Journal of Surface Engineered Materials and Advanced Technology, 2013, 3, 7-10
http://dx.doi.org/10.4236/jsemat.2013.33A002 Published Online September 2013 (http://www.scirp.org/journal/jsemat)
7
ATR-FTIR and XPS Evaluation of Alkyl Immobilization
by Hydrosilylation on n-Si(111) for Photoelectrochemical
Cell Electrode
Toshihito Ohtake
Department of Mechanical Systems Engineering, Faculty of Engineering, Aich University of Technology, Gamagori, Japan.
Received July 16th, 2013; revised August 20th, 2013; accepted August 30th, 2013
Copyright © 2013 Toshihito Ohtake. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
An electrode development was needed with high efficiency and low costs as next generation solar cells. We attempted
the electrode fabrication for a photoelectrochemical cell by immobilizing functional groups on a n-Si(111) surface. The
immobilization was applied by hydrosilylation terminated with ester (hydrophobic) or carbonyl (hydrophilic) group.
Results confirmed the immobilization on the Si surface by measuring ATR-FTIR and XPS.
Keywords: ATR-FTIR; XPS; Si Surface; Hydrosilylation; Immobilization; Photoelectrochemical Cell
1. Introduction
We are faced with problems about energy and global
environment, and solar energy has been noticed to solve
them. Solar power generation is studied actively, and
high efficient solar cells are produced recently. However,
there are high costs to be complicated manufacturing
processes or the use of expensive materials for transpar-
ent conductive oxide including indium etc. Hence, solar
cell developments of high efficiently and low costs are
required to spread them largely [1,2].
It is known that photoelectrochemical cell (PEC) by
using n-Si electrode onto supporting with Pt shows high
open circuit photovoltage over 0.6 V comparing with
conventional p-n junction Si solar cell [3]. PEC is inter-
ested with very low costs, but the stability of Si electrode
in electrolytic solution is not so good to form SiO2 layer
on the surface by oxidation of Si.
Researches have been reported about alkyl termination
on Si surface [4-9]. Especially bio-tips for detecting
DNA or protein etc. are applied by immobilizing func-
tional groups [10]. On the other hand, it is known that the
immobilization particularly makes Si surface stable for
oxidation [5,11,12]. Furthermore, controls of electrode
properties are expected for the termination by the func-
tional groups on Si surface.
In this study, termination with ester or carboxy group
was carried out by a hydrosilylation on hydrogen-termi-
nated Si surface. The termination was estimated by ATR-
FTIR and XPS measurement, simultaneously with evalua-
tion of Si surface oxidation.
2. Methodology
A n-Si(111) was performed by RCA washing to termi-
nate with hydrogen after washed with aceton to remove
organic matters. The Si was etched to termination of hy-
drogen by 5% HF solution for 5 min and 40% NH4F for
15 min. The ester termination directly was made use of
the hydrosilylation on the hydrogen-terminated Si in
Scheme 1. The Si was immersed in 0.1 M methyl
propiolate/hexan solution for 24 h at room temperature
under Ar atmosphere in schlenk flask, after washed with
diethyl ether. Furthermore, the immersed time was
Scheme 1. Termination process by hydrosilylation.

