Effect of surface energy on the growth of boron nanocrystals

Abstract

The surface energies of α-rhombohedral (α-rh), β-rhombohedral (β-rh), α-tetragonal (α-t), and β-tetragonal (β-t) boron were calculated from first principles to investigate their role in nano-scale crystal growth. Equilibrium shapes of boron crystals were obtained using Wulff's theorem. Our results shows that α-t boron, despite its low cohesive energy, is more stable than the other structures as a result of its low surface energy when the number of atoms is less than about 216. Since the nanowire of α-t boron that was obtained experimentally was larger than this, it was probably in a metastable state. The difference between the surface energy of the ab-plane and that of the ac-plane explains why the α-t nanowires grow in the c direction.