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Diamond Morphology
Published in Mark A. Prelas, Galina Popovici, Louis K. Bigelow, Handbook of Industrial Diamonds and Diamond Films, 2018
Morphology as used in this chapter is defined as the internal and external form and structure of a diamond material, either a single crystal or polycrystalline assembly. Morphology is discussed in relation to the processes that created it. The morphology of diamond, natural or man-made, is a consequence of the basic diamond cubic crystal structure and the quality and rate of crystal growth in various crystallographic directions which are, in turn, strongly influenced by the growth conditions. The morphology of diamond materials is especially important because first, so many of the mechanical, physical and chemical properties of diamond single crystals are strongly anisotropic; and second, once the diamond material is created, it is difficult or impossible to significantly modify its structure, defects or impurities by practical processesi.
Graphene
Published in Andre U. Sokolnikov, Graphene for Defense and Security, 2017
The electronic structure of carbon gives rise to its ability to bond in many different configurations and form structures with distinctly different characteristics. This is clearly manifested in diamond and graphite, which are the two most commonly observed forms of carbon. Diamond forms when the four valence electrons in a carbon atom are sp3 hybridized (i.e., all bonds shared equally among four neighboring atoms), which results in a three-dimensional 3-diamond cubic structure. Diamond is the hardest material known to humankind due to its 3D network of carbon-carbon (C – C) bonds. It is also special by the fact that it is one of the very few materials in nature that is both electrically insulating and thermally conductive. On the other hand, graphite is the sp2 hybridized form of carbon and contains only three bonds per carbon atom. The fourth valence electron is in a delocalized state, and is consequently free to float or drift among the atoms, since it is not bound to one particular atom in the structure. This creates a planar hexagonal structure (called graphene) and gives rise to the layered structure of graphite that is composed of stacked two-dimensional (2D) graphene sheets. Graphite contains strong covalent bonds between the carbon atoms within individual graphene sheets, which gives rise to its outstanding in-plane mechanical properties. However, the van der Waal’s forces between adjacent graphene sheets in the layered structure are relatively weak and, therefore, graphite is much softer than diamond. Similar to diamond, graphite (in-plane) is a good conductor of heat, however, the free electrons present in graphite also endow it with high in-plane electrical conductivity, unlike diamond. The crystal structure of diamond and graphite is depicted schematically in Fig. 3.1.
Displacement Cascades in Monocrystalline Silicon: Effects of Temperature, Strain, and PKA Energy
Published in Nuclear Technology, 2020
Yuan Zhou, Bing Chen, Hongyu He, Bo Li, Xinlin Wang
Monocrystalline silicon is arranged in diamond cubic structure, which consists of a face-centered-cubic lattice with a basis of two atoms. To reduce computational cost and avoid overlapping between displacement cascades and model boundaries, two single crystal Si samples are constructed for different PKA energies. The dimensions are about 152 × 152 × 136 Å3 and 191 × 191 × 163 Å3 for EPKA ≤2 keV and EPKA = 5 keV, respectively. Corresponding system sizes are 156 800 and 448 000 atoms. The coordinate system of cascade simulations is defined in Fig. 1. The x-, y- and z-axes are along [100], [010], and [001], respectively. The as-constructed sample is first relaxed and thermalized for 30 ps at specified temperature (T = 100, 300, 600, or 900 K) and zero pressure with the constant-pressure-temperature ensemble under three-dimensional (3-D) periodic boundary conditions. As mentioned before, four typical temperatures were chosen to explore the influence of temperature on displacement cascades. To investigate the effects of strain, a strain is applied to the sample relaxed under ambient condition. The new configuration is then subjected to extra equilibration at 300 K with constant-volume-temperature ensemble for 10 ps. Two forms of strain, uniaxial and hydrostatic strain, are studied. The magnitude of strain varies from −2% to 2% at an increment of 1%. According to previous studies, the final configurations are in elastically prestrained states.22–24
Research on controllable ozone oxidation on diamond surface
Published in Functional Diamond, 2022
Tao Qiu, Meihua Liu, Tangbangguo Zhou, Xu Lin, Bin Xu
As a typical representative of diamond cubic crystals, because of its reaction inertia, extremely high electrical insulation and high thermal conductivity, diamonds are widely used in various fields, such as machinery, materials, electronics, lubrication, coating, filling, polishing and so on [1].