R.M. Erasmus

Low-temperature magnetic property of polymer encapsulated gold nanoparticles

Gold-polyaniline composite is reported by the polymerization of aniline hydrochloride monomer using HAuCl4 as the oxidant. HAuCl4 was dissolved in toluene using a phase-transfer catalyst, Aliquat 336. The oxidative polymerization of aniline hydrochloride leads to the formation of polyaniline with a diameter of <50 nm, while the reduction in auric acid results in the formation of gold nanoparticles with an average diameter ∼4 nm. The resultant composite material was characterized by means of different techniques, such as UV-vis, IR, and Raman spectroscopies, which offered the information about the chemical structure of polymer, whereas electron microscopy images provided information regarding the morphology of the composite material and the distribution of the metal particles in the polymer matrix. dc-magnetization measurements down to low temperatures (2 K) enabled the identification of a small, but field-independent paramagnetic behavior of the composite, and this is argued to originate from the charge t...

A study of plastic deformation profiles of impressions in diamond

Abstract In the last decade it has been shown that, when a diamond is subjected to any configuration of line or point loading (e.g. indentation) at temperatures in the vicinity of 1000°C, dislocation mobility in diamond is considerable [C.A. Brookes, in: J.E. Field (Ed.), The Properties of Natural and Synthetic Diamond, Academic Press, London, 1982, pp. 515–546]. The nature of the stress field associated with indentation using a rigid indenter is complex and very often leads to fracture in the diamond. The development of the indentation technique to permit the introduction of limited levels of strain in ultra-hard covalent materials, by replacing the rigid indenter with a soft impressor, has allowed the controlled plastic deformation of diamond. This takes the form of multiple intersecting slip, without fracture, and can be induced at temperatures less than 0.3Tm. Linking this technique to optical measurement methods, such as cathodoluminescence, photoluminescence and Raman spectroscopy, gives information about the interaction between point defects present in natural and synthetic diamond and the dislocations introduced during the indentation process. This investigation represents the first opportunity to report on a programme of work designed to provide a more satisfactory understanding of the plasticity in diamond on which to evaluate the mechanical properties and the performance of different types of diamond system.

Synthesis of tungsten oxide nanostructures by laser pyrolysis

Since the proposal to synthesise materials by laser assisted pyrolysis in the 1970s, and its practical realisation in 1982, a number of researchers have used this method in obtaining nano-powders from liquid droplets. This study revisits this technique by introducing a new aspect in that it considers obtaining thin films rather than powders. A full experimental arrangement, including laser optimisation, optical layout and materials processing procedures is described. Synthesis of WO3 nanostructures by this method is reported for the first time, with the mean diameter and length determined to be 51 nm and 6.8 µm, respectively. A possible mechanism for production of such nanostructures is proposed owing to the selective dissociation of the O-C bonds in the tungsten ethoxide precursor liquid which resonate with the 10.6 µm emission wavelength of the CO2 laser employed.

Formation of tungsten oxide nanostructures by laser pyrolysis: stars, fibres and spheres

In this letter, the production of multi-phase WO3 and WO3-x(where x could vary between 0.1 and 0.3) nanostructures synthesized by CO2-laser pyrolysis technique at varying laser wavelengths (9.22-10.82 mm) and power densities (17-110 W/cm2) is reported. The average spherical particle sizes for the wavelength variation samples ranged between 113 and 560 nm, and the average spherical particle sizes for power density variation samples ranged between 108 and 205 nm. Synthesis of W18O49 (= WO2.72) stars by this method is reported for the first time at a power density and wavelength of 2.2 kW/cm2 and 10.6 μm, respectively. It was found that more concentrated starting precursors result in the growth of hierarchical structures such as stars, whereas dilute starting precursors result in the growth of simpler structures such as wires.

UV-assisted synthesis of indium nitride nano and microstructures

Indium nitride (InN) has been made the first time by a combined thermal/UV photo-assisted process. Indium oxide (In2O3) was reacted with ammonia using two different procedures in which either the ammonia was photolysed or both In2O3 and ammonia were photolysed. A wide range of InN structures were made by these procedures that were determined by the reaction conditions (time, temperature). The reaction of In2O3 with photolysed NH3 gave InN rod-like structures that were made of stacked cones (6 h/750 °C) or discs (6 h/800 °C) and that contained some In2O3 residue. In contrast, photolysis of both In2O3 and NH3 gave InN nanowires and pure InN nanotubes filled with In metal (>90%). The transformation of the 3D In2O3 particles to the tubular 1D InN was monitored as a function of time (1–4 h) and temperature (700–800 °C); the product formed was very sensitive to temperature. The band gap of the In filled InN nanotubes was found to be 1.89 eV.

