High-pressure structural transitions of Sc2O3 by X-ray diffraction, raman spectra, and ab initio calculations

The high-pressure behavior of scandium oxide (Sc₂O₃) has been investigated by angle-dispersive synchrotron powder X-ray diffraction and Raman spectroscopy techniques in a diamond anvil cell up to 46.2 and 42 GPa, respectively. An irreversible structural transformation of Sc₂O₃ from the cubic phase to a monoclinic high-pressure phase was observed at 36 GPa. Subsequent ab initio calculations for Sc₂O₃ predicted the phase transition from the cubic to monoclinic phase but at a much lower pressure. The same calculations predicted a second phase transition at 77 GPa from the monoclinic to hexagonal phase.

Temperature-dependent Raman spectra of bamboo-like boron nitride nanotubes

Phonon properties of boron nitride nanotubes (BNNTs) were investigated using Raman spectroscopy at different temperatures and new sp3- bonded BN vibrations were identified. The Raman peak of the E2g mode of BNNTs is found to be downshifted and broadened compared to that of hexagonal BN at the same temperature. By increasing the temperature, the energy of the E2g mode and the sp3-bonding mode are downshifted, with the temperature coefficients being -0.010 and -0.069cm-1/K, respectively. We attribute this downshifting to anharmonic effects as well as the elongation of the B-N bond in BNNT structures with increasing temperature. © 2014 The Japan Society of Applied Physics.

Measurement of lactose crystallinity using Raman spectroscopy

Raman spectroscopy (RS) was used to determine the crystallinity of lactose (a commonly used carrier in dry powder inhaler (DPI) formulations). Samples of α-lactose monohydrate and amorphous lactose were prepared using ethanol precipitation and lyophilisation respectively. The anomeric forms were confirmed using DSC at a rate of 10 °C/min and heated to 250 °C. The Raman spectra of both α-lactose monohydrate and amorphous lactose were obtained. Distinguishable differences were seen between the two spectra including peak areas and intensities. Depolarisation ratios (ρ) of each form were then determined to identify the crystallinity of the lactose carrier samples. At the prominent Raman bands 865 and 1082 cm−1, significant differences in ρ values were observed for crystalline (0.80 ± 0.07, 0.89 ± 0.06 respectively) and amorphous samples (0.44 ± 0.07, 0.51 ± 0.10).

Ab initio calculations, Raman and NMR investigation of the plastic crystal di-methyl pyrrolidinium iodide

Above 110 °C the symmetric di-methyl-pyrrolidinium iodide salt forms a plastic crystal phase of interest in the area of new electrolyte materials. In this study ab initio calculations of this material has been conducted in order to assign the vibrational spectra. Raman spectroscopy measurements on the solid salt as well as on the salt dissolved in different solvents has been performed and these have been compared to the theoretical spectra. Furthermore, Raman spectra as a function of temperature have been recorded to investigate possible changes in inter-ionic interaction and/or structure through the phase transition. 1H NMR linewidth measurements as a function of temperature showed a large decrease in linewidth above 100 °C, attributed here to an increase in mobility in agreement with a previously reported phase transition at ~110 °C.

Comparative analysis of surface-enhanced Raman spectroscopy of daidzein and formononetin

Phytoestrogens daidzein (4′,7-dihydroxy-isoflavone) and formononetin (4′-methoxy-7-hydroxy-isoflavone) have been studied by surface-enhanced Raman (SER) spectroscopy. Spectra were acquired in the presence of citratereduced silver colloids, over a range of pH and concentrations. Density functional theory calculations were used to assist assignment of the normal Raman spectra and help determine the mode of interaction of isoflavones with the silver nanoparticles. Formononetin does not show SER activity unless the 7-OH group is deprotonated, and accordingly, the interaction with the silver surface occurs via the deprotonated site. Daidzein, on the other hand, appears to contain multiple species at the surface, interacting via both the hydroxyl groups at 7-OH and 4′-OH, after deprotonation. This is an important result that points to potential future SERS applications in phytoestrogen analysis and provides a foundation for understanding the SER spectra of isoflavones.

Compression and probing C−H···I hydrogen bonds of iodoform under high pressure by x-ray diffraction and raman scattering

High-pressure methods were applied to investigate the structural stability and hydrogen bonding of polar molecules of iodoform by synchrotron radiation X-ray diffraction and Raman spectra measurements, respectively. Up to a pressure of 40 GPa, no phase transitions were observed. The discontinuous frequency shift of the C−H stretching band is believed to be related to the enhancement of the C−H···I weak hydrogen bonds under high pressures. Ab initio calculations were performed, and the results predict the frequency shift of the C−H stretching vibration as C−H···I interacts via hydrogen bonding. The bulk modulus is 17.3 ± 0.8 GPa, with a pressure derivative of 5.2.

