Photon Factory Activity Report 2004 #22 Part B (2005)
Surface and Interface

7A, 11A/2004G326

X-ray photoelectron diffraction study for structural determination ofcobalt thin films on the Pd(111) surface
Daiju MATSUMURA, Kenta AMEMIYA, Toru SHIMADA, Jun MIYAWAKI,Hitoshi ABE,
Takumi OTSUKI, Enju SAKAI, Toshiaki OHTA*Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo,
Bunkyo-ku, Tokyo 113-0033, Japan
Introduction
The structural determination of ultrathin magnetic films
deposited on a non-magnetic substrate is of a fundamental
importance for understanding the magnetic properties ofsuch systems. Some magnetic thin films such as Fe on theCu(001) substrate have been widely investigated to reveal
the relation between the structure and the magneticproperty. Co thin films prepared on the Pd(111) substrate
are known to have a perpendicular magnetic easy axis at athickness of under 4 monolayer (ML). Recently, we foundthat the molecular adsorption enhances the perpendicularmagnetic anisotropy under a certain condition [1]. There
are some other parameters of the thin films that affect themagnetic anisotropy. Especially the anisotropy in thestructure might strongly affect the magnetic anisotropy
due to the magnetostriction although the precise structure
is not well understood in this system. X-ray photoelectron
diffraction (XPD) is a powerful tool to determine thesurface structures. In this study, we have applied thismethod for the magnetic thin film structures in order toclarify the relation between the structure and the magnetic
anisotropy in the magnetic thin film of Co/Pd(111).

temperature and atmospheric pressure, while palladiumshows a fcc structure. From the Fig. 1, we can observe a
typical threefold symmetry in the Co 2p photoelectron
intensities. This indicates that the Co thin films show a
fcc structure due to the epitaxial growth on the Pd(111)substrate.
We also took the photoelectron diffraction images atseveral other photon energies and observed several photon
energy dependent oscillations at some electron emission
angles. The analyses of those spectra are now in operation.
Reference[1] D. Matsumura et al., Phys. Rev. B, 66, 024402 (2002).
* ohta@chem.s.u-tokyo.ac.jp

Experiments
Sample preparation and all the spectral measurements
were carried out under an ultrahigh vacuum condition. APd(111) substrate was cleaned by the repeated cycles of+
Ar sputtering and successive annealing. The Co thinfilms were deposited on the Pd(111) substrate by theelectron bombardment method at room temperature. Co
2p photoelectrons were collected with the hemisphericalelectron analyzer (GAMMADATA-SCIENTA, SES-2002).
The intensities of the emitted electrons were measured asfunctions of polar and azimuthal angles by rotating thesample both in polar and azimuthal directions, while theelectron analyzer was set at the fixed position.
Results and discussion
Figure 1 shows the full hemispheric images of Co 2p
photoelectron diffraction intensities from the Co 6 ML
thin film on the Pd(111) substrate. Photon energy wasfixed to 1200 eV in this case. Since the photon energy issufficiently high, the forward scattering contributes to theintensities dominantly. The photoelectron intensities
simply indicate the atomic positions under the conditionof the dominant forward scattering and the structures ofthe thin films can be determined without complicatedanalysis. Cobalt shows a hcp structure at room-<112><211>

Fig. 1. Full hemispheric Co 2p XPD pattern of the 6 ML
Co thin film on the Pd(111) substrate. The XPD
intensities are expressed by a color scale in whichbrighter spots indicate higher intensities. The center ofthe circle corresponds to the surface normal direction
for the emitted electrons.

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