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Crystalline films of lead-free all-inorganic Cs3Bi2X9 (X = Br, I) perovskites have been deposited by radio frequency (RF)-magnetron sputtering providing high-quality, single-phase films as confirmed by structural, morphological, and optical property characterization. Progressive tuning of crystal structure characteristics and optical absorbance has been achieved in mixed Br/I phases Cs3Bi2(I1–xBrx)9 (0 ≤ x ≤ 1), highlighting a shift of the band gap from about 2.0 eV for Cs3Bi2I9 to 2.64 eV for Cs3Bi2Br9. X-ray diffraction and Raman scattering allowed defining the range of alloyed compositions where single-phase compositions are found. Finally, preliminary photocatalytic activity tests on the degradation of methylene blue provided solid data indicating the future possible exploitation of Bi-based perovskite derivative materials as active photocatalysts., High-quality films of the Cs3Bi2(I1−xBrx)9 (0 ≤ x ≤ 1) system have been grown by the vapor phase method for the first time. Crystal structure investigation revealed a phase change around x = 0.4, as demonstrated by X-ray diffraction and Raman spectroscopy. Halide alloying provided a continuous modulation of the band gap from 2.0 eV for Cs3Bi2I9 to about 2.64 eV for Cs3Bi2Br9.

GdFeO3 perovskite attracted large interest in different fields thanks to peculiar magnetic and optical properties that are further tunable by means of doping processes and achievable on both Gd and Fe sites or by properly choosing the synthesis routes. In this paper, nanometric GdFeO3 compounds, undoped and doped with diamagnetic Ca2+ and Mg2+ ions, were synthesized by microwave assisted, sol–gel, and polyol syntheses and characterized by X-ray diffraction, showing solid solutions formation. Raman spectroscopy allowed us to confirm, from peak enlargements, the Ca and Mg substitution on Gd and Fe sites, respectively. The magnetic data showed the presence of magnetic domains as consequence of doping with diamagnetic ions, which seem to play a crucial role in the magnetic activity of the compounds. A superparamagnetic behaviour is evidenced; nevertheless, its intrinsic character is not definitely demonstrated. Indeed, the possible presence of traces of magnetic impurities, which are easily obtainable in these samples, such as iron oxides, must be taken into account.

FeNb11O29, pure or doped with metal transition ions, is a very promising material with advanced multifunctionalities and interesting applicative perspectives. It is isostructural with Nb12O29, one of the rare compounds in which Nb displays a local magnetic moment and shows both antiferromagnetic ordering and metallic conductivity at low temperatures. In this work we have synthesized and studied Fe0.8V0.2Nb11O29 monoclinic powders. In particular we monitored the effects on structural, electronic and magnetic properties in samples produced in different atmospheres to stabilize cations with different oxidation states. We have demonstrated that the reaction atmosphere influences the phase homogeneity, the crystallite size and the amount of paramagnetic centres, with a transformation of Fe3+ in Fe2+ when an inert atmosphere is used, as proved by the absence, in this case, of any electron paramagnetic resonance signal. Also the Raman spectra result to be affected due to the change of coordination polyhedra. Subsequent re-oxidation of reduced powders brings to the monophasic iron niobate again containing Fe3+ demonstrating the reversibility of redox process. This reversibility is accompanied by a complete restoring of monoclinic structure evidenced by X-ray diffraction data and by Raman measurements, which allowed also to follow in situ the spectral changes induced by laser heating.

Black phosphorus (BP) is a two-dimensional material potentially of great interest for applications in the fields of energy, sensing, and microelectronics. One of the most interesting methods to obtain BP is the conversion from red phosphorus (RP) by means of high-energy mechanochemical synthesis. To date, however, this synthesis process was not well characterized. In this work, starting from the mathematical model of energy transfer during the ball milling process, we investigate the effects on RP → BP conversion of three experimental parameters, the rotation speed, the milling time, and the weight ratio between the spheres and the milled material (BtPw ratio). The efficiency of the conversion process was verified by solid-state NMR, Raman spectroscopy, and X-ray diffraction. Whereas the first two parameters have a minor importance, the BtPw ratio plays a primary role in the RP → BP conversion. Yields approaching 100% can be obtained also with short milling times (15 min) and adequate rotation speed (e.g., 500 r.p.m.), provided that the BtPw ratio >40:1 is used. These results confirm the energy sustainability of the mechanochemical synthesis approach.

