Thermal conductivity of plasma deposited amorphous hydrogenated boron and carbon rich thin films

Abstract Owing to a unique combination of low density, high mechanical stiffness, and high neutron capture cross section, boron rich solids are of interest for a number of applications ranging from fusion shielding and neutron absorbing materials to solid state neutron detection. In many of these applications, the boron containing materials may be exposed to extreme temperatures and thermal gradients where heat dissipation is a significant concern. While there have been several reports of the thermal conductivity for crystalline boron solids, comparitively little is known regarding the thermal conductivity for amorphous boron thin films used in many nuclear applications. In this investigation, we report time-domain thermoreflectance (TDTR) measurements for a series of plasma deposited boron rich thin films with nominal compositions of a-B:H and a-BP:H. The results were compared to additional measurements performed on a-C:H films with similar mass density and which are also utilized as fusion plasma shielding materials. The values of thermal conductivity determined by TDTR for the a-B:H and a-BP:H films ranged from 1 to 2 W/mK. These values are reduced relative to those reported for crystalline boron (4–400 W/mK) but compare well to those obtained for a-C:H (0.5–1.5 W/mK).