Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

27A/2003G254

Study on ion-irradiation induced diffusion in Pd/Si system using synchrotron
radiation x-ray photoelectron spectroscopy
A. Iwase1*, Y. Chmi2, N. Ishikawa2, R. Nakatani1, Y. Kato1, M. Fukuzumi1, H. Tsuchida3, Y. Baba2
1
Osaka Prefecture University, Sakai-shi, Osaka, 599-8570, Japan
2
Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki, 319-1195, Japan3
Kyoto University, Kyoto-shi, 606-8501, Japan
Introduction
It is well known that solute atoms in metal matricesdiffuse more rapidly under irradiation field than under thethermal equilibrium condition. This phenomenon is called“radiation induced (or enhanced ) diffusion”, and has
been explained as due to the interaction between soluteatoms and radiation-produced defects[1,2]. To examine
the electronic structure and chemical bonding state forsolute atom segregation region, we have recently started
experiments of an x-ray photoelectron spectroscopy for
ion-irradiated Si-metal systems by using a synchrotron
radiation facility. Synchrotron radiation photoelectron
spectroscopy is a good tool for the study of electronic andchemical properties of material surfaces because of thewide range selectivity of high flux x-rays. In this paper,
we report the result of the x-ray photoelectron
measurement for Si-Pd system irradiated with 1MeV
oxygen ions.

segregation of Si atoms at the surface of Pd film. The
shift of Si 1s binding energy to a higher value suggests a
chemical interaction between Si and Pd atom at surface; i.
e., a charge transfer from Si atom to Pd atom. We
performed the RBS measurements both for theunirradiated Pd(100nm)/Si and the ion-irradiatedspecimen, but we never found any effect of irradiation on
RBS spectra. The Si atom segregation at Pd surface wastoo small to detect by RBS measurement. The present
result shows that synchrotron radiation photoelectron
spectroscopy is a very powerful tool to detect a small
amount of irradiation-induced diffusion/segregation andto study the details in chemical status of radiationinduced segregation.
References[1] L. E. Rehn, P. R. Okamtoto, in Phase Transformations
during Irradiation, ed. F. V. Nofli, Jr., (Applied SciencePublications, London, 1982) p. 247.
[2] V. Naundorf, Int. J. Mod. Phys. B6(1992) 2925.

Experimental procedure
Si single crystals were coated with Pd by using rf
magnetic sputtering. The Pd film thickness was about 100
nm. The specimens were irradiated from the side of Pd
film at room temperature with 1MeV O ions to the162
fluence of 1x10 /cm using 1.7MV Pelletron accelerator
at Nara Women’s University. For the irradiatedspecimens, x-ray photoelectron (XP) spectra weremeasured at the end station of the 27A beam line at HighEnergy Accelerator Research Organization (KEK). The
monochromated photon energy for the measurements wasjust 2200.0 eV. For comparison, we also performed thesame measurements for unirradiated Pd(100nm)/Sispecimen, unirradiated Si crystal and Si crystal irradiatedwith 1MeV O ions. The incident angle of the x-ray waso
35 from the specimen surface normal, and thephotoelectrons of surface-normal emission were collected.
Results and discussion
Fig. 1a shows the XP spectra for the unirradiatedPd(100nm)/Si specimen. We cannot find any trace of XPspectra for Si bulk or SiO2 layer. This result is quite
reasonable because photoelectrons come only from a few
layers of Pd film. The XP spectrum for Pd(100nm)/Siirradiated with 1 MeV O ions is shown in Fig. 1b. As canbe seen in the figure, an XP peak appears at the binding
energy of 1844.0 eV, which is 3.0 eV higher than that ofbulk Si. The experimental result can be explained asoriginating from the diffusion of Si atoms from Si
substrate under the irradiation and the resulting

130

Users' ReportFig. 1 (a) X-ray photoelectron spectrum for unirradiatedPd(100nm)/Si. (b) X-ray photoelectron spectrum forPd(100nm)/Si irradiated with 1 MeV O ions to the162
fluence of 1x10 /cm .
* iwase@mtr.osakafu-u.ac.jp