Showing papers on "Raman spectroscopy published in 2004"
TL;DR: It is shown how to use resonant Raman spectroscopy to determine structure and composition of carbon films with and without nitrogen, and the assignment of the peaks at 1150 and 1480 cm−1 often observed in nanodiamond.
Abstract: Raman spectroscopy is a standard characterization technique for any carbon system. Here we review the Raman spectra of amorphous, nanostructured, diamond-like carbon and nanodiamond. We show how to use resonant Raman spectroscopy to determine structure and composition of carbon films with and without nitrogen. The measured spectra change with varying excitation energy. By visible and ultraviolet excitation measurements, the G peak dispersion can be derived and correlated with key parameters, such as density, sp(3) content, elastic constants and chemical composition. We then discuss the assignment of the peaks at 1150 and 1480 cm(-1) often observed in nanodiamond. We review the resonant Raman, isotope substitution and annealing experiments, which lead to the assignment of these peaks to trans-polyacetylene.
2,172 citations
TL;DR: The symmetry–imposed selection rules for double–resonant Raman scattering in graphite are developed and an excellent agreement is found between the graphite phonon dispersion from double– ResonantRaman scattering and other experimental methods.
Abstract: We present a review of the Raman spectra of graphite from an experimental and theoretical point of view. The disorder-induced Raman bands in this material have been a puzzling Raman problem for almost 30 years. Double-resonant Raman scattering explains their origin as well as the excitation-energy dependence, the overtone spectrum and the difference between Stokes and anti-Stokes scattering. We develop the symmetry-imposed selection rules for double-resonant Raman scattering in graphite and point out misassignments in previously published works. An excellent agreement is found between the graphite phonon dispersion from double-resonant Raman scattering and other experimental methods.
1,132 citations
TL;DR: Coherent anti-Stokes Raman scattering (CARS) microscopy permits vibrational imaging with high-sensitivity, high speed, and three-dimensional spatial resolution as discussed by the authors, and the development of multiplex CARS microspectroscopy, which allows high-speed characterization of microscopic samples.
Abstract: Coherent anti-Stokes Raman scattering (CARS) microscopy permits vibrational imaging with high-sensitivity, high speed, and three-dimensional spatial resolution. We review recent advances in CARS microscopy, including experimental design, theoretical understanding of contrast mechanisms, and applications to chemical and biological systems. We also review the development of multiplex CARS microspectroscopy, which allows high-speed characterization of microscopic samples, and CARS correlation spectroscopy, which probes fast diffusion dynamics with vibrational selectivity.
921 citations
Book•
12 Mar 2004
TL;DR: In this article, the authors present a character and correlation table of the Raman Spectra of single-walled carbon nanotubes with respect to the properties of room temperature, room-temperature conductance, and vibrational properties.
Abstract: Preface. 1 Introduction. 2 Structure and Symmetry. 2.1 Structure of Carbon Nanotubes. 2.2 Experiments. 2.3 Symmetry of Single-walled Carbon Nanotubes. 2.3.1 Symmetry Operations. 2.3.2 Symmetry-based Quantum Numbers. 2.3.3 Irreducible representations. 2.3.4 Projection Operators. 2.3.5 Phonon Symmetries in Carbon Nanotubes. 2.4 Summary. 3 Electronic Properties of Carbon Nanotubes. 3.1 Graphene. 3.1.1 Tight-binding Description of Graphene. 3.2 Zone-folding Approximation. 3.3 Electronic Density of States. 3.3.1 Experimental Verifications of the DOS. 3.4 Beyond Zone Folding - Curvature Effects. 3.4.1 Secondary Gaps in Metallic Nanotubes. 3.4.2 Rehybridization of the sigma and pi States. 3.5 Nanotube Bundles. 3.5.1 Low-energy Properties. 3.5.2 Visible Energy Range. 