Activation energies and reaction paths for diffusion and nucleation of mono- and divacancy defects in hexagonal boron nitride layers were theoretically investigated. Migration paths were derived using the nudged elastic band method combined with density-functional-based techniques. A different behavior was found for the migration of single B and N vacancies with the existence of intermediate metastable states along the migration paths. The temperature dependence of entropic and vibrational contributions to the free Gibbs energies was explicitly taken in account. A rich phase diagram for vacancy migration was then obtained. Boron vacancies were first thermally activated and could migrate to form more stable BN divacancies. At high temperatures, the divacancies could further be activated. In the contrary, N vacancy migration was energetically unfavorable within all the temperature range below the melting point of h-BN.

Vacancy Migration in Hexagonal Boron Nitride. A.Zobelli, C.P.Ewels, A.Gloter, G.Seifert: Physical Review B, 2007, 75[9], 094104 (7pp)