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Fracture-filling rose-like clusters of bladed calcite crystals are found in the northern sector of the Cad&iacute, thrust sheet (SE Pyrenees). This unusual calcite crystal morphology has been characterized by using optical and electron microscope, X-ray diffraction, Raman spectroscopy, &delta, 18O, &delta, 13C, 87Sr/86Sr, clumped isotopes, and major and rare earth elements + yttrium (REEs + Y) analysis. Petrographic observations and powder X-ray diffraction measurements indicate that these bladed crystals are mainly made of massive rhombic crystals with the conventional (104) faces, as well as of possibly younger, less abundant, and smaller laminar crystals displaying (108) and/or (108) rhombic faces. Raman analysis of liquid fluid inclusions indicates the presence of aromatic hydrocarbons and occasionally alkanes. Clumped isotopes thermometry reflects that bladed calcite precipitated from meteoric fluids at ~60&ndash, 65 &deg, C. The 87Sr/86Sr ratios and major elements and REEs content of calcite indicate that these fluids interacted with Eocene marine carbonates. The presence of younger &lsquo, nailhead&rsquo, calcite indicates later migration of shallow fresh groundwater. The results reveal that rose-like calcite clusters precipitated, at least in the studied area, due to a CO2 release by boiling of meteoric waters that mixed with benzene and aromatic hydrocarbons. This mixing decreased the boiling temperature at ~60&ndash, C. The results also suggest that the high Sr content in calcite, and probably the presence of proteins within hydrocarbons trapped in fluid inclusions, controlled the precipitation of bladed crystals with (104) rhombohedral faces.

We report a joint experimental and theoretical study of the lattice dynamics of cubic Tb2O3. Up to 16 optical Raman‐active modes have been observed with polarized and unpolarized Raman scattering measurements on a high‐quality Tb2O3 single crystal. The measured wavenumbers have been compared with those of other rare‐earth (RE) and related sesquioxides with cubic (C‐type or bixbyite) structure. First‐principles calculations have allowed us to assign the symmetry of the experimentally observed Raman‐active modes. Additional lattice‐dynamical calculations on the related cubic RE sesquioxides Dy2O3, Gd2O3, Eu2O3, and Sm2O3 indicate that the phonon wavenumbers of the Raman‐active modes in these compounds are monotonically reduced with increasing the lattice parameter along the Dy2O3‐Tb2O3‐Gd2O3‐Eu2O3‐Sm2O3 series, thus prompting for a revision of the experimental Raman spectra of some of these compounds (mainly Eu2O3 but also Gd2O3)., This study was supported by the Spanish Ministerio de Economía y Competitividad under Projects MAT2015‐ 71070‐REDC, MAT2015‐71035‐R, MAT2016‐75586‐C4‐2‐ P/3‐P, and FIS2017‐2017‐83295‐P.

Recent investigations have revealed the great potential of Raman spectroscopy for the characterization of clinker minerals and commercial Portland cements. The usefulness of this technique for the identification of anhydrous, hydrated, and carbonated phases in cement-based materials has been demonstrated. In the present work, the application of micro-Raman spectroscopy for the characterization of the main clinker phases of calcium aluminate cements and calcium sulfoaluminate cement is explored. The main stable hydrated phases as well as several important carbonated phases are investigated. Raman measurements on the following phases are reported: (i) pure, unhydrated phases: CA, C12A7, CA2, C2AS, cubic-C 3A, C4AF, and C4A3S̄; (ii) hydrated phases: ettringite, monosulfoaluminate, and hydrogarnet (C 3AH6); (iii) carboaluminate phases: hemicarboaluminate and monocarboaluminate. The present results, which are discussed in terms of the internal vibrational modes of the aluminate, carbonate, and sulfate molecular groups as well as stretching O-H vibrations, show the ability of Raman spectroscopy to identify the main hydrated and unhydrated phases in the aluminate and sulfoaluminate cements. The Raman spectra obtained in this work provide an extended database to the existing data published in the literature. © 2013 The American Ceramic Society., This study was funded by the MINECO (Ministerio de Economıa y Competitividad) through BIA0767-2008 project.

Antimony trisulfide (Sb2S3), found in nature as the mineral stibnite, has been studied under compression at room temperature from a joint experimental and theoretical perspective. X-ray diffraction and Raman scattering measurements are complemented with ab initio total-energy, lattice-dynamics, and electronic structure calculations. The continuous changes observed in the volume, lattice parameters, axial ratios, bond lengths, and Raman mode frequencies as a function of pressure can be attributed to the different compressibility along the three orthorhombic axes in different pressure ranges, which in turn are related to the different compressibility of several interatomic bond distances in different pressure ranges. The structural and vibrational properties of Sb2S3 under compression are compared and discussed in relation to isostructural Bi2S3 and Sb2Se3. No first-order phase transition has been observed in Sb2S3 up to 25 GPa, in agreement with the stability of the Pnma structure in Bi2S3 and Sb2Se3 previously reported up to 50 GPa. Our measurements and calculations do not show evidence either for a pressure-induced second-order isostructural phase transition or for an electronic topological transition in Sb2S3. © 2016 American Chemical Society., This work has been performed under financial support from Spanish MINECO under Projects MAT2013-46649-C4-2/3-P and MAT2015-71070-REDC. This publication is fruit of “Programa de Valoración y Recursos Conjuntos de I+D+i VLC/CAMPUS” and has been financed by the Spanish Ministerio de Educación, Cultura y Deporte, as part of “Programa Campus de Excelencia Internacional” through Projects SP20140701 and SP20140871.

