A. G. Fitzgerald

Umbravirus-encoded movement protein induces tubule formation on the surface of protoplasts and binds RNA incompletely and non-cooperatively.

Various functions of the cell-to-cell movement protein (MP) of Groundnut rosette virus (GRV) were analysed. The GRV ORF4-encoded protein was shown by immunofluorescence microscopy to generate tubular structures that protrude from the surface of the protoplast. The protein encoded by ORF4 was assessed also for RNA-binding properties. This protein was tagged at its C terminus with six histidine residues, produced in Escherichia coli using an expression vector and purified by affinity chromatography. Gel retardation analysis demonstrated that, in contrast to many other viral MPs, including the 3a MP of Cucumber mosaic virus (CMV), the ORF4-encoded protein bound non-cooperatively to viral ssRNA and formed complexes of low protein:RNA ratios. Competition binding experiments showed that the ORF4-encoded protein bound to both ssRNA and ssDNA without sequence specificity, but did not bind to dsDNA. UV cross-linking and nitrocellulose membrane-retention assays confirmed that both the GRV and the CMV MPs formed complexes with ssRNA and that these complexes showed similar stability in NaCl. Probing the MP-RNA complexes by atomic force microscopy demonstrated that the ORF4-encoded protein bound RNA incompletely, leaving protein-free RNA segments of varying length, while the CMV 3a protein formed highly packed complexes. The significance of the two properties of limited RNA binding and tubule formation of the umbraviral MP is discussed.

Microstructural properties of amorphous carbon nitride films synthesised by dc magnetron sputtering

Amorphous carbon nitride (a-C:N) films have been prepared on silicon(1 0 0) substrates by direct current magnetron sputtering of graphite using a gaseous mixture of Ar and N2. Raman spectra have shown that these a-C:N films have a graphitic structure. The incorporation of nitrogen in the films has been confirmed by Fourier transform infrared (FTIR) spectroscopy. Graphitic and disordered sp2-bonded carbon which are present in Raman spectra and are normally forbidden (not observed) in FTIR become infrared active in our films as the symmetry of the hexagonal carbon rings is broken by nitrogen incorporation. X-ray photoelectron spectroscopy has been used to study the type of chemical bonding in these a-C:N films. The C 1s and N 1s X-ray photoelectron peaks have been deconvoluted and studied. We have found that for the C6-point triple bond; length half of m-dashN and C=N components of the C 1s and N 1s photoelectron peaks, there is a maximum peak intensity ratio of C6-point triple bond; length half of m-dashN:C=N in the films deposited when the gaseous mixture contains 35% N2 in the sputter gas.

X-ray photoelectron spectroscopy studies of the effects of plasma etching on amorphous carbon nitride films

The effects of post-treated oxygen plasma etching procedures have been investigated for amorphous carbon nitride (a-C:N) films deposited by dc magnetron sputtering. X-ray photoelectron spectroscopy (XPS) has been used to study the microstructure of these films. It has been found that the relative concentration of the beta-C3N4-like phase in the a-C:N films is enhanced significantly by oxygen plasma etching and by increasing the dc bias voltages during the etch experiments. This study reveals that an oxygen plasma can work as an effective chemical etchant for the graphite-like carbon-nitrogen phase in a-C:N films. This suggests a very promising way of obtaining harder a-C:N films.

Low temperature plasma chemical vapour deposition of carbon nanotubes

Carbon nanotubes have been grown on alumina-supported iron compound catalysts by 2.45 GHz microwave plasma chemical vapour deposition, without additional substrate heating, using methane/argon gas mixtures with no added hydrogen, and with microwave powers typically up to 100 W. The conditions that produced a stable plasma were investigated by statistical selection of the values of power, pressure and gas flow rates. The conditions for abundant multi-walled nanotube formation were determined within this parameter space by SEM and TEM observations of the deposited material. The temperatures of the plasma and of the substrate in the reactor were investigated by optical emission spectroscopy and melting point samples, respectively.

X-ray photoelectron spectroscopy studies of thin GexSb40−xS60 chalcogenide films

Thin GexSb40-xS60 (x = 5, 15, 20, 25 and 27) chalcogenide films have been investigated by X-ray photoelectron spectroscopy (XPS). X-ray photoelectron spectra show that there is a peculiarity in the relative intensity ratio of the Sb 4d photoelectron peak associated with Sb2S3 to the Sb 4d photoelectron peak associated Sb2S5 at an average co-ordination number Z of 2.65-2.67. After contamination and photo-oxidation layers were removed from the surface of the films, X-ray photoelectron spectra were measured again. It has been found that binding energies of the Ge 2p and Sb 3d(3/2) photoelectron peaks, which reflect the electronic structure at lower core energy levels, are independent of Z. However, the binding energies of the Ge 3d and Sb 4d photoelectron peaks are more sensitive to Z and have a discontinuity at Z = 2.65.

