Abstract Raman spectroscopy-based temperature sensing usually tracks the change of Raman wavenumber, linewidth and intensity, and has found very broad applications in characterizing the energy and charge transport in nanomaterials over the last decade. The temperature coefficients of these Raman properties are highly material-dependent, and are subjected to local optical scattering influence. As a result, Raman-based temperature sensing usually suffers quite large uncertainties and has low sensitivity. Here, a novel method based on dual resonance Raman phenomenon is developed to precisely measure the absolute temperature rise of nanomaterial (nm WS 2 film in this work) from 170 to 470 K. A 532 nm laser (2.33 eV photon energy) is used to conduct the Raman experiment. Its photon energy is very close to the excitonic transition energy of WS 2 at temperatures close to room temperature. A parameter, termed resonance Raman ratio (R3) Ω = I A 1g / I E 2g is introduced to combine the temperature effects on resonance Raman scattering for the A 1g and E 2g modes. Ω has a change of more than two orders of magnitude from 177 to 477 K, and such change is independent of film thickness and local optical scattering. It is shown that when Ω is varied by 1%, the temperature probing sensitivity is 0.42 K and 1.16 K at low and high temperatures, respectively. Based on Ω, the in-plane thermal conductivity ( k ) of a ∼25 nm-thick suspended WS 2 film is measured using our energy transport state-resolved Raman (ET-Raman). k is found decreasing from 50.0 to 20.0 Wm −1 K −1 when temperature increases from 170 to 470 K. This agrees with previous experimental and theoretical results and the measurement data using our FET-Raman. The R3 technique provides a very robust and high-sensitivity method for temperature probing of nanomaterials and will have broad applications in nanoscale thermal transport characterization, non-destructive evaluation, and manufacturing monitoring.
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Effect of temperature on Raman intensity of nm-thick WS 2 : combined effects of resonance Raman, optical properties, and interface optical interference
Temperature dependent Raman intensity of 2D materials features very rich information about the material's electronic structure, optical properties, and nm-level interface spacing. To date, there still lacks rigorous consideration of the combined effects. This renders the Raman intensity information less valuable in material studies. In this work, the Raman intensity of four supported multilayered WS 2 samples are studied from 77 K to 757 K under 532 nm laser excitation. Resonance Raman scattering is observed, and we are able to evaluate the excitonic transition energy of B exciton and its broadening parameters. However, the resonance Raman effects cannot explain the Raman intensity variation in the high temperature range (room temperature to 757 K). The thermal expansion mismatch between WS 2 and Si substrate at high temperatures (room temperature to 757 K) make the optical interference effects very strong and enhances the Raman intensity significantly. This interference effect is studied in detail by rigorously calculating and considering the thermal expansion of samples, the interface spacing change, and the optical indices change with temperature. Considering all of the above factors, it is concluded that the temperature dependent Raman intensity of the WS 2 samples cannot be solely interpreted by its resonance behavior. The interface optical interference impacts the Raman intensity more significantly than the change of refractive indices with temperature.
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- Award ID(s):
- 1930866
- NSF-PAR ID:
- 10191855
- Date Published:
- Journal Name:
- Nanoscale
- Volume:
- 12
- Issue:
- 10
- ISSN:
- 2040-3364
- Page Range / eLocation ID:
- 6064 to 6078
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9NR10186A
