Nanoscopic detection of anisotropic heat transports (follow-up application)

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 nanosystems 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.

Duration: 1.11.2018 - 31.10.2021

Projectleader: Dr. R. Heiderhoff