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By: Aitor Lopeandía Fernández
UAB Senior Researcher and member of the ICN2 Thermal Properties of Nanoscale Materials Group

Abstract:
We have recently developed a modification of the 3ω-Völklein technique that operating at low frequencies shows an exceptional resolution in the determination of the in-plane thermal conductance of ultrathin films, down to D(K·t)=0.065·nm·W/(m·K). The extreme sensitivity of the technique permits to use the phonons as sensitive probes to monitor the thin film growth of vapor deposited films, determining in real time the evolution of films microstructure during growth, from incipient clustering to continuous film formation.
Here we show the principle of the methodology and its application to measure the in-plane thermal conductivity of small molecule and polymeric thin films. We anticipate that the described methodology may provide a suitable and efficient approach to determine the in-plane thermal conductivity of both vapor-deposited or solution-processed organic materials. As an example, we will show how the thermal conductivity of vapor deposited thin-film semiconductor glasses is anisotropic and controlled by the deposition temperature. The extreme sensitivity has allowed to find that molecular orientation heavily influences heat flow propagation in glassy films of small molecule organic semiconductors.