A new Raman metric for the characterisation of graphene oxide and its derivatives

Raman spectroscopy is among the primary techniques for the characterisation of graphene materials, as it provides insights into the quality of measured graphenes including their structure and conductivity as well as the presence of dopants. However, our ability to draw conclusions based on such spectra is limited by a lack of understanding regarding the origins of the peaks. Consequently, traditional characterisation techniques, which estimate the quality of the graphene material using the intensity ratio between the D and the G peaks, are unreliable for both GO and rGO. Herein we reanalyse the Raman spectra of graphenes and show that traditional methods rely upon an apparent G peak which is in fact a superposition of the G and D' peaks. We use this understanding to develop a new Raman characterisation method for graphenes that considers the D' peak by using its overtone the 2D'. We demonstrate the superiority and consistency of this method for calculating the oxygen content of graphenes, and use the relationship between the D' peak and graphene quality to define three regimes. This has important implications for purification techniques because, once GO is reduced beyond a critical threshold, further reduction offers limited gain in conductivity.

Self-assembly and film stability of a micelle of a single-chain quaternary ammonium amphiphile containing azobenzene on mica

The self-assembling behavior of a single-chain quaternary ammonium amphiphile bearing azobenzene (C₁₂AzoC₆N⁺) on freshly cleaved mica sheet has been investigated by atomic force microscopy (AFM) method. Confocal microscopic Raman spectra confirm the adsorption of the self-assembled monolayer structure. Ex-situ AFM reveals that C₁₂AzoC₆N⁺ forms branch-like stripes indicating the fusion and reorganization of the micelles during drying in air as the in-situ AFM has revealed that surfactant forms spherical micelles on the mica surface. The nano-sized surface structure is strongly dependent on the change of molecular structure, which resulted from photo-induced isomerization. The nano-sized stripe is quite stable even being annealed at 90 °C for 4 h.

Spectroscopic and model compound studies relevant to wool processing

Describes the development of a cell to hold loose wool fibre, fabric and yarn samples for the collection of Fourier Transform Raman spectra. Then follows a detailed study of reactions of Lanasol (Ciba) dyes with wool, the dyes forming covalent bonds with various amino acids in the fibres.

Conductivity percolation in polyiodide/polymer complexes

Variable-temperature four-probe conductivity measurements and Raman spectroscopy were investigated for iodine in poly(propylene oxide) (PPO) and NaI₃ in PPO. The Raman spectra indicate the presence of both triiodide and polyiodide species in samples of I₂-doped PPO. The conductivity of these PPO/I₂ samples increased with increasing I₂ concentration and reached a plateau at approximately 12 vol % iodine. Raman spectra at 20 °C indicate that, at concentrations less than 23 vol % I₃-, the dominant species is the triiodide. Polymer salt complexes with varying amounts of I₃- appear to display a conductivity threshold near T_g, at 0.2 vol fraction of triiodide.

Influence of praseodymium - synergistic corrosion inhibition in mixed rare-earth diphenyl phosphate systems

Mixed rare-earth organophosphates have been investigated as potential corrosion inhibitors for AA2024-T3, and previously have shown synergistic inhibition behavior; however, the mechanism was not identified. In this paper, a key factor contributing to corrosion inhibition of AA2024-T3 with mischmetal diphenyl phosphate [Mm(dpp)3] is the unique stability of Pr(dpp)3 compared to other key rare earths in mischmetal. Although increasing pH causes precipitation of other components, the Pr compound is stable at higher pH. Electrochemically, a synergy is evident when Ce(dpp)3 and Pr(dpp)3 are combined. Raman mapping indicates the Pr(dpp)3 inhibitor leads to a more uniform coverage of the alloy.

Surface evolution of a gradient structured Ti in hydrogen peroxide solution

In this work, the interaction between hydrogen peroxide (H₂O₂) and a gradient structured Ti was investigated extensively. The gradient structured Ti (SMAT Ti) was produced by surface mechanical attrition treatment (SMAT), and then it was immersed in H₂O₂ solution for different time until 48 h at room temperature (25 °C). The structure and surface morphology evolution were examined by Raman spectra and scanning electron microscopy (SEM). The formation mechanism of nanoporous titania was discussed based on above results.

Spectroscopic characterization of alkali-metal exchanged natrolites

Synchrotron infrared (IR) and micro-Raman spectroscopic studies have been performed on zeolite natrolites as a function of the non-framework composition at ambient conditions. This establishes the spectroscopic characterization of the ion-exchanged natrolites in the alkali-metal series both in the as-prepared hydrated (M-NAT-hyd, M = Li, Na, K, Rb, and Cs) and some stable dehydrated forms (M-NAT-deh, M = Rb and Cs). The former series exhibits non-framework cation-size dependent opening of the helical channels to span ca. 21° range in terms of the chain rotation angle, ? (or ca. 45° range in terms of the chain bridging angle, T-O2-T). For these hydrated phases, both IR and Raman spectra reveal that the degree of the red-shifts in the frequencies of the helical 8-ring channel as well as the 4-ring unit is proportional to the ionic radius of the non-framework cations. Linear fits to the data show negative slopes of -55.7 from Raman and -18.3 from IR in the 8-ring frequencies and ionic radius relationship. The spectroscopic data are also used to identify the modes of the dehydration-induced "collapse" of the helical 8-ring channels as observed in the stable anhydrous Rb-NAT-deh and Cs-NAT-deh. In addition, we demonstrate that the spectroscopic data in the hydrated series can be used to distinguish different water arrangements along the helical channels based on the frequency shifts in the H-O-H bending band and the changes in the O-H stretching vibration modes.