We study the effect of characteristic size variation on the phonon thermal transport in crystalline GeTe for a wide range of temperatures using the first-principles density-functional method coupled with the kinetic collective model approach. The characteristic size dependence of phonon thermal transport reveals an intriguing collective phonon transport regime, located in between the ballistic and the diffusive transport regimes. Therefore, systematic investigations have been carried out to describe the signatures of phonon hydrodynamics via the competitive effects between grain size and temperature. A characteristic nonlocal length associated with phonon hydrodynamics and a heat wave propagation length has been extracted. The connections between phonon hydrodynamics and these length scales are discussed in terms of the Knudsen number. Further, the scaling relation of thermal conductivity as a function of characteristic size in the intermediate size range emerges as a crucial indicator of the strength of the hydrodynamic behavior. A ratio concerning normal and resistive scattering rates has been employed to understand these different scaling relations, which seems to control the strength and prominent visibility of the collective phonon transport in GeTe. This systematic investigation emphasizes the importance of the competitive effects between temperature and characteristic size on phonon hydrodynamics in GeTe, which can lead to a better understanding of the generic behavior and consequences of the phonon hydrodynamics and its controlling parameters in low-thermal conductivity materials.
Coherent phonon study of (GeTe)$_{l}$(Sb$_{2}$Te$_{3}$)$_{m}$ interfacial phase change memory materials
在室温和高于RESET-SET相变温度下，对界面相变存储（iPCM）材料（[（GeTe）$_{2}$（Sb $_{2}$ Te $_{3}$）$_{4}$ ] $_{8}$和[（GeTe）$_{2}$（Sb $_{2}$ Te $_{3}$）$_{1}$] $_{20}$）以及常规Ge $_{2}$ Sb $_{2}$ Te $_{5}$合金进行时间分辨反射率测量。在高温阶段，在iPCM样品中清楚地观察到相干声子，而在合金中诱导了相干声子的急剧衰减。这种差异强烈表明，在相变过程中的iPCM的原子重排是远远小于在合金。这些结果是一致的独特的相变模型，其中的准一维位移的Ge原子发生iPCM和常规的非晶-结晶相变发生的合金。
Thermal conductivity of GeTe/Sb$_{2}$Te$_{3}$ superlattices measured by coherent phonon spectroscopy
利用飞秒相干声子谱研究了GeTe/Sb $_{2}$ Te $_{3}$超晶格的晶格热导率。在非晶和晶态GeTe/$_{2}$ SL薄膜中获得的时间分辨瞬态反射率在太赫兹（THz）频率下具有皮秒退相时间的相干$A_{1}$光学模式。基于德拜理论，我们计算了晶格热导率，包括晶界散射、点缺陷散射、umklapp过程和声子共振散射。结果表明，在非晶SL的热导率是较小的温度依赖性，归因于占主导地位的声子缺陷散射。
Crystallization and Vitrification Kinetics by Design: The Role of Chemical Bonding
控制材料在其结晶相和玻璃相之间的状态已经促进了许多现实世界的应用。然而，结晶和玻璃化动力学的设计规则仍然缺乏预测能力。在这里，我们确定这些过程中的相变材料的化学计量的趋势，即沿着GeTe-GeSe，GeTe-SnTe，和GeTe-Sb 2 Te 3伪二进制线采用泵浦-探测激光装置和量热法。我们发现了一个明确的化学计量的依赖结晶速度沿连接区域的两个基本的键合类型，金属和共价键合的线。增加共价使结晶减慢六个数量级，并促进玻璃化。化学计量依赖性与材料性质相关，例如结晶相的光学性质和键指示剂，相邻原子之间共享的电子数。量子化学图谱解释了这些趋势，并提供了设计结晶动力学的蓝图。
Charge Transport in Thin-Film Transistors Based on Liquid-Crystalline Phthalocyanines
Universidade Federal de Santa Catarina（圣卡塔琳娜联邦大学）；Institut national de la recherche scientifique, Centre Énergie Matériaux Télécommunications（国家科学研究研究所，能源材料电信中心）；Centre de Recherche Paul Pascal, Université de Bordeaux & CNRS（保罗·帕斯卡研究中心，波尔多大学与法国国家科学研究中心）
Atomistic simulations of the crystalline-to-amorphous transformation of gamma-Al2O3 nanoparticles: delicate interplay between lattice distortions, stresses, and space charges
