Chemical Vapor Deposition of Diamond Directly on MgO Substrates without Surface Pretreatment

Direct diamond growth without pretreatment was demonstrated on MgO single-crystal substrates with (111), (110), and (100) surface orientations using microwave plasma chemical vapor deposition. Raman spectroscopy confirmed diamond formation only on MgO (111) and (110) substrates, with growth most pronounced on MgO (111), where the nucleation density exceeded 10⁸ cm⁻², leading to the formation of a free-standing diamond film. This orientation-dependent growth behavior was attributed to the polarity of the MgO crystal structure, as the (111) polar surface possesses a larger surface energy than the other orientations. Density functional theory calculations of CH₃ radical adsorption energies on MgO surfaces further supported this, showing that the (111) surface had the largest adsorption energy. The present study demonstrates that diamond can be grown directly on insulating materials without pretreatment, thereby expanding the range of substrate materials suitable for diamond growth.