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In this study, We demonstrate mono and few layers MoS2 samples on the SiO2(270nm)/Si substrate from bulk MoS2 crystal by micromechanical exfoliation technique. We have systematically studied Atomic Force Microscopy, Raman and PL properties of mono and few layer MoS2 on the SiO2(270nm)/Si substrate. First, we find that the number of layer values dependent the Raman and PL emission. First, Raman intensity area ratio of the MoS2E12g, A1g and 2LA modes to that area of the Si substrate increased linear with increasing number of layers MoS2. Second, Normalized PL intensity area of the (A) peak decreased linear with increasing number of layers MoS2. The value of those graphs is a method to understand the number of layers the exfoliated MoS2.

The doping concentration of B doped single-crystal Czochralski Si(1 0 0) wafers (6 × 1014-5 × 1019 cm−3) has been monitored via micro-Raman spectroscopy using visible (633 and 532 nm) and near-UV (355 nm) laser excitations at low power (5 mW). Data have been analysed with unprecedented accuracy via a convoluted Fano-Gaussian model of the first-order Raman Stokes mode of Silicon. This allowed the determination of the fitting spectral parameters (peak position and width) with an accuracy of 0.01 cm−1, which enables a reliable probing of the concentration. We observed, independently on the excitation wavelength used, a widening (up to 6.5 cm−1), a frequency-softening (up to 1.5 cm−1) and an intensity reduction (down to 90 % ) of the Si peak with the doping concentration. The widening and frequency-softening follow a strictly linear dependence with doping concentration, allowing a calibration. A linear dependence of the reciprocal Fano asymmetry parameter ( q - 1 ) with excitation energy is verified, with the slope showing a linear behavior with the doping concentration and providing a direct estimate on the hole-phonon interaction strength. Results are reproduced with surface-sensitive near-UV Raman spectroscopy on BF 2 + ion implanted and laser thermal annealed (LTA) Si, demonstrating the full portability of the Raman technique to state-of-the-art nanoelectronics.

Via experiments performed by varying the doping level of single-layer mechanically exfoliated MoS2via post exfoliation thermal annealing in the 200-300 °C temperature range, we study the power dependent room temperature (RT) photoluminescence (PL), which is dominated by A type excitons. The PL spectral yields of the as-exfoliated and annealed samples show sub-linear behaviour as a function of the excitation laser power. The PL signal of the 200 °C annealed sample is dominated by the charged exciton (trion) related peak, while the PL signal of the 300 °C annealed sample is dominated by the neutral exciton related peak, and the PL spectral weight of excitons is tunable in this temperature range. The PL signal increase due to annealing and the intensity ratio of the A type excitons are related, showing a hyperbolic tangent trend. We directly quantitatively demonstrate the one-to-one correlation of the RT resonant Raman (632.8 nm) integrated spectral intensity with the corresponding PL spectral yield, providing experimental evidence of the exciton-phonon coupling effect. The in-plane E2g1 Raman mode exhibits strong coupling with A excitons, while the out-of-plane A1g Raman mode does not. This is an indication of the in-plane spatial symmetry of the A excitons.

We explore the structure of two ionic liquids based on the choline cation and the monoanion of the maleic acid. We consider two isomers of the anion (H-maleate, the cis-isomer and H-fumarate, the trans-isomer) having different physical chemical properties. H-maleate assumes a closed structure and forms a strong intramolecular hydrogen bond whereas H-fumarate has an open structure. X-ray diffraction, infrared and Raman spectroscopy and molecular dynamics have been used to provide a reliable picture of the interactions which characterize the structure of the fluids. All calculations indicate that the choline cation prefers to connect mainly to the carboxylate group through OH⋯O interactions in both the compounds and orient the charged head N(CH3)3+ toward the negative portion of the anion. However, the different structure of the two anions affects the distribution of the ionic components in the fluid. The trans conformation of H-fumarate allows further interactions between anions through COOH and CO2&minus, groups whereas intramolecular hydrogen bonding in H-maleate prevents this association. Our theoretical findings have been validated by comparing them with experimental X-ray data and infrared and Raman spectra.