3.6 Summary. 4 Optical P roperties. 4.1 Absorption and Emission. 4.1.1 Selection Rules and Depolarization. 4.2 Spectra of Isolated Tubes. 4.3 Photoluminescence Excitation - (n1, n2) Assignment. 4.4 4-A-diameter Nanotubes. 4.5 Bundles of Nanotubes. 4.6 Excited-state Carrier Dynamics. 4.7 Summary. 5 Electronic Transport. 5.1 Room-temperature Conductance of Nanotubes. 5.2 Electron Scattering. 5.3 Coulomb Blockade. 5.4 Luttinger Liquid. 5.5 Summary. 6 Elastic Properties. 6.1 Continuum Model of Isolated Nanotubes. 6.1.1 Ab-initio, Tight-binding, and Force-constants Calculations. 6.2 Pressure Dependence of the Phonon Frequencies. 6.3 Micro-mechanical Manipulations. 6.4 Summary. 7 Raman Scattering. 7.1 Raman Basics and Selection Rules. 7.2 Tensor Invariants. 7.2.1 Polarized Measurements. 7.3 Raman Measurements at Large Phonon q. 7.4 Double Resonant Raman Scattering. 7.5 Summary. 8 Vibrational Properties. 8.1 Introduction. 8.2 Radial Breathing Mode. 8.2.1 The RBM in Isolated and Bundled Nanotubes. 8.2.2 Double-walled Nanotubes. 8.3 The Defect-induced D Mode. 8.3.1 The D Mode in Graphite. 8.3.2 The D Mode in Carbon Nanotubes. 8.4 Symmetry of the Raman Modes. 8.5 High-energy Vibrations. 8.5.1 Raman and Infrared Spectroscopy. 8.5.2 Metallic Nanotubes. 8.5.3 Single- and Double-resonance Interpretation. 8.6 Summary. 8.7 What we Can Learn from the Raman Spectra of Single-walled Carbon Nanotubes. Appendix A: Character and Correlation Tables of Graphene. Appendix B: Raman Intensities in Unoriented Systems. Appendix C: Fundamental Constants. Bibliography. Index.
822 citations
TL;DR: A study of step edges in graphite with different atomic structures combining Raman spectroscopy and scanning probe microscopy is presented, explaining the effect by applying the double resonance theory to a semi-infinite graphite crystal.
Abstract: A study of step edges in graphite with different atomic structures combining Raman spectroscopy and scanning probe microscopy is presented. The orientation of the carbon hexagons with respect to the edge axis, in the so-called armchair or zigzag arrangements, is distinguished spectroscopically by the intensity of a disorder-induced Raman peak. This effect is explained by applying the double resonance theory to a semi-infinite graphite crystal and by considering the one-dimensional character of the defect.
624 citations
TL;DR: This is believed to be the first report showing bacterial discrimination using SERS, and the resultant ordination plots and dendrograms showed correct groupings for these organisms, including discrimination to strain level for a sample group of Escherichia coli.
Abstract: Raman spectroscopy has recently been shown to be a potentially powerful whole-organism fingerprinting technique and is attracting interest within microbial systematics for the rapid identification ...
622 citations
TL;DR: It is found that SERS enhancements on nanoshell films are dramatically different from those observed on colloidal aggregates, specifically that the Raman enhancement follows the plasmon resonance of the individual nanoparticles.
Abstract: Au and Ag nanoshells are investigated as substrates for surface-enhanced Raman scattering (SERS). We find that SERS enhancements on nanoshell films are dramatically different from those observed on colloidal aggregates, specifically that the Raman enhancement follows the plasmon resonance of the individual nanoparticles. Comparative finite difference time domain calculations of fields at the surface of smooth and roughened nanoshells reveal that surface roughness contributes only slightly to the total enhancement. SERS enhancements as large as 2.5 × 1010 on Ag nanoshell films for the nonresonant molecule p-mercaptoaniline are measured.
602 citations
TL;DR: Tip-enhanced Raman spectroscopy is reported on with smooth single crystalline surfaces as substrates, based on the optical excitation of localized surface plasmons in the tip-substrate cavity, which provides a large but local field enhancement near the tip apex.
