Raman Articles

Characterizing Modified Celluloses Using Raman Spectroscopy

Characterizing Modified Celluloses Using Raman Spectroscopy

Raman spectra of celluloses modified for use in the pharmaceutical, food, and materials industries are compared and analyzed, with the goal of determining spectroscopic features that can be of use in aiding in the determination of physical and chemical properties.

Published in November 2016 issue

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Tip-enhanced Raman spectroscopy, or TERS

TERS—Ready or Not?

Tip-enhanced Raman spectroscopy, or TERS, integrates scanning probe microscopy (SPM) for nano-scale imaging with confocal Raman spectroscopy for chemical characterization. Challenges with tip quality, optical alignment, consistency and speed, however, have made the technique difficult and complex. New instrumentation is addressing these challenges, allowing TERS to migrate from pure research to routine laboratory analysis. These systems provide correlated nano-scale Raman imaging, enabling scientists to visualize, chemically characterize and implement change, even at the single-molecule level. 

Published in September 2016 issue

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Photoluminescence SpectroscopyUsing a Raman Spectrometer

Photoluminescence Spectroscopy Using a Raman Spectrometer

Photoluminescence can provide information about the composition and solid-state structure of a material. The high spectral resolution of a Raman spectrometer can be useful in performing photoluminescence spectroscopy of solid-state materials, particularly when the emission spectra consist of narrow bands or even lines. Having the capability to perform photoluminescence and Raman spectroscopies simultaneously with the same instrument is advantageous, especially when studying two-dimensional (2D) crystals. When used to perform photoluminescence spectroscopy, the Raman spectrometer becomes two instruments in one.

Published in September 2016 issue

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Selecting an Excitation Wavelength for Raman Spectroscopy

Selecting an Excitation Wavelength for Raman Spectroscopy

Were it not for the problem of photoluminescence, only one laser excitation wavelength would be necessary to perform Raman spectroscopy. Here, we examine the problem of photoluminescence from the material being analyzed and the substrate on which it is supported. We describe how to select an excitation wavelength that does not generate photoluminescence, reduces the noise level, and yields a Raman spectrum with a superior signal-to-noise ratio. Furthermore, we discuss the phenomenon of resonance Raman spectroscopy and the effect that laser excitation wavelength has on the Raman spectrum.

Published in March 2016 issue

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Raman Mapping of Spectrally Non-Well-Behaved Species

Raman Mapping of Spectrally Non-Well-Behaved Species

The use of Raman spectroscopy to produce material images whose contrast is derived from chemical or crystallographic species has been quite useful since the introduction of the Raman microscope in 1976, but particularly with the more recent development of more-sensitive and easier-to-use instruments. When the various species in the field of view have spectra with nonoverlapping analytical bands, simple univariate analysis can provide good images. When overlapping bands are present, multivariate techniques, especially multivariate curve resolution (MCR), have been successfully applied. However, there are cases where even MCR results may be problematic. In this installment, we look at some maps of a ceramic composite containing silicon carbide, silicon, boron carbide, and carbon, where each of these species has nonunique spectra to see what type of results flexible software can produce. What is the goal in this type of exercise? For some of us, creating images is like a teenager’s computer game. But really what we are trying to do is to extract information about a sample from its Raman image. A beautiful rendition is nice, but it must yield information. The following installment shows how Raman maps can provide useful information about a sample.

Published in February 2016 issue

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The Correlation Method for the Determination of Spectroscopically Active Vibrational Modes in Crystals

The Correlation Method for the Determination of Spectroscopically Active Vibrational Modes in Crystals

The application of vibrational selection rules is usually taught with respect to the vibrational motions of individual molecules. However, many of the materials studied by infrared or Raman spectroscopy are solids and even single crystals. Furthermore, some materials such as covalent or ionic solids have no molecular species associated with them. Consequently, there is a need to understand the application of group theory for the determination of spectro- scopically active vibrational modes of crystals. The correlation method is ideal for that purpose.

Published in December 2015 issue

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SERS: An Update of Progress Made

SERS: An Update of Progress Made

This column is a mini survey of progress that has been made in the area of surface enhancement over the last few years since my previous column on surface-enhanced Raman scattering (SERS) in 2008. The potential of SERS to provide signals of analytes at very low concentrations continues to beckon the analytical chemist. What the last few years has produced is a body of work describing the role of the plasmonic properties of metals, based on their geometrical and electronic properties, in enhancing the signals. As this field matures, we foresee production of surface-enhancing films and particles, engineered to provide large enhancements at selected wavelengths that will provide reproducible Raman signals for applications in areas such as environmental and biomedical studies.

