Photon Factory Activity Report 2016 #34 (2017)
BL-3A, BL-4C/2015G121,2016G588

Structures of Pt Ultra-Thin Films on Au(111) Prepared by Self-Terminated Deposition
Toshihiro Kondo1,2,*, Momoko Ishizaki1, Misako Hirota1, Maya Ueda1, Sayaka Seino1, Takuya
Masuda2, and Kohei Uosaki2
1
Ochanomizu University, Ohtsuka, Bunkyo-ku, Tokyo 112-8610, Japan2
Natinao Institute for Materials Science, Namiki, Tsukuba 305-0044, Japan
1 Introduction
It is very important to construct apseudomorphic precious metal ultra-thin layers on aforeign metal surface not only for basic science but also
for technological application, because they often havehigh electrocatalytic acitivities [1,2]. Since platinum is
one of the most widely used electrocatalysts, it has been
expected to prepare the pseudomorphic Pt layers on theforeign metal surface, especially on Au(111) [3-9]. Using
underpotential deposition (UPD) and Galvanic
replacement techniques, Pt monolayer forms on Au(111)[3,4], but there are no reports, in which preudomorphic Ptmonolayer forms, because atomic-atomic distancemismatch between UPD metal and Pt is relatively high.
By using resonance surface x-ray scattering (RSXS)
technique, we previously succeeded to electrochemicallyconstruct the pseudomorphic Pt monolayer on Au(111) bycontrol of electrochemical conditions such as Pt complex
concentration, deposition potential, and deposition period[5-7] and its high electrocatalytic activity for oxygen
reduction reaction (ORR) was confirmed [10]. Recently,
Moffat et al. reported that the atomically controlled Pt
monolayer formation on Au(111) by a self-terminating
effect of Pt complex ion used as a Pt source [8,9].
However, no one know whether the formed Pt ultra-thinlayer is preudomorphic or not, because they used (111)textured Au thin films, not Au(111), as a substrate.
In this report, we investigated the structures of
the ultra-thin Pt layers prepared on Au(111) by the selfterminated electrochemical deposition using RSXS.
2 Experiments
Prior to RSXS measurements, Au(111) disk wasannealed by a Bunsen gas burner and quenched bydipping it in ultra-pure water [11]. After that, the potentialof the Au(111) disk was stepped for 1 or 2 times fromopen circuit potential (OCP) to ca. -0.5 V (vs. Ag/AgCl),
where hydrogen evolution takes place on the Pt surface,in a deaerated buffered electrolyte solution (pH=4.0)