Defect clustering and self-healing of electron-irradiated boron-rich solids

Transmission-electron-microscopy observations are used to evaluate damage produced by irradiating boron-rich metals, semimetals, and semiconductors of three different structure types with energetic electrons. The propensity for damage increases with decreasing carrier concentration except for borides based on twelve-atom icosahedral units. In these semiconducting icosahedral borides neither defect clusters nor amorphorization were observed. In accord with studies of other icosahedral borides, we conclude that radiation-induced boron vacancies and interstitials self-heal in icosahedral borides. We explain this self-healing as having its origin in the unusual structural and electronic stability of fragments of boron-rich icosahedra, termed degraded icosahedra.