Growth and Crystal Orientation Regulation of Aluminum Diboride Films Induced by an Al Template

A series of aluminum diboride (AlB2) films were grown on sapphire and Si(111) substrates by molecular beam epitaxy, using a single crystalline Al template to induce the AlB2 growth. The crystal orientation of the as-grown AlB2 films is (100), and appropriate post-annealing can promote atom rearrangement and change the orientation from (100) to (001), which may be attributed to the better lattice matching between AlB2(001) and the Al template. The orientation regulation and charge transfer during this process are confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. A chemically more stable structure is achieved. The anisotropic thermal property of AlB2 is measured by time-domain thermoreflectance, and a factor of 2 increase in thermal conductivity is observed when the crystal orientation is changed from (100) to (001). This work reports an approach to utilize an Al template to grow AlB2 films and regulate the crystal orientation in such layered materials.