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Zn1-xMexTe (Me = Mg, Mn) nanowires (NWs), with Mg content up to x = 0.75, and Mn content up to x = 0.6, have been investigated by Raman scattering. NWs were grown on GaAs substrates by catalytically enhanced molecular beam epitaxy (MBE). In the whole composition range the NWs crystallize in the zinc-blende structure with their axis ( direction) aligned along the direction of the GaAs substrate, independently of the crystallographic orientation of this substrate. The NWs' diameters vary in the range from 30 to 70 nm, and their typical length is 1000-2000 nm. Raman scattering was measured in “near” resonant condition with the excitation energy close to the direct energy gap of the NW material. This enabled the observation of several LO phonon replicas on a collection of NWs and of up to three phonon replicas (2LO and 3LO) on a single NW. The dependence of the Raman spectra on the Me concentration shows the behavior typical of bulk Zn1-xMexTe mixed crystal, which confirms the incorporation of Me2+ ions into the cation substitutional sites of the ZnTe matrix of the NWs. For the composition range x < 0.2, the high crystalline quality of the investigated mixed crystal NWs, characterized by the width of the observed Raman structures, is comparable to that of pure ZnTe NWs. The crystalline quality of NWs degrades slightly when the Me content rises above x = 0.2. This effect can be attributed to an increasing number of defects or stacking faults in the mixed crystal NWs with higher compositions. Zn1-xCdxTe NWs (with x < 0.2) were also grown and investigated for comparison. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The formation and optical response of VOx nanoparticles embedded in amorphous aluminium oxide (Al2O3) thin films by pulsed laser deposition is studied. The thin films have been grown by alternate laser ablation of V and Al2O3 targets, which has resulted in a multilayer structure with embedded nanoparticles. The V content has been varied by changing the number of pulses on the V target. It is found that VOx nanoparticles with dimensions around 5 nm have been formed. The structural analysis shows that the vanadium nanoparticles are oxidized, although probably there is not a unique oxide phase for each sample. The films show a different optical response depending on their vanadium content. Optical switching as a function of temperature has been observed for the two films with the highest vanadium content, at transition temperatures of about -20 °C and 315 °C thus suggesting the presence of nanoparticles with compositions V4O7 and V2O5, respectively. © 2007 Elsevier B.V. All rights reserved., This work was partially funded by CICYT (Spain), under MAT2003-01490 project. Electron microscopy was performed at Argonne National Laboratory, supported under contract #DE-AC02-06CH11357 between UChicago Argonne, LLC and y the U.S. Department of Energy. SN-S acknowledges the Ministerio de Educación y Ciencia for the support of a FPU grant. JGL acknowledges the “Ramón y Cajal” program of the Spanish MEC for financial support.

We present evidence of the influence of the substrate (GaAs and CdZnTe) on the magnetic properties and on the surface structure of (001) zinc-blende MnTe grown by molecular beam epitaxy. High-resolution X-ray diffraction and atomic force microscopy were employed in the characterisation of the MnTe structure. The temperature dependence of collective spin excitations (magnons) was determined via Raman scattering and subsequently analysed in order to study selected magnetic properties. Differences in both the Neel temperature and magneto-elastic coupling between the MnTe layer and the given substrate were demonstrated, and mechanisms contributing to these effects are discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The antiferromagnetic (AFM) interlayer exchange coupling for sputtered Fe/Si multilayers have been studied by magnetometry, wide-angle neutron diffraction, and spin-polarized neutron reflectometry. Ferromagnetic resonance and Raman scattering measurements have been applied for the characterization of the multilayers. To look for a possible modification of exchange coupling when Si is replaced by Ge, similar Fe/Ge multilayers have been prepared by the same technique. No AFM coupling has been found for Fe/Ge system. Present results differ in part from the literature data and suggest an influence of the sample preparation on the details of its magnetic properties.

Experimentally, when compared with III-V, II-VI, or IV-IV layered systems, the InSe Raman spectrum does not change very much as a function of the number of InSe layers. A simple linear chain model is sufficient to explain this effect. In our model, two parameters are used to characterize Raman spectra: the halfwidth Γ characterizing the sample quality and the coherence length Λ determined by the sample thickness n. Our analysis shows that the coherence length Λ is linear in n. We obtain a fair agreement between computed and experimental Raman spectra.

Structural inhomogeneities in amorphous silicon layers, prepared by r.f. magnetron sputtering, were detected and characterized by X-ray diffraction (XRD) and Raman scattering using samples either as-deposited or post-annealed at increasing temperatures. These inhomogeneities, which can be interpreted in terms of disordered domains around the voids and which depend on the annealing temperature, are identified through analysis of the first halo profiles of XRD patterns as well as of the low-frequency part of the Raman spectra. The first halo profile has been well reproduced by using two components, one located at the low wave vector (left side) of the 111 line of c-Si (relaxed domains), the other one at the other side (disordered domains). The Raman spectra at low frequency (ω

Thin films of MoO3 and WO3 have been obtained by pulsed laser deposition. The structure of the films and of the splashed species were studied by Raman microscopy. In the case of WO3 a single monoclinic phase was observed. For MoO3 the deposited material corresponds to its metastable phase known as β-MoO3. In the splashed species a mixture of the α-MoO3 and β-MoO3 phases is found.

