Raman Spectra Of Carbon Research Articles

Externally Heated Diamond ANvil Cell Experimentation (EH-DANCE) for studying materials and processes under extreme conditions.

Externally heated diamond anvil cells provide a stable and uniform thermal environment, making them a versatile device to simultaneously generatehigh-pressure and high-temperature conditions in various fields of research, such as condensed matter physics, materials science, chemistry, and geosciences. The present study features the Externally Heated Diamond ANvil Cell Experimentation (EH-DANCE) system, a versatile configuration consisting of a diamond anvil cell with a customized microheater for stable resistive heating, bidirectional pressure control facilitated by compression and decompression membranes, and a water-cooled enclosure suitable for vacuum and controlled atmospheres. This integrated system excels with its precise control of both pressure and temperature for mineral and materials science research under extreme conditions. We showcase the capabilities of the system through its successful application in the investigation of the melting temperature and thermal equation of state of high-pressure ice-VII at temperatures up to 1400K. The system was also used to measure the elastic properties of solid ice-VII and liquid H2O using Brillouin scattering and Raman spectra of carbonates using Raman spectroscopy, highlighting the potential of the EH-DANCE system in high-pressure research.

Raman spectroscopy as a tool for magnesium estimation in Mg‐calcite

Despite their strong Raman scattering and importance in several applications in the geological and biological sciences, Mg‐calcites have not been thoroughly investigated by Raman spectroscopy. In this study, we investigated whether Raman spectra of carbonates are sensitive to the structural and chemical changes occurring when Mg2+ substitutes Ca2+ in the calcite lattice. Different carbonate samples with variable Mg content (from 0 to 20 mol% MgCO3) of biological and inorganic origin have been first beamed under a Raman spectrometer and then analysed by scanning electron microscopy‐energy dispersive spectrometer and electron microprobe analysis‐wavelength dispersive spectrometer microprobes to determine their chemistry. The biological samples (foraminifers, algae, barnacles and echinoderms) were collected from areas situated at different latitudes and water temperature and saturation, factors affecting the chemical and isotopic composition of shells in marine organisms. The Raman band positions are directly linked to the amount of magnesium present in the calcite lattice, and all peaks of Mg‐calcite spectra show a consistent and linear increase in Raman shifts according to their Mg content, which is a consequence of the decreased inter‐atomic distances following the substitution of Ca2+ with the smaller Mg2+ ion.This study demonstrates that Raman spectroscopy provides an innovative work perspective in marine biology, provenance studies and oil exploration when estimates of mineralogical and chemical changes are the focus of the study. Raman spectroscopy is even more attractive – for the mentioned fields of research – than many other methods because of the non‐destructive nature and its very short analytical time. Copyright © 2017 John Wiley & Sons, Ltd.

Electrochemical performance of controlled porosity resorcinol/formaldehyde based carbons as electrode materials for supercapacitor applications

Controlled porosity carbons aerogels were synthesized by sol–gel polycondensation of resorcinol (R) and formaldehyde (F) using sodium-carbonate as the catalyst (C). The Effect of variation of R/C ratio and carbonization temperature on the porous structure of resultant gels and carbons was investigated by characterizing the porous structure of the materials using nitrogen adsorption–desorption measurements at 77 K. It was shown that carbons with surface areas ranging between 537 and 687 m2 g−1 and average pore size in the range of 1.80–4.62 nm can be produced when controlling the resorcinol to catalyst (R/C) molar ratio between 100 and 500 and carbonization temperature in the range of 800–1000 °C.The resultant polymeric carbons were used as the electroactive material for the fabrication of electrodes for electrochemical cells. Contact angle measurements were performed to study the wettability of the electrodes using 6 M KOH as the probing liquid. The contact angles were in the range of 106°–125° indicating the carbon based electrodes are hydrophobic in nature and no significant change in contact angles was observed with the change in R/C ratio.XRD patterns of the carbon electrodes show a typical broad peak at 2θ of about 23 indicating a disordered structure corresponding to the amorphous nature of the materials as expected for polymeric based hard carbons with crosslinked structure. These results are in line with Raman spectra of carbons which indicate two peaks in 1590 cm−1 and 1340 cm−1 wavenumber.The electrochemical performance of the electrodes was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The CV results showed that high specific capacitance of 136 Fg−1 can be achieved for the carbon with average pore diameter of 1.80 nm at a scan rate of 5 mV s−1 when using 6M KOH as the electrolyte. Electrochemical impedance (EIS) measurements also revealed that the capacitance of the cell deteriorates with increase in pore size of the carbon probably due to pore flooding by the electrolyte. The results of this study show the applicability of these carbons as potential electrode materials for supercapacitor applications.

