Search

Confocal Raman microspectroscopy (CRM) with 633- and 785-nm excitation wavelengths combined with optical clearing (OC) technique was used for ex-vivo study of porcine skin in the Raman fingerprint region. The optical clearing has been performed on the skin samples by applying a mixture of glycerol and distilled water and a mixture of glycerol, distilled water and chemical penetration enhancer dimethyl sulfoxide (DMSO) during 30[Formula: see text]min and 60[Formula: see text]min of treatment. It was shown that the combined use of the optical clearing technique and CRM at 633[Formula: see text]nm allowed one to preserve the high probing depth, signal-to-noise ratio and spectral resolution simultaneously. Comparing the effect of different optical clearing agents on porcine skin showed that an optical clearing agent containing chemical penetration enhancer provides higher optical clearing efficiency. Also, an increase in treatment time allows to improve the optical clearing efficiency of both optical clearing agents. As a result of optical clearing, the detection of the amide-III spectral region indicating well-distinguishable structural differences between the type-I and type-IV collagens has been improved.

We have studied the light emission properties of aged glassy (g-) and crystalline (c-) As 2 S 3 and freshly fractured glassy As 2 S 3 with photosensitive realgar inclusions in the 1.5–4.5 eV spectral range and applying different excitation photon energies. Additionally, Raman scattering measurements were performed on g-As 40 S 60 to investigate structural changes caused by corrosion of the glass in air. Major features in the luminescence spectra were observed at 1.65, 1.87, 2.04, 2.26, 2.80 and 3.25 eV photon energies. The 1.65 eV band in photoluminescence spectra of g-As 2 S 3 was identified to be related to the As side by comparison of the photoluminescence spectrum with literature data for As 4 S 4 realgar crystal. A newly observed band at 1.87 eV was assigned to the As side in pararealgar occurring due to the light induced transformation from realgar to pararealgar phase. An oxidation process was found to take place during the aging and photo-aging accompanied with formation of As oxides, indicated by the emission bands at 2.04 and 2.26 eV. A rapid photo-oxidation process was observed in freshly fractured surfaces at room temperature which was connected with the light stimulated realgar-pararealgar transformation.

As₂₀Se₈₀, As₄₀Se₆₀ and As₅₀Se₅₀ films were studied by Raman spectroscopy in order to examine the local- and medium-range order of the structure. In addition, X-ray photoelectron, Raman and surface enhanced Raman spectroscopy were used to characterize the structural peculiarities at the top surface of As-Se nanolayers. Raman investigations reveal the dominance of the As₂Se₃ and As₄Se₄ molecules in the volume of the As₄₀Se₆₀ and As₅₀Se₅₀ films and significant contribution of Se in the structure of the As₂₀Se₈₀ film. The composition and local structure of the surfaces were determined by curve fitting of the experimental X-ray photoelectron As 3d and Se 3d core level spectra. A significant Se-enrichment was found at the near-surface layers in comparison with the composition of deeper layers which is confirmed by the dominance of As-3Se structural units in all compositions. This enrichment was also observed by surface enhanced Raman spectroscopy. Processes of arsenic oxidation and desorption of the oxidized products are impacting the structure of the surface layers of As₂₀Se₈₀, As₄₀Se₆₀ and As₅₀Se₅₀ films.

Light-induced structural changes of As-S glasses and films were probed both by macro FT-Raman and photon-energy dependent micro-Raman spectroscopy using different spectral composition of photoactive light: polychromatic or different wavelengths of laser radiation. The polychromatic illumination and thermal treatment leads to continuous decrease in intensity of characteristics vibrational modes of molecular or cage-like species like As4S4, As4S3, etc. Under laser illumination the picture is different, new observed features in the Raman spectra of As-rich As-S glass are related to transformations of As4S4 molecules: α(β)-As4S4 transform into pararealgar p -As4S4 form during laser illumination. The effectiveness of transformations depends mainly on photon energies used for irradiation, but the tendency to transform is observed for all used photon energies ranging from 1.65 to 2.54 eV. Experimental photon-energy dependent Raman spectroscopy used together with ab initio DFT calculations indicate that the mechanism of photo-induced changes in As-S glasses and films is defined by spectral width of illumination source (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Imidazolium-based ionic liquids (ILs) involving anions of variable coordinating strength have been investigated using infrared (IR) and Raman spectroscopies, density functional theory (DFT) calculations and selective deuteration of the imidazolium CH groups. Particular emphasis has been placed on the vibrational assignments of the anion and cation internal vibrations, a prerequisite before any interpretation of spectral changes due to ion-ion interactions in these unconventional liquids. The vibrations of highly symmetric and weakly coordinating anions, such as PF(6)(-), have unperturbed wavenumbers, but unexpected IR or Raman activity for some modes, showing that the anion is subjected to an anisotropic electric field. The stretching as well as the in-plane and out-of-plane bending modes of the imidazolium CH groups are anharmonic. They give broad bands that reflect a large distribution of interactions with the surrounding anions. All the bending modes are mixed with ring vibrations and the stretching modes are complicated by Fermi resonance interactions with overtones and combination of in-plane ring modes. However, the stretching vibration of the quasi-diatomic C((2))-D bond appears to be a good spectroscopic probe of the increasing cation-anion interactions when the coordinating strength of the anion increases. The broad absorption observed in the far IR with weakly coordinating anions remains practically unchanged when the acidic C((2))-H imidazolium bond is methylated and even when the imidazolium cation is substituted by tetra-alkyl ammonium or pyrrolidinium cations. It is concluded that this absorption is a general feature of any IL, coming from the relative translational and librational motions of the ions without needing to invoke C((2))-H anion hydrogen bonds.

