Computer simulation of the structure and raman spectra of GaAs polytypes
M. B. SmirnovA. O. KoshkinС. В. КарповB. V. NovikovA. N. SmirnovI. V. ShtrohmG. É. CirlinA. D. BouravleuvYu. B. Samsonenko
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Solid-state physics
Deep UV Raman spectroscopy is emerging as a useful tool for the characterization of carbon materials that has many advantages over visible Raman spectroscopy. However, because of resonance enhancement and other effects, UV Raman spectra are often different from visible Raman spectra. UV Raman spectra have not been reported for even some of the most widely known carbon materials. We report Raman spectra of single-walled carbon nanotubes (SWNTs) collected with deep ultraviolet (4.8 eV) laser excitation. There are significant differences between the deep UV and the visible Raman spectrum of SWNTs for the graphitic "G" modes and "disorder-induced" "D" modes, which are common to a wide range of forms of carbon. Furthermore, only semiconducting tubes are observed in the UV Raman spectrum, which is not consistent with an expected resonance enhancement of the scattering from metallic tubes at 4.8 eV.
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Raman spectroscopy and in situ Raman spectroelectrochemistry have been used to study the influence of defects on the Raman spectra of semiconducting individual single-walled carbon nanotubes (SWCNTs). The defects were created intentionally on part of an originally defect-free individual semiconducting nanotube, which allowed us to analyze how defects influence this particular nanotube. The formation of defects was followed by Raman spectroscopy that showed D band intensity coming from the defective part and no D band intensity coming from the original part of the same nanotube. It is shown that the presence of defects also reduces the intensity of the symmetry-allowed Raman features. Furthermore, the changes to the Raman resonance window upon the introduction of defects are analyzed. It is demonstrated that defects lead to both a broadening of the Raman resonance profile and a decrease in the maximum intensity of the resonance profile. The in situ Raman spectroelectrochemical data show a doping dependence of the Raman features taken from the defective part of the tested SWCNT.
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Abstract The Raman spectra of the nanotube (7,0) with point defects (monovacancy, divacancy, and Stone–Wales defect) were simulated in order to derive spectroscopic signatures of defective nanotubes. First, we calculated the electronic band structure and the phonon dispersion of the defective nanotubes using supercells within a non‐orthogonal tight‐binding model. We found that new optical transitions and Raman‐active phonons appeared in comparison with the perfect nanotube. Secondly, we calculated the resonance Raman excitation profile for all Raman‐active phonons of the defective nanotubes and simulated their Raman spectra at specific laser excitation energies. The predicted high‐intensity Raman lines can be used as spectroscopic signatures of the defective nanotubes.
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Theory of Raman scattering evolution and revolution of Raman instrumentation - application of available technologies to spectroscopy and microscopy Raman spectroscopy and its adaptation to the industrial environment Raman microscopy - confocal and scanning near-field Raman imaging the quest for accuracy in Raman spectra chemometrics for Raman spectroscopy Raman spectra of gases Raman spectroscopy applied to crystals - phenomena and principles, concepts and conventions Raman scattering of glass Raman spectroscopic applications to gemmology Raman spectroscopy on II-IV-semiconductor nanostructures medical applications of Raman spectroscopy - in vivo Raman spectroscopy some pharmaceutical applications of Raman spectroscopy low-frequency Raman spectroscopy and biomolecular dynamics - a comparison between different low-frequency experimental techniques collectivity of vibrational modes Raman spectroscopic studies of ion-ion interactions in aqueous and non-aqueous electrolyte solutions environmental applications of Raman spectroscopy to aqueous solutions Raman and surface enhanced resonance Raman scattering - applications in forensic science application of Raman spectroscopy to organic fibres and films applications of IR and Raman spectra of quasi-elemental carbon process Raman spectroscopy the use of Raman spectroscopy to monitor the quality of carbon overcoats in the disk drive industry Raman spectroscopy in the undergraduate teaching laboratory Raman spectroscopy in the characterization of archaeological materials.