The aim of the study was to qualitatively investigate the structure of the surface layer of TiO2 on dental implants made of Ti-6Al-4V subjected to different manufacturing treatments. M (machined), B (Al2O3-blasted), E (HNO3\HF-etched), B + E and A (B + E + anodized) implants and a further group receiving the same treatments as the first group with the addition of a final decontamination with cold plasma were included in the study. Examination was performed using micro-Raman spectroscopy. The surface treatments evaluated did not achieve the formation of crystalline TiO2. The increase in the complexity of surface treatment produced a proportional increase in the thickness of amorphous TiO2 oxide. In the B + E group, the plasma treatment enhanced the amorphous oxide thickness of TiO2. The other surfaces treated by plasma decontamination did not show a difference to the respective untreated ones. The investigated surface treatments did not change the crystalline cage of TiO2 in Ti-6Al-4V implants but affected the thickness of the oxide layer. The biological response could be influenced by different oxide thicknesses. Additional information on superficial TiO2 structural organization can be obtained by micro-Raman evaluation of dental implants. Dental implants with B + E + plasma and A superficial treatments allowed the maximum formation of the amorphous oxide thickness.

ZnFe2O4 ferrite nanoparticles are arousing a great interest in the biomedical field, in particular for magnetic hyperthermia application, thanks to their superparamagnetic behaviour at room temperature. In order to better tuning the magnetic properties, different doping substitution and synthesis methods have been tried to reduce particle sizes and to vary the cation distribution on the spinel sites. In this paper, we focused on the microwave combustion synthesis method of Ca (on Zn site) and Gd (on Fe site) substituted ferrites. Undoped ZnFe2O4 and Sr and Al doped samples were also synthesized for comparison. The use of X-ray powder diffraction, microscopic and spectroscopic techniques allowed us to ensure the good quality of the spinel structure for all the investigated samples, to determine a homogeneous distribution of the dopants and an average particle size lower than 11 nm. In addition, we estimated the inversion degree of the spinels by using the Rietveld structural refinement and Raman spectroscopy. By means of SQUID magnetometry we found, for all the samples, a superparamagnetic behaviour with saturation magnetization between 6 and 10 emu/g at the maximum applied magnetic field of 3T, with a more effective role played by Ca ions with respect to Gd ions substitution.

We report the structural analysis of the highly-doped lithium fulleride Li12C60, performed using low-temperature neutron powder diffraction. Although the main reflections could be initially indexed with a fcc cell, Monte Carlo Simulated Annealing suggests an unusual monoclinic arrangement for the fullerene molecules. In this structure, C60 units with the same orientation are alternatively stacked to form layers, thus maximising their sterical crowding. Rietveld refinement allowed to localise Li ions, which are organised in clusters belonging to the pseudo-tetrahedral voids with a non-complete charge transfer as confirmed by Raman spectroscopy.

We prepared and characterized recyclable surface enhanced Raman spectroscopy (SERS) active glass chips. Gold nanostars were grafted on properly functionalized glasses by means of electrostatic interactions and then they were coated with a silica layer of controllable thickness in the nanometer range. The SERS activity of the obtained substrates were tested in terms of reproducibility and homogeneity intra-samples and inter-samples from different batches using the Raman reporter as the model compound rhodamine 6G. The uncoated substrates were used as reference to evaluate the effect of silica spacers on SERS enhancement factors (EFs). The chemical route to obtain silica-coated SERS chips is described in detail, and the morphology and the optical response of substrates have been characterized. We demonstrate that SERS substrates coated with 1 nm silica conserve a good EF, and that the coating confers to the SERS platform an extreme robustness leading to reusability of the substrates.

Thermal stability and phase homogeneity of the triphylite LiFePO4 compound were investigated by means of Raman spectroscopy. A detailed check of phase homogeneity of undoped samples obtained from different preparation routes—hydrothermal, sol–gel, and solid state synthesis—and Mn-doped compounds from solid-state synthesis was performed by means of a mapping of the Raman spectra. The triphylite compositional and structural properties were carefully investigated also with the help of structural refinements and magnetic techniques, which also allowed us to reveal and identify the impurity phases formed together with the olivine LiFePO4. The effect of laser irradiation on the triphylite thermal stability was thoroughly investigated and related to the synthesis route, to the doping, and to the sample homogeneity. The thermal stability of iron oxides, present both as synthesis products and as consequence of the irradiation itself, was also analyzed following the magnetitemaghemitehematite phase transformation. All the experimental observations concur in indicating that the effectiveness of the laser heating on these compounds mainly depends on grain size and the degree of order of the olivine structure, the highest thermal stability being displayed in the case of the nonhomogenous undoped samples obtained from solid-state preparation, which show a highly ordered triphylite phase. Copyright © 2010 John Wiley & Sons, Ltd.