Carbon spheres of nanometric dimension are known since the first studies on the synthesis of fullerenes. Their shape originates from the curvature of a carbon sheet similar to fullerenes, but with numerous graphitic rings that regulate the inside structure and the formation of open edges at the surface. This paper focuses on the structural and electronic characterization of carbon spheres obtained from a chemical vapor deposition synthesis process. Two different sets of samples are analyzed in detail, in particular, electron microscopies and Raman spectroscopy help understanding the morphology and the graphitic-sp2 arrangement of the carbon atoms in the architectures. In addition, the iron catalyst used during the reaction process confers the carbon spheres a ferromagnetic response at room temperature. Therefore, both the structural properties of the samples and the active contribution of iron mark the difference in the measured photoresponse as well as in the electrochemical behavior. The X-ray photoelectron spectroscopy study addresses these points by giving information on the composition and the iron chemical state in the assembly. The collected results underline the advantages offered by this nanomaterial for sustainable applications.

We report on the fabrication, the morphological, structural, and chemical characterization, and the study of the electrical response to NO 2 and other gases of resistive type gas sensors based on liquid chemically exfoliated (in N-methyl pyrrolidone, NMP) MoS 2 flakes annealed in air either at 150 °C or at 250 °C. The active material has been analyzed by scanning electron microscopy (SEM), and micro Raman and X-ray core level photoemission spectroscopies. SEM shows that MoS 2 exfoliated flakes are interconnected between electrodes of the sensing device to form percolation paths. Raman spectroscopy of the flakes before annealing demonstrates that the flakes are constituted by crystalline MoS 2 , while, annealing at 250 °C, does not introduce a detectable bulk contamination in the expected form of MoO 3 . The sensor obtained by thermal annealing in air at 150 °C exhibits a peculiar p -type response under exposure to NO 2 . In line with core level spectroscopy evidences, this behavior is potentially ascribed to nitrogen substitutional doping of S vacancies in the MoS 2 surface (nitrogen atoms being likely provided by the intercalated NMP). Thermal annealing the MoS 2 flakes in air at 250 °C irreversibly sets an n -type behavior of the gas sensing device, with a NO 2 detection limit of 20 ppb. This behavior is assigned, in line with core level spectroscopy data, to a significant presence of S vacancies in the MoS 2 annealed flakes and to the surface co-existence of MoO 3 arising from the partial oxidation of the flakes surface. Both p- and n -type sensors have been demonstrated to be sensitive also to relative humidity. The n -type sensor shows good electrical response under H 2 exposure.

WS2 exfoliated by a combined ball milling and sonication technique to produce few-layer WS2 is characterized and assembled as chemo-resistive NO2, H2 and humidity sensors. Microstructural analyses reveal flakes with average dimensions of 110 nm, &ldquo, aspect ratio&rdquo, of lateral dimension to the thickness of 27. Due to spontaneous oxidation of exfoliated WS2 to amorphous WO3, films have been pre-annealed at 180 &deg, C to stabilize WO3 content at &asymp, 58%, as determined by X-ray Photoelectron Spectroscopy (XPS), Raman and grazing incidence X-ray Diffraction (XRD) techniques. Microstructural analysis repeated after one-year conditioning highlighted that amorphous WO3 concentration is stable, attesting the validity of the pre-annealing procedure. WS2 films were NO2, H2 and humidity tested at 150 &deg, C operating Temperature (OT), exhibiting experimental detection limits of 200 ppb and 5 ppm to NO2 and H2 in dry air, respectively. Long-term stability of the electrical response recorded over one year of sustained conditions at 150 &deg, C OT and different gases demonstrated good reproducibility of the electrical signal. The role played by WO3 and WS2 upon gas response has been addressed and a likely reaction gas-mechanism presented. Controlling the microstructure and surface oxidation of exfoliated Transition Metal Dichalcogenides (TMDs) represents a stepping-stone to assess the reproducibility and long-term response of TMDs monolayers in gas sensing applications.