Published in November 2015 issue

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Raman Spectroscopy and Imaging of Low-Energy Phonons

Raman Spectroscopy and Imaging of Low-Energy Phonons

Raman bands in the low-energy region of the spectrum of crystals are attributed to so-called external lattice vibrational modes. The Raman bands from these external vibrational modes (low-energy phonons) are very sensitive to crystal structure and orientation with respect to the incident laser polarization and to molecular interactions within the crystal. The low-energy vibrational modes of many organic molecular crystals have very high Raman scattering cross-sections. Raman spectra and images of low-energy phonons in two-dimensional (2D) crystals such as few-layer MoS2 reveal spatial variations in the solid-state structure that are not evident in the higher-energy bands. 

Published in September 2015 issue

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Current Uses of Raman Microscopy in Biomedical Studies

Current Uses of Raman Microscopy in Biomedical Studies

There is growing interest in using Raman as a spectroscopic probe of biological systems based on its high information content, its compatibility with an aqueous environment, and the spatial resolution that is consistent with physical optics (as good as ~0.5 μm). Sampling hardware innovations in recent

Published in June 2015 issue

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Resonance Raman and Photoluminescence Spectroscopy and Imaging of Few-Layer MoS2

Resonance Raman and Photoluminescence Spectroscopy and Imaging of Few-Layer MoS2

Resonance and off-resonance Raman spectroscopy and imaging are used to examine the spatial variation of the solid-state structure and electronic character of few-layer MoS2 flakes. Simultaneous acquisition of photoluminescence spectra with the Raman scattering provides complementary ways of rendering Raman and photoluminescence spectral images of thin-film MoS2.

Published in March 2015 issue

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Multiparticle Analysis by Raman Microscopy

Multiparticle Analysis by Raman Microscopy

There are multiple circumstances where characterization of a collection of particles has value to analysts. In some environments, materials are plagued by particulate contamination that impacts product quality. In the case of small-molecule pharmaceuticals, the solid form of the active pharmaceutical ingredient has to be controlled because of its impact on stability, bioavailability, and intellectual property protection. Raman analysis of relatively large areas with sparsely dispersed particles is now integrated with particle statistics. Results of some simple studies are shown in this column.

Published in February 2015 issue

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Raman Spectroscopy and Microscopy Enable Life Science Discoveries

Raman Spectroscopy and Microscopy Enable Life Science Discoveries

The first article in this two-part series looked at Raman spectroscopy applications in tumor surgery, endoscopy and bacterial identification. This second part examines applications in cell sorting, laser trapping, biology probing and more.

Published in BioPhotonics, February/March 2015 issue

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Raman Spectroscopy and Microscopy: Solving Outstanding Problems in the Life Sciences

Raman Spectroscopy and Microscopy: Solving Outstanding Problems in the Life Sciences

This first article in a two-part series will examine Raman spectroscopy applications in tumor surgery, endoscopy, bacterial identification and more. The second part will cover applications in cell sorting, laser trapping and probing biology.

Published in BioPhotonics, January 2015 issue

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Three-Dimensional Raman Imaging of Ion-Exchanged Waveguides

Three-Dimensional Raman Imaging of Ion-Exchanged Waveguides

Segmented channel waveguides have been fabricated in single-crystal KTiOPO4 through a topotactic process of partial cation exchange. The ion-exchanged waveguides maintain the high nonlinear susceptibility of KTiOPO4 to function as frequency doubling laser light sources. We applied three-dimensional Raman imaging to understand and characterize the changes to the chemical bonding and crystalline structure as well as measure the volumetric structure of waveguide segments.

Published in Spectroscopy, December 2014

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Raman Spectra of Metal Oxides

Raman Spectra of Metal Oxides

Metal oxides often occur in crystals where there are no molecular units. In contrast to Raman analysis of organic compounds in which there are molecular vibrating units with functional subunits, many of whose vibrations are isolated from the remainder of the molecule, the analysis of spectra of oxides requires understanding how atoms move in crystal lattices. These oxides occur in diverse materials such as paint and ceramic pigments, corrosion films, catalysts, and minerals. This column installment attempts to introduce analysts who often work with organic materials to the concepts that need to be understood in analyzing these materials.