Abstract: Tip-enhanced Raman spectroscopy (TERS) is based on the optical excitation of localized surface plasmons in the tip-substrate cavity, which provides a large but local field enhancement near the tip apex. We report on TERS with smooth single crystalline surfaces as substrates. The adsorbates were CN- ions at Au(111) and malachite green isothiocyanate (MGITC) molecules at Au(111) and Pt(110) using either Au or Ir tips. The data analysis yields Raman enhancements of about 4 x 10(5) for CN- and up to 10(6) for MGITC at Au(111) with a Au tip, probing an area of less than 100 nm radius.
561 citations
TL;DR: A review of the strengths and pitfalls of the Raman technique for the analysis of diamond and diamond films can be found in this article, where some of the latest developments hold the promise of providing a more profound understanding of the outstanding properties of these materials.
Abstract: The optimization of diamond films as valuable engineering materials for a wide variety of applications has required the development of robust methods for their characterization. Of the many methods used, Raman microscopy is perhaps the most valuable because it provides readily distinguishable signatures of each of the different forms of carbon (e.g. diamond, graphite, buckyballs). In addition it is non-destructive, requires little or no specimen preparation, is performed in air and can produce spatially resolved maps of the different forms of carbon within a specimen. This article begins by reviewing the strengths (and some of the pitfalls) of the Raman technique for the analysis of diamond and diamond films and surveys some of the latest developments (for example, surface-enhanced Raman and ultraviolet Raman spectroscopy) which hold the promise of providing a more profound understanding of the outstanding properties of these materials. The remainder of the article is devoted to the uses of Raman spectroscopy in diamond science and technology. Topics covered include using Raman spectroscopy to assess stress, crystalline perfection, phase purity, crystallite size, point defects and doping in diamond and diamond films.
520 citations
TL;DR: It was concluded that the primary factor for the enhanced activity of combustion-synthesized catalyst is a larger amount of surface hydroxyl groups and a lowered band gap.
Abstract: Nanocrystalline TiO2 was synthesized by the solution combustion method using titanyl nitrate and various fuels such as glycine, hexamethylenetetramine, and oxalyldihydrazide. These catalysts are active under visible light, have optical absorption wavelengths below 600 nm, and show superior photocatalytic activity for the degradation of methylene blue and phenol under UV and solar conditions compared to commercial TiO2, Degussa P-25. The higher photocatalytic activity is attributed to the structure of the catalyst. Various studies such as X-ray diffraction, Raman spectroscopy, Brunauer−Emmett−Teller surface area, thermogravimetric−differential thermal analysis, FT-IR spectroscopy, NMR, UV−vis spectroscopy, and surface acidity measurements were conducted. It was concluded that the primary factor for the enhanced activity of combustion-synthesized catalyst is a larger amount of surface hydroxyl groups and a lowered band gap. The lower band gap can be attributed to the carbon inclusion into the TiO2 giving Ti...
518 citations
TL;DR: In this paper, single-walled carbon nanotubes (SWNTs) are grown by a plasma enhanced chemical vapor deposition (PECVD) method at 600 °C.
Abstract: Single-walled carbon nanotubes (SWNT) are grown by a plasma enhanced chemical vapor deposition (PECVD) method at 600 °C. The nanotubes are of high quality as characterized by microscopy, Raman spectroscopy, and electrical transport measurements. High performance field effect transistors are obtained with the PECVD nanotubes. Interestingly, electrical characterization reveals that nearly 90% of the nanotubes are semiconductors and thus highly preferential growth of semiconducting over metallic tubes in the PECVD process. Control experiments with other nanotube materials find that HiPco nanotubes consist of ∼61% semiconductors, while laser ablation preferentially grows metallic SWNTs (∼70%). The characterization method used here should also be applicable to assessing the degree of chemical separation of metallic and semiconducting nanotubes.
TL;DR: Small-diameter (<5 nm), single-crystalline SnO2 nanorods were synthesized in solution with a mean length of 17 +/- 4 nm (mean aspect ratio of 4:1) with the [001] direction along the major axis.
