Volume 83, Issue 3, 01 February 1998
Index of content:
83(1998); http://dx.doi.org/10.1063/1.366897View Description Hide Description
Low-temperature (550 °C) ultraviolet-assisted oxidation of epitaxially grown strained layers on (100) Si substrates leads to the formation of nanocrystallineGe (nc-Ge) particles embedded in a layer which exhibit visible photoluminescence with an emission maximum situated at around 2.18 eV. Grazing incidence x-ray diffraction investigations of the remaining SiGe layer which was continually rejected by the advancing oxide layer have shown the presence of the (311) diffraction peak. This implies that the unoxidized SiGe layer has been fractured in many regions misoriented with respect to the initial layer. The displacement of the SiGe (311) peak position recorded for samples which had their grown oxide layer stripped away when compared with as-grown samples indicates the presence of a significant stress in these low-temperature grown oxide layers. This stress is believed to explain both the survival of the nc-Ge particles during prolonged oxidation and the fracturing of the buried SiGe layer.
83(1998); http://dx.doi.org/10.1063/1.366898View Description Hide Description
We report low-temperature polarized-photoluminescence (PL) measurements on (110) cleaved edges of ordered alloys. By comparing the intensity of the forbidden PL polarized along the ordering axis with that of the allowed PL polarized orthogonal to the ordering axis, we study the effect of coulomb interaction on the excitonic transition rate. The experimentally obtained polarization ratios of 13–20 are consistent with calculations based on an eight-band model.
83(1998); http://dx.doi.org/10.1063/1.366899View Description Hide Description
It is reported that annealing of oxidized porous silicon in water vapor at about 250 °C drastically enhances its blue emission. Infrared absorption studies indicate that this annealing increases all the absorption peaks related to O–H vibrations, except for that of free silanol which disappears completely. No traces of carbon-related signals are observed. The latter result makes a clear objection to blue-band luminescence models based on adsorbed carbon compounds. Although the possibility of silanol-related origins cannot be ruled out, we suggest that some passivation effect of adsorbed hydroxyls on Si nanostructures surrounded by is also likely.
83(1998); http://dx.doi.org/10.1063/1.366900View Description Hide Description
The magnetic properties of compounds were investigated in the temperature range of 5–800 K and fields up to 8 T. Magnetic susceptibilities of compounds with and 0.8, at are described by a dependence. The temperature range where this behavior is evidenced is gradually diminished as the nickel content increases. At high temperatures, the compounds with show a Curie–Weiss type behavior. The effective cobalt moments decrease slightly when increasing nickel content. The magnetic behavior of the above system is analyzed in a spin fluctuation model.
83(1998); http://dx.doi.org/10.1063/1.366901View Description Hide Description
Phase separation in polymer blend thin films is directly observed by near-field scanning optical microscopy. Time-resolved fluorescence spectra indicate that the phase domains are composed of different fractions of the two constituent polymers. The mixing homogeneity was found to vary with the blending ratio.