We present the results of a systematic study performed by micro-Raman spectroscopy on pure anatase, pure rutile and mixed anatase–rutile TiO2 thin films, deposited by radio frequency magnetron sputtering on quartz substrates, with different thicknesses. The crystal structures of the as-deposited films were unambiguously determined and a good crystalline homogeneity was revealed by a systematic mapping of the samples. In the mixed-phase films, the relative amount of the two phases was monitored by a simple analysis of the components of the multi-Lorentzian fitting curves. For the single-phase films, the influence of the thickness and the effect of different thermal treatments, carried out to obtain series of thin films differing only for oxygen content, are discussed. The analysis of the scattered light has provided indication about the presence of an interface layer between the substrate and the film, which can play a role in driving the interesting magnetic properties exhibited by our samples, which are of potential usefulness for spintronics application. The results obtained from other techniques are briefly reported and discussed in relation to our systematic Raman characterization. This study points out how Raman investigation can provide suggestions toward the understanding of the complex physical phenomena leading to room-temperature ferromagnetism in TiO2 thin films. Copyright © 2009 John Wiley & Sons, Ltd.

Micro Raman and static magnetization data on manganese or cobalt-implanted (at 3 or 5 at.%) strontium titanate (Mn,Co):SrTiO3 single crystals are presented. Micro Raman results reveal a cubic perovskite structure at 300 K with no evidence of any secondary phase. All samples show ferromagnetism both at 300 K and at 10 K. Moreover, micro Raman spectra at low temperature reveal the presence of polar ordering, which allow to consider the investigated materials as possible host matrices for multiferroic phenomena. Obtained results are discussed in connection to supplementary outcomes derived by content, optical absorption and electron paramagnetic resonance (EPR) measurements.

Crystalline inclusions, commonly called stones, are very dangerous defects present in industrial glass products. Refractory materials of the furnace, raw materials and ceramic grains introduced with glass cullet, are the main sources of stones. To improve the quality of glass products, the understanding of the mechanisms responsible for the formation and the transformation of these defects is required. At the interface glass melt/stone surface several reactions occur leading to the formation of new glassy and crystalline micro-phases. These phases are usually studied by scanning electron microscopy and X-ray microanalysis on polished cross sections. Nevertheless SEM-EDX chemical analysis alone does not allow the complete identification of the different phases. In this work, the reactions occurring between refractory materials and the molten glass were studied with a micro-chemical and micro-textural approach completed by micro-structural investigation. Compositional and textural features were investigated by SEM-EDX and by μ-Raman spectroscopy. Raman spectra of pure crystalline well identified compounds were compared with those of the unknown phases. This technique allowed to identify the nature of the re-crystallized phases. The combined use of SEM-EDX and μ-Raman techniques revealed to be very promising in the study of the origin and in the characterization of stones in glass.

We report on micro-Raman spectroscopy as a tool to improve the quality of the industrial glass production. Crystalline inclusions, commonly called stones, are very dangereous defects present in industrial glass products. To minimize this technological problem, the detailed knowledge of the formation and transformation processes of these defects is required, and a complete identification of the different phases requires a multianalytical approach. Micro-Raman measurements were performed on a series of laboratory samples with different chemical compositions. Performing linear scanning and mapping of Raman features, we obtained a well-defined characterization of the evolution and nature of stones. In addition, information on the crystallization degree of the reaction layers was obtained by correlating the shape and intensity of the photoluminescence of Cr3+ impurities. Copyright © 2008 John Wiley & Sons, Ltd.

Microstructural modifications, induced by femtosecond laser irradiation on Lithium Niobate (LN) crystals were investigated by means of optical microscopy and micro-Raman spectroscopy. Commercial z-cut congruent LN substrates were irradiated with focused ultra-short laser pulses at 810 nm. At the focus region either structural changes or material removal were observed by varying the irradiation conditions. The mapping of Raman spectrum revealed the insurgence of Raman modes, which are forbidden in the used scattering geometry. This phenomenon increases gradually by approaching the ablation region. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work we report on micro-Raman analysis on lithium niobate (LN) substrates in order to study the compositional homogeneity of the crystals and to clear up the effects of etching and polishing processes on the surface of wafers and crystals. The fact that the linewidth of some Raman modes scale with the composition of LN crystals, together with the use of a confocal microscope, allowed a three-dimensional determination of the sample stoichiometry and of the crystalline quality. This local tool can supply additional information, which can be complementary to the electro-optic coefficients, carefully measured as well in order to check functional parameters. Raman spectra from buried regions were obtained on as-grown, etched and polished crystals and wafers. The depth profile of the peak energy and the linewidth of the Raman mode at 872 cm −1 indicate that mechanical processing of surfaces causes, in some cases, structural modifications till a depth of 15 μm.

