R.D. Maclear

The distribution of hydrogen in polycrystalline CVD diamond

Abstract The location of the hydrogen prevalent in chemical vapor deposition (CVD) diamond has long been of much interest, not least because of the information it reveals about the H-driven growth mechanism. We have used micro-scanning elastic recoil detection analysis to map the hydrogen distribution in three dimensions in polycrystalline CVD diamond. The interface between two CVD layers, one grown with, and one grown without oxygen in the growth mixture has been studied for its hydrogen concentration. An upper limit on bulk hydrogen concentration has been determined. The possibility of hydrogen trapping in the bulk is also discussed.

Diffusion characteristics of hydrogen in diamond

Abstract Hydrogen is known to play a significant role in the growth of diamond, and has been reported to influence its electrical properties. Despite some successes made in studying hydrogen in diamond, the configuration, chemistry and behaviour are not yet well established. This work is aimed at reporting on some of the outstanding questions about hydrogen in diamond. We report on micro-scanning Heavy Ion-Elastic Recoil Detection Analysis (μHI-ERDA) measurements of hydrogen in a type IIa diamond. The diamond was subjected to various treatments. These include plasma loading of hydrogen, creation of vacancies by ion implantation and annealing. The results show no evidence of the presence of hydrogen in the diamond bulk due to plasma loading, even after the creation of vacancies followed by plasma loading of hydrogen.

Quantum diffusion of tetrahedral interstitial muonium in diamond

Abstract Transverse field muon spin rotation measurements on diamonds with deliberately prepared defects show strong temperature dependence of the spin relaxation rate of the tetrahedral interstitial muonium species, MuT. These results are explained by considering coherent tunneling, below 300 K, followed by deep trapping at the defects. Our results hence provide the first evidence of quantum diffusion of neutral MuT in diamond.

3-D-micro-ERDA microscopy of trace hydrogen distributions in diamond using a 2-D-PSD with event reconstruction

Abstract A fast-imaging technique for the total elemental hydrogen concentration distribution is described, which is helpful in the study of its chemistry and dynamics in the diamond system. The micro-scanned Heavy-Ion Elastic Recoil Detection Analysis (HI-ERDA) technique can deliver information on hydrogen distributions in three dimensions. In our system, the count rate is enhanced by use of a 2-D position and energy sensitive detector for the hydrogen recoils. Software geometry collimation and recoil energy rebinning ensure that the increased rate is in fact accompanied by an improvement in effective energy resolution. The system has been used to study the mobility and trapping behaviour of a collimated implant of hydrogen into a pre-damaged natural type IIa diamond sample as well as the mobility and trapping behaviour of collimated implants of hydrogen into diamond, which has not been pre-damaged.

The Schonland Micro-Scanning Ion Beam Analysis Facility

Abstract The Schonland Micro-Scanning Ion Beam Analysis Facility is used for interdisciplinary research, uniting physics and many other disciplines. It has a unique dual accelerator input configuration. A wide range of high energy heavy and light ions is available from an EN Tandem van de Graaff accelerator with 6.0 MV terminal voltage. Light ions at lower energy but with much increased luminosity are available from a 2.5 MV single-ended van de Graaff accelerator. The sample chamber is equipped to image radiation and particles from a wide range of ion-beam interactions with matter. These include the ion beam analytical techniques of RBS, ERDA, PIXE, NRA, SecEM and STIM. Some of these techniques have been performed tomographically or under channeling conditions. Sub- or near-micron spot sizes for many of these techniques are available. The user interface to the sample chamber is highly automated, allowing safe and friendly interaction. The OMDAQ system developed at Oxford University is dedicated to on-line acquisition and preliminary analysis of singles spectra. The Physics Analysis Workstation (PAW + +) system developed for CERN and ported to a CAMAC-PC environment manages the more sophisticated multi-parameter acquisition and post-processing.

