Broad Raman Band Research Articles

Theoretical Raman spectrum of boron carbide B4.3C under pressure

The most striking features of the Raman spectrum of boron carbide under pressure are explained theoretically by computing the Raman tensor using density functional perturbation theory and the second-order response. While the observed pressure-induced changes in frequencies and intensities of all of the peaks above 450 cm−1 are convincingly explained by the vibrations of (B11C) icosahedra and C-B-C chains – that have been identified for long as the two main components of the atomic structure of pristine B4C –, the puzzling non-monotonic behavior of a broad Raman band at low frequency, whose intensity increases under pressure up to 44 GPa, decreases and then vanishes, was so far unexplained. We find that the behavior under pressure of both the frequency and intensity of this band turns out to be remarkably accounted for, in the calculations, by the activation of the chain bending mode in atypically flexured chains. We show that the flexion of the chain occurs at high pressure in presence of interstitial B atoms that, at ambient pressure, sit in the prolongation of standard C-B-C chains. We propose the ambient-P mode observed at 270 cm−1 as a fingerprint for the identification of both such B-C-B-C chain-defects in boron carbide and local deviations from the rhombohedral symmetry.

Structure and Dielectric Studies of Lanthanum Oxide Activated Niobium-Barium Titanate for Energy Storage Applications

A 10 mol% of La2O3 doped niobium-barium titanate (60-y) BaO –(40-x) TiO2 – y Nb2O5 – La2O3x (BTNb10La10) (where x = y = 10), BTNb10 and BTLa10 ferroelectric ceramics were prepared by solid state reaction, those are sintered at temperatures 1000 oC for 8 h and calcined at 1250 oC for 6 h to investigate various properties such as structure, morphology and dielectric that include electric hysteresis. Different phases of the BTNb10La10 ceramics were revealed and identified in XRD profile. La–O bending vibration band was identified at 541 cm-1 in the FTIR spectra of BTNb10La10 samples. A broad phonon vibrational Raman band was identified at 770 cm-1of BTNb10La10 ceramics due to the presence of La2O3. 132, 143 and 148 nm are the average particle sizes revealed in scanning electron microscope (SEM) for BTNb10, BTLa10 and BTNb10La10ferroelectrics, respectively. The recoverable energy storage density (Wrec) of the BTNb10La10 ferroelectric is found to be Wrec = 0.3370 J/cm3 with an energy storage efficiency of η = 94%. The slim and antiferroelectric features of electric hysteresis indicates that the BTNb10La10 ferroelectric could be a potential candidate for energy storage pulsed capacitor applications.

Label‐free detection of polysulfides and glycogen of Cyanidium caldarium using ultra‐multiplex coherent anti‐Stokes Raman scattering microspectroscopy

AbstractLiving microalga Cyanidium caldarium was visualized using ultra‐multiplex coherent anti‐Stokes Raman scattering (CARS) microspectroscopy. The Raman band related to the SO42− ion at 982 cm−1 was detected at the peripheral part of the cells and showed a signal amplitude that was approximately threefold larger than that in the medium, indicating accumulation of SO42− ions. Depending on the incubation conditions, a broad and sharp Raman band at approximately 505 cm−1 was observed at the peripheral part and inside the cells, respectively. Based on comparison of the results with model substances, these broad and sharp bands were assigned to polysulfides and glycogen, respectively.

Pressure-dependent nonlinear optical properties in a group III–V/II–VI core/shell quantum dot

ABSTRACT Simultaneous effects of hydrostatic pressure and the geometrical confinement on the excitonic and some nonlinear optical properties of an exciton confined in an InP/ZnS core/shell quantum dot are investigated. Pressure associated exciton binding energy, oscillator strength, absorption coefficient, changes of refractive index and optical Raman gain are brought out for various values of ratio of radii of core/shell quantum dot. The results show that the binding energy of the exciton enhances with the application of hydrostatic pressure for all the ratio of radii. The enhancement of resonance amplitude and shifting towards the higher energies in absorption spectra is noted with the applied pressure and the peak values of refraction properties are found to reduce monotonically. The bare broad Raman band is observed at 335 cm−1 and this band shifts towards the higher values when the hydrostatic pressure is applied. They are in good agreement with the existing available literature.

