Broad Raman Band Research Articles

A vibrational spectroscopic study of the silicate mineral harmotome – (Ba,Na,K)1-2(Si,Al)8O16⋅6H2O – A natural zeolite

The mineral harmotome (Ba,Na,K)1-2(Si,Al)8O16⋅6H2O is a crystalline sodium calcium silicate which has the potential to be used in plaster boards and other industrial applications. It is a natural zeolite with catalytic potential. Raman bands at 1020 and 1102cm−1 are assigned to the SiO stretching vibrations of three dimensional siloxane units. Raman bands at 428, 470 and 491cm−1 are assigned to OSiO bending modes. The broad Raman bands at around 699, 728, 768cm−1 are attributed to water librational modes. Intense Raman bands in the 3100 to 3800cm−1 spectral range are assigned to OH stretching vibrations of water in harmotome. Infrared spectra are in harmony with the Raman spectra. A sharp infrared band at 3731cm−1 is assigned to the OH stretching vibration of SiOH units. Raman spectroscopy with complimentary infrared spectroscopy enables the characterization of the silicate mineral harmotome.

Phonon anomalies, orbital-ordering and electronic raman scattering in iron-pnictide Ca(Fe0.97Co0.03)2As2: temperature-dependent Raman study

We report inelastic light scattering studies on Ca(Fe0.97Co0.03)2As2 in a wide spectral range of 120–5200 cm − 1 from 5 to 300 K, covering the tetragonal to orthorhombic structural transition as well as magnetic transition at Tsm ~ 160 K. The mode frequencies of two first-order Raman modes B1g and Eg, both involving the displacement of Fe atoms, show a sharp increase below Tsm. Concomitantly, the linewidths of all the first-order Raman modes show anomalous broadening below Tsm, attributed to strong spin-phonon coupling. The high frequency modes observed between 400 and 1200 cm − 1 are attributed to electronic Raman scattering involving the crystal field levels of d-orbitals of Fe2+. The splitting between xz and yz d-orbital levels is shown to be ~25 meV, which increases as temperature decreases below Tsm. A broad Raman band observed at ~3200 cm − 1 is assigned to two-magnon excitation of the itinerant Fe 3d antiferromagnet.

A vibrational spectroscopic study of the silicate mineral pectolite – NaCa2Si3O8(OH)

The mineral pectolite NaCa2Si3O8(OH) is a crystalline sodium calcium silicate which has the potential to be used in plaster boards and in other industrial applications.Raman bands at 974 and 1026cm−1 are assigned to the SiO stretching vibrations of linked units of Si3O8 units. Raman bands at 974 and 998cm−1 serve to identify Si3O8 units. The broad Raman band at around 936cm−1 is attributed to hydroxyl deformation modes. Intense Raman band at 653cm−1 is assigned to OSiO bending vibration. Intense Raman bands in the 2700–3000cm−1 spectral range are assigned to OH stretching vibrations of the OH units in pectolite. Infrared spectra are in harmony with the Raman spectra. Raman spectroscopy with complimentary infrared spectroscopy enables the characterisation of the silicate mineral pectolite.

Hexagonal Si-IV Silicon Phase Instead Amorphous Silicon after Electrochemical Lithiation/Delithiation of Silicon in Ionic Liquids?