Published in Spectroscopy, October 2014

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Headspace Raman Spectroscopy

Headspace Raman Spectroscopy

We examine vapor-phase Raman spectroscopy through the acquisition of spectra from gas molecules confined to the headspace of sealed containers. Studying the Raman spectra of the liquid and vapor phases of compounds with different functional groups, degrees of hydrogen bonding, and polarity provides insight into the energetics of molecular interactions.

Published in Spectroscopy, September 2014

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Raman Microscopy for Detecting Counterfeit Drugs — A Study of the Tablets Versus the Packaging

Raman Microscopy for Detecting Counterfeit Drugs — A Study of the Tablets Versus the Packaging

With the increasing proliferation of counterfeit drug products, there is an incentive to screen drugs for legitimacy. One method is to examine the tablet itself, which is usually a destructive operation. Another method that has been explored is to characterize the packaging, which enables nondestructive screening of the product. Raman microscopy has been found to be a useful tool, and it is often the tool of choice for these measurements.

Published in Spectroscopy, June 2014

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High-Speed TERS Imaging: The Latest Achievements in nano-Raman Spectroscopy

High-Speed TERS Imaging: The Latest Achievements in nano-Raman Spectroscopy

This article presents developments in tip-enhanced Raman spectroscopy (TERS) that make possible nanoscale imaging of chemical and physical properties of graphene and other carbon species: Advances in near-field optical probes now provide reliable nanoscale spectroscopy solutions for academic and industrial researchers.

Published in Spectroscopy, June 2014

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Practical Group Theory and Raman Spectroscopy, Part II: Application of Polarization

Practical Group Theory and Raman Spectroscopy, Part II: Application of Polarization

In this second installment of a two-part series we present polarized Raman spectra and discuss the association of the symmetry species of the normal vibrational mode and the depolarization ratio of Raman scattering. We discuss those aspects of molecular symmetry and Raman polarization rules that can be applied with normal Raman instrumentation. Materials include liquids, single crystals, and polycrystalline compounds.

Published in Spectroscopy, March 2014

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Practical Group Theory and Raman Spectroscopy, Part I: Normal Vibrational Modes

Practical Group Theory and Raman Spectroscopy, Part I: Normal Vibrational Modes

Group theory is an important component for understanding the fundamentals of vibrational spectroscopy. The molecular or solid state symmetry of a material in conjunction with group theory form the basis of the selection rules for infrared absorption and Raman scattering. Here we investigate, in a two-part series, the application of group theory for practical use in laboratory vibrational spectroscopy.

Published in Spectroscopy, February 2014

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Considerations of Grating Selection in Optimizing a Raman Spectrograph

Considerations of Grating Selection in Optimizing a Raman Spectrograph

The performance of a Raman spectrograph for a particular application will depend, among other things, on its sensitivity and spectral resolution. The sensitivity will determine how long it will take to record a spectrum with a given signal-to-noise ratio.

Published in Spectroscopy, October 2013

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Raman Imaging of Silicon Structures

Raman Imaging of Silicon Structures

Here we examine what is commonly called a Raman image and discuss how it is rendered. We consider a Raman image to be a rendering as a result of processing and interpreting the original hyperspectral data set.

Published in Spectroscopy, September 2013

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Resonance Enhancement of Raman Spectroscopy: Friend or Foe?

Resonance Enhancement of Raman Spectroscopy: Friend or Foe?

The presence of electronic transitions in the visible part of the spectrum can provide enormous enhancement of the Raman signals, if these electronic states are not luminescent. In some cases, the signals can increase by as much as six orders of magnitude.

Published in Spectroscopy, June 2013

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Classical or Transmission Raman, SERS or TERS: Which Raman Spectroscopy Technique Is Right for You?

Classical or Transmission Raman, SERS or TERS: Which Raman Spectroscopy Technique Is Right for You?

This article explains different Raman techniques are compared with respect to their main field of applications, possibilities, advantages, difficulties, and limits.

Published in Spectroscopy, June 2013

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Raman for Oil Shale Exploration

Raman for Oil Shale Exploration

Discussion and examples of the practical application of Raman micro-spectroscopy for the analysis of materials directly related to oil shale exploration.