Financial support from the Spanish Ministry and Innovation (Project MAT2010-16116) and from CSIC (PIE 2009) is acknowl- edged.

We have used Raman scattering to investigate a series of undoped and As-doped GaN epilayers grown on sapphire substrates by plasma-assisted molecular beam epitaxy with different Ga-to-N ratios. We find that the frequency of the E2h phonon mode of GaN is very sensitive to the Ga-to-N ratio used to grow both types of samples, which may be attributed to strain effects arising from the different growth conditions. We observe Raman signatures corresponding to the formation of submicron cubic domains in some of the spectra of the As-doped samples. We discuss the origin of a broad band located at 232 cm−1 that appears in both the undoped and the As-doped epilayers. We speculate that this band, reported in previous Raman studies on As-doped and Bi-doped GaN, may be attributed to the formation of Ga clusters.

We investigate the optical properties of high-quality Si nanocrystals $(\mathrm{NCs})/\mathrm{Si}{\mathrm{O}}_{2}$ multilayers under high hydrostatic pressure with Raman scattering and photoluminescence (PL) measurements. The aim of our study is to shed light on the origin of the optical emission of the Si $\mathrm{NCs}/\mathrm{Si}{\mathrm{O}}_{2}$. The Si NCs were produced by chemical-vapor deposition of Si-rich oxynitride $(\mathrm{SRON})/\mathrm{Si}{\mathrm{O}}_{2}$ multilayers with 5- and 4-nm SRON layer thicknesses on fused silica substrates and subsequent annealing at 1150 \ifmmode^\circ\else\textdegree\fi{}C, which resulted in the precipitation of Si NCs with an average size of 4.1 and 3.3 nm, respectively. From the pressure dependence of the Raman spectra we extract a phonon pressure coefficient of $8.5\ifmmode\pm\else\textpm\fi{}0.3\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}/\mathrm{GPa}$ in both samples, notably higher than that of bulk $\mathrm{Si}\phantom{\rule{0.28em}{0ex}}(5.1\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}/\mathrm{GPa})$. This result is ascribed to a strong pressure amplification effect due to the larger compressibility of the $\mathrm{Si}{\mathrm{O}}_{2}$ matrix. In turn, the PL spectra exhibit two markedly different contributions: a higher-energy band that redshifts with pressure, and a lower-energy band which barely depends on pressure and which can be attributed to defect-related emission. The pressure coefficients of the higher-energy contribution are $(\ensuremath{-}27\ifmmode\pm\else\textpm\fi{}6)$ and $(\ensuremath{-}35\ifmmode\pm\else\textpm\fi{}8)\phantom{\rule{0.16em}{0ex}}\mathrm{meV}/\mathrm{GPa}$ for the Si NCs with a size of 4.1 and 3.3 nm, respectively. These values are sizably higher than those of bulk $\mathrm{Si}\phantom{\rule{0.28em}{0ex}}(\ensuremath{-}14\phantom{\rule{0.16em}{0ex}}\mathrm{meV}/\mathrm{GPa})$. When the pressure amplification effect observed by Raman scattering is incorporated into the analysis of the PL spectra, it can be concluded that the pressure behavior of the high-energy PL band is consistent with that of the indirect transition of Si and, therefore, with the quantum-confined model for the emission of the Si NCs.

We present resonant UV Raman-scattering measurements on GaN epilayers implanted to different doses of Be+ ions. The Raman spectra are dominated by outgoing multiphonon resonant Raman lines, the intensity of which is very sensitive to the implantation dose. We discuss the criteria, based on the intensities and widths of the observed lines, which allow one to assess the crystal quality of the implanted samples.

We use cathodoluminescence and Raman spectroscopy to investigate GaN layers grown by plasma-assisted molecular beam epitaxy with different Bi fluxes. We find that the growth of GaN with an additional Bi flux favours the formation of submicron cubic domains, which results in layers with reduced crystalline quality and lower luminescence emission. We detect a Bi-related Raman feature at low frequencies that we tentatively assign to local Bi modes in GaN, which indicates that a fraction of Bi atoms incorporates into the GaN lattice. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We have studied the wavevector dispersion of the L+ coupled mode in n-type In0.53Ga0.47As by means of Raman scattering using several excitation wavelengths in the range between 457.9 and 720 nm. The optical properties of In0.53Ga0.47As in the range of excitation energies used are strongly affected by the presence of the E1 and E1+Δ1 critical points, and set an upper limit to the wavevector that can be probed by decreasing the excitation wavelength in Raman scattering experiments. The Raman scattering results are analysed using a Lindhard–Mermin model, and it is found that optical absorption strongly affects the coupled-mode Raman peaks excited with the more energetic lines.

Mg+ is the most suitable ion to produce p-type InP layers by means of ion-beam implantation. We present a Raman-scattering study of lattice recovery by rapid thermal annealing on InP implanted with Mg+ at 80 keV, with a dose of 1014 cm−2. Rapid thermal annealings for 10 s at different temperatures between 300°C and 875°C were carried out to study the effect of annealing temperature in the recovery of the InP lattice and on implant activation.

We have carried out a systematic evaluation of the accuracy of the charge density values obtained by fitting a modified hydrodynamical model to Raman spectra. The hydrodynamical model has been extended to provide a more accurate evaluation of wave vector dependence, conduction band nonparabolicity and free carrier thermal distribution effects through an energy dependent effective mass, so that it can be applied to a wide range of carrier densities. We have used this extended model to fit the coupled-mode Raman spectra obtained from a series of n-InP samples with electron densities in the 10 17 -10 19 cm -3 range, and the carrier density values obtained follow closely the results of the more elaborate Lindhard-Mermin model over the whole density range.