The amorphisation of the lithiated crystalline silicon after the extraction of lithium in LiPF6/carbonates mixture based electrolyte has been demonstrated by the work of Obrovac and Christiansen [1] ten years ago.Within this work, we focus on the structural changes of the crystalline nanosilicon (nSi, 30-50nm) during electrochemical cycling in ionic liquid (IL) based electrolytes. By means of Raman Spectroscopy and X-Rays Diffraction we investigate the nSi electrodes after 1 cycle of lithium insertion/extraction in 0.8 M LiTFSI in 1-Methyl-1-propylpyrrolidiniumbis (trifluoromethylsulfonyl) imide (P13TFSI) and 1-Methyl-1-propylpiperidiniumbis (trifluoromethylsulfonyl) imide (PP13TFSI). For comparison, nSi electrode is also cycled in conventional LP30 electrolyte. The electrodes consist of 85 wt-% of nSi, 5 wt-% carbon black and 10 wt-% of CMC, the electrode is loading about 0.2 mg*cm-2, insertion/extraction current is 180 mA*g-1.During the first lithium insertion/extraction similar electrochemical behavior is observed in all electrolytes (Fig.1). Nevertheless, during extended cycling the capacity fade is much faster in ionic liquids with respect to LP30. The Raman spectra (Fig. 2) taken after lithium extraction in LP30 show clearly the broad band of amorphous silicon between 430 – 500 cm-1. In contrary no amorphous silicon is found after lithium extraction from nSi electrode in ionic liquids. Instead, the band located at ~ 506 cm-1 is registered in reproducible manner. The sample heating effect leading to the silicon phase transformation and peak of the shift can be excluded as low power of the laser was applied (less than 3 mW) and no significant difference was registered in three subsequent measurements. This shift has already been observed for lithiated silicon, however it has not been commented [2]. On the other hand, very detailed Raman spectroscopy investigation of the phase evolution of crystalline cubic silicon Si-I evolution under stress by means of Vickers indentation has been performed [3] [4]. In the center of the indent, amorphisation of the silicon leading to the broad Raman band at ~480 cm-1 was observed, while a pileup at the border of the indent was assigned to hexagonal silicon Si-IV, appearing as a band at 500-510 cm-1in Raman spectra. Direct phase transition of Si -I to Si-IV requires a high level of a shear deformation. Since the same shift of the Raman peak is observed in our electrochemical experiments of lithiation/delithiation of crystalline cubic nSi, it could be intuitively assumed that hexagonal silicon Si-IV is formed in ionic after cycling in ionic liquids. The XRD measurements confirm Raman Spectroscopy findings. The investigation, if the observed structural differences are the reason of the faster capacity fading of silicon electrode in ILs, is in progress.Is it possible that silicon is exposed to high shear deformation when cycled in ILs? Is it related to the insertion/reaction of TFSI anion which takes place at 0.8 – 1V? Within this work we try at least partially answer these questions. To our best knowledge the basic characteristic of silicon behavior in ILs has never been addressed in electrochemical setups in such context. Therefore, taking into account the interest of the scientific community towards application of silicon anodes as well as ionic liquids electrolytes, we consider this basic study of high importance.Fig. 1 Lithium insertion - extraction curves into nSi electrode recorded in LP30, P13TFSI and PP13TFSI, 180 mAg-1 Fig. 2 Raman Spectra of the nSi electrodes, pristine and after one cycle (Fig.1).[1] M.N. Obrovac, L. Christensen, Electrochemical and Solid-State Letters, 7 (2004) A93-A96.[2] H. Li, X. Huang, L. Chen, G. Zhou, Z. Zhang, D. Yu, Y.J. Mo, N. Pei, Solid State Ionics, 135 (2000) 181-191.[3] A. Kailer, Y.G. Gogotsi, K.G. Nickel, Journal of Applied Physics, 81 (1997) 3057-3063.[4] T. Wermelinger, R. Spolenak, Journal of Raman Spectroscopy, 40 (2009) 679-686.

Magnetism in a Spintronic Compound Zr<sub>0.8</sub>Cr<sub>0.2</sub>O<sub>2</sub> of Small Crystallites

A transition metal ion Cr4+(3d2 spins) doped ZrO2 of small crystallites presents tailored magnetic, electrical and optical properties useful for magnetodielectric and spintronic applications. A liquid polymer precursor gel (Cr4+ and Zr4+ complex with glycerol) when heated in an autoclave at a small pressure 0.6-0.7 atm at 420–470 K results in a compound Zr0.8Cr0.2O2 with an average 5 nm crystallite size of a stabilized cubic (c)-ZrO2-type phase (after 2 h annealing at 773 K in air). A broad Raman band is observed at ~300 cm-1 in acoustic and transverse optic phonons characteristic of the c-ZrO2-type structure, with a prominent O–Cr–O stretching band at 878 cm-1 in a ferromagnetic order. A CrO2/Cr2O3 surface layer exhibits two weak bands at ~1011 cm-1 and 1032 cm-1. The sample exhibits an ‘S’-shaped ferromagnetic hysteresis loop (does not saturate below 60 kOe fields) at 5 K, with a magnetization M = 85.79 emu/g (in the CrO2 part) at 60 kOe and coercivity Hc = 100 Oe. With warming above 5 K, the loop converges progressively with only a weak ferromagnetism at room temperature, M = 9.08 emu/g and Hc = 54.2 Oe. As a pinning barrier, the uncompensated spins in the surface layer supports coercivity at low temperature. A model magnetic structure describes the magnetic properties in correlation to the microstructure.

