The effect of thermal oxidation on the luminescence properties of nanostructured silicon.
ABSTRACT Herein is reported a detailed study of the luminescence properties of nanostructured Si using X-ray excited optical luminescence (XEOL) in combination with X-ray absorption near-edge structures (XANES). P-type Si nanowires synthesized via electroless chemical etching from Si wafers of different doping levels and porous Si synthesized using electrochemical method are examined under X-ray excitation across the Si K-, L(3,2) -, and O K-edges. It is found that while as-prepared Si nanostructures are weak light emitters, intense visible luminescence is observed from thermally oxidized Si nanowires and porous Si. The luminescence mechanism of Si upon oxidation is investigated by oxidizing nanostructured Si at different temperatures. Interestingly, the two luminescence bands observed show different response with the variation of absorption coefficient upon Si and O core-electron excitation in elemental silicon and silicon oxide. A correlation between luminescence properties and electronic structures is thus established. The implications of the finding are discussed in terms of the behavior of the oxygen deficient center (OCD) and non-bridging oxygen hole center (NBOHC).
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ABSTRACT: Herein we demonstrate a novel electroless etching synthesis of monolithic, single-crystalline, mesoporous silicon nanowire arrays with a high surface area and luminescent properties consistent with conventional porous silicon materials. These porous nanowires also retain the crystallographic orientation of the wafer from which they are etched. Electron microscopy and diffraction confirm their single-crystallinity and reveal the silicon surrounding the pores is as thin as several nanometers. Confocal fluorescence microscopy showed that the photoluminescence (PL) of these arrays emanate from the nanowires themselves, and their PL spectrum suggests that these arrays may be useful as photocatalytic substrates or active components of nanoscale optoelectronic devices.Nano Letters 10/2009; 9(10):3550-4. · 13.03 Impact Factor
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ABSTRACT: Various uv and vacuum-uv optical-absorption bands found in as-manufactured high-purity SiO2 glass were studied. Two types of absorption bands were found near 5.0 eV, one of which is attributed to the oxygen vacancy (?Si-Si?). The absorption band at 7.6 eV is also found to be caused by the same oxygen vacancy. Observation of the decay lifetime of photoluminescence and calculations using the ab initio molecular-orbital program show that the 7.6-eV band is caused by a singlet-to-singlet transition, while the 5.0-eV band is caused by a singlet-to-triplet transition.Physical review. B, Condensed matter 02/1989; 39(2):1337-1345.
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ABSTRACT: The effects of ArF excimer laser irradiation on dehydrated high-purity silica glass were investigated on both the optical-absorption bands due to oxygen-deficient centers (ODC) and the formation of E' centers. With an intense uv flux from an excimer laser, an E'-center density of the order of 1015 cm-3 was created. The 7.6-eV absorption band remains at the original level, while the 5.0-eV absorption band having the 4.3-eV emission band decreased. Both bands were reduced by heat treatment in an O2 atmosphere. These results suggest that there exist two types of ODC:ODC(I), which is responsible for the 7.6 eV band, and ODC(II), for the 5.0-eV band. The concentrations of ODC(I) and ODC(II) were evaluated to be 1×1018 cm-3 through an analysis of the gas treatment data and of the order of 1014 cm-3 through the growth curve of the E' centers, respectively. The structural origin of ODC(I) has been attributed to the Si-Si homopolar bond, judging from the fact that the peak energy and cross section of the absorption were in close agreement with those of the Si2H6 molecule. Theoretical calculations on defect energy levels by O'Relly and Robertson supported the structural model for ODC(I) and suggested an unrelaxed oxygen vacancy for ODC(II). These assignments were also consistent with the results of a quenching experiment in which the fictive temperature of samples was changed; the equilibrium between concentrations of ODC(I) and ODC(II) shifted in a reasonable manner.Physical review. B, Condensed matter 01/1989; 38(17):12772-12775.