Standoff spatial heterodyne Raman spectrometer for mineralogical analysis

Raman spectroscopy is ideally suited for planetary exploration because of its ability to unambiguously identify minerals, organic compounds, and biomarkers. Traditionally, Raman spectra were acquired with grating‐based dispersive spectrometers that require tens of micrometer‐sized entrance slits and thus limited light throughput. Recently, we have evaluated a new type of Fourier transform Raman spectrometer, the spatial heterodyne Raman spectrometer that provides high spectral resolution in a compact system without limiting light throughput. In this work, we present time‐resolved Raman spectra of carbonate, sulfate, and silicate minerals, including low Raman scattering efficiency olivine and feldspar minerals, in the 100–1260 cm−1 Raman fingerprint region with spatial heterodyne Raman spectrometer using 1.5‐cm‐diameter pulsed 532.078‐nm Nd:YAG laser beam. Copyright © 2017 John Wiley & Sons, Ltd.

Crystallization characteristics and chemical bonding properties of nickel carbide thin film nanocomposites

The crystal structure and chemical bonding of magnetron-sputtering deposited nickel carbide Ni1−xCx (0.05 ⩽ x⩽0.62) thin films have been investigated by high-resolution x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, and soft x-ray absorption spectroscopy. By using x-ray as well as electron diffraction, we found carbon-containing hcp-Ni (hcp-NiCy phase), instead of the expected rhombohedral-Ni3C. At low carbon content (4.9 at%), the thin film consists of hcp-NiCy nanocrystallites mixed with a smaller amount of fcc-NiCx. The average grain size is about 10–20 nm. With the increase of carbon content to 16.3 at%, the film contains single-phase hcp-NiCy nanocrystallites with expanded lattice parameters. With a further increase of carbon content to 38 at%, and 62 at%, the films transform to x-ray amorphous materials with hcp-NiCy and fcc-NiCx nanodomain structures in an amorphous carbon-rich matrix. Raman spectra of carbon indicate dominant sp2 hybridization, consistent with photoelectron spectra that show a decreasing amount of C–Ni phase with increasing carbon content. The Ni 3d–C 2p hybridization in the hexagonal structure gives rise to the salient double-peak structure in Ni 2p soft x-ray absorption spectra at 16.3 at% that changes with carbon content. We also show that the resistivity is not only governed by the amount of carbon, but increases by more than a factor of two when the samples transform from crystalline to amorphous.

Nano-Carbon Coating Layer Prepared by the Thermal Evaporation of Fullerene C<SUB>60</SUB> for Lithium Metal Anodes in Rechargeable Lithium Batteries

A nano carbon coating layer was prepared by the thermal evaporation of fullerene C60 on the surface of lithium metal anodes for rechargeable lithium batteries. The morphology and structure of the carbon layer was firstly investigated by Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effects of the nano-carbon coating layer on the electrochemical performance of the lithium electrode were then examined by charge-discharge tests and impedance spectroscopy. Raman spectra of carbon coating layer showed two main peaks (D and G peaks), indicating the amorphous structure of the film. A honey comb-like structure of carbon film was observed by TEM photographs, providing a transport path for the transport of lithium ions at the electrode/electrolyte interface. The carbon coated lithium electrodes exhibited a higher initial coulombic efficiency (91%) and higher specific capacity retention (88%) after the 30th cycle at 0.2 C-rate between 3.4 and 4.5 V. Impedance measurements showed that the charge transfer resistance was significantly reduced after cycle tests for the carbon coated electrodes, revealing that the more stable solid electrolyte (SEI) layer was established on their surface. Based on the experimental results, it suggested that the presence of the nano-carbon coating layer might suppress the dendritic growth on the surface of lithium metal electrodes, as confirmed by the observation of SEM images after cycle tests.

