STRUCTURE AND STABILITY OF FCC FE FILMS ON CU(100) FOR COVERAGES BELOW 5 MONOLAYERS

The strong correlation between magnetism, growth and structure of ultrathin fee Fe films on Cu(100) has caused much interest in these films recently. However, whilst the film structure has been extensively studied in the coverage regime 5 < theta < 10 ml, the structural properties for lower coverages are only poorly known. We present LEED structure determinations of the 4 x 1 and 5 x 1 superstructures observed at coverages 2 and 4 mi, respectively. The results show that different from current assumptions the entire Fe films are heavily reconstructed. Atomic rows in the [110] direction buckle and shift in all iron layers leading to a complex film structure with atomic layers everything else but flat fee (100) layers. So, in the coverage regime theta < 5 ml flat fee (100) layers seem to be unstable and exhibit a highly distorted fee structure. In addition, we find that ail Fe interlayer distances are expanded which is nicely related to the ferromagnetic state of the films.