Hydrogen mobility in diamond studies using HI-ERDA microscopy

Abstract Hydrogen plays a significant role in the growth of diamond and in the determination of its physical, electrical and optical properties. However, despite this significance, the configuration, chemistry and behaviour of hydrogen in the diamond lattice is still not very well understood. In this work, the stability of a collimated hydrogen implant distribution, as well as the intrinsic hydrogen distribution in a single crystal natural type IIa diamond are studied by imaging with the micro-scanned Heavy-Ion Elastic Recoil Detection Analysis (μHI-ERDA) technique in three dimensions. To investigate possible trapping of hydrogen at vacancies a shallow pre-damaged layer was created between the implanted hydrogen distribution and the surface by collimated bombardment of the sample with 50 keV 12C ions. No evidence of migration of the implanted or the intrinsic hydrogen to the pre-damaged region was observed even after annealing at 1473 K. The stability of the implanted hydrogen indicates the deep trapping of this species within its own implanted range distribution. The results confirm similar measurements previously performed on a natural type Ia diamond as well as on a synthetic type Ib diamond. The current sample was exceptionally pure, enabling an extension of these measurements to a situation where the intrinsic hydrogen concentration, as well as the hydrogen trapping behaviour might be expected to be different. Our results suggest complex trap configurations for hydrogen in diamond, not necessarily associated with nitrogen related defects.

Hydrogen and oxygen chemistry and dynamics in diamond studied by nuclear microscopic techniques

Abstract Hydrogen and oxygen play a significant role in the growth of diamond chemical vapour deposition (CVD), and also influence its electrical, optical and structural properties. Using the microERDA technique, trapping and diffusion of hydrogen in a range of different types of natural and synthetic diamond have been investigated under different conditions such as high dose hydrogen implants after creation of vacancies and plasma loading of hydrogen. Recently, these have been extended to include natural p-type semiconducting diamond. Resonance RBS and forward scattering in channelling transmission mode with thin diamond single crystals have been used to determine the concentration and lattice site occupancy of surface oxygen.

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.

Muonium studies of p-type semi-conducting diamond under conditions of UV-visible illumination

This work reports on the promptly forming fraction and the spin relaxation rate of the isotropic muonium (MuT) component in p-type semi-conducting diamond, measured under the condition of illumination. The data are the first such investigations for diamond. A broad band illumination with wavelengths ranging from 0.5 μm to 3 μm was obtained from a Xenon lamp. The energy of the photons was sufficient to excite electrons from the valence band to the 0.28 ppm boron impurity band (0.37 eV). The Transverse Field Muon Spin Rotation (TF-μSR) measurements were conducted as a function of temperature, ranging from 5 K to 300 K. An illumination effect at temperatures below 100 K is observed. It is not yet clear from these data whether the effect is due to Mut scattering off delocalized holes, which are removed by illumination or whether there is prompt trapping of Mut at boron impurities (passivation) which is affected by illumination.

Heavy ion and proton beams in high resolution imaging of a fungi spore specimen using STIM tomography

Abstract Scanning transmission ion microscopy (STIM) tomography as a 3-D imaging technique has been shown to have a range of applications. The energy of the transmitted ion is detected with nearly 100% efficiency as a function of position in the transverse plane. The parameters relating to transmitted ion energy loss in the sample are imaged with statistics given by the energy loss process rather than Poisson counting statistics. This enables very fast collection of a set of relatively noise-free 2-D images. Each image is collected after a small rotation of the sample, and a complete 3-D representation of the sample may be tomographically reconstructed. The small beam currents necessary mean that the technique is non-destructive. One of the fields where these non-destructive 3-D density structure maps are particularly useful is in the analysis of biological tissue. The variation of energy loss with projectile atomic number may be exploited to tune the energy loss contrast to the size and density of the sample (heavy ion STIM). This work develops this point, and applies it to the imaging of the microscopic structure of a 90 μm diameter mycorrhiza fungi spore. This specimen has been imaged non-destructively in 3-D using both a 36 MeV 12 C beam and a 2.2 MeV proton beam, both with a spatial resolution of about 1 μm. The gain in contrast in the carbon median energy loss maps was dramatic as expected. The corresponding improvement in the tomogram was found to be visible but less dramatic. The tomographic sections as well as the median energy loss maps of the vesicular-arbuscular mycorrhiza fungi spore clearly show the internal structure. Wall morphology data has relevance to germination behaviour of the spores.