ATR-FTIR and XPS Evaluation of Alkyl Immobilization by Hydrosilylation on N-Si(111) for
Photoelectrochemical Cell Electrode
8
changed from 2 h to 15 h in methyl propiolate/hexan
solution. Carbonyl group termination on the hydro-
gen-terminated Si was performed by the hydrosilylation
with an unsaturated carboxylic acid. Similarly, the Si was
immersed in 0.1 M propiolic acid/hexan solution for 24 h.
The Si surface was measured by MIR-FTIR and XPS,
and cumulative number was 256 and 64 respectively.
3. Results and Discussion
3.1. MIR-FTIR Measurement
The ester termination on Si surface was estimated about
C=C, C=O and Si-H stretching vibration. Figure 1 shows
MIR-FTIR spectra of the n-Si(111) surface terminated
with methyl propiolate by 24 h immersing time in line (a)
and terminated with hydrogen by RCA washing in line
(b). This result would show the ester termination by
applying methyl propiolate because peaks of C=O at
1728 and C=C at 1588 stretching vibration based on the
ester was appeared, and Si-H stretching vibration at 2083
cm−1 was disappeared simultaneously.
Furthermore, Figure 2 shows the spectra of the termi-
nation by a various methyl propiolate immersing time
from 1 to 24 h. We obtained that the intensity of C=O
and C=C peaks was increasing and that of Si-H peak was
decreasing with immersing time. These results would
conclude that the ester termination by the hydrosilylation
progressed instead of the hydrogen termination on Si
surface.
The carbonyl group termination on Si surface was
similarly evaluated in Figure 3 line (a). The spectra
showed peaks of C=O at 1709 cm−1 and C=C at 1586
stretching vibration based on the carbonyl group, hence
the Si surface would be immobilized by the carbonyl
group. Moreover, spectra of the sample applied in 0.01
M NaOH solution obtained a peak of C=O based on
-COO- at about 1550 cm−1 instead of decrease in the
Figure 1. MIR-FTIR spectra of (a); methyl propiolate ter-
mination, (b): hydrogen termination on n-Si(111) surface.
2200 2100 20001900 1800 17001600 1500
C=C
Si-H
C=O
Wavenumbe r/c m-1
Absorbance
0.01
Figure 2. Dependence of immersing time in methyl propi-
olate on MIR-FTIR spectra. The time is 1, 3, 6, 9, 12, 15, 18,
21, 24 h from the front row.
Figure 3. MIR-FTIR spectra on Si surface (a): carboxy
group termination, (b): after immersing in 0.01 M NaOH
and (c): after immersing in 2.0 M HCl subsequently.
peak of C=O based on -COOH at 1709 cm−1 showed in
Figure 3 line (b). Subsequently, spectra of the sample
applied in 2.0 M HCl aq showed the peak of C=O based
on -COOH at 1709 cm−1 instead of disappear at the peak
based on -COO- at about 1550 cm−1 in Figure 3 line (c).
Hence, the carbonyl group terminated on the Si surface
will cause acid-base reaction with the NaOH or HCl so-
lution. Then, a peak of C≡C stretching vibration at 2119
cm−1 disappeared by the acid-base reaction. However the
peak is not clear yet, dimers formed between the immo-
bilized carbonyl group and an unreacted propiolic acid
might exist on the Si surface in Scheme 2. Consequently,
the peak based on C≡C at 2119 cm−1 might be appeared
by the termination, and disappeared by acid-base reac-
tions.
3.2. XPS Measurement
Figure 4 shows XPS spectra of C1s about the ester ter-
mination (a) and the carbonyl group termination (b) on
the Si surface, which indicated three peaks of C-H, C-O

ATR-FTIR and XPS Evaluation of Alkyl Immobilization by Hydrosilylation on N-Si(111) for
Photoelectrochemical Cell Electrode
9
Scheme 2. Possibility of dimers formed between the immo-
bilized carboxy group and an unreacted propiolic acid.
(a)
(b)
Figure 4. XPS spectra of C1s (a); the ester, (b): the carbonyl
group termination on n-Si(111) surface.
and O=C-O [13]. These results would confirm the termi-
nation by the ester or carbonyl group followed by the
MIR-FTIR measurements in the same way. The oxida-
tion on the Si surface was estimated by the spectra of
Si2p in Figure 5. A spectrum for (a); the hydrogen ter-
minated on the Si surface showed no oxidation at about
103 eV except a main peak at about 100 eV [14]. Al-
though a spectrum for (b); the ester terminated on the Si
surface indicated a peak barely at about 103 eV, the sur-
face would not be effected by the oxidation. A spectrum
for (c); the carbonyl group terminated on the Si surface
was obtained slightly at about 103 eV, which will be
caused by immersing in the propiolic acid/hexan solu-
(a)
(b)
(c)
Figure 5. XPS spectra of Si2p (a); the hydrogen, (b); the
ester, (c); the carbonyl group termination on n-Si(111) sur-
face.
tion. The peak for the carbonyl group termination was
larger than that of the ester termination. This result might
show a difference of hydrophobic or hydrophilic func-
tional groups. These terminated Si would be applied as
the functional electrodes.
4. Conclusion
The hydrosilylation on the hydrogen-terminated Si re-
acted as the ester termination in the propiolate/hexan

ATR-FTIR and XPS Evaluation of Alkyl Immobilization by Hydrosilylation on N-Si(111) for
Photoelectrochemical Cell Electrode
10
solution, and was confirmed by the MIR-FTIR meas-
urements. Similarly, the carbonyl group termination was
also performed and estimated in the propiolic acid/hexan
solution, and the Si surface was immobilized by the hy-
drophobic or hydrophilic functional groups. Although the
Si surface was hardly oxidized by XPS measurement, it
will be necessary to form more pure Si surface.
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