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Related Concept Videos

Raman Spectroscopy: Overview01:20

Raman Spectroscopy: Overview

324
The underlying principle of Raman spectroscopy is based on the interaction between light and matter, specifically molecules' inelastic scattering of photons. When a monochromatic beam of light, typically from a laser source, interacts with a sample, most scattered light has the same frequency as the incident light. This is known as Rayleigh scattering.
However, a small fraction of the scattered light exhibits a frequency shift due to the exchange of energy between the incident photons and...
324
Two-Dimensional (2D) NMR: Overview01:12

Two-Dimensional (2D) NMR: Overview

631
The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily interpreted using 2-dimensional (2D) NMR. Unlike 1D NMR, 2D NMR has two frequency axes that provide the coupling information between the nucleus A and nucleus B in a molecule. The process from which 2D spectra are obtained has four steps.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse....
631
IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations01:08

IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations

933
Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single...
933
Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals01:17

Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals

2.4K
Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...
2.4K
Raman Spectroscopy Instrumentation: Overview01:26

Raman Spectroscopy Instrumentation: Overview

297
A conventional Raman spectrophotometer includes a laser source, a sample holding system, a wavelength selector, and a detector.
The monochromatic laser source, typically using visible or near-infrared radiation, generates a highly focused beam of light. This light interacts with the molecules of the sample, scattering some of the light. Liquid and gaseous samples are usually tested in ordinary glass capillaries, while solids can be analyzed as powders packed in capillaries or as potassium...
297
¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

1.3K
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
1.3K

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Resonance Raman Spectroscopy of Extreme Nanowires and Other 1D Systems
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Anomalous 2D and D + D'' Raman signatures in few-layer graphene.

Surjyasish Mitra1, Sushanta K Mitra1

  • 1Department of Mechanical & Mechatronics Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue W, Waterloo, ON N2L 3G1, Canada.

Nanotechnology
|May 30, 2025
PubMed
Summary

Raman spectroscopy reveals anomalies in few-layer graphene. This study details the complex Lorentzian peak structures of the 2D and D + D'' peaks in graphene layers, offering new insights into electron-phonon interactions.

Keywords:
2D materialsRaman spectroscopygraphene

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Area of Science:

  • Materials Science
  • Condensed Matter Physics
  • Spectroscopy

Background:

  • Raman spectroscopy is crucial for characterizing carbon materials, with graphene's discovery driving its expanded use.
  • Anomalies in Raman signatures of graphene-based systems persist, necessitating further investigation.
  • Understanding these anomalies is key to accurately characterizing graphene's properties.

Purpose of the Study:

  • To re-examine the Raman spectroscopy of mono- and few-layer graphene using high-resolution data.
  • To characterize the Raman 2D and D + D'' peaks using Lorentzian fitting.
  • To interpret observed anomalies through group theory analysis of electron-phonon interactions.

Main Methods:

  • Acquisition of high-resolution experimental Raman spectroscopy data for graphene.
  • Application of Lorentzian fitting to analyze the 2D and D + D'' Raman peaks.
  • Utilized group theory to analyze electron-phonon interactions and explain spectral anomalies.

Main Results:

  • The Raman 2D peak of bilayer graphene comprises four uniform Lorentzian peaks.
  • The Raman 2D peak of four-layer graphene exhibits an anomaly with eight varying Lorentzian peaks.
  • Raman D + D'' peaks show asymmetric profiles; few-layer graphene requires 3-4 Lorentzian sub-peaks for accurate characterization, unlike monolayer and bulk graphite.

Conclusions:

  • The study provides a detailed characterization of anomalous Raman signatures in few-layer graphene.
  • Findings offer a deeper understanding of electron-phonon interactions in graphene systems.
  • The results highlight the necessity of advanced fitting methods for accurate Raman spectral analysis of few-layer graphene.