Hyperfine parameters for

Table 2.2 Hyperfine parameters for xylene radical anions17...

THE ISOTROPIC MUON HYPERFINE PARAMETER FOR Mu IN SEMICONDUCTORS. THE s DENSITY (rj ) IS EQUAL TO THE REDUCED HYPERFINE PARAMETER A/Afree where Afrcc = 4463.302 mhz. the data marked T — 0 WERE EXTRAPOLATED TO T = 0 K... 

To put this in better perspective, although it is true that the hyperfine values for Mu in GaAs and GaP are closer than for any other pair of similar crystals (they differ by 30 MHz or 1.0% see Table II), there are several other cases in which A values are close but just not that close. For example, Table II shows that the hyperfine parameters for ZnS and ZnSe differ by 91 MHz or 2.6% and those for Mu" in CuCl and CuBr differ by 39 MHz or 3.1%. All of these could be explained if they corresponded to muonium in a tetrahedral interstitial surrounded by four cations to which they more strongly bond than to the anions, a suggestion similar to that of Souiri et al. (1987) and Cox (1987). Whether this could also be consistent with the closeness of the A values for Mu1 and Mu11 in CuCl and in CuBr, with the pLCR observation of appreciable anion bonding for Mu" in CuCl (see Section IV.4) and with the cluster of hyperfine parameters in SiC near the average of the diamond and silicon values (see Section IV.5), will probably require further experimentation and especially theoretical study to determine. 

The most convincing evidence for the BC model of Mu in III-V materials comes from the nuclear hyperfine structure in GaAs. The hyperfine parameters for the nearest-neighbor Ga and As on the Mu symmetry axis and the corresponding s and p densities are given in Table I. One finds a total spin density on the As(Ga) of 0.45 (0.38) with the ratio of p to 5 density of 23 (4) respectively. The fact that 83% of the spin density is on the two nearest-neighbor nuclei on the Mu symmetry axis agrees with the expectations of the BC model. From the ratios of p to s one can estimate that the As and Ga are displaced 0.65 (17) A and 0.14(6) A, respectively, away from the bond center. The uncertainties of these estimates were calculated from spin polarization effects, which are not known accurately, and they do not reflect any systematic uncertainties in the approximation. These displacements imply an increase in the Ga—As bond of about 32 (7)%, which is similar to calculated lattice distortions for Mu in diamond (Claxton et al., 1986 Estle et al., 1986 Estle et al., 1987) and Si (Estreicher, 1987). 

The muonium centers observed in the curpous halides (see Table II) are unusual in several respects compared with Mu in other semiconductors and insulators. Figure 12 shows the reduced hyperfine parameters for Mu in semiconductors and ionic insulators plotted as a function of the ionicity (Philips, 1970). The positive correlation is especially apparent for compounds composed of elements on the same row of the periodic table where the lattice constants and valence orbitals are similar (see solid points in Fig. 12). Note however that the Mu hyperfine parameters in cuprous halides lie well below the line and in fact are smaller than in any other semiconductor or insulator (Kiefl et al., 1986b). The reason for this unusual behaviour is still uncertain but may be related to other unusual properties of the cuprous halides. For example the upper valence band is believed... 

The impurity interacts with the band structure of the host crystal, modifying it, and often introducing new levels. An analysis of the band structure provides information about the electronic states of the system. Charge densities, and spin densities in the case of spin-polarized calculations, provide additional insight into the electronic structure of the defect, bonding mechansims, the degree of localization, etc. Spin densities also provide a direct link with quantities measured in EPR or pSR, which probe the interaction between electronic wavefunctions and nuclear spins. First-principles spin-density-functional calculations have recently been shown to yield reliable values for isotropic and anisotropic hyperfine parameters for hydrogen or muonium in Si (Van de Walle, 1990) results will be discussed in Section IV.2. 

Results for hyperfine parameters for muonium at the bond-center site in Si are given in Table I. In elemental semiconductors, symmetry requires that the Is orbital does not couple to the antibonding combination of... 

Hyperfine coupling constant, 22 267, 269 Hyperfine interaction, ESR data for, 22 274 Hyperfine parameters for O, 32 128-130 Hyperfine splitting, 31 81 Hyperfine structure, trimer species, 31 98-99 Hyperfine tensor, 22 267, 273-279, 336, 340 constants, 32 20-21 dioxygen species, 32 18-25 equivalent oxygen nuclei, 32 18-21 ionic oxides, 32 40... 

If the spin density not contributing to the muon hyperfine parameter were assumed to be equally divided among the ten closest silicons around the tetrahedral interstice and if at these silicon sites the unpaired spin were assumed to be in sp3 hybridized atomic orbitals, then the isotropic hyperfine parameter for a 29Si on any of these 10 sites would be about - 60 MHz. 

For CuCl, we can obtain additional estimates for the delocalization using a variety of complementary experimental techniques. These results are presented in Table 1. A calculation of hyperfine parameters for CuCl, using the Jesuits of a crystaj fiejd... 

The results of calculation of hyperfine parameters for the Cornet) approximation to the plastocyanin site, along with those for... 

Optically-Detected Magnetic Resonance (ODMR) has provided magnetic and hyperfine parameters for excited states of defects in SiC. Since ODMR combines EPR with photoluminescence, it gives a link between the information provided by each experiment. In SiC, most of the publications describe donor- and acceptor-resonances detected on distant donor-acceptor-pair (DAP) recombination. As in the other experiments, interesting effects occur due to the different symmetries which arise from the polytypism of SiC. 

Mossbauer spectra of normal human adult (a), rabbit (b), and pig (c) oxyhemoglobins measured at 90 K in 4096 channels and presented in 1024 channels (components are the results of the best fit 1—a-subunits, 2—(3-subunits, 3—carboxyhemoglobin) and differences of Mossbauer hyperfine parameters for normai human adult (A), rabbit (O), and pig ( ) oxyhemoglobins at T = 90 K (approximation with one quadrupoie doubiet (d) and with two quadrupole doubiets for a-subunits (e) and for (3-subunits (f) indicated errors are instrumental errors for hyperfine parameters evaluated for the spectra presented in 1024 channels or calculated errors obtained during the spectra fitting if these errors exceeded instrumental errors) [95],... 

Mossbauer spectra of human liver ferritin (a), Imferon (b), Maltofer (c), and Ferrum Lek(d) measured atT = 295 K with a high velocity resolution and presented in 2048 channels (a, b, d) and in 4096 channels (c), indicated components are the results of the best fit and relationship between the spectral hyperfine parameters for Imferon ( ), Maltofer (A), Ferrum Lek ( ), and human liver ferritin (A) obtained using one quadrupole doublet fit (e) [129],... 

Mossbauer spectra of chicken liver (a) and spleen (b) tissues measured at 295 K and presented in 1024 channels and differences of Mossbauer hyperfine parameters for normal human liver ferritin (O). chicken liver ( ), and spleen (A) tissues obtained by fitting with one (c) and two (d and e) quadrupole doublets [133]. 

Mossbauer spectra of a sample at 4.2 K containing 250 xM ferryl (IV). The red lines show contribution from ferryl(IV), representing about 50% of total Fe. Hyperfine parameters for Z D = 9.7(7)cm ... 

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