Raman scattering from highly-stressed anvil diamond* *Project support by the National Natural Science Foundation of China (Grant No. 11774247).

The high-frequency edge of the first-order Raman mode of diamond reflects the stress state at the culet of anvil, and is often used for the pressure calibration in diamond anvil cell (DAC) experiments. Here we point out that the high-frequency edge of the diamond Raman phonon corresponds to the Brillouin zone (BZ) center Γ point as a function of pressure. The diamond Raman pressure gauge relies on the stability of crystal lattice of diamond under high stress. Upon the diamond anvil occurs failure under the uniaxial stress (197 GPa), the loss of intensity of the first-order Raman phonon and a stress-dependent broad Raman band centered at 600 cm−1 are observed, which is associated with a strain-induced local mode corresponding to the BZ edge phonon of the L 1 transverse acoustic phonon branch.

Raman scattering from irradiated nanocrystalline zinc oxide thin films: Perspective view on effects of energy loss, ion fluence, and ion flux

Raman scattering were used to study lattice damage in nanocrystalline zinc oxide (nc-ZnO) thin films implanted with 300 keV Ar and 1.2 MeV Xe ions at different ion fluences and ion fluxes. Raman spectra of all of the implanted samples show a broad Raman band at the lower Raman shift side along with A1 (LO) phonon mode. The A1 (LO) phonon modes get evolved with an increase in ion fluence with the reduction in the intensity of E2 (high) mode which is the characteristic mode of the wurtzite phase of ZnO. The implanted films show broadening and softening of A1 (LO) phonon mode upon an increase in ion fluences and observed to be more prominent in the case of 1.2 MeV Xe ions as compared to 300 keV Ar ions. The evolution of A1 (LO) phonon mode and broadening of Raman band assigned to the damage induced in the system upon ion-implantation and correlated well with the damage profile, while the peak broadening and softening could be assigned to the stress-induced into the films due to implantation. Thus, for a better understanding, the Raman tensor of first-order optical Raman modes in back-scattering geometry is also presented in the manuscript.

Calculational Raman spectra investigation of nitrogen-hyperdoped silicon formed in different conditions

The Raman spectra difference of the N-hyperdoped silicon prepared under different conditions is due to the different dominant configurations of N in silicon. The separate substitutional N atoms in silicon show several strong Raman peaks which can be also observed in the chalcogen-hyperdoped silicon. The configuration with separate substitutional and interstitial N atoms displays a strong and broad Raman band at 480 cm−1, which is in accordance with our experiment. The introduction of the vacancies may lead to the disappearance or appearance of the Raman peaks, which depends on the dominant configurations of the N atoms. For the compound of interstitial N atoms and vacancies, the calculational Raman spectrum is similar to that of the NF3-prepared silicon and N2-prepared silicon with a lower laser power.

Ferroelectric ordering and energy storage capacity in lead-free Ba(Zr0.2Ti0.8)O3 nanoscale film capacitors fabricated using pulsed laser deposition technique

