Properties Of Lattice Vibrations Research Articles

Analysis of the terahertz characteristics of pesticide residue isomers

The detection of pesticide isomers is a great advantage in the agricultural pharmaceutical industry. Terahertz spectroscopy can be used in such applications because it is very sensitive to intermolecular interactions. Although it is challenging to understand the basic properties of lattice vibrations that cause terahertz absorption, it can be achieved by calculation. In this paper, the terahertz spectra of dimethylamine and dimethylamine-p isomers of pesticide residues were determined by terahertz spectroscopy, and their terahertz absorption vibration properties were analyzed by the quantum chemistry method. The results show that terahertz spectroscopy can realize the identification and quantitative analysis of isomers and verify the reliability and practicability of quantum chemistry in calculating low-frequency vibration motion.

Influence of Impurities on Polarization Properties of Lattice Vibrations

On the example of synthetic single crystal diamond with negatively charged nitrogen-vacancy center (NV)—center, we have experimentally reviled the changes in the polarized spectrum of the first-order Raman scattering due to the presence of nitrogen impurities. It has been found the appearance of rather intense spectra of the Brillouin zone-center optical phonons in an unpredictable crossed polarization of the incident and scattered light, while in the previously reported Raman data it was observed only in parallel polarization of the incident and scattered light. Such a recovery of Raman intensity is prescribed to the change of the local symmetry from the point group Oh to C3v in accordance with the results of Raman scattering polarization rules based on conclusions of the group theory. The data make obvious also the observation of the strong in-coming resonance with the nitrogen NV 0 center electronic transition.

Probing the properties of lattice vibrations and surface electronic states in magnetic semiconductor CrPS4.

Searching for multifunctional materials with magnetism and semiconductivity is one of the goals of research into two-dimensional (2D) systems. Herein, we report a chemical vapor transport method to successfully synthesize a layered magnetic semiconductor, CrPS4. Under parallel and perpendicular polarization configurations, the anisotropic optical response of the (001) surface was investigated by polarized Raman spectroscopy; the Raman peak intensity was recorded with the crystal rotated from 0° to 360°, taking the symmetry of the Raman tensor into account; the A or B vibrational mode of different Raman peaks can be clearly distinguished. Moreover, the electronic state of the (001) single-crystal surface was investigated by ultraviolet photoelectron spectroscopy (UPS), which reveals the valence band position and work function of the (001) surface.

Specific features of the properties of lattice vibrations in the Cd1–y Hg y Te alloy formed by the CdTe semiconductor and the HgTe semimetal

The specific features of the properties of Hg-Te lattice vibrations have been considered within the percolation model of a mixed Cd1–yHgyTe crystal (alloy), in which the composite medium is formed by the alloy regions enriched in HgTe and CdTe with different Hg-Te vibrational states and, hence, with different characteristics of vibrational modes (frequency and damping parameter). In the HgTe-enriched alloy, the properties of Hg-Te lattice vibrations are determined by a double-well lattice potential for the Hg atom with the off-center localization at low temperatures. In the CdTe-enriched alloys, the properties of Hg-Te lattice vibrations are determined by a single-well lattice potential for the Hg atom in the center of the anion tetrahedron, and the Hg-Te vibrational states are localized. For the HgTe-enriched alloy, the Hg-Te vibrational states are extended. In the percolation scheme of the transformation of the vibrational spectrum of the Cd1 - yHgyTe alloy with the composition y, the “137 cm−1” mode is a split-off mode of Hg-Te vibrations, or one of the modes of the percolation doublet of HgTe-like vibrations.

Specific features of the properties of Hg-Te lattice vibrations in Cd1 − y Hg y Te alloys enriched with CdTe

In alloys (solid solutions) Cd1 − yHgyTe enriched with CdTe, the properties of Hg-Te lattice vibrations are determined by a single-well lattice potential for the Hg atom located at the center of the anion tetrahedron. The HgTe-enriched alloys retain the anomalous properties of Hg-Te lattice vibrations, which are determined by a double-well lattice potential for the Hg atom located in the off-center position at low temperatures; a shallower well of the potential for the Hg atom located at the center of the anion tetrahedron is filled upon thermal activation. The polarizability of the ion pair in the TO mode of Hg-Te lattice vibrations with the Hg atom located at the center of the anion tetrahedron for the CdTe-enriched alloys considerably exceeds the polarizability of the pair with the off-center Hg atom for the HgTe-enriched alloys.

