Crystal Structures of Diamond

Diamond is a relatively simple substance in the sense that its structure and properties are essentially isotropic, in contrast to the pronounced anisotropy of graphite. However, unlike graphite, it has several crystalline forms and polytypes. 

Cubic and Hexagonal Diamond. Each diamond tetrahedron combines with four other tetrahedra to form strongly-bonded, three-dimensional and entirely covalent crystalline structures. Diamond has two such structures, one with a cubic symmetry (the more common and stable) and one with a hexagonal symmetry found in nature as the mineral lonsdaleite (see Sec. 2.5). 

Structure of Cubic Diamond. Cubic diamond is by far the more common structure and, in order to simplify the terminology, will be referred to as simply diamond . The covalent link between the carbon atoms of diamond is characterized by a small bond length (0.154nm) andahighbond energy of 711 kJ/mol (170 kcal/mol).l i Each diamond unit cell has eight atoms located as follows 1/8 x 8 at the corners, 1/2 x 6 at the faces and 4 inside the unit cube. Two representations of the structure are shown in Fig. 11.3, /a and (b/.PPl 

The cubic structure of diamond can be visualized as a stacking of puckered infinite layers (the 111 planes) or as a two face-centered interpenetrating cubic lattices, one with origin at 0,0,0, and the other at 1/4,1/4,1/4, with parallelaxes, as shown in Fig. 11.3(c). Thestacking sequence of the 111 pianes is ABCABC, so that every third layer is identical. 

Density of Diamond. With its fourfold coordinated tetrahedral (sp ) bonds, the diamond structure is isotropic and, except on the (111) plane, is more compact than graphite (with its sp anisotropic structure and wide interlayer spacing). Consequently diamond has higher density than graphite (3.515 g/cm vs. 2.26 g/cm.  

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Silicon has the crystal structure of diamond and its properties are influenced by the crystal orientation. ] CVD silicon can be... 

Fig. 4.3 (a) Crystal structure of diamond and (b) the smallest nanodiamond adamantine... 

Figure 9.1. Crystal structure of diamond, (a) Three-dimensional representation ...

The element carbon occurs in nature in two so-called allotropic forms, different crystal structures with the same chemical formula. In Fig. 3.13 the crystal structure of diamond and graphite have been represented. In diamond the C atoms are closely packed and each C atom is linked with four other C atoms. Thus a tight network of atoms is formed which, together with the binding strength, is responsible for the extreme hardness of diamond. Graphite has a layered structure and the space between the layers is relatively large. 

The crystal structure of diamond. Each carbon atom is covalently bonded to four others. 

Figure 2. Idealized crystal structures of diamond and graphite...

Can these large variations in stiffness be explained in terms of the stiffness of the chemical bonds within a material Qualit tatively, they can, although it is not just the stiffness of the individual bonds that is important, but how they are arranged. Take a diamond, for example. In the crystal structure of diamond each carbon atom is covalently bonded to four other carbon atoms, as illustrated for the central carbon atom in Figure 13-22 (some bonds on the other atoms are omitted for clarity of presentation). The... 

The crystal structure of diamond combined with the strong interatomic chemical bonding accounts for most of its unique properties. Although the properties of CVD diamond are slightly inferior to those of natural single crystal diamond (due to the presence of nondiamond... 

Table E.l. Crystal structures of diamond and substrate materials for heteroepitaxial diamond growth (data taken from Ref. [205]).

FIGURE 1.7. The crystal structure of diamond. Stereoview showing several unit cells. Each carbon atom is tetrahedrally surroimded by four others. The arrangement of carbon atoms found in cyclohexane and in tetramethylmethane (shown with black bonds) can also be picked out from this rigid structure,... 

The earliest demonstration of the regular tetrahedral arrangement of carbon bonds was provided by the analysis of the crystal structure of diamond. In this crystal... 

By making an updated and systematic review of diamond CVD processes, the objective of this book is to familiarize the reader with the scientific and engineering aspects of diamond CVD, and to provide experienced researchers, scientists, and engineers in academic and industry community with the latest developments in this growing field. The scope of the present book encompasses the development and applications of diamond CVD, starting with a brief description of atomic and crystal structures of diamond and a review of the various processing techniques used in diamond CVD. It is followed by an extensive discussion of fundamental phenomena, principles and processes involved in diamond CVD, with emphasis on the... 

But, just as among the compounds of carbon, one can find among the minerals instances in which the skeleton is tightly cross-linked. Compare, for example, the crystal structure of diamond with that of cristobalite, one of the many structures adopted by silicon dioxide, whose more usual structure is quartz. As Fig. 9.10 shows, the silicon atoms occupy sites that form a diamondlike structure opened out by the bridging oxygen atoms. 

FIGURE 8.11 Crystal structures of diamond-type monophosphides (a) AlP, (b) BN, (c) ZnSiP and (d) diamond (or Si). All atoms are tetrahedrally coordinated. 

Figure 39.1 The crystal structure of diamond. The C-C distance is 1.54 A. The edge of the unit cell is 3.57 A.

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