W.J.P. van Enckevort

Growth of {100} textured diamond films by the addition of nitrogen

Localized {100} fiber textured diamond films were grown by addition of 20–200 ppm nitrogen into the gas phase during hot‐filament chemical‐vapor deposition (CVD). Cathodoluminescence indicates the presence of the nitrogen‐vacancy system in the {100} textured diamond, whereas a blue ‘‘band A’’ luminescence is normally observed in diamond films grown without nitrogen addition. The results demonstrate that the nature of the substrates used for growth has no appreciable influence on the {100} texture, which implies that this fiber texture is obtained by competitive growth and selection of facets. The interaction of nitrogen with the {100} surface is a highly important factor in this process. Homoepitaxial growth shows that the addition of a small amount of nitrogen greatly enhances the growth rate of the {100} faces, making 〈100〉 the fastest growth direction in comparison with the 〈110〉 and 〈111〉 directions. This is attributed to breaking of a part of the dimers on the (2×1) reconstructed {100} surface by nit...

CVD diamond deposition on steel using arc-plated chromium nitride interlayers

This paper reports on hot filament CVD diamond deposition onto steel using arc-plated chromium nitride (CrN) as the interlayer. Direct deposition of diamond onto steel leads to the formation of a non-adhering layer of graphitic soot covered by poor-quality diamond. However, if arc-plated CrN coatings with a thickness of 2.5 μm are used, diamond formation takes place. Adherent and good-quality diamond coatings are obtained after several hours of deposition at a substrate temperature as low as 650 °C. Micro-Raman spectroscopy, scanning electron microscopy, X-ray diffraction and EDAX analysis have been employed to study the phases, morphology, composition, quality and residual stresses of the grown diamond layers and the modified substrate interlayers. The Scotch tape test is used to assess the adhesion of the diamond coatings.

Oxidative etching of diamond

Abstract Three different ways are used to etch diamond {001} and {111} faces by oxidative methods: gas phase etching in dry oxygen, gas phase etching in a mixture of oxygen and water vapour, and liquid etching in molten potassium nitrate. The surface topography of the etched surfaces is compared with the theoretically predicted morphology. It appears that in most cases the experimental results are in contradiction to theory. These discrepancies are explained by the reactions between the diamond surfaces and the adsorbed oxygen, which are able either to stabilise or to destabilise the surfaces. Of these three methods, etching in molten potassium nitrate was found to be the best for revealing dislocations.

CVD DIAMOND GROWTH MECHANISMS AS IDENTIFIED BY SURFACE-TOPOGRAPHY

Abstract The surface morphologies of numerous homoepitaxial, chemical-vapour-deposition-grown diamond films have been examined by phase-sensitive optical microscopy. The layers were produced by the hot filament technique as well as by the acetylene-oxygen combustion method. The {111} and {100} faces manifest themselves as F faces below the roughening temperature and grow via steps nucleated at three-dimensional diamond particles or at dislocations. The rate-determining step in {111} diamond growth is a hindered surface diffusion of the growth species towards the steps. The layer-by-layer growth on the 100 faces is discussed in terms of (2 × 1) surface reconstruction in combination with the presence of a 41 screw axis. The {113} face on flame-grown diamonds is made up of strong 〈110〉 chains of bonds which are interconnected by weak forces due to surface reconstruction. The slight curvature of this face points to an F face close to the roughening point. The {110} face is rough, i.e. K/S type, and no layer growth occurs. The different modes of crystal growth as well as local differences in step spacing are replicated as variations in the intensity of band A and 575 nm cathodoluminescence.