We report a compared analysis of inelastic X ray scattering (IXS) and of low frequency Raman data of glassy 3-methylpentane. The IXS spectra have been analysed allowing for the existence of two distinct excitations at each scattering wavevector obtaining a consistent interpretation of the spectra. In particular, this procedure allows us to interpret the linewidth of the modes in terms of a simple model which relates them to the width of the first sharp diffraction peak in the static structure factor. In this model, the width of the modes arises from the blurring of the dispersion curves which increases approaching the boundary of the first pseudo-Brillouin zone. The position of the boson peak contribution to the density of vibrational states derived from the Raman scattering measurements is in agreement with the interpretation of the two excitations in terms of a longitudinal mode and a transverse mode, the latter being a result of the mixed character of the transverse modes away from the center of the pseudo-Brillouin zone.

We report here a combined experimental and theoretical study on the bio-compatible salicylate choline ionic liquid. The liquid structure has been investigated by X-ray diffraction and vibrational (IR and Raman) spectroscopy. Local structure has been obtained from ab initio calculations on static ion pairs and from dynamic simulations of a small portion of the liquid. The theoretical models indicate that salicylate is connected by hydrogen bonding to choline mainly through the carboxylate group and forms stable ion pairs. A strong intramolecular interaction hinders internal rotations of the OH group of salicylate and competes with the hydrogen bonding with choline. When the liquid has been simulated by classical force fields we found a good agreement with the X-ray experimental features, comparable to that obtained from AIMD simulations. Important insights on hydrogen bonding between carboxylate and choline have been also derived from the analysis of the CO stretching modes of carboxylate measured in the Raman and IR spectra and calculated from VDOS-Wannier centers procedures.

In this paper we accurately revisit the mechanical exfoliation and layer number determination of MoS2. By modelling the exfoliation itself as a random vertical (lateral) exfoliation (fragmentation) phenomenon, a rationale is given to optimise the number of iterations in the scotch-tape peeling technique and we rigorously demonstrate that since the second cleavage the occurrence of monolayers is the most likely. For the unambiguous layer number identification, experiments have been carried out with a unified complementary approach based on optical microscopy, atomic force microscopy, resonant and non resonant Raman spectroscopy, and photo-luminescence spectroscopy. The experimental analysis has been carried out on a statistically significant set of few-layer MoS2 flakes (from one to five layers). The work stresses the strong need of such complementary multi-technique approach to really unambiguously determine the layer number of flakes (that neither optical microscopy, nor AFM alone can give). Optical microscopy contrast analysis experiments (carried out on flakes deposited onto 270 nm SiO2/Si(1 0 0) substrates) demonstrate that for few-layer MoS2 (from the mono to the epta-layer) the optical contrast is weakly depending on the radiation wavelength and is a non-monotonic function of the layer number. Thus, flakes from ten to twelve layers exhibit the same contrast of monolayers, as demonstrated by parallel AFM analysis. AFM clearly shows that the stacking between the silicon oxide substrate and the first MoS2 layer is strongly unpredictable and likely depending on the degree of surface contamination of the substrate. A parallel systematic resonant Raman study is performed ranging from one to five layers clearly exhibiting systematic layer dependent spectral features in the one-five layers range. For the first time a layer estimation number based on a quantitative analysis of resonant Raman and PL spectra is proposed.

Density functional theory and vibrational spectroscopy are used to investigate a class of bioionic liquids consisting of a choline cation and carboxylate anions. Through quantum mechanical studies of motionless ion pairs and molecular dynamics of small portions of the liquid, we have characterized important structural features of the ionic liquid. Hydrogen bonding produces stable ion pairs in the liquid and induces vibrational features of the carboxylate groups comparable with experimental results. Infrared and Raman spectra of liquids have been measured, and main bands have been assigned on the basis of theoretical spectra.

We report an extensive study of strained $\text{Ge}/{\text{Si}}_{0.2}{\text{Ge}}_{0.8}$ multiquantum wells grown by ultrahigh-vacuum chemical-vapor deposition. The microstructural properties of the samples were characterized by transmission electron microscopy and Raman spectroscopy. Their electronic properties have been investigated by means of infrared absorption measurements. Both interband and intersubband transitions were analyzed. Intersubband absorption energies were found in the 20--50 meV range, depending on the quantum well width. Interband and intersubband transition energies have been successfully described by means of both a $\mathbit{k}\ensuremath{\cdot}\mathbit{p}$ approach and a tight-binding model. In particular, we found a conduction-band offset between the L edges of 124 meV, well suited for the development of optoelectronic devices operating in the terahertz range. We also found that the energy difference between the ${\ensuremath{\Delta}}_{2}$ minima in the barrier and the L minima in the well is only $\ensuremath{\sim}40\text{ }\text{meV}$. This explains the observed ineffectiveness of the transfer doping in the strained heterostructures considered.