Raman scattering is used to study the photoexcited electron-hole plasma generated under continuous-wave laser excitation in semiconducting and semi-insulating InP at room temperature and at 80 K. Coupled plasmon\char21{}LO-phonon modes are detected in both types of samples, even at low laser excitation power. The coupled modes are clearly resolved from the depletion-zone LO mode in high-resolution measurements. This makes possible the accurate determination of the frequency and width of the unscreened LO-phonon peak. The photoexcited-plasma density is obtained for different incident laser powers by fitting the Raman spectra with a line-shape calculation based on a Lindhard-Mermin dielectric function that takes into account electron and hole contributions.

We present an experimental and theoretical lattice-dynamical study of InN at high hydrostatic pressures. We perform Raman scattering measurements on five InN epilayers, with different residual strain and free electron concentrations. The experimental results are analyzed in terms of ab initio lattice-dynamical calculations on both wurtzite InN (w-InN) and rocksalt InN (rs-InN) as a function of pressure. Experimental and theoretical pressure coefficients of the optical modes in w-InN are compared, and the role of residual strain on the measured pressure coefficients is analyzed. In the case of the LO band, we analyze and discuss its pressure behavior considering the double-resonance mechanism responsible for the selective excitation of LO phonons with large wave vectors in w-InN. The pressure behavior of the L- coupled mode observed in a heavily doped n-type sample allows us to estimate the pressure dependence of the electron effective mass in w-InN. The results thus obtained are in good agreement with k·p theory. The wurtzite-to-rocksalt phase transition on the upstroke cycle and the rocksalt-to-wurtzite backtransition on the downstroke cycle are investigated, and the Raman spectra of both phases are interpreted in terms of DFT lattice-dynamical calculations. © 2013 American Physical Society., Work was supported by the Spanish Ministerio de Econom´ıa y Competitividad through Projects MAT2010- 16116, MAT2010-21270-C04-04 and MALTA Consolider Ingenio 2010 (CSD2007-00045).

We have performed Raman-scattering measurements under high hydrostatic pressure on CdO thin films grown by metal-organic vapor phase epitaxy on sapphire substrates. The pressure dependence of the second-order Raman bands is discussed in terms of ab initio lattice-dynamical calculations, which allow us to obtain mode Grüneisen parameters for the zone-center TO and LO modes of CdO. Our experiments and calculations suggest that at low pressures (4¿GPa) the spectra mainly display contributions from disorder-activated first-order modes., This work was supported by the Spanish Government under projects MAT2010-16116 and TEC2011-28076-C02-02 and by Generalitat Valenciana under projects Prometeo/2011-035 and ISIC/2012/008.

We report a Raman scattering investigation of InAs vibrational modes in multiple layers of InAs self-assembled quantum dots in a GaAs matrix. The Raman peak associated with quantum-dot phonons shows a downward frequency shift as the interlayer spacing decreases. We attribute this frequency shift to the relaxation of the elastic strain in the stacked quantum-dot layers. From the phonon frequency shift, we estimate the magnitude of the strain in the quantum dot layers, which we relate to the energy of the photoluminescence emission of the dots.

Raman spectroscopy has become a widely used characterization tool in today’s semiconductor research. In this chapter, we provide an introductory background to the physics of Raman scattering and discuss present-day applications of Raman spectroscopy in the field of compound semiconductor physics. Illustrative examples of Raman studies are given on a variety of topics such as crystal quality assessment, strain determination, alloy composition, impurities, and free-charge characterization in doped semiconductors.

We investigate the influence of a low-growth-rate InN buffer layer on structural and optical properties of wurtzite nanocrystalline InN films deposited on Si(111) substrates by reactive radio-frequency sputtering. The deposition conditions of the InN buffer layer were optimized in terms of morphological and structural quality, leading to films with surface root-mean-square roughness of ∿ 1 nm under low-growth-rate conditions (60 nm/h). The use of the developed InN buffer layer improves the crystalline quality of the subsequent InN thick films deposited at high growth rate (180 nm/h), as confirmed by the narrowing of X-ray diffraction peaks and the increase of the average grain size of the layers. This improvement of the structural quality is further confirmed by Raman scattering spectroscopy measurements. Room temperature PL emission peaking at ∿ 1.58 eV is observed for InN samples grown with the developed buffer layer. The crystal and optical quality obtained for InN films grown on Si(111) using the low-growth-rate InN buffer layer become comparable to high-quality InN films deposited directly on GaN templates by RF sputtering. © 2011 Elsevier B.V. All rights reserved., Spanish Government Projects, TEC2009-14423-C02-02 and MAT2010-16116, Comunidad de Madrid ProjectS-0505/AMB-0364, and CSIC Project PIE-2009 provided partial financial support.

We present a structural characterization by means of Raman scattering measurements of Si layers implanted with very high doses of Ti+ ions. After implantation the layers were pulsed laser melted (PLM) to recover the lattice crystal and looking for the intermediate band (IB) formation. The Raman spectra permit us to evaluate the degree of crystallinity for the different implanted doses and detect the Ti lattice presence. We discuss, based on the laser line excitation (visible or UV), the probe depth to assess the crystal quality only in the implanted layers.

