Three-dimensional diamond crystal

Elemental silicon does not occur free in nature rather it is found as silicon dioxide (sometimes called silica Si02) and in an enormous variety of silicate minerals. In contrast to the oxides of carbon, which are volatile molecular species held together by London forces in the solid state, Si02 forms very stable, nonvolatile, three-dimensional network crystals. One of the three crystal modifications of SiOj has a lattice that may be considered to be derived from the diamond lattice, with silicon atoms replacing carbon atoms and an oxygen atom midway between each pair of them. 

Graphite is another solid form of carbon. In contrast to the three-dimensional lattice structure of diamond, graphite has a layered structure. Each layer is strongly bound together but only weak forces exist between adjacent layers. These weak forces make the graphite crystal easy to cleave, and explain its softness and lubricating qualities. 

The total energy of the system is one of the most important results obtained from any of the calculational techniques. To study the behavior of an impurity (in a particular charge state) in a semiconductor one needs to know the total energy of many different configurations, in which the impurity is located at different sites in the host crystal. Specific sites in the diamond or zinc-blende structure have been extensively studied because of their relatively high symmetry. Figure 1 shows their location in a three-dimensional view. In Fig. 2, some sites are indicated in a (110) plane... 

Cosmic Radiation charged atomic particles originating from space Covalent Bond chemical bond in which electrons are shared between atoms Covalent Crystal crystal in which atoms are held together by covalent bonds in a rigid three-dimensional network, for example, diamond... 

Two later sections (1.6.5 and 1.6.6) look at the crystalline structures of covalently bonded species. First, extended covalent arrays are investigated, such as the structure of diamond—one of the forms of elemental carbon—where each atom forms strong covalent bonds to the surrounding atoms, forming an infinite three-dimensional network of localized bonds throughout the crystal. Second, we look at molecular crystals, which are formed from small, individual, covalently-bonded molecules. These molecules are held together in the crystal by weak forces known collectively as van der Waals forces. These forces arise due to interactions between dipole moments in the molecules. Molecules that possess a permanent dipole can interact with one another (dipole-dipole interaction) and with ions (charge-dipole interaction). Molecules that do not possess a dipole also interact with each other because transient dipoles arise due to the movement of electrons, and these in turn induce dipoles in adjacent molecules. The net result is a weak attractive force known as the London dispersion force, which falls off very quickly with distance. 

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

The different structures of the carbon allotropes lead to widely different properties. Because of its three-dimensional network of strong single bonds that tie all atoms in a crystal together, diamond is the hardest known substance. In addition to its use in jewelry, diamond is widely used industrially for the tips of saw blades... 

Nonmetals that form more than one covalent bond can give crystals based on three-dimensional frameworks such as a diamond, or they give large discrete molecules. Boron, carbon, and sulfur are interesting examples of the latter. 

The three-dimensional network structure of diamond can be considered as constructed from the linkage of nodes (C atoms) with rods (C-C bonds) in a tetrahedral pattern. From the viewpoint of crystal engineering, in a diamondoid network the node can be any group with tetrahedral connectivity, and the linking rods (or linker) can be all kinds of bonding interactions (ionic, covalent, coordination, hydrogen bond, and weak interactions) or molecular fragment. 

The four types of interaction that occur in the solid state have been shown to be dictated by a common principle. Pure covalent interaction only occurs in a few crystals, such as diamond, Si, Ge, silicon carbide and gray, or, a-Sn. However, it is the dominant interaction in most small molecules, including diatomic molecules, in which the three-dimensional distribution is easily over-... 

Covalent Solids. These are substances such as graphite, diamond, and quartz in which the atoms are bonded to nearest neighbors by covalent linkages forming a macromolecular, two- or three-dimensional network. Atoms at the surfaces and edges of such crystals may be chemically unsaturated and can thus act as centers for initiating free radical or redox reactions. 

At the top of systems proposed for processors of quantum computers, there are systems in which electronic and nuclear spins of various defects and impurities in diamond are used as stationary qubits [1,2]. Single NV-centers having electronic spin S=1 in the ground electronic state are the most promising [3]. To improve optical read-out of such spin-states, various three-dimensional nanostructures in diamond such as micro resonators, waveguides, photon-crystal structures, etc. [1,4,5] are being developed. Besides, the methods of NV-center... 

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