Abstract: Small-diameter (<5 nm), single-crystalline SnO2 nanorods were synthesized in solution with a mean length of 17 +/- 4 nm (mean aspect ratio of 4:1) with the [001] direction along the major axis. Two characteristic peaks at 576 and 356 cm-1 in the Raman spectrum further confirmed the small crystal size. The SnO2 nanorods exhibit a red emission at 580 nm.
07 May 2004
TL;DR: In this paper, a wide variety of surfactants for their efficiency in dissolving isolated single-walled carbon nanotubes (SWNTs) in water was investigated.
Abstract: We have investigated a wide variety of surfactants for their efficiency in dissolving isolated single-walled carbon nanotubes (SWNTs) in water. In doing so, we have completely avoided the harsh chemical or mechanical conditions, such as acid or ultrasonic treatments, that are known to damage SWNTs. Bile salts in particular are found to be exceptionally effective in dissolving individual tubes, as evidenced by highly resolved optical absorption spectra, bright bandgap fluorescence, and the unprecedented resolution (∼ 2.5 cm - 1 ) of the radial breathing modes in Raman spectra. This is attributed to the formation of very regular and stable micelles around the nanotubes providing an unusually homogeneous environment. Quantitative information concerning the degree of solubilization is obtained from absorption spectroscopy.
TL;DR: The carbon nanosheets were synthesized on a variety of substrates by radio-frequency plasma-enhanced chemical vapor deposition without any catalyst or special substrate treatment.
Abstract: Free-standing graphite sheets with thickness less than 1nm, “carbon nanosheets,” were synthesized on a variety of substrates by radio-frequency plasma-enhanced chemical vapor deposition without any catalyst or special substrate treatment. The nanosheets consist of one to three graphene layers with a large smooth surface topography, standing roughly vertical to the substrate. Due to the atomic thickness and corrugated nature of nanosheets, low-energy vibrational modes are present in the Raman spectra. The low turn-on field of 4.7 V/μm for electron field emission suggests that the carbon nanosheets could be used as a potential edge emitter.
TL;DR: UV-Vis DRS and photoluminescence (PL) spectroscopy, combined with excitation selective Raman spectroscopic, allow us to understand the main optical and vibrational properties of a metal-organic MOF-5 framework.
TL;DR: Wet chemical methods involving ultrasound and amide solvents were used to purify and separate large bundles of single-walled carbon nanotubes into individual nanot tubes that could then be transported to silicon or mica substrates to remove amorphous carbon.
Abstract: Wet chemical methods involving ultrasound and amide solvents were used to purify and separate large bundles of single-walled carbon nanotubes (SWNTs) into individual nanotubes that could then be transported to silicon or mica substrates. The SWNTs studied were produced by the arc-discharge process. Dry oxidation was used in an initial step to remove amorphous carbon. Subsequently, two acid purification schemes were investigated (HCl- and HNO(3)-reflux) to remove the metal growth catalyst (Ni-Y). Finally, ultrasonic dispersion of isolated tubes into either N,N-dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP) was carried out. Raman scattering, atomic force microscopy (AFM), and electron microscopy were used to study the evolution of the products. Raman scattering was used to probe possible wall damage during the chemical processing. We found that both HCl and HNO(3) could be used to successfully remove the Ni-Y below approximately 1 wt %. However, the HNO(3)-reflux produced significant wall damage (that could be reversed by vacuum annealing at 1000 degrees C). In the dispersion step, both amide solvents (DMF and NMP) produced a high degree of isolated tubes in the final product, and no damage during this dispersion step was observed. HNO(3)-refluxed tubes were found to disperse the best into the amide solvents, perhaps because of significant wall functionalization. AFM was used to study the filament diameter and length distributions in the final product, and interesting differences in these distributions were observed, depending on the chemical processing route.
