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Longitudinal Optical (longitudinal + optical)

Distribution by Scientific Domains
Physics and Astronomy66%

Selected Abstracts

Raman studies of cubic BC2N, a new superhard phase

JOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2004
H. W. Hubble
Abstract UV and visible Raman scattering spectra of a new superhard phase, cubic BC2N, were measured for the first time. The Raman band at 1326 cm,1 was attributed to the longitudinal optical (LO) mode of cubic BC2N, whereas the transverse optic (TO) mode is missing in the spectra. Raman scattering was found to be a sensitive method for detecting new diamond-like BCN phases. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Anomalous Dynamical Charge Change Behavior of Nanocrystalline 3C-SiC upon Compression

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2004
Haozhe Liu
Using diamond anvil cell (DAC) technique, in situ high-pressure Raman scattering and energy-dispersive X-ray diffraction (EDXRD) experiments were used at room temperature to study 3C-SiC with an average grain size of 30 nm. In contrast to its bulk counterpart, a decrease of the Born's transverse effective charge of these nanocrystals was observed with increasing pressure from measurements of the longitudinal and transverse optical phonon modes (longitudinal optical,transverse optical) splitting. This is therefore indicative of a diminishing ionicity of nanocrystalline 3C-SiC on compression. [source]

Magneto-optical spectroscopy of spin injection and spin relaxation in ZnMnSe/ZnCdSe and GaMnN/InGaN spin light-emitting structures

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2007
I. A. Buyanova
Abstract In this paper we review our recent results from in-depth investigations of physical mechanisms which govern efficiency of several processes important for future spintronic devises, such as spin alignment within diluted magnetic semiconductors (DMS), spin injection from DMS to non-magnetic spin detectors (SDs) and also spin depolarization within SD. Spin-injection structures based on II,VIs (e.g. ZnMnSe/Zn(Cd)Se) and III,Vs (e.g. GaMnN/Ga(In)N) were studied as model cases. Exciton spin relaxation within ZnMnSe DMS, important for spin alignment, was found to critically depend on Zeeman splitting of the exciton states and is largely facilitated by involvement of longitudinal optical (LO) phonons. Optical spin injection in ZnMnSe/Zn(Cd)Se was shown to be governed by (i) commonly believed tunneling of individual carriers or excitons and (ii) energy transfer via localized excitons and spatially separated localized electron,hole pairs (LEHP) located within DMS. Unexpectedly, the latter mechanism is in fact found to dominate spin injections. We shall also show that spin depolarization in the studied structures is essentially determined by ef- ficient spin relaxation within non-magnetic spin detectors, which is an important factor limiting efficiency of spin detection. Detailed physical mechanisms leading to efficient spin depolarization will be discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Hot phonons in GaN channels for HEMTs

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2006
A. Matulionis
Abstract Accumulation of non-equilibrium longitudinal optical (LO) phonons (termed hot phonons) is considered as a possible cause for limitation of hot-electron drift velocity at high electric fields in a GaN biased channel with a two-dimensional electron gas (2DEG). Equivalent hot-phonon temperature and hot-phonon lifetime are estimated from experimental results on hot-electron noise at a microwave frequency. Dependence of the hot-phonon parameters on electron density and channel composition is investigated, and frequency performance of high-electron-mobility transistors (HEMTs) is discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Analysis of Raman modes in Mn-doped ZnO nanocrystals

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2009
Shuxia Guo
Abstract Mn-doped ZnO was synthesized using a co-precipitation technique. X-ray diffraction (XRD) measurements and photoluminescence (PL) spectra show that Mn ions are doped into the lattice positions of ZnO. The modes at 202, 330, and 437,cm,1 in the Raman spectrum are assigned as 2E2 (low), E2 (high),E2 (low), and E2 (high) modes of ZnO base, respectively. The mode at 528,cm,1 is ascribed to a local vibrational mode related to Mn. The mode at 580,cm,1 should be an intrinsic mode of ZnO and assigned to E1 longitudinal optical (LO). Its reinforcement should result from a combination of resonance at the excitation wavelength and impurity-induced scattering. [source]

Well-width dependence of coupled Bloch-phonon oscillations in biased InGaAs/InAlAs superlattices

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004
Michael Först
Abstract The coupling between Bloch oscillations and longitudinal optical (LO) phonons is investigated in ternary In0.53Ga0.47As/In0.52Al0.48As superlattices of different well widths. In femtosecond time-resolved studies, a strong increase of the coherent LO phonon amplitudes is observed when the Bloch oscillations are subsequently tuned into resonance with the different optical phonon modes of the ternary semiconductor materials. In a narrow-well superlattice where electronic minibands are energetically shifted close to the confining barrier potential, the phonon amplitudes are asymmetrically enhanced on the high-frequency edge of the resonance. Here, at high electric fields, field induced tunneling into above-barrier continuum states leads to a rapid dephasing of Bloch oscillations. The associated polarization change provides an additional excitation process for coherent LO phonons. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]