Structure of Nanodiamonds

Yushin GN, Osswald S, PadaUco VI, Bogatyieva GP et al (2005) Effect of sintering on structure of nanodiamond. Diamond Related Mater 14(10) 1721-1729 Osswald S, Gurga A, Kellogg F, Cho K et al (2007) Plasma pressure compaction of nanodiamond. Diamond Related Mater 16(11) 1967-1973... 

As mentioned in Section 5.2 on the structure of nanodiamonds, they possess certain, but not very large number of unsaturated bonds owing to the saturation of free valencies by n-bond formation. The residual radical centers are normally surrounded by sp -structures, so eventual reagents caimot access them freely. Hence this approach to surface functionalization does not bear the desired results. 

Regarding the structure of nanodiamond, a distinction has to be made between the diamond core that usually features a cubic lattice and, on the other hand, the surface. Depending on particle size, the portion of surface atoms may amount to as much as 50%. Generally the surface structure plays a major role for the material properties observed. At particle dimensions of more than 2nm, the bandgap of nanodiamond corresponds to that of macroscopic diamond. Quantum effects are not observed, but there are interband states that can be attributed to partial surface graphitization and lattice defects, respectively. 

Fang, X., Mao, J., Levin, E.M., and Schmidt-Rohr, K. Nonaromatic core shell structure of nanodiamond from solid-state NMR spectroscopy. 2009 131 1426-1435. 

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

ATOMIC AND SPIN STRUCTURE OF SINGLE NV -CENTERS NEAR NANODIAMOND SURFACE... 

C MAS-NMR spectroscopy was used to quantify the different carbon species in synthetically produced nanodiamonds.430 A 13C study has been reported to study the modification of the electronic properties of SWCNT by alkali intercalation.431,432 13C MAS-NMR data were used to study the structure of 13C-enriched SWCNT, prepared by catalytic decomposition of CH4.433 H, 13C and 15N MAS-NMR spectra of amorphous carbon nitride (a-CNx) films were consistent with sp2 hybridised nitrogen atoms in an aromatic carbon... 

However, the particles small dimensions give rise to one of the characteristic structural features of nanodiamond The large portion of surface atoms causes strain within the particles that shows in an altered bonding situation close to the surface. In NMR-examinations, for instance, the carbon atoms on the surface exhibit another chemical shift than those situated in the core of the particle. This is due to the attachment of functional groups or due to sp -hybridized atoms arising from a reconstruction of the surface (Section 5.2.2). 

Examining the electronic properties of nanodiamond turns out to be rather complicated by the variable sample quality and the associated differences in the electronic structure, so in this chapter, just some important aspects of electronic properties and structure will be discussed. For a more detailed presentation refer to the respective original literature given in the appendix. 

The electronic structure of a nanodiamond sample may be examined by various spectroscopic techniques. Depending on the choice of method, the information obtained from doing so corresponds to different depths of the lattice. The Auger spectroscopy, for instance, has a low penetration depth, so it may serve to determine the situation of n-electrons on the surface. In the Cls-loss spectrum, on the other hand (Section 5.4.1.3), no 7i-transitions are observed as this method chiefly yields information on the second to seventh layer of atoms below the surface. 

In comparison to bulk diamond, nanodiamond particles are distinctly more reactive. This may be explained by the larger number of defects and by a markedly enlarged surface. Both effects increase the number of potential sites for the attack of a reagent, thus facihtating chemical modifications of nanodiamond particles. These include not only a functionalization of the surface, but also a conversion into other forms of carbon as discussed in Section 5.5.3. Due to the defective structure and to the presence of small graphitic domains on the particle surface, these transformations as well proceed much easier here than with macroscopic diamond particles. 

By varying the process parameters and precursors, it is possible to select and control the resulting nanostructures. For example, by introducing the proper concentration of hydrogen into the chlorine-treatment process of SiC, it is possible to induce the formation of nanodiamond (5-10 nm) at fairly low temperatures (<1000°C) and ambient pressures. The choice of carbide may dictate the propensity of the CDC to form a specific carbon structure. Nanobarrels were observed to form in significant fraction in AI4C3CDC. These multiwalled structures were observed by various researchers. " ... 

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