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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.

Structural properties as a function of temperature of bismuth nanocrystals embedded in amorphous germanium thin films, synthesised by laser ablation are investigated by Raman spectroscopy and X-ray diffraction. In addition to temperature anharmonic effects, Raman spectroscopy results reveal a melting solidification hysteresis, which takes place below the melting point of bulk bismuth. Furthermore, preliminary X-ray diffraction results suggest that the nanocrystals change in structure upon heating until melting occurs. However, the nanocrystals recover their original structure once the sample is cooled at room temperature.

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)

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.

The Raman and ir spectra of a murine IgG2a monoclonal antibody molecule are reported. In accordance with previous studies on immunoglobulins, the secondary structure is predominantly of the b-sheet type. The low frequency region of the Raman spectrum was also analyzed in detail. A structured band with two maxima near 43 and 94 cm 21 was observed. This band has been attributed to vibrations of elastic body. The results are interpreted using a simple elastic model. © 2000 John Wiley & Sons, Inc. Biopoly 53: 342-349, 2000

The hypothesis of the relation between the local environment of polyhydride $[({\mathrm{SiH}}_{2}{)}_{n}]$ groups and structural inhomogeneities (due to the presence of voids) of an amorphous silicon network has been tested in hydrogenated amorphous silicon films prepared by rf magnetron sputtering (RF MS). Comparative infrared (IR) absorption, Raman spectroscopy and optical transmission measurements have been performed on samples deposited under the same plasma conditions at various substrate temperature (T). The results of the IR studies show that all samples exhibit the same hydrogen content incorporated as isolated monohydride (SiH) groups responsible for the absorption band at 2004 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. As a consequence, the gradual decrease in the total bonded hydrogen content as T increases is essentially due to the decrease in the amount of hydrogen bonded as polyhydride $[({\mathrm{SiH}}_{2}{)}_{n}]$ groups which absorb around 2086 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. A direct relationship is established between the changes in the IR spectra and the variation of structural inhomogeneities observed by Raman spectroscopy. The linewidth in the low-frequency side of the transversal acoustic (TA) -like band in the Raman spectra decreases monotonously as T increases. This decrease is attributed to a decrease in density of quasilocalized vibrational modes in structural inhomogeneities (disordered domains around the surface of voids) in the amorphous network. The good correlation between the IR and Raman results indicates that the $({\mathrm{SiH}}_{2}{)}_{n}$ groups are located in structural inhomogeneities due to the presence of voids in the amorphous network where the formation of these complexes is favorable. This interpretation is corroborated by the variation of both the static refractive index, which gives information about the density of material, and the dispersion energy, which measures the mean coordination number of Si atoms and the effective number of valence electron per Si atom in the amorphous network.

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

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; A novel material, namely, Fe-containing lithium-metal triphosphate (LiM2P3O10; M=Fe), has been synthesized by wet-chemical method. The phase shows the monoclinic structure (P2(1)/m equivalent to C-2h(2)). The crystal chemistry and chemical structural characteristics have been analyzed by X-ray-diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Surface chemical composition, valence state, and chemical bonding and local structure analysis have been performed by X-ray photoelectron (XPS) and Raman scattering (RS) spectroscopy. EDS and HAADF-STEM indicate the chemical homogeneity and purity of LiFe2P3O10 samples. Both XPS and RS experiments show the existence of an amorphous carbon deposit at the surface of the LiFe2P3O10 particles. Comparison between XPS results for LiFe2PO4 Olivine and LiFe2P3O10 revealed the change in the binding energy of Fe(II) ions. Studies of the local structure characterized by Raman scattering show the evolution of the chemical bonding with the increased number of interconnected PO4 oxo-anionic groups. The electrochemical characteristics of LiFe2P3O10 demonstrate their applicability in lithium batteries.

4 pags. ; 3 figs., The synthesis by pulsed laser deposition of a bismuth nano-plane embedded in an amorphous germaniummatrix is reported. The structural changeswere studied by Raman spectroscopy as a function of temperature. Upon heating, the Bi nano-plane melts and, as the sample is cooled, it re-crystallizes at a temperature well below the melting point. The results show a broad melting–solidification hysteresis cycle (170 K) that is compared to the ones obtained earlier on nanoparticles. Furthermore, a metal-induced crystallization effect was also observed in the germanium matrix., acknowledges a grant from the Ministerio de Educaci´on Cultura y Deporte of Spain to support a sabbatical stay. The financial aid of the Consejo Nacional de Ciencia y Tecnolog´ıa of M´exico (CONACYT) is greatly acknowledged. This work is partially supported by the CICYT (Spain) under Project No. TIC202-03235.