Published in Spectroscopy, March 2013

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Raman Microscopy Analysis of Molecular Orientation in Organic Fibres

Raman Microscopy Analysis of Molecular Orientation in Organic Fibres

The processes involved in creating fibers from organic polymers - either man-made or natural - have the potential to orient the molecules in the fibres.  Examination of a number of fibres confirms that orientation is a more or less ubiquitous phenomenon that can be detected and quantified by Raman microscopy.

Published in Spectroscopy, February 2013

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From Micro– to Macro–Raman Spectroscopy:Solar Silicon for a Case Study

From Micro– to Macro–Raman Spectroscopy:Solar Silicon for a Case Study

The paper explains the use of the Raman spectroscopy to the stress analysis in Silicon based panel solar materials.

Published by InTech Advanced Aspects of Spectroscopy as a chapter of a book "Advanced Aspects of Spectroscopy"., 2012.

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Multivariate data processing of spectral images: The Ugly, the Bad and the True

Multivariate data processing of spectral images: The Ugly, the Bad and the True

The paper demonstrates the difference between 'pretty' and 'true' Raman chemical images, and how to achieve true and pretty Raman chemical images.

Published in Spectroscopy, August 2007

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Raman Imaging: Defining the Spatial Resolution of the Technology

Raman Imaging: Defining the Spatial Resolution of the Technology

Chemical images of polystyrene beads on silicon acquired using Raman mapping and image processing are reviewed. The effects of the objective on the quality of the final image, particularly its magnification and numerical aperture, and the step size of the map, are discussed as well.

Published in Spectroscopy, supplement Raman, June 2006

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Spectroscopic imaging for the life sciences - more than just a pretty picture

Spectroscopic imaging for the life sciences - more than just a pretty picture

It has long been a major goal of scientists to understand the many complex processes taking place within living organisms, ranging from microscopic species such as bacteria and viruses at one extreme, through to the human at the other. This article shows that micro-spectroscopic imaging is a key technique for biological research.

Published in Spectroscopy Europe Life Science supplement, August/September 2005

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Spectroscopy Solutions for Materials Analysis

Spectroscopy Solutions for Materials Analysis

Raman and EDXRF Chemical Imaging for Formulation Process Development and Quality Control Compounds of magnesium and calcium are common components of pharmaceutical formulations.

Spectroscopic imaging can provide a complete understanding of a formulation. This paper compares two spectral imaging techniques - energy dispersive X-Ray Fluorescence (EDXRF) microscopy and Raman microscopy.

Published in Spectroscopy, June 2005

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Biopharma Imaging and Analysis

Biopharma Imaging and Analysis

Advancing Towards a More Detailed Picture of Chemistry

There is a wealth of analytical and imaging techniques available for the measurement of biopharma samples. The samples themselves can be wide ranging and take numerous forms: single cells, tissues, crystals or blended formulations. To study and develop such samples many techniques, including fluorescence microscopy, NIR imaging, AFM and SEM, have been used. Published in European Biopharmaceutical Review, Spring 2005

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Refined Raman Spectroscopy

Refined Raman Spectroscopy

Bringing new insight into industrial processes

Fibre probes and ease of use make Raman spectroscopy systems attractive for monitoring process control in many industries, ranging from pharmaceuticals to petrochemicals. The authors describe the Raman effect and discuss systel and monitoring basics.

Published in Optics & Photonics News, June 05

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A new dimension in cell imaging

A new dimension in cell imaging

Combining chemical and spatial information

There are many microscopic imaging techniques used to investigate the complexities of cell structure, including optical microscopy, confocal laser scanning microscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). These techniques provide highly detailed images of the cells, but they fail to characterize the chemistry and composition of the sample under examination. Spectroscopic techniques, however, can do just that, and in particular Raman micro-spectroscopy is fast becoming established for probing cellular biochemistry on the micron scale.

Published in BIOforum Europe, April 2005

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Micro-spectroscopy - shedding light on rock formation

Micro-spectroscopy - shedding light on rock formation

Whilst there are many imaging techniques available to a research scientist, the information which is provided is often only of a visual/topographical nature. What they fail to provide is true compositional (chemical/elemental) analysis of the materials. However, microspectroscopic techniques such as Raman or X-Ray Fluorescence (XRF) can fill this gap, allowing highly detailed images to be generated based upon the sample's material composition.

 Published in Spectroscopy Europe, June 2005

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