Dielectric thin film capacitors, storing large charge density, are useful in electric energy storing devices. Highly oriented lead-free BaZr0.20Ti0.80O3 (BZT20) thin films were grown on a conducting bottom layer La0.7Sr0.3MnO3 deposited on a MgO (100) substrate under an oxygen atmosphere using a pulsed laser deposition technique. X-ray diffraction studies indicate that BZT20 films were stabilized in a (100) oriented tetragonal phase. Microstructural studies on thin films indicate a smooth film (a roughness of ∼1.25 nm) with a thickness of around 320 nm. The structural sensitive A1(TO2) Raman band exhibits a discontinuous change across the tetragonal-cubic phase transition temperature Tc ∼ 275 K. The appearance of the broad Raman band in the cubic (Pm−3m) phase at an elevated temperature suggests the activation of symmetry forbidden Raman active bands. The temperature dependent band frequency and integrated intensity of the structural sensitive A1(TO2) band show anomaly across Tc. Temperature dependent dielectric studies (100–650 K) carried out in a wide range of frequencies 102–106 Hz on a fabricated Pt/BZT20/LSMO metal-insulator-metal capacitor suggest a broad dispersive peak of around 290 K. The polarization relaxation follows the Vogel-Fulcher relation with an activation energy of Ea = 0.047 eV and a freezing temperature of Tf = 246 K. The slim polarization P-E loops with a remanent polarization of ∼89.6 μC/cm2 and an EC value of ∼0.29 MV/cm were observed, suggesting its local ferroelectric ordering in corroboration with Raman and dielectric findings. From the P-E loop analysis, a large energy storage density of 31.9 J/cm3 and an energy storage efficiency of 56% were obtained. Our experimental results revealed that the BZT20 thin film capacitors have potential for energy storage device applications.

Enhanced energy storage density in Sc3+ substituted Pb(Zr0.53Ti0.47)O3 nanoscale films by pulse laser deposition technique

Highly oriented Pb(Zr0.53Ti0.47)0.90Sc0.10O3 (PZTS) thin films were deposited on La0.67Sr0.33MnO3 (LSMO) buffer layer coated on MgO (100) substrates by following two subsequent laser ablation processes in oxygen atmosphere employing pulse laser deposition technique. The PZTS films were found to grow in tetragonal phase with orientation along (100) plane as inferred from x-ray diffractometry analysis. The structural sensitive symmetric E (LO2) Raman band softened at elevated temperature along with its intensity continuously decreased until it disappeared in the cubic phase above 350 K. The existence of broad Raman bands at high temperature (>350 K) is attributed to the symmetry forbidden Raman scattering in relaxor cubic phase due to symmetry breaking in nano length scale. The temperature dependent dielectric measurements were performed on metal-ferroelectric-metal capacitors in the frequencies range of 102–106 Hz was observed to be diffused over a wide range of temperature 300–650 K and exhibits high dielectric constant ~5700 at room temperature. An excellent high energy storage density (Ure) ~54 J/cm3 with efficiency ~70% was estimated at applied voltage 1.82 MV/cm. High DC breakdown strength, larger dielectric constant and high restored energy density values of our PZTS thin films indicate its usage in high energy storage applications.

Effect of the crystal size on the infrared and Raman spectra of bio hydroxyapatite of human, bovine, and porcine bones

AbstractThe optical properties of hydroxyapatites (HAps) and bio HAps have been studied using Raman and infrared (IR) spectroscopies to describe their crystalline quality. However, the size of the HAp crystals and their crystalline order effects have not been considered yet. This paper focuses on the study of the effect of the change in the crystallites size have on the width of the IR and Raman spectra for defatted and deproteinized bones as well as incinerated biogenic HAp obtained from bovine, porcine, and human bones. Bone samples were analyzed through Raman and IR spectroscopies, X‐ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma (ICP), and scanning electron microscopy (SEM). The Raman and IR spectra for raw samples showed broad bands but, after calcination at 720 °C, became narrow and well defined. TEM images showed that all raw crystallites are ordered nanoplates contrary to the so far well‐established concept that biogenic HAps have low crystalline quality. XRD data confirmed that raw samples display broad peaks that correlated with the HRTEM images of ordered nanocrystals. This fact confirmed that the broad Raman and IR bands of raw clean bones come from nanocrystal plates. SEM analysis confirmed the increase in the crystal size after calcination from nanomicron to submicron dimensions due to a coalescence phenomenon. These results imply that the interpretation of Raman and IR spectra in the case of HAp nanoparticles has been erroneous. These results contribute to the design of biomaterials for tissue engineering based on biogenic HAp for bone regeneration.

