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Tetrahedral amorphous carbon films with 70%–88% sp3 content are studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), and Raman spectroscopy as a function of annealing temperature in the range 25–1100°C. Using a high-resolution AFM current imaging, we directly image the formation and growth of conducting graphitic (sp2-bonded) nanoclusters in the ta-C films. Overall results from all the techniques used show that the structural and electronic changes in the films depend sensitively on the initial sp3 content. Cross-sectional TEM confirms that the clusters appear not only at the surface of the films but in the bulk as well. The growth and, perhaps, the partial orientation of the sp2-bonded nanoclusters in the size range of 1–3nm is accompanied by a large reduction in the film stress, which decreases sharply in the temperature range 500–600°C.

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Schottky barrier porous silicon diodes have been fabricated showing electroluminescence peaking at 500 nm, with an internal efficiency for blue–green emission of about 0.1%. The structures, on low-resistivity n-type silicon, operate in reverse bias. Scanning tip light emission measurements show a peak emission at 630 nm, closer to that of photoluminescence from the identical surface at 700 nm than that of the electroluminescence. The latter is concluded to arise from nonquantum effects, at the metal interface. The threshold for visible light emission is at 0.2 mA/cm2, and for infrared light is an order of 10 higher. The lifetime in air is short when unencapsulated, but longer in vacuum.

The stability and reproducibility of current–voltage curves of Schottky barrier structures on particular porous silicon surfaces used for obtaining electroluminescence is greatly improved by first coating the surface with a conducting polymer, poly-4-dicyanomethylene-4H-cyclopenta [2,1-b:3,4-b′] dithiophene. With such coated structures it is possible to fit the usual diode formula at room temperatures with a quality factor of 3.0, obviating the need for more complex theories. The stability of electroluminescence, which shows a redshift from 500 to 580 nm after coating, is also greatly improved. The coating appears to chemically react with the hydride surface and also mechanically strengthens the structure.

We report the emission of significant infra-red as well as visible electroluminescence (EL) from lightly spark-processed Si (LSP-Si). Studies by scanning tunnelling microscopy (STM) reveal the presence of small globules down to around 2 nm in diameter, the sizes necessary for significant quantum confinement and blue-shifted interband radiation to occur. However, studies with oxidized samples and samples processed in non-oxygen gases suggest that silicon oxides play a major role. Measurements by elastic recoil detection analysis and Rutherford back scattering analysis show that LSP-Si has a 150-250 nm thick oxidized surface layer. This layer is some four times thicker in medium sparked samples. There is negligible foreign material other than oxygen and slight C and N. Samples without encapsulation show changes in resistance but no change in efficiency after 500 hours of pulse operation.

Scanning tunnelling microscopy observations on cleaved Si surfaces in ultra-high vacuum have revealed several new features. These include much deeper measured valleys between the 2 × 1 rows, and occurrences of chain bridging. The higher resolution surface profile data are readily compatible with the three-bond scission model but are difficult to reconcile with a modified Pandey chain model. Several surface structures are possible.