Electron-beam-induced patterning of thin film arsenic-based chalcogenides

Abstract Amorphous chalcogenides in contact with silver possess a remarkable sensitivity to radiation and have therefore been widely investigated. The present study concentrates on an investigation of nanometer dimension silver lines that can be formed by scanning a focused electron beam across the surface of As 2 Se 3 /Ag and As 2 S 3 /Ag films. The influence of different parameters, such as film thickness, silver content and exposure conditions, has been systematically studied. It was found that the width and height of these lines depend strongly on the accelerating voltage and the deposition order. The best width-to-height ratio could be obtained for As 2 Se 3 /Ag films of ca. 100 nm thickness at an accelerating voltage of 15 kV.

The effect of postdeposition annealing on chemical bonding in amorphous carbon nitride films prepared by DC magnetron sputtering.

Abstract The effects of thermal annealing on the surface morphology, composition and chemical bond structure of amorphous carbon nitride (a-C:N) films deposited by dc magnetron sputtering are reported. Atomic force microscopy (AFM) results show that thermal annealing can gradually change the surface structure of the films from a cauliflower-like texture eventually to a uniform granular texture. Fourier transform infrared absorption (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) have been used to characterise the change of chemical bonding induced by annealing. By detailed analysis of both C 1s and N 1s photoelectron spectra, we have found that annealing can break the CN bonds in the films and that the graphite-like CN bonds are relatively more stable with the increase of anneal temperature.

A microbeam analytical characterization of diamond films

Abstract Diamond films prepared in an ASTeX plasma deposition system and the Heriot-Watt UHV compatible microwave deposition system have been characterized by a range of techniques including electron microscopy, electron diffraction, electron energy loss spectroscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy and secondary ion mass spectrometry. XPS studies have concentrated on a comparison of the valence band structure, the X-ray excited Auger peaks, and the characteristic loss region of the carbon l s photoelectron peak. AES work has involved a study of the structure of the C KVV Auger peak. Microtwinning and grain structure in the diamond films has been studied by TEM. In EELS the fine structure at the carbon K-edge has been studied to give information on the form of carbon bonding. Reflection electron diffraction has been used to determine the interplanar spacings of the films. The interface formed between the diamond and the silicon substrate has been studied by electron beam induced conductivity (EBIC) in the SEM. The film morphology has also been studied in the SEM.

Scanning probe microscopy and spectroscopy of CVD diamond films

Abstract. The surface morphology and electronic properties of as-deposited CVD diamond films and the diamond films which have been subjected to boron ion implantation or hydrogen plasma etching have been systematically studied by high resolution scanning probe microscopy and spectroscopy techniques. AFM and STM image observations have shown that (a) both the as-deposited CVD diamond films and the boron ion implanted films exhibit similar hillock morphologies on (100) crystal faces and these surface features are formed during the deposition process; (b) boron ion implantation does not cause a discernible increase in surface roughness; (c) atomic flatness can be achieved on crystal faces by hydrogen plasma etching of the film surface. Scanning tunnelling spectroscopy analysis has indicated that (a) the as-deposited diamond films and the hydrogen plasma etched diamond films possess typical p-type semiconductor surface electronic properties; (b) the as-deposited diamond films subjected to boron implantation exhibit surface electronic properties which change from p-type semiconducting behaviour to metallic behaviour; (c) the damage in the boron implanted diamond films is restricted to the surface layers since the electronic properties revert to p-type on depth profiling.

Nanoscale surface modification and nanostructural fabrication of YBa2Cu3O7−x thin films by scanning tunneling microscopy

The scanning tunneling microscope has been used to modify the surface of YBa2Cu3O7−x (YBCO) high Tc superconducting thin films by operating the instrument in the so-called mechanical milling or field-induced evaporation mode. Nanostructures such as holes, lines, and trenches were fabricated on the YBCO thin film surface in a controlled manner. In the surface modification and nanostructure fabrication processes, the effect of bias voltage, tunneling current, and scanning feedback control parameters on the modification efficiency have been investigated.