We have used Raman spectroscopy, transmission electron microscopy, x-ray diffraction, and x-ray photoemission spectroscopy to investigate strain relaxation mechanism of Si(0.22)Ge(0.78) heteroepitaxial layer deposited on Si substrates in tensile, neutral, and compressive strain conditions. The three regimes have been obtained by interposing between the SiGe layer and the substrate a fully relaxed Ge layer, a partially relaxed Ge layer, or growing directly the alloy on Si. We found that the deposition of a Ge buffer layer prior to the growth of the SiGe is very promising in view of the realization of thin virtual substrates on silicon to be used for the deposition of strain-controlled high Ge content SiGe alloys. We demonstrate that this is mainly due to the strain relaxation mechanism in the Ge layer occurring via insertion of pure edge 90 degrees misfit dislocations (MDs) and to the confinement of threading arms in to the Ge layer due to a second MD network formed at the SiGe/Ge heterointerface.

High resolution depolarized Raman spectra of n-pentanol in the - 30 to 60-degrees-C temperature range are reported. The spectra appear as a continuously decreasing line shape centered at zero frequency. A quantitative analysis of this line shape shows a high frequency exponential tail, which can safely be assigned to intermolecular collision phenomena, and a low frequency narrow contribution. The line shapes of the low frequency contribution are seen to deviate from a single Lorentzian, the effect being more pronounced as the temperature is increased. The data have been analyzed assuming the non-Lorentzian line shape as due either to a distribution of Debye relaxation times or to a single non-Debye relaxation mechanism. The analysis in terms of a distribution of relaxation times suggests a broadening of the distribution as the temperature increases, while the "average" relaxation time shows an Ahrenius behavior which compares well with the one observed in the ultrasonic attenuation measurements. Similar results have been obtained considering the nonexponential relaxation mechanisms. Absolute intensities are also evaluated with respect to the Brillouin doublet and discussed in terms of the possible microscopic scattering mechanisms.

Disorder phenomena related to formation conditions of natural and synthetic spinels, both stoichiometric (MgO·Al2O3) and those exhibiting different Al/Mg ratios, are investigated by photoluminescence spectroscopy. The same approach appears to be less adequate when dealing with more complex materials, such as beryls (3BeO·Al2O3·6SiO2). On the other hand, Raman spectroscopy allows easy identification of different varieties of beryls and of their inclusions, together with that of widely used imitations. The above techniques are totally non-destructive and do not require any treatment of the samples. The apparatus developed at our laboratories allows investigation of irregularly shaped samples within a large range of sizes.

The most commonly used blue pigments in medieval manuscripts are azurite and lapis-lazuli. The first one is a copper-based pigment; the coloring compound of the latter is lazurite, a sodium silicoaluminate in a sulfur matrix. Knowledge of the chemical composition of the materials is essential for the study of illuminated manuscripts. In this paper, micro-Raman and LIBS have been used for the study of azurite and lapis-lazuli, as well as different mixtures of these pigments applied to parchment to simulate an illuminated manuscript. The results of our work show the importance of using more than one technique for a good comprehension of a manuscript. In particular, the Ž. opportunity of combining elemental information obtained from laser induced breakdown spectroscopy and Ž. vibrational spectroscopy information obtained from Raman will be fully exploited. 2001 Elsevier Science B.V. All rights reserved.

The hydrogen projected OH stretching density of states has been determined by an inelastic neutron scattering experiment in liquid and supercritical water. The results, compared with new measurements of the isotropic Raman spectra at the same state conditions, support the interpretation of the Raman spectra in terms of superposition of the allowed ν1 band with the overtone of the ν2 band.

Recent experimental results obtained on normal and deuterated water using light-scattering spectroscopy from Brillouin to librational Raman frequencies are reviewed. Particular attention is devoted to the librational mode region and to the Rayleigh wing where both new measurements (including depolarization ratio measurements and absolute intensities analysis) and computer simulation have pointed out the importance of “interaction-induced” scattering contributions in interpreting quantitatively this low-frequency part of the spectrum. The agreement between experimental and simulated data extends up to the 400 wavenumbers band, excluding the presence of direct electronic disturbances created by hydrogen-bond formation dynamics in this spectral region.

