Angular dependence of the Raman active phonon modes of Black Phosphorus

University essay from Lunds universitet/Atomfysik; Lunds universitet/Fysiska institutionen

Abstract: This Master’s project presents on the angular dependence of the intensity of the Raman active phonon modes of Black Phosphorus (BP), a layered 2D material with unique and attractive characteristics to the scientific and engineering community. Raman spectroscopy is an indispensable tool in quick and unobtrusive analysis of chemical structures. In this Master project, the structure of BP is analyzed through polarized Raman excitation. The incident polarization is varied to investigate the effect on the various detectable Raman active modes in BP. A Raman microscope with a 532 nm laser was used to excite BP flakes mechanically exfoliated from a source. The amplitude of the peaks in the Raman spectra are plotted against the angle that they were measured in. The classical model for the Raman tensor was used but it was inadequate in it’s ability to predict data in the cross polarized configuration. An improved model taking the linear dichroism and the degradation effects of BP into account substantially improved the fit. All in all, with the strange characteristics of BP factored, phonon mode control through polarized Raman excitaion much of the modes followed the complex angular dependence set by theory but not all of the data points were accounted for by the complex dependence and degradation.

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