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In Raman detection, the most popular solution for the samples is tri-distilled water. But the effect of aqueous solution is barely studied in Raman spectroscopy. In fact Raman spectroscopy of solid-state and liquid-state are obvious different. In addition, FWHM of Raman spectral peaks also change evidently. In this paper, several samples were selected for the experiment; including sodium nitrate, sodium nitrite, glucose and caffeine. By comparing the Raman spectroscopy of samples at different concentrations, it is found that the concentration of the sample can affect the strength of Raman spectroscopy, but it can hardly impact FWHM of Raman spectral peaks. By comparing the Raman spectroscopy of liquid-state with the Raman spectroscopy of solid-state, it is observed that the FWHM of some Raman spectral peaks varied obviously; that may be because when the sample was dissolved into the water, the crystal lattice structure was broken, and for some samples atom form became ion form in aqueous solution. Those structural variations caused the variation of the FWHM. The Raman spectroscopy of caffeine aqueous solution at very low concentration was also detected and analyzed. Compared with the Raman spectra of solid-state samples, it is found that some Raman spectral peaks disappeared when the sample was dissolved in water. It is possible that the low concentration of the sample result in the weakening of Raman signals and the disappearing of some weak Raman spectral peaks. Then Ag nanoparticles were added into the caffeine aqueous solution, the results suggest that surface enhanced Raman spectroscopy (SERS) not only can enhance the Raman spectral signal, but also can reduce the effect of aqueous solution. It is concluded that the concentration of sample only affects the strength of Raman spectroscopy; the aqueous solution can affect the FWHM of Raman spectral peaks; and SERS can reduce the effect of aqueous solution.
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This chapter contains sections titled: Non-visible Excited Raman Spectroscopy Resonant Raman Spectroscopy (RRS) High-Order/Multiple-Phonon Raman Spectroscopy (MPRS) Raman Spectroscopy under Extreme Conditions Polarized Raman Spectroscopy (PRS) Time-Resolved (Transient) Raman Spectroscopy (TRRS) Space-Resolved Micro-Raman Spectroscopy and Raman Microscopy Surface-enhanced Raman Spectroscopy (SERS) Near-Field Raman Spectroscopy (NFRS) Tip-enhanced Raman Spectroscopy (TERS) Non-linear and Coherent Raman Spectroscopy (NLRS) Coherent Anti-Stokes Raman Scattering (CARS) Stimulated Raman Scattering (SRS) References
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Raman forbidden modes and surface defect related Raman features in SnO_2 nanostructures carry information about disorder and surface defects which strongly influence important technological applications like catalysis and sensing. Due to the weak intensities of these peaks, it is difficult to identify these features by using conventional Raman spectroscopy. Tip enhanced Raman spectroscopy (TERS) studies conducted on SnO_2 nanoparticles (NPs) of size 4 and 25 nm have offered significant insights of prevalent defects and disorders. Along with one order enhancement in symmetry allowed Raman modes, new peaks related to disorder and surface defects of SnO_2 NPs were found with significant intensity. Temperature dependent Raman studies were also carried out for these NPs and correlated with the TERS spectra. For quasi-quantum dot sized 4 nm NPs, the TERS study was found to be the best technique to probe the finite size related Raman forbidden modes.
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Abstract Raman imaging has proven to be an important tool in the analysis of astromaterials. Raman imaging can describe the composition and mineralogy of astromaterials in a nondestructive manner preserving precious samples for additional study. Raman bandwidth is a common spectroscopic marker used to elucidate information such as composition, latent strain, and thermal processing history. The observed Raman bandwidth of a sample is a result of a convolution of the true Raman lineshape and the spectrometer's slit function. Thus, to compare Raman bandwidths across spectra and instruments, one needs to calibrate the Raman spectrum to account for effects of the slit function. Astromaterials are heterogeneous requiring the collection of large Raman images for adequate sampling. It is well known that the wavenumber calibration of an instrument drifts with time throughout Raman image collection. Here, we find that the spectrometer slit function also varies with time and laboratory temperature throughout Raman image collection. We utilize a mercury–argon (Hg–Ar) lamp integrated into our Raman microscope in a novel manner to calibrate the bandwidth in each Raman spectrum within our Raman image. We can do this because the narrow Hg–Ar lamp emission lines approximate the spectrometer slit function for each Raman spectrum allowing for the calculation of the true Raman bandwidth from each Raman spectrum within the Raman image. Our technique allows for the comparison of Raman bandwidth throughout a Raman image and between Raman images/spectra collected using different instruments, facilitating scientific analyses that are reproducible across multiple laboratories.
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