Local vibrational modes of isolated hydrogen in germanium

Two distinct isolated hydrogen defects are observed in crystalline Ge by in situ infrared absorption spectroscopy. Implantation of protons into Ge at cryogenic temperatures gives rise to two intense absorption lines at 745 and 1794 cm(-1). The lines originate from distinct defects, each of which contains one H atom located on a <111> axis. The 1794-cm(-1) line is assigned to bond center H in the positive charge state, whereas the 745-cm(-1) line is ascribed to negatively charged H located on a <111> axis close to the tetrahedral site.     

Raman studies of lattice and local vibrational modes of GaInNAs prepared by molecular beam epitaxy

Polarized Raman spectra have been studied on the lattice-matched Ga_0.94In_0.06N_0.025As_0.975 epitaxial layers grown on (100) GaAs by molecular beam epitaxy. Polarization dependence of TO and LO phonon modes has been examined. The N-related local vibrational mode (LVM) in GaInNAs has been studied with emphasis on the light polarization and the effect of the thermal annealing. The thermal annealing-induced change of the N-related LVM in GaInNAs is discussed in terms of the local atomic arrangement around N atoms.     

Lifetimes of hydrogen and deuterium related vibrational modes in silicon

Lifetimes of hydrogen and deuterium related stretch modes in Si are measured by high-resolution infrared absorption spectroscopy and transient bleaching spectroscopy. The lifetimes are found to be extremely dependent on the defect structure, ranging from 2 to 295 ps. Against conventional wisdom, we find that lifetimes of Si-D modes typically are longer than for the corresponding Si-H modes. The potential implications of the results on the physics of electronic device degradation are discussed.     

Coherent dynamics of the localized vibrational modes of hydrogen in CaF2

We report the observation of giant quantum coherence effects in the localized modes of ionized hydrogen in synthetic fluorite. Infrared free induction decay experiments on the substitutional H- center show dramatic modulations at negative delay times due to interference between multiple vibrational levels. Spectrally resolving the degenerate four wave mixing signal allows unambiguous assignments of the participating vibrational states. The dependence of the signal intensity upon the delay path between the exciting free electron laser pulses can be accounted for in terms of the resonant third order polarization with a common dephasing time for the excited states.     

The vibrational modes of hydrogen adsorbed on Ni(110)

By studying the vibrational modes of H on Ni(110) as a function of coverage and temperature, a local picture of H site occupation is obtained in the lattice gas regime and on the (1 × 2) reconstructed surface at low temperature and for the irreversibly disordered surface formed by thermal conversion. Threefold sites are deduced from our data in both the lattice gas and the (1 × 2) reconstructed low temperature phases, with an additional loss in the latter phase ascribed to a second layer site. After thermal conversion, the threefold sites are depleted with a ? 0.5 monolayer (ML) transfer of H to second layer sites which appear to stabilize the surface and with ~ 0.5 ML H desorbing. Readsorption on the disordered surface indicates that a small amount of empty threefold Ni sites are still present after conversion. Various other models and site assignments are also discussed for comparison to the results of this study.     

Ultrafast redistribution of vibrational excitation of CH-stretching modes probed via anti-Stokes Raman scattering

Resonant infrared femtosecond light pulses in the 3 μm region are used to excite specific CH-stretching modes of liquid 1,1,1-trichloroethane, cyclopentane, and cyclohexane. The ultrafast redistribution of vibrational excitation between different CH-stretching modes and the vibrational relaxation of these modes are monitored by spontaneous anti-Stokes Raman scattering of properly delayed and spectrally shaped probe pulses. The results are treated with a rate-equation system, yielding energy-redistribution and energy-relaxation times. Received: 16 December 1999 / Published online: 7 August 2000     

Raman and infrared spectroscopical investigation of the optical vibrational modes in GaSb/AlSb superlattices

The vibrational spectrum of ultra-thin layer GaSb/AlSb superlattices was investigated in detail by infrared (IR) and Raman spectroscopies. The effect of confinement of the transverse and longitudinal optical phonons in both types of the layers was studied. The dispersions of optical phonons of the GaSb and the AlSb obtained from the analysis of the Raman and IR spectra are in a good accordance with the theoretical data and results of neutron scattering experiments. First- and second-order Raman spectroscopy indicates the presence of intermixture of atoms at the interfaces in the GaSb/AlSb superlattices. Received: 11 May 1998 / Accepted: 21 July 1998     

Bi-induced vibrational modes in GaAsBi

We have studied GaAs_1−xBi_x (up to x3%) using Raman scattering with two different polarization configurations. Two Bi-induced phonon modes are observed at 186 cm⁻¹ and 214 cm⁻¹ with increasing Raman intensity as the Bi concentration increases. By comparing Raman selection rules for the observed Bi-induced phonon modes with those for the substitutional N vibrational mode (GaN mode) in GaAsN, the phonon mode at 214 cm⁻¹ is identified as originating from substitutional Bi at the As site in GaAsBi.     

