Diamond nitrogenated

Fig. 2.15 Isosteric heat of adsorption of nitrogen on molecular (low-evergy) solids and on carbons (high-energy solids), plotted as a function of i/n . (A) Diamond (B) gruphitized carbon black. P.33 (D) Benzene (E) Teflon. The curve for amorphous carbon was very close to Curve (A). (Redrawn from a Figure of Adamson . )...

The concentration of B ia natural Ilb diamonds is about 0.25 ppm and as much as 270 ppm ia synthesized crystals a crystal with about 10 ppm B is essentially deep blue. Dissolved nitrogen can range up to 2500 ppm atomic ia Type la natural stones and to about 500 ppm atomic for synthesized Type Ib. References 9, 14—19 provide qualifications on these data. 

Because Raman spectroscopy requires one only to guide a laser beam to the sample and extract a scattered beam, the technique is easily adaptable to measurements as a function of temperature and pressure. High temperatures can be achieved by using a small furnace built into the sample compartment. Low temperatures, easily to 78 K (liquid nitrogen) and with some diflSculty to 4.2 K (liquid helium), can be achieved with various commercially available cryostats. Chambers suitable for Raman spectroscopy to pressures of a few hundred MPa can be constructed using sapphire windows for the laser and scattered beams. However, Raman spectroscopy is the characterizadon tool of choice in diamond-anvil high-pressure cells, which produce pressures well in excess of 100 GPa. ... 

Nitrogen forms binary compounds with almost all elements of the periodic table and for many elements several stoichiometries are observed, e.g. MnN, Mn Ns, Mn3N2, MniN, Mn4N and Mn tN (9.2 < jc < 25.3). Nitrides are frequently classified into 4 groups salt-like , covalent, diamond-like and metallic (or interstitial ). The remarks on p. 64 concerning the limitations of such classifications are relevant here. The two main methods of preparation are by direct reaction of the metal with Ni or NH3 (often at high temperatures) and the thermal decomposition of metal amides, e.g. ... 

Hardness on the Mohs scale is often above 8 and sometimes approaches 10 (diamond). These properties commend nitrides for use as crucibles, high-temperature reaction vessels, thermocouple sheaths and related applications. Several metal nitrides are also used as heterogeneous catalysts, notably the iron nitrides in the Fischer-Tropsch hydriding of carbonyls. Few chemical reactions of metal nitrides have been studied the most characteristic (often extremely slow but occasionally rapid) is hydrolysis to give ammonia or nitrogen ... 

The Tetrahedral Carbon Atom.—We have thus derived the result that an atom in which only s and p eigenfunctions contribute to bond formation and in which the quantization in polar coordinates is broken can form one, two, three, or four equivalent bonds, which are directed toward the corners of a regular tetrahedron (Fig. 4). This calculation provides the quantum mechanical justification of the chemist s tetrahedral carbon atom, present in diamond and all aliphatic carbon compounds, and for the tetrahedral quadrivalent nitrogen atom, the tetrahedral phosphorus atom, as in phosphonium compounds, the tetrahedral boron atom in B2H6 (involving single-electron bonds), and many other such atoms. 

Like synthetic diamond, C-BN is normally obtained by high-pressure processing. Efforts to synthesize it by CVD at low pressure are promising. It is deposited in an electron-cyclotron-resonance (ECR) plasma from a mixture of BF3 and either ammonia or nitrogen at 675°C on an experimental basis.F l Like CVD diamond, it is also deposited by the hot-filament method using diborane and ammonia diluted with hydrogen at 800°C.P 1... 

Koskinen, J., Hirvonen, J. P., Levoska, J., andTorri, R, "Tribological Characterization of Carbon-Nitrogen Coatings Deposited by Using Vacuum Arc Discharge, Diamond Relat. Mater., Vo. 5, No. 6-8,1996,pp. 669-673. 

The diffraction pattern obtained in the detector plane when the beam scan in a STEM instrument is stopped at a chosen point of the image comes from the illuminated area of the specimen which may be as small as 3X in diameter. In order to form a probe of this diameter it is necessary to illuminate the specimen with a convergent beam. The pattern obtained is then a convergent beam electron diffraction (CBED) pattern in which the central spot and all diffraction spots from a thin crystal are large discs rather than sharp maxima. Such patterns can normally be interpreted only by comparison with patterns calculated for particular postulated distributions of atoms. This has been attempted, as yet, for only a few cases such as on the diffraction study of the planar, nitrogen-rich defects in diamonds (21). 

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