Raman Spectroscopy

Raman spectroscopy has been put to good use in applications such as nanomaterials development as well as in quality control laboratories. Participants in this Technology Forum are David Tuschel of HORIBA Scientific, Richard Larsen of Jasco, Inc., Scot Ellis of Thermo Fisher Scientific, and Harald Fischer of WITec GmbH.

What areas of new materials development have benefited from Raman measurements?

Tuschel: Raman spectroscopy has had a significant role in the development of carbon-based nanomaterials. These would include the fullerene buckyballs and nanotubes and more recently graphene and graphene oxide. The ability to detect even a single monolayer of graphene by Raman spectroscopy is remarkable enough. Beyond that, the ability to differentiate single, double, and multiple layers of graphene has been so important to the development of these materials, particularly for electronic device applications. I expect that micro-Raman spectroscopy will play an important role in the development and characterization of carbon nanotube and graphene based electronic devices.

Larsen: Certainly, nanomaterials development, including nanotubes and nanowires, as well as graphene and other carbon complexes are actively studied using Raman spectroscopy. In addition, new materials for semiconductors and rechargeable batteries have benefited from analysis using Raman spectroscopy. We have also demonstrated Raman spectroscopy for the analysis of medical devices, development of new materials for energy sources, and the investigation of various types of polymer laminates.

Ellis: Raman’s ability to give insight into structure and morphology, in addition to molecular composition, has led to extensive use across the broad field of materials science. Since the field is interested in linking materials to properties and behavior in applications, techniques like Raman that can provide a multidimensional analysis get adopted quickly. For example, a graphene measurement can give you information about defects and uniformity, strain, functionalization, and doping and sheet count. These can, in turn, be correlated to traits such as electronic and thermal conductivity and band gap, which, in turn, predict performance in real world applications including composites, electronic displays, and sensor technologies.

Fischer: Materials whose developments have been facilitated by Raman measurements certainly include graphene, carbon nanotubes, and other related carbon materials, as the technique allows the analysis of various properties of such materials very easily and comprehensively. Beyond that the pharmaceutical industry can benefit from Raman measurements by developing new drug delivery systems such as membranes, coatings, or emulsions with distinct features. What we also see is that the structure of polymer materials can be optimized when analyzed with Raman or Raman imaging.

Have you seen any areas where Raman has been helpful in manufacturing, either in quality control or in on-line process monitoring?

Tuschel: The detection and identification of submicrometer or larger contaminants or off-specification impurities in manufacturing and device fabrication are primary reasons for the use of micro-Raman spectroscopy in industry. Quite often, individual quality control labs will construct Raman spectral databases that correspond to the types of contaminants or raw materials specific to a company’s processes or products. Knowledge of the chemistry or materials science involved in the manufacturing process is essential to a correct identification and source analysis when a spectral search identifies several matches of the defect or impurity.

Larsen: We have discussed these types of applications with users, but we also realize that there are other companies that have dedicated instruments and solutions for these types of analyses.

Ellis: Both areas are benefiting from Raman, and the pharmaceutical industry is a notable example of increased awareness and adoption of the technique as a tool for manufacturing operations. The high specificity of Raman as a spectroscopic technique, coupled with the form factor of rugged and dedicated handheld Raman analyzers, have made it an ideal technique for checking materials in real time as they flow into and along processes. The robustness of both physical design (for example, rugged and portable handheld units) and software-for-purpose allow much lower reliance on the laboratory. It provides high confidence and can be implemented and managed with lower investment than some other techniques.

Fischer: Off-line quality control with Raman already plays an important role in many industrial fields. This can range from the analysis of the basic products with a handheld Raman spectrometer to the characterization of more complex structures with Raman imaging in a later stage of production. The types of industries can vary from chemical or pharmaceutical production to coating or thin-film manufacturers or even semiconductors. For on-line process monitoring highly sensitive Raman spectroscopy is a particularly powerful tool for chemical and photovoltaic production.

How can the Raman community help novice analytical chemists/spectroscopists with interpretive skills and experimental design?

Tuschel: I believe that there is a great need for individual mentoring of those new to Raman spectroscopy by those of us with years and even decades of experience. There is a great deal of craft in any of the scientific disciplines and it is acquired and developed over time. That fact has been recognized and incorporated in the mechanical trades with the practice of the apprenticeship working and studying under a journeyman. It is a practice that has its origins in the medieval guilds. No amount of automation or software can replace the judgment and interpretive skills that come with experience. We have a professional obligation to pass that on and develop it in others through individual mentoring.

Larsen: Continued development of Raman instrumentation will provide new methods for sample analysis. Our interaction with potential customers helps us to provide feedback to our engineers for hardware and software modifications to suit new experimental requirements. As well, the publication of research efforts by experienced Raman users can provide additional information for novice users of Raman spectroscopy.

Ellis: By not thinking in these terms anymore, when it comes to instrument and software design. Many traditional spectroscopists will still interpret data, optimize instrument performance by hand, and approach measurements with due care and discipline. These aren’t great options for many newer users who are experts in their applied fields, products, or processes and for whom Raman is a tool to get important answers — rather they’re barriers. New people coming online with Raman need the benefits of Raman but not the learning curve or overhead of what historically has been an advanced spectroscopic technique. One approach to Raman microscopy, for example, has borrowed heavily from what made FT-IR ubiquitous in analytical laboratories. By making instruments more self-managing and answer-focused without sacrificing high performance, the systems become much more accessible for analytical services, troubleshooting, defect analysis, and research in applied fields outside of analytical chemistry.

Fischer: From the standpoint of a Raman instrument manufacturer it is necessary to provide easy-to-use Raman systems guiding a new user clearly through an experiment but also providing advanced features once the user is more experienced. Integrated software for data evaluation also plays an important role in helping new users with challenges in the interpretation of the data.