A vibrational spectroscopic study of the phosphate mineral rimkorolgite (Mg,Mn2+)5(Ba, Sr)(PO4)4·8H2O from Kovdor massif, Kola Peninsula, Russia

We have studied aspect of the molecular structure of the phosphate mineral rimkorolgite from Zheleznyi iron mine, Kovdor massif, Kola Peninsula, Russia, using SEM with EDX and vibrational spectroscopy. Qualitative chemical analysis shows a homogeneous phase, composed by P, Mg, Ba, Mn and Ca. Small amounts of Si were also observed. An intense Raman peak at 975cm−1 is assigned to the PO43− ν1 symmetric stretching mode. The Raman band at 964cm−1 is attributed to the HPO42− ν1 symmetric stretching vibration. Raman bands observed at 1016, 1035, 1052, 1073, 1105 and 1135cm−1 are attributed to the ν3 antisymmetric stretching vibrations of the HPO42− and PO43− units. Complexity in the spectra of the phosphate bending region is observed. The broad Raman band at 3272cm−1 is assigned to the water stretching vibration. Vibrational spectroscopy enables aspects on the molecular structure of rimkorolgite to be undertaken.

A vibrational spectroscopic study of the borate mineral ezcurrite Na4B10O17·7H2O – Implications for the molecular structure

We have studied the boron containing mineral ezcurrite Na4B10O17·7H2O using electron microscopy and vibrational spectroscopy. Both tetrahedral and trigonal boron units are observed. The nominal resolution of the Raman spectrometer is of the order of 2cm−1 and as such is sufficient enough to identify separate bands for the stretching bands of the two boron isotopes. The Raman band at 1037cm−1 is assigned to BO stretching vibration. Raman bands at 1129, 1163, 1193cm−1 are attributed to BO stretching vibration of the tetrahedral units. The Raman band at 947cm−1 is attributed to the antisymmetric stretching modes of tetrahedral boron. The sharp Raman peak at 1037cm−1 is from the 11-B component such a mode, then it should have a smaller 10-B satellite near (1.03)×(1037)=1048cm−1, and indeed a small peak at 1048 is observed. The broad Raman bands at 3186, 3329, 3431, 3509, 3547 and 3576cm−1 are assigned to water stretching vibrations. Broad infrared bands at 3170, 3322, 3419, 3450, 3493, 3542, 3577 and 3597cm−1 are also assigned to water stretching vibrations. Infrared bands at 1330, 1352, 1389, 1407, 1421 and 1457cm−1 are assigned to the antisymmetric stretching vibrations of trigonal boron. The observation of so many bands suggests that there is considerable variation in the structure of ezcurrite. Infrared bands at 1634, 1646 and 1681cm−1 are assigned to water bending modes. The number of water bending modes is in harmony with the number of water stretching vibrations.

Evolution of Barnett Shale organic carbon structure and nanostructure with increasing maturation