TL;DR: A three-component band fitting is used to characterize the Raman amide I band of alpha-synuclein, phosvitin, alpha- casein, beta-casein, and the non-A beta component (NAC) of Alzheimer's plaque, demonstrating the ability of Raman spectroscopy to characterized the ensemble of secondary structures present in natively unfolded proteins.
Abstract: The application of Raman spectroscopy to characterize natively unfolded proteins has been underdeveloped, even though it has significant technical advantages. We propose that a simple three-component band fitting of the amide I region can assist in the conformational characterization of the ensemble of structures present in natively unfolded proteins. The Raman spectra of α-synuclein, a prototypical natively unfolded protein, were obtained in the presence and absence of methanol, sodium dodecyl sulfate (SDS), and hexafluoro-2-propanol (HFIP). Consistent with previous CD studies, the secondary structure becomes largely α-helical in HFIP and SDS and predominantly β-sheet in 25% methanol in water. In SDS, an increase in α-helical conformation is indicated by the predominant Raman amide I marker band at 1654 cm-1 and the typical double minimum in the CD spectrum. In 25% HFIP the amide I Raman marker band appears at 1653 cm-1 with a peak width at half-height of ∼33 cm-1, and in 25% methanol the amide I Raman b...
TL;DR: In this article, the authors showed that the enhancement of the Raman signal is provided by surface plasmon (SP) modes excited at the array of nanoholes, which leads to spatial localization of the electromagnetic fields in nanometric regions close to the surface.
Abstract: Periodic arrays of sub-wavelength apertures (nanoholes) in ultrathin Au films were used as substrates for enhanced-Raman spectroscopy in the optical range. Nanohole-enhanced (resonance) Raman scattering from oxazine 720 (oxa) adsorbed on arrays of different periodicities (distance between the center of the holes) was obtained. The overall Raman intensity of the adsorbed molecule was dependent on the periodicity of these arrays. The enhancement factor reached a maximum for the array that presented the largest transmission at the excitation wavelength of the laser. This shows that the enhancement of the Raman signal is provided by surface plasmon (SP) modes excited at the array of nanoholes. SP excitations lead to spatial localization of the electromagnetic fields in nanometric regions close to the surface. This field localization, allied to the unique vibrational signature of the Raman scattering and the simplified optical arrangement from the transmission optics, suggests that arrays of nanoholes should b...
TL;DR: In this article, the Raman and infrared spectra of a series of 1-alkyl-3-methylimidazolium hexafluorophosphate ([C2-4MIM]PF6) ionic liquids have been recorded and analyzed using density functional theory (DFT) and RHF methods at the 6-311+G(2d,p) computational level.
Abstract: The Raman and infrared spectra of a series of 1-alkyl-3-methylimidazolium hexafluorophosphate ([C2-4MIM]PF6) ionic liquids have been recorded and analyzed using density functional theory (DFT) and RHF methods at the 6-311+G(2d,p) computational level. The DFT calculations reproduce the vibrational spectra of 1-ethyl-3-methyl imidazolium hexafluorophosphate [EMIM]PF6, 1-propyl-3-methyl imidazolium hexafluorophosphate [PMIM]PF6, and 1-butyl-3-methyl imidazolium hexafluorophosphate [BMIM]PF6 using correction factors of 0.964−0.967 with correlation coefficients R2 of 0.999. The vibrational spectra calculated at the RHF/6-311+G(2d,p) level require a correction factor of 0.89 and a correlation coefficient R2 of 0.999 using the fully optimized structures. The 1-alkyl-3-methyl hexafluorophosphate ionic liquids have common Raman C−H stretching frequencies that may serve as possible probes in studies of ionic liquid interactions. The DFT (B3LYP) and RHF gas-phase molecular structures of the [C2-4MIM]PF6 ion pairs in...
TL;DR: In this paper, the structure of tecto-aluminosilicate and peraluminous glasses were studied using Raman spectroscopy, X-ray absorption at the Al K-edge and 27Al NMR spectrograms with two different high fields (400 and 750 MHz).
