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Abstract This work explores the 2D interfacial energy transport between monolayer WSe2and SiO2while 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 (ΔTOA) 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 ΔTOAfor supported monolayer WSe2can be as high as 48% of the total temperature rise revealed by optothermal Raman methods—a significant proportion that can introduce sizeable error toR′′tcmeasurements 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 resistanceR′′tc(determined by acoustic phonon transport). Additionally, a novel ET‐Raman technique is developed to determine the energy coupling factorGbetween optical and acoustic phonons (on the order of 1015W m−3K−1). This work demonstrates the need for special consideration of thermal nonequilibriums during laser–matter interactions at the nanoscale.
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Direct Characterization of Thermal Nonequilibrium between Optical and Acoustic Phonons in Graphene Paper under Photon Excitation
Abstract Raman spectroscopy has been widely used to measure thermophysical properties of 2D materials. The local intense photon heating induces strong thermal nonequilibrium between optical and acoustic phonons. Both first principle calculations and recent indirect Raman measurements prove this phenomenon. To date, no direct measurement of the thermal nonequilibrium between optical and acoustic phonons has been reported. Here, this physical phenomenon is directly characterized for the first time through a novel approach combining both electrothermal and optothermal techniques. While the optical phonon temperature is determined from Raman wavenumber, the acoustic phonon temperature is precisely determined using high‐precision thermal conductivity and laser power absorption that are measured with negligible nonequilibrium among energy carriers. For graphene paper, the energy coupling factor between in‐plane optical and overall acoustic phonons is found at (1.59–3.10) × 1015W m−3K−1, agreeing well with the quantum mechanical modeling result of 4.1 × 1015W m−3K−1. Under ≈1 µm diameter laser heating, the optical phonon temperature rise is over 80% higher than that of the acoustic phonons. This observation points out the importance of subtracting optical–acoustic phonon thermal nonequilibrium in Raman‐based thermal characterization.
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- PAR ID:
- 10446367
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Science
- Volume:
- 8
- Issue:
- 12
- ISSN:
- 2198-3844
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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