S. C. Bayliss

Blue photoluminescence and local structure of Si nanostructures embedded in SiO2 matrices

Strong and stable blue photoluminescence (PL), visible to the naked eye under 0.4 μW of 300 nm and 2.7 μW of 370 nm excitation, has been observed for samples of Si clusters embedded in SiO2 matrices, prepared by rf co‐sputtering followed by N2 annealing at 800 °C. Si K‐edge extended x‐ray absorption fine structure (EXAFS) and near‐edge x‐ray absorption fine structure (NEXAFS) strongly suggest the existence of Si nanoclusters with crystalline cores in the efficient emitting material. The PL excitation dependence is explained by an increase in the conduction band density of states deep in the band, and the formation of a band tail.

The culture of neurons on silicon

We have investigated the adherence and subsequent viability of rat neuronal (B50) cells cultured directly on the nanostructured semiconductors porous silicon (PS), PECVD polycrystalline silicon and bulk silicon wafers. In contrast to our previous work on culturing CHO cells on nanostructured silicon, where the cell count was greatest on nanocrystalline PECVD Si (nc-Si) substrates, with B50 cells the optimum surface was PS, with much reduced cell viability observed for cells cultured on bulk or nc-Si. These preliminary studies indicate that PS and nc-Si offer advantages over bulk Si surfaces for neuron cell adherence and viability since they do not require coating with substances such as polylysine to support cell growth, PS is light-addressable, and nanostructured coatings can be applied to most object shapes, allowing flexibility in their deployment.

Nature of the Silicon-Animal Cell Interface

The paper reports the results of the study of cell culture growth at the surface of porous silicon. They show that porous and poly(nano)crystalline Si offer significant advantages over bulk Si surfaces for cell adherence and viability: these materials do not require coating with substances such as polylysine to support cell growth; porous Si is light-addressable because of photoluminescence and photovoltaic effects noted [Unal and Bayliss, J. Appl. Phys. 80, 3532 (1996)], allowing the potential for optical data transfer and less susceptibility to interference from external electronic equipment; finally nanostructured coatings can be applied to most object shapes, giving flexibility in their application.

The correlation of dimensionality with emitted wavelength and ordering of freshly produced porous silicon

Freshly produced red, yellow and green emitting porous Si specimens have been studied by NEXAFS and EXAFS (near edge and extended x‐ray absorption fine structure). The emission peaks are at 690, 580, and 520 nm, which almost covers the full visible range that direct anodization can achieve. The correlation between the co‐ordination numbers of the first, second and third Si neighbor shells from Fourier transform fitting of EXAFS and both emission peak energies and optical band gaps estimated by PLE (photoluminescence excitation dependence) suggests that the nanostructures of the PS are nanowires, rather than nanocrystalline. Two types of quantum nanowire with one and one‐plus‐a‐fraction dimensionality are proposed to interpret the correlation. The order factors of the theoretical fits suggest the nanowires of the freshly produced PS have crystalline cores.

Characterization of Ge nanocrystals embedded in SiO2 by Raman spectroscopy

Ge nanocrystals formed in a SiO2 matrix by ion implantation were studied by Raman spectroscopy. It is shown that Raman analysis based on the phonon confinement model yields a successful explanation of the peculiar characteristics resulting from the nanocrystals. A broadening and a shift in the Raman peak are expected to result from the reduced size of the crystals. Asymmetry in the peak is attributed to the variations in the size of the nanocrystals. These effects were observed experimentally for the Ge nanocrystals prepared by ion implantation and explained theoretically by incorporating the effect of size and size distribution into the theoretical description of the Raman shift. A comparison with the transmission electron microscopy images indicated that this analysis could be used to estimate the structural properties of nanocrystals embedded in a host matrix. The evolution of nanocrystal formation with annealing temperature, i.e. the size growth, was monitored by Raman spectrometry for several samples and the corresponding nanocrystal sizes were estimated using the phonon confinement model.

Transmission of light across the adult and neonatal eyelid in vivo

Light transmission characteristics of the human adult and neonatal eyelid were measured in vivo. Light was delivered via a grating monochromator through a fibre-optic mounted onto a contact lens placed under the eyelid, and detected using a photodiode on its external skin surface. Data from 5 adult and 9 preterm neonatal subjects indicate that the eyelid acts as a predominantly red-pass filter, with mean transmissions at 700 nm of 14.5% in the adult and 21.4% in the neonate, declining to less than or equal to 3% in both groups below 580 nm. The relevance of this data to clinical electrophysiology and to estimates of retinal irradiance is discussed.

Phosphate and cell growth on nanostructured semiconductors

Abstracts are not published in this journal

Hardening of fullerite C60 during temperature-induced polymerization and amorphization under pressure

We report a detailed study of Vicker’s hardness and ultrasonic elastic moduli for carbon phases prepared by heating fullerite C60 at pressures of 3.5, 5, and 8 GPa. It is shown that the transformation of two-dimensional C60 polymers into graphite-like amorphous carbon is accompanied by an increase in hardness of 100–200 times, as well as an increase in bulk and shear moduli by 4–5 and 2–3 times, respectively, with no density jump taking place. It is proposed that the high hardness (up to 40 GPa) of the disordered phases synthesized is caused by the three-dimensional ordering of sp2-based network. It was found that, in the 3.5–8 GPa interval, the mechanical properties of the phases obtained depend basically on the temperature rather than on the pressure of synthesis.

A study of the optical, electrical and structural properties of reactively sputtered InOx and ITOx thin films

Abstract Films of InO x and ITO x were prepared by DC reactive sputtering from indium and indium-tin alloy targets, respectively, in an oxygen/argon atmosphere. The compositions of the InO x films, determined from EDX, have been used to show how x varies as a function of O 2 partial pressure in the flow to the sputtering system. Reflectance and transmittance of the InO x films and ITO x films were measured in the photon energy range 0.5–6.0 eV, leading to determination of absorption coefficients as a function of x . The optical band gap, which appears as x is increased, was found to increase monotonically with x . The DC resistivity of InO x films has been determined as a function of composition, as have the refractive indices for transparent films and thickness of all InO x and ITO x films. The local structure of InO x and ITO x samples is shown by extended X-ray absorption fine structure to have much configurational disorder throughout the composition range.

Simultaneous micro-Raman and photoluminescence study of spark-processed germanium: Report on the origin of the orange photoluminescence emission band

Microstructure and origin of the orange photoluminescence (PL) band of visible luminescing spark-processed germanium (sp-Ge) has been studied using simultaneous micro-Raman and -PL spectroscopy and scanning electron microscope. Instability of the sp-Ge film to energetic electron beams (⩾5 keV) during SEM measurements suggested that sp-Ge is not composed exclusively of purely Ge–Ge bonded material (elemental Ge) but also of other form(s) of material(s) of different chemistry. Indeed, micro-Raman spectra of the films showed that sp-Ge is composed of mainly substoichiometric germanium oxides (GeOxs) and elemental Ge (in the form of nano- or micro-crystals). Further, it is proposed that the Ge particles were embedded in thick GeOx (0<x<2) layers. Sizes of the Ge nanocrystals were estimated using a phonon confinement model and it was found that the spark processing method can generate Ge crystals with sizes as small as 6–8 nm. However, the micro-PL of sp-Ge indicated unambiguously that the orange PL band (near...