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Paper No. 14-8
Presentation Time: 10:10 AM
ELUCIDATING NANOPARTICLE SIZE-DEPENDENCE EFFECTS ON THE RAMAN SPECTRUM OF HEMATITE
Despite the importance of nanoparticle (NP) hematite in materials science, geological applications, and astrobiology, the Raman spectrum acquired from this material is poorly understood. While the study of the Raman spectroscopy of bulk single-crystals has recently been well documented[1,2], very few studies have centered on understanding the size-dependent changes in Raman spectra of hematite NPs[3]. Chernyshova[3] showed that as particle size decreases, the Raman bands become broader, shifting towards lower relative wavenumbers, which is common for NPs. In addition, they proposed that the Raman bands associated with movements of the iron ions (i.e., 225, 245, and 298 cm-1) experience observably-greater broadening, as compared to the remaining, oxygen-related Raman bands[3]. Here, we undertake a systematic study of elucidating the changes in Raman spectra with respect to the size-dependence of hematite NPs by fabricating progressively smaller nanoparticles utilizing mechanochemical synthesis. Our work demonstrates that the Raman bands that change with respect to size-dependence are the A1g (225 cm-1), Eg Translational (245 cm-1), EgLibrational (294 cm-1), Eg (412 cm-1), 1LO (660 cm-1), and 2LO (1320 cm-1). Our work reveals the Raman bands that change most significantly with respect to size dependence are the Eg Librational mode at 294 cm-1 and the Eg mode at 412 cm-1, which is in disagreement with Chernyshova[3]. Moreover, our work reveals a linear correlation of increasing bandwidth of the Eg Librational mode at 294 cm-1 and the Eg mode at 412 cm-1 with respect to progressively decreasing nanoparticle size, yielding a calibration curve to determine particle size for NP hematite by Raman spectroscopy.
[1] Marshall, C. P., Dufresne, W. J., & Rufledt, C. J. (2020). Polarized Raman spectra of hematite and assignment of external modes. Journal of Raman Spectroscopy, 51(9), 1522-1529.
[2] Marshall, C. P., & Dufresne, W. J. (2022). Resonance Raman and polarized Raman scattering of single‐crystal hematite. Journal of Raman Spectroscopy, 53(5), 947-955.
[3] Chernyshova, I. V., Hochella Jr, M. F., & Madden, A. S. (2007). Size-dependent structural transformations of hematite nanoparticles. 1. Phase transition. Physical Chemistry Chemical Physics, 9(14), 1736-1750.