Multiphonon Scattering

B. Atom-Multiphonon Scattering Time-of-Flight Scattering Instrument Clean Crystalline Surfaces Ionic Insulators A. Alkali Halides... 

The atom-multiphonon component of the inelastic scattering can be obtained from the theory of Manson [44] by subtracting off the zero- and first-order terms from the power series expansion of the exponential displacement correlation function. With the assumption that the major contribution to the multiphonon scattering is due to low-energy, long-wavelength phonons, he is able to arrive at an expression with a very simple form for the transition rate. 

As indicated in Section III.B, the multiphonon scattering can also be investigated and interpreted in terms of the atom-surface potential. Most of this work has been carried out with alkali halides, but some experiments have also been done using metals. Figure 29 shows the typical behavior seen for... 

The history of polymer neutron spectroscopy can be divided in two different time domains. The enthusiasm for INS experiments in polymers reached its highest peak in the 1970s, but the experiments have been restricted to a few polymers with a limited number of data [84, 85] which could hardly solve particular problems in polymer dynamics. The availability of modern instruments with higher resolution and with the possibility of removing most of multiphonon scattering has presently revived the field and vibrational spectroscopists await with great interest for the revival of this important field of research. 

W. Richter, Resonant Raman Scattering in Semiconductors Electric Susceptibility. Light Scattering. Experimental Method.s. One-Phonon Deformation Potential Scattering. Infrared Active LO Phonons. Multiphonon Scattering. Conclusions. List of Symbols. References. Subject Index. 

Fig. 14. Constant = 8 meV scans for UPtj at T = 1.2 K. Solid lines through data are guides to the eye the solid line below the data in (a) represents estimated multiphonon scattering. Dashed lines departing in the vertical direction in (b) correspond to phonons. (From Goldman et al. 1987.)...

Section III.D.l treats the multiphonon scattering in II-VI nanostructures and the dependence of the resonance enhancement on the excitation energy and temperature Section III.D.2 shows the determination of the size dependence of the electron-phonon coupling parameter. 

From Eq. (6.56), it may be seen that the relative intensity of multiphonon scattering as compared with single-phonon scattering is increased as the temperature is raised and as the magnitude of the momentum-transfer vector is chosen larger. 

Accordingly, if multi-phonon processes were not involved, the phonon density corresponds to the amplitude-weighted frequency distribution as multiplied with the Debye-Waller factor. Actually, however, multiphonon scattering is not negligible and peaks due to multi-phonon processes appear in the phonon density curves. 

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