Analyzing Nanomaterials with Raman

Mircea Chipara of the University of Texas-Pan American talks about the use of Raman spectroscopy in the analysis of carbonaceous nanomaterials.

What are some applications of Raman spectroscopy in your research, and under what circumstances do you choose this technique over others?

Chipara: I first started using Raman spectroscopy for the study of various carbon nanostructures dispersed within polymeric matrices. Tentatively, I also exploited the Raman lines of the polymeric matrix to obtain a richer picture of the effect of carbon nanostructures. Later, I used Raman spectroscopy to assess the polymerization of dicyclopentadiene in self-healing polymers.

Typically, it is easier to perform a Raman measurement than a Fourier-transform infrared (FT-IR) spectrum in the attenuated total reflectance (ATR) mode. Hence, a commercially available Raman confocal microscope is sometimes more versatile than an FT-IR spectrometer.

You have a paper that’s going to be published soon in Spectroscopy magazine on carbonaceous materials including nanomaterials. What are some of the particular issues involved in using Raman to study these types of materials?

Chipara: In the study of polymer-based nanocomposites, the polymeric matrix is destroyed thermally by the incoming laser beam (especially if the filler is a carbon nanostructure). Hence, frequently we do Raman at low laser power (at or below 10 mW) and small magnification, with many accumulations, As a result, it takes about 30–60 min to record a nice Raman spectrum ready for lineshape analysis.

You are involved in the NANOSMAT conference on nanoscience. How important a role does Raman play in the study of nanomaterials?

Chipara: Raman has become an important technique in the study of carbonaceous materials. However, it is often forgotten that Raman is a first-degree relative of FT-IR and hence not many studies focus on Raman investigations of the polymeric matrix. The special relationship between Raman and FT-IR is not usually exploited.

I cannot say that Raman is the most important technique, but if you want to pick 10 most frequently used techniques in nanomaterials you should add Raman, or at least think about it.

I do think that Raman has not yet reached the maturity level. We may see more developments in the near future.

What future developments in Raman spectroscopy techniques do you expect to see?

Chipara: I expect to see many. Here are a few:

a. Real time/time-domain/high speed/high resolution Raman spectroscopy. This is of particular importance for biology related issues (and for me, I would enjoy recording the full Raman spectrum in few seconds!).

b. A spill of Raman spectroscopy over a wide frequency range (IR, near infrared [NIR], visible, UV–vis and beyond) ultimately in a single spectrometer equipped with a tunable laser. Temperature dependence, polarization capabilities, and mapping possibilities are always welcomed. Raman imaging would be a very nice addition to existing nuclear magnetic resonance (NMR) capabilities.

c. A fusion between FT-IR and Raman in a powerful research tool focused on the study of vibrations in molecules.

d. A final combination of Raman, UV–vis, NIR, and FT-IR (and I do hope that fluorescence will be added later) in a single solid and extremely powerful spectroscopic tool, ignited by the availability of new wide wavelength tunable laser systems.

And this can continue (for example, by adding the angular dependence of the reflected/transmitted electromagnetic radiation and the time domain). Polarization capabilities would eventually add new capabilities such as the magneto-optical Kerr effect. The list is still long.