Laser Raman spectroscopy as a technique for identification of seafloor hydrothermal and cold seep minerals

In situ sensors capable of real-time measurements and analyses in the deep ocean are necessary to fulfill the potential created by the development of autonomous, deep-sea platforms such as autonomous and remotely operated vehicles, and cabled observatories. Laser Raman spectroscopy (a type of vibrational spectroscopy) is an optical technique that is capable of in situ molecular identification of minerals in the deep ocean. The goals of this work are to determine the characteristic spectral bands and relative Raman scattering strength of hydrothermally- and cold seep-relevant minerals, and to determine how the quality of the spectra are affected by changes in excitation wavelength and sampling optics. The information learned from this work will lead to the development of new, smaller sea-going Raman instruments that are optimized to analyze minerals in the deep ocean. Many minerals of interest at seafloor hydrothermal and cold seep sites are Raman active, such as elemental sulfur, carbonates, sulfates and sulfides. Elemental S 8 sulfur is a strong Raman scatterer with dominant bands at ∼ 219 and 472 Δcm − 1 . The Raman spectra of carbonates (such as the polymorphs calcite and aragonite) are dominated by vibrations within the carbonate ion with a primary band at ∼ 1085 Δcm − 1 . The positions of minor Raman bands differentiate these polymorphs. Likewise, the Raman spectra of sulfates (such as anhydrite, gypsum and barite) are dominated by the vibration of the sulfate ion with a primary band around 1000 Δcm − 1 (∼ 1017 for anhydrite, ∼ 1008 for gypsum, and ∼ 988 for barite). Sulfides (pyrite, marcasite, chalcopyrite, isocubanite, sphalerite, and wurtzite) are weaker Raman scatters than carbonate and sulfate minerals. They have distinctive Raman bands in the ∼ 300–500 Δcm − 1 region. Raman spectra from these mineral species are very consistent in band position and normalized band intensity. High quality Raman spectra are obtained from all of these minerals using both green and red excitation lasers, and using a variety of sampling optics. The highest quality spectra (highest signal-to-noise) were obtained using green excitation (532 nm Nd:YAG laser) and a sampling optic with a short depth of focus (and thus high power density). Significant fluorescence was not observed for the minerals analyzed using green excitation. Spectra were also collected from pieces of active and inactive hydrothermal chimneys, recovered from the Kilo Moana vent field in 2005 and 11°N on the East Pacific Rise in 1988, respectively. Profiles of sample J2-137-1-r1-a show the transition from the chalcopyrite-rich “inner” wall to the sphalerite-dominated “outer” wall, and indicate the presence of minor amounts of anhydrite. Spectra collected from sample A2003-7-1a5 identify Cu–S tarnishes present on the surface of the sample.

Determination of bonding in diamond-like carbon by Raman spectroscopy

Raman spectroscopy is a very popular, non-destructive tool for the structural characterisation of carbons. Raman scattering from carbons is always a resonant process, in which those configurations whose band gaps match the excitation energy are preferentially excited. Any mixture of sp3, sp2 and sp1 carbon atoms always has a gap between 0 and 5.5 eV, and this energy range matches that of IR-vis-UV Raman spectrometers. The Raman spectra of carbons do not follow the vibration density of states, but consist of three basic features, the G and D peaks at approximately 1600 and 1350 cm−1 and an extra T peak, for UV excitation, at ∼980–1060 cm−1. We propose to rationalise the vast range of experimental data available in literature at any excitation wavelength by a simple model, which considers the main factors influencing the Raman spectra. The great advantages of multi-wavelength Raman spectroscopy will be clarified by a series of examples. In particular we show how it can be used to probe the structural changes induced by annealing and by nitrogen introduction. UV Raman spectroscopy also probes heteropolar σ bonds in a complementary way to infrared spectroscopy. We demonstrate the direct detection of CH vibrations in hydrogenated DLC samples, SiH and SiC vibrations in amorphous silicon and amorphous silicon–carbon alloys and the easier probe of CN sp bonds in amorphous carbon nitrides.