We perform a structural and optical characterization of InAs1¿xNx epilayers grown by molecular beam epitaxy on InAs substrates x 2.2% . High-resolution x-ray diffraction HRXRD is used to obtain information about the crystal quality and the strain state of the samples and to determine the N content of the films. The composition of two of the samples investigated is also obtained with time-of-flight secondary ion mass spectroscopy ToF-SIMS measurements. The combined analysis of the HRXRD and ToF-SIMS data suggests that the lattice parameter of InAsN might significantly deviate from Vegard"s law. Raman scattering and far-infrared reflectivity measurements have been carried out to investigate the incorporation of N into the InAsN alloy. N-related local vibrational modes are detected in the samples with higher N content. The origin of the observed features is discussed. We study the compositional dependence of the room-temperature band gap energy of the InAsN alloy. For this purpose, photoluminescence and optical absorption measurements are presented. The results are analyzed in terms of the band-anticrossing BAC model. We find that the room-temperature coupling parameter for InAsN within the BAC model is CNM=2.0 0.1 eV.

The effect of photoexcited electron-hole pairs on the LO-phonon-plasmon coupled modes has been observed in InN layers by means of micro-Raman experiments performed at different excitation laser powers. The L− Raman peak displays an upward shift of about 10 cm−1 over the range of increasing excitation powers studied. The L− behavior is well accounted for by a dielectric line-shape model based on the Lindhard-Mermin dielectric function. The photoexcited carrier density has been extracted from line-shape fits to the Raman spectra and a linear increase in the photoexcited carrier density with incident power is found. A simple diffusion model is used to estimate the surface recombination velocity in the layers, which is found to be in the 4.6–4.9 104 cm s−1 range for the bare InN surface.

We perform visible and ultraviolet (UV) Raman-scattering experiments to study a series of undoped and Mn-doped c-GaN thin films grown by plasma-assisted molecular beam epitaxy under Ga-rich and N-rich conditions. The visible, non-resonant experiments confirm that the Ga-rich growth yields the improved crystal quality. New Raman features, most probably related to Mn-induced disorder, show up in the spectra of the c-GaMnN epilayers grown under N-rich conditions. We find that the introduction of an AlN buffer favors the growth of the hexagonal phase. In the UV spectra of the samples with better crystal quality, we detect multiphonon mA1(LO) peaks up to m = 4 together with strong PL signal from c-GaN. In the more disordered samples the PL emission is quenched, and this allows us to detect multiphonons up to m = 6. The intensity of the multiphonon peaks can be used to assess the crystal quality of the c-GaN and c-GaMnN samples., This work was supported by the Spanish Ministry of Science and Innovation under contract MAT2007-63617 and by the FPI and Ramon y Cajal Programs.

We use a hydrodynamical approach to analyse the long-wavelength LO-phonon–plasmon coupled modes observed in a set of high-quality MBE-grown InN epilayers with electron densities varying over one order of magnitude, from ∼2 × 1018 to ∼2 × 1019 cm−3. The samples were characterized by scanning electron microscopy, x-ray diffraction and Hall measurements. The correlation observed between the Ehigh 2 mode frequency, and hence residual strain, and the electron density measured in the layers indicates that the differences in background electron density may be associated with threading dislocations. Owing to the low Raman signal, only the L− branch of the coupled modes can be unambiguously observed. The frequency of the L− Raman peak is, however, sensitive enough to the free electron density to allow its determination from lineshape fits to the spectra. These were carried out using an extended hydrodynamical model. Given the small bandgap energy and large conduction band nonparabolicity of InN, suitable expressions for the optical effective mass and mean square velocity that enter the hydrodynamical model were derived. Electron density values extracted from L− lineshape fits agree reasonably well with Hall determinations., This work has been supported by the Spanish Ministry of Science and Innovation under contract MAT 2007-63617 and by the FPI Programme.

We have studied the laser thermal annealing LTA effects on single crystal GaP. The samples have been analyzed by means of Raman spectroscopy, glancing incidence x-ray diffraction GIRXD , and transmission electron microscopy TEM measurements. After LTA process, the Raman spectra of samples annealed with the highest energy density show a forbidden TO vibrational mode of GaP. This result suggests the formation of crystalline domains with a different orientation in the annealed region regarding the GaP unannealed wafer. This behavior has been corroborated by GIXRD measurements. TEM images show that the LTA produces a defective layer with disoriented crystalline domains in the surface. The depth of this defective layer increases with the energy density of LTA. The lack of crystallinity after LTA processes could be related with the high bond energy value of GaP. © 2009 American Institute of Physics., This work was made possible because of the FPI program (Grant No. BES-2005- 7063) and the Spanish Ministry of Education and Science under Contract No. MAT2007-63617. This work was partially supported by the Project NUMANCIA (Grant No. S-0505/ENE/000310) funded by the Comunidad de Madrid and by the Project GENESIS-FV (Grant No. CSD2006- 00004) funded by the Spanish Consolider National Program.

