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

11A/2001G125

Polarization-dependent dissociation selectively induced by core-electron
excitation in methyl ester terminated self-assembled monolayerusing rotatable TOF-MS
Hiroyuki KIZAKI1, Shin-ichi WADA*1, Erika O. SAKO2, Ryohei SUMII1, Satoshi WAKI1,Kouji ISARI3, Tetsuji SEKITANI1, Tetsuhiro SEKIGUCHI4, Kenichiro TANAKA1
1
Department of Physical Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan2
Department of Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan3
Research Center for Nanodevices and Systems, Hiroshima University,Higashi-Hiroshima 739-8527, Japan
4
Japan Atomic Energy Research Institute, Tokai-mura 319-1195, Japan*+

CHn ions in the C1s(OCH3)→σ (O-CH3) excitation, and+*+CHn and OCH ions in the O1s(OCH3)→σ (O-CH3) and*σ (C-OCH3), respectively, while the ion yields induced bynon-selective dissociation in the other excitations hardly
depend on the angle. In addition, such independence of+ion yields is also seen in non-selective C2Hm desorption.
++The clear polarization dependence in the CHn and OCH
ionic dissociation reactions indicates that initial memoryof site-selective excitations is conserved during
subsequent Auger decay and ionic dissociation.
References
O K-edge

C K-edge402.5/degree
1535506575*

σ (O-CH3)+

CH3020/degree
1030
35506570*

σ (O-CH3)

+

CH2
2.0

1.5

10
1.00

2.520

Intensity / arb. units

Intensity / arb. units

Introduction
Polarized nature of SR has hardly been utilized forphoton stimulated ion desorption (PSID) experiments,
although PSID in inner-shell region reveals specificphenomena. When the localization character of coreelectron is memorized in the excitation of core electron to**σ , π , and Rydberg states, it is possible to break a bond in
the vicinity of the excited atom: this phenomenon iscalled site-selective ionic dissociation.
In this paper, polarization-dependent PSID induced bycore-excitation of methyl ester terminated self-assembled
monolayer (CH3OCO(CH2)15S/Au, MHDA-SAM) has
been investigated [1]. It is expected that SAM has anadvantage to observe polarization dependence in surfacesensitive ion desorption because SAM can be preparedwith highly oriented functional group on the topmost
surface. The results indicated different dependence on
incident angle between the site-selectively and nonselectively desorbing ions.
Experimental
Measurements of polarization-dependent PSID in coreexcited MHDA-SAM were carried out at the beamline
BL11A. Time-of-flight (TOF) spectra were measured toobtain partial ion yield (PIY) spectra for each desorbing
ion at various incident angles of SR light using therotatable TOF mass spectrometer (MS) [2]. The incident
angle was changed by rotating both the sample holder andthe TOF-MS device simultaneously, which were kept at aright angle. All measurements were performed with thespectral resolving power (E/∆E) of about 1000. MHDASAM was prepared by immersing Au coated quartz
substrate (Tanaka Kikinzoku Kogyo corp., ≥99 % ofAu(111) surface) into 1.0 mM ethanol solutions ofMHDA (NARD institute ltd.) during 72 hours.
Results and Discussion
Fig.1 shows SR incident angle dependence of+representative PIY spectra for CHn (n=1-3) ions in the C++
K-edge region, and CHn (n=2,3) and OCH ions in the O
K-edge region. An incident angle is defined as an angle
from the surface, that is an angle of electric field vector ofSR from the surface normal. It is clearly seen that theyields is enhanced at the shallower incident angle for*+σ (O-CH3)

CH21510505*

σ (O-CH3)

+

CH3

*

σ (O-CH3)

+

CH3
2.0

1.5

1.0

2.5

*

σ (C-OCH3)+

OCH42.03
1.5
21.0

1290295

Photon Energy / eV300530535

540545Photon Energy / eV

Fig.1 Typical PIY spectra for MHDA-SAM were measured
at various incident angles of SR from the surface. The graphs++
show PIYs for CHn (n=1-3) in C K-edge, and CHn (n=2,3)+and OCH in O K-edge. Spectra were normalized in thepre-edge region to exclude variation of irradiation area dueto the change of incident angle.
[1] H. Kizaki et al., J. Electron Spectrosc. Relat. Phenom.
144-147 (2005) 447.
[2] T. Sekiguchi et al., Appl. Surf. Sci. 169-170 (2001)
287.
* swada@sci.hiroshima-u.ac.jp

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