The possibility of the “giant” isotope effect for ultrasound absorption in crystals

Relaxation of quasi-transverse phonons in the Herring mechanism and ultrasound absorption in cubic crystals with positive and negative anisotropies of the second-order elastic moduli

“…If this contribution is larger than the contribution from the scattering by defects at low temperatures, the specific features of the ultrasound absorption, which are related to the relaxation mechanisms under study, will not be observed in these crystals. The role of the boundary scattering is discussed more comprehensively in [13].…”

“…Using experimentally determined elasticity moduli of the second and third orders, the researchers [12] derived an equation for the elastic energy associated with the lattice anharmonicity in cubic crystals and calculated phonon relaxation rates for some anharmonic scattering processes. The transverse ultrasound absorption in cubic Ge, Si and diamond crystals was discussed in [13]. If the cubic anisotropy in the matrix element describing threephonon scattering processes was taken into account, the dependences of the relaxation rates on the wave-vector of transverse phonons were shown to be qualitatively different from the classical linear Landau-Rumer dependence [14].…”

“…If the cubic anisotropy in the matrix element describing threephonon scattering processes was taken into account, the dependences of the relaxation rates on the wave-vector of transverse phonons were shown to be qualitatively different from the classical linear Landau-Rumer dependence [14]. However, the analysis [12,13] was performed in the isotropic approximation for the spectrum and the polarization of phonons: the effect of the cubic anisotropy on the phonon spectrum was disregarded in the energy conservation law. Moreover, the vibrational modes were assumed to be pure (purely longitudinal or purely transverse) modes.…”

Isotope-Selective Chemical Vapor Deposition via Vibrational Activation

“…Therefore, we can represent f exc (x,y) in terms of the maximum excitation fraction at the center of the inhomogeneously broadened absorption profile, f exc, max () 0.096 in our experiments) and a Gaussian function, G(w,x). (6) The number of 13 CH 3 methyls produced by laser-excited molecules and detected by TPD is the laser-enhanced density integrated over the entire surface area.…”

“…Isotopically enriched reagents have found wide use as mechanistic probes and markers in chemistry for many decades, and isotopically engineered materials, nanostructures, and superlattices exhibit unique thermal, electronic, and spin properties that may prove useful in new technologies. – Isotopic composition dictates a bulk solid’s phonon (vibrational) structure and, therefore, many of its physical properties. For example, when the 12 C content of a diamond film is increased from 98.89% (natural abundance) to 99.95%, its thermal conductivity is increased 40% at room temperature and 10-fold at lower temperatures .…”