First order Raman spectra in the region 200–800 cm−1 have been collected for AMn2O4 (A = Mn, Mg and Zn) tetragonal spinels. A possible correlation between Raman phonons and AO4 and MnO6 unit vibrations is proposed. Structural changes have been analyzed following the evolution of the Raman spectra with x for the Mg1−xMnxMn2O4 solid solution; the effect of the spinel inversion has been also studied on MgMn2O4 quenched samples from high temperatures. The results, taking into account also the X-ray diffraction and electron paramagnetic resonance data, show the influence of the Jahn–Teller effect on the Raman scattering for this class of materials.

The Y2BaNiO5 compound, prototypical Haldane system characterized by anti-ferromagnetic behaviour, and its analogs Y2BaNi12xMxO5 (M ¼ Mg, Zn; 0:05 # x # 0:65) are investigated by X-ray diffraction and Raman spectroscopy. Structural features and phase stability ranges of the doped samples are first determined. The first order Raman scattering for the different solid solutions is measured at room temperature in order to gain new insight on lattice dynamics of the Y2BaNiO5 compound when Zn 2þ or Mg 2þ ions progressively substitute into Ni site.

KTaO 3 with small amount ( x < 0.01) of Li and simultaneously diluted by Nb (K 1 m x Li x Ta y Nb 1 m y O 3 , KLTN) reveals original dipole ordering structural effects. Small Nb co-dopings ( y < 0.007) enhance the trend of the Li + off-centers related subsystem towards cooperative ordering and order-disorder phase transitions. At 0.01 < y < 0.05 the intrigue features of displacive and order-disorder transitions reveal. The most interesting features are the appearance of soft-mode driven ferroelectric transitions accompanied by a Li + off-centers system freezing followed by a reentrant dipole glass-like phase formation, and the emergence of a narrow transition with giant magnitude of l '(T). Evidences of reentrant dipole glass formation were observed in KTa 0.981 Nb 0.019 O 3 too. A possible model developed is based on the Li-Nb polar clusters, local configuration instabilities and superparaelectricity conceptions.

We present a detailed investigation of structural properties of manganese doped strontium titanate ceramics and Verneuil grown single crystals, the last prepared with Sr deficiency compensated by proper Mn amount. EXAFS, TEM, ESR and Raman techniques, combining local and lattice probes, allows to inspect the local chemical environment and electronic structure of manganese taking into account possible chemical non-homogeneities and/or phase segregation. On the basis of experimental evidences, structural models for Mn insertion in SrTiO3 are discussed considering possibility for Mn ions to occupy both Ti4+ and Sr2+ sites as well as manganese segregation and Mn incorporation related non-homogeneities.

Raman investigations on single crystals of K 1-x Li x Ta 1-y Nb y O 3 were performed to identify structural effects arising from the simultaneous presence of off-centre Li and Nb ions in the incipient ferroelectric KTaO 3 . Two soft-mode transitions were evidenced at 45 K and 30 K in a sample with x = 0.0014 and y = 0.024 after both zero-field and field cooling. These temperatures are close to the maximum and to the extrapolated Curie temperature for non-relaxing permittivity reported in the same system. A sample with x = 0.0028 and y = 0.013 displayed a ferroelectric transition just below 30 K only after field cooling, also being consistent with permittivity data.

Polycrystalline EuBa 2 Cu 3 O y (EuBCO) samples with various oxygen contents ( y =6.25, 6.38 and 6.8) have been analysed by means of microRaman spectroscopy. The usual Raman features of REBa 2 Cu 3 O y high temperature superconductors (RE=Y, Eu, Sm, Er…) have been confirmed also for EuBCO. A correlation between the crystal structure and the conductivity properties as a function of the oxygen content has been established by studying in detail the features of the different Raman spectra. In particular, the analysis of the peak profiles of lattice vibrations involving oxygen atoms provides important information to understand the anomalous superconducting properties found in the sample with y =6.38. In addition, the appearance in the superconducting samples of a new mode centred at 223 cm −1 may be correlated to ordering phenomena which have been called to justify the conductivity results.