We have investigated the pulse laser melting (PLM) effects on single crystal GaP. The samples have been studied by means of Raman spectroscopy, glancing incidence X-ray diffraction (GIRXD), van der Pauw and Hall effect measurements. After PLM process, the Raman spectra of samples annealed with the highest energy density show a forbidden TO vibrational mode of GaP. This suggests the formation of crystalline domains with a different orientation in the GaP PLM region regarding to the GaP unannealed region. This behavior has been corroborated by glancing incidence x-ray diffraction measurements. A slightly increase in the sheet resistivity and a suppression of the mobility in PLM samples have been observed in all the measured temperature range. Such annealing effects are a cause of great concern for intermediate band (IB) materials formation where PLM processes are required first, to recovery the lattice crystallinity after high dose ion implantation processes and second, to avoid impurities outdiffusion when the solid solubility limit is exceeded., This work was made possible thanks to the FPI program (Grant No. BES-2005- 7063) and to the contract MAT2007-63617 of the Spanish Ministry of Education and Science. This work was partially supported by the Project NUMANCIA (Grant No. S- 0505/ENE/000310) funded by the Comunidad de Madrid and by the Project GENESIS-FV (Grant No. CSD2006-00004) funded by the Spanish Consolider National Program.

We use Raman scattering to study the LO–plasmon coupled modes (LOPCMs) of n-type GaAs1−x N x epilayers grown by molecular beam epitaxy (0.1% ≤ x ≤ 0.36%). We find that the LOPCMs are heavily damped in n-GaAs1−x N x even for x as low as 0.1%. From a lineshape analysis based on the hydrodynamical model, we evaluate the lifetime of the LOPCMs in our samples. We compare the values thus obtained with the corresponding Hall mobilities. We find that both quantities decrease strongly with increasing x, which can be attributed to N-related alloy scattering of conduction band electrons in the GaAs1−x N x alloy., Work funded by the Spanish Ministry of Education and Science under Contracts Ref. MAT2004-0664, MAT2007-63617 and by the Ramon y Cajal Program.

We have analyzed the degree of crystalline lattice recovery in samples implanted with Ti concentrations well above the Mott limit and subsequently Pulsed-Laser Melting (PLM) annealed by means of Raman spectroscopy and Rutherford Backscattering Spectroscopy (RBS). Since very recently, theoretical studies predicted Ti interstitial sites for the Intermediate Band (IB) formation, the knowledge of the Ti impurity lattice location after PLM annealing is an essential point that can be elucidated by means of RBS measurements. After PLM annealings, Raman and RBS measurements have shown a decrease in the lattice crystalline quality as implanted dose is increased, yielding a significantly improvement of the lattice quality at the highest energy density studied. The RBS channeling spectra show that after PLM annealings Ti impurities are mostly occupying interstitial lattice sites.

We use Raman scattering to investigate a series of In x Ga1–x As1–y N y epilayers (x ∼ 20% and y ∼ 3%) coherently grown on (100) and on (N11) GaAs substrates (N = 1, 3, 4, and 5). We use biaxial-strain theory to evaluate the effect of N alloying on the frequency of the GaAs-like phonon optical modes of dilute InGaAsN. We find that N alloying reduces the TO–LO splitting of the GaAs-like modes. We investigate the effect of substrate orientation on the N-related vibrational modes. Our results suggest that the growth direction does not affect substantially the local bonding of N atoms in InGaAsN., Work supported by the Spanish Ministry of Education and Science under Contract Ref. MAT2004-0664 and the Ramon y Cajal Program.

We present UV Raman scattering measurements on Bx Ga1-x N epilayers with boron composition up to 3.6%. The resonant enhancement of the longitudinal optical modes allows us to detect multiphonon scattering by A1(LO) modes. For low boron compositions (2%), both the E2 and the A1(LO) modes show a consistent frequency increase with boron composition due to alloying effects. Higher disorder and expansive strain are observed in alloys with higher boron content. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim), This work has been supported by the Spanish Ministry of Education and Science (Contract No. MAT2004-0664 and Ramón y Cajal Program).

We present a far-infrared transmission study on group-III nitride thin films. Cubic GaN and AlN layers and c-oriented wurtzite GaN, AlN, and AlxGa1−xN x 0.3 layers were grown by molecular beam epitaxy on GaAs and Si 111 substrates, respectively. The Berreman effect allows us to observe simultaneously the transverse optic and the longitudinal optic phonons of both the cubic and the hexagonal films as transmission minima in the infrared spectra acquired with obliquely incident radiation. We discuss our results in terms of the relevant electromagnetic theory of infrared transmission in cubic and wurtzite thin films. We compare the infrared results with visible Raman-scattering measurements. In the case of films with low scattering volumes and/or low Raman efficiencies and also when the Raman signal of the substrate material obscures the weaker peaks from the nitride films, we find that the Berreman technique is particularly useful to complement Raman spectroscopy. © 2008 American Institute of Physics., This work was supported by the Spanish Ministry of Science and Technology Contract No. MAT2007-63617 and the Ramon y Cajal Programme and by the British EPSRCGB

We present a Raman scattering study of wurtzite $\mathrm{ZnO}$ over a temperature range from 80 to $750\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Second-order Raman features are interpreted in the light of recent ab initio phonon density of states calculations. The temperature dependence of the Raman intensities allows the assignment of difference modes to be made unambiguously. Some weak, sharp Raman peaks are detected whose temperature dependence suggests they may be due to impurity modes. High-resolution spectra of the ${E}_{2}^{\mathrm{high}}$, ${A}_{1}(\mathrm{LO})$, and ${E}_{1}(\mathrm{LO})$ modes were recorded, and an analysis of the anharmonicity and lifetimes of these phonons is carried out. The ${E}_{2}^{\mathrm{high}}$ mode displays a visibly asymmetric line shape. This can be attributed to anharmonic interaction with transverse and longitudinal acoustic phonon combinations in the vicinity of the $K$ point, where the two-phonon density of states displays a sharp edge around the ${E}_{2}^{\mathrm{high}}$ frequency. The temperature dependence of the linewidth and frequency of the ${E}_{2}^{\mathrm{high}}$ mode is well described by a perturbation-theory renormalization of the harmonic ${E}_{2}^{\mathrm{high}}$ frequency resulting from the interaction with the acoustic two-phonon density of states. In contrast, the ${A}_{1}(\mathrm{LO})$ and ${E}_{1}(\mathrm{LO})$ frequencies lie in a region of nearly flat two-phonon density of states, and they exhibit a nearly symmetric Lorentzian line shape with a temperature dependence that is well accounted for by a dominating asymmetric decay channel.

