Nanoscopic detection of anisotropic heat transports

Thin layers 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 layers contribute to the basic functionality of a number of technical components (e.g. microelectronic devices and MEMS), their thermal characteristics are of very high interest, important for the efficient operation and reliability. Especially thermal conductivity measurements on organic thin film devices have attracted significant attention within the last years, because the device operating temperature influences both: lifetime and performance. Temperature changes in organic electronic devices may induce shifts in the material band gap, induce thermo-mechanical failures, increase transport mobilities under variable range hopping (amorphous materials), or decrease mobility under band-type transport (crystalline materials). However, commonly used techniques for thermal conductivity measurements are limited either in spatial resolution or in directional analyses of the heat transport. The thermal conductivity is just regarded as a scalar quantity in examinations of the heat flow through a layer and in in-plane heat transport investigations. Nevertheless, the heat transport can either be anisotropic or has nonlinear characteristics at interfaces.

Therefore, the local detection of the anisotropic heat transport by means of Scanning Near-field Thermal Microscopy techniques is the focus of this project. Thermal transport mechanisms of thin conducting, semiconducting, as well as dielectric films and interfaces will be evaluated quantitatively in all three directions in space with highest spatial resolution for the first time. Thus, this technique gives access to the directional heat transport mechanism of interfaces, e.g. nonlinear thermal characteristics, and can be usefully be applied for research activities on nanostructured multilayers. The non-destructive recognition of amorphous as well as crystalline structures in organic and inorganic thin films is one target within the frame of this project. Thereby, entirely new and innovative perspectives on failure analyses and reliability investigations of prospective devices will open up, e.g. thermal studies of gas diffusion barriers and injection layers in organic light emitting devices or organic solar cells. In addition, thermophysical considerations on nanosystems can be explored and verified by measurements previously performed only by simulations. Finally, limits of classical heat conduction laws at nanoscale dimensions can be discovered.

13.02.2014 - 12.02.2017

Dr. R. Heiderhoff

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