A wet thermal oxidation method is proposed to passivate the electrochemically etched porous silicon. Bright and stable photoluminescence is achieved by wet oxidation at relatively low temperatures of 400–500 °C. The Fourier transform infrared absorption shows that the formation of SiH(O3), SiH(SiO2), SiH2(O2) bonds may be responsible to the stabilization of luminescence under the laser illumination.
The adsorption of carbon monoxide on copper covered Ni (111) surfaces has been studied by high resolution electron energy loss spectroscopy (HREELS). CO is used to titrate the various adsorption sites present, yielding information about the structure and composition of the two metal species at the surface. The results show that CO adsorbs at locations which resemble the top and bridge sites of pure Cu(111) and Ni(111) surfaces, and on a new mixed Cu–Ni bridge site. For a Cu coverage greater than one monolayer, the CO HREEL spectra are very similar to those observed on the clean Cu(111) surface. For Cu coverages less than one monolayer, and deposition at 80 K, small Cu clusters and Cu islands are observed. For submonolayer Cu deposition at temperatures >300 K, a mixed Cu–Ni layer can be formed. The HREELS results for the mixed surface with low Ni concentration show that CO adsorbs on the Ni top sites first (at T<400 K), Cu top sites next (at T<150 K), and then a mixed Cu–Ni bridge site (at T<120 K). Strong evidence suggests that the mixed CuNi bridge site is occupied by depopulating the Ni–CO top-site species.
Articles you may be interested inFabrication and properties of Cu-Ni mixed-metal periodical array for midinfrared filtering and hydrophobic application J.High-resolution electron energy-loss spectroscopy (HREELS) has been used to study ca~bon monoxide adsorption on mixed overlayers of Cu on Ni( 111) an~ Ni on Cu(111). The mixed CuNi layers are formed by controlling deposition and anne~lmg te~perat~res, and metal I er coverage HREELS shows top and bridge CO adsorption on sites which resemble CO over ay . b 'd" . . hich CO on pure Cu and Ni( 111) surfaces. We also observe ~ new ~ix~d n gl?g ~Ite species m w . is bridge bonded between Cu and Ni atoms. The mixed bndgmg ~pe~les IS ~nly observed ~t hl~h CO coverages and low temperatures ( < 130 K), and appears comcl~ent With a decrease m NI-CO top site occupancy. A thermodynamic model is proposed to explam the CO transfer from the Ni top to the mixed NiCu bridge sites.
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