Local phenomena in bismuth sodium titanate perovskite studied by Raman spectroscopy

AbstractIn this work, 0.8Na0.5Bi0.5TiO3‐0.2K0.5Bi0.5TiO3 (BNKT) is studied by electrical characterizations, in situ Raman spectra in conjunction with the phenomenological Landau predictions to reveal the local phenomena. An electric field‐induced nonergodic relaxor‐to‐ferroelectric phase transition and domain switching start to take place at a critical field of 3 kV/mm. The polar phase was disrupted into the disordered relaxor phase at ferroelectric‐relaxor transition temperature (TFR) along with the discontinuous phonon anomalies caused by the decoupling between the off‐centered Bi and Ti cations. The R3c and P4bm polar nanoregions (PNRs) can coexist in a wide temperature range and can be transformed reversibly below the temperature of dielectric maximum (Tm). The broad Raman bands were found to persist in high‐temperature paraelectric state induced by the existence of off‐centered Ti cation and ferroically deformed TiO6 octahedra. A phenomenological Landau model and local structural evolution sequence at different thermal history were proposed to further elucidate the underlying mechanisms. This work will be conducive to understanding the local structure‐physical property correlations of high‐performance lead‐free piezoelectrics.

In Situ Raman Study of Liquid Water at High Pressure.

A pressure shift of Raman band of liquid water (H2O) may be an important tool for measuring residual pressures in mineral inclusions, in situ barometry in high-pressure cells, and as an indicator of pressure-induced structural transitions in H2O. However, there was no consensus as to how the broad and asymmetric water Raman band should be quantitatively described, which has led to fundamental inconsistencies between reported data. In order to overcome this issue, we measured Raman spectra of H2O in situ up to 1.2 GPa using a diamond anvil cell, and use them to test different approaches proposed for the description of the water Raman band. We found that the most physically meaningful description of water Raman band is the decomposition into a linear background and three Gaussian components, associated with differently H-bonded H2O molecules. Two of these components demonstrate a pronounced anomaly in pressure shift near 0.4 GPa, supporting ideas of structural transition in H2O at this pressure. The most convenient approach for pressure calibration is the use of "a linear background + one Gaussian" decomposition (the pressure can be measured using the formula P (GPa) = -0.0317(3)·ΔνG (cm-1), where ΔνG represents the difference between the position of water Raman band, fitted as a single Gaussian, in measured spectrum and spectrum at ambient pressure).

Observation of magnetoelastic effects in a quasi-one-dimensional spiral magnet

We present a systematic study of spin and lattice dynamics in the quasi-one-dimensional spiral magnet ${\mathrm{CuBr}}_{2}$, using Raman scattering in conjunction with infrared and neutron spectroscopy. Along with the development of spin correlations upon cooling, we observe a rich set of broad Raman bands at energies that correspond to phonon-dispersion energies near the one-dimensional magnetic wave vector. The low-energy bands further exhibit a distinct intensity maximum at the spiral magnetic ordering temperature. We attribute these unusual observations to two possible underlying mechanisms: (1) formation of hybrid spin-lattice excitations and/or (2) ``quadrumerization'' of the lattice caused by spin-singlet entanglement in competition with the spiral magnetism.

Pressure induced transformations in sorbic acid

This research reports a pressure dependent Raman study of the sorbic acid between 0.0 and 10.0GPa. The unpolarized Raman spectra were measured in the spectral range of 20–3000cm−1. The high-pressure Raman scattering study of the sorbic acid showed that it underwent a gradual, disordering process. At the room temperature and at the ambient pressure conditions, the crystal structure of the sorbic acid belongs to the monoclinic system with a C2/c (C2h6) space group. The pressure increase induced a higher disorder in the monoclinic unit cell, since a single bending mode, and only very broad stretching Raman modes are present at pressure of ~10GPa. Upon pressure release the high-pressure phase transforms directly into the ambient-pressure phase. The presence of the internal vibrational modes is a guarantee that the molecular structure is maintained. Beyond this, the presence of external modes shows that the crystal has a memory to reverse the process and suggest that the crystal, which was in high disorder (broad Raman bands), does not suffer decomposition in the crystalline structure. The DFT calculations for the sorbic acid were performed in order to understand the vibrational properties. The theoretical study showed that the volume of the unit cell and beta angle decrease significatively when passing from the 0.0GPa to 8.0GPa. The decreases in the volume and beta angle of this particular unit cell were supposed to induce the larger increase in the bandwidths of the observed bands, pointing to some disorder in the monoclinic phase.

