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

13C/2004G028

Experimental Determination of Electron Effective Attenuation Lengthin Al Thin Film
Motoyasu IMAMURA*1, Nobuyuki MATSUBAYASHI1, Eiichi KOBAYASHI2
1
AIST, Tsukuba, Ibaraki 305-8565, Japan
2
KEK-PF, Tsukuba, Ibaraki 305-0801, Japan

Results and Discussion
Figure 1 shows the XPS spectra of the Al thin film
excited by various energy. Al2p peak from the film andSi2p peak from the substrate appear, whose intensities
varies with the excitation energy. The change of therelative intensities of the peaks is caused by the change ofthe analysis depth which reflects the EALs of the Al. TheEALs were calculated using the peak intensities of Al2p
and Si2p peaks.
Figure 2 shows the EALs as a function of the kinetic
energy of the electron determined from the intensities of
the XPS spectra of thin film, comparing to the theoreticalvalues calculated from the NIST database. The EALs
determined from the spectra agreed with those calculated

Al2p
Si2p
Photoelectron Yield (a.u.)

Experimental
The Al thin film was fabricated by evaporation in ahigh vacuum chamber. The Si(111) plate was cleaned by
H2SO4 /H2O2 and 5%-HF solution and vacuumed in theload-lock chamber. After evacuation for a night, thesample was transferred to the evaporation chamber. Al
was evaporated on the Si(111) plate in the preparationchamber using a K-cell. The temperature of the crucible
was set at 1370K. The pressure during evaporation was-5
1x10 Pa.
SR-XPS measurements were performed at beamline
13C of the Photon Factory. The energy resolution wasabout 3000 for x-ray energy below 500 eV, and was about
1500 for x-ray energy over 500 eV. Photoelectron spectra
were measured by using a hemispherical analyzer (PHI1600C). The angle between analyzer axis and surface
normal was 55°. The analysis area was circular with adiameter of 0.8 mm, and the analyzer acceptance angle
was ±7°.

from the database in the region above 400 eV. However,in the region below 400 eV, EALs determined form thespectra show higher values than the calculated EALs.
The difference might be caused by the elastic scatteringof the electrons in the thin films, which is not consideredin the calculation model of the database.

(d) hν=850eV(c) hν=750eV(b) hν=550eV(a) hν=250eV
110

1009080Binding Energy (eV)70

Fig.1 XPS spectra of Al/Si(111) thin film.
2.0
experiment
theory1.5
EAL (nm)Introduction
Values of effective attenuation lengths (EALs) ofelectrons are needed in quantitative investigations byAuger electron spectroscopy (AES) and x-ray
photoelectron spectroscopy (XPS). The inelastic mean
free paths (IMFPs) are often used for this purpose, withIMFPs obtained from optical data or a predictive formula.
However, recent calculations have shown that elastic
electron scattering is not negligible .
In this study, we measured EALs of photoelectrons ofvarious energies in Al thin films using synchrotron
radiation (SR) as an excitation source and compared theseEALs with calculated EALs.

1.00.50.00200
400600800
Kinetic Energy (eV)1000

Fig.2 EALs determined from the XPS spectra
and calculated by the NIST database.

* e-mail : motoyasu@ni.aist.go.jp

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