The organic nanopore network of shales is believed to be the location of hydrocarbon trapping in source rocks. Better understanding of organic carbon structure and nanostructure constitutes a key point for estimating the oil and gas in-place at the local and basinal scale. Here we characterize, a maturation series from Mississippian Barnett Shale at multiple scales down to the nanometer scale. Organic petrography, Rock–Eval pyrolysis and Raman microspectroscopy are used to determine the organic matter properties (e.g. maturity, type, TOC content). Organic pore network attributes (e.g. pore size distribution, surface area, polyaromatic layers characteristics) are estimated using low pressure gas adsorption analyses and direct imaging by high-resolution transmission electron microscopy (HRTEM). Based on Raman data we show that Barnett Shale organic matter has only reached the level of carbonization, even within overmature samples; graphitization has not yet been triggered. Interestingly, the investigated samples exhibit an additional broad Raman band centered at about 1480cm−1, likely due to the presence of retained hydrocarbons within the organic matter nanoporosity. Low pressure gas adsorption analyses evidence a positive correlation between surface areas, mesopores (pores of about 2–50nm of diameter) and maturity level. HRTEM images confirm Raman data: even the overmature organic matter remains disordered. Such disorientation of nanometer sized polyaromatic layers creates a nanoporosity network in organic matter that appears most developed in samples of gas window maturity. Furthermore, carbon nanoparticles of concentric nanostructures, known to result from the thermal cracking of hydrocarbons, are detected in overmature samples.

A vibrational spectroscopic study of the silicate mineral inesite Ca2(Mn,Fe)7Si10O28(OH)⋅5H2O

We have studied the hydrated hydroxyl silicate mineral inesite of formula Ca2(Mn,Fe)7Si10O28(OH)⋅5H2O using a combination of scanning electron microscopy with EDX and Raman and infrared spectroscopy. SEM analysis shows the mineral to be a pure monomineral with no impurities. Semiquantitative analysis shows a homogeneous phase, composed by Ca, Mn2+, Si and P, with minor amounts of Mg and Fe.Raman spectrum shows well resolved component bands at 997, 1031, 1051, and 1067cm−1 attributed to a range of SiO symmetric stretching vibrations of [Si10O28] units. Infrared bands found at 896, 928, 959 and 985cm−1 are attributed to the OSiO antisymmetric stretching vibrations. An intense broad band at 653cm−1 with shoulder bands at 608, 631 and 684cm−1 are associated with the bending modes of the OSiO units of the 6- and 8-membered rings of the [Si10O28] units. The sharp band at 3642cm−1 with shoulder bands at 3612 and 3662cm−1 are assigned to the OH stretching vibrations of the hydroxyl units. The broad Raman band at 3420cm−1 with shoulder bands at 3362 and 3496cm−1 are assigned to the water stretching vibrations. The application of vibrational spectroscopy has enabled an assessment of the molecular structure of inesite to be undertaken.

Growth and characterization of silicon nanowires catalyzed by Zn metal via Pulsed Plasma-Enhanced Chemical Vapor Deposition

High-density silicon nanowires (SiNWs) were grown via Pulsed Plasma-Enhanced Chemical Vapor Deposition at 400°C. Zinc (Zn) metal thin films with varying thickness from 10nm to 100nm were used as a catalyst to synthesize the SiNWs. The surface morphology, crystalline structure, and optical properties of the grown SiNWs were investigated. Results indicated that increasing the Zn thickness from 10nm to 100nm led to an increase in wire diameter from 65nm to 205nm, resulting in a reduction of SiNW density. The wires grown with Zn thicknesses of 10 and 80nm exhibited high crystallinity as shown by the X-ray diffraction patterns. Three emission bands (green, blue, and red) were observed in the photoluminescence spectra of the SiNWs prepared using various Zn catalyst thicknesses. The SiNWs prepared using 10 and 80nm Zn thicknesses displayed a sharp Raman peak that corresponded to the first-order transverse optical phonon mode in contrast to the other samples that produced SiNWs with a broad Raman band.

