Raman Spectroscopic Investigation of the Stress State in Silicon Substrates near Edges of Pt/PZT Microstructures

Hydrostatic stresses in Si substrates near edges of Pt/PZT microstructures used in pyrosensor fabrication have been predicted theoretically by finite element (FE) calculations. Within the absorption limited depth zone from which Raman radiation can be detected the substrate stress varies considerably. The characteristic lateral length scale of the average stress profile perpendicular to the film edges is less than 50 μm resulting from contributions of different depth. These stresses could be measured by spatially resolved Raman spectroscopy with an accuracy of 1‐2 μm.The values of the film stress of Pt and PZT have been estimated by fitting the FE models to the measured curves of the stress distribution in the Si substrate.     

Structural relaxation of SiO2 at elevated temperatures monitored by in situ Raman scattering

Raman scattering spectra of high-purity synthetic silica glass were measured in situ in the temperature range from 950 to 1200 °C by means of an experimental approach which gives very low thermal background. The temperature dependence of the scattering permits an analysis of the spectra into the first-order and overtone contributions in a consistent manner. For low-OH content the dynamics of relaxation of the D₂ defect follow a single exponential decay, but more complex relaxation is found when OH content is high. In the latter case a double-exponential fit describes the observed relaxation well. The activation energies found are: for creation of D₂ defects 0.53 ± 0.07 eV; for single exponential relaxation in low-OH material, 6.0 ± 0.3 eV; for high-OH material, primary relaxation 5.1–5.2 ± 0.3 eV, secondary relaxation 2.4–2.5 ± 0.5 eV.     

Inelastic neutron and low-frequency Raman scattering in a niobium-phosphate glass for Raman gain applications

We present measurements of the vibrational spectrum of a binary niobium-phosphate glass in the THz frequency range using inelastic neutron and Raman scattering. The spectra of these glasses show a low-frequency enhancement of the vibrational density of states (“boson peak”). Using a recently developed theory of vibrational excitations in disordered solids we are able to reconcile the measured neutron and Raman spectra using fluctuating elastic and Pockels constants as a model concept. As the spontaneous Raman susceptibility is a key parameter for Raman amplification our results suggest a significant gain profile for application of niobium-phosphate glasses in Raman amplifiers.     

XRD,IR, and Raman investigations of structural properties of Dy2‐xHox O3 prepared by sol gel procedure

The Rare earth mixed oxides Dy_2‐xHo_x O₃ (0.0 ≤ x ≤ 2.0) solid solution was synthesized by a sol–gel process. X‐ray diffraction (XRD) data were collected and crystal structure and microstructure analyses were performed applying Rietveld refinement method. Infrared and Raman spectroscopy were used to define the microstructure and to locally probe the structure of the samples. The cationic distribution over the two non‐equivalent sites 8b and 24d of the space group Ia3 is found to be randomly. The crystallite size and microstrain as well as Raman modes positions are influenced by Ho³⁺ concentration. The apparent size is isotropic but significant anisotropy is found for the microstrain with its largest value along the crystallographic direction [h00]. Inspite the single phase solid solution confirmed by Rietveld analysis for all samples, Raman spectra detected the coexistence of two phases; cubic and distorted monoclinic of too small amount or highly disordered, i.e. amorphous like, to be detected by XRD. The result indicates the ability of Raman spectroscopy to detect minor phases in solid solutions. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

FTIR,powder XRD,TEM and dielectric studies of pure and zinc doped nano‐hydroxyapatite

Hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂ or HAP, is an important bio‐material, which is having application in bone implants and dentistry. In the present study, zinc doped nano‐hydroxyapatite (Zn‐HAP) was synthesized via chemical precipitation route using surfactant mediated approach. The doping of zinc was confirmed by EDAX. The powder X‐ray diffraction (XRD) pattern revealed the typical hydroxyapatite pattern with broadening and extra peaks were observed for higher concentration. The average crystallite size was calculated by applying the Scherrer's formula to powder XRD pattern and was found in the range of 16 to 33 nm. The morphology of synthesized nano‐particles was also confirmed using TEM. FTIR spectroscopy was used to confirm the presence of various bonds. The dielectric study was carried out at room temperature within the frequency range from 10² Hz to 10⁷ Hz and the variations of dielectric constant with frequency of applied field as well as with the concentration of zinc were studied. It was found that as the concentration of zinc increased the dielectric constant increased. The variations of dielectric loss and a.c. conductivity with frequency of applied field were studied. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ex situ XRD,TEM, IR,Raman and NMR spectroscopy of crystallization of lithium disilicate glass at high pressure

