Multiple twinning and nitrogen defect center in chemical vapor deposited homoepitaxial diamond

Homoepitaxial diamond films were grown on polished {100} faces of single crystal type IIa diamond substrates using microwave plasma assisted chemical vapor deposition system. 14 homoepitaxial diamond films were grown under a variety of substrate temperatures (1000–2000°C), methane concentration (1–6% in hydrogen gas) and processing pressure (60–200 Torr). Electron paramagnetic resonance (EPR) studies demonstrate that nitrogen is incorporated as a singly substitutional impurity (P1-defect center) and the nitrogen concentration is in the range 10–100 parts per million (ppm). The substitutional nitrogen concentration in homoepitaxial diamond was observed to decrease with increasing substrate temperature. Multitwin percentages of all grown diamonds derived from EPR spectra are correlated with the growth parameter α, which is simply the growth velocity along the 〈100〉 direction divided by the growth velocity along the 〈111〉 direction. With the aid of multitwin morphology and multitwin percentages derived from EPR, we describe conditions under which a twin-free and low defect single crystal diamond can be grown from the vapor phase on the {100} oriented substrates.     

Arrowhead-like diamond crystals formed by hot-filament chemical vapor deposition

Arrowhead-like diamond crystals have been formed by using a simple method of hot-filament-assisted chemical vapor deposition. These are contact twins with {111} as the twin plane, of which each individual is composed of {100}, {110} and {111} faces. These twins flatten along {110} face and elongate parallel to {111} contact plane. The flattened {110} face consists of many {110} terraces sided by 〈110〉 and 〈112〉 steps. So the twinned crystal looks like an arrowhead. These twins are formed just underneath the uppermost substrate temperature for diamond growth.     

A geometric model of growth for cubic crystals: Diamond

A mathematical and software implementation of a geometrical model of the morphology of growth in a cubic crystal system, such as diamond, is presented based on the relative growth velocities of four low index crystal planes: {100}, {110}, {111}, and {113}. The model starts from a seed crystal of arbitrary shape bounded by {100}, {110}, {111} and/or {113} planes, or a vicinal (off axis) surface of any of these planes. The model allows for adjustable growth rates, times, and seed crystal sizes. A second implementation of the model nucleates a twinned crystal on a {100} surface and follows the evolution of its morphology. New conditions for the stability of penetration twins on {100} and {111} surfaces in terms of the alpha, beta, and gamma growth parameters are presented.     

Growth of homoepitaxial diamond doped with nitrogen for electron emitter

Although we had reported the remarkable low threshold emission from polycrystalline diamond heavily doped with nitrogen (N) [Nature 381 (1996) 140], the problems caused by polycrystallinity still remain for understanding the electron emission mechanism. This paper describes the growth of N-doped homoepitaxial diamond film {100}, {111} and {110}, and their electron emission properties. N-doped homoepitaxial diamond is grown on synthetic diamond by hot filament chemical vapor deposition. Urea [(NH₂)₂CO] is used as a dopant for N. Atomic force microscope (AFM) observations indicate that the relatively smooth surface morphologies are obtained for all the films. The epitaxial growth of all the film is confirmed using reflective high energy electron diffraction (RHEED) patterns. Reflective electron energy loss spectra (REELS) indicate that the very surfaces of {100} and {111} are diamond while {110} is graphite rather than diamond. Raman spectra suggest that the bulk of the obtained films are diamond. The resistivities of the films are found to be much higher than the detection limit of the system. The relatively low threshold emission was observed even from the smooth surface and the threshold voltage is confirmed to depend on the crystal orientation. It is speculated from the film characterizations and the electron emission properties that the low threshold emission is due to high resistance rather than rough surface and/or grain boundaries.     

Morphology of chemical vapor deposition diamond particles grown at high temperature

{113} facets and irregular shapes of chemical vapor deposition (CVD) diamond particles are observed at high deposition temperature of 1200°C on Co base substrate. Microwave plasma CVD is used for the diamond deposition with 2 percent of methane in hydrogen under 1.2×10⁴ Pa (90 Torr). {113} facets form between {100} and {111} facets of diamond particles grown on heterogeneous substrate. This verifies that the condition for the stable {113} facet exists in CVD diamond growth. New small angle boundaries evolve on a flat surface of a growing single crystal diamond particle. Solid segments surrounded by the boundaries look like new grains, whose lattice orientations are misoriented to each other. The misorientation between the solid segments is small initially, but increases as the growth proceeds. Such evolution appears only on the upper particle surface which is parallel to the substrate surface irrespective of the facet index. The formation mechanism of the solid segments is discussed in terms of the lattice misfit within the diamond particle.     

