Interface Thermal Resistance between Monolayer WSe2 and SiO2: Raman Probing with Consideration of Optical-Acoustic Phonon Nonequilibrium

This work explores the 2D interfacial energy transport between monolayer WSe2 and SiO2 while considering the thermal nonequilibrium between optical and acoustic phonons caused by photoexcitation. Recent modeling and experimental work have shown substantial temperature differences between optical and acoustic phonons (Delta T-OA) in various nanostructures upon laser irradiation. Generally, characterizations of interfacial thermal resistance (R ''(tc)) at the nanoscale are difficult and depend on Raman-probed temperature measurements, which only reveal optical phonon temperature information. Here it is shown that Delta T-OA for supported monolayer WSe2 can be as high as 48% of the total temperature rise revealed by optothermal Raman methods-a significant proportion that can introduce sizeable error to R ''(tc) measurements if not properly considered. A frequency energy transport state-resolved Raman technique (FET-Raman) along with a 3D finite volume modeling of 2D material laser heating is used to extract the true interfacial thermal resistance R ''(tc) (determined by acoustic phonon transport). Additionally, a novel ET-Raman technique is developed to determine the energy coupling factor G between optical and acoustic phonons (on the order of 10(15) W m(-3) K-1). This work demonstrates the need for special consideration of thermal nonequilibriums during laser-matter interactions at the nanoscale.