A Model to Interpret the Raman Spectra of Disordered, Amorphous and Nanostructured Carbons

ABSTRACTRaman spectroscopy is a very popular, non-destructive tool for the structural characterisation of carbons. Raman scattering from carbons is always a resonant process, in which those configurations whose band gaps match the excitation energy are preferentially excited. The Raman spectra of carbons do not follow the vibration density of states, but consist of three basic features, the G and D peaks around 1600 and 1350 cm-1 and an extra T peak, for UV excitation, at ∼980–1060 cm-1. TheRaman spectra at any wavelength depend on 1) clustering of the sp2 phase, 2)bond length and bond angle disorder, 3) presence of sp2 rings or chains, and 4) the sp2/sp3 ratio. It will be shown how the basic features of the Raman spectra vary by rationalising them within a three-stage model of order of carbons. It is shown how the three-stage model can account for the vast range of experimental data available for Raman experiments at any excitation wavelength. This model can also account for apparently contradictory trends reported in literature, since the clustering of the sp2 phase and the sp3 to sp2 conversion are separately treated.

Raman scattering spectra in C-implanted GaN epilayers

ABSTRACTWe have investigated the Raman scattering spectra in C-implanted GaN epilayers. (a) In as-implanted GaN, new Raman bands at 293, 376, 669, 1027, 1094 and 1053 cm−1 appeared. From phonon-dispersion curves for hexagonal GaN, the 293 cm−1 and 669 cm−1 bands were tentatively assigned to the highest acoustic-phonon branch and the optical-phonon branch at the Brillouin zone boundaries, respectively; the 1027 and 1094 cm−1 peaks might be caused by two-phonon scattering involving the 376 and 669 cm−1 phonons, and the 376 cm−1and A1(LO) phonons respectively. (b) Two sharp bands at ∼1350 and ∼1600 cm−1 were observed in the Raman spectra of carbon- implanted GaN after post-implantation annealing treatments. The intensities of these two bands increased while their full widths at half maximum decreased with increasing annealing temperature. We assigned them, respectively, to the D and G bands of small graphite crystallites arising from C implantation and post-implantation annealing. The observation of these two bands indicates the formation of small graphite crystallites in C-implanted GaN.

Raman Spectroscopic Study of Ion Pairing of Alkali Metal Ions with Carbonate and Sulfate in Aqueous Solutions

Raman spectra of carbonate and sulfate ions were recorded in aqueous solutions in the presence of large excesses of M′X (M′+ = Na+, K+ or Cs+; X– = OH– or Cl–) at 25°C. The positions of the v1(A1′) symmetric stretching vibrations for both CO32– (at ~1060 cm–1) and SO42– (at ~980 cm–1) shift, by up to 10 cm–1, to lower frequencies and broaden (by up to 25%) with increasing concentrations of M′X. The shifts are slightly smaller for SO42– than for CO32– and also differ somewhat between M′OH and M′Cl solutions. The changes in the peak positions, which are indicative of contact ion pairing, show a clear dependence on the nature of the cation. However, the observed order, Na+ < K+ < Cs+, is directly opposite to the magnitudes of the (overall) ion-pairing constants. This anomaly is thought to be due to decreased hydration of Cs+ cf. Na+ in these highly concentrated, water-deficient solutions. Some implications of this for understanding ionic interactions in concentrated electrolyte solutions are suggested.

