Elastic scattering of acoustic phonons on point mass defects

The relaxation of homogeneous states of long-wave acoustic phonon gas scattered by point mass defects in transversely—isotropic media is studied. The spectrum of the suitable collision operator of the Boltzmann-Peierls equation is investigated. It consists of a continuous part and several discrete eigenvalues. Both continuous and discrete part of the spectrum depend on the values of components of the elastic constant tensor. For some values of elastic constants the continuous part splits up into two separate intervals and some of the discrete eigenvalues appear in the gap. The number of discrete eigenvalues and their arrangement are also affected by elastic properties of medium.     

Elastic scattering of holes by acoustic phonons in thin GaAs/GaAlAs quantum wells

The rates of scattering by acoustic phonons _γi→j${\gamma }_{i\to j}$ from subband i→j$i\to j$ are calculated for holes in a narrow GaAs quantum well using the deformation potential, the Luttinger hamiltonian and the Debye approximation. At room temperature, we find that the energy dependences for both intra- and inter-subband scattering rates follow roughly the behavior of the density of states in the subband to which the hole scatters. Moreover, we study the influence of the overlap between the initial and final states, and for elastic processes we find that, unlike for the case of wide quantum wells, for narrow ones integration over the phonon transverse wavevector _qz$q_z$ should be restricted to about 4% of the bulk Brillouin zone extent. In addition the impact of the well width on _γi→j${\gamma }_{i\to j}$ is investigated.     

Resonant brillouin scattering by injected acoustic phonons in ZnSe

Measurements are reported on the dispersion curve of the Brillouin scattering cross section of TA phonons in ZnSe by making use of hihigh-intensity phonon flux obtained by transmitting the acoustoelectric domain in CdS. Resonant cancellation and enhancement of the scattering efficiency was observed in the region near the absorption edge at room temperature.     

Elastic interaction of point defects on biological membranes

The interaction between inclusions mediated by biological membranes undulations is analyzed. The interaction law is interpreted in terms of symmetries associated with inclusions. We show, in particular, that for a C3 and C3v symmetries the interaction law falls as 1/r3. We show that for completely isotropic inclusions, the dominant interaction vanishes to all orders, and the first contribution stems from the induced interaction which behaves as 1/r4. The same law holds for any other symmetry which is higher than C4. We introduce a straightforward method to compute these interactions. We point out important differences with results in the literature and explain the discrepancies.     

Inelastic neutron scattering study of acoustic phonons of black phosphorus

Dispersion relations of acoustic phonons of the orthorhombic black phosphorus have been measured at room temperature and atmospheric pressure. Very anisotropic dispersion surfaces were observed along the three principal directions. Comparison is made between the present measurements and the recent calculations of dispersion curves by Kaneta et al.     

Measurement of acoustic phonons in beryllium by inelastic X-ray scattering

We present measurements of inelastic scattering of X-rays with high energy resolution. Acoustic phonons in beryllium with an energy transfer of E up to 20 THz were detected. A conventional X-ray source with a power of 8 kW was used.     

Strain-field scattering of fast-transverse acoustic phonons by dislocations in LiF

The mean-free-paths of transverse acoustic phonons generated in surface hot spots and propagating ballistically along [100] in LiF are calculated exactly for the case of scattering by the static strain fields of edge and screw dislocations of Burger's vector $\text{1}\text{2}\text{a [}\text{1}\text{10}\text{]}$. Due to wavevector conservation the screw dislocations are shown not to scatter such phonons at all while the edge dislocations lead to mean-free-paths greater than 12 cm for dislocation densities ?2×10⁸ cm^-2 and frequencies ?5×10¹¹ Hz. This is consistent with the observation by Northrop et al. (1982) of the ballistic propagation of such heat-pulse phonons across deformed crystals of 1 cm dimensions.     

Elastic interaction of point defects with dislocations

Elastic interaction between dislocation and point defects with spherical symmetry is investigated theoretically by means of the sphere-in-hole model. The interaction energy due to the different elastic moduli of the point defect and matrix is computed and then added to the interaction energy due to the size effect. The force on and the probable position of the point defect is determined. The numerical results for some selected solute atoms are computed by means of available experimental data.The results are compared with other recent papers and some experimental applications are briefly discussed.The author is much indebted to F. Kroupa, CSc., for fruitful discussions and valuable comments.     

Light scattering from surface acoustic phonons in metals and semiconductors

Several examples of Brillouin scattering from thermally excited surface acoustic phonons in metals and opaque semiconductors are presented. The measured surface velocities are consistently lower by 1–5% than the values calculated from the bulk elastic constants. The spectra also show the continuum of Lamb excitations having some surface-type character with velocities ranging between the bulk transverse velocity and the bulk longitudinal velocity.     