Isotropic Raman spectra of liquid (isotope) mixtures: Intermolecular coupling of vibrational modes

The theory presented in this paper investigates the isotropic Raman spectra of liquid binary mixtures. It is found that the collective vibrational modes of different molecular species can be significantly coupled. This is a consequence of the (nearly) resonant vibrational transfer processes, which give rise to distinct vibrational correlations (i.e. correlations between adjacent molecules). The coupling, however, occurs only with weakly-separated or overlapping bands. The more general results of the theory are applied to isotope mixtures. The spectral information available from relevant dilution experiments is interpreted. In particular it is shown that the spectral properties of the vibrational self-correlation part can be concluded from the observed collective correlation function. The significance of the distinct vibrational correlations with respect to the infrared and depolarized Raman spectra is discussed.     

Resonance Raman studies of the structures and vibrational assignments of photochromic S-alkyldithizones

The resonance Raman spectra of S-methyldithizone (MeHDz), S-ethyldithizone (EtHDz) and S-isopropyldithizone (iPrHDz) have been measured in the solid state and in solution. It is shown that the red and yellow isomers of these S-alkyldithizones adopt in solution the trans-syn-s-trans and trans-anti-s-trans configurations, respectively, with respect to the NN, CN and C N bonds of the formazan skeleton. It is also demonstrated that for EtHDz the red and yellow isomers can be isolated as different crystal forms. Vibrational assignments are given for both red and yellow isomers of MeHDz based on the frequency shifts of five kinds of isotopically substituted species.     

Simultaneous measurements of global vibrational spectra and dephasing times of molecular vibrational modes by broadband time-resolved coherent anti-Stokes Raman scattering spectrography

In broadband coherent anti-Stokes Raman scattering (CARS) spectroscopy with supercontinuum (SC), the simultaneously detectable spectral coverage is limited by the spectral continuity and the simultaneity of various spectral components of SC in an enough bandwidth. By numerical simulations, the optimal experimental conditions for improving the SC are obtained. The broadband time-resolved CARS spectrography based on the SC with required temporal and spectral distributions is realised. The global molecular vibrational spectrum with well suppressed nonresonant background noise can be obtained in a single measurement. At the same time, the measurements of dephasing times of various molecular vibrational modes can be conveniently achieved from intensities of a sequence of time-resolved CARS signals. It will be more helpful to provide a complete picture of molecular vibrations, and to exhibit a potential to understand not only both the solvent dynamics and the solute-solvent interactions, but also the mechanisms of chemical reactions in the fields of biology, chemistry and material science.     

Low-frequency vibrational modes of glutamine

High-resolution terahertz absorption and Raman spectra of glutamine in the frequency region 0.2 THz-2.8 THz are obtained by using THz time domain spectroscopy and low-frequency Raman spectroscopy. Based on the experimental and the computational results, the vibration modes corresponding to the terahertz absorption and Raman scatting peaks are assigned and further verified by the theoretical calculations. Spectral investigation of the periodic structure of glutamine based on the sophisticated hybrid density functional B3LYP indicates that the vibrational modes come mainly from the inter-molecular hydrogen bond in this frequency region.     

Normal vibrational modes in benzil crystals

A group-theoretical analysis of the vibrational spectrum of benzil crystals was carried out. The selection rules and normal coordinates were found. Raman scattering spectra of benzil single crystals were studied in polarized light within a broad temperature range from 100 K to the melting point (T _m=96°C). The experimental data were found to correlate with theory. The temperature dependences of the spectral-line half-widths were used to separate the observed vibrations into translational and librational modes, and the correspondence between the experimentally observed vibrations and their normal coordinates was established in some cases.     

Surface vibrational modes in disk-shaped resonators

The natural frequencies and distributions of displacement components for the surface vibrational modes in thin isotropic elastic disks are calculated. In particular, the research is focused on even solutions for low-lying resonant vibrations with large angular wave numbers. Several families of modes are found which are interpreted as modified surface modes of an infinitely long cylinder and Lamb modes of a plate. The results of calculation are compared with the results of the experimental measurements of vibrational modes generated by means of resonant excitation in duraluminum disk with radius of ≈90 mm and thickness of 16 mm in the frequency range of 130–200 kHz. An excellent agreement between the calculated and measured frequencies is found. Measurements of the structure of the resonant peaks show splitting of some modes. About a half of the measured modes has splitting Δ_fsplit/_fmode$\mathrm{\Delta }{f}_{\mathrm{split}}/f_{\mathrm{mode}}$ at the level of the order of 10⁻⁵. The Q-factors of all modes measured in vacuum lie in the interval (2…3) × 10⁵. This value is typical for duraluminum mechanical resonators in the ultrasonic frequency range.