Phonon diamond

Figure 8 shows visible-Raman spectra for moderately boron-doped ( — 10 cm ) microcrystalline and nanocrystalline diamond thin films. The spectrum for the microcrystalline film consists of the one-phonon diamond line centered at 1333 cm The line width (FWHM) is ca. 10 cm and, to a first approximation, is inversely related to the phonon lifetime [123,130]. The line position is negligibly shifted from that for a reference... 

The level of sp -bonded carbon can be detected either electrochem-ically or by Raman spectroscopy. Figure 14 shows a series of Raman spectra for the films shown in Fig. 13. It can be seen that the one-phonon diamond line at 1333 cm decreases in amplitude and increases in width from 12 to 43 cm as the CH4/H2 ratio increases. The scattering intensity centered at ca. 1525 cm also increases with increasing CH4/H2 ratio, indicative of higher levels of sp -bonded carbon. This nondiamond carbon is actually a mixture of sp - and sp -bonded carbon-diamondlike carbon and is not graphitic in nature. The higher defect density, due to the increased secondary nucleation, causes the increased line width and the increased opacity from the nondiamond carbon causes the re-... 

Figure 4. Phonon dispersion for fee FeaNi (renormalized with the eleetron-phonon eoupling). Foree eonstants have been obtained from ab initio ealeulations. Diamonds mark experimental results. ...

CuZn. We have investigated the phonon dispersion of the B2 phase. Our result compares well with the experimental findings marked as diamonds in Fig. 7. Similar to the fee FcsNi phase, a soft transversal mode is detected in bcc CuZn. This [110]... 

Figure 7. Phonon dispersion including the electron-phonon interaction for bcc CuZn. Force constants have been obtained from ah initio calculations. Dashed line is the phonon dispersion without the V-i contribution. Diamonds mark experimental data. ...

Fig. 2.12. Left transient anisotropic reflectivity change of the (001) surface of single crystal type Ha diamond. Inset shows the FT spectrum of the oscillation, demonstrating a narrow peak of the optical phonon at 40THz. Right pump and probe polarizations to detect the optical phonon. Adapted from [50]...

Recent development of ultrashort intense laser pulses has enabled the observation of small-amplitude, high-frequency phonons in wide-gap materials. Typical examples include diamond (Sect. 2.5.1), GaN [72], ZnO [73,74], and TiC>2 [75,76]. Onishi and coworkers observed the bulk and surface phonon modes of TiC>2 at four different frequencies in their TRSHG measurements... 

Figure 1137 Normalized phonon spectra for and in graphite (A) and diamond (B). Reprinted from Bottinga (1969b), with kind permission from Elsevier Science Publishers B.V, Amsterdam, The Netherlands.

Our study of time-resolved luminescence of diamonds revealed similar behavior (Panczer et al. 2000). Short-decay spectra usually contain N3 luminescence centers (Fig. 4.71d 5.69a,b) with decay time of r = 30-40 ns. Despite such extremely short decay, sometimes the long-delay spectra of the same samples are characterized by zero-phonon lines, which are very close in energy to those in N3 centers. At 77 K Aex = 308 nm excitation decay curve may be adjusted to a sum of two exponents of ti = 4.2 ps and i2 = 38.7 ps (Fig. 5.69c), while at 300 K only the shorter component remains. Under Aex = 384 nm excitation an even longer decay component of 13 = 870 ps may appear (Fig. 5.69d). The first type of long leaved luminescence may be ascribed to the 2.96 eV center, while the second type of delayed N3 luminescence is ascribed to the presence of two metastable states identified as quarfef levels af fhe N3 cenfer. 

Diamond luminescence was studied mainly with the two following aims to carry out a fundamental investigation of its physical properties and to determine the optimal conditions for luminescent sorting of diamond bearing rocks. For the first task, diamond photoluminescence was studied at liquid nitrogen temperature at which luminescence centers are marked by characteristic zero-phonon fines and are much more informative then at room temperature. For the second task, were diamond is one of the first minerals for which luminescence sorting was used, liuninescence properties should be studied at 300 K. In the first stages it was established that X-ray luminescence of the A-band... 

Weber, W. (1977) Adiabatic bond charge model for the phonons in diamond. Phys. Rev. B 15, 4789-803. 

Because of the special bonding conditions (short bonding length) c-BN and diamond exhibit high hardness. Both materials are insulators because of missing 7r-bonds. The high thermal conductivity is caused by phonons and not by electrons like in metals. 

Fig. 2. Temperature dependence of the homogeneous width (a) and the peak shift (b) of the 637 nm zero-phonon line in luminescence spectrum of N-V centers in diamond films points experiment the line theoretical approximations according to the laws y — y0 + aT3 + bT1 and 8 = fiT2 - vT4.

In the next section the rare-earth compounds that have been studied by optical means under pressure so far will be reviewed. Then, after a brief introduction of the most commonly used high pressure device, the diamond anvil cell, sect. 4 presents a discussion of the pressure-induced changes of the crystal-field levels and their interpretation. In sects. 5 and 6 some aspects of the dynamical effects under pressure are discussed. These include lifetime and intensity measurements, the influence due to excited configurations and charge transfer bands, and the electron-phonon coupling. 

Fig. 12 Left Generalised phonon density-of-states, G(co) of (NH3)NaRb2C60 between 0 and 120 meV at 300 K. Right Evolution of G(oo) of (NH3)NaRb2C60 between 0 and 14 meV with T open squares 300 K, open diamonds 150 K, open triangles 100 K and open circles 50 K...

To evaluate the crystallinity of the films, Raman spectroscopy is used. A typical Raman spectrum is presented in Fig. 4. Of the crystalline diamond, a narrow peak at a frequency of 1332 cur1 is characteristic, which is caused by the first-order phonon scattering by the crystal lattice. The non-diamond carbon is represented in the spectrum by two diffuse bands at ca. 1350 and 1550 cm-1. When comparing the peaks height, one should keep in mind that the Raman signal is 50 times more sensitive to the non-diamond carbon than to the crystalline diamond [20], In the high-quality diamond films used as electrodes, the non-diamond carbon component rarely exceeds 1%. Raman spectroscopy data have been corroborated by the independent impedance spectroscopy measurements (see below). According to [21], the inner layer of a diamond film is enriched with the admixture of non-diamond carbon as compared to its outer layer. 

Hayashi et al [1] have studied phonon modes up to x = 0.15 in z(x,x+z)y right angle scattering and identify Ai(TO) (open triangles), Ei(TO) (open squares), E2 (open diamonds) and Ei(LO) (open squares) modes. Samples were grown in MOVPE with an AlGaN layer thickness of 2 - 12 pm using a 50 nm... 

Fig. 17.3 Polarization anisotropy ratio as a function of reduced optical radius ka, where e is the dielectric constant of the material. Solid (broken) lines are the theoretical curves for Si (SiC) NWs. Circles (diamonds) are the experimental values for Si (SiC) NW optical phonon (TO) lines (With permission from reference [12]. Copyright (2006) by the American Physical Society)...

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