Quantum‐chemical perspective of nanoscale Raman spectroscopy with the three‐dimensional phonon confinement model

Raman spectroscopy of crystalline/molecular systems is well grounded with quantum‐chemical calculations and group theory, making it a unique tool for material characterization. For the ‘intermediate’ case of nanometer‐scale systems, however, the application of Raman spectroscopy is limited by the lack of such theoretical bases. Here, we couple a scaled quantum‐chemical calculation with the phonon confinement model to construct a universal and physically consistent basis for nanoscale Raman spectroscopy. Unlike the commonly assumed one‐dimensional approximation of phonon dispersion, we take into account the confinement along all the three dimensions of the k‐space. We apply it to diamond nanoparticles of sub‐50‐nm size, a system with pronounced anisotropy of dispersion for which consideration of three‐dimensional dispersion is a requisite. The model excellently reproduces size‐sensitive Raman spectral features, including the peak position, bandwidth, and asymmetry of the sp3 C–C stretch Raman line. This fundamental approach can be easily generalized to contribute the future development of quantitative nanoscale Raman spectroscopy. Copyright © 2017 John Wiley & Sons, Ltd. We introduce a general quantitative approach to interpret the Raman spectra of nanoscale materials. We combine a quantum‐chemical calculation with the 3D phonon confinement model to successfully reproduce the size‐dependent Raman spectra of nano‐diamonds.