Correlation analysis of vibration modes in physical vapour deposited Bi 2 Se 3 thin films probed by the Raman mapping technique.

In this work, the Raman spectroscopy mapping technique is used for the analysis of mechanical strain in Bi 2 Se 3 thin films of various (3-400 nm) thicknesses synthesized by physical vapour deposition on amorphous quartz and single-layer graphene substrates. The evaluation of strain effects is based on the correlation analysis of in-plane (E 2 g ) and out-of-plane (A 2 1g ) Raman mode positions. For Bi 2 Se 3 films deposited on quartz, experimental datapoints are scattered along the line with a slope of ∼0.85, related to the distribution of hydrostatic strain. In contrast to quartz/Bi 2 Se 3 samples, for graphene/Bi 2 Se 3 heterostructures with the same thicknesses, an additional negative slope of ∼-0.85, which can be associated with the distribution of the in-plane ( a - b ) biaxial tensile strain due to the film-substrate lattice mismatch, is observed. The algorithm of phonon deformation potential (PDP) calculation based on the proposed strain analysis for the 3 nm thick Bi 2 Se 3 film deposited on the graphene substrate, where the strain is considered to be coherent across the thickness, is demonstrated. The PDPs for biaxial in-plane strain of the Bi 2 Se 3 3 nm film in in-plane and out-of-plane modes are equal to -7.64 cm -1 /% and -6.97 cm -1 /%, respectively.