including their structural and electrical properties, were dramatically improved compared to those of films with N-face polarity. This important conclusion is considered to be a breakthrough in the realization of high-quality III-nitride films by MBE for device applications.
We demonstrated the first room temperature continuous wave lasing in InAs quantum-dot microdisk lasers with a standard air-cladding optical confinement structure. The spectrum shows the single strong lasing peak at a wavelength of 1280 nm. The threshold pump power is 410 muW, and the corresponding effective threshold obtained by considering the absorption efficiency is 81 muW. This achievement is mainly attributed to the increase in Q factor by the improved disk shape.
GaN films with N- and Ga-polarity were grown on sapphire (0001) substrates using different buffer layers by plasma-assisted molecular-beam epitaxy. The surface stability of each lattice-polarity film during the growth interruption was studied by reflection high-energy electron diffraction (RHEED). It was found that the surface of N-polarity film was unstable against the exposure to the nitrogen plasma flux, while that of Ga-polarity one was stable. This provides a method to clarify the lattice polarity by the in situ RHEED observation directly. A model is proposed to explain the observed phenomenon, where the origin of the phenomenon is mainly attributed to the differences in surface dynamics processes and morphologies between the two kinds of lattice-polarity films.
An immunoglobulin enriched bovine colostrum preparation, IMMULAC™ (New Zealand Dairy Group, Cambridge, New Zealand), contains antibodies against various bacterial antigens. In the present study, we investigated the protective effects of a commercial bovine colostrum preparation against infections with enterohaemorrhagic Escherichia coli (EHEC) O157:H7 in a murine model. Balb/c mice were given drinking water containing streptomycin for 3 days before and following oral challenge with streptomycin‐resistant EHEC O157:H7 strain (O157‐SMR). In mice pretreated with streptomycin, EHEC O157:H7 maintained stable levels of bacterial colonization in the intestines for the 3‐week experimental time period. Oral administration of colostrum resulted in rapid decrease in the bacteria numbers compared with administration of skim‐milk. Colostrum showed no direct in vitro bactericidal properties against either EHEC O157:H7. When sections prepared from cecum walls of streptomycin‐pretreated mice were incubated in vitro with EHEC O157:H7, the colostrum significantly prevented the attachment of the organisms to the sections when compared with skim‐milk. These results indicate that oral administration of bovine colostrum effectively protects mice against food‐borne infections by inhibiting bacterial attachment to the intestinal mucous membrane, colonization and growth in the intestinal tract.
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