Reflection high-energy electron diffraction study of the growth of NiO and CoO thin films by molecular beam epitaxy

Abstract

NiO thin films have been prepared under UHV conditions by metal evaporation on both ex-situ and in-situ cleaved MgO(100) using O 2 and NO 2 as oxidants. Changes in the film morphology are monitored with reflection high-energy electron diffraction (RHEED). While it is possible to grow films epitaxially using O 2, we find films grown using NO 2 to be of superior quality. Using NO 2 as an oxidant, films synthesized between 200 and 450°C grow layer by layer, while an increase in surface disorder is observed in films grown below 200°C. Pronounced RHEED intensity oscillations are observed for 200 < T < 450°C, allowing for the measurement of film thickness. We also observe RHEED intensity oscillations at room temperature when NiO thin films grown at high temperatures are used as a substrate. The general form of the oscillations and associated changes in the RHEED pattern (and thus surface morphology) are markedly different at this low temperature We also report results of CoO epitaxial growth on MgO(100) using NO 2 as an oxidant.