Tuning of Surface Roughness and Lattice Constant in MgO(111)/Al2O3(0001) Grown by Laser Energy Controlled Pulsed Laser Deposition

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We have studied the effect of variable laser energy on pulsed laser deposition (PLD) grown MgO(111) films on Al2O3(0001) substrates by X-ray diffraction and reflectivity measurements, atomic force microscopy and reflection high energy electron diffraction. In spite of the polar instability of MgO(111) surface, the surface roughness drastically decreases from ${\sim}2$ to ${\sim}0.5$ nm as the laser energy increases from ${\sim}50$ to ${\sim}150$ mJ. The in-plane lattice constant is larger than the bulk value at the smaller laser energy while it is smaller than the bulk value at the larger laser energy. This indicates that the balance between the electrostatic energy due to the polar structure, which favors a larger in-plane lattice constant, and the interface epitaxial strain, which favors a smaller in-plane lattice constant in MgO(111)/Al2O3(0001), can be tuned by varying the laser energy in PLD.
2011-08-25