D.T. Jiang

Observations on the surface and bulk luminescence of porous silicon

Using the x‐ray excited optical luminescence technique, we have investigated the soft x‐ray induced photoluminescence of porous silicon in the optical region (200–900 nm) and the Si K‐edge x‐ray absorption fine structures of porous silicon in the near edge region. It is found that while porous silicon prepared at low current density (20 mA/cm2 for 20 min) exhibits a single broad luminescence band, porous silicon prepared at high current density (200 mA/cm2 for 20 min) exhibits three optical luminescence channels; i.e., in addition to the broad peak characteristic of all porous silicon, there are at least two additional optical luminescence channels at shorter wavelengths, one with modest intensity at ∼460 nm and the other a weak and very broad peak at ∼350 nm. These optical channels have been used to monitor the Si K‐edge absorption of porous silicon in the near edge structure region. Analysis of the data shows that while the band at ∼627.5 nm corresponds to the bulk emission, the other channels are of a ...

VUV INDUCED LUMINESCENCE FROM POROUS SILICON

Abstract We report the observation of multiple emission peaks in the visible as well as in the UV from porous silicon induced by excitation photons with energies of 15–40 eV. The UV luminescence at ∼ 4.2 eV, to our knowledge, was observed for the first time. We attribute this luminescence to be of a surface origin. The similarity between this surface luminescence to that from defects in amorphous silicon oxide is noted.

A Systematic Study of Synchrotron Light Induced Luminescence from Porous Silicon: Implications to Morphology and Chemical Effect Dependent Electronic Behaviour

Using synchrotron as a tunable excitation source, we have carried out a study on the photoluminescence systematics from a series of porous silicon samples prepared under different conditions, Luminescence spectra were recorded with excitation photon energies tuned to the Si L3,2 absorption edge (∼100 eV). The luminescence yield was in turn used to monitor the Si L3,2-edge absorption characteristics of porous silicon. A trend of luminescence wavelength and intensity as a function of preparation conditions emerges. Other related observations are also noted.

Optical luminescence yield spectra of KCl:Tl produced by Cl K- and K K-edge excitations

Abstract The yield spectra of XEOL (X-ray Excited Optical Luminescence) on single crystal of Tl-activated KCl are reported. The luminescence yield spectra excited with x-rays in the energy ranges of Cl K- and K K-edges are investigated. All the yield spectra show negative jump at the K edges of Cl and K irrespective of the observation wavelength channels except for the channel of 550 nm. The inversion of the yield spectra can be understood as the self absorption of the photons produced at the inner part of the crystal by the color center at the surface by the x-ray irradiation.

XAFS of silver(I) metallothionein

Abstract Silver K-edge XAFS has been measured on Ag17-MT formed by adding Ag(I) to Zn7-MT at pH 7. The nearest neighbor bond length and coordination number are determined by curve-fitting using theoretical scattering amplitude and phase. It is found that the silver atom is coordinated with two sulfurs at 2.43 ± 0.024 A and one Ag at 2.91 ± 0.05 A . The results are compared to those of Zn7-MT, Cd7-MT, Hg7-MT and Hg18-MT. The generality of the coordination geometry of AgS clusters in various metallothioneins is noted.

Si core-level excitation of hexamethyldisilane studied by synchrotron radiation and multiple-scattering X α calculation

Abstract The Si 1s, Si 2s and Si 2p core-level photoabsorption spectra of hexamethyldisilane have been recorded by synchrotron radiation and calculated by the multiple-scattering (MS) X α method. The results of the calculation are in semiquantitative agreement with the experimental spectra. The relative intensity of corresponding transitions at the (1s, 2s) or (2p) edges differs greatly on account of atomic-like propensity rules (s → p, p → s, d). Comparison of the gas phase and solid state Si 2p spectra with the MS-X α results indicates that many of the features in the Si 2p spectrum of hexamethyldisilane correspond to transitions to states of mixed valence and Rydberg character.

XEOL XANES of ZnS(Cu) and porous Si

Abstract Using X-ray excited optical luminescence (XEOL), L- and K-edge photoluminescence yield (PLY) XANES of S and Si have been obtained on P31 (ZnS: Cu) and porous Si (PS), respectively. Both P31 and PS have a negative edge jump in PLY XANES at the L-edges. At S K-edge, for P31 the edge jump is positive. For PS both the positive and negative edge jumps have been observed at Si K-edge, depending on the sample preparation and the optical channel used. The PLY XANES correlate well with the total electron yield spectra. The site selectively of PLY XANES is discussed.

VUV- and Soft X-Ray-Induced Optical Luminescence and X-Ray Absorption Fine Structures of Porous Silicon

Optical luminescence in porous silicon induced by soft X-ray and vacuum UV excitation with energies in the vicinity of the Si K-edge (1838 eV) and the Si L-edge (99 eV) has been observed. The luminescence has been used, together with total electron yield, to record X-ray absorption fine structure (XAFS) in the near-edge region of both Si edges. The near- edge spectra recorded simultaneously with either luminescence or total electron yield were compared, and the implications of these measurements for the structure of porous silicon are discussed.

XANES of organosilicon clusters at the Si K- and L-edge

Abstract The Si K- and L2,3-edge XANES of tetrakis(trimethylsilyl)silane in gas phase have been recorded. The general shape of the L2,3-edge spectra closely resembles that of the K-edge. With the aid of the MS-Xα calculation, the relation between the spectral features and molecular structure is discussed.