Boundary scattering in five natural type-IIadiamonds

The thermal conductivity in the boundary scattering region of five type-II $a$ diamonds with different surface finishes was investigated. With polished surfaces the boundary scattering was found to be nearly temperature independent but with a phonon mean free path two to three times the Casimir value. After a chemical etch or a high-vacuum high-temperature anneal the scattering became temperature dependent, and the conductivity was more in agreement with the height of the surface asperities. It is suggested that in polished diamonds the phonons interact with the strain field associated with the network of microcracks underneath the abraded surface.