Raman Spectroscopic Study of Ag-, W- and Pd-Ions Implanted Polyimde Films

AbstractA study has been made of the carbon formation in the surface layer of Ag-, W- and Pd-ions implanted polyimide films. The doses of 130 KeV Ag-ions and 190 KeV W-ions ranged from lxlO16 to 5×1017 atoms/cm2. The doses of 100 KeV Pd-ions ranged from 5×1016 to 2×1017 atoms/cm2. The carbon structure in implanted layers was characterized by laser Raman spectroscopy (LRS). Non-implanted polyimide film has very strong intensity of fluorescence, and the intensity of all W-, Ag- and Pd-ions implanted specimens decreases with the increase in dose. The intensity of Raman spectra for both W- and Ag-ions implanted specimens increases with the increase in dose. For Pd-ion implanted specimens, the Raman spectrum of carbon is hardly observed even with a high dose. Raman spectra for W- or Ag-ions implanted specimens with a high dose show that the diamond-like carbon (DLC) exist in the implanted layers. It is found that the DLC structures in the W- and Ag-ions implanted layers have graphite-like and amorphous-like structures, respectively. We propose that transparency carbon structure in implanted layers is generated by Pd-ion implantation. It is concluded that marked DLC formation in surface layer of polyimide films can be caused by Ag- or W-ions implantation except Pd-ion implantation, and carbon structure in implanted layers depends strongly on the implanted elements.

New Lines in the Raman Spectra of Carbons and Graphite

An extensive survey of the Raman spectral activity of a wide variety of carbon materials has produced experimental evidence for at least five structure‐sensitive lines or bands. In addition to the well‐known, always present 1580 cm−1 graphite line and the 1360 cm−1 disordered carbon line, there is a disorder line at ∼1620 cm−1 that is responsible for the apparent blue‐shift of the graphite line in very disordered carbons; and there are lines at ∼2700 and ∼2735 cm−1 that are strong in graphite and annealed carbons but absent in very disordered carbons. These additional lines increase the capability of Raman spectroscopy to characterize carbon materials.

Direct evidence for homonuclear bonds in amorphous SiC

The Raman Spectra of carbon- deficient sputtered amorphous SiC films contain an intense band centered at 1442 cm −1. This band is attributed to the presence of C-C bonds. Similarly a peak at ∼508 cm −1 is attributed to Si-Si bonds. The depolarization spectrum was found to be constant at ϱ(Δ v ̃ ) = 0.32 ± 0.03 for 0 < Δ v ̃ < 1800 cm −1 . Our results indicate a degree of compositional disorder which prevents an identification of the observed like-atom bonds with those predicted by a modified Polk model.

The Raman Spectra of Carbon and Silicon Tetrafluorides

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Some new features in the raman spectra of carbon and silicon tetrachlorides

The Raman spectra of CCl4 and SiCl4 have been examined under low and high dispersion. In both cases a faint line has been observed close to the line corresponding to the total symmetric vibration. This faint line has a frequency shift of 434 cm.-1 in the case of CCl4 and is interpreted as the octave of the fundamental frequency 217·9 cm.-1 The corresponding line in the case of SiCl4 shows a frequency shift of 440·5 cm.-1 and is interpreted as the octave of the fundamental frequency 221 cm.-1 It is pointed out that the appearance of the octave in these cases might probably be due to its proximity to the total-symmetric vibration frequency which is respectively 459 cm.-1 and 423 cm.-1 in the case of CCl4 and SiCl4. An additional faint line with a frequency shift of 145 cm.-1 has been observed in the Raman spectrum of CC14 which is interpreted as a differential tone arising from the fundamental frequencies 459 cm.-1 and 314 cm.-1, the summational of which causes the splitting of the fourth frequency, and the octave of whose summational appears as a faint broad line at 1538 cm.-1 The broadening of the fourth frequency in the case of SiCl4 might be due to a cause similar to that which causes the splitting of the fourth frequency in the case of CCl4. The total symmetric vibration in the case of CCl4 shows a well-defined wing to its red side, sharply separated from the principal line.