Conduction-electron spin resonance

The issue of defects in nanotubes is very important in interpreting the observed properties of nanotubes. For instance, electronic and magnetic properties will be significantly altered as is already clear from observation of the conduction electron spin resonance]20,23]. 

Reactions of KI with Cl2 and of NaCl and KC1 with F2 have been studied [92, 93, 103, 104] and a variety of properties have been measured as a function of the extent of reaction in the conversion of CuCl to CuCl2 by reaction with Cl2 [89, 105, 106]. A consistent feature of all these studies is that, together with or sometimes preceding nucleation and growth of new solid phases, the solid reactant is damaged by electron withdrawal, leading to the formation of various types of electronic defect of the trapped-hole or V-centre type. Studies of electrical conductivity, electron spin resonance spectra and UV absorption are useful in elucidating the behaviour of these defects. 

EPR measurements were first performed on wurtzite GaN in 1993 by Carlos and co-workers [2-4] and on cubic GaN by Fanciulli and co-workers at about the same time [5], The primary resonance in the wurtzite films is slightly anisotropic (gy = 1.9510 and gi = 1.9483) with a width 0.5 mT at 4.2 K and generally acknowledged to be due to a band of delocalised effective mass (EM) donor electrons. The average g value is consistent with the expectations of a 5-band k.p analysis and is also similar to that obtained by Fanciulli [5] for a much broader line (—10 mT) in their conduction electron spin resonance experiments on zincblende films. With this exception all of the work discussed in this Datareview is on the wurtzite phase. 

The direct synthesis by anodic oxidation of a new series of electrically conducting poljnners is described.. Our polymers derive from sulfur and/or nitrogen containing hetero-cycles such as 2-(2-thienyl)pyrrole, thiazole, indole, and phthalazine. The anodic oxidation of these monomers is carried out in acetonitrile solutions containing tetrabu-tylammonium salts (TBA X ) ith X = BF, tetraethylammonium salt, TEA H C-C H -S0. Characterization of the materials by electrical conductivity, electron spin resonance, uv-visible spectroscopy, and cyclic voltammetry is discussed. 

An underlying question in many of the ESR measurements of the lineshape of the N-donor and its temperature dependence is the possible existence of an additional broad line at a similar g-value to the three-line spectrum. Most authors agree that the three lines in the isolated N-donor spectrum should have symmetric lineshapes and, since there is a slight asymmetry to the full spectrum, this leads to the conclusion that there is another relatively broad ESR line shifted slightly from the three-line spectrum. This could be due to a second donor, a conduction electron spin resonance or a structural defect. A weak signal, possibly due to a Si vacancy, is also observed at higher temperatures (T > 50 K) in some samples. 

Recently, both polycrystalline and microcrystalline ( 200 A crystallite size) Si films have been investigated by ESR (Hasegawa ft a/., 1981b, 1983b). A dangling bond resonance in microcrystalline silicon films is observed at g = 2.0049. The spin density of this resonance is typically between 10 and 10 spins cm. In P-doped samples a conduction-electron spin-resonance signal is observed at = 1.997. 

Table 6. Conduction electron spin resonance signals in zeolite X and Y ...

The Peierls instability and the high degree of one-dimensionality are observable in a whole series of different experiments. These include the dc conductivity in low applied fields (see Sect 9.6.1 and Fig. 1.13), the diffuse reflections of the Ikp superlattice in X-ray scattering (Sect 9.6.2), the reflection spectra from the FIR up to the UV spectral ranges (Sect 9.6.3), the magnetic susceptibihty (Sect 9.6.4), the conduction electron spin resonance, and nuclear resonances (Sect 9.6.5), as well as the nonlinear electrical conductivity at high apphed electric fields or at high frequencies (Sect. 9.6.6). Most of these methods are also employed for the study of the other radical-ion salts, e.g. TTF-TCNQ or the DCNQl salts. They will therefore be treated as examples in this Sect 9.6. 

Danilczuk, M., Lund, A., Saldo, J., Yamada, H., and Michalik, J. Conduction electron spin resonance of small silver partieles. Spec. Acta A-Mol. Biomol. Spec., 63, 189-191 (2006). 

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