题　目：Nanoscale Heat Transfer: Thermal Conductivity of Hybrid Organic-Inorganic Materials
主讲人：Ronggui Yang 教授（科罗拉多大学博尔德校区）
时　间：6月19日（周五），下午2:00~3:00
地　点：南校区第一实验楼423会议室
语　言：英语

Thermal transport plays an important role in energy and information technologies. There have been significant progresses on the understanding of thermal conductivity and phonon transport mechanisms over the past 2 decades, owing much to the challenging needs in high efficiency energy conversion, high speed electronics, and high power lasers. In concurrence with such technical challenges, significant progresses in computational power makes first-principles prediction of materials possible. Ultrafast lasers can now probe materials both at sub-femtosecond timescale and at atomic or sub-nanometer length scale. In this seminar, I will quickly highlight a few notable accomplishments in the field within the context of establishing multiscale-multiphysics simulation and characterization platforms for the study of phonon transport and thermal conductivity in nanostructured materials.

  Atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques with atomic level control enable a new class of hybrid organic–inorganic materials with improved functionality. The cross-plane thermal conductivity and volumetric heat capacity of three types of hybrid organic–inorganic zincone thin films fabricated by MLD and alternate ALD/MLD processes were measured. We revealed the critical role of backbone flexibility in the structural morphology and thermal conductivity of MLD zincone thin films by comparing the thermal conductivity of MLD zincone films with an aliphatic backbone to that with aromatic backbone. This work suggests that dramatic material difference between organic and inorganic materials may provide a route for producing materials with ultralow thermal conductivity.

  Coupled with its low thermal conductivity, polymer thermoelectric composites are attractive for energy harvesting and localized cooling where temperature gradients are moderate, surfaces are irregular, toxic or rare elements are avoided, and low-cost processing is preferred. Though great progresses have been made for p-type polymers with a thermoelectric figure of merit (ZT) up to 0.42, there has been a paucity of unipolar n-type composites for this purpose. I will report the measurement and the understanding on the low thermal conductivity of an n-type flexible hybrid TiS₂-organic superlattice showing ZT > 0.1, making possible the realization of flexible thermoelectric devices for wearable electronics, with both n- and p-type materials available.

参考文献：

1. X. Gu, X. Li, and R. G. Yang, Phys. Rev. B, 91, 205313 (2015).
2. X. Gu and R. G. Yang, J. Appl. Phys. 117, 025102 (2015).
3. C. Wan, X. Gu, F. Dang, T. Itoh, Y. Wang, H. Sasaki, M. Kondou, K. Koga, K. Yabuki, G. Snyder, R. G. Yang, and K. Koumoto, Nature Mater. 14, 622 (2015).
4. K. M. Hoogeboom-Pot, et al., PNAS 112, 4846 (2015).
5. J. Liu, B. Yoon, E. Kuhlmann, M. Tian, X. Gu, S. George, Y. Lee, and R. G. Yang, Nano Lett. 13, 5594 (2013).
6. M. Siemens, et al., Nature Mater. 9, 26 (2010).

个人简介：

• 2001-2005，MIT，博士 
• 2005-2011，美国科罗拉多大学博尔德校区，助理教授
• 2011-现在，美国科罗拉多大学博尔德校区，副教授(tenured)