TL;DR: An ultrathin sheet-like carbon nanostructure, carbon nanosheet, has been effectively synthesized with CH4 diluted in H2 by an inductively coupled radio-frequency plasma enhanced chemical vapor deposition.
TL;DR: In this paper, the third-order Kerr nonlinearities and Raman gain were studied experimentally in high-purity As2Se3 optical fibers for wavelengths near 1.55 μm.
Abstract: Third-order Kerr nonlinearities and Raman gain are studied experimentally in high-purity As2Se3 optical fibers for wavelengths near 1.55 μm. Kerr nonlinear coefficients are measured to be nearly 1000 times higher than those for silica fibers. In pulsed mode, nonlinear phase shifts near 1.2-π rad are measured in fibers only 85 cm long with peak pulse powers near 3 W. However, there are nonlinear losses near 20% for nonlinear phase shifts near π. By use of a cw optical pump, large Raman gains nearly 800 times that of silica were measured. In the cw case there were losses in the form of index gratings formed from standing waves at the exit face of the fiber. Discrete Raman amplifiers and optical regenerators are discussed as possible applications.
TL;DR: In this paper, a method of preparing gold scanning tunneling microscopy (STM) tips by direct current electrochemical etching in concentrated HCl and ethanol solution is described, which can be efficiently used for STM imaging, tipenhanced Raman spectroscopy, and light emission investigations on the same sample.
Abstract: We describe a method of preparing gold scanning tunneling microscopy (STM) tips by direct current electrochemical etching in concentrated HCl and ethanol solution. Gold tips with tip apex radius lower than 30 nm can be reproducibly prepared by this method. The influence of the solution composition, etching voltage on the surface structure, and sharpness has been investigated. These tips can be efficiently used for STM imaging, tip-enhanced Raman spectroscopy, and light emission investigations on the same sample.
TL;DR: In this paper, thin films of tungsten-doped vanadium oxide were prepared on glass substrates from the atmospheric pressure chemical vapor deposition of vanadium(IV) chloride, Tungsten(VI) ethoxide, and water at 500−600 °C.
Abstract: Thin films of tungsten-doped vanadium(IV) oxide were prepared on glass substrates from the atmospheric pressure chemical vapor deposition of vanadium(IV) chloride, tungsten(VI) ethoxide, and water at 500−600 °C. The films were characterized by Raman microscopy, glancing angle X-ray diffraction (GAXRD), X-ray photoelectron spectroscopy (XPS), Rutherford backscattering (RBS), scanning electron microscopy (SEM), and vis/IR reflectance−transmittance. The films showed a reduction in thermochromic transition temperatures from 68 °C in VO2 to 42 °C in V0.99W0.01O2approaching that required for commercial use as an intelligent window coating.
TL;DR: From resonant Raman scattering on isolated nanotubes, the optical transition energies, the radial breathing mode frequency, and the Raman intensity of both metallic and semiconducting tubes are obtained.
Abstract: From resonant Raman scattering on isolated nanotubes we obtained the optical transition energies, the radial breathing mode frequency, and the Raman intensity of both metallic and semiconducting tubes. We unambiguously assigned the chiral index (n(1),n(2)) of approximately 50 nanotubes based solely on a third-neighbor tight-binding Kataura plot and find omega(RBM)=(214.4+/-2) cm(-1) nm/d+(18.7+/-2) cm(-1). In contrast to luminescence experiments we observe all chiralities including zigzag tubes. The Raman intensities have a systematic chiral-angle dependence confirming recent ab initio calculations.
TL;DR: It is hypothesized that the body biochemically imposes a specific state of atomic order and crystallinity on its different apatite precipitates (bone, dentin, enamel) in order to enhance their ability to carry out tissue-specific functions.
TL;DR: This review presents the recent progress achieved mainly in the laboratory on the improvement of detection sensitivities as well as spectral, temporal, and spatial resolutions in SERS.
