Dielectrics diamond

The semiconductor nature of diamond manifests itself in a photoelectrochemical response caused by the photogeneration of free charge carriers. With the dielectric diamond, photoconductance (that is, an increase in the conductance due to an increase in majority carrier concentration) can be observed. With the conducting... 

Moroz, A., Metallo-dielectric diamond and zinc-blende photonic crystals, Phys. Rev. B, 66, article no. 115109, 2002. 

Electrical and Electronic. Diamond is an electrical insulator (-- lO H/cm) unless doped with boron when it becomes ap-ty e semiconductor with a resistivity in the range of 10 to 100 Q/cm. n-Ty e doping has often been claimed but is less certainly estabUshed. The dielectric constant of diamond is 5.58. 

The Johnsonfigure of merit, based on saturated carrier velocity and dielectric strength (product of power x frequency squared x impedance), predicts the suitability of a material for high power applications. It is normalized with the value of one given to silicon. As shown in Table 13.2 below, diamond is clearly the preferred material on this basis. 

Fig. 4.8 Temperature dependence of the dielectric characteristic times obtained for PB for the a-relaxation (empty triangle) for the r -relaxation (empty diamond), and for the contribution of the -relaxation modified by the presence of the a-relaxation (filled diamond). They have been obtained assuming the a- and -processes as statistically independent. The Arrhenius law shows the extrapolation of the temperature behaviour of the -relaxation. The solid line through points shows the temperature behaviour of the time-scale associated to the viscosity. The dotted line corresponds to the temperature dependence of the characteristic timescale for the main peak. (Reprinted with permission from [133]. Copyright 1996 The American Physical Society)...

Fig. 4.9 Temperature dependence of the characteristic time of the a-relaxation in PIB as measured by dielectric spectroscopy (defined as (2nf ) ) (empty diamond) and of the shift factor obtained from the NSE spectra at Qmax=l-0 (filled square). The different lines show the temperature laws proposed by Tormala [135] from spectroscopic data (dashed-dotted), by Ferry [34] from compliance data (solid) and by Dejean de la Batie et al. from NMR data (dotted) [136]. (Reprinted with permission from [125]. Copyright 1998 American Chemical Society)...

Fig. 4.10 a Characteristic relaxation times determined from dielectric measurements [137] (diamonds), and from NSE spectra at (triangles) for triol (open symbols) and PU (solid symbols). The full lines correspond to Vogel-Fulcher and the dotted lines to Arrhenius descriptions, b Relaxation times from NSE spectra have been arbitrarily multiplied by a factor 6 for triol and 40 for PU to build a normalized relaxation map. (Reprinted with permission from [127]. Copyright 2002 Elsevier)... 

Fig. 4.20 Temperature dependence of the average relaxation times of PIB results from rheological measurements [34] dashed-dotted line), the structural relaxation as measured by NSE at Qmax (empty circle [125] and empty square), the collective time at 0.4 A empty triangle), the time corresponding to the self-motion at Q ax empty diamond),NMR dotted line [136]), and the application of the Allegra and Ganazzoli model to the single chain dynamic structure factor in the bulk (filled triangle) and in solution (filled diamond) [186]. Solid lines show Arrhenius fitting curves. Dashed line is the extrapolation of the Arrhenius-like dependence of the -relaxation as observed by dielectric spectroscopy [125]. (Reprinted with permission from [187]. Copyright 2003 Elsevier)...

The parameter is obtained by relating the static dielectric constant to Eg and taking in such crystals to be proportional to a - where a is the lattice constant. Phillips parameters for a few crystals are listed in Table 1.4. Phillips has shown that all crystals with a/ below the critical value of0.785 possess the tetrahedral diamond (or wurtzite) structure when f > 0.785, six-fold coordination (rocksalt structure) is favoured. Pauling s ionicity scale also makes such structural predictions, but Phillips scale is more universal. Accordingly, MgS (f = 0.786) shows a borderline behaviour. Cohesive energies of tetrahedrally coordinated semiconductors have been calculated making use... 

Figure 2.33 Dielectric permittivity of 5CB. Experimental data [2] (solid line), and theoretical results obtained with the IEF method (filled diamonds) and with the Maier-Meier theory [4] (open diamonds).

Fig. 15. Comparison of experimental (for the CLD-OMet chromophore in PMMA) and theoretical (equilibrium statistical mechanical calculations described in the text) data. Experimental data are denoted by solid diamonds. The solid line theoretical curve was computed without adjustable parameters. Quantitative agreement can be obtained by adjusting parameters (chromophore dipole moment, molecular polarizability, shape, and host dielectric constant) within reasonable limits. The theoretical curve can be broken down into two parts. The purely electronic part of the electrostatic interaction is shown by the dashed line. The steric effect of nuclear repulsive interactions is shown by the dotted line...

Owing to its extraordinary chemical stability, semiconductor diamond undoubtedly offers serious competition to other electrode materials. However, unlike other carbonaceous materials (e.g. graphite, glassy carbon, etc.), which gained a wide application in electrochemistry, diamond became an object of electrochemical investigation only as late as the decade of the 1990s. Until then, there was a serious handicap to such an investigation. First, diamond was an extremely rare, hard-to-access material. Second, diamond as such is a dielectric hence, it cannot be used as electrode. 

The diamond films specific resistance (p) depends on the boron content and varies, e.g., from some 104 2 cm at a boron concentration of 1018 cm 3 to a value of tenths and even thousandths of 2 cm for boron concentration as high as 1021 cm 3. Correspondingly, diamond changes its nature, starting as a dielectric, then sequentially converting to a semiconductor, degenerate semiconductor, and finally a quasimetal. 

In Section 2 we showed that the properties of amorphous carbon vary over a wide range. Graphite-like thin films are similar to thoroughly studied carbonaceous materials (glassy carbon and alike) in their electrode behavior. Redox reactions proceed in a quasi-reversible mode on these films [75], On the contrary, no oxidation or reduction current peaks were observed on diamondlike carbon electrodes in Ce3+/ 41, Fe(CN)63 4. and quinone/hydroquinone redox systems the measured current did not exceed the background current (see below, Section 6.5). We conventionally took the rather wide-gap DLC as a model material of the intercrystallite boundaries in the polycrystalline diamond. Note that the intercrystallite boundaries cannot consist of the conducting graphite-like carbon because undoped polycrystalline diamond films possess excellent dielectric characteristics. 

The adsorption of hydrocarbon molecules on Si surfaces is an interesting topic of study under various viewpoints. For example, a thin hydrocarbon film coating Si may be applied as a low dielectric in microelectronics and may passivate the surface if covalent bonds are formed between Si atoms and the adsorbate species. Further, unsaturated hydrocarbons play an important role as precursor species for chemical vapor deposition (CVD) of diamond - like films on the Si surface, and of silicon carbide (SiC). 

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