Defect assisted thermal synthesis of crystalline aluminum borate nanowires
I. Gonzalez-Martinez, A. Bachmatiuk, S. Gorantla, J. Kunstmann, V. Bezugly, T. Gemming, B. Büchner, G. Cuniberti, and M. H. Rümmeli
Journal of Applied Physics 112, 024308 (2012)
Aluminum borate is attractive in that the material has excellent mechanical properties, chemical inertness, high temperature stability, and a low coefficient of thermal expansion. Moreover, aluminum borate has advantages over a more traditional material, SiC, in that it does not readily oxidize at high temperature and can be produced at lower cost. In this study, we demonstarte a facile route to grow single crystal aluminum borate nanowires directly on bare sapphire surfaces without the need for a catalyst. Our findings point to a growth mechanism in which lattice defects allow B or B2O2 diffusion. The nanowire formation occurs as a means to relieve residual stress that arises due to thermal expansion mismatch between the aluminum borate and alumina phases. Indeed, at a more local scale, this same stress process facilitates diffussion. By adding iron oxide, which has a high diffusion rate in sapphire, one can accelerate this process. The growth mechanism is fundamentally different to the more usual fabrication routes which employ vapor-solid-liquid or vapor-solid growth processes.