Li admixture greatly enhances n-type photoconductivity of KTaO3 crystals. Thermally stimulated current experiments indicate that this phenomenon is related with the presence of hole-trapping levels with depths of 50–100 meV. This is in good agreement with recent energy structure calculations showing the existence of levels at these energies above the top of the VB, due to perturbed O2- p-states. The study of visible photoluminescence and thermo-luminescence shows that the hole-trapping centre also controls the emission process. We conclude in favour of radiative recombination involving O−Ta4+polaron pairs. Keywords: ferroelectric perovskites: photoconductivity

Raman observations in the region of the TO 1 soft mode were performed on samples of K 1-x Li x Ta 1-y Nb y O 3 , having x in the range 0.6 - 1.0 % mol. and y in the range 0.2 - 0.3 % mol. The analysis of temperature evolution and spectral shape allowed to evidence the spontaneous splitting of the TO 1 mode and its relative stiffness below 50 K, accompanied by an abrupt increase of first order scattering strengths. Such effects are not observed when Li or Nb are separately introduced in the KTaO 3 matrix, at the given concentrations.

Raman scattering observations were performed on samples of K1-xLixTa1-yNbyO3, with x in the range 0.6-1.0 mol% and y in the range 0.2-0.3 mol%. Concentrations of Li and Nb, determined by analytical methods, were below the known thresholds at which these substituents can separately induce a ferroelectric transition in the quantum paraelectric KTaO3. The temperature evolution of TO1 and TO4 spectra was monitored. The results show a critical behaviour below 50 K, characterized by an abrupt increase of first-order scattering strengths and by spontaneous splitting of the non-softening TO1 mode. From our data, we infer the occurrence of a ferroelectric phase transition of order-disorder character. This proves that small additions of Nb enhance the tendency of the Li subsystem towards cooperative ordering in the KTaO3 matrix.

The temperature evolution of TO1 Raman spectra was investigated in single crystals of K1−xLixTa1−yNbyO3:Cu with different Li and Nb amounts. Auxiliary observations of TO4 spectra were also performed. In a sample with x = 0·002 and y = 0·025 and containing 190 ppm of Cu, the results indicate a clear-cut transition to an ordered phase around 55 K, in good agreement with previous findings from dielectric measurements in the same crystal. However, no evidence was found of a role of Cu in this structural modification. Samples with x = 0·01 and y = 0·003 revealed features of an order-disorder phase transition around 45 K, irrespective of the presence of Cu.

Encapsulated Fe3O4 nanoparticles of average diameters d = 12 nm are obtained by coprecipitation, in the presence of 2-methoxyethanol hemiester of poly(maleic anhydride-alt-butyl vinyl ether) 5% grafted with poly(ethylene glycol) (VP-MAG nanoparticles). A complete characterization of nude and encapsulated nanoparticles through structural techniques (namely XRD, TEM, SEM), Raman spectroscopy and magnetic measurements has been performed. These nanoparticles compared with commercial compounds (ENDOREM (R)) present superparamagnetic behavior and nuclear relaxivities that make them promising as magnetic resonance imaging (MRI) contrast agents (CAs). We found that our nanostructures exhibit r(2) relaxivity higher than those of commercial CAs over the whole frequency range. The MRI efficiency of our samples was related to their microstructural and magnetic properties.

In the present work we report on Raman study of Ba0.77Ca0.23TiO3 crystals in the temperature region between 12 K–300 K. We believed to gain insight on the role of Ca admixture, and search manifestations of the possible low temperature tetragonal-orthorhombic phase transition. A special attention was paid to the temperature evolution of A1 and E components of the Γ15 modes. Signatures of the presence of CaTiO3 modes are evidenced at around 100 cm−1. The Raman data give no clear indications of the soft mode driven low temperature phase transitions presence, at least down to 12 K, revealing, however, increasing of disordering at cooling.

Surface modification of noble metal nanoparticles with mixed molecular monolayers is one of the most powerful tools in nanotechnology, and is used to impart and tune new complex surface properties. In imaging techniques based on surface enhanced Raman spectroscopy (SERS), precise and controllable surface modifications are needed to carefully design reproducible, robust and adjustable SERS nanoprobes. We report here the attainment of SERS labels based on gold nanostars (GNSs) coated with a mixed monolayer composed of a poly ethylene glycol (PEG) thiol (neutral or negatively charged) that ensure stability in biological environments, and of a signalling unit 7-Mercapto-4-methylcoumarin as a Raman reporter molecule. The composition of the coating mixture is precisely controlled using an original method, allowing the modulation of the SERS intensity and ensuring overall nanoprobe stability. The further addition of a positively charged layer of poly (allylamine hydrocloride) on the surface of negatively charged SERS labels does not change the SERS response, but it promotes the penetration of GNSs in SH-SY5Y neuroblastoma cells. As an example of an application of such an approach, we demonstrate here the internalization of these new labels by means of visualization of cell morphology obtained with SERS mapping.