Impurity blocking of crystal growth: a Monte Carlo study

Abstract The well-known phenomenon of the blocking of crystal growth at low supersaturations by a low density of immobile impurities adsorbed on the crystal surface has been investigated by the Monte Carlo technique. The computer simulations were carried out for [1 0 0] steps on the (0 0 1) face of a solid-on-solid Kossel crystal covered by a square array of immobile impurities. Above and slightly below the roughening temperature, blocking of crystal growth was found to be due to the creation of an extra internal surface free energy as a result of the incorporation of impurities. Here the width of the dead supersaturation zone is inversely proportional to the squared distance between the impurities. At lower temperatures growth is blocked by pinning of the growth steps at the impurity centres as proposed in an early paper by Cabrera and Vermilyea (1958), in which the width of the “dead zone” is inversely proportional to the impurity separation. Further issues addressed to in this paper are a kinetic impurity blocking for rough faces and the blocking of step propagation by randomly deposited impurities as well as by the smallest possible impurities of one growth unit in size.

Controlled deposition of diamond from an acetylene-oxygen combustion flame

Abstract An experimental set-up for the deposition of diamond by an acetylene-oxygen combustion flame was developed in which it is possible to control the deposition temperature within 10°C during long-term experiments. This degree of accuracy is obtained by cooling the back of the substrate holder with an electronically controlled water injection system and using soldered substrates, ensuring a good thermal contact. With this set-up a large number of experiments were performed with deposition times of 1 h. Special attention was given to the growth of diamond layers with uniform thickness and morphology because these properties are considered essential for future applications. It was found that the deposition temperature, the total gas flow, the composition of the gas phase and the position of the substrate in the flame all have major influences on the deposit. Not only the growth rate and the quality of the diamond are strongly influenced by the deposition conditions, but also the preferred crystal habit and the homogeneity.

Electrical conduction in homoepitaxial, boron-doped diamond films

Epitaxial, boron-doped diamond films were grown by hot-filament-assisted chemical vapour deposition (CVD) on (100) and (110) natural diamond substrates. Resistivity measurements for 10 K<T<500 K showed a clear transition from band to hopping conduction upon lowering of temperature. In the band conduction regime, the (100) films had higher conductivity than the (110) samples. The reverse was found in the hopping regime. This is explained by the difference in crystal growth mechanisms, leading to higher boron concentrations and lower carrier mobilities for (110) samples than for (100) oriented films. Hall effect measurements were performed for the most lightly doped (100) film at a boron level of 2.7*1018 cm-3 in the band conduction region up to 750 K. A mobility maximum of mu H=590 cm2 V-1 s-1 at 295 K was found, and the compensation ratio was determined to be smaller than 0.02. Some preliminary values for the Hall effective mass of valence band holes are given.

Characterization of single-crystal diamond grown by chemical vapour deposition processes

Abstract Homoepitaxial diamond films have been deposited on natural diamond substrates by the hot-filament-assisted chemical vapour deposition technique and by the oxygen-acetylene combustion flame method. From the surface microtopographic, the fractographic and especially the spectroscopic characterization of these films it was observed that the crystallographic orientation of the substrate is an important factor for the quality of the epilayer. The incorporation of point defects such as boron, hydrogen and nitrogen is strongly dependent on both the substrate orientation and the deposition temperature. The best results were obtained for epilayers grown by the combustion flame on {100} substrates.

X-ray diffraction studies of potassium dihydrogen phosphate (KDP) crystal surfaces

We have studied the surface atomic structure of KDP crystals using X-ray scattering. These crystals were grown from an aqueous solution and we have done measurements both ex situ and in situ. The ex situ measurements were performed in vacuum or in air. In order to be able to do in situ measurements, we designed and built a crystal growth chamber which is compatible with X-ray diffraction experiments. The atomic arrangement of the two naturally existing faces of KDP has been determined. Preliminary results are presented of measurements performed during growth. Furthermore, the influence of metal impurities on the atomic structure of the growing interface is examined.

In situ observations of the growth behaviour of the {010} face of potassium hydrogen phthalate

Abstract The surface morphologies of the {010} face of potassium hydrogen phthalate crystals, growing in an aqueous solution, have been studied in situ by means of optical reflection microscopy. The observations have been recorded by means of a videosystem. Several phenomena have been investigated by this method, namely: spiral growth via high (10–250 nm) and low steps (2.8–10 nm), step acceleration near reentrant corners in step patterns, inclusion formation via step overhangs, the formation of etch pits and the reactivation of the centre of a blocked spiral.