Calculation of the temperature distribution at the HPHT growing of diamond single crystals in cells with two growth layers

Finite element method was used to calculate the distribution of temperatures in growth cells of the toroid TC-40 -type HPA. The experimental investigations of the process of growing type IIa diamond single crystals were performed in high-pressure cells with two growth layers. It is shown that in using the cell materials having appropriate properties and defined configuration of the system of the resistive heating the temperature gradients are 5.4–5.6°C/mm and the growth rate is 2.46 mg/h. The total weight of obtained structurally perfect type IIa diamond single crystals in the upper and lower growth layers is 1.18 and 1.13 carats, respectively, the nitrogen content in all grown crystals is 1–3 ppt.     

Effect of synthesis conditions on the impurity composition of STM Almazot diamond single crystals

Diamond single crystals synthesized under various conditions have been characterized by absorption spectroscopy and electron paramagnetic resonance. The results demonstrate that preannealing of the reaction cell materials in an argon-hydrogen mixture and the use of a metal-carbon system containing 3 wt % aluminum allow the concentration of process-related impurities in the single crystals to be reduced. The growing crystal captures more impurities in the initial stages of the process, so the impurities are concentrated in the central part of the crystal, near the seed. The concentration of the process-related impurities near the corners of the crystal is substantially lower.     

大尺寸掺硼宝石级金刚石单晶的高温高压合成及电学性质研究

在5.4GPa、1200～1400℃条件下,进行掺硼金刚石单晶的合成研究。成功合成出了重0.2g,径向尺寸达6.0mm的优质掺硼金刚石单晶。考察了合成体系中硼添加量对晶体透光度的影响。利用伏安特性和霍尔测试,得到了掺硼金刚石单晶常温电阻率、霍尔系数及霍尔迁移率和合成体系中硼添加量的关系。研究发现,随着合成体系中硼添加量的增加,晶体的电阻率和霍尔迁移率都呈下降趋势;霍尔系数随硼添加量的增加先下降后上升。随着硼添加量的增加:晶体常温电阻率下降,表明硼杂质已进入到金刚石晶体中。霍尔迁移率的下降,可能是晶体缺陷增多对载流子散射所致。霍尔系数先减小后增大,这可能与进入金刚石的硼元素量增大及晶体缺陷增多有关。     

Knoop hardness studies on anthracene single crystals

Knoop microhardness studies were carried out on anthracene single crystals. The hardness vs load plot shows two peaks, one at 5g and another at 17·5 g having hardness values 13·0 kg/mm² and 11·4 kg/mm² respectively. The present observation shows that the dislocations split into partials.     

Morphology and spectral characteristics of octahedral diamond crystals from Yubileinaya diamond pipe (Yakutiya)

An attempt has been made to explain the relation between the morphological characteristics of diamond crystals and the nitrogen concentration in them using a new method of analyzing spectra, which after the spectra decompose makes it possible to calculate nitrogen concentrations in the A-, B1-, C-, B2-defects in order to define the genetic reasons for the diamond crystal formation.     

Distribution of nitrogen-related defects in diamond single crystals grown under nonisothermal conditions

Experimental data are presented on the distribution of nitrogen-related defects in synthetic diamond single crystals grown by the temperature-gradient method in the Fe-Ni-C system at p = 6.0 GPa and a temperature varied stepwise in the range 1370 to 1550°C. The sectorial and zonal structures of plates cut from the crystals are investigated, and the concentration profiles of C, A, and N⁺ centers are obtained using Fourier transform IR spectroscopy. The zonal and sectorial variations in the concentrations of nitrogen centers and total nitrogen are analyzed. The total nitrogen concentration in the structure of diamond is shown to increase by 50–60 ppm as the temperature is lowered by 100°C. The conclusion is drawn that, at a constant composition of the system, the temperature (as well as its variation with time) plays a key role in determining the rate of nitrogen incorporation into the structure of diamond and subsequent transformations of nitrogen-related defects.     

Contact electrization of natural diamond crystals

The triboelectric charging of natural diamond crystals as a result of the contact electrization on a metal surface has been experimentally studied. It is established that the contact electrization of diamond crystals is related to the accumulation of a positive charge due to the filling of hole traps with an activation energy of 1.1–2.17 eV. A physical model is proposed to describe this process.     

Investigation on defects in HPHT-grown diamond single crystals

In the diamond single crystals synthesized at high temperature and high pressure using FeNi as catalyst, there are usually supersaturated vacancies and inclusions formed during the diamond crystal growth and rapid cooling from high temperature. Some defects such as prismatic dislocation loops, stacking faults and array of dislocations are closely related to such supersaturated vacancies and inclusions. The supersaturated vacancies agglomerate into discs on the (111) close-packed planes, subsequent collapse of the discs forms the dislocation loops and stacking faults. The thermal internal stresses, which are caused by the difference of thermal contraction between the diamond and the inclusions due to the difference of thermal coefficients between them as the diamond is cooled from high temperature, may be relieved by the formation of array of dislocations. In the present paper, these defects in the diamond single crystals were directly examined by transmission electron microscopy (TEM). The characteristics and formation process of these defects were analyzed briefly.     

Knoop hardness anisotropy in anthracene and phenanthrene single crystals

Microhardness anisotropy in single crystals of anthracene and phenanthrene has been observed by the Knoop indentation technique. The Knoop hardness variation with respect to the [010] direction shows opposite trends. Both these crystals have the same crystal structure and space group. The present observations are explained in terms of orientation and disposition of molecules in the unit cells.     

