General Raman

Raman spectroscopy is a non-destructive light scattering technique spanning a wide range of scientific and industrial applications. Most often, Raman spectroscopy is used to characterize or identify the chemical composition and structure of an unknown material. Incident laser light in the UV, visible or NIR, is scattered inelastically from molecular vibrational modes. In a typical experiment [see Figure 2], a frequency-doubled Nd:YAG laser emitting monochromatic green radiation at λ_ex = 532.2 nm (18,790 cm^-1 see Eq 1) will scatter from a molecule with vibrational modes of up to ~4,000 cm^-1.

The frequency difference (measured in relative cm^-1) between the incident and scattered photons is termed the Raman shift. The majority of inelastically scattered photons are found at positive Raman shifts, corresponding to lower energies and longer wavelengths. This is referred to as Stokes scattering. The scattered photons are analyzed by a spectrometer to produce a Raman spectrum. The Stokes spectrum from 0 to 4,000 relative cm^-1, or λ_RS = 532.2 to 676 nm (see Eq 2) in this case, gives a complete picture of the Raman-active modes of the molecule under investigation. Unknown molecules can be identified by their Raman spectrum, which is often termed a molecular fingerprint.
Equation 1: (cm^-1) _ex = 10⁷/λ_ex(nm)
Equation 2: rel cm^-1 = 10⁷/λ_ex(nm) - 10⁷/λ_RS(nm)

Stokes and Anti-Stokes scattering

See Figure 1, b) and c). In Stokes, the energy of the molecule increases and the Raman scattered photons are red-shifted. In Anti-Stokes, energy of the molecule decreases and the Raman scattered photons are blue-shifted. Molecules giving rise to anti-Stokes scattering must have been originally in a vibrationally excited state, which represents a small fraction of thermally equilibrated molecules. See equation 3, Boltzmann population, , with kBT = 207 cm^-1 at room temperature.

An Anti-Stokes Raman spectrum can be used to measure the vibrational temperature of a sample.

$x-ray diffraction 3D image$

Figure 2: Principle of Raman Spectroscopy

$x-ray diffraction 3D image$
Figure 3: Confocal Stokes and Anti-Stokes spectra of L-cystine, acquired with Acton TriVista 555 Stokes

Micro-Raman Setup

Raman spectroscopy instrumentation - Dr. Elizabeth Vargis - Utah State University

Very low light—only 1 in 10⁷ scattered photons are inelastically scattered. Advantage: with UV-visible-NIR excitation, highly sensitive detectors may be used. IR detectors are less sensitive. Sensitive detectors, efficient spectrographs and some means of Rayleigh filtration are required.

Publications

Pavel M. Usov, Deanna M. D'Alessandro et al.

2018

Probing charge transfer characteristics in a donor–acceptor metal-organic framework by Raman spectroelectrochemistry and pressure-dependence studies
Pressure dependent and resonance Raman spectroscopy

R. Wulundari, Y. Einaga et al.

2019

Modification of Boron-doped Diamond Electrodes with Platinum to Increase the Stability and Sensitivity of Haemoglobin-based Acrylamide Sensors
Biosensing, Food and Environmental Monitoring, Acrylamide sensing, Material Science

T. Fu, A. Trunschke et al.

2019

Single-site vanadyl species isolated within molybdenum oxide monolayers in propane oxidation
Investigating chemical reactions using Raman spectroscopy.

S. Di Fonzo, A. Cesaro et al

2019

PEG hydration and conformation in aqueous solution: Hints to macromolecular crowding
Material and Life Science related. Use of UV Raman spectroscopy to avoid sample autofluorescence.

Haishan Zeng et. al.

2017

Autofluorescence and white light imaging-guided endoscopic Raman and diffuse reflectance spectroscopy for in vivo nasopharyngeal cancer detection
Raman and diffuse reflectance spectroscopy, Cancer Detection, In-Vivo measurements

Yong-qing Li et. al.

2010

Multiple-trap laser tweezers Raman spectroscopy for simultaneous monitoring of the biological dynamics of multiple individual cells
multiple-trap laser tweezers Raman spectroscopy (LTRS), physiological environments

Zhiwei Huang et. al.

