Raman Spectra and Corresponding Strain Effects in Graphyne and Graphdiyne

We systematically studied the Raman spectra of graphyne (GY) and graphdiyne (GDY), analyzing their features under mechanical strain by group theory and first-principles calculations. The G bands in GY and GDY were softened compared with that in graphene, which provides a fingerprint useful in detecting their synthesis. We established a unified formulation to describe the effects of both uniaxial and shear strains, and combined this with calculated results to reveal the relationship underlying the changes in Raman evolution under various strains. Each doubly degenerate mode splits into two branches under strain, both of which are red-shifted with tensile uniaxial strain, but one is red-shifted and the other is blue-shifted under shear strain. The splitting under shear strain is double that under uniaxial strain.