Phonon confinement effect on breathing vibrations of monolayer and few-layer metal dichalcogenides

Abstract

Two-dimensional 4H-SnS<inf>2</inf> single crystals of several square millimeters were grown using chemical vapor transport method. A bulk 4H-SnS<inf>2</inf> can be easily exfoliated into few-layer 4H-SnS<inf>2</inf> using mechanical exfoliation technique. Few-layer and multilayer 4H-SnS<inf>2</inf> of 3, 8, 13, 27, 43, and 71 monolayers were stably obtained in ambient. The Raman spectra of few-layer and multilayer 4H-SnS<inf>2</inf> reveal a single dominant A<inf>1g</inf> Raman mode. The A<inf>1g</inf> Raman mode of few-layer 4H-SnS<inf>2</inf> is redshifted and broadened with reduced layer number, indicating that the phonon confinement effect is layer-dependent. The Raman tensor of the few-layer 4H-SnS<inf>2</inf> can be fixed with the phonon confinement effect. This effect also significantly influences the thermodynamic properties of few-layer 4H-SnS<inf>2</inf>. The results provide valuable insights for the design of next-generation photonic and thermoelectric devices based on 4H-SnS<inf>2</inf>. © 2025 The Physical Society of the Republic of China (Taiwan).