We present a micro-Raman study on the hydration and carbonation of the main silicate phases of Portland cement, i.e. monoclinic dicalcium silicate (C 2S) and monoclinic tricalcium silicate (C3S). We investigate the reaction products and the loss of crystallinity induced by hydration on these two compounds. In the CO2-contaminated pastes we find that calcite, aragonite, and vaterite are inhomogeneously formed. We study sample cross sections to evaluate the maximum depth at which CaCO3 is formed. We find that carbonation is limited to the first 500-1000 μm from the surface in the C3S pastes, while in C2S pastes CaCO3 is formed well beyond this depth. Our results show the great potential of Raman spectroscopy in the study of the chemistry of cements. Copyright © 2006 John Wiley & Sons, Ltd.

Raman scattering measurements were carried out on a bulk, single crystal of wurtzite ZnO over a temperature range from 80 to 760 K and the temperature-dependent shift and broadening of the E2high and A1(LO) modes was analyzed. The E2high mode exhibits a visibly asymmetric line shape that can be related to the interaction with the continuum of acoustic two-phonon density of states. A Fermi resonance model was used to describe the E2high temperature dependence. On the other hand, the anharmonic shift and broadening of the A1(LO) mode are adequately accounted for by a decay model with a dominating Ridley channel involving TO and LA modes. Phonon lifetimes of ∼0.9 and 0.5 ps are found for the E2high and A1(LO) modes, respectively, which corroborates that anharmonic decay involves in both cases a three-phonon process. The A1(LO)lifetime is one order of magnitude lower than that of GaN, which suggests that hot phonon effects should be expected to play a less relevant role in carrier relaxation in ZnO as compared with GaN.

We use Raman scattering to investigate LO phonon‐plasmon coupled modes (LOPCMs) in a series of heavily doped n‐GaAs1−yNy samples with y in the 0.1–0.3% range. We find that the LOPCMs are highly damped in GaAs1−yNy, which is attributed to the disorder introduced by N. LOPCM lineshape calculations allow us to estimate the optical electron effective mass of GaAs1−yNy from the Raman spectra.

We use Raman scattering to investigate the size distribution, built-in strains and the crystalline degree of Si-nanoclusters (Si-nc) in high-quality Si-rich oxynitride/SiO2 multilayered samples obtained by plasma enhanced chemical vapor deposition and subsequent annealing at 1150 °C. An initial structural characterization of the samples was performed by means of energy-filtered transmission electron microscopy (EFTEM) and X-ray diffraction (XRD) to obtain information about the cluster size and the presence of significant amounts of crystalline phase. The contributions to the Raman spectra from crystalline and amorphous Si were analyzed by using a phonon confinement model that includes the Si-nc size distribution, the influence of the matrix compressive stress on the clusters, and the presence of amorphous Si domains. Our lineshape analysis confirms the existence of silicon precipitates in crystalline state, in good agreement with XRD results, and provides also information about the presence of a large compressive stress over the Si-nc induced by the SiO2 matrix. By using the Raman spectra from low temperature annealed samples (i.e., before the crystallization of the Si-nc), the relative scattering cross-section between crystalline and amorphous Si was evaluated as a function of the crystalline Si size. Taking into account this parameter and the integrated intensities for each phase as extracted from the Raman spectra, we were able to evaluate the degree of crystallization of the precipitated Si-nc. Our data suggest that all samples exhibit high crystalline fractions, with values up to 89% for the biggest Si-nc. The Raman study, supported by the EFTEM characterization, indicates that this system undergoes a practically abrupt phase separation, in which the precipitated Si-nanoclusters are formed by a crystalline inner part surrounded by a thin amorphous shell of approximately 1-2 atomic layers. © 2014 AIP Publishing LLC., The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007–2013) under Grant Agreement No: 245977, under the project title NASCEnT. The present work was supported by the Spanish national project LEOMIS (TEC2012-38540-C02-01) and MAT2010-16116.

We perform high-pressure Raman-scattering measurements on different In xGa1-xN/Si(111) epilayers (0.19 < x < 0.45). We find that the experimental pressure coefficient of the A 1(LO) mode measured in these samples is larger than that expected from the linear interpolation between the corresponding values of GaN and InN. Similar measurements in InGaN epilayers grown on GaN/sapphire templates yield much lower values, below the linearly interpolated pressure coefficients. We conclude that the phonon pressure coefficients measured in InGaN are mainly determined by the different compressibility of the substrate and epilayer material. Neglecting substrate effects may yield highly inaccurate phonon pressure coefficients and mode Grüneisen parameters., The work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under project MAT2010-16116.

We have studied LO phonon-plasmon coupled modes by means of Raman scattering in n-InP for carrier densities between 6x10(16) and 1x10(19) cm(-3). A line-shape theory based on the Lindhard-Mermin dielectric function that takes into account the nonparabolicity of the InP conduction band as well as temperature and finite wave-vector effects is used to fit the Raman spectra and extract accurate values of the electron density. The results obtained from the Lindhard-Mermin model are compared with the charge density determinations based on the Drude and the hydrodynamical models, and the approximations involved in these models are discussed.

