No abstract

Luminescence produced by the decay of excitons bound to neutral boron acceptors in diamond is reported at higher resolution than hitherto. The line-widths of the phonon-assisted processes are consistent with the electron and hole of the bound exciton having a spatial localization within an effective Bohr radius of about 0.85 nm. New fine structure is reported in the no-phonon components of the luminescence, caused by splittings in both the ground and excited states of the localized particles.

A cathodoluminescence (CL) study of free- and bound-exciton recombination in high purity high pressure high temperature (HPHT) synthetic diamond is presented, including temperature dependence measurements of the free-exciton intensity and luminescence decaytime. The results are compared with those from device quality diamond produced using the chemical vapour deposition (CVD) process.

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Practical considerations for the detection, characterisation and analysis of sub-100nm particles in the field emission SEM have been investigated using a sample consisting of Ag nano-particles on a PZT thin film substrate.The principle for lowering beam accelerating voltage is well established and can be used to constrain the electron-sample interaction and X-ray generation to a small volume. In dense materials, interaction volumes of less than 100nm are practical at less than 5kV [1]. To achieve good lateral resolution in the FEGSEM at these voltages, the probe diameter must not significantly degrade the analytical resolution so beam current can only be increased to a point where the probe diameter is still much smaller than the feature being analysed. Furthermore, X-ray yield drops off with reduced beam voltage so there is a limit to what count rate can be generated. Therefore, high detector solid angle is an important parameter. Even with the benefit of a 30mm 2 detector, in our experiments on Ag nanoparticles we achieved count rates of typically 2-3kcps and no change in detector type or electronics would have improved the count rate achieved. An SDD or Si(Li) detector with area 10mm 2 in the same position would detect less than 1kcps.Ag nano-particles in the size range 30-80nm have been analysed (Fig. 1). It has been found that drift of the sample can be substantial and exceed the size of the particle in a time much shorter than is practicable for analysis (<<60s). Therefore we used software that effectively tracked the movement of the particles and locked the position of analysis by periodic correction of the scanning coordinates. This allowed us to collect EDS spectra from the particles as well as building up a full drift-corrected spectrum image of the sample.Monte carlo simulations at 4kV (Fig. 3) showed that substrate X-rays would be expected for a 60nm thick particle. However, even spectra collected from the 80nm particles (Fig. 2) showed a substrate contribution whereas Fig. 3 suggests this would be unlikely. We therefore used a thin film analysis method [2] to measure particle thickness and found it to be in the range 4-20nm for particles of 40-125nm diameter (Fig. 4). Although these measurements are known to slightly underestimate the true thickness, it is clear that these nano-particles have shapes closer to squashed domes rather than spheres. Clearly the visible diameter of nano-particles does not necessarily provide an accurate indication of actual particle size and whether the interaction volume will be fully contained within the particle. However, electron penetration into the substrate can be used to obtain useful information about the morphology of particles.