Microcrystalline silicon ( μ c-Si) layers have been obtained by thermal annealing of amorphous films prepared by radio frequency (r.f.) magnetron sputtering. X-ray diffraction (XRD) and Raman spectra were measured. A systematic effect has been observed in these samples on both the diffraction lines and the Raman spectrum profiles, i.e., a distribution of the crystal size peaking at two different means. The diffraction pattern has tails superimposed on the 111, 220, 311 powder lines, while the Raman spectra have a shoulder on the low wave number side of the 520-cm −1 band at about 500 cm −1 . A relationship is established between this effect and the local order inhomogeneities observed in the initial amorphous state by XRD. The first halo of the diffraction pattern can be reproduced by two components, one being located on the low angle side (left side) of the theoretical 111 line of c-Si (relaxed domains), the other one on its right side (disordered domains). This bimodal size distribution is the result of heterogeneous nucleation and crystal growth process during the amorphous–crystalline transition. Relaxed domains favor a nucleation rate leading to small crystals, while disordered domains increase the nucleation activation energy, i.e., yield fewer nuclei and larger crystals.

We report on the catalytically enhanced molecular beam epitaxial growth of Zn1−xMnxTe‐based nanowire structures, with manganese content up to x = 0.6, and on their basic structural and optical properties. The measurements that have been carried out confirm the incorporation of Mn2+ ions in the cation substitutional sites of ZnTe lattice.

International audience; Single crystals of bulk ZnO containing up to about 3% of Mn or Co were grown by chemical vapour transport method and characterized by Raman scattering. By comparison with Raman data taken on pure ZnO samples, a few new structures were observed in the spectra of the doped crystals. The determined frequencies of the new modes were compared with existing Raman data, corresponding to ZnO crystals containing various dopants, taken from the literature. A possible attribution of the observed modes to local impurity modes is discussed. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

International audience; The Brillouin light scattering was used to investigate elastic properties of the zinc blende, MBE-grown MnTe layer that was deposited on a (001) GaAs substrate covered by CdTe buffer layer. The three elastic constants of the zinc blende MnTe, namely c11, c12, and c44, were directly determined for the first time from the frequency of the Rayleigh mode, of the pseudo-surface mode, and of the shear horizontal bulk mode traveling parallel to the layer surface. The value of c11 was checked using the frequency of longitudinal bulk waves propagating at different angles from the normal of the layer plane. This value was also independently determined by results of the folding of acoustic phonons, observed for MnTe/CdTe superlattices by the Raman scattering. Finally, the bulk modulus given by the formula B=(c11+2c12)/3 was determined for zinc blende MnTe by ab initio calculations making use of the density functional theory and atomic pseudopotentials; spin polarization of MnTe was taken into account. A satisfactory agreement between theoretical and experimental values was obtained.

Structural properties of calcined ${\mathrm{ZrO}}_{2}$ nanopowders having various sizes were investigated by Raman spectroscopy, x-ray diffraction, and high-resolution transmission electron microscopy. For grain sizes of the order of a few nanometers the Raman spectrum is typical of an amorphous material as is the corresponding x-ray diffractogram. As the size of the grains increases, the spectra progressively evolve towards that of a crystallized sample, furthermore, two regimes of growth, vitreous and crystalline, are evidenced. As opposed to the acoustical, the optical branches exhibit a strong discontinuity near the amorphous-crystalline transition. From the analysis of the Raman spectra as a function of size one can infer the phonon dispersion curves that has so far been inaccessible by neutron diffraction. A simple analysis using a classic elastic model shows that the Raman frequencies of the acoustical phonon bands of the nanograins are linearly dependent upon their size.

The Coulomb interaction is calculated for thin ionic slabs of any structure and orientation. For ions lying on different planes, parallel to the plane of the slab, the direct-space double sum is transformed into a rapidly converging double sum in reciprocal space only, while for ions lying on the same plane, a two-dimensional version of Ewald's method is used. Finally we comment on the macroscopic field associated with long-wavelength vibrations of an infinite lattice on the basis of a two-dimensional summation method.

For free carrier concentration larger than 10 20 cm −3 donors or 10 19 cm −3 acceptors, silicon is degenerate and electronic interconduction band or intervalence band transitions are possible for energies of the order of the optical phonon energy. Light scattering experiments show that the coupling of these two elementary excitations leads to a bound state broadened and shifted to lower energy. Analysis of the variation of the line width and the shift of the band as a function of the impurity concentration is presented. Results obtained on silicon heavily doped by ion implantation followed by laser annealing show even more pronounced shift related to band structure and phonon dispersion modifications due to the very high dopant concentration.

