I. Coulthard

Novel preparation of noble metal nanostructures utilizing porous silicon

Pt and Au nanostructures were prepared utilizing a reductive deposition method where porous silicon acts both as a reducing agent and as a substrate for the resulting metal nanostructures. The morphology and electronic structure of these nanostructures was studied using SEM, XPS and XAS. As expected, the electronic structures of these nanoparticles is noticeably different from that of the bulk metal.

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 ...

Photoluminescence imaging of porous silicon using a confocal scanning laser macroscope/microscope

This letter describes a confocal scanning beam macroscope/microscope that can image specimens up to 7 cm in diameter using both photoluminescence and reflected light. The macroscope generates digital images (512×512 pixels) with a maximum 5 μm lateral resolution and 200 μm axial resolution in under 5 s, and in combination with a conventional confocal scanning laser microscope can provide quality control at a macroscopic/microscopic level for porous silicon specimens, wafers, detectors, and similar devices. This combination of instruments can also be used as a method for evaluating preparation parameters involved in the manufacture of porous silicon. Various confocal and nonconfocal photoluminescence and reflected‐light images of porous silicon are shown using both a macroscope and a conventional confocal scanning laser microscope. A 3D profile of a porous silicon structure reconstructed from confocal slices is also shown.

Morphology of porous silicon layers : image of active sites from reductive deposition of copper onto the surface

We report a scanning electron microscopy (SEM) investigation of the morphology of porous silicon layers and comparisons between our observations and a recent theory for its formation and morphology. Also examined was the use of porous silicon as a reducing agent in the preparation of Cu dispersed on the surface of the porous silicon. The morphology of the resulting copper deposits on the surface of the porous silicon layers in turn was used to infer the morphology of the hydrogenated, chemically active sites of the porous silicon. Conditions necessary for the reduction to take place, and the effect of the deposition upon the optical luminescence of the porous silicon are noted.

M3,2‐edge x‐ray absorption near‐edge structure spectroscopy: An alternative probe to the L3,2‐edge near‐edge structure for the unoccupied densities of d states of 5d metals

We report M3,2‐edge x‐ray absorption near‐edge structure (XANES) measurements for a series of 5d metals, Ta, W, Pt, and Au using a total electron yield technique. It is found that the M3,2 XANES absorption features and their systematics are comparable to their L3,2 counterparts. These results clearly indicate that M3,2‐edge XANES can be used as an alternative probe for the unoccupied densities of d states of the 5d metals and their compounds. The implication of these results is discussed.

Semiconductor Growth and Junction Formation within Nano-Porous Oxides

We report a systematic study of the chemical properties of porous silicon as a moderate reducing agent and a nano-structure template for the reductive formation of nano-metal cluster aggregates. This study investigates the consequences of the interaction of silver ions in aqueous solution with porous silicon. The nature of the redox reaction, especially the role of surface hydrogen and silicon atoms, is established through the study of the morphology, structure, and electronic and optical properties of Ag on porous silicon. The specimens were characterized with SEM and X-ray absorption fine structure (XAFS) spectroscopy using synchrotron radiation

X-ray excited optical luminescence (XEOL): a potential tool for OELD studies

Abstract An X-ray excited optical luminescence (XEOL) technique using laboratory soft X-rays and synchrotron radiation in the visible-UV and soft X-ray region will be discussed. It is shown that XEOL takes advantage of the penetration power of the X-rays and the tunability of the photons from a synchrotron source. Thus XEOL provides some sampling depth and site selectivity and allows for the probing of underlayers and buried interfaces. XEOL studies of porous silicon and a poly-vinyl-carbazole film will be used to illustrate that this technique is suited for the study of organic luminescent materials and organic electroluminescence devices (OELD).

Luminescence from porous silicon: an optical X-ray absorption fine structures study at the Si L3,2-edge

Abstract We report optical luminescence from porous silicon (PS) using excitation photons with energies above and below the Si L 3,2 -edge. The yield of the luminescence was in turn used to obtain the X-ray absorption fine structures (XAFS) of PS at these edges. It is shown that the small chemically capped nm nodules and pillars as well as encapsulated Si crystallites attached to the “bulk” of the PS network are primarily responsible for the luminescence, not the entire network. It is also noted that the combined use of the total electron yield, the photo luminescence yield and the fluorescence yield in measuring the Si L 3,2 -edge absorption greatly enhances the capability of the XAFS in site and sampling depth selectivity. K-edge data were also shown for comparison.

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.