Preparation of clean MgO surface by oxygen plasma: Comparison with standard substrate cleaning procedures

Different surface preparation methods for cleaning MgO, a widely used substrate in oxide epitaxy, are summarized and compared. We find that in situ surface preparation methods are preferable to ex situ preparation methods. We show that the complete removal of hydroxide, carbonate, and adventitious carbon from the MgO surface can be achieved via oxygen plasma exposure at 200 °C without high temperature annealing. Using this process, an atomically flat surface with root mean square roughness values of ∼0.1 nm is demonstrated. Surfaces treated thus also exhibit sharp RHEED streaks indicating good crystalline order of the surface. We also show that high temperature annealing of MgO, either by itself or following other ex situ cleaning methods, such as solvent cleaning, is a reasonably effective method for the removal of surface contaminants, enabling one to achieve a surface roughness of ∼0.2 nm. We show that wet etching or other ex situ cleaning methods alone without annealing cannot eliminate all surface contaminants and may even worsen the surface roughness significantly.