scispace - formally typeset
Search or ask a question
Topic

Raman spectroscopy

About: Raman spectroscopy is a research topic. Over the lifetime, 122605 publications have been published within this topic receiving 2891083 citations. The topic is also known as: Raman Spectrum Analysis & spectrum Analysis, Raman.


Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, the influence of uniaxial tensile mechanical strain in the range 0-2.2% on phonon spectra and bandstructures of monolayer and bilayer molybdenum disulfide (MoS2) two-dimensional crystals was reported.
Abstract: We report the influence of uniaxial tensile mechanical strain in the range 0-2.2% on the phonon spectra and bandstructures of monolayer and bilayer molybdenum disulfide (MoS2) two-dimensional crystals. First, we employ Raman spectroscopy to observe phonon softening with increased strain, breaking the degeneracy in the E' Raman mode of MoS2, and extract a Gruneisen parameter of ~1.06. Second, using photoluminescence spectroscopy we measure a decrease in the optical band gap of MoS2 that is roughly linear with strain, ~45 meV% strain for monolayer MoS2 and ~120 meV% strain for bilayer MoS2. Third, we observe a pronounced strain-induced decrease in the photoluminescence intensity of monolayer MoS2 that is indicative of the direct-to-indirect transition of the character of the optical band gap of this material at applied strain of ~1.5%, a value supported by first-principles calculations that include excitonic effects. These observations constitute the first demonstration of strain engineering the band structure in the emergent class of two-dimensional crystals, transition-metal dichalcogenides.

327 citations

Journal ArticleDOI
TL;DR: In this article, the effect of biaxial strain on optical phonons in high-quality GaN epitaxial layers grown on 6H-SiC substrates by metal organic chemical vapor deposition has been studied.
Abstract: The effect of biaxial strain on optical phonons in high-quality GaN epitaxial layers grown on 6H–SiC substrates by metal organic chemical vapor deposition has been studied. The deformation potential constants for the E2(1), A1(TO), E1(TO), and E2(2) optical phonon modes in hexagonal GaN have been obtained. A method for calculating strain in hexagonal GaN layers from Raman data alone is suggested. A comparative analysis of the strain measured by x-ray diffraction and Raman spectroscopy shows that these data agree well. It is found that the biaxial stress of 1 GPa results in a shift of the excitonic photoluminescence lines of 20±3 meV.

327 citations

Journal ArticleDOI
TL;DR: In this paper, a ray-tracing analysis was used to predict the effect of refraction at the sample/air interface, on the depth resolution of confocal Raman microscopy, where the laser beam incident normal to the sample surface, and spectra are recorded sequentially as the focus is moved deeper into the material.
Abstract: A simple ray-tracing analysis has been used to predict the effect of refraction at the sample/air interface, on the depth resolution of confocal Raman microscopy. This analysis applies to the ''z-scanning'', or ''optical sectioning'', approach to obtaining depth profiles, where the laser beam is incident normal to the sample surface, and spectra are recorded sequentially as the focus is moved deeper into the material. It is shown that when a ''dry'' metallurgical objective (the most common configuration for commercial Raman microscopes) is used, both the position and the depth of focus increase dramatically as the beam is focused deeper into the sample. It quickly becomes impossible to obtain ''pure'' spectra of thin layers that are buried more than a few micrometers below the air interface. Equations are presented which model the intensity response expected when focusing through a coating into a substrate. The model requires knowledge of the sample refractive index, the numerical aperture, and the laser beam intensity distribution at the limiting aperture, of the objective. Given these values, one can predict the substrate Raman intensity as a function of the nominal focal point within the sample. For a 36μm coating on a thick substrate, we predict that even for a perfectly sharp interface (1μm), substrate bands rise slowly (over an apparent distance of 10μm or more), and are strong when the focus is apparently only ~18μm below the air/coating interface. This prediction was confirmed through experimental observation. The model was also used to analyze literature data that had been interpreted previously as showing interfacial diffusion in polymer laminates. The model correctly reproduced the main features of the observed data without invoking interfacial penetration - the optical aberrations alone accounted for almost all the observed broadening and the fact that the apparent thickness of the buried layer is also distorted. It was concluded that, with the use of this illumination geometry, it is very difficult to detect or quantify interfacial broadening unless it occurs on a very large scale indeed (tens of micrometers). It is concluded that ''optical sectioning'' cannot be recommended for quantitative depth profiling at significant depths using metallurgical objectives. The optimum practical solution is to cut a cross section and map laterally across the sample, thereby utilizing and maintaining the excellent (lateral) resolution of the Raman microprobe. An alternative solution is to use an immersion objective to minimize refraction at the sample surface.

327 citations

Journal ArticleDOI
TL;DR: In this article, the authors reported the modification of graphene oxide by thermal reduction to obtain reduced graphene oxide (RGO) and subsequent modification by sulfophenyl groups as well as the characterization of these materials by thermogravimetric analysis coupled with mass spectroscopy (TGA-MS).
Abstract: We report the modification of graphene oxide (GO) by thermal reduction to obtain reduced graphene oxide (RGO) and subsequent modification by sulfophenyl groups as well as the characterization of these materials by thermogravimetric analysis coupled with mass spectroscopy (TGA-MS) The chemical modification of RGO was carried out by the spontaneous reaction of RGO with in situ generated sulfophenyl diazonium ions The three different types of materials were also characterized by elemental analysis, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) The characteristic absorption band at 1034 and 1160 cm−1 in the FTIR spectrum of the sulfophenyl-modified RGO (SRGO), as well as Raman spectroscopy and TGA-MS data indicated that sulfophenyl groups were successfully grafted on RGO The presence of organic molecules at the SRGO surface was also demonstrated by elemental analysis, transmission electron microscopy, energy dispersive X-ray spectroscopy and XPS TGA data and elemental analysis results showed that the loading of sulfophenyl groups was about 12 wt% and UV-visible-near IR spectroscopy confirms the slight increase of the optical band gap of RGO after covalent grafting of sulfophenyl groups on its surface

327 citations

Journal ArticleDOI
TL;DR: This paper compares popular analytical techniques, including scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TGA), and Raman and near-infrared (NIR) spectroscopy, for the evaluation of the purity of bulk quantities of single-walled carbon nanotubes (SWNTs).
Abstract: We compare popular analytical techniques, including scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TGA), and Raman and near-infrared (NIR) spectroscopy, for the evaluation of the purity of bulk quantities of single-walled carbon nanotubes (SWNTs). Despite their importance as imaging techniques, SEM and TEM are not capable of quantitatively evaluating the purity of typical inhomogeneous bulk SWNT samples because the image frame visualizes less than 1 pg of SWNT material; furthermore, there is no published algorithm to convert such images into numerical data. The TGA technique is capable of measuring the amount of metal catalyst in an SWNT sample, but does not provide an unambiguous separation between the content of SWNTs and carbonaceous impurities. We discuss the utilization of solution-phase near-infrared spectroscopy and solution-phase Raman spectroscopy to quantitatively compare arbitrary samples of bulk SWNT materials of different purities. The primary goal of...

327 citations


Network Information
Related Topics (5)
Oxide
213.4K papers, 3.6M citations
93% related
Graphene
144.5K papers, 4.9M citations
92% related
Thin film
275.5K papers, 4.5M citations
91% related
Carbon nanotube
109K papers, 3.6M citations
91% related
Nanoparticle
85.9K papers, 2.6M citations
91% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20235,220
202210,775
20214,240
20204,764
20194,957
20184,893