The structure of Li₂O · 2SiO₂ (LS₂) glass was investigated as a function of pressure and temperature up to 6 GPa and 750 °C, respectively, using XRD, TEM, IR, Raman and NMR spectroscopy. Glass densified at 6 GPa has an average Si–O–Si bond angle ∼7° lower than that found in glass processed at 4.5 GPa. At 4.5 GPa, lithium disilicate crystallizes from the glass, while at 6 GPa new high pressure form of lithium metasilicate crystallizes. This new phase, while having lithium metasilicate crystal symmetry, contains at least four different Si sites. NMR results for 6 GPa indicate the presence of Q⁴ species with (Q⁴)Si–O–Si(Q⁴) bond angles of ∼157°. This is the first reported occurrence of Q⁴ species with such large bond angles in alumina free alkali silicate glass. No five- or six-coordinated Si are found.     

EPR,optical absorption,MIR and Raman spectral studies on libethenite mineral

Libethenite, a copper phosphate mineral originated from Congo is used in the present studies. Optical absorption spectrum is due to Cu(II), which is in rhombic distortion. Whereas EPR results show that Fe(III) and Mn(II) are also present in the mineral. MIR and Raman spectral features are attributed to phosphate fundamentals and lattices vibrations of CuO respectively. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Broadband terahertz time-domain spectroscopy and low-frequency Raman scattering of glassy polymers: Boson peak of PMMA

The low-energy vibrational properties of polymethyl methacrylate (PMMA) were studied by terahertz time-domain spectroscopy and Raman scattering. The real and imaginary parts of a complex dielectric constant were accurately determined in the frequency range from 0.2 to 5.0 THz. The imaginary part of the dielectric constant shows a line-shape similar to the imaginary part of the Raman susceptibility measured by Raman scattering. These two spectra show broad peaks at about 2.3 THz. We also separately determined the Raman and far-infrared light-vibration coupling constants of the PMMA using the vibrational density of states determined by cold neutron inelastic scattering in the literature.     

Synthesis and characterization of magnesium doped lead titanate

Magnesium (Mg) doped lead titanate powders (PT: Mg) ceramics, with various Mg contents (0, 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20, and 30 mole %), are prepared by the sol‐gel method and characterized by X‐Ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. XRD results show that the magnesium diminishes the lattice tetragonality of PT:Mg. The average particle size and morphology were studied by SEM. The investigations done by Raman spectroscopy allow the analyzis of the substitution mechanism behavior related to the Mg incorporation into PT structure. A concentration threshold appears around 10% of Mg corresponding in a change of the compensation process with Mg²⁺ ions replacing Pb²⁺ ions below and both Pb²⁺ and Ti⁴⁺ above. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Raman scattering and electrical characterizations studies of hydrogenated amorphous silicon-germanium alloys prepared by 40 MHz plasma-enhanced CVD

This paper presents results on Raman scattering and electrical characterizations in a-SiGe:H films prepared by 40 MHz very-high frequency plasma-enhance chemical vapor deposition (VHF-PECVD) technique from various gas mixtures of silane and germane. We found that when GeH₄/SiH₄ + GeH₄ ratio increases, Raman spectrum results observed that the Si-Si peaks intensity decreases and the Ge-Ge peaks intensity increase, respectively. This can be attributed to incorporation of Ge, an increase disorder in a-SiGe:H film. The conductivity characterizations were shown that when GeH₄/SiH₄ + GeH₄ ratio increases, the deterioration of a-SiGe:H films also increases, which is in agreement with Raman spectrum analysis results.     

Computational and Raman studies of phospho-tellurite glasses as ultrabroad Raman gain media

Molecular orbital calculations of two phospho-tellurite model clusters were performed to clarify the origins of the Raman bands in the Stokes region of over 1000 cm^− 1 in phospho-tellurite glasses. The Raman bands could be attributed to two components of 900-1050 cm^− 1 of symmetrical stretching vibrations of PO₄ units and 1050-1200 cm^− 1 of anti-symmetrical stretching vibrations of PO₄ units. It was also clarified that the top of the valence band of phospho-tellurite glasses consists of the lone pair electrons in a TeO_4 + 1 unit and the bottom of the conduction band of the glass consists of the antibonding hybrids of Te 5p and O 2p orbitals in the equatorial plane of a TeO₄ unit.We have developed new phospho-tellurite glasses which have the Raman gain peak of 30 times as large as silica glass or the Raman gain bandwidth of more than 1200 cm^− 1.     

