Bonding diamond-like carbon

Diamond is a carbon material with a specific crystallographic structure (diamond structure) and specific chemical bonding (sp bonding). Diamond-like carbon is an a-C material with mostly sp bonding that exhibits many of the desirable properties of the diamond material. The DLC material is sometimes called amorphous diamond - an oxymoron that should be avoided. 

Raman spectroscopy A nondestructive method for the study of the vibrational band structure of materials, which has been extensively used for the characterization of diamond, graphite, and diamond-like carbon. Raman spectroscopy is so far the most popular technique for identifying sp bonding in diamond and sp bonding in graphite and diamond-like carbon. 

On the other hand, in covalently bonded materials like carbon, silicon, and germanium, the formation of energy bands first involves the hybridization of the outer s- and p-orbitals to form four identical orbitals, ilnh, which form an angle of 109.5° with each other, that is, each C, Si, and Ge atom is tetrahedrally coordinated with the other C, Si, and Ge atom, respectively (Figure 1.16), resulting in a diamond-type structure. 

Carbon materials liave particular characteristics due to differences in chemical bond formation. Allotropic forms of carbon drat luive been discovered can be categorized into five types from file standpoint of the type of hybridization of the valence orbitals (1) sp -hybridization (2) sp -hybridization (3) sp-hybrid-ization (4) mixed hybridization (sp + sp ) and (5) a valance state characterized by a fractional degree of hybridization (sp , where 1 diamond-like carbon, and fullcrcnes correspond to groups (1), (3), (4), and (5), respectively. 

Ferrari, A.C. Determination of bonding in diamond-like carbon by Raman spectroscopy. Diamond Rel. Mater. 2002, 11, 1053-1061. 

Figure 11.20 shows the influence of electron beam irradiation with =100keV in a transmission electron microscope on thin film structure during 2 s of deposition. As can be seen in Figure 11.20 the electron irradiation of the film results in its amorphization, as the main maximum at d= 0.435 nm attributing to the linear chain structure disappears the film structure transforms into diamond-like carbon. This means that the electron beam excitation of carbon atoms leads to cross-linkages among carbon chains and, as a result, the transformation of sp bonds into sp" and sp" bonds takes place. 

This general scheme of surface nucleation processes, as described above, may be adequate only for nucleation on a perfect substrate. It is well known that in many important practical situations, nucleation occurs at defect sites on the substrate surface. In addition, the interactions of gas-phase species with the substrate surfece in diamond CVD may lead to surface carbon atoms of different chemical bonding states and structures, for example, sp, sp, or sp bonded carbon, amorphous carbon, diamond-like carbon or carbon in carbides. These factors further increase the difficulty in understanding surface nucleation processes of diamond in CVD. 

Channel surface passivation or modification can also be performed using sputtering. Examples include the deposition of Si02, SiC, or even diamond-like carbon (DEC), fri addition to this, sputter deposited Ta has been used to promote anodic bonding for device fabrication. 

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