Abstract: Over the past three decades, surface-enhanced Raman spectroscopy (SERS) has gone through a tortuous pathway to develop into a powerful surface diagnostic technique for in situ investigation of surface adsorption and reactions on electrodes. This review presents the recent progress achieved mainly in our laboratory on the improvement of detection sensitivities as well as spectral, temporal, and spatial resolutions. Various surface roughening procedures for electrodes of different metals coupled with maximum use of a high-sensitivity confocal Raman microscope enable us to obtain good-quality SER spectra on the electrode surfaces made from net Pt, Ni, Co, Fe, Pd, Rh, Ru, and their alloys that were traditionally considered to be non-SERS active. A novel technique called potential-averaged SERS (PASERS) has been developed for the quantitative study of electrochemical sorption. Applications are exemplified on extensively studied areas such as coadsorption, electrocatalysis, corrosion, and fuel cells, and several advantages of in situ electrochemical SERS are demonstrated. Finally, further developments in this field are briefly discussed with emphasis on the emerging methodology.
TL;DR: The collapse pressure is found to be independent of the nanotube chirality, and a lower limit on the largest SWNT that remains inflated at atmospheric pressure is established.
Abstract: Introduction.—Since their identification in 1991, interest in carbon nanotubes has continued to grow, focusing on both their intrinsic properties and potential applications. The behavior of individual tubes has been explored via experiment [1‐3] and computer simulation, e.g., [4 ‐7], in both axial and bending geometries. Elastic properties have generally been found to be broadly consistent with the in-plane properties of graphite, but strengths have proved harder to assess, with simulation results consistently predicting higher values than have been observed experimentally, probably as a result of defects in the real materials. Carbon nanotubes have also been explored under hydrostatic pressure, using Raman spectroscopy [8‐13], x-ray diffraction [14,15], and neutron diffraction techniques [16]. Raman spectroscopy, in particular, has proved to be a very useful tool in the characterization of single-wall carbon nanotubes (SWNTs), revealing information about crystallinity, diameter, and even chirality. Under increasing hydrostatic pressure, the Raman peaks shift to higher frequencies, corresponding to a stiffening of the carbon framework. Some authors have noticed that the peak position of the tangential mode, corresponding to in-plane vibrations of adjacent carbon atoms in the graphene sheet, shifts linearly over two regimes with a change in gradient at a critical pressure of approximately 2 GPa, depending on the type of nanotube material used. A number of studies also reported the disappearance of the radial breathing mode (RBM) from the spectrum above that critical pressure. Similarly, x-ray results demonstrate the disappearance of scattering associated with the hexagonally close-packed lattice into which the SWNT bundles are organized [14]. Clearly, a structural phase transition occurs at this critical pressure, but the exact nature of this change has proved controversial. Most authors seem to favor a transition to a close-packed structure of hexagonally deformed nanotubes (‘‘polygonization’’), while others propose a complete flattening or ‘‘collapse’’ [17]. A previous TEM study of multiwall nanotubes (MWNT) found evidence for collapse to form ribbons, although the cause was unclear [18]. In a recent study [19], we used Raman spectroscopy to compare the behavior of bundles of single and a range of MWNTs to that of graphite, under hydrostatic pressure. The initial gradient of the peak shift could be explained entirely in geometric terms, using a continuum mechanics model and the relevant internal and external diameters. Above the critical pressure, the gradient was equal to that of the graphite, which exhibited no transition over the pressure range up to 10 GPa. We interpreted these results as evidence supporting the complete collapse of the hollow core of the nanostructures to produce materials resembling graphite in terms of density and hybridization. The peak shifts appeared to be completely reversible within experimental accuracy, as long as the maximum pressure was kept below 10 GPa. The SWNTs in this experiment were supplied by Tubes@Rice, and are generally considered to be predominantly either (10,10) nanotubes or other chiralities with similar diameters. The critical pressure for these nanotubes to collapse was found to be 2:1 0:2 GPa.
TL;DR: In this article, it was shown that trans-polyacetylene originates from the diamond film and the diamond mode around 1332 cm−1 does not, while the deuterium and H-D substituted hydrocarbon sources do.