Room temperature rotational Raman spectra of N2 in the 56–135 amagat density range are employed to test the memory function approach to rotational dynamics. Memory functions of order one and two in the Mori hierarchy are derived from the spectra and compared with the corresponding calculated free rotor memory functions. It is found that the free rotor memory function multiplied by a decaying function approximately reproduces the experimental curves, the degree of approximation being sensibly better for the second order memory function. Exponentially decaying functions are required to reproduce the long time behaviour of both experimental memory functions. At short times a gaussian decay is found to be more adequate for the first order memory function. Decay parameter values are discussed and compared with available theories.

Rotational and rotovibrational spectra of fluid N2 at T = 119 K and ρ = 570 and 625 amagatare reported. Substantial agreement is found with a recent molecular dynamics simulation which takes into account all dipole–induced-dipole effects including the cross interference term betwen permanent and induced anisotropy. A procedure is described to derive the nonrotational contribution from the experimental spectra using a rotational model spectrum based on a parametrized memory function.The derived lineshapes (collision induced plus cross term) are in agreement with molecular dynamics results.

Orientational correlation functions derived from the rotational and rotovibrational Raman spectra of N2 at 150 K and 585 amagat are compared with the results of a molecular dynamics simulation available in the literature. The angular momentum correlation function is also estimated from the experimental memory function and compared with the one obtained by simulation. Mean square torques, intermolecular correlations and interaction induced contributions are also discussed.

Rotational Raman spectra for an accidentally or nearly symmetric rotor are discussed in detail. The spectral-moment theory is used to yield expressions for the polarizability invariants and for the different orientational correlation times involved. A generalization of Gordon'sJ-diffusion is presented which is able to reproduce also spectra in which the quantization of the rotational states is still present. A further generalization of the model is suggested to account for the molecular anisotropy during the collision process.

A comparison is made between the rotovibrational Raman bands of fluid nitrogen at room temperature in the 180–355 amagat density range and the corresponding pure rotational bands reported previously. Accurate moment values are derived from the Raman spectra, accounting for the response of the entire experimental apparatus, after subtraction of the unwanted isotope band and of the leaking polarized Q branch. Correlation times are also calculated for both rotovibrational and pure rotational spectra accounting for the finite instrumental slitwidth. Intermolecular torques and orientational correlation times derived from the two spectra are in good agreement for almost the entire available density range. Small discrepancies, particularly evident in the low density correlation times, are discussed and related to the rotation-vibration interaction. Intermolecular correlations are found to be negligible.

The Raman scattering cross-section in molecular systems is calculated with the aim of accounting for the low frequency spectrum of disordered media. It is shown that, as far as translational motions are concerned, the isotropic polarizability correlation function is not strongly affected by the structural disorder and is essentially determined by the density-density correlation function. In contrast the anisotropic term depends strongly on the disorder of the system. Its contribution to the scattered light spectrum is governed by single molecule dynamics, thus reflecting in some cases the entire density of translational states, while the intensity is determined by the rotational—translational coupling.

Polarized and depolarized Raman spectra in the translational and librational region of liquid water and heavy water have been measured as a function of temperature. A detailed analysis of the isotropic spectrum is performed. This component, which cannot arise from any 'allowed' molecular contribution in this frequency region, shows two distinct spectral features which can be obtained from an analysis of temperature dependent lineshapes. The first one, which dominates the spectrum up to 500crn-1, shows on the basis of a H20-DzO comparison a translational behaviour at very low frequency and a librational one at higher frequencies. It is assigned on the basis of its frequency profile, of its absolute intensity and of its temperature dependence to rototranslational spectra due to long range induction mechanisms already found in many molecular liquids. The second one, which is peaked at roughly 800 cm-1 in water and extends up to the bending mode region suggests the existence of a short range interaction induced polarizability.