Anisotropic scattering of holes by acoustic and optical phonons in germanium

The anisotropic scattering of holes by acoustic and optical phonons in germanium is investigated with allowance for the complex structure of the energy spectrum and the specifics of the scattering mechanisms. The temperature dependence of the hole mobility is analyzed in the temperature interval 10°K T 300°K. The results are in good agreement with the experimental data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 3–7, May, 1982.     

Raman scattering by folded acoustic phonons in InGaN/GaN superlattices

We use Raman scattering to investigate the folded longitudinal acoustic (LA) phonons in a series of In_xGa_1−xN/GaN superlattices (SLs) grown by molecular beam epitaxy with different compositions (15% < x < 38%) and SL periods (from 8 to 20 nm). A novel, ultralow wavenumber filtering module, which provides access to ultralow wavenumber Raman modes on single‐grating spectrometers, has been used to perform the Raman measurements. Zone‐folding effects are observed, and the wavenumber behavior of the folded LA modes is well reproduced with a linear dispersion for the folded LA modes as predicted by elastic continuum theory. We employ the wavenumber of the doublets to evaluate the period of the SLs. Copyright © 2011 John Wiley & Sons, Ltd.     

Elastic interaction of dislocation loops and point defects

The elastic interaction energy of a circular dislocation loop with interstitial atoms and vacancies characterized as dilatation or relaxation centres is calculated. Further, the forces which the dislocation loops exert on point defects through elastic interaction are discussed.     

Low frequency Raman scattering from acoustic phonons confined in ZnO nanoparticles

We report here the first observation of the low frequency Raman scattering from acoustic phonons in semiconducting zinc oxide (ZnO) nanoparticles without embedding in any solid matrix. ZnO nanoparticles (size 5-10 nm) with nearly spherical shape have been synthesized using a chemical route. A shift in the phonon peaks toward higher frequencies along with broadening was observed with a decrease in particle size. The size dependence of the acoustic phonons in ZnO nanoparticles is explained using Lamb's theory that predicts the vibrational frequencies of a homogeneous elastic body of spherical shape. Our results show that the observed low frequency Raman scattering originates from the spherical (l = 0) and quadrupolar vibrations (l = 2) of the spheroidal mode due to the confinement of acoustic vibrations in ZnO nanoparticles.     

Temperature dependence of mobility in scattering on point defects

Scattering amplitude in the field of a short-range force center is calculated using factorization of the potential. The results obtained are used to study the temperature dependence of charge-carrier mobility in the random field of chaotically distributed structural point defects.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 50–57, September, 1985.In conclusion, the author sincerely thanks V. L. Bonch-Burevich for his interest in the study and most valuable discussions.     

The multiple scattering theory of phonons in mass disordered lattices

A version of the multiple scattering theory previously applied to the electronic problem of substitutional alloys is completed and modified in order to handle the problem of vibrations of general mass-disordered crystal lattices. The Born series is expressed in terms describing the scattering corrections to the appropriate effective medium. A new physical interpretation of the effective medium condition is given and the total partial summation of the Born series for the full scattering T-matrix is completed to the infinite order. The T-matrix is thus re-expressed in terms corresponding to resonant “ping-pong” scattering of renormalized phonons on all possible clusters of scattering centres. Confining to clusters of only limited number of scattering centres yields a set of successive approximations. The one-centre approximation for cubic crystals complies with the Taylor's selfconsistent procedure. A simple illustrative example in the two-centre approximation is solved and discussed.     

Inelastic scattering of phonons by quadrupole defects with internal degrees of freedom

We solve the quantum mechanical problem of the inelastic scattering of phonons by a quadrupole defect in a crystal lattice for the case of solid parahydrogen whose matrix contains pair complexes of H₂ orthomolecules. By employing the pseudospin approximation for the operator of the energy of quadrupole-quadrupole interaction of the molecules in an orthopair we derive an effective Hamiltonian that describes the interaction of phonons with a pair quadrupole orthodefect in the lattice. We set up the scattering matrix and calculate the effective phonon relaxation time τ(ω, T) as a function of the frequency ω and the crystal temperature T. We also find that a pair quadrupole defect, which has a complicated system of levels, can be replaced by an effective two-level system with temperature-dependent parameters. The fact that a pair quadrupole orthocluster has internal degrees of freedom results in a resonant scattering peak near a certain critical temperature T ₀. Our estimates for H₂ yield T ₀≃ 6–7 K. Finally, we discuss the contribution of this mechanism to the low-temperature thermal conductivity of solid hydrogen. Zh. éksp. Teor. Fiz. 114, 555–569 (August 1998)     

Inelastic light scattering by acoustic phonons in quantum dots and quantum films

The Raman scattering spectra were analyzed in order to find and explain similarities and differences in the interaction between electrons and acoustic phonons in quantum dots and quantum films.