Diamond and Nanodiamonds

In general, C-C bonding involves only the valence electrons. A brief recap of chemistry courses would be useful to the further discussion. The valence electrons of carbon atoms fill in the 2s and 2p orbitals, which represent electron distribution in 3D space as the square of amplitude of their wave function (Fig. 4.1). 

As the valence electrons s and p are not equivalent to one another, a molecule that is nonsymmetrical and energetically disadvantaged would result if the electrons fill their nonequivalent orbitals. Hence, one of the 2s electrons is promoted to the 2p level, which results in four half-filled atomic orbitals. The s orbital combines 

Varin et at., Nanomaterials for Solid State Hydrogen Storage, 

Each lobe of the sp orbital containing one-electron overlap head-on carbon atoms and translational repetition of this tetragonal C-C cluster makes diamond. The three tetrahedral arms of orbital can also be terminated by hydrogen atoms that overlap head-on. If terminated by hydrogen, the tetrahedral C-H cluster makes the CH molecule of gas methane (Fig. 4.4). 

Like a single carbon atom capped with tetrahedrically coordinated hydrogen atoms, Fig. 4.4, a cluster of sp -bonded carbon atoms can also be capped with hydrogen to form hydrogenated fragments of a diamond structure diamondoids. 

---

Figure 5.26 Comparison of surface band structures for bulk diamond and nanodiamond. The extra levels result from additional surface states (refer to the text). For...

A pure form of sp3 hybridized carbon is known as diamond and this may also be synthesized at the nanoscale via detonation processing. Depending on their sizes, these are classified as nanocrystalline diamond (10 nm 100 nm), ultrananocrystalline diamond (< 10 nm) and diamondoids (hydrogenated molecules, 1 nm-2 nm). Nanodiamond exhibits low electron mobility, high thermal conductivity and its transparency allows spectro-electrochemistry [20,21]. However, ultrananocrystalline diamond exhibits poor electron mobility, poor thermal conductivity and redox activity [21,22]. 

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

Schranda AM, Daia L, Schlager JJ et al (2007) Differential biocompatibUity of carbon nanotubes and nanodiamonds. Diamond Relat Mater 16(12) 2118-2123... 

Diamond, especially micro- and nanodiamond, is a widely occurring mineral and is probably one of the most abundant forms of carbon in the Galaxy (Alexander, 2001 Allamandola et al, 1993). As such, its geochemistry has implications... 

Particulate nanodiamond, nanocrystalline diamond and nanostructured diamond-like carbon for orthopedic medical applications... 

A. Krueger, and T. Boedeker, Deagglomeration andfimctionahsation of detonation nanodiamond with long alkyl chains. Diamond and Related Materials, 17 (7-10), 1367-1370, 2008. 

H.A. Girard, J.C. Arnault S. Perruchas, S. Saada, T. Gacoin, J.-P. Boilot, et al.. Hydrogenation of nanodiamonds using MPCVD A new route toward organic functionalization. Diamond and Related Materials, 19 (7-9), 1117-1123, 2010. 

Barnard, A.S., Rnsso, S.P., Snook, I.K., 2003, Coexistence of bucky diamond with nanodiamond and fiiUerene carbon phases, Phys. Rev. B 68,073406. 

Here, UV Raman spectroscopy is chosen in order to give a better Raman signal of diamond and to confirm its presence in the centre of the nanoparticles. As first shown by Sun et ai, the spectrum of nanodiamond excited by a visible radiation contains a luminescent background which should be removed [53]. Mykhaylyk et al. recently compared spectra obtained at 633, 488 and 244 nm (Figure 3.14) [16]. This comparison clearly demonstrated the advantage of using UV excitation, which also allows the intense diamond optic mode to generate in the spectrum. 

In Chapter 2, the development of composite materials based on improved nanodiamonds is reported by P. Ya Detkov, V. A. Popov, V. G. Kuhchikhin and S. I. Chukhaeva. The authors describe methods for improving the quality of diamond nanopowders obtained by detonation synthesis, as well as some commercial applications of nanodiamonds. The authors prove that the synthetic detonation diamond is a promising material that can be used in many fields. Of special interest are its applications in compos ite materials both with a metal and polymer matrix. Commercial production of ultradisperse diamonds (or nanodiamonds) has been developed, and it is synthesized on a scale sufficient for particular industries. 

Recently Butler et al. [4] reported the deposition of nanocrystalline diamond films with the conventional deposition conditions for micrometer-size polycrystalline diamond films. The substrate pretreatment by the deposition of a thin H-terminated a-C film, followed by the seeding of nanodiamond powder, increased the nucleation densities to more than 10 /cm on a Si substrate. The resultant films were grown to thicknesses ranging from 100 nm to 5 fim, and the thermal conductivity ranged from 2.5 to 12 W/cm K. 

The next point to realize is that the best emitter is a metal. Many forms of carbon initially studied are semiconductors or even insulators, including nanodiamond [8-11] and diamond-like carbon (DLC) [12-13,4]. Combine this with local field enhancement means that there is never uniform emission from a flat carbon surface, it emits from local regions of field enhancement, such as grain boundaries [8-11] or conductive tracks burnt across the film in a forming process akin to electrical breakdown [13]. Any conductive track is near-metallic and is able to form an internal tip, which provides the field enhancement within the solid state [4]. Figure 13.2 shows the equipoten-tials around an internal tip due to grain boundaries or tracks inside a less conductive region. 

The spectral features d d transform into broad peculiarity tf after diamond nanopowder Alit treatment in hydrogen. As a result, after diamond nanopowder Alit treatment, its CXa-emission band becomes similar to reference refined diamond powder (Fig. le). So far as nanodiamond powders CKa-bands investigation was carry out at minimum anode current densities (1 mA), the unrefined diamond powder surface remained chemisorbed atoms and molecules. However, owing to electron bombardment in sample emission focus, some of chemisorbed atoms disappeared. Therefore it was important to obtain CA -spectra... 

---