High pressure Raman spectroscopic study of phase transformation in TaO2F

High pressure Raman spectroscopic measurements on nearly zero thermal expansion material TaO2F are carried out up to 19GPa. Earlier report of high pressure X-ray diffraction studies shows two phase transitions, one at 0.7 and the other at 4GPa with rhombohedral (R-3c) structure above 4GPa, but the structure between 0.7GPa and 4GPa remained unclear. In high pressure Raman measurements, a reversible, cubic to rhombohedral phase transformation onsets around 0.8GPa and gets completed at 4.4GPa with all four predicted normal modes corresponding to R-3c phase and retaining the structure up to 19GPa. A mixture of cubic and rhombohedral phases is observed between 0.8 and 4.4GPa. Optically silent modes in the ambient cubic structure exhibit strong, broad Raman bands due to anionic (O/F) disorder in TaO2F altering the local symmetry and allowing for first order Raman scattering. On compression, these disorder induced first order Raman bands gradually decrease in intensity and disappear around 4.4GPa due to inhibition of local distortion caused by anions, and the modes corresponding to the rhombohedral phase appear. This is a clear evidence of disorder-free rhombohedral single phase exists above 4.4GPa in agreement with the reported HPXRD results. Temperature dependent Raman measurements reveal that the intensities of Raman bands remain almost unchanged with rise in temperature indicating static disorder in TaO2F. Disorder-induced first order Raman modes at 176, 212, 381 and 485cm−1 soften with increase in pressure whereas the other modes show low positive Gruneisen parameter. The thermal expansion coefficient calculated using these Gruneisen parameters (−2.91ppmK−1) is in fair agreement with the reported values (−1 to +1ppmK−1). On the other hand, all four modes of disorder-free rhombohedral phase show the usual hardening behavior with increase in pressure contributing to positive thermal expansion.

Infrared and Raman spectroscopic characterization of the borate mineral hydroboracite CaMg[B3O4(OH)3]2⋅3H2O – Implications for the molecular structure

We have studied the mineral hydroboracite CaMg[B3O4(OH)3]2·3H2O using electron microscopy and vibrational spectroscopy. Both tetrahedral and trigonal boron units are observed. The nominal resolution of the Raman spectrometer is of the order of 2cm−1 and as such is sufficient enough to identify separate bands for the stretching bands of the two boron isotopes. The Raman band at 1039cm−1 is assigned to BO stretching vibration. Raman bands at 1144, 1157, 1229, 1318cm−1 are attributed to the BOH in-plane bending modes. Raman bands at 825 and 925cm−1 are attributed to the antisymmetric stretching modes of tetrahedral boron. The sharp Raman peak at 925cm−1 is from the 11-B component such a mode, then it should have a smaller 10-B satellite near (1.03)×(925)=952cm−1, and indeed a small peak at 955 is observed. Four sharp Raman bands observed at 3371, 3507, 3563 and 3632cm−1 are attributed to the stretching vibrations of hydroxyl units. The broad Raman bands at 3076, 3138, 3255, 3384 and 3551cm−1 are assigned to water stretching vibrations. Infrared bands at 3367, 3505, 3559 and 3631cm−1are assigned to the stretching vibration of the hydroxyl units. Broad infrared bands at 3072 and 3254cm−1 are assigned to water stretching vibrations. Infrared bands at 1318, 1349, 1371, 1383cm−1 are assigned to the antisymmetric stretching vibrations of trigonal boron.

Vibrational spectroscopy of the borate mineral gaudefroyite [formula omitted] from N’Chwaning II mine, Kalahari, Republic of South Africa

Gaudefroyite Ca4Mn3-x3+(BO3)3(CO3)(O,OH)3 is an unusual mineral containing both borate and carbonate groups and is found in the oxidation zones of manganese minerals, and it is black in color. Vibrational spectroscopy has been used to explore the molecular structure of gaudefroyite. Gaudefroyite crystals are short dipyramidal or prismatic with prominent pyramidal terminations, to 5cm. Two very sharp Raman bands at 927 and 1076cm−1 are assigned to trigonal borate and carbonate respectively. Broad Raman bands at 1194, 1219 and 1281cm−1 are attributed to BOH in-plane bending modes. Raman bands at 649 and 670cm−1 are assigned to the bending modes of trigonal and tetrahedral boron. Infrared spectroscopy supports these band assignments. Raman bands in the OH stretching region are of a low intensity. The combination of Raman and infrared spectroscopy enables the assessment of the molecular structure of gaudefroyite to be made.

