R. Carles
Paul Sabatier University
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Featured researches published by R. Carles.
Solid State Communications | 1981
N. Saint-Cricq; R. Carles; J.B. Renucci; A. Zwick; M.A. Renucci
Abstract We report Raman scattering experiments in mixed crystals Ga1−xAlxAs in the spectral range 20 – 400 cm−1. We performed the measurements for several incident and scattered light polarizations. Besides the D.A.L.A. already observed1 we find a new band at lower energy. We interpret this structure as due to disorder activated transverse acoustical phonons and label it D.A.T.A. Several weaker bands corresponding to disorder activated optical processes are also seen. Our results are compared with recent calculations of Talwar et al2.
Solid State Communications | 1982
R. Carles; A. Zwick; M.A. Renucci; J.B. Renucci
Abstract The one phonon density of states in GaAs is obtained from the measured disorder-activated-first-order Raman-scattering in Ga 1− x Al x As x alloys. The agreement with several theoretical determinations is excellent. We discuss the requirements that, both the isoelectronic substitution and the experimental conditions must fullfil in order to apply this method to other III–V compounds.
Solid State Communications | 1984
G. Landa; A. Zwick; R. Carles; M.A. Renucci; Arne Kjekshus
Abstract The Raman spectra of ZrTe 5 are recorded at various temperatures between 10 and 500 K. The data give no evidence for a structural phase transition, in spite of appreciable temperature dependent effects in some of the Raman modes. The lack of Raman spectroscopic evidence for a low temperature structural phase transition in ZrTe 5 is also confirmed by powder X-ray and neutron diffraction data collected over 100 to 295 and 10 to 295 K, respectively. The present findings strongly suggest that the reported anomaly in the electrical resistivity at 141 K must reflect change(s) in the electronic band structure of ZrTe 5 , and the temperature dependences of the Raman spectra could be caused by variations in the first order susceptibility.
Solid State Communications | 1984
G. Landa; A. Zwick; R. Carles; M.A. Renucci; Arne Kjekshus
Abstract Fresh Raman data collected from the (001) face of a ZrTe5 single crystal and from polycrystalline powders of ZrTe5 and HfTe5 are presented. A simple model assuming only central interactions between nearest neighbour atoms is used for lattice dynamical calculations at k = 0 . The model accounts for the observations and places emphasis on the virtually lacking dynamical coupling between the two basic structural units in these pentatellurides [trigonal-prismatic (MTe3)n rods and zig-zag (Te2)2 chains].
Solid State Communications | 1985
R. Carles; G. Landa; J.B. Renucci
Abstract In regard with very recent studies which evidence the bond relaxation phenomenon in III–V solid solutions, a new approach is proposed to determine theoretically the isoelectronic impurity modes frequencies. It is based on an embedded molecular unit model which accounts for the relaxation in the neighboring of the substituted atom and so avoids both the single-site and virtual crystal approximations. The results obtained for GaAs in some III–V compounds are compared with the experimental available data.
Physica B-condensed Matter | 1981
A. Zwick; M.A. Renucci; R. Carles; N. Saint-Cricq; J.B. Renucci
Abstract We have investigated by Raman spectroscopy the long wavelength optical phonons of NbS 3 at 300 and 80 K. We have detected 20 phonons among the 24 k = 0 Raman active modes predicted by group theory. The Raman spectra exhibit a remarkable similarity with the analogous spectra of ZrS 3 . This may be understood from the close relationship between the structures of the two compounds. We could relate most of the k = 0 phonons in NbS 3 to zone center and zone edge phonons of ZrS 3 in the b ∗ direction. The occurrence of doublets may be explained by the flatness of the optical branches of the dispersion curves along the b ∗ -reciprocal axis of ZrS 3 , deduced from second order Raman measurements.
Il Nuovo Cimento D | 1983
R. Carles; N. Saint-Cricq; A. Zwick; M.A. Renucci; J.B. Renucci
SummaryWe present resonant Raman experiments on first-order disorder-activated bands in Ga1−xAlxAs alloys. Selective enhancements occur, in particular, in the acoustic region. These resonances enable us to assign unambiguously the features revealed and to determine their mode behaviour. The enhanced disorder-activated bands are compared with the structures appearing in the Raman spectra of GaAs-AlAs superlattices.RiassuntoSi presentano esperimenti di Raman risonanti su bande di primo ordine attivate dal disordine in leghe Ga1−xAlxAs. Aumenti selectivi avvengono in particolare nella regione acustica. Queste risonanze permettono di assegnare in modo non ambiguo le caratteristiche rivelate e di determinare il loro comportamento di modo. Le bande aumentate attivate dal disordine sono confrontate con le strutture che compaiono negli spettri di Raman dei superreticoli di GaAs-AlAs.РезюмеМы предлагаем резонансные Рамановские зксперименты на неупорядоченных возбужденных зонах первого порядка в сплавах Ga1−xAlxAs. В частности, селективные усиления имеют место в акустической области. Зти резонансы дают возможностъ однозначно овъяснить овнаруженные особенности и определить поведение мод. Усиленные неупорядоченные возбужденные зоны сравниваются со структурами, возникаюЩими в Рамановских спектрах суперрешеток GaAs-AlAs.
Physica Status Solidi B-basic Solid State Physics | 1998
A. Sayari; A. Mlayah; F.F. Charfi; R. Carles; R. Planel
We present a comparison between resonant Raman scattering experiments on a type II GaAs/ AlAS superlattice of short period and a single GaAs quantum well. Under resonant excitation, a continuous emission is observed in the low-frequency range of the two heterostructure Raman spectra. This scattering is analyzed in terms of breakdown of the wavevector conservation law due to single quantum-well effects. In the optical regions, strong similarities are also observed. Doubly resonant Raman scattering processes of symmetric and antisymmetric interface modes are specified and discussed within disorder effects. Finally, lateral extents of in-plane microroughnesses detected by acoustic and interface phonons, are estimated.
Solid State Communications | 1997
A. Sayari; A. Mlayah; M. Maaref; F.F. Charfi; R. Carles; R. Planet
Abstract In this paper, we present resonant Raman scattering experiments on type II GaAs AlAs superlattices of short period. Doubly resonant Raman scattering processes of symmetric and antisymmetric interface modes are specified and discussed within disorder effects. Evolution of the interface mode frequencies and the shape of Raman peaks vs AlAs layer widths are studied. The selection rule of symmetric and antisymmetric interface modes is established. Finally, lateral extends of in-plane microroughnesses are estimated.
Solid State Communications | 1982
A. Zwick; G. Landa; R. Carles; M.A. Renucci; Arne Kjekshus