Recently, very intriguing dipole-ordering phenomena near the critical temperature and down into the low temperature phase were reported for K{sub 1-x}Li{sub x}Ta{sub 1-y}Nb{sub y}O{sub 3}. The understanding of these processes is a crucial aspect of basic research and applications. In the present work, we report on Raman experiments in K{sub 1-x}Li{sub x}Ta{sub 1-y}Nb{sub y}O{sub 3} crystals with x -0.004 and y -0.031. Systematic analysis of TO{sub 1} and TO{sub 4} spectra within the temperature range of 17-150 K was performed. All the measurements were performed after both zero-field and field cooling. The results enable us to gain new evidence of the competition between long-range order and the Li-related dipole glasslike subsystem.

Recently we reported on an reentrant dipole glass-like phase formation in K0.9986Li0.0014Ta0.976Nb0.024O3 (V. Trepakov et al.: Phys. Rev. B 63 (2001) 172203). Here we present the detailed low-frequency dielectric permittivity and Raman scattering data for nearly the same composition but without Li admixture, namely for KTa0.982Nb0.018O3 (KTN 1.8). We found that upon cool down, KTN 1.8 exhibits soft-mode-driven long-range displacive dynamics with phase transition at TC = 27 K. Below TC the randomness of the Nb distribution leads to a pronounced crossover to the order-disorder polar microregion dynamics which is also accompanied, nevertheless, by TO1 mode stiffness upon cooling. The application of a dc-bias returns the long-range displacive behavior to the system.

We report a facile strategy to obtain multiwalled carbon nanotubes (MWCNTs) functionalized with covalently bonded lysozyme. The functionalization procedure has been investigated by means of several techniques, including thermogravimetry, Raman spectroscopy, transmission electron microscopy, and cyclic voltammetry. A functionalization of about 1 lysozyme molecule every 4000 carbon atoms is obtained. The modified lysozyme-CNTs nanocomposite shows a significant increase of the antibacterial activity towards the Gram-positive S. aureus if compared with lysozyme in solution.

Aim: We investigate the effect of four different types of sterilization procedures on the structural properties and morphological features of single-wall carbon nanotube samples approachable by micro-Raman spectroscopy. Sterilization procedures (treatment in humid heat autoclave or ethylene oxide and irradiation with γ-rays or UV light) are necessary in view of the use of carbon nanotube sterile samples in in vivo toxicity tests on laboratory rats. Micro-Raman spectroscopy allows us to estimate several details about the morphology of the single-wall carbon nanotube mixture (mainly the presence of disorder and diameter distribution) before and after the sterilization treatment. Results: The best of these treatments, in other words, the one that least affected the morphology and structural properties of carbon nanotubes, was found to be UV irradiation and has thus been selected for future in vivo tests on rats.

This work deals with the strain relaxation mechanism in InGaAs metamorphic buffers (MBs) grown on GaAs substrates and overgrown by InAs quantum dots (QD). The residual strain is measured by using Raman scattering and X-ray diffraction, both in Reciprocal Space Map and in single omega-2 theta scan modes (omega and theta being the incidence angles on the sample surface and on the scattering planes, respectively). By relating the GaAs-like longitudinal optical phonon frequency omega(LO) of InGaAs MBs to the in-plane residual strain epsilon measured by means of photoreflectance (PR), the linear epsilon-vs.-omega(LO) working curve is obtained. The results of Raman and XRD measurements, as well as those obtained by PR, are in a very satisfactory agreement. The respective advantages of the techniques are discussed. The measurements confirm that strain relaxation depends on the thickness t of the buffer layer following a -t(-1/2) power law, that can be explained by an energy-balance model.

Lithium niobate crystals doped with hafnium exhibit a significant suppression of the photorefractive effect and represent a promising substrate for wavelength converter devices. In this work we present a systematic investigation of their physical properties.

The room temperature cation occupancy in LiMgVO(4) and LiZnVO(4) crystallographic sites is obtained by means of the combined use of X-ray powder diffraction (XRPD), (7)Li and (51)V magic angle spinning nuclear magnetic resonance (MAS NMR), and micro-Raman measurements. In the LiMgVO(4) Cmcm orthorhombic structure, the 4c (C(2)(v) symmetry) tetrahedral vanadium site is fully ordered; on the contrary, the Li 4c tetrahedral site and the 4b (C(2)(h) symmetry) Mg octahedral site display about 22% of reciprocal cationic exchange. Higher cationic disorder is observed in LiZnVO(4): the three cations can distribute on the three tetrahedral and distinct sites of the R-3 structure. XRPD and MAS NMR analysis results highly agree for what concerns vanadium ion distribution on the three cationic sites (about 25, 26, and 47%). From the full profile fitting of XRPD patterns with the Rietveld method, it is also obtained that Li(+) displays a slightly preferred occupation of the T1 position (approximately 55%) and Zn(2+) of the T2 position (approximately 46%). The vibrational spectra of the two compounds are characterized by different peak positions and broadening of the Raman modes, reflecting the cation distribution and the local vibrational unit distortion. A comparison is also made with recent Raman results on Li(3)VO(4). High temperature XRPD measurements rule out possible structural transitions up to 673 K for both compounds.

