A low-energy electron diffraction investigation of the surface deformation induced by misfit dislocations in thin MgO films grown on Fe(001)

Abstract

The elastic deformation of the surface of thin MgO films grown on Fe(001) induced by the presence of misfit dislocations at the Fe/MgO interface has been put into evidence using low-energy electron diffraction. Satellite spots surrounding the fundamental Bragg reflections appear once the critical thickness is exceeded and undergo a shift in position as thickness of MgO increases, gradually blending in with the fundamental reflections. The evolution of the position of the spots is in good agreement with kinematical diffraction calculations in which the surface deformation is determined from the displacement field of a single misfit dislocation using both isotropic and anisotropic elasticity theory.

Structure and morphology of thin MgO films on Mo(001)

“…The splitting decreases with increasing thickness and temperature, indicating the progressive flattening of the tilted surface areas due to relaxation, in accordance with the observations on MgO/Fe͑001͒ and MgO/Ag͑001͒. 3,4 Furthermore, with increasing thickness an additional broadening appears along the ͗110͘ MgO directions, particularly evident above 10 ML thickness ͓Fig. 3͑c͔͒.…”

“…16 For MgO on Fe͑001͒ and Ag͑001͒, the appearance of a surface tilting in LEED parallel to the ͓100͔ direction is attributed to the formation of ͓100͔ dislocations by the glide system 1 2 ͓110͔͑110͒. 3,4,12 The long-range order of the dislocation network is, however, not discussed in those papers. Additionally the lattice mismatch with the MgO is rather small for substrates such as Ag ͑−3.2%͒ and Fe ͑+3.8%͒, compared to the present case.…”

“…These mechanisms have been investigated extensively for semiconductors and metals, while few works give detailed insights into the relaxation of thin oxide films grown on metallic surfaces. 3,4 MgO is a suitable model oxide to study strain relief because of its stable and inert character and its simple rocksalt structure. In addition, MgO thin films are used as support in heterogeneous catalysis and in magnetoelectronic devices, and a good understanding of their relaxation behavior is therefore required to improve such applications.…”

Self-organized nano-structuring of CoO islands on Fe(001)

“…Similar effects have been reported in several other cases, related to oxide films characterized by the development of a misfit dislocation network, and were attributed to the surface mosaic spread (i.e. to the local tilting of the surface) [10,11,50,51,53,54].…”

Growth, structure, electronic, and magnetic properties of MgO/Fe(001) bilayers and Fe/MgO/Fe(001) trilayers

“…The LEED patterns show that the splitting increases proportionally with the electron beam energy. This behavior can be explained by a model which includes edge dislocation formation 10 at the Fe/MgO interface. The MgO lattice warps in a narrow region above the misfit dislocation lines.…”