The crystallographic relationship of heteroepitaxial diamond films on scratched silicon substrates

By using the straight hot filament chemical vapor deposition method with one falt horizonatal filament, diamond films were rapidly grown on a scratched silicon substrate. Observing two kinds of interface structures of the samples by cross-section high-resolution transmission electron microscopy, we found that diamond {111}-oriented films are epitaxially grown on β-SiC{111} planes with a tilt angle of about 7° around the common [110] axis. We also found that diamond771 planes are parallel to silicon111 planes on which diamonds are directly epitaxially grown on silicon substrate. The interface dislocations are of either 60°-type or Schockley partial dislocation in relation to our observations.     

Templated Grain Growth of Barium Titanate Single Crystals

BaTiO₃ single crystals were grown via templated grain growth (TGG), which is a process in which a single-crystal "template" is placed in contact with a sintered polycrystalline matrix and then heated to migrate the single-crystal boundary into the matrix. Millimeter-sized, stoichiometric single crystals of BaTiO₃ were produced by heating polycrystalline matrix with a relative density of 97% and a Ba/Ti ratio of <1.00, which was bonded to a BaTiO₃ single crystal, at temperatures above the eutectic temperature. Growth rates of 590–790, 180–350, and 42–59 μm/h were observed for {111}-, {100}-, and {110}-oriented single-crystal templates, respectively. Lower-surface-energy facets were formed for {111}- and {100}-oriented templates, whereas {110} crystals maintained a {110} growth front, which indicated that this plane orientation was the lowest-energy surface in this system. SrTiO₃ also was shown to be a suitable substrate for TGG of BaTiO₃.     

Growth of {111}-oriented diamond on Pt/Ir/Pt substrate deposited on sapphire

Highly 〈111〉-oriented diamond films with azimuthal alignment were successfully deposited on platinum{111}/iridium{111}/platinum{111} formed on sapphire{0001} by microwave enhanced chemical vapor deposition. With oriented nucleation density of approximately 1×10⁸ cm⁻², the heteroepitaxial {111}-oriented diamond films were grown over a 10×10 mm² area without crack or delamination from the substrate. X-Ray diffraction rocking curve of diamond{111} has a full-width at half maximum value of 1.1°, which endorses a high crystal quality of the diamond film. The high density of oriented nucleation and improved adhesion of the diamond can be attributed to the Ir film inserted between the two Pt layers, which hinders diffusion of carbon through the Pt and graphite formation at the Pt/sapphire interface.     

Effect of substrate facets on homoepitaxial growth of diamonds during plasma-assisted hot filament chemical vapor deposition

In this report, the effect of substrate facets has been investigated during homoepitaxial growths of diamonds on polyhedral diamond grains in a plasma-assisted hot filament chemical vapor deposition (HFCVD) system. Homoepitaxial diamonds grown on the (100) planes present smooth surfaces, whereas textured surfaces form on the (111) facets, which is attributed to the different growth modes corresponding to the single-crystal substrate facets. With the accretion of the methane concentration in the gas supply, a few crystallites appear on the smooth growing surfaces of the (100) facets, and a change from (111) to (100) textured surface takes place on the (111) facets, showing that the variation of plasma vapor chemistry further significantly adjusts the homoepitaxy of diamonds. Photoluminescence spectroscopy investigations reveal that the 575-nm N–V peaks of the homoepitaxial grown layers on the (100) facets are much weaker than those of the (111) facets, demonstrating that there are less vacancies in the diamonds homoepitaxially grown from the (100) facets than the (111) ones.     

Tribological behaviour of <100> and <111> fibre textured CVD diamond films under dry planar sliding contact

<100> and <111> fibre textured diamond films are grown on SSiC sliding rings by hot filament CVD and are tribologically tested in dry planar contact under ambient air.The wear of the self-mated textured diamond coating takes place initially at protruding grains of the as-deposited micro rough diamond surface. After 10 km of dry sliding against <100> textured diamond the respective counterparts with <100> and <111> textures exhibit smoothly polished diamond faces without visible surface failures. After dry sliding against <111> textured diamond as static counterpart {100} diamond faces of isolated grains show Hertzian cone cracks and propagation of cracks preferred along {111} easy cleavage planes whereas {111} diamond faces reveal no crack propagation in substrate direction.The results are visualised in a tribo map in which the linear wear of the dynamic diamond face is plotted against the mean coefficient of friction. The best tribological behaviour in terms of low friction and little diamond wear is achieved for sliding couples with <100> fibre texture on the rotating sliding ring and <111> fibre texture on the static ring as mating diamond faces.     

