S.R. Naidoo

Quantitative trace hydrogen distributions in natural diamond using 3D-micro-ERDA microscopy

Abstract A 3-D quantitative microscopy for minor distributions of surface and near-surface bulk hydrogen in solid samples has been developed. The technique employs a 15 MeV Si 7+ microbeam and a two-dimensional position sensitive detector (2D PSD) with event reconstruction in an Elastic Recoil Detection Analysis (ERDA) geometry. Lateral resolutions of 10 μm and depth resolutions of 300 A at an MDL of 100 ppm are currently possible. The technique is quantitative due to the use of an internal implanted spot standard or by cross calibration to an H implanted reference sample using RBS as a normalisation transfer. Hydrogen content and configuration in diamond illuminates the genesis mechanism and environment. A hydrogen rich diamond exhibiting zoned cloud-like ensembles of micro-inclusions as well as smaller pockets of these inclusions has been interrogated for its near-surface-bulk hydrogen distribution. The sample has also been well characterised with optical microscopies and with bulk optical spectroscopies. A striking correlation between the hydrogen distribution and the optically visible inclusion have been obtained. This is the first direct evidence for aggregations of hydrogen associated with cloudy inclusions in natural hydrogen rich diamonds.

Imaging the atomic structure and local chemistry of platelets in natural type Ia diamond

In the past decades, many efforts have been devoted to characterizing {001} platelet defects in type Ia diamond. It is known that N is concentrated at the defect core. However, an accurate description of the atomic structure of the defect and the role that N plays in it is still unknown. Here, by using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy we have determined the atomic arrangement within platelet defects in a natural type Ia diamond and matched it to a prevalent theoretical model. The platelet has an anisotropic atomic structure with a zigzag ordering of defect pairs along the defect line. The electron energy-loss near-edge fine structure of both carbon K- and nitrogen K-edges obtained from the platelet core is consistent with a trigonal bonding arrangement at interstitial sites. The experimental observations support an interstitial aggregate mode of formation for platelet defects in natural diamond.The accurate structure of the platelet defects in diamond is now resolved by transmission electron microscopy, and, out of all the proposed models, it agrees well with the zigzag atomic model.

Raman studies on the effect of multiple-energy ion implantation on single-crystal hexagonal boron nitride

Single energy ion implantation of hexagonal boron nitride (h-BN) at various fluences and keV energies has shown that there is a change in the local symmetry of the crystal from hexagonal to the cubic (c-BN) symmetry. These conclusions have been primarily based on Raman scattering (RS) and Fourier transform infrared spectroscopy. Transmission electron microscopy (TEM) analyses have been a challenge because the sample preparation for cross-sectional study of both the polycrystalline substrates and single-crystal material used in the study presented problems that were difficult to circumvent. A multiple-energy implant with different fluence fractions has been used to create a uniform implanted layer in the material from the surface to the end of range of the implant in this study. We report on the initial RS studies on these samples.

Range parameters of aluminium implants in medium and heavy mass metals

Abstract Nuclear reaction analysis was used to determine the range profiles of 150 keV aluminium ions implanted into a variety of metal targets in the atomic number region of 23⩽Z 2 ⩽78 . Implantations were performed at room temperature with fluences of 5×10 16 Al+ cm−2 and dose rates below 1013 Al+ cm−2 s−1 to prevent excessive target heating. Profiles were determined by detecting the 10.76 MeV photons from the 27Al(p,γ)28Si resonance reaction at 992 keV as a function of proton energy. Range profiles were extracted from the excitation curve after correcting for proton straggling. The experimental profiles and range moments are compared with TRIM predictions, taking target sputtering effects into account.

Study of the diffusion behaviour of aluminium in silicon up to 900°C by nuclear reaction analysis

Abstract Diffusion behaviour of aluminium in silicon at temperatures up to T=900°C was investigated by nuclear reaction analysis (NRA). Previously published results predict diffusion coefficients ranging from 3×10−15 to 1.3×10 −13 cm 2 s −1 at T=900°C. In a first series aluminium films were vapour deposited onto Si 〈1 0 0〉 substrates, followed by isochronal annealing. The diffusion coefficient was found to be less than 10 −15 cm 2 s −1 at 900°C. In a second series Si 〈1 0 0〉 and Si 〈1 1 1〉 samples were implanted at room temperature and at 250°C with a fluence of 5×1016 Al+ cm−2. For the samples implanted at 250°C and subsequently annealed at 900°C, the diffusion coefficient was again found to be less than 10 −15 cm 2 s −1 , while diffusion coefficients of the order of 10 −13 cm 2 s −1 were observed for the room-temperature implanted samples. Channeling analyses revealed extensive radiation damage in the latter samples, which was still present after annealing for 1 h at 900°C. In contrast to this, the samples implanted at 250°C were virtually defect-free. From this it is concluded that the high values observed for the room-temperature implants are due to defect-assisted diffusion.