Nanoscopic detection of anisotropic heat transports

薄膜由于其优异的电子、光学和机械性能，在广泛的技术应用中变得越来越重要。由于这些薄膜的热特性有助于许多技术组件（例如微电子和热电子器件或MEMS）的基本功能，因此它们的热特性是最感兴趣的。特别是，薄膜器件的热导率测量近年来引起了人们的极大关注，因为器件的工作温度影响寿命和性能。然而，常用的技术来评估导热系数是有限的，无论是在空间分辨率或关于热传输的方向分析。导热系数通常被简单地看作是一个标量性质。然而，热传输可以是各向异性的，也可以有一些非线性的贡献在interfaces.It已被证明在本项目的第一阶段，各向异性的跨平面和平面内的热传输在薄膜可以成功地研究与扫描热显微镜（SThM）。热传输特性，以前只能通过模拟，例如Stefan-Boltzmann传输方程，第一次被实验证明。弹道输运机制已被证明在膜厚度显着大于平均自由声子路径长度，这是在矛盾的通常的宏观diffusivedescription.Therefore，在该项目的第二阶段，我们申请，在这里，非晶和多晶层的静态和动态的热输运性质的定量研究与最高的空间分辨率依赖于温度。一方面，铅卤化物钙钛矿薄膜将被考虑，这是目前非常感兴趣的应用，如太阳能电池，LED和激光器。最有利的是，它们通过适当选择它们的阳离子和卤素来获得取决于晶体结构、维度和晶体取向的热导率。同样地，热传输研究在晶界处是可访问的，由此。另一方面，由原子层沉积产生的分层结构提供了在多层系统的界面处和从二维到三维热传导的过渡处的定向热传递机制的通路。因此，全新的和创新的前景器件的失效分析和可靠性调查的观点将打开。此外，对纳米系统的热物理考虑迄今为止仅在理论上进行了研究，现在可以通过测量进行探索和验证。最后，在低维系统的经典热传导定律的限制将被发现。

Thin films are becoming more and more important in a wide range of technical applications due to their outstanding electronic, optical, and mechanical properties. Since the thermal properties of these thin films contribute to the basic functionality of a number of technical components (e.g. micro- and thermo-electronic devices or MEMS), their thermal characteristics are of uttermost interest. Especially, thermal conductivity measurements on thin film devices have attracted significant attention within the recent years, because the device operating temperature influences both: lifetime and performance. However, commonly used techniques to assess thermal conductivity are limited either in spatial resolution or with regard to directional analysis of heat transport. The thermal conductivity is often simply regarded as a scalar property. Nevertheless, the heat transport can either be anisotropic or may have some nonlinear contributions at interfaces.It has already been demonstrated within the first phase of this project that anisotropic cross-plane and in-plane thermal transport in ultrathin films can be studied successfully with Scanning Thermal Microscopy (SThM). Heat transport characteristics, that were previously accessible only by simulations, e.g. the Stefan-Boltzmann transport equation, were evidenced experimentally for the first time. Ballistic transport mechanisms have been demonstrated at film thicknesses significantly larger than the mean free phonon path lengths, which is in contradiction to the usual macroscopic diffusive description.Therefore, in the second phase of the project, that we apply for, here, the static and dynamic thermal transport properties of amorphous and polycrystalline layers are quantitatively studied with highest spatial resolution in dependence on the temperature. On the one hand, thin film of lead-halide perovskites will be considered which are of great current interest for applications such as solar cells, LEDs and LASERs. Most favorably, they grant access to the thermal conductivity in dependence on the crystal structure, the dimensionality, and the crystal orientation by suitable choice of their cations and halogens. Likewise, heat transport investigations are accessible at grain boundaries, hereby. On the other hand, layered structures, produced by atomic layer deposition, provide access to the directed heat transfer mechanisms at interfaces of multilayer systems and at the transitions from two-dimensional to three-dimensional heat conduction. Thereby, entirely new and innovative perspectives on failure analyses and reliability investigations of prospective devices will open up. In addition, thermo-physical considerations on nano-systems which were as of yet only studied theoretically, can now be explored and verified by measurements. Finally, limits of classical heat conduction laws at low dimensional systems will be discovered.