Microstructure of iron thin films evaporated at oblique incidence

Evaporated iron thin films of thickness in the range 250 to 3400 Å were deposited on plastic films at oblique incident beam angles φ{symbol}. Using a microtome technique, the microstructure of the films were directly observed by TEM. The nature of the surfaces have been investigated using the RHEED method. At incidence angles of 55 and 65° an elongated wall lies in the direction perpendicular to the incidence angle. At incidence angles of 75 and 80° the structure varies along the thickness direction of the film and columns are approximately oriented to the [001] axis. Although the columnar angle α_s does not follow the tangent rule 2 tan α_s = tan φ{symbol}, the packing density of the film is as expected from the columnar angle. TEM observations and the RHEED method also reveal the process of crystal growth during deposition. The growth of columns appears to be determined by the geometric shadowing effect and the diffusion of adatoms.