Preparation, characterization, and conductivity of YLnTiZrO7 (Ln = La, Nd, Sm, and Eu)

The pyrochlore oxide of composition YLnTiZrO7 (Ln = La, Nd, Sm, and Eu) was prepared by sol–gel method. All the samples were characterized by powder X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), diffused reflectance spectroscopy, and impedance spectroscopy. The powder XRD and Raman studies reveal that these samples were crystallized in cubic lattice with pyrochlore structure. The Rietveld analysis of the samples was carried out to obtain the unit cell parameters and reliability factors. The broad Raman bands observed for all the samples are due to cation/anion disorder in the lattice and nanosize. The XPS analysis of the samples shows the characteristic peaks belonging to Y3+, Ln3+ (Ln = La, Nd, Sm, and Eu), Ti4+, and Zr4+. Electrical conductivity of YLaTiZrO7 (YLTZ) and YEuTiZrO7 (YETZ) samples was calculated from the impedance as a function of frequency and temperature. These samples have shown conductivity of the order of 10−5 scm−1 at 500 °C.

Vibrational spectroscopic characterization of the sulphate mineral khademite Al(SO4)F⋅5(H2O)

Vibrational spectroscopy has been used to characterize the sulphate mineral khademite Al(SO4)F⋅5(H2O). Raman band at 991cm−1 with a shoulder at 975cm−1 is assigned to the ν1 (SO4)2− symmetric stretching mode. The observation of two symmetric stretching modes suggests that the sulphate units are not equivalent. Two low intensity Raman bands at 1104 and 1132cm−1 are assigned to the ν3 (SO4)2− antisymmetric stretching mode. The broad Raman band at 618cm−1 is assigned to the ν4 (SO4)2− bending modes. Raman bands at 455, 505 and 534cm−1 are attributable to the doubly degenerate ν2 (SO4)2− bending modes. Raman bands at 2991, 3146 and 3380cm−1 are assigned to the OH stretching bands of water. Five infrared bands are noted at 2458, 2896, 3203, 3348 and 3489cm−1 are also due to water stretching bands. The observation of multiple water stretching vibrations gives credence to the non-equivalence of water units in the khademite structure. Vibrational spectroscopy enables an assessment of the structure of khademite.

Raman and infrared spectroscopic study of the mineral goyazite SrAl3(PO4)2(OH)5·H2O

We have studied the mineral goyazite using Raman and infrared spectroscopy. Goyazite is a member of the crandallite subgroup of the alunite supergroup. The crystal structure is of the alunite-type and consists of sheets of corner-sharing AlO6 octahedra parallel to (0001). The octahedrally coordinated Sr2+ cations occupy cavities between pairs of octahedral sheets and are surrounded by six oxygen atoms from the Al3+O6 octahedra.The very intense sharp band at 983cm−1 is assigned to the ν1PO43- symmetric stretching mode. The observation of a single band supports the concept that all the phosphate units are equivalent in the structure of goyazite. Raman bands observed at 1029cm−1 and 1037cm−1 are assigned to the ν3PO43- antisymmetric stretching vibrations. Two Raman bands at 895 and 927cm−1 are attributed to the stretching vibrations of H2PO4; thus indicating some hydrogen phosphate units in the structure of goyazite. Raman bands at 556, 581, 596 and 612cm−1 are assigned to the ν4PO43- bending modes, suggesting a reduction of symmetry of phosphate units. Two sharp Raman bands at 3609 and 3631cm−1 are attributed to OH stretching vibrations from the goyazite hydroxyl units. Broad Raman bands at 2924, 3043, 3210, 3429 and 3511cm−1 are assigned to water stretching vibrations. This research shows that from a vibrational spectroscopic point of view, the formula SrAl3(H PO4,PO4)2(OH)6⋅H2O is a better formulation for the mineral goyazite. Vibrational spectroscopy enables subtle details of the molecular structure of goyazite to be determined.

Vibrational spectroscopy of the mineral meyerhofferite CaB3O3(OH)5·H2O – An assessment of the molecular structure

Meyerhofferite is a calcium hydrated borate mineral with ideal formula: CaB3O3(OH)5·H2O and occurs as white complex acicular to crude crystals with length up to ∼4cm, in fibrous divergent, radiating aggregates or reticulated and is often found in sedimentary or lake-bed borate deposits.The Raman spectrum of meyerhofferite is dominated by intense sharp band at 880cm−1 assigned to the symmetric stretching mode of trigonal boron. Broad Raman bands at 1046, 1110, 1135 and 1201cm−1 are attributed to BOH in-plane bending modes. Raman bands in the 900–1000cm−1 spectral region are assigned to the antisymmetric stretching of tetrahedral boron. Distinct OH stretching Raman bands are observed at 3400, 3483 and 3608cm−1. The mineral meyerhofferite has a distinct Raman spectrum which is different from the spectrum of other borate minerals, making Raman spectroscopy a very useful tool for the detection of meyerhofferite in sedimentary and lake bed deposits.

