Polarized Resonance Raman Spectroscopy Research Articles

Modification of transition pathways in polarized resonance Raman spectroscopy for carbon nanotubes by highly confined near-field light

We observed a modification of transition pathways in polarized resonance Raman spectroscopy during tip-enhanced Raman spectroscopy (TERS) analysis of metallic carbon nanotubes (CNTs). At a spatial resolution reaching up to the sub-nanometer regime, the signal intensity of the typical D-band is observed to be even higher than the intensity of the G-band all over the probed CNTs in TERS imaging. The measured D-band is attributed to the non-vertical transitions of electrons in k-space that are facilitated by highly confined near-field light at the tip–sample junction of our scanning tunneling microscope based TERS system. The D-band signal was observed even when the CNTs were excited by light polarized perpendicular to the tube axis that corresponds to electronic excitations between different cutting line numbers of a CNT. By combining the electron pathways brought about by both the near-field light and its polarization, we found a unique optical transition of electrons of CNTs in near-field Raman spectroscopy.

DNA-wrapped carbon nanotubes aligned in stretched gelatin films: Polarized resonance Raman and absorption spectroscopy study

We present the study of DNA-wrapped single-walled carbon nanotubes (SWNTs) embedded in the stretched gelatin film by the polarized resonance Raman spectroscopy and visible-NIR optical absorption. The polarized dependent absorption spectra taken along and normal to the stretching direction demonstrate a comparatively high degree of the alignment of isolated SWNTs in the gelatin matrix. The analysis of Raman spectra of isolated SWNTs in the gelatin stretched films showed that the degree of the alignment of carbon nanotubes along the stretching direction is about 62%. The dependence of the peak position of G+-band in Raman spectra on the polarization angle θ between the polarization of the incident light and the direction of the stretching of films was revealed. This shift is explained by the different polarization dependence of the most intensive A and E1 symmetry modes within the G+-band. The performed studies of embedded DNA-wrapped nanotubes in the gelatin film show the simple method for obtaining the controlled ordered biocompatible nanotubes inside a polymer matrix. It can be used for manufacturing sizable flexible self-transparent films with integrated nanoelectrodes.

Optical Properties of Monodispersed AlGaN Nanowires in the Single-Prong Growth Mechanism

Growth of monodispersed AlGaN nanowires of ternary wurtzite phase is reported using the chemical vapor deposition technique in the vapor–liquid–solid process. The role of distribution of Au catalyst nanoparticles on the size and shape of AlGaN nanowires is discussed. These variations in the morphology of the nanowires are understood invoking Ostwald ripening of Au catalyst nanoparticles at high temperature followed by the effect of single and multiprong growth mechanism. Energy-filtered transmission electron microscopy is used as an evidence for the presence of Al in the as-prepared samples. A significant blue shift of the band gap, in the absence of quantum confinement effect in the nanowires with diameter ∼100 nm, is used as a supportive evidence for the AlGaN alloy formation. Polarized resonance Raman spectroscopy with strong electron–phonon coupling along with optical confinement due to the dielectric contrast of nanowire with respect to that of surrounding media are adopted to understand the crystall...

Low-Frequency Mode Activity of Heme: Femtosecond Coherence Spectroscopy of Iron Porphine Halides and Nitrophorin

The low-frequency mode activity of metalloporphyrins has been studied for iron porphine-halides (Fe(P)(X), X = Cl, Br) and nitrophorin 4 (NP4) using femtosecond coherence spectroscopy (FCS) in combination with polarized resonance Raman spectroscopy and density functional theory (DFT). It is confirmed that the mode symmetry selection rules for FCS are the same as for Raman scattering and that both Franck-Condon and Jahn-Teller mode activities are observed for Fe(P)(X) under Soret resonance conditions. The DFT-calculated low-frequency (20-400 cm (-1)) modes, and their frequency shifts upon halide substitution, are in good agreement with experimental Raman and coherence data, so that mode assignments can be made. The doming mode is located at approximately 80 cm (-1) for Fe(P)(Cl) and at approximately 60 cm (-1) for Fe(P)(Br). NP4 is also studied with coherence techniques, and the NO-bound species of ferric and ferrous NP4 display a mode at approximately 30-40 cm (-1) that is associated with transient heme doming motion following NO photolysis. The coherence spectra of three ferric derivatives of NP4 with different degrees of heme ruffling distortion are also investigated. We find a mode at approximately 60 cm (-1) whose relative intensity in the coherence spectra depends quadratically on the magnitude of the ruffling distortion. To quantitatively account for this correlation, a new "distortion-induced" Raman enhancement mechanism is presented. This mechanism is unique to low-frequency "soft modes" of the molecular framework that can be distorted by environmental forces. These results demonstrate the potential of FCS as a sensitive probe of dynamic and functionally important nonplanar heme vibrational excitations that are induced by the protein environmental forces or by the chemical reactions in the aqueous phase.

Polarized resonance Raman spectroscopy of single-wall carbon nanotubes within a polymer under strain

The ${D}^{*}$ Raman band of single-wall carbon nanotubes aligned by shear flow in a polymer matrix has been measured as a function of tensile strain. The Raman intensity varies with the optical polarization direction, an effect which is used here to assess the degree of tube alignment. The strain dependence of the Raman shift depends strongly on the nanotube orientation and the polarization direction. We show that, using polarized light, unoriented nanotubes can be used as strain sensors so that no tube alignment is necessary and the strain can be measured in all directions in a single sample.