Three-dimensional mapping of stresses in plastically deformed diamond using micro-Raman and photoluminescence spectroscopy

The extreme mechanical properties of diamond have made it the material of choice for many industrial applications, ranging from cutting and grinding to wire-drawing dies. A detailed knowledge of its mechanical properties, also at high temperature, is thus of importance. Micro-Raman and photoluminescence (PL) spectroscopy were used to map the three-dimensional (3D) stress distribution surrounding a plastic impression made in a synthetic, type Ib single crystal diamond. The impression was created on a (100) face of the crystal with an Si3N4 impressor at 1400 °C using the so-called soft impressor technique. The diamond Raman peak was mapped at room temperature at the surface and at fixed intervals of 10 μm below the surface using a motorised X-Y stage. The depth (Z)-resolution was limited to 10 μm by means of a confocal pinhole. Using data from the Raman peak position, a 3D map of the stress contours surrounding the impression was generated, while the Raman width data yielded a map of the plastic deformation...

Possible Diamond-Like Nanoscale Structures Induced by Slow Highly-Charged Ions on Graphite (HOPG)

The interaction between slow highly-charged ions (SHCI) of different charge states from an electron-beam ion trap and highly oriented pyrolytic graphite (HOPG) surfaces is studied in terms of modification of electronic states at single-ion impact nanosizeareas. Results are presented from AFM/STM analysis of the induced-surface topological features combined with Raman spectroscopy. I-V characteristics for a number of different impact regions were measured with STM and the results argue for possible formation of diamond-like nanoscale structures at the impact sites.

Anomalous Raman features of silicon nanowires under high pressure

The potential of silicon nanowires (SiNWs), (diameter = 5 GPa establishes a highly anisotropic and mode-dependent pressure response of these SiNWs. Properties of the novel structures are superior compared to other nano-structured silicon and bulk-Si in terms of increased linear modulus, more localized phonon confinement and less anharmonicity.

EXAFS and Raman scattering studies of Y and Zr doped nano-crystalline tin oxide

Nanocrystals of Y and Zr doped SnO2 have been prepared by sol-gel route and annealed at 200, 400, 600, 800 and 1000 oC. The X-ray diffraction (XRD) results showed the average size of the particles in the freshly prepared samples to be ~ 3 nm. The Extended Absorption Fine Structure (EXAFS) technique was used to study the dopant environments in nanocrystalline tin oxide. In all Y-doped samples, except the one annealed at 1000 oC, there is clear evidence that Y has not entered the SnO2 lattice. This is clearly supported by the Raman scattering results. In all Zr-doped samples, there is a simple substitution for Sn by Zr.

Investigation of the superionic behaviour of BaF 2 ( x mol% LaF 3 ) by raman and brillouin scattering and molecular dynamics simulations

High temperature Raman and Brillouin light scattering experiments have been combined with molecular dynamics simulations to provide a comprehensive study of the superionic state of BaF 2 ( x v mol% LaF 3 ) over a particularly wide range of LaF 3 dopant concentrations from x =0 to 50. Room temperature Raman spectra for x =0, 5 and 10 show the usual T 2g symmetry mode at 241 v cm m 1 , but for samples with x =20, 30 and 50 the dominant Raman mode is at higher frequencies and of E g symmetry. The temperature dependence of the Raman line-widths show initial near linear increases followed by substantial increases above temperatures ( T c ) at 1200, 850, 800, 975, 950 and 920 v K for x =0, 5, 10, 20, 30 and 50. In the Brillouin scattering experiments, the acoustic modes respectively related to elastic constants C 11 and C 44 initially showed a quasi-linear decrease in frequency with increasing temperature. Above the same characteristic values of T c , where the Raman line-widths show marked increases, there are substantial decreases in the elastic constant C 11 for all samples with x =0 to 50. Only the doped samples showed significant decreases in C 44 at corresponding values of T c . Molecular dynamics (MD) simulations have been carried out on the same systems. From the calculated mean square displacements, the diffusion coefficients ( D ) of the mobile fluorine ions were calculated as a function of temperature for each of the samples. Substantial increases in the values of D occur above the respective values of T c determined in the light scattering experiments. The MD simulations also provide details of the mechanisms of diffusion of the mobile fluorine ions. The results emphasize the role of motional effects as an explanation of the mechanisms responsible and provide a self-consistent explanation of the dominant processes in the superionic phase of doped fluorites.