SEM–EDX, Raman and infrared spectroscopic characterization of the phosphate mineral frondelite (Mn2+)(Fe3+)4(PO4)3(OH)5

We have analyzed a frondelite mineral sample from the Cigana mine, located in the municipality of Conselheiro Pena, a well-known pegmatite in Brazil. In the Cigana pegmatite, secondary phosphates, namely eosphorite, fairfieldite, fluorapatite, frondelite, gormanite, hureaulite, lithiophilite, reddingite and vivianite are common minerals in miarolitic cavities and in massive blocks after triphylite. The chemical formula was determined as (Mn0.68, Fe0.32)(Fe3+)3,72(PO4)3.17(OH)4.99.The structure of the mineral was assessed using vibrational spectroscopy. Bands attributed to the stretching and bending modes of PO43- and HOPO33- units were identified. The observation of multiple bands supports the concept of symmetry reduction of the phosphate anion in the frondelite structure. Sharp Raman and infrared bands at 3581cm−1 is assigned to the OH stretching vibration. Broad Raman bands at 3063, 3529 and 3365cm−1 are attributed to water stretching vibrational modes.

In situ measurement of the temperature of water in microchannels using laser Raman spectroscopy

For an improved understanding of physical and chemical processes in microreactors and their optimization, it is important to know the temperature distribution within microchannels. For this purpose, laser Raman spectroscopy can be applied. In this work, a 32mm long microchannel with 0.4mm width and 0.2mm depth was used. Its temperature was controlled between 30°C and 58°C. The beam of a continuous argon ion laser was coupled into the tube of a microscope and focused through a quartz plate into the microchannel. The scattered Raman light of the molecules was measured with a spectrometer and a CCD camera. For first investigations, pure water was used. The broad vibrational Raman band of the OH stretch is bimodal with peaks at about 3250cm−1 and 3450cm−1 and leads to different shapes, which are dependent on temperature. The dependence of the peak intensities on temperature shows a linear course, and the temperature can be determined with an accuracy of ±1.2°C. Further own investigations with the same Raman system show that the measuring procedure used here has a lateral local resolution of approximately 15μm and a depth resolution of 25μm. Therefore, the temperature profile inside microchannels can be determined with this spatial resolution.

LUMINESCENT SILICON NANOSTRUCTURES VIA TIN OXIDE DOPING

Tin oxide ( SnO2 )-doped Si nanorings of diameter in the range of 100 nm to 170 nm with an average width of 25 nm are synthesized by off-axis laser ablation (PLD) and are characterized by different techniques. The AFM observations show that the surface morphological features of films depend on the tin oxide concentration. The bandgap energies of undoped quantum dots are found to be 2.29 eV, while it decreases to 2.15 eV and 1.5 eV for 3 wt.% and 0.1 wt.% SnO2 -doped samples, respectively. The increase in the value of bandgap energy can be attributed to size reduction of particles. The Raman spectra of SnO2 -doped films are characterized by a broad Raman band with intensity maximum around 478 cm-1. Raman spectrum shows frequency shift which may be due to changes in the Si – O bond length or Si – O – Si bond angle. The activation energy at higher temperature is found to be 16.99 meV for 3 SnSi 209, 21 meV for 0.1 SnSi 209 and 18.1 meV for undoped silicon which shows that defect levels are present in all the samples, the conduction is due to the presence of holes. The synthesized films exhibit PL peak in the visible region. The PL emission peak and PL intensity depend on dopants and it is concluded that luminescence does not originate from localized states in gap but from extended states. The size and shape of nanostructures depend on the SnO2 concentration and the doping effects can be used as a significant guideline for tuning the electronic and optical properties of Si .