NiO thin film with an extremely high index (7(1)over-bar4) on r-plane sapphire substrate

Thin film epitaxy is essential for state-of-the-art semiconductor applications. The combination of different substrates and deposition methods leads to various crystallographic orientation relationships between thin films and substrates, which have a decisive impact on thin film performance. By utilizing pulsed laser deposition, we discovered a very high-index (7 (1) over bar4)-oriented NiO thin film when deposited on r-plane (10 (1) over bar2) sapphire substrates. The in-plane epitaxial relations are [13 (1) over bar] NiO||[1 (2) over bar 10](Sapphire) and [(1) over bar 12] NiO ||[10 (1) over bar1](Sapphire), and the lattice mismatch is 3.2% and 0.4% along two directions, respectively. Exchange bias studies by the deposition of Co on NiO (111) and NiO (7 (1) over bar4) show different behaviors, which may be associated with the spin density and alignment on the surface.