Single crystals of TiO(2) rutile doped with Cr, Mn, Fe, Co, Ni, and Cu were grown with the flux method in a Na(2)B(4)O(7) melt. The samples, checked in their structural and phase homogeneity by x-ray diffraction and micro-Raman spectroscopy, were single-phase needle-shaped crystals several millimetres long. Paramagnetic and ferromagnetic behaviours at room temperature were observed and they are discussed also in connection with the magnetic properties of undoped TiO(2) crystals.

42.65.Hw, 72.40.+w, 76.30.–v, 77.84.Dy, 78.30.–j In this work we report on the characterization of structural and defect-related properties of a series of lith-ium niobate single crystals with congruent and stoichiometric composition containing Fe and Mg dopant. In particular we investigate the role of UV and visible irradiation in the charge trapping mechanisms which control the photorefractive (PR) behaviour. Complementary techniques (Raman microscopy, Elec-tron Paramagnetic Resonance, absorption measurements) were used to characterize the degree of crystal imperfections. This is the basic starting point for an exhaustive comprehension of PR behaviour, moni-tored observing photovoltaic current and photoconductivity.

The paper reports on the first crystal growth and Raman scattering studies in K0.992Rb0.008Ta0.96Nb0.04O3 (KRTN) and KTaO3:Rb (3% mol. in the melt), in which Rb+ ions (ionic radius 1.47 angstrom) substitute K+(1.33 angstrom). The experiments were performed in the range 10-300 K and focused on the behavior of TO1 and TO4 modes. The results confirm indications by previous dielectric permittivity data about the ferroelectric nature of the phase transition in KRTN. It appears that a small amount of Rb changes the character of the phase transition induced by Nb from mainly displacive to mainly order-disorder, whereas no evidence of ferroelectricity is revealed in the KTaO3:Rb sample.

This study deals with the effects of 5 and 10% chromium additions on the transport and structural properties of Li3VO4. The Cr substitution is easily obtained without impurity phases and does not affect the room- and high-temperature host crystal structure, as evidenced by X-ray powder diffraction and micro-Raman analysis. The EPR signals are interpreted in terms of quantified amounts of Cr ions in 5+ and 3+ valence states. Suitable 7Li and 51V MAS NMR spectra simulations agree with the EPR results about the relative amount of Cr5+ and Cr3+ ions substituted in V5+ and Li+ sites, respectively. The Cr3+ presence on Li site, also suggested by Raman results and Rietveld refinements, requires Li vacancies to maintain the charge neutrality. The p-type conductivity, suggested by the positive thermoelectric power coefficients, significantly increases by the cation doping up to an order of magnitude.

Various material and functional properties have been measured in lithium niobate crystals (LiNbO3) with different compositions, starting from conventional congruent composition, up to off-congruent and quasi-stoichiometric ones. The UV absorption edge has been measured and correlated with the crystal composition, showing the edge shift towards shorter wavelengths. The ferroelectric transition Curie temperatures have been determined by differential scanning calorimetry, and it increases with Li2O content in the crystal. The surface composition has been checked by micro-Raman spectroscopy. A narrowing of the linewidths has been observed for quasi-stoichiometric crystal, showing an ordered structure, if compared with congruent composition. The coercive field has been measured as a function of temperature for two different crystal compositions, and it has been found lower in the off-congruent substrate. The Ti-indiffusion process has been studied and compared in congruent and off-congruent LiNbO3 substrates by secondary ion mass spectrometry. The main diffusion process parameters have been determined. The Ti diffusion process has been found considerably slower in off-congruent substrates, if compared with conventional congruent LiNbO3, and resulted almost isotropic. The Li-outdiffusion phenomenon has been observed and correlated wit the Ti concentration profile. A careful control on LiNbO3 composition and material properties allows one to find the proper compositional window for the realization of various advanced optical and electro-optical devices.

