Stimulated Raman scattering imaging of atomically thin layers and a strained nanotent of hexagonal boron nitride

Abstract

The development of microscopy and spectroscopy techniques to characterize and study two-dimensional (2D) materials is key for diverse optoelectronic and biomedical applications. Spontaneous Raman microscopy is one of the most employed techniques due to its simple and non-destructive procedure, though it relies on weak Raman signals, which can limit its imaging speed and image details as well as spectroscopic applications. Here, we report vibrational imaging with stimulated Raman scattering (SRS) microscopy for atomically thin layers and a strained nanostructure in 2D hexagonal boron nitride (h-BN). Our SRS microscope system enables hyperspectral SRS imaging of mono- and few-layer h-BN. From the obtained SRS spectra, we observe a linear tendency of the integrated SRS intensities as the thickness increases by a monolayer step. As a spectroscopic application of our system, we also demonstrate SRS imaging of a strained nanotent in thick h-BN. The SRS spectra in the nanotent area exhibit large red shifts of their peaks due to tensile strain induced by the tent-shaped geometry. By a combination of its height profile and the strain-induced peak shifts, we show that the Grüneisen parameter of h-BN can be estimated. Our approach based on SRS microscopy will pave the way for fast and high-resolution vibrational imaging of atomically thin and strained 2D materials.