The super-bandgap laser irradiation of the in situ prepared As-S chalcogenide films was found to cause drastic structural transformations and unexpected selective diffusion processes, leading to As enrichment on the nanolayer surface. Excitation energy dependent synchrotron radiation photoelectron spectroscopy showed complete reversibility of the molecular transformations and selective laser-driven mass transport during "laser irradiation"-"thermal annealing" cycles. Molecular modeling and density functional theory calculations performed on As-rich cage-like clusters built from basic structural units indicate that the underlying microscopic mechanism of laser induced transformations is connected with the realgar-pararealgar transition in the As-S structure. The detected changes in surface composition as well as the related local and molecular structural transformations are analyzed and a model is proposed and discussed in detail. It is suggested that the formation of a concentration gradient is a result of bond cleavage and molecular reorientation during transformations and anisotropic molecular diffusion.

As a probe of local structure, the vibrational properties of the 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4] ionic liquid were studied by infrared (IR), Raman spectroscopy, and ab initio calculations. The coexistence of at least four [bmim]+ conformers (GG, GA, TA, and AA) at room temperature was established through unique spectral responses. The Raman modes characteristic of the two most stable [bmim] + conformers, GA and AA, according to the ab initio calculations, increase in intensity with decreasing temperature. To assess the total spectral behavior of the ionic liquid both the contributions of different [bmim] + conformers and the [bmim]+- [BF4]- interactions to the vibrational spectra are discussed.

The calculated and experimental Raman spectra of the (EMI+)TFSI− ionic liquid, where EMI+ is the 1-ethyl-3-methylimidazolium cation and TFSI− the bis(trifluoromethanesulfonyl)imide anion, have been investigated for a better understanding of the EMI+ and TFSI− conformational isomerism as a function of temperature. Characteristic Raman lines of the planar (p) and non-planar (np) EMI+ conformers are identified using the reference (EMI+)Br− salt. The anion conformer of C2 symmetry is confirmed to be more stable than the cis (C1) one by 4.5 ± 0.2 kJ mol−1. At room temperature, the population of trans (C2) anions and np cations is 75 ± 2% and 87 ± 4%, respectively. Fast cooling quenches a metastable glassy phase composed of mainly C2 anion conformers and p cation conformers, whereas slow cooling gives a crystalline phase composed of C1 anion conformers and of np cation conformers. Copyright © 2006 John Wiley & Sons, Ltd.

Technologically modified g-GeS 2 (TiVj) glasses prepared by melt quenching from different temperatures (T i ) and with different cooling rates (Vj) were studied using Raman spectroscopy and model calculations. Differential Raman spectra {I R GeS 2 (T i V 1 )-I R GeS2(T 2 V 1 )} showed the splitting of the main, most intensive wide-band, centered at 340 cm -1 . The position of the peaks found in the differential Raman spectra near 340 and 360 cm -1 and position of the main vibrational modes in the ordinary Raman spectra of low- and high-temperature crystalline phases (α-, β-GeS2) were found to be in good agreement. Vibrational spectra of 4- and 6-member ring fragments selected from crystalline structure of β-GeS 2 were also determined using model calculations. Based on rings composed of GeS 4 tetrahedrons connected by corners and edges the structural interpretation of the vibrational bands of g-GeS 2 (TiVj) at 360, 370 and 433 cm -1 in their Raman spectra was performed. The existence of homopolar Ge-Ge and S-S “defect” bonds in the structure of germanium disulfide glasses was proved by formation of 5-member rings. Formation of fragments of both low- and high-temperature α-, β-GeS 2 crystalline phases in the structure of g-GeS 2 (TiVj) glasses indicates the existence of mixed medium-range ordering in g-GeS 2 .