Raman spectra of single-wall carbon nanotubes (CNTs) either in the form of micrometer sized bundles or thin layers prepared by dilution and sonication of powders have been compared. We have been able to collect the Raman spectrum of nanotube bundles that are not in touch with the substrate, and therefore not affected by interactions with the substrate surface. This spectrum resulted to be similar to that of the precursor nanotube powders, whereas relevant changes in the Raman spectrum are detected when the diluted powders form very thin layers on either metallic or insulating surfaces, as probed by confocal microraman imaging on well defined areas of the CNTs layers. In the case of thin layers, the intensity of the Raman D band, detected between 1 320 and 1 340 cm-1 and ascribed to disorder effects, is strongly enhanced. This enhancement occurs independently on the kind of substrate.

Waveguides obtained by proton exchange in LiNbO3 were characterized by Secondary Ion Mass Spectrometry and m-lines technique. Additional micro-Raman investigations evidenced marked changes in the spectra of the waveguide with respect to the substrate. This suggests that micro-Raman spectroscopy may constitute a direct non-destructive method to determine the depth of the exchanged layer, with a limit which is set by the diffraction-limited spot size.

The Raman spectrum of the metastable Mn5O8 phase, obtained from slow oxidation of Mn3O4 at low temperature, is presented and analysed for the first time and the thermal stability is monitored by the changes in Raman spectra due to laser-induced thermal treatments. A structural transformation toward the spinel phase Mn3O4 is observed at temperature higher than 1000 K. Other Mn oxides, characterised by intermediate Mn oxidation states, are not detected below or during the transition. A compositional model of the sample grains is also proposed by comparing Raman data with X-ray diffraction and scanning electron microscopy measurements. (C) 1999 Elsevier Science Ltd. All rights reserved.

The kinetics of phase transitions and phase segregation induced by annealing temperature on the Ti–W–O gas-sensing layer was studied by x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The main goal was to identify, on the basis of kinetics studies, structurally stable Ti–WO3 thin film phases and compare their response to polluting gases in order to determine possible correlations between structural and electrical properties of the sensing layers.

We investigated the composition dependence of photorefractivity, beam distortion, Raman lines, and birefringence in reduced pure lithium niobate. When lithium content reaches the value of 49.4 mol %, abrupt changes were observed for all these optical properties except birefringence. We suggest that such a behavior may be due to a change in the phonon spectrum occurring around the critical composition.

The dielectric permittivity (100 Hz–1 MHz) and IR reflectivity of SrTiO3:Mn(0.1 at.%) crystals and SrTiO3:Mn(0.1–3 at.%) ceramics prepared maintaining the ratio (Sr+Mn)/ Ti = 1 or (Ti+Mn)/Sr = 1 (A- and B-type ceramics, respectively) were studied. Surprisingly, the magnitude and e'(T) dependence for the crystals and B-type ceramics with 0.1 at.% of Mn appeared to be nearly the same; the magnitudes rise on cooling and reach ~3000 at T = 7 K. At the same time, IR spectra of SrTiO3:Mn(0.1 at.%) crystals reveal that TO (transverse optical) phonons yield a magnitude of low frequency permittivity of ~4000 at T = 5 K, evidencing crystal inhomogeneity. Both crystals, like B-type SrTiO3:Mn(0.1 at.%) ceramics, reveal faint low temperature relaxations with the Arrhenius activation energies ~37–40 meV and ~120–130 meV (P- and T-relaxations). These relaxations emerge in losses only and were tentatively attributed to reorientation of defects associated with MnTi2+–O−-type polaronic centres and Oh1–D4h18 phase transition related effects, respectively. In reduced crystals P-relaxation strongly enhances, becoming distinctly seen in the real part of the permittivity. More heavily Mn doped A- and B-type ceramics reveal strongly pronounced Arrhenius-type dielectric relaxation with activation energy ~59–68 meV depending on the Mn concentration.

Thin films of the Ti-W-O system grown by r.f. reactive sputtering from a Ti-W (10%–90% weight) target have been studied by Raman and microraman spectroscopy, X-ray diffraction and scanning electron microscopy with the aim to investigate their microstructural and morphological properties. To this purpose, the kinetics of structural transformations at different temperatures (600 °C, and 800 °C) have been studied, and the effect of Ti on the WO3 lattice has been singled out. The results show that annealing at different temperatures induces a microstructural evolution from the amorphous phase of the as-deposited thin film to WO3 crystalline phases via an intermediate cubic disordered phase of WO3. The effect of Ti on this cubic phase and on the thin film morphology is also investigated with the aid of microraman and scanning electron microscopy analysis. The results show that two distinct phases arise upon long annealing treatments; namely, small crystallites belonging to the WO3 monoclinic phase are dispersed on a layer composed of a disordered cubic WO3 phase with a high Ti content.