Advanced stress imaging in periodically strained, suspended, quasi-2D membranes: Manifestation of Fano resonance and phonon dynamics insights

Abstract

Raman imaging is a robust tool for probing nanomaterials, especially 2D systems, regarding phase conformation, composition, defects, internal stress, interfacial interactions, and phonon dynamics. This work presents the first proof-of-concept demonstration of mapping stress distribution, charge-phonon coupling, phonon lifetime, and associated vibrational attributes using a point-by-point, full-spectrum Breit-Wigner-Fano (BWF) analysis over a scalable mesh, cast upon the Raman image. Starting from ultrathin nanostructures, the potency of this technique extends to multi-layered quasi-2D flakes, encompassing vibrational modulations of particular molecular bonds compelled by interlayer van der Waals interactions. The experimental realization involves wrapping chemically processed reduced graphene oxide (rGO) over uniformly spaced, vertically aligned e-beam lithographed pillars. The theoretical foundation is derived from density functional theory (DFT)-based calculations on phonon dispersion, Raman spectra, and associated thermodynamic attributes for layer-specific graphene against varying biaxial tensile stress. Our results unlock the true spectroscopic potential of Raman microscopy in characterizing ‘on-chip’ stressed membranes for emerging applications.