Electrocrystallization of copper on single crystal spheres—I. Morphology of the deposit

The electrodeposition of copper from an acid copper bath on single crystal copper spheres in the current density range of 1 to 20 mA/cm² results in characteristic growth structures which depend on the underlying base crystal. These growth structures are dominantly determined by a nearby principal pole representing one of the densest planes of copper, {100}, {110} and {111}. In the region of a {100} pole, the structure is one of layers with faces parallel to the {100} plane. The {110} poles are surrounded by a ridged structure and the {111} poles by triangular pyramids. Between these are transition regions of little distinguishable structure. The areas of the sphere occupied by the various structures depend upon the current density.     

Crystallographic anisotropy of growth and etch rates of CVD diamond

The investigation of orientation dependent crystal growth and etch processes can provide deep insights into the underlying mechanisms and thus helps to validate theoretical models. Here, we report on homoepitaxial diamond growth and oxygen etch experiments on polished, polycrystalline CVD diamond wafers by use of electron backscatter diffraction (EBSD) and white-light interferometry (WLI). Atomic force microscopy (AFM) was applied to provide additional atomic scale surface morphology information. The main advantage of using polycrystalline diamond substrates with almost random grain orientation is that it allows determining the orientation dependent growth (etch) rate for different orientations within one experiment. Specifically, we studied the effect of methane concentration on the diamond growth rate, using a microwave plasma CVD process. At 1% methane concentration a maximum of the growth rate near <100> and a minimum near <111> is detected. Increasing the methane concentration up to 5% shifts the maximum towards <110> while the minimum stays at <111>. Etch rate measurements in a microwave powered oxygen plasma reveal a pronounced maximum at <111>. We also made a first attempt to interpret our experimental data in terms of local micro-faceting of high-indexed planes.     

Electron microscopy of interfaces in chemical vapour deposition diamond films on silicon

The structure of interfaces in diamond films grown on Si(100) has been investigated by transmission electron microscopy for the early stages of microwave-assisted chemical vapour deposition. Using conditions optimized for achieving so-called highly-oriented diamond films the depositions were performed in two steps, a bias-enhanced nucleation step and a subsequent growth step. Characteristic for the early deposition stages is the self-organized formation of regular arrays of predominantly {111}-facetted Si substrate surface grooves and islands elongated along [1̄10] and [110] directions. Subsequently, an interlayer of nanocrystalline β-silicon carbide islands forms, followed by the formation of epitaxially oriented diamond nanocrystals with high fractions of {111} interfaces. High-resolution electron microscopy of the interface regions depicts arrays of terminating {111} diamond planes at an average ratio of five diamond to four SiC lattice planes which corresponds to a remaining lattice mismatch of 2.3%. The orientation relationships between the lattices may be described by a coincidence site lattice model if the elastic lattice distortions are taken into account. Only small fractions of amorphous inclusions are present near interfaces, essentially consisting of amorphous carbon as could be deduced from analyses of the C K edge fine structure in electron energy loss spectra. The observations are compared with cases for which diamond nucleation directly on silicon has been obtained.     

Phonon-assisted electronic transitions in phosphorus-doped n-type chemical vapor deposition diamond films

One year ago we published the first results on the electronic structure of the P-level in 1000 ppm PH₃/CH₄ doped {111}-oriented n-type diamond films, using the quasi-steady-state photocurrent technique (PC) and photothermal ionization spectroscopy (PTIS). In this work we have extended our measurements at various temperatures (4.2–77.4 K) to samples with various doping levels (100, 500 and 1000 ppm PH₃/CH₄). This allowed us to obtain more precise results for the electronic structure of the phosphorus defect in homoepitaxial n-type CVD diamond films, making use of the 155 meV LO-phonon to explain the oscillatory photoconductivity. These results are confirmed by the PTIS maxima and Fourier transform infra-red (FTIR) data. In addition we present first measurements on a 2000-ppm doped {100}-oriented sample.     