Systematic hardness measurements on single crystals and polycrystalline blanks of cesium halides

Vickers and knoop hardness measurements were carried out on CsBr and CsI single crystals. Polycrystalline blanks of CsCl,CsBr and CsI were prepared by melting and characterized by X-ray diffraction. Vickers hardness measurements were carried out on these blanks. The hardness values were correlated with the lattice constant and the Schottky defect formation energy.     

Vickers microindentation hardness studies of β-Sn single crystals

The Vickers microindentation hardness anisotropy profile and load dependence of apparent hardness of white tin (β-Sn) single crystals having different growth directions were investigated. Indentation experiments were carried out on the (001) crystallographic plane at indentation test loads ranging from 10 to 50 mN. Examinations reveal that the degree of the hardness anisotropy decreases with increasing indentation test load. Also, the materials examined exhibit significant peak load dependence (i.e., indentation size effect (ISE)). The traditional Meyer's law, proportional specimen resistance (PSR) model and modified PSR (MPSR) model, were used to analyze the load dependence of the hardness. While Meyer's law can not provide any useful information about the observed ISE, the load-independent hardness (i.e., H_PSR and H_MPSR) values can be estimated for different crystallographic directions, using the PSR and MPSR models. Briefly, for microindentation hardness determinations of β-Sn single crystals, the MPSR model is found to be more effective than the PSR model.     

Special features of growing diamond single crystals in the Fe-Co-Zr-C system

The results have been considered of the investigations into the effect of various concentrations of zirconium addition to the Fe-Co alloy solvent on the growth rate and habit of a diamond single crystal grown by the temperature gradient method in the diamond thermodynamic stability region. The dependence of the defect and impurity state of grown crystals on the percentage of the zirconium addition has been established. The maximum zirconium content and temperature of the alloy solvent, which provide the growth of structurally perfect type IIa diamond single crystals, have been defined.     

Boron-doped diamond single crystals for probes of the high-vacuum tunneling microscopy

The results of studying the structure of diamond single crystals grown by the temperature gradient method with the aim to obtain samples having maximum uniform characteristics for manufacturing probes for scanning electron microscopes with a specified axial orientation and controlled distribution of the dopant have been considered. It has been shown that the use of similar probes in scanning tunneling microscopy decreases the probability of incidental tunneling channels with participation of the surface states caused by the presence of boron atoms in the diamond structure and increases the reliability of experimental data. The high stability of monocrystalline diamond probes and the possibility to attain the atomic resolution with the help of them have been demonstrated by the investigations of the (0001) graphite plane using scanning tunneling microscopy.     

Extracting uniaxial responses of single crystals from sharp and spherical hardness measurements

This investigation provides a mechanistic background to mechanical property extractions performed from single-crystal microhardness measurements. The analysis concerns both spherical and sharp (pyramidal) indentations. We show that the uniaxial stress–strain curves inferred from hardness measurements in single crystalline units of material are coincidental with those attained under true uniaxial loadings along specific crystalline orientations. Landmark hardness relations that were originally developed for power-law strain hardening polycrystalline aggregates are extended to single-crystal indentations. Mechanical property extractions in crystals violating power-law hardening because of a marked critical resolved shear stress and/or extreme strain hardening saturation are subsequently addressed. The analysis is pertinent to the assessment of multiple-glide deformation stage-II and strain hardening saturation stage-III of cubic single crystals from indentation experiments.     

Influence of material swelling on surface roughness in diamond turning of single crystals

Abstract

The effect of material swelling on the surface roughness in ultraprecision diamond turning has been investigated. Experimental results from the power spectrum analysis indicate that the profile of the tool marks is distorted by the effect of swelling of the materials being cut. A good correlation exists between the surface roughness and the amount of swelling that has occurred in the machined layer. Radically different surface roughness profiles were obtained when machining aluminium and copper single crystals with the same cutting plane and tool shape. The difference in the machining behaviour could not be accounted for by elastic recovery alone but could be explained by considering the plastic deformation induced in the machined layer.     

Anisotropy of surface roughness in diamond turning of brittle single crystals

This paper deals with an investigation of the effect of crystallographic orientation and process parameters on the surface roughness of brittle silicon single crystals in ultraprecision diamond turning. The process parameters involve the depth of cut, feed rate, and spindle speed. Experimental results indicate that anisotropy in surface finish occurs when the cutting direction relative to the crystal orientation varies. There exists a periodic variation of surface roughness per workpiece revolution, which is closely related to the crystallographic orientation of the crystals being cut. Such an anisotropy of surface roughness can be minimized with an appropriate selection of the feed rate, spindle speed, and depth of cut. The findings provide a means for the optimization of the surface quality in diamond turning of brittle silicon single crystals.     

Defect-and-impurity state of type Ib diamond single crystals of cubic habit

Type Ib diamond single crystals of size to 5–6 mm and to 2.4 carats in weight have been grown at high pressures and temperatures. The defect-and-impurity state and dislocation structures of these crystals have been studied using the IR and optical microscopies as well as the method of the selective etching. To produce type Ib crystals of cubic habit has been made possible by the minimization of the growing temperature. Defect regions in the form of a cone with the basis 0.2–1.8 mm in diameter and 0.5–2.5 mm in height are contained by these crystals. The study of the cone-shaped defect regions using the selective etching showed that at the exposure on the faces the etching pits are of the tetragonal shape and the dislocation density in them exceeds the density of dislocations in crystals that were grown under the usual conditions by 70 to 100 times. The observed defect regions are formed in the course of the diamond crystals growth as the temperature decreases by ~ 30–35°C at the crystallization front because of the increasing heat sink in the direction of a seed crystal.