Smoothening of ultrathin Fe films grown on GaAs(100) observed by scanning tunneling microscopy and Brillouin light scattering

We report on an in situ scanning tunneling microscopy study of the growth of Fe on the GaAs(100)-pseudo-4x6 reconstructed surface in the thickness range of 1-4 ML (monolayers). We observe that at 1 ML, the Fe islands have nucleated on the As dimer rows, and that subsequent growth is primarily directed along the [0 (1) over bar1] direction. Initially, the islands are well separated, but as more Fe is deposited, the islands start to coalesce in both the [011] and [0 (1) over bar1] directions. Percolation probably occurs between 2 and 3 ML. Scanning tunneling microscopy studies of a nominally 2 ML thick film over a period of 30 h reveal that the islands relax primarily growing in the [0 (1) over bar1] direction, reducing the roughness of the film. The smoothening of the film is also corroborated by Brillouin light scattering measurements on slightly thicker films of 4.25 and 6.2 ML as evidenced by an increase in the spin-wave frequency and a decrease of the linewidth over a period of 11 h.