Manifestation of anomalous properties of HgTe lattice vibrations in Hg1 − x Z x Te (Z = Cd, Mn, Zn) alloys

Alloys (solid solutions) Hg1 − xZxTe (Z = Cd, Mn, Zn) with a variation in their composition are characterized by the double-mode type of rearrangement of the vibrational spectrum of the crystal lattice, and these alloys retain the properties of lattice vibrations of the binary alloy components. The HgTe-enriched alloys under consideration also retain the anomalous properties of HgTe lattice vibrations with their additional low-frequency 105 cm−1 mode, which is forbidden according to the symmetry selection rules. An analysis has been made of the specific features of the manifestation of the 105 cm−1 mode in the alloys as compared to HgTe, in particular, its splitting into several modes ωn (n = 0, 1, 2) due to the presence of two cations Hg and Z (Cd, Mn, Zn) in the cation sublattice. The thermal activation of the low-frequency 105 cm−1 mode in the HgMnTe and HgZnTe alloys almost coincides with that observed in HgTe, but the activation energy of the mode for HgCdTe differs substantially from that for HgTe. Moreover, the conditions providing the activation of the 105 cm−1 mode in the n-HgCdTe and p-HgCdTe alloys are different.

Anomalous properties of optical lattice vibrations in HgTe: A double-well model of the lattice potential for a Hg atom

A double-well potential model has been proposed for a Hg atom in the HgTe crystal lattice in which the Hg atom either occupies the center of the anion tetrahedron or is located at the off-center position. The fundamental TO mode of the Hg-Te vibrations at a frequency of ∼120 cm−1 corresponds to the vibrations of the off-center Hg atom, and the additional mode is associated with the vibrations of the Hg atom located at the center of the anion tetrahedron. The model has made it possible to explain both the strong increase in the intensity of the additional mode with increasing temperature, which, at T = 300 K, is comparable to the intensity of the fundamental mode, and the anomalous change (decrease) in the damping parameter of the fundamental TO mode with increasing pressure, which corresponds to a more ordered crystal structure.

Properties of IR-active lattice vibrations in the vicinity of kinks in the Frenkel-Kontorova model

The properties of infrared lattice vibrations in the presence of kinks in the Frenkel-Kontorova model are analyzed. Our results show that the vibration of particles involved in kink formation is very similar to that in a gap mode around a force-constant defect. We found that the IR phonon mode intensity possesses a universal dependence on a certain combination of system parameters and kink concentration. On the basis of these results a criterion is proposed for separating the regime of weakly interacting kinks in the system from the regime of a kink lattice.

On the phase space in FPU lattices

We investigate f −μ fluctuations in the Fermi-Pasta-Ulam equation, which is one of the simplest lattice models, to describe fundamental properties of lattice vibrations. Based on the Lyapunov spectrum, we classify the motion in the phase space and have found that the phase space has an onion-like structure.

A one-lattice formulation of crystal microelasticity—I. The crystals with a microstructure

The paper deals with a new formulation of the lattice microelasticity which bridges a gap between the strictly microscopic and the continuum approaches. The aim of the present paper is to develop a scheme to derive a unified formalism for the description of microelastic behaviour of crystalline materials in both the preasymptotic and asymptotic range. The description is intended to make tractable the analysis of any crystal including complex ones, and is especially useful when treating some properties of physical interest. Conceptually the method of the derivation combines some elements of the pseudocontinuum approach with those of spectral properties of lattice vibrations.

Vibration Spectra and Symmetry of Crystals

The French edition of this book, published in 1970, is well established as a good systematic account of the effects of crystal symmetry on the spectroscopic properties of lattice vibrations. The appearance of an excellent English translation is most welcome.

Phonons and Resonances in Solids

B DiBartolo and R C Powell Chichester: J Wiley 1976 pp xvi + 515 price £15.45 The main theme of this book is the application of the methods of group theory to the properties of crystal lattice vibrations. This is used in conjunction with standard quantum mechanics in the treatment of such topics as the optical spectra of impurities in solids, the scattering of neutrons and x-rays by crystals, and the infrared and Raman scattering by phonons.

Optical Properties of Lattice Vibrations in Molecular Crystals

AbstractA classical microscopic theory is presented for the optical properties of lattice vibrations in molecular crystals, which are composed of electrically neutral molecules bound by van der Waals forces. It is shown, that Huang's theory, which until now has been applied to ionic crystals only, is also valid for molecular crystals. Finally, oscillator strengths as well as LO and TO frequencies are calculated for thiourea according to the “oriented gas” model. A comparison shows, that the calculated oscillator strengths have the same order of magnitude as those of α‐quartz.

The Raman effect in crystals

A review is given of progress in the theoretical and experimental study of the Raman effect in crystals during the past ten years. Attention is given to the theory of those properties of long-wavelength lattice vibrations in both cubic and uniaxial crystals which can be studied by Raman scattering. In particular the phenomena observed in the Raman scattering from crystals which lack a centre of inversion are related to the theory. The angular variations of the scattering by any type of lattice vibration in a crystal having any symmetry can be easily calculated using a complete tabulation of the Raman tensor. Recent measurements of first-order lattice vibration spectra are listed. A discussion of Brillouin scattering is included. The relation of second-order Raman spectra to critical points in the lattice vibration density of states is discussed, and measurements of the second-order spectra of diamond and the alkali halides are reviewed. The theory and experimental results for Raman scattering by electroni...