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  • 1.
    Dyakov, Sergey
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Trinity College Dublin.
    Perova, T. S.
    Miao, C. Q.
    Xie, Y. -H
    Cherevkov, S. A.
    Baranov, A. V.
    Influence of the buffer layer properties on the intensity of Raman scattering of graphene2013In: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555, Vol. 44, no 6, p. 803-809Article in journal (Refereed)
    Abstract [en]

    Using a model of oscillating dipoles, we simulate the intensity of the G-band in the Raman signal from structures consisting of graphene, separated by an arbitrary buffer layer from a substrate. It is found that a structure with an optimized buffer layer refractive index and thickness exhibits a Raman signal which is nearly 50 times more intense than that from the same structure with a non-optimized buffer layer. The theoretical simulations are verified by Raman measurements on structures consisting of a layer of graphene on SiO2 and Al2O3 buffer layers. The optical contrast of the single graphene layer is calculated for an arbitrary buffer layer. It was found that both the Raman intensity and optical contrast can be maximized by varying the buffer layer thickness.

  • 2. Ehn, A.
    et al.
    Levenius, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Jonsson, M.
    Aldén, M.
    Bood, J.
    Temporal filtering with fast ICCD cameras in Raman studies2013In: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555, Vol. 44, no 4, p. 622-629Article in journal (Refereed)
    Abstract [en]

    A common problem when applying Raman scattering in applied research is spectral interference from laser-induced fluorescence. Extensive work has been invested in developing spectral and polarization filters as well as modulation schemes to refine spontaneous Raman signals. This current work, however, focuses on utilizing the temporal domain using a picosecond laser system and ICCD cameras with relatively short decay of the camera gate to prevent the fluorescence tail from being captured in Raman experiments. Further, the approach of using an ICCD camera to perform temporal filtering is compared to earlier proposed detection schemes using streak cameras or Kerr gates. The temporal-filtering scheme is evaluated in a spectroscopic investigation where a background subtraction algorithm is presented. The temporal-filtering scheme was also evaluated for Raman imaging of a levitated water droplet surrounded by fluorescing toluene vapor. Furthermore, the temporal-filter detection scheme was simulated in order to provide straight forward evaluation tools to estimate the potential of performing temporal filtering with a laser/camera system considering: laser-pulse duration, time jitter, camera-gate characteristics, gate delay times, fluorescence lifetimes, and relative signal strength between the Raman and fluorescence signal. The fluorescence signal was modeled with a closed two-level system, and the simulated results were compared to results from an investigation of the rising slope of toluene fluorescence. These evaluation tools and experimental investigations may serve as guidelines for planning and performing Raman measurements in situations where traditional filter-rejection schemes are insufficient.

  • 3.
    Lin, Ke
    et al.
    University of Science and Technology of China.
    Hu, Naiyin
    University of Science and Technology of China.
    Zhou, Xiaoguo
    University of Science and Technology of China.
    Liu, Shilin
    University of Science and Technology of China.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Reorientation dynamics in liquid alcohols from Raman spectroscopy2012In: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555, Vol. 43, p. 82-88Article in journal (Refereed)
    Abstract [en]

    Polarized Raman spectroscopy has been employed to study the reorientational, or more specifically the translational relaxation dynamics, of alcohol molecules in pure liquids and aqueous solutions. It is found from the spectral width measurements that alcohol molecules in pure liquids have typically translational relaxation times on the order of picoseconds, following the order methanol < ethanol < i-propanol < n-propanol. Temperature-dependent measurements show that hydrogen-bonding (HB) and hydrophobic interactions control the translational motion. The hydrophobic interaction reduces the relaxation time more apparently in view of the –CH3 group than the skeleton motion. For alcohol–water mixtures, the increaseofwater concentration generally slows down the relaxation process in a non-monotonic behavior. However, the trend stops at a certain point and the motion of alcohol molecules becomes faster when the alcohol concentration further drops. Different mechanisms have been proposed to interpret these observations, which might be helpful to gain deeper insight into the HB networks of alcohols with water. Our study strongly illustrates that Raman spectroscopy can be applied to the study of fast translational motion of molecules in HB systems.

