Journal of Electron Spectroscopy and Related Phenomena 197 (2014) 80–87
Contents lists available at ScienceDirect
Journal of Electron Spectroscopy and
Related Phenomena
journal h om epa ge: www.elsevier.com/ locate/elspec
New method for the determination of the correction function of a
hemisperical electron analyser based on elastic electron images
Mohamed Aymen Mahjoub
a,b
, Guillaume Monier
a,b,∗
, Christine Robert-Goumet
a,b
,
Luc Bideux
a,b
, Bernard Gruzza
a,b
a
Clermont Université, Université Blaise Pascal, Institut Pascal, BP 10448, F-63000 Clermont-Ferrand, France
b
CNRS, UMR 6602, IP, F-63171 Aubière, France
a r t i c l e i n f o
Article history:
Received 6 May 2014
Received in revised form
15 September 2014
Accepted 15 September 2014
Available online 5 October 2014
Keywords:
Transmission function
Hemispherical analyser (HSA)
Electron spectroscopy
XPS
Quantitative interpretation
Surface analysis
a b s t r a c t
The correction function of a hemispherical analyzer (HSA) is determined for quantitative interpretations
of electron spectroscopy. In this way, electron elastic images are performed using a scanning electron
gun. This new method allowed the determination of the analysis area A(E
K
) of a HSA for the first time.
An important result is the dependence of this analysis area on the electron kinetic energy E
K
. Indeed,
results show that A(E
K
) varies as E
K
-1.2
regardless of the spectrometer configuration. This parameter
is different from the so-called transmission function and must be taken into account for quantitative
interpretation. Moreover, the transmission function T(E
K
) is also determined in this work and varies as
a power function E
K
x
where x is a fitting parameter which depends only on the width in the energy
dispersive direction of the hemisphere entrance slit. These two apparatus functions are then validated
thanks to XPS measurements by comparing results obtained on two different Ag surfaces. Then a general
methodology to use these functions is given.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
Electron spectroscopies are useful methods for determining
chemical and bonding states of surfaces. Today X-ray photoelec-
tron spectroscopy (XPS) is the most frequently used technique
for surface chemical analysis. This technique needs a very precise
spectrometer and the most common is the hemispherical analyzer
(HSA). Thanks to this apparatus, the photoelectron intensity I
X
TH
of
the peak of element X can be described by the following empirical
formula [1–4]:
I
X
TH
= ˚
X
LD(E
p
)T (E
K
)A(E
K
)
∞
0
N
X
(z). exp(
-z
i
(E
K
). cos
)dz (1)
where ˚ is the flux of incident X-ray,
X
is the photo-ionization
cross-section, L is the cross-section anisotropy, D(E
P
) is the detec-
tion efficiency depending only on the analyzer pass energy (E
P
) [5],
A(E
K
) is the analysis area and T(E
K
) is the transmission efficiency of
the analyzer at the electron kinetic energy E
K
. The integral term of
∗
Corresponding author at: CNRS, UMR 6602, Institut Pascal, F-63171Aubière,
France. Tel.:+33 4 73 40 71 18; fax: +33 4 73 40 73 40.
E-mail address: guillaume.monier@univ-bpclermont.fr (G. Monier).
Eq. (1) presents the density N
X
of element X at depth z and inten-
sity attenuation coefficient where
i
(E
K
) is the inelastic mean free
path (IMFP) and is the photoelectron emission angle to the surface
normal.
Eq. (1) contains two types of parameter: physical parameters
related to the material (
X
, L, N
X
and
i
(E
K
)) and parameters
depending on the analyzer configuration (D(E
P
), T(E
K
), A(E
K
) and ).
Different methods could be used to determine the physical param-
eters [6,7] but the quantitative interpretations of the XPS signals
also need a good knowledge of the analyser parameters. Indeed,
the spectrometer has an important effect on data collection [8].
This paper is focused on the determination of the parameters of
a HSA which is the most widely used spectrometer for XPS experi-
ments.
Many authors have proposed methods for determination of
these spectrometer parameters. Nevertheless, they determine a
correction function (named N
L
(E
K
) in the following) which encom-
passes all spectrometer parameters. The works of Cross et al. [9],
Weng et al. [10] and Zommer [11] could be mentioned. These meth-
ods give nearly the same result and suggest that the correction
function varies as E
K
-x
in constant pass energy mode (CAE) for a
hemispherical spectrometer where x is a fitting parameter. Follow-
ing these methods, the correction function is defined as the ratio of
signal intensities recorded by the analyzer to signal intensities from
the surface. This approach also suggests that the analysis area A(E
K
)
http://dx.doi.org/10.1016/j.elspec.2014.09.010
0368-2048/© 2014 Elsevier B.V. All rights reserved.