YIG Films Through Synthesis by Means of the Polymeric Precursor Method: Correlation Between the Structural and Vibrational Properties with Magnetic Behavior

Yttrium iron garnet (YIG, Y3Fe5 O 12) films were synthesized from a polymeric precursor and they were deposited by spin coating onto amorphous silica substrates; where the films were annealed at T a = 450, 600, 700, 800, and 900 ∘C under air. Vibrational and magnetic properties of YIG films were followed by means of Raman spectroscopy, vibrant sample magnetometry (VSM), and ferromagnetic resonance (FMR), respectively. X-ray diffraction and Raman spectroscopy indicated that the YIG films are crystalline after annealing at T a ≥ 800 ∘C, but they are amorphous below T a. The amorphous films have a broad Raman band to 670 cm−1, due to higher states in the phonon state density of YIG, suggesting the existence of a short order around tetrahedral Fe3+ ions. Magnetic hysteresis measurements are indicative of a superparamagnetic behavior in amorphous YIG films and with a soft magnetic behavior in the crystalline ones. The deconvolution in FMR spectra shows that the amorphous precursor films have two different absorption modes corresponding to different sites for Fe3+ ions: the first is associated with magnetic local ordering around tetrahedral Fe3+ centers corresponding with superexchange interactions J aa in tetrahedral sites, while the other absorption is associated with an amorphous matrix in the paramagnetic state. Finally, FMR spectra in crystalline films show the presence of two different sites for Fe3+ ions, and that they are associated with magnetic local ordering around tetrahedral and octahedral Fe3+ centers.

Spin liquid like Raman signatures in the hyperkagome iridate Na4Ir3O8

Combining Raman scattering measurements with mean field calculations of the Raman response we show that Kitaev-like magnetic exchange is dominant in the hyperkagome iridate Na$_4$Ir$_3$O$_8$. In the measurements we observe a broad Raman band at $\sim$~3500 cm$^{-1}$ with a band-width $\sim 1700$~cm$^{-1}$. Calculations of the Raman response of the Kitaev-Heisenberg model on the hyperkagome lattice shows that the experimental observations are consistent with calculated Raman response where Kitaev exchange interaction ($J_K$) is much larger than the Heisenberg term J$_1$ ($J_1/J_K \sim 0.1$). A comparison with the theoretical model gives an estimate of the Kitaev exchange interaction parameter.

Mesoporous Iron Doped Carbons Based on Protic Ionic Salt with Tunable Oxygen Reduction Activity

