A study of growth and the relaxation of elastic strain in MgO on Fe(001)

The deposition of MgO on the Fe(001) surface at room temperature and at elevated temperatures has been carried out using molecular beam epitaxy (MBE). MgO is observed to grow epitaxially with a 45 degrees rotation between the Fe(001) and MgO(001) unit cell axes. The growth mode has been studied as a function of temperature using reflection high-energy electron diffraction (RHEED), while the chemical and structural characteristics of the MgO film have been studied using Auger electron spectroscopy and high resolution electron microscopy. The relaxation of the in-plane lattice parameter during growth at room temperature has been measured in situ using RHEED and ex situ using glancing incidence x-ray diffraction and during growth at elevated temperatures by means of RHEED. Pseudomorphic growth is observed up to a thickness of 4-5 monolayers, after which the in-plane lattice parameter starts to evolve towards the MgO bulk parameter as 1/2[011] misfit dislocations are introduced at the Fe/MgO interface. The degree of relaxation as a function of epilayer thickness is compared with that expected for an equilibrium dislocation spacing in an array of dislocations of alternating orientation, and with that predicted by Freund's criterion for the blocking of a threading segment by an orthogonal misfit dislocation [J. Appl. Phys. 68, 2073 (1990)]. (C) 1996 American Institute of Physics.