Hydrogen local modes

Chevallier et al. (1990) summarize hydrogen local mode vibrations that have been observed either in as-grown (Riede et al., 1988 Dischler and... 

FREQUENCIES OF THE HYDROGEN LOCAL MODES OF VIBRATION AT 5 K OBSERVED IN BULK III-V MATERIALS. WHEN OBSERVED, THE CORRELATION WITH A DOPANT IS INDICATED. 

The most commonly accepted model for the hydrogen-acceptor pairs locates H at the BC site (see Fig. 4). This model was originally proposed for the H—B complex on the basis of satisfied bonds to explain the increased resistivity (Pankove et al., 1983), SIMS profiles (Johnson, 1985), and a hydrogen local-mode frequency consistent with a perturbed hydrogen-silicon bond (Pankove et al., 1985 Johnson, 1985 Du et al., 1985). The acceptor deactivation by atomic hydrogen was subsequently observed for Al, Ga, and In acceptors in silicon (Pankove et al., 1984). Hydrogen local-mode vibrations were identified as well for the H—Al and H—Ga complexes (Stavola et al., 1987). The boron vibrational frequency for the H—B pair was first identified by Stutzmann (1987) and Herrero and Stutzmann (1988a). 

The observation of most of the lines reported in Table IV is not correlated with the doping of the material. At least two possibilities exist to explain them they are either due to the neutralization by hydrogen of accidental impurities or to the local mode of vibration of hydrogen at a lattice defect site. 

The second type of absorption concerns local modes of vibration of defects or complexes involving hydrogen or deuterium. 

Because of the lattice damage, the absorptions due to the local modes of vibration are usually broader in implanted materials than, for instance, in plasma diffused samples. For proton energies around 1 MeV, the line-widths are in the range 5-100 cm-1 (as compared with 0.1-5 cm-1 for plasma hydrogenation). 

Table V summarizes all the sharp absorptions due to local modes of vibration in proton and deuteron implanted GaP, GaAs and InP. It has to be noted that the results depend upon the reports. For instance, for GaP implanted with protons, Newman and Woodhead (1980) observed only one line at 1849 cm-1 whereas Sobotta et al. (1981) observed only one line at 2204 cm-1. These differences probably come from the differences in implantation conditions. However, unfortunately, these conditions are not always well described in the literature the ion energy and dose are usually given, but the ion current is specified only by Tatarkiewicz et al. (1987, 1988). This parameter is of importance as it contributes to control local temperature and therefore the defect creation and the binding of hydrogen to the lattice. 

FREQUENCIES OF THE LOCAL MODES OF VIBRATION AT 5 K OF HYDROGEN SATURATING A DANGLING BOND IN A VACANCY IN VARIOUS SEMICONDUCTORS. 

As an introduction to the theory as it relates to these defect complexes, we point out that the most conspicuous experimental feature of a light impurity such as hydrogen is its high local-mode frequency (Cardona, 1983). Therefore, it is essential that the computational scheme produce total energies with respect to atomic coordinates and, in particular, vibrational frequencies, so that contact with experiment can be established. With total-energy capabilities, equilibrium geometries and migration and reorientation barriers can be predicted as well. 

Besides the peaks of the local proton modes typical for hydrogen bond, a sharp peak at 28 meV was observed in KDP [34] and attracted much attention [34,38,39]. This peak exists in DKDP at somewhat higher frequency its intensity decreases in both crystals and its width decreases upon the transition from the FE to the PE phase, without any softening of its frequency [38]. Hence, it is concluded that this mode is connected with the phase transition dynamics, i.e., coupled to the polarization fluctuations. This mode is not the tunneling mode or any local mode of proton or deuteron, but rather some collective optical mode of the lattice that involves substantial proton or deuteron displacement. It has been suggested [38] that this mode corresponds to the mode that has a peak at about 200 cm (25 meV) in Raman scattering and infrared reflectivity spectra, and that it is coupled to the soft mode and usually... 

The initial step in the double-resonance scheme is the excitation of a local mode hydrogen stretch vibration localized in a hydrogen halide moiety. In principle, this can be done either at the fundamental or one of the overtones. With presently available Ti sapphire lasers and parametric oscillators (OPOs), it is possible to saturate fundamentals and first overtones, thus ensuring maximum population transfer. Second overtones cannot be pumped as efficiently, but offer enormous discrimination against background and can be used to shift frequencies out of the vacuum ultraviolet and into a more user-friendly part of the ultraviolet. Thus, first and second overtones are very attractive. 

As shown in Fig. 1-33, metalloporphyrins exhibit a number of porphyrin core vibrations in which local modes such as v(C=C) and v(C=N) are strongly coupled (Section 1.21) due to its planar 7r-conjugated structure. Several groups of workers (5-8) have carried out normal coordinate analysis on metalloporphyrins. If we consider the simplest metalloporphyrin in which all the peripheral groups are the hydrogen atoms, it should have 105 (3 x 37 - 6) normal vibrations, which can be classified under D4h symmetry as shown in Table 4-4. Table 4-5 shows major local coordinates that describe general characters of 35 Raman-active in-plane vibrations (8) together with observed frequencies for Ni(OEP) (Fig. 1-32). These normal mode descriptions are applicable to other metalloporphyrins with minor modifications. 

Key words Hydrogen binding energy, hydrogen local vibrational modes, hydrogen concentration, hydrogen density-of-states distribution... 

Although NH s is a highly localized mode, and therefore not likely to be sensitive to chain conformation, its frequency depends strongly on the strength of the N—H O=C hydrogen bond, and it can be expected that this will be a sensitive reflection of structure and its variations. 

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