Electrochemical energy systems such as fuel cells and metal–air batteries [1, 4] are based on oxygen reduction reaction (ORR) which is intrinsically sluggish in kinetics. So, the importance of efficient, low-cost and stable electrocatalysts for such systems is paramount. In this study, we prepared metal (Fe) and nitrogen (N) doped mesoporous carbons (Fe/N/C) as an ORR electrocatalyst by using low cost precursors, which are protic ionic salt, 1,10-phenanthrolinium dibisulfate [Phen][2HSO4], and iron (III) chloride (FeCl3) via facile and scalable strategy termed as nanocasting. Colloidal silica was used as a hard template for the introduction of mesopores [2] in the catalyst structure. Structural characterizations and electrochemical features i.e., performance and stability were investigated and compared with the state of the art Pt/C. Mesoporous Fe/N/C catalysts were synthesized by direct carbonization (Scheme 1: PR-I & PR-II) of the mixture of [Phen][2HSO4], FeCl3 and silica for 2h under an Ar flow of 100 mL/min from 600 oC to1000 oC. Composition of iron precursor was also varied. Also, after the removal of template by HF the second carbonization (selected samples) was done for 1h. To test the catalyst in acidic media, it was washed with 6M HCl; dried and carbonized. Electrochemical measurements were carried out in 0.1 M KOH and 0.1M HClO4(in progress) using a temperature controlled water-jacketed three-electrode cell. Ag/AgCl and Pt coil were used as the reference and counter electrodes, respectively. The mesoporous catalyst was dispersed in a mixture of deionized water, ethanol, and Nafion (5 wt%) and sonicated for 1h. Definite amount of the ink was then dropped for the desired loading onto the surface of a glassy carbon electrode (4 mm) and dried naturally. Successful fabrication of mesopores was observed by HR-TEM and BET. XRD pattern of Fe/N/C showed (002) and (100) diffraction peaks at 2θ = 24.7o and 43.7o, respectively for the graphitic structure. In addition, broad Raman bands were observed at ν =1589 and 1349 cm-1 which could be attributed to the G mode and D mode peak, respectively, and the low value of I G/I D ratio indicates the presence of defects and disorders in the carbons. EDX elemental analysis revealed the presence of C, N, O, S, and Fe in the prepared mesoporous carbon also supported by XPS survey scan. HR-XPS exhibited that the N1s spectrum of Fe/N/C is comprised of pyridinic N, pyrrolic/pyriodonic N and graphitic-type quaternary N structures. The slight impurity that appeared at a higher binding energy was assigned to oxidized N species [2]. The S2p spectrum was also resolved into well-defined peaks related to S2p3/2 and S2p1/2 in the lower binding energy and those at the higher binding energies were ascribed to oxidized species stemming from the anion. But, it was not possible to obtain well-resolved spectra for iron owing to the low amount of iron confirmed from ICP-AES measurements. Electrochemical measurements revealed that the Fe/N/C has an electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline solution. Figure 1 shows rotating disk electrode (RDE) voltammograms of Fe/N/C prepared under carbonization profile, i.e., PR-I and PR-II by keeping other parameters constant in 0.1M KOH solution under O2 atmosphere at 30 oC. In comparison with Pt/C (Sigma-Aldrich) catalyst, mesoporous Fe/N/C synthesized by following PR-II showed improved activity in terms of onset potential and half-wave potential under the same catalyst loading. Chronoamperometry measurements (20000s) and cyclic performance (1500 cycles) study vindicated that the Fe/N/C mesoporous carbon was stable in alkaline media. Electrochemical measurement in acidic media is currently under study. We found that in alkaline electrolyte the feed composition of iron, carbonization procedure (temperature, profile, and second carbonization) and acid treatment played pivotal role to fine-tunethe ORR activity of the metal doped carbons. The performance of Fe/N/C electrocatalyst was affected by the balance between surface area, graphitic degree, and Fe/N doping [1-3] which could be controlled by the synthetic parameters. Moreover, protic ionic salt platform could be considered as a viable candidate for utilization of non-precious metal based carbon materials for fuel cells. References (1) H.-W. Liang, X. Zhuang, S. Bruller, X. Feng, and K. Mullen, Nat. Commun. 5, 4973 (2014). (2) S. Zhang, A. Ikoma, K. Ueno, Z. Chen, K. Dokko, and M. Watanabe, ChemSusChem 8, 1608 (2015). (3) K. Strickland, E. Miner, Q. Jia, U. Tylus, N. Ramaswamy, W. Liang, M-T Sougrati, F. Jaouen and S. Mukerjee, Nat. Commun. 6, 7343 (2015). (4) Y. Gogotsi, A. Nikitin, H. H. Ye, W. Zhou, J. E. Fischer, B. Yi, H. C. Foley, M. W. Barsoum, Nat. Mater. 2, 591 (2003). Figure 1