We have studied the lattice recovery by rapid thermal annealing of Si+-implanted InP using Raman spectroscopy. The crystallinity recovery for different annealing temperatures of samples totally amorphized by the implantation can be monitored by means of their Raman spectra. However, free-charge coupling with the LO mode and possible misorientation of the recrystallized material may alter substantially the first-order Raman spectrum, making it unreliable for a good characterization of the lattice recovery. The study of second-order Raman spectrum overcomes the problems present in the analysis of first-order Raman spectrum and provides suitable criteria to assess the recrystallization of the implanted and annealed samples. After rapid thermal annealing at 875 degrees C for 10 s, the intensity of the second-order peaks approaches 70% of its value in virgin InP, and third-order Raman peaks are also clearly detected, evidencing the good lattice recovery achieved.

We present a study of photoexcited plasmons in semi-insulating, Fe-doped InP at room temperature and at 80 K by means of Raman spectroscopy. Two peaks are detected in the frequency region of the LO mode. Whereas the low-energy peak does not change with incident laser power, the high-energy peak shifts to higher energies with increasing laser power, and therefore is assigned to the L/sup +/ branch of the LO-plasmon coupled mode. The LO and the L/sup +/ modes could be resolved at room temperature for high incident power, and were clearly resolved at 80 K for all the incident powers studied. The Raman spectra were fitted using a L/sup +/ lineshape model based on the Lindhard-Mermin dielectric function, in which contributions from electron, heavy-hole and light-hole intraband transitions as well as heavy-hole-light-hole interband transitions were taken into account. The fitting procedure allows us to determine the photoexcited plasma density as a function of the incident laser power.

We use Raman scattering to investigate the composition behavior of the E 2h and A 1(LO) phonons of In xGa 1-xN and to evaluate the role of lateral compositional fluctuations and in-depth strain/composition gradients on the frequency of the A 1(LO) bands. For this purpose, we have performed visible and ultraviolet Raman measurements on a set of high-quality epilayers grown by molecular beam epitaxy with In contents over a wide composition range (0.25 < x < 0.75). While the as-measured A 1(LO) frequency values strongly deviate from the linear dispersion predicted by the modified random-element isodisplacement (MREI) model, we show that the strain-corrected A 1(LO) frequencies are qualitatively in good agreement with the expected linear dependence. In contrast, we find that the strain-corrected E 2h frequencies exhibit a bowing in relation to the linear behavior predicted by the MREI model. Such bowing should be taken into account to evaluate the composition or the strain state of InGaN material from the E 2h peak frequencies. We show that in-depth strain/composition gradients and selective resonance excitation effects have a strong impact on the frequency of the A 1(LO) mode, making very difficult the use of this mode to evaluate the strain state or the composition of InGaN material. © 2012 American Institute of Physics., Work supported by the Spanish Ministry of Science and Innovation (MICINN) through Project MAT2010-16116.

We assess the degree of crystallinity by means of UV and visible Raman scattering measurements of Ti implanted Si layers with very high doses (10 15-5 × 1016 cm-2) subsequently annealed by nanosecond pulsed laser melting (PLM). We obtain ultraheavily impurified Si layers with Ti concentrations six orders of magnitude above the solid solubility limit in a layer several tens of nanometers thick. The PLM annealing processes are needed to recover the crystal quality and to keep the high Ti concentration required to form an intermediate band (IB). The UV Raman analysis permits us to evaluate the lattice crystallinity of the different implanted doses probing only the implanted region and points out Ti interstitial location in the host lattice in agreement with theoretical predictions for IB formation. By contrast, visible Raman spectra are only sensitive to the presence of a fully amorphized implanted layer as in the rest of the crystalline layers the probing depth far exceeds the implanted layer thickness and the signal is dominated by the undamaged Si. © 2011 IOP Publishing Ltd.

We report a Raman scattering determination of the energy difference EΓ−L between the Γ conduction-band minimum and the L valley minima in n-type Ga1−xInxAsySb1−y lattice matched to GaSb (x=0.15, y=0.13). A frequency downshift in the L+ phonon–plasmon coupled mode is observed between 80 K and room temperature that is attributed to electron transfer from the Γ to the L valleys. We use the L+ frequency shift to evaluate EΓ−L by performing Lindhard–Mermin L+ line-shape fits for different EΓ−L values. The EΓ−L value increases with electron concentration due to band gap renormalization. A value EΓ−L=154 meV is derived for intrinsic material.

We present a lattice-dynamics study of rocksalt cadmium oxide (CdO). We use Raman scattering to investigate a series of high-quality CdO epilayers grown on sapphire substrates by means of metal-organic vapor phase epitaxy. Two main features are found to dominate the Raman spectra of CdO: a sharp peak at ∼265 cm−1 and a broad feature at ∼390 cm−1. To assign these and other weaker second-order features that appear in the Raman spectra, we have carried out an ab initio calculation of the phonon dispersion in CdO. From the calculated two-phonon density of states (PDOS) we tentatively assign the peak at 265 cm−1 to a 2TA(L) mode. The broadband centered at ∼390 cm−1 seems to reflect the high two-PDOS in the 300–450 cm−1 spectral region.

