Molecular-dynamics study of thin iron films on copper

We have studied the structural stability of thin gamma-iron films on Cu(001) and Cu(111) substrates using molecular-dynamics simulations in combination with a semiempirical model. Experimentally, the stability of such films has turned out to depend on (growth) temperature and film thickness. On increasing the thickness or decreasing the temperature the films undergo a structural change to the bcc structure, which is well reproduced by our simulations. An analysis of the local atomic environment of the films after the structural transformation shows that, especially on Cu(001), only parts of the film accomplish the transformation into the bcc structure. Considerations of the atomic displacements during the transformation allow us to give an explanation of the different stability of the films on Cu(001) and Cu(111) as well as the observed orientational relationships.