A thermogravimetric, scanning electron microscope and vibrational spectroscopic study of the phosphate mineral santabarbaraite from Santa Barbara mine, Tuscany, Italy

A santabarbaraite mineral sample from Italy has been examined by thermal analysis, scanning electron microscopy with energy dispersive spectroscopy and vibrational spectroscopy. Chemical composition shows a Fe phosphate phase with minor amounts of Mn, Mg, K and Na were also observed. The santabarbaraite mineral was characterized by thermal analysis. Thermogravimetric analysis of the santabarbaraite mineral were obtained by using TA Instruments Inc. Q50 high-resolution TGA operating at a 10 °C min−1 ramp with data sample interval of 0.50 s pt−1 from room temperature to 1000 °C in a high-purity flowing nitrogen atmosphere (100 cm3 min−1). Two mass loss steps are observed at 105 and 364.8 °C and are attributed to dehydration and dehydroxylation. Not all phosphate units are identical in the structure of santabarbaraite. This is reflected in the width of both the Raman and infrared bands. Two strong broad Raman bands observed at 1007 and 1095 cm−1 are assigned to the phosphate ν 1 symmetric and ν 3 antisymmetric stretching mode. Raman bands observed at 561, 592 and 630 cm−1 are assigned to the ν 4 out of plane bending modes of the phosphate units. The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Broad Raman bands observed at 3544 and 3611 cm−1 are attributed to the OH stretching vibrations of the hydroxyl units. Vibrational spectroscopy enables subtle details of the molecular structure of santabarbaraite to be determined. Thermal analysis characterises the stability of the mineral.

Quantitative Determination of the Raman Enhancement of Ag30(CO)25 and Ag50(CO)40 Matrix Isolated in Solid Carbon Monoxide

Size-selected Ag clusters in the range Ag3–Ag50 were prepared by sputtering a silver substrate, mass-selecting Ag cation clusters using a Wien filter, neutralizing and matrix-isolating them at cryogenic temperatures in solid CO. The Raman spectra of the resulting silver-cluster carbonyls were recorded using excitation wavelengths in the range 457.9 to 514.5 nm. For Ag30 and Ag50, the “adsorbed” carbon monoxide (which we estimated to number ∼25 and ∼40, respectively) gave rise to broad Raman bands centered at ∼2110 cm–1. Because both the metal cluster and the CO density were measured quantitatively, a good estimate was computed for the increase in the Raman scattering cross-section per CO molecule adsorbed on the silver particle. For Ag50 and 457.9 nm laser excitation, an enhancement of ∼1850 was measured, which dropped to ∼1350 at 514.5 nm excitation. For Ag30 (and 457.9 nm excitation) the enhancement was ∼530. The enhancements of Ag3, Ag5, and Ag9 were too low to measure accurately (i.e., <10). Extrapola...

MoO3 incorporation in alkaline earth aluminosilicate glasses

ABSTRACTAlkaline earth aluminosilicate glasses (AeAS) with different MoO3 additions have been produced and assessed. MoO3 solubility increases with the equimolar substitution of smaller to larger alkaline earths and reaches 5.34 mol% in magnesium aluminosilicate glass (MAS). All visibly homogeneous glasses are X-ray amorphous, while the partially crystallised glasses exhibit some small X-ray diffraction peaks which are probably due to corresponding molybdates. The addition of MoO3 decreases glass transition and crystallisation temperatures and creates two broad Raman bands which are assigned to vibrations of MoO42‒ tetrahedra. The intensities of these bands increase along with MoO3 incorporation until the maximum solubility is reached. Electron microscopy shows that these separated particles are spherical, with sub-micron diameters and are randomly dispersed within glass. The separated phases are formed through liquid-liquid separation and thereafter crystallisation. Overall AeAS glasses look quite promising for molybdate immobilisation with MAS glasses being particularly attractive.