Lattice disorder created during ion bombardment, thickness of perturbed layer and subsequent annealing behaviour have been studied in implanted silicon using Raman spectroscopy. Saturation of the disorder occurs for energy of 3 × 1024 eV cm−3 deposited into atomic (nuclear) processes. The thickness of the perturbed layer at this energy varies between 500 and 1000 A depending upon the projectile mass. These results compare favorably with Rutherford measurements. The annealing of implantation damage in silicon bombarded with P, Ar, As occurs at approximately 600 °C and varies only slightly with implanted impurity. The localisation of boron in the silicon lattice has been monitored using the Raman active localized mode induced by substitutional boron and boron-phosphorus pairs. Die wahrend Ionenbeschus erzeugte Gitterfehlordnung, die Dicke der gestorten Schicht und das nachfolgende Temperungsverhalten wurden an implantiertem Silizium mit Ramanspektroskopie untersucht. Sattigung der Fehlordnung tritt fur eine Energie von 3 × 1024 eV cm−3 auf, die wahrend des Atom(kern)prozesses aufgebracht wurde. Die Dicke der gestorten Schicht variiert zwischen 500 und 1000 A in Abhangigkeit von der Projektilmasse. Die Ergebnisse stimmen gut mit Rutherfordmessungen uberein. Die Ausheilung der Implantationsschaden in mit P, As, Ar beschossenem Silizium tritt bei etwa 600°C ein und andert sich nur schwach mit den implantierten Verunreinigungen. Die Lokalisierung von Bor in Siliziumgitter wurde mit der Raman-aktiven lokalisierten Mode des substituierten Bor und der Bor-Phosphor-Paare verfolgt.

The resonant behaviour of second harmonic generation, in GaSe, has been observed, at room temperature, when the energy of the fondamental photon is close to the ground state of the first partially allowed exciton. The experiment has been carried out using a tunable, CW, dye laser. At resonance, a breakdown of the selection rules is observed.

Raman spectroscopy of laser annealed implanted Silicon shows a phonon peak shifted up to ten cm-1 compared with a perfect crystalline sample. This shifted peak is interpreted as being due to the finite size of microcrystallites existing in the annealed region where the energy is below the fusion threshold. A simple model describing the vibrationnal properties of such crystallites has been established and compared to the experimental results.

An attempt is made to evaluate the polarizability of amorphous silicon. These evaluations are carried out for samples prepared by chemical vapour deposition (CVD) and glow-discharge (GD). Spectroscopic models like that of Wemple-Didomenico and Ance are employed for the purposes of calculation. This study may serve as a bridge between experimental results that follow from Raman or infra-red spectroscopy and those that are obtained from absorptance/reflectance studies. Es wird versucht, die Polarisierbarkeit von amorphem Silizium zu berechnen. Diese Rechnungen werden fur Proben durchgefuhrt, die mittels chemischer Dampfabscheidung (CVD) und Glimmentladung (GD) hergestellt werden. Spektroskopische Modelle, wie das von Wemple-Didomenico und Ance werden fur die Berechnung benutzt. Diese Untersuchung kann als Brucke zwischen experimentellen Ergebnissen, die aus Raman- oder Infrarotspektroskopie und denen, die aus Absorptions/Reflexionsuntersuchungen erhalten werden, dienen.

Ion implanted silicon with two types of impurities is studied using Raman scattering. The splitting of the localized modes into two pair modes is observed. In the case of 10B31P pairs the two modes are ω ∥ = 650 cm−1, ω ⊥ = 620 cm−1, and for 11B31P pairs, ω ∥ = 628 cm−1, ω ⊥ = 605 cm−1. Results for BAs pairs in silicon are also reported. It is believed that for the first time the second order Raman scattering by pair modes is observed. The second order spectrum gives information about the density of states of these modes. Mittels Ramanstreuung wird ionenimplantiertes Silizium mit zwei Arten von Storstellen untersucht. Die Aufspaltung der lokalisierten Moden in zwei Paarmoden wird beobachtet. Im Falle der 10B31P-Paare sind die beiden Moden ω ∥ = 650 cm−1, ω ⊥ = 620 cm−1 und fur 11B31P-Paare ω ∥ = 628 cm−1, ω ⊥ = 605 cm−1. Ergebnisse fur BAs-Paare in Silizium werden ebenfalls mitgeteilt. Es wird angenommen, das die Ramanstreuung zweiter Ordnung von Paarmoden erstmalig beobachtet wurde. Das Spektrum zweiter Ordnung ergibt Informationen uber die Zustandsdichte dieser Moden.

Reflection Raman spectroscopy has been performed on boron doped uncompensated silicon wafers. The doping of 1.5 10 20 cm −3 is obtained by diffusion. Two localized modes associated with B 10 and B 11 are observed respectively at 642 and 619 cm −1 . The position of the peaks does not differ more than 2 cm − from the infrared absorption results, obtained with compensated samples.