Diamond films grown by a 60-kW microwave plasma chemical vapor deposition system

In order to use chemical vapor deposition (CVD) diamond films for electronic devices, it is necessary to establish technologies for producing diamond wafers with controlled quality. Most of existing diamond CVD systems are, however, designed primarily for laboratory use. To cross the technological gap between the commercial production and the laboratory experiments, the current CVD technologies of diamond must be scaled up and upgraded. Development of large-scale diamond deposition processes was undertaken by using a microwave plasma CVD system, equipped with a 915-MHz, 60-kW generator for generating a large-size plasma. Polycrystalline diamond films were deposited from a hydrogen/methane gas mixture with typical gas pressures and substrate temperatures of 80–120 torr and 800–1050°C, respectively. It was found that depending on the growth conditions, the deposited films have various surface morphologies. Some of the samples have well-defined {111} and {100} facets of up to tens of micrometers in size. The Raman spectra had an intense main peak due to diamond at 1333 cm⁻¹ without a trace of non-diamond carbon. The film quality in terms of Raman spectra was relatively uniform across the samples of 100 mm in diameter. Both 〈111〉 and 〈001〉 textured diamond films were obtained by selected growth conditions.     

Bi12SiO20晶体的生长习性

分别沿[001],[110]及[111]3种方向用提拉法生长Bi_(12)SiO_(20)晶体,研究了生长条件对晶体形态的影响。应用PBC理论,分析了各晶面的特性:{100}和{110}为F面,{211}为S面,{111}属于K面。并依据连接能的计算,得到晶面的重要性顺序。PBC解析形态与在特定条件下生长的晶体形态相当一致。     

Internal stresses in {111} homoepitaxial CVD diamond

Undoped and phosphorus-doped diamond thin films grown by microwave plasma-enhanced chemical vapour deposition (MPCVD) on Ib {111}-oriented diamond substrates have been studied by confocal micro-Raman spectroscopy. Thanks to the confocal optics, the Raman signal arising from the epilayer could be discriminated from that arising from the substrate. In this study, a distinct Raman peak, broader and approximately 6 cm⁻¹ lower than the optical phonon line of the substrate, was systematically detected and showed that the homoepitaxial layers were under an intense tensile stress. The magnitude of this stress increased with deposited thickness up to a few GPa. In the thicker films, a high compressive stress was also detected at the substrate near surface. Finally, it was observed that a network of oriented cracks could relieve the internal stress.     

Electrochemical grooving

The present work describes a combined micro-interferometric and electrochemical investigation of the dissolution (and growth) behaviour of gross linear defects (GLD) observed on electrolytically grown separate faces {100} and {111} of silver single crystals (the crystals have been grown in glass capillary tubes). By the microscopic investigation was found that the plane defects, which bring about the appearance of GLD lie in {111}-plane. The values found for the specific energies of the defects (15–20 erg cm^?2) and their crystallographic position characterize them as stacking faults. Grooves were formed electrochemically, by means of anodic potentiostatic pulses, on the crystal faces in the region of their intersection with the defect planes. The investigation of the electrochemical grooving kinetics shows that it occurs by Ohmically controlled direct transport.     

Investigation of heterostructure between diamond and iridium on sapphire

Diamond thin film has outstanding physical and chemical properties. Diamond-on-iridium configurations have been prepared by several methods, such as microwave enhanced plasma CVD, direct currency plasma CVD, and hot filament CVD. In this study, an Ir interlayer was deposited on single crystal sapphires (Al₂O₃) with A-planes {1120} by an RF magnetron sputtering method after annealing samples. In addition, a diamond thin film was deposited by a microwave enhanced plasma chemical vapor deposition (MPCVD) method using a mixture of hydrogen and methane gases after a bias enhanced nucleation (BEN) procedure.Ir (001) was grown on the A-plane of sapphire by X-ray pole figure measurement. Diamond thin films were synthesized on each Ir/sapphire substrate and characterized by SEM, Raman spectroscopy. D {100} faces were exhibited in substantial areas of diamond films, and a flat D {100} plane was partially obtained. It is considered that diamond thin films on Ir {100} were mainly grown towards the <100> direction and were epitaxially grown in part.     

Habit Modifications of SnO2 Crystals in SnO2–Cu2O Flux System in the Presence of Trivalent Impurity Cations

SnO₂ single crystals have short prismatic habits bounded by well-developed {110} and {111} faces in a pure SnO₂–Cu₂O flux system. When trivalent cations are added to the system, the habits drastically change to needle, acicular, or whisker forms with large aspect ratios. The addition of trivalent cations also greatly increases the nucleation rate and drastically decreases the crystal size. SEM observations and EPMA investigations reveal that the flat {111} faces transform to rounded or rough { hkl } faces by the addition of trivalent cations. This roughening transition of {111} faces, keeping {110} faces unchanged, is the cause of drastic habit modification that is attributed to the breaking of the periodic bond chain in {111} faces by impurity cations.