Review of a Workshop on Thin Film Thermal Conductivity Measurements

On a subject of considerable import to the laser-induced damage community, a two-day Workshop on the topic, Thin Film Thermal Conductivity Measurement was held as part of the Thirteenth Symposium on Thermophysical Properties at the University of Colorado in Boulder CO, June 25 and 26, 1997. The Workshop consisted of 4 sessions of 17 oral presentations and two discussion sessions. Two related subjects of interest were covered: 1) methods and problems associated with measuring thermal conductivity (kappa) of thin films, and 2) measuring kappa of chemical vapor deposited (CVD) diamond. On the subject of thin film kappa measurement, several recently developed imaginative techniques were reviewed. However, several authors disagreed on how much kappa in a film differs from kappa in a bulk material of the same nominal composition. A subject of controversy was the definition of an interface. In the first discussion session, several questions were addressed, a principal one being, how do we know that the values of kappa we obtain are correct and is there a role for standards in thin film kappa measurement? The second discussion session was devoted to a round-robin interlaboratory comparison of kappa measurements on a set: of CVD diamond specimens and several other specimens of lower thermal conductivity. Large interlaboratory differences obtained in an earlier pound robin had been attributed to specimen inhomogeneity. Unfortunately, large differences were also observed in the second round robin even though the specimens were more homogeneous. There was good consistency among the DC measurements, however, the AC measurements showed, much greater variability. There was positive feedback from most of the attenders regarding the Workshop with nearly all respondents recommending another Workshop in three or fewer years. There was general recognition that thin film thermal conductivity measurements are important for predicting the resistance of optical coating materials to laser damage.