Long-Wei Yin

Transmission electron microscopic study of some inclusions in synthetic diamond crystals

Abstract Diamonds synthesized under a high temperature of 1570 K and a high pressure of 5.5 GPa in the presence of FeNi catalyst contain inclusions related to the graphite and the metallic catalyst. Several kinds of inclusions contained in the synthetic diamond were for the first time successfully identified by transmission electron microscopy (TEM). The inclusions trapped in the diamond crystals consist of amorphous graphite, face-centered cubic SiC and face-centered cubic (FeNi) 23 C 6 .

Observation of etch pits and defects in diamond single crystals prepared under high temperature–high pressure

Abstract As-grown diamond single crystals synthesized under high temperature–high pressure in the presence of FeNi catalyst were directly observed by scanning electron microscopy and transmission electron microscopy (TEM). Etch pits on the (1xa01xa01) surface of the diamond, which are generated by the screw dislocations meeting the diamond (1xa01xa01) surface at the points of emergence of dislocations, can be revealed by electrolytic etching and be used to study the motion of dislocations under the action of applied stress. Stacking-fault tetrahedral and stacking faults were investigated by moire images. The stacking-fault tetrahedral and stacking faults may be derived from supersaturated vacancies generated during rapid cooling from high temperature to room temperature. Dislocation networks and an array of parallel dislocations were directly examined by TEM, which are related to the thermal stress caused by the inclusions in the diamond.

TEM Investigation on Micro-Inclusions and Dislocations in a HPHT-Grown Diamond Single Crystal from Ni-C System

In this paper, microstructures of diamond single crystal grown from Ni-C system under high temperature and high pressure (HPHT) were examined by transmission electron microscopy (TEM). It was shown that there exist growth defects such as micro-inclusions, dislocation networks, an array of dislocations and dislocation pileup in the diamond. The formation process and characteristics of these defects were analyzed briefly. The micro-inclusions are composed of hexagonal Ni 3 C, hexagonal SiO 2 and amorphous graphite, which may be derived from the starting materials and the medium (pyrophyllite) for transmitting the pressure. The dislocations are related to internal stress in the diamond, which may be correlative with the micro-inclusions in the diamond.

Defect formation in diamond single crystals grown from the Fe-Ni-C system at high temperature and high pressure

Some defects were formed in diamond single crystals grown from an Fe-Ni-C system at high temperature high pressure (HPHT). These defects were successfully examined by transmission electron microscopy (TEM) and a kind of indirect lattice image called moire fringe. These defects are mainly composed of vacancy-type prismatic dislocation loops, stacking-fault tetrahedra, an array of parallel dislocation lines, and dislocation networks. The formation process of these defects was analyzed briefly. It was suggested that these defects in the diamond crystal were derived from vacancies and inclusions, which were contained in the diamond single crystal during the diamond synthesis at high temperature and high pressure.

Inclusions related to catalyst and medium for transmitting pressure in diamond single crystals grown at high temperature and high pressure from the Fe-C system

Inclusion entrapment in a crystal is one of the most important characteristics for the crystal growth technique from solution. Diamond single crystals grown from the Fe-C system at high temperature-high pressure usually contain inclusions related to the molten catalyst and the medium (pyrophyllite) for transmitting pressure. During the growth of the diamond, the inclusions are trapped by the growth front or are formed through reaction between the contaminants trapped in the diamond. In the present article, the inclusions related to the catalyst and pyrophyllite were systemically examined by transmission electron microscopy. The chemical composition and crystal structure of the inclusions were, for the first time, determined by selected area electron diffraction pattern combined with energy dispersive x-ray spectrometry. It was shown that the inclusions are mainly composed of orthorhombic Fe3C, orthorhombic FeSi2, hexagonal SiO2 and face-centred cubic SiC.

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.