We investigate inelastic light scattering by longitudinal optic phonon-plasmon coupled modes LOPCMs in a series of heavily Se-doped, n-type GaAs1−xNx epilayers with x 0.4%. We perform a line shape analysis of the LOPCM spectra to estimate the optical effective mass, mopt , and the scattering time of the conduction electrons in GaAsN. We use these results to evaluate an effective carrier mobility for our samples. The values thus obtained, which we compare with measured electron Hall mobilities, indicate that the x-dependence of the mobility in GaAs1−xNx is dominated by the scattering time, rather than by the variation of the electron effective mass. The Raman analysis yields mopt values that are lower than those obtained from the band anticrossing model. © 2008 American Institute of Physics., This work is supported by the Spanish Government Projects MAT 2004-0664 and MAT2007-63617, and Ramon y Cajal Program and the EPSRC, United Kingdom. 1M. Henini, Dilute Nitride Semiconductors Elsevier Science, Amsterdam

6 pages, 4 figures.-- PACS: 63.20.Dj; 71.45.Gm; 78.30.Fs; 78.66.Fd; 68.60.Bs, We present a Raman-scattering study on strain-free dilute Ga(As,N) epilayers grown by molecular beam epitaxy. The aim of our work is to discriminate the effect of alloying from the effect of biaxial strain on the frequency behavior of the optical phonon modes of Ga(As,N). In the relaxed epilayers, we observe the following: (i) for the GaN-like LO mode, an upward frequency shift with increasing N which is larger than previously observed in strained samples; (ii) for the GaAs-like LO mode, a redshift with increasing N content which is lower than those reported in the literature on strained samples; and (iii) for the GaAs-like TO mode, we observe a very minor blueshift with increasing N fraction. We discuss the origin of the observed shifts, with particular attention to the reduction of the GaAs-like TO-LO splitting in Ga(As,N). Our data and analysis suggest that such reduction cannot be explained only by a reduction of the total number of Ga–As oscillators due to the substitution of As by N. We discuss the effects of disorder and of ionic plasmon coupling between the GaAs and GaN sublattices of Ga(As,N) on the behavior of the GaAs-like LO mode of the alloy. We conclude that the behavior of this mode is determined by long-range effects., This work was supported by the Spanish Ministry of Science and Technology (Contract No. MAT2004-0664 and Ramon y Cajal Program).

We use Raman scattering to study the composition of InAs self-assembled quantum dots (QDs) embedded in an AlxGa1−xAs matrix. When Al is introduced into the matrix (0.15

We show that Raman scattering is a sensitive technique for probing the degree of Ga intermixing in In(Ga)As∕GaAs self-assembled quantum dots (QDs). The shifts of the QD phonon frequency that we observe are explained by the modification of the strain due to Ga incorporation into the QDs from the GaAs matrix during growth. Using an elastic continuum model, we estimate the average In content of the dots from the QD phonon frequency. The varying amount of intermixing in QDs grown with different In compositions, QD layer thicknesses, growth temperatures, and stacking spacer layer thicknesses are investigated. The Raman data indicate that Ga intermixing is larger for QD samples with low In(Ga)As coverage thickness and∕or high growth temperature and, in multilayered systems, for samples with small GaAs spacer layers.

InAsSb quantum dots (QDs) grown by metalorganic vapor phase epitaxy on In0.53Ga0.47As∕InP under different TMSb∕AsH3 flow ratios have been characterized by means of continuous wave and time-resolved photoluminescence (PL) as well as Raman scattering. It was found that the flow ratio has a very strong influence on the QD composition, PL peak energies, and carrier recombination times. While the samples prepared using low TMSb∕AsH3 flow ratios show a bimodal character with both InAs and InAsSb QDs present, in the structures grown at high flow ratios the InAsSb QDs dominate, showing strong photoluminescence intensity, fast carrier capture and slow recombination.

We report high-pressure Raman-scattering measurements on the transition-metal dichalcogenide (TMDC) compound HfS2. The aim of this work is twofold: (i) to investigate the high-pressure behavior of the zone-center optical phonon modes of HfS2 and experimentally determine the linear pressure coefficients and mode Grüneisen parameters of this material; (ii) to test the validity of different density functional theory (DFT) approaches in order to predict the lattice-dynamical properties of HfS2 under pressure. For this purpose, the experimental results are compared with the results of DFT calculations performed with different functionals, with and without Van der Waals (vdW) interaction. We find that DFT calculations within the generalized gradient approximation (GGA) properly describe the high-pressure lattice dynamics of HfS2 when vdW interactions are taken into account. In contrast, we show that DFT within the local density approximation (LDA), which is widely used to predict structural and vibrational properties at ambient conditions in 2D compounds, fails to reproduce the behavior of HfS2 under compression. Similar conclusions are reached in the case of MoS2. This suggests that large errors may be introduced if the compressibility and Grüneisen parameters of bulk TMDCs are calculated with bare DFT-LDA. Therefore, the validity of different approaches to calculate the structural and vibrational properties of bulk and few-layered vdW materials under compression should be carefully assessed. © 2018, The Author(s)., Work supported by the Spanish Government through projects MAT2015-71035-R and FIS2017-83295-P, and by the National Science Centre (NCN) Poland POLONEZ 3 no. 2016/23/P/ST3/04278 and grant OPUS 11 no.2016/21/B/ST3/00482. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 665778. T.W. acknowledges support within the Maestro grant from NCN (no. 2014/14/A/ST3/0065). F. D. acknowledges the support within the FUGA grant from the NCN (No. 2014/12/S/ST3/00313). DFT calculations were performed at ICM at the University of Warsaw, and at ICTJA-CSIC.