Use of Polarized Resonance Raman Spectroscopy of a Polyene Probe, and FT-IR Dichroism, to Probe Amorphous-Phase Orientation in Uniaxially Drawn Poly(Ethylene)

The linear diphenyl polyene Φ–(C=C–)4Φ has been investigated as a resonant Raman-active probe for molecular orientation, suitable for incorporation into polymers prior to melt extrusion and drawing. By examination of the polarization properties of the Raman scattered radiation, it is possible to determine the P200 and P400 orientation parameters for the dye molecule as a function of draw ratio. Assuming that the dye resides only in amorphous polymer regions, it is expected that the data will give insight into the orienting forces present in the amorphous phase during processing. Expressions were derived relating P200 and P400 to the polarized Raman intensities. An expression for Hermans' orientation parameter was also derived—it was shown that f was always slightly higher than P200 when evaluated from the same Raman data. These Raman measurements were illustrated by using the example of uniaxially drawn poly(ethylene) (PE) tubing. As an alternative approach, FT-IR dichroic ratios of bands due to the PE itself were used to determine the orientation ( P200) of the crystalline phase and also of gauche conformers present only in the amorphous phase; these results were compared with the Raman measurements on the dye probe. The orientation was examined as a function of draw ratio and subsequent thermal annealing. In general, both crystalline and amorphous phases oriented increasingly with draw ratio, but whereas annealing the samples only slightly relaxed the crystal orientation, the amorphous orientation decreased dramatically when measured by using either the probe molecule or the gauche conformer as a probe of the amorphous phase. This result support the assumption that the dye is localized in amorphous regions. This work is important since it shows how a cheap, commercially available probe molecule may be used to probe the amorphous-phase orientation of a polymer without requiring any chemical synthesis; simple melt-mixing is sufficient to dope the amorphous network. This capability will be useful for systems where convenient vibrational band: specific to the polymer amorphous phase are absent.

Polarized resonance Raman scattering of iodine-doped polyacetylene with high conductivity

We investigated the structure and alignment of iodine dopant in the highly conducting polyacetylene (HCPA) with different doping concentration by using polarized resonance Raman spectroscopy (PRRS). It was found for the first time that the I 3 − species is predominant in the highly stretched HCPA film even for the highly doping level ((CHI 0.25) x), in contrast with traditional polyacetylene. We also observed that the intensity ratio of I 3 −/I 5 − and the orientation of I 3 − species increase greatly with increasing initial draw ration of the polyacetylene films.

Resonance Raman spectra of chlorophylls dissolved in liquid crystal matrices

The molecular ordering of molecules embedded in a uniaxial liquid crystalline system has been considered. In particular, planar Chl a molecules in an MBBA + EBBA mixture have been studied by using polarized resonance Raman spectroscopy. The second- and fourth-rank order parameters and the orientational distribution function of Chl a in the nematic MBBA + EBBA liquid crystalline phase are discussed.

Phthalocyanine-based electrically conductive, processible molecular/macromolecular hybrid materials

This contribution relates new information on the properties of electrically conductive, processible Ni(Pc)/polymer/I 2 hybrid materials. Both the temperature and composition dependence of the electrical conductivity of Ni(Pc)/Kevlar/I 2 fibres are strongly reminiscent of the behaviour of composites. Using a variant of our fibre spinning methodology, it is also possible to produce Ni(Pc)/Kevlar/I 2 ribbons. Polarized resonance Raman spectroscopy indicates that the ribbons are structurally anisotropic (Ni(Pc)I c axes are preferentially aligned in the extrusion direction), while four-probe transport measurements indicate significant anisotropy in the conductivity ( σ ‖ σ hu ≈ 8 where ‖ denotes the extrusion direction). This anisotropy is nearly temperature independent. Electrically conductive fibres can also be prepared using Nomex or poly( p-phenylene-2,6-benzobisthiazole) (PBT) instead of Kevlar as the host polymer.

Polarized resonance Raman spectroscopy of fully-oriented crystalline trans-(CH) x

Fully-oriented non-fibrous crystalline trans-(CH) x films prepared by stress-orientation and conversion of poly-7,8-bis-(trifluoromethyl)-tricyclo-{4.2.2.0.}-deca-3,7,9,-triene, poly-(BTFM-TCDT), are investigated by polarized resonance Raman spectroscopy. With an excitation wavelength of 647.1 nm and parallel polarization (parallel to the c-axis, i.e., the stretching direction), two strong Raman bands are observed at 1078 cm −1 and 1469 cm −1, whereas for perpendicular polarization, no Raman scattered light can be detected. This polarization behaviour proves the perfect alignment of long unperturbed conjugated sequences parallel to the c-axis. Upon excitation with blue laser light ( λ l = 457.9 nm ), for which preferentially short conjugated sequences come into resonance, an increase of the depolarization ratio compared to the red excitation is observed. These results are discussed in terms of conjugation length distributions and resonance conditions with respect to the polarized optical absorption spectra.

Polarized resonance Raman spectroscopy of Langmuir-Blodgett films

Preliminary resonance Raman spectroscopy experiments on Langmuir-Blodgett (LB) films made of a small number of porphyrin layers are reported. It is shown that the angular molecular distributions inside LB films can be obtained from these data.

Polarized resonance Raman spectroscopy of the photointermediate of oxyhemoglobin on the picosecond time scale

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPolarized resonance Raman spectroscopy of the photointermediate of oxyhemoglobin on the picosecond time scaleMark Nagumo, Malcolm Nicol, and Mostafa A. El-SayedCite this: J. Phys. Chem. 1981, 85, 17, 2435–2438Publication Date (Print):August 1, 1981Publication History Published online1 May 2002Published inissue 1 August 1981https://doi.org/10.1021/j150617a003RIGHTS & PERMISSIONSArticle Views30Altmetric-Citations13LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (540 KB) Get e-Alerts