  • 4. Luo, Zhixun
    et al.
    Yang, Wensheng
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Peng, Aidong
    Ma, Ying
    Fu, Hongbing
    Yao, Jiannian
    Loo, Boon H.
    Potential-induced Raman behavior of individual (R)-di-2-naphthylprolinol molecules on a Ag-modified Ag electrode2011In: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555, Vol. 42, no 5, p. 951-957Article in journal (Refereed)
    Abstract [en]

    The applicability of surface-enhanced Raman spectroscopy is demonstrated to probe the adsorption behavior of individual molecules on a Ag electrode. High-quality SERS spectra of (R)-di-2-naphthylprolinol (DNP) were obtained from ultradilute solutions (10(-12) M) on the Ag-nanoparticle-modified Ag electrode, which is attributed to the high electromagnetic (EM) effect of the SERS-active system as well as to the strong adsorption and interaction of DNP molecules with Ag. The stable SERS spectra present remarkable potential dependence, which gives evidence for the behavior of individual DNP molecules on the Ag surface. Based on statistical analysis for the probability of DNP molecules located in 'hot spots', we propose an SERS mechanism for individual molecules in the electrode system, in combination with the hot-spot model and orientation of the probemolecules.

  • 5. Sajan, D.
    et al.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Joe, I. Hubert
    Jayakumar, V. S.
    Dimerisation and vibrational spectroscopic properties of (RS)-phenylsuccinic acid2006In: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555, Vol. 37, no 11, p. 1307-1318Article in journal (Refereed)
    Abstract [en]

    Single crystals of (RS)-phenylsuccinic acid (RSPSA) were grown by the slow evaporation technique and vibrational spectral analysis was carried out using near-IR Fourier transform Raman and Fourier transform IR spectroscopy. The density functional theoretical (DFT) computations were also performed at the B3LYP/6-31G(d) level to derive the equilibrium geometry, vibrational wavenumbers, intensities and atomic charges. Vibrational spectral investigation confirmed the formation of cyclic dimers in the crystal, with the carboxyl groups of each acid molecule being hydrogen bonded to those of the adjacent molecules. Each molecule is connected to two other molecules, forming infinite chains. The wavenumber difference observed between the carbonyl modes in the IR and Raman spectra might be attributed to the intramolecular association based on C=O center dot center dot center dot H type hydrogen bonding in the molecule. In a hydrogen-bonded carbonyl, resonance can occur, which places a partial negative charge on the oxygen atom accepting the hydrogen bond and a positive charge on the atom donating the hydrogen. The resulting partial 'transfer of allegiance' of the proton enhances resonance and lowers the carbonyl stretching wavenumber. The O-H stretching vibrational wavenumber is red-shifted owing to the formation of strong O-H center dot center dot center dot O hydrogen bonds by hyperconjugation between carbonyl oxygen lone electron pairs and O-H sigma* antibonding orbitals. Vibrational analysis was used to investigate the C-H center dot center dot center dot O interaction and electronic effects, induction of the methylene group by an adjacent electronegative atom and the resulting increase of stretching mode wavenumbers and decrease of infrared intensities.

  • 6. Taylor, M. J.
    et al.
    Kloo, Lars A.
    KTH, Superseded Departments, Chemistry.
    Raman investigations of indium iodide complexes: evidence for the In2I7- ion2000In: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555, Vol. 31, no 6, p. 465-468Article in journal (Refereed)
    Abstract [en]

    Raman spectra of some indium iodide complexes were studied, including alpha- and beta-InI3 and In2I4. InI3 with KI yields K+InI4-. With CsI the spectra reveal, in addition to Cs+InI4-, the complex anion In2I7- in the solid phase CsI:2InI(3), This structure consists of InI3 groups with a linking In-I-in bridge which appears to be linear. The vibrational spectra were calculated for the dimeric In2I6 molecule at the HF, B3LYP and MP2 levels, but the structure turned out to be unstable when such calculations were attempted for In2I7-.

  • 7. Taylor, M. J.
    et al.
    Kloo, Lars A.
    KTH, Superseded Departments, Chemistry.
    Seakins, J. M.
    Raman investigations of indium iodide complexes: the species present in aqueous and diethyl ether solutions2001In: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555, Vol. 32, no 12, p. 1015-1017Article in journal (Refereed)
    Abstract [en]

    Raman spectra of aqueous indium (III) iodide solutions, with and without added HI, reveal an equilibrium between two species: the complex anion InI4- (nu(1) = 139 cm(-1)) and the solvated molecule InI3(H2O), (nu(sym) = 158 cm(-1)). The complex acid HInI4 is transferred from the aqueous acidic solution by solvent extraction; spectra of this species and the ether adduct InI3 (.) Et2O (nu(sym) = 151 cm(-1)) are reported.

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