Analysis of external surface and internal lattice curvatures of freestanding heteroepitaxial diamond grown on an Ir (001)/MgO (001) substrate

Abstract

We carried out in situ and ex situ observations to investigate the bending behavior of heteroepitaxial diamond grown on Ir(001)/MgO(001) substrates. Observations of the in situ curvature revealed that the substrate was heavily bent toward the convex direction at the growth temperature because of the high coefficient of thermal expansion of the MgO substrate. The substrate curvature was approximately −1100 km−1 at 1300 K. Thus, the coalescence of diamond was conducted on the heavily convex-shaped Ir/MgO substrate surface. During the growth, the accumulation of tensile stress was observed. The lattice curvature was speculated to be changed during the growth with increasing growth thickness. This behavior indicated that the lattice curvature was not always parallel to the physical curvature. After the growth, the freestanding diamond sample was physically convexly bent (approximately −8500 km−1 for top surface). The lattice curvature was also bent convexly corresponding to this physical change; however, the lattice curvature at the top surface region of diamond films was found to be −3900 km−1, which was much smaller than the physical curvature.