2017

Real-time In vivo Diagnosis of Nasopharyngeal Carcinoma Using Rapid Fiber-Optic Raman Spectroscopy
In vivo Diagnosis, Fiber-Optic Raman Spectroscopy, nasopharyngeal cancer identification

S. Ghosh, N. Das et al.

2019

Fabrication of Reduced Graphene Oxide/Silver Nanoparticles Decorated Conductive Cotton Fabric for High Performing Electromagnetic Interference Shielding and Antibacterial Application
Research on new materials with antibacterial properties. Characterized using Raman spectroscopy

H. Ouyang, X. Zheng et al

2019

Noncoincidence Effects of Dimethyl Carbonate in Binary Mixtures Probed by Raman Spectroscopy: Experimental and DFT Calculations
Basic Raman spectroscopy use in physical chemistry.

K. Berzins, K. Gordon et al.

2019

Application of low-wavenumber Raman spectroscopy to the analysis of human teeth
Bio Raman spectroscopy application

S. Chen, K. Koski et al.

2019

Mn-Intercalated MoSe$_2$ under pressure: electronic structure and vibrational characterization of a dilute magnetic semiconductor
High pressure investigations of 2D materials using Raman spectroscopy

H. Yuan, D. Errandonea et al.

2019

Putting the Squeeze on Lead Chromate Nanorods
Raman Spectroscopy,Material Science,Nanotechnology,Diamond Anvil Cells,High pressure science

M. Rahman, E. Bilgili et al.

2019

Hybrid nanocrystal–amorphous solid dispersions (HyNASDs) as alternative to ASDs for enhanced release of BCS Class II drugs
FERGIE, Raman Spectroscopy, Material Science, Nanotechnology, Pharmaceuticals

C. Eom, J. Suntivich et al.

2019

In Situ Stimulated Raman Spectroscopy Reveals Phosphate Network in Amorphous Cobalt Oxide Catalyst and Its Role in the Catalyst Formation
Chemical reaction analysis using Stimulated Raman scattering

W. Tillmann, A. Brümmer et al.

2019

Investigation of the Tribofilm Formation of HiPIMS Sputtered MoSx Thin Films in Different Environments by Raman Scattering
Thin films, Magnetron Sputtering, Transition Metal Dichalcogenides, Material Science, Coating Technology

J. Su, Q. Liu et al.

2019

Depth-sensitive Raman spectroscopy for skin wound evaluation in rodents
Bio-Raman, Life Science

K. Bagnall, E. Wang et al.

2016

Electric field dependence of optical phonon frequencies in wurtzite GaN observed in GaN high electron mobility transistors
This research uses sensitive micro-Raman measurements to characterize the temperature of GaN transistors.

G. Borstad,J. Ciezak-Jenkins

2017

Hydrogen-Bonding Modification in Biuret Under Pressure
An IsoPlane SCT320 spectrograph with an air-cooled PIXIS 400BR eXcelon CCD and the LightField software (Princeton Instruments) were used to collect the Raman spectra

C. Krafft, J. Popp et al.,

2016

Raman-based Identification of Circulating Tumor Cells for Cancer Diagnosis
An IsoPlane 160 spectrograph and PIXIS camera were used by researchers in their presentation of the use Raman-based methodologies to distinguish cancer cells from normal blood cells. In a first approach, a microfluidic chip was developed to collect Raman spectra from optically trapped cells.

Bhavaya Sharma, Amber S. Moody

2017

Detection of neurotransmitters through the skull by surface enhanced spatially-offset Raman spectroscopy
Researchers at University of Tennessee present results on surface-enhanced spatially-offset Raman spectroscopy (SESORS) measurements of epinephrine at 50 mM and 100 µM in a brain tissue mimic through a cat skull.

Yong-Le Pan, et. al.

2017

Detection and characterization of chemical aerosol using laser-trapping single-particle Raman spectroscopy
Researcher at the US Army Research Lab and Sandia National Lab utilize a IsoPlane 320 and a ProEM EMCCD to perform Raman spectroscopy to detect and characterize the presence of chemical agent aerosals in various complex atmospheric environments for a defense mission.

S. Krause, T. Vosch et al

2018

Photon Energy Dependent Micro-Raman Spectroscopy with a Continuum Laser Source
Monochromator based tunable Raman excitation filter and detection of weak Raman signals

Tech Notes

A New Dawn for NIR Spectroscopy - BLAZE
Breakthrough technology greatly enhanced NIR quantum efficiency, and enables superior quantitative spectroscopic measurements.