Synthesis, Fourier-transform Raman and infrared spectroscopic analysis, and crystal structure of (NiL)2, (L = bis(2,4-dimethyldipyrrin-3-yl)methane)

The Ni(II) complex with bis(2,4-dimethyldipyrrin-3-yl)methane, (NiL)₂, has been synthesized and characterized by ¹H-NMR, UV–Vis, FT-IR, FT-Raman, MS, and elemental analysis. X-ray diffraction analysis at room temperature indicates that the complex crystallizes in triclinic system, space group P–1 with a = 11.344(4), b = 12.703(4), c = 14.936(5) Å, = 87.017(6)°, = 75.379(5)°, = 75.318(5)°, M _r = 826.31, V = 2014.5(11) ų, Z = 2. The crystal structure of the title complex reveals that it is a dinuclear double-stranded helical entity. The ligands perform as tetradentate ligands and the ratio of Ni(II) to ligand is 2:2. The central Ni(II) atom is tetracoordinated by four nitrogen donors of two ligands and the coordination geometry of Ni(II) can be considered as a distorted tetrahedron configuration. The IR and Raman spectral analysis, assignment, and discussion are presented.     

Raman investigation of the drawing effects on Ge-doped fibers

We have investigated the Raman activity of various germanosilicate fibers and their associated preforms. Our data indicate an enhancement in small rings' (3-member rings) concentration in the silica-based matrix of the fibers during the drawing process. The generation of such rings appears compatible with an increase of the sample density and fictive temperature. The data regarding the drawing effects on the fiber stress appear less clear, and it is possible to suggest that in some cases the drawing could lower the tensile stress. Finally we have also provided evidence that changing the drawing conditions within the usual range of application leads to no significant changes of the matrix structure as can be observed using Raman spectroscopy.     

Characterization of Vacuum Evaporated Polycrystalline Cd0.96Zn0.04Te Thin Films by XRD,Raman Scattering and Spectroscopic Ellipsometry

Cd_0.96Zn_0.04Te thin films are deposited onto well cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation and the films are annealed at 423 K. Rutherford Backscattering Spectrometry and X‐ray diffraction techniques are used to determine the thickness, composition and crystalline structure and grain size of the films respectively. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the as‐deposited films is 3.7 nm and on annealing the films at 423K, the rms roughness value decreases to 3.4 nm. The Raman spectra of the Cd_0.96Zn_0.04Te films are recorded at room temperature to study lattice vibrations and their interactions with other excitations. The intensity of the peak increases and the FWHM decreases on annealing the films. The pseudodielectric‐function spectra, ε(E) = ε₁(E) + i ε₂(E), of polycrystalline Cd_0.96Zn_0.04Te thin films in the 1.3 ‐ 5.5eV photon energy range at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E₁, E₁+Δ₁ and E₂ critical points are due to interband transitions.     

Growth and characterization of Nd,Yb – yttrium oxide nanopowders obtained by sol‐gel method

Nanopowders of Y₂O₃ pure, doped and codoped by Nd³⁺, Yb³⁺ were obtained by sol‐gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one‐phased compounds of Y₂O₃ doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y₂O₃ doped 0.5 at% Nd and 2 at% Yb are presented. Y₂O₃ containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co‐doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The selenium based chalcogenide glasses with low content of As and Sb: DSC, StepScan DSC and Raman spectroscopy study

Thermal properties and structure of As_xSe_100−x and Sb_xSe_100−x glass-forming systems (x = 0, 1, 2, 4, 8 and 16) were studied by conventional and StepScan DSCs and Raman spectroscopy. Compositional dependence of the glass transition temperature, T_g, was determined from reversible part of StepScan DSC records and discussed. The attention was also focused on the crystallization of undercooled melts of these systems. It was found that only selenium crystallizes from undercooled melts of As–Se system and its tendency to crystallize decreases markedly with increasing As content, for arsenic content higher than 4 at.% no crystallization was observed. In the case of Sb–Se system Sb₂Se₃ crystallizes in the first step followed by trigonal selenium crystallization from non-stoichiometric undercooled melt. Sb₂Se₃ crystallizes from incongruent melt with crystallization enthalpy ΔH_c(Sb₂Se₃) = −52 ± 2 J/(g of Sb₂Se₃), Johnson–Mehl–Avrami kinetics of crystallization and kinetic exponent close to 3 was found. Raman spectra were measured to obtain basic information on the structure of both glassy systems.     

