Electronic states of the interfacial cobalt on Co/N/Cu(001) surfaces

Nakatsuji, Kan; Takagi, Yasumasa; Yoshimoto, Yoshihide; Tomatsu, Kota; Yaji, Koichiro; Iimori, Takushi; Harada, Yoshihisa; Tokushima, Takashi; Takeuchi, Tomoyuki; Takata, Yasutaka; Shin, Shik; Ishikawa, Tetsuya; Komori, Fumio Japan

When cobalt is deposited on a nitrogen saturated Cu(001) c(2×2)-N surface, the exchange of Co and substrate Cu atoms is inhibited and the N atoms segregate on top of the Co nano-islands according to the recent scanning tunneling microscopy (STM) and x-ray photoelectron spectroscopy studies[1]. This will lead to the ideal Co/Cu interface without intermixing between them in contrast to that in the case of Co on a clean Cu(001) surface. To explore the 3d occupied electronic states of interfacial Co in the initial growth process, soft x-ray photoemission spectroscopy (XES) would be a powerful tool because of its ability of element specific measurements. In the present study, we will show the electronic states of this interfacial Co measured by XES and their qualitatively good correspondence with those obtained by the first-principles calculation.
The experiments have been done by using horizontally polarized incident light at the beamline 27SU at SPring-8 at the photon energies of 777.5eV and 810eV which can excite the Co 2p core level in resonant and off-resonant conditions, respectively. We examined the Co films on N-saturated Cu surface at 0.25 mono-layer (ML), 0.5ML, and 2.0ML on average. From the STM observations, mono- and two- atomic height islands exist at 0.25ML whereas at 2ML, almost all the surface is covered by two- or three-atomic height film. The XES spectra show the peak energy shift to the higher energy side and the reduction of the peak width with the decrease of the Co coverage. The observed spectrum can be deconvoluted into three gaussian components; two of them have their peak positions at lower energies with wider widths and another has a peak at higher energy with narrower width. The intensity of the latter decreases with the increase of Co coverage, which suggests that this component originates from the mono-atomic height Co islands whereas the former from the two-atomic height islands. These experimental results qualitatively well correspond to the calculated Co 3d partial density of states of mono- and two- atomic height Co layers with N on top of them obtained by the first-principles calculations.
[1] D. Sekiba et al., Surf. Sci. 590 (2005) 138.

---

back