Energy relaxation analysis in thermoelectric materials using temperature measurement by Raman scattering spectroscopy

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K05343
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 29030:Applied condensed matter physics-related
• Research Institution: Japan Advanced Institute of Science and Technology
• Principal Investigator: Koyano Mikio 北陸先端科学技術大学院大学, 先端科学技術研究科, 教授 (60195873)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 熱電変換 / ラマン散乱 / エネルギー緩和 / フォノン / 遷移金属ダイカルコゲナイド / グラフェン

Outline of Final Research Achievements

In this study, we investigate the energy relaxation process and heat transport in the thermal steady state using Raman scattering experiments with the aim of clarifying the elementary process of the conversion of thermal energy ⇔ electrical energy that occurs in thermoelectric materials.
We discovered a new phenomenon in which the optical phonon temperature and the lattice temperature are different in transition metal dichalcogenides. We clarified that the cause is the decrease in the phonon occupancy due to the difference in the energy dissipation rate from the excited state. Furthermore, it was found that the temperature difference is not so large in graphene, which is a typical nanomaterial. This result suggests that the energy dissipation process differs greatly depending on the type of material.

Free Research Field

固体物性・熱電変換

Academic Significance and Societal Importance of the Research Achievements

本研究で発見された「光学フォノン温度と格子温度が高温領域で一致しない」という新しい現象は，熱定常状態においてもエネルギー緩和は速やかに行われるものであるという今までの常識に一石を投じるものであり，非平衡熱輸送の分野における重要なものである．応用科学の観点からも，熱エネルギーを電気エネルギーに変換する熱電変換の素過程を理解し産業応用につなげるうえで重要な情報である．
本研究で開発した温度計測法は，非接触・非破壊で局所温度を測定できるものであるため，このような材料系以外にも広く応用が可能である．今後発展が見込まれるマイクロデバイスや微小試料の温度測定への道を開くものである．