Raman scattering and electron spin resonance studies of fluorozirconate glasses

Electron spin resonance and Raman spectra are reported for fluorozirconate glasses which contain transition metal impurities. From the observed g values at 2.0 and a broad signal from 1 to 10, it is concluded that the dominant contribution to the ESR signal is due to Fe³⁺ in sites with rhombic distortion. The Raman spectra are shown to be superposed by luminescence emissions for paramagnetic impurity concentrations as low as ∼10¹⁶ spin/mol of ZrF₄. However, the amplitude and frequency of the dominant polarized Raman mode near 580 cm⁻¹ are observed to be relatively independent of impurities.     

Application of the constant stoichiometry grouping concept to the Raman spectra of Pb(PO3)2-TeO2 glasses

Pb(PO₃)₂-TeO₂ glasses in the whole range of glass composition were first obtained and their properties (refractive index, density, T_g and light scattering losses) were determined. Based on the vibrational spectroscopy data a new approach was applied to investigate the interactions of initial oxides in melts resulted in so-called constant stoichiometry groupings (CSGs) formation symbolizing intermediate range order in glasses. Vibrational spectra of glasses are interpreted as a superposition of unchangeable spectral forms (principal spectral components (PSCs)) belonging to CSGs: PbO · P₂O₅, TeO₂ · 2PbO · 2P₂O₅, TeO₂ · PbO · P₂O₅, TeO₂, and possibly 2TeO₂ · PbO · P₂O₅ and 6TeO₂ · PbO · P₂O₅. In this work Multivariate Data Analysis has been applied as the independent mathematical tool to decompose Raman spectra of glasses and reveal the number of PSCs. It is shown that application of factor analysis results in the same five PSCs that confirms our data obtained from the CSG concept. This concept allows also the prediction of the existence of unknown compounds, and correspondingly some crystals (TeO₂⋅ 2PbO⋅2P₂O₅ and others) were revealed by XRPD of the crystallized glasses. The CSG concept opens the way for elaboration of low scattering glasses as candidates for Raman amplifiers. It is shown that Pb(PO₃)₂-TeO₂ glasses with small content of TeO₂ are of interest to photonic technology.     

掺氮四配位非晶碳薄膜的拉曼光谱和表面形貌

采用磁过滤真空溅射离子沉积技术,用氩气和氮气共溅射石墨靶,在不同氮气分压下,制备了一组不同氮含量的四配位非晶碳薄膜(ta-C:N).用X射线光电子能谱确定ta-C:N薄膜中的氮含量;研究了氮含量对ta-C薄膜的拉曼光谱和表面形貌的影响.结果表明:不含氮的ta-C薄膜的拉曼光谱是中心在1580cm-1、范围从1200cm-1至2000cm-1的类高斯峰,表面均匀光滑;含氮的ta-C:N薄膜,其拉曼光谱分裂为1360 cm-1的D带和1580 cm-1的G带,且D带与G带的最大强度比, 以及薄膜的表面粗糙度随氮含量的增加而增大.最后讨论了氮含量对ta-C薄膜的微结构的影响.     

Cross‐sectional and surface Raman mapping of thick GaN layers

Raman scattering spectroscopy was utilized for investigation of the structural properties of thick GaN layers. These layers with thickness ∼ 40 μm have been grown by HVPE technique on the sapphire substrates. The investigations have been focused on the strain distribution in GaN layer cross‐section as a function of distance from an interface sapphire/GaN and mapping of the surface and of the inner layer, near the sapphire/GaN interface. From the observed phonon shifts in the Raman spectra strain differences lower than 6.4×10^–4 corresponding to stress differences of 240 MPa were estimated across the thick GaN epitaxial layer. The measurements exhibit that strain in the layer causes changes in the Raman spectra and allow determining the relaxation process in the crystal. The obtained results confirmed, that the mode frequencies in the measured Raman spectra in both directions (parallel or perpendicular to the growth direction) for layer thicknesses over 30 µm are comparable with typical values for bulk material and match the low strain in the structure due to relaxation processes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)