The low frequency region of the Raman spectrum has significant potential, including increased sensitivity to crystal structure and to chemical bond interactions within the crystal. Raman spectra and images of low energy phonons in 2D crystals reveal spatial variations in the solid state structure that are not evident in the higher energy bands.
David Tuschel, Manager of Raman Applications, Horiba Scientific, will discuss this topic on Wednesday, March 8 at Pittcon 2017 in his presentation “What the Low Frequency Region of the Raman Spectrum Reveals about Chemical Bonding and Structure of Solid State Materials.” He discussed the highlights of his upcoming talk and the role of low frequency Raman spectroscopy in an exclusive interview with R&D Magazine.
R&D Magazine: What is your goal in doing this presentation?
Tuschel: What I am trying to do is communicate how this low frequency portion of the Raman spectrum really provides data that, when correctly interpreted, can be converted into information about chemical bonding and solid state structure of these materials. It turns out in the very low frequency portion of the spectrum—I’m talking about 1 wavenumber out to about 50 wavenumbers —you have this great sensitivity to their relative orientation, the way they are stacked and how many layers there are. The difference in this low frequency portion of the spectrum is significantly greater than in the higher energy modes, around 390-400 wavenumbers. Most of the Ramen work that you will find on these 2D crystals requires a higher energy region. I thought by talking about the lower energy region that it would be scientifically interesting.
Do you feel this is an area that isn’t as well known?
I don’t think it’s as well known in the analytical chemistry community or analytical instrumentation community. Most of the people working with these materials are solid state physicists. Pittcon has historically been the world of analytical chemistry and analytical chemists. In that sense, it is not the most obvious fit here, except for the fact that you use Raman spectrometers to study these materials. As an aside, in reading many of the papers on these 2D crystals, most of the people working on these are material scientists or they are solid state physicists who are using Raman spectroscopy more or less as a characterization tool. They are not primarily Raman spectroscopists. Having said that, there are quite a few Raman spectroscopist that are working on these materials that do fine work; I don’t want to dismiss that. What I am saying is that most of the people who work on the materials do so, not specifically for the purpose of Raman spectroscopy, they just use Raman as a tool.
What are the biggest benefits of low frequency Raman spectroscopy?
It will, first off, tell you the number of layers that are there—if you have one, two, three, four. The main part of my talk is about what you can learn regarding their relative orientation to each other. This allows you to understand, even if you don’t have the crystal habit, what orientation of the multiple layer you have and their stacked orientations. Furthermore, when you get into the chemical physics of it, you can start to look at how these different orientations effect the properties of it, and maybe we can understand that through the changes in the Raman spectra.
Who should be interested in these advancements?
Right now I think the people that are most interested in it are in academia. Major semi-conductor industries would also have an interest in this because they always want to make sure they are not left out of the next advancement. It started with silicon and then we had gallium arsenide, and then along comes gallium nitride. So now you have these interesting materials that maybe you can end up fabricating devices on flexible substrate. I don’t mean to say it will replace silicon, but I think it should be funded because it is a really particular material that has some interesting electro-optic behavior, and maybe by studying this a little bit more we can find some applications in these areas. It could be used for sensors, because it is very sensitive to several gasses. These 2D crystals could be created that can detect gasses that are perhaps a contaminant or a hazardous material. Another application could be the production of electronic devices on flexible substrates.
This interview has been edited for clarity and length