Deuterium diffusion through hexagonal boron nitride thin films

We evaluated the deuterium diffusion coefficient in hexagonal boron nitride (h-BN) thin films deposited by radio frequency magnetron sputtering on metallic substrate. The measurements were carried out by studying the transient of the deuterium permeation flux through substrates coated with h-BN thin films 400 nm thick, for temperatures ranging from 535 to 752 K. The deuterium diffusion coefficient was in the range between 1.4×10−13 and 5.3×10−12 cm2/s and was characterized by an activation energy of 0.52±0.04 eV and pre-exponential factor of the order of 10−8 cm2/s. In steady-state transport conditions the deuterium concentration in the h-BN layers was close to 3×1021 at./cm3. Starting from the earlier data we suggest a model in which the deuterium migration process is controlled by diffusion of D atoms in the volume fraction of the h-BN films relative to grain boundaries, just in connection with the structure of the deposited samples which consists of nanocrystals with 2 nm average diameter.