Graphene nanoribbons (GNRs) are the current focus of my work, with Raman spectroscopy playing a major role in the characterization of their properties and material quality.
GNRs are synthesized from precursor molecules under ultra-high vacuum conditions and have to be transferred to silicon chips with nanostructured electrods for electrical characterization. As the fabrication of these chips is quite time-intensive we want to routinely make sure that the quality of GNRs to be transferred is as expected and that we can assess this after transfer and independent of their electrical properties. Towards that end, we employ Raman spectroscopy that allows us to obtain precise information about the structure of the GNRs based on their spectroscopic fingerprint – in particular also on insulating substrates and without the need for vacuum.
To be able to routinely apply this technique on all chips, we employ a layered structure of materials optimized for constructive interference which maximizes the Raman signal. This structure combines the technological benefits of using widely available silicon chips without disturbance by their background signal. This allows us to detect particularly informative Raman modes that are otherwise masked by that background.
We have revcently published a detailed desciption of this approach alongside optimized measurement routines:
Overbeck, J., Borin Barin, G., Daniels, C., Perrin, M.L., Liang, L., Braun, O., Darawish, R., Burkhardt, B., Dumslaff, T., Wang, X., Narita, A., Müllen, K., Meunier, V., Fasel, R., Calame, M. and Ruffieux, P. (2019), Optimized Substrates and Measurement Approaches for Raman Spectroscopy of Graphene Nanoribbons. Phys. Status Solidi B, 256: 1900343. doi:10.1002/pssb.201900343
The preprint can be found on arXiv: https://arxiv.org/abs/1907.01797