The interpretation of light scattering spectra in disordered solids is from many aspects, an incompletely solved problem, expecially when it is desired to extract from the spectra information about the dynamics of the particles of the system. In this paper, we outline a formalism that can be easily applied to disordered molecular solids, and which can be extensively used in several other cases, even for some liquid samples when certain conditions are satisfied. This formalism is then applied to two particular cases of partially disordered crystals: α-AgI and Ice Ih. In both cases the relation between Raman scattering lineshapes and the densities of vibrational states is clarified; acoustic and optic phonon densities of states are derived and compared with neutron scattering experiments. The results are encouraging and suggest further applications of the formalism.

Raman spectra have been collected in iodine single crystal at room temperature in the pressure range 1-14 GPa using a micro-Raman apparatus. The pressure at the sample was generated by means of a diamond anvil cell. Single crystals were grown in situ over the inner diamond surface. A careful analysis of the frequencies and intensities of internal (stretching) and external (libration) modes as a function of the pressure is reported. In particular, analysis of the relative intensities of the Raman modes confirms a theoretical prediction about the pressure evolution of the A g stretching mode eigenvector and the huge intensity increase of the external modes with respect to the internal ones is well consistent with the predicted increased role of the charge-transfer interaction when approaching the metallization transition pressure. At pressures higher than 10 GPa, spectral features were observed simultaneously with the appearance of two peaks forbidden in the adopted sample geometry. The experimental results obtained are eventually discussed in comparison with recent experimental and theoretical works.

Polarized and depolarized room temperature light scattering spectra of normal alcohols from methanol to pentanol have been measured up to 80 cm−1 frequency shift. At low frequency shifts (smaller than 4 cm−1), resolutions as high as 0.04 cm−1 have been used. The possibility of using the same spectrometer for measuring both low frequency Brillouin structures and high frequency depolarized tails allows for the first time a precise determination of both lineshapes and relative integrated intensities between the various spectral components. The experimental results are presented and briefly discussed on the basis of the existing theories for depolarized scattering from molecular liquids.

An interpretation of the low frequency Raman scattering in all disordered systems including liquids is suggested in terms of phononlike excitations damped by anharmonicity and by structural relaxations. In principle, owing to the disorder‐induced breakdown of the k vector selection rule, all of these excitations are allowed to participate to the scattering process. An ad hoc simplified model is also proposed to calculate the low frequency Raman scattering, and it is found to reproduce at least qualitatively the main features of the depolarized spectrum in amorphous solid and liquid 10M KOH water solutions at different temperatures.

Depolarized Rayleigh spectra of water have been measured as a function of density along several isotherms in both liquid and supercritical phases. At all the thermodynamical states the spectral line shape can be fitted by a Lorentzian line superimposed to an exponential background. The behavior of the fitting parameters shows that at temperatures lower than ∼470 K the temperature is the most relevant parameter in determining the dynamics of the system, whereas above this temperature both temperature and density play a relevant role. Both the line shape and intensity of the spectra can be consistently interpreted in the framework of the first‐order dipole induced dipole approximation to the collision‐induced light scattering. The data show a clear evidence for cancellation effects.

We analysed, using micro-Raman spectroscopy, two decorations of a medieval manuscript containing the 'Canzoniere' and the 'Trionfi' of Francesco Petrarca; namely a drawing attributed to Botticelli and the illumination of the Incipit of the 'Trionfi'. All measurements were carried out at two excitation wavelengths (l632.8; l514.5 nm). The spectra of the drawing showed the presence of lazurite, Na8(Al6Si6O24)Sn, the coloured matter of lapis-lazuli, and of lead dioxide, coming from the oxidation of lead white or biacca, 2 PbCO3·Pb(OH)2. The illumination on a nearby page is a flower decoration, surely drawn by a different artist, in which we recognized the presence of cinnabar, HgS, lead tin yellow (type I), PbSnO4 and azurite, 2 CuCO3·Cu(OH)2, a blue pigment cheaper than lazurite. © 2000 Editions scientifiques et medicales Elsevier SAS

The newly built ultraviolet Raman–Brillouin spectrometer at the Universita di L'Aquila is described. We have used it to perform accurate ultraviolet and visible Brillouin spectra of glass-forming glycerol. Data with high contrast and high dynamic range in the unexplored region of wave vectors from 40 up to about 70 µm−1 have been obtained for the first time. The spectra are analysed in terms of generalized hydrodynamics with a frequency-dependent viscosity.