Low frequency acoustic vibrations have been observed by Raman spectroscopy in a wide variety of nano-metric objects in various conditions. A simple elastic model has been used in many cases to give account for the observed results. In this work results obtained on bismuth nanocrystals embedded in an amorphous matrix, free standing zirconia powders and a monoclonal antibody molecule are analyzed and compared.

Bismuth nanocrystals, embedded in amorphous germanium thin films and synthesized by pulsed-laser deposition, are investigated by Raman spectroscopy. Raman spectra are strongly dependent upon the size of the deposited nanocrystals. For the larger nanocrystals, two peaks corresponding to the optical phonons A1g and Eg can be observed. As the size of the particles decreases, the Eg mode shifts to higher frequencies while the A1g mode shifts to lower frequencies. Such behavior is a result of the curvature of the respective phonon-dispersion curves in Bi. A third size-dependent low-frequency mode has also been observed and attributed to acoustic phonons confined in Bi nanocrystals. ©1999 The American Physical Society., The present work has been partially supported by the Consejo Nacional de Ciencia y Tecnologı´a of Me´xico and the Consejo Superior de Investigaciones Cientı´ficas of Spain through the agreement CONACYT-CSIC for travel support.

Mn-doped GaAs nanowires were grown in the self-catalytic growth mode on oxidized Si(100) surface by molecular beam epitaxy and characterized by scanning and transmission electron microscopy, Raman scattering, photoluminescence, cathodoluminescence, and electron transport measurements. The transmission electron microscopy studies evidenced the substantial accumulation of Mn inside the catalyzing Ga droplets at the top of the nanowires. Optical and transport measurements revealed that the limit of Mn content for self-catalysed growth of GaAs nanowires corresponds to the doping level, i.e., is much lower than the Mn/Ga flux ratio (about 3%) used during the MBE growth. The resistivity measurements of individual nanowires confirmed that they are conductive, in accordance with the photoluminescence measurements which showed the presence of Mn2+ acceptors located at Ga sites of the GaAs host lattice of the nanowires. An anomalous temperature dependence of the photoluminescence related to excitons was demonstrated for Mn-doped GaAs nanowires., 19 pages, 11 figures

GaSe is a Ill-VI semiconductor, which exciton at 2 eV is observable at room temperature. In the experiments reported herein, a 15 im thick sample was excited by a 2eV, 150 fs, pump pulse and the transmission was measured with a delayed "white light"probe pulse. At early times (t < 100 fs) the exciton undergoes a fast shift towards highenergy which has been interpreted in terms of optical Stark effect. Because of the resonant excitation, the optical Stark shift of the exciton depends on the electromagnetic field amplitude rather than on the field intensity, as in the non-resonant case. Despite this less favourable situation, excitonic shifts of 10 meV are observed for the highest pumpintensities (of the order of 16 GW/cm2). Taking advantage of these large shifts, we demonstrate the realization, at the exciton energy, of an optical gate having a rise time of150 fs, associated with an "off-on" transmission ratio of 2. 1. INTRODUCTION Optical Stark effect in semiconductors has been widely studied during the past few

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.

Light scattering is shown to be a powerful tool for the investigation of laser annealed ion implanted semiconductors. The results reported here concern boron implanted in silicon which shows up as localized mode where in substitutional position and boron-phosphorous pairs giving also localized modes. The characteristics of the amorphous layer obtained after ion inplantation are also investigated by Raman spectroscopy and detailed results on the amorphous crystalline transition achieved by laser annealing are presented.

The introduction of disorder in silicon caused by the implantation of 70 keV argon ions has been studied using electron paramagnetic resonance and Raman scattering. It is observed that the EPR signal is not saturated when the crystalline structure (as seen by Raman scattering) has totally disappeared. The disorders measured using these two methods are compared with each other and with previously published data. It is concluded that when the saturation of the disorder is observed, it is not possible to assert that a continuous amorphous layer is formed because this saturation is not independent of the experimental technique used. It is also shown that Raman scattering can be a useful and precise technique to monitor the introduction of disorder within an implanted layer.

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.

Optical nonlinearities of bulk GaAs and GaAs/A1GaAs multiple quantum well samples are measured and compared over the wavelength region in the vicinity of bandgap at room temperature. The maximum index variation (An) is found to increase by a maximum of a factor of 3 as the well size is decreased from bulk to 76 A. The nonlinear absorption spectra are analyzed using a semi-empirical fit.