Barrier height imaging of magnetic films: Use for studying the initial growth of Co films and the surface structure of FePt films

Barrier-height (BH) imaging using scanning tunneling microscopy (STM) was used to study the growth of Co films on Au(001) surfaces. We have observed BH of metastable bcc Co film (>1ML) for the first time, and that showed a large BH value (~6eV), whereas the observed BH of the Au(001) surface (~3.5eV) was consistent with the previous results. The origin of the large BH was qualitatively understood by considering that 3d electrons for tunneling are dominant for the Co(001) surface. We have observed numerous islands with different sizes and heights after 0.15ML Co coverage and successfully obtained, from the BH imaging, an element-specific contrast, i.e. recognizing aggregated Au islands and Co islands, and information about inhomogenities of BH with proper consideration of the artifacts near the step edges. The height modification by the large BH difference is discussed. STM/BH studies of FePt films revealed two kinds of monolayer heights, the sum which was equal to the c axis lattice constant of L10 FePt. Two different dI/dz signal levels were observed on atomically flat terraces. ► We used STM/BH imaging for studying growth of bcc Co films on Au(001). ► The BH of metastable bcc Co film was observed for the first time. ► It showed a large BH value (~6eV) and the origin was also discussed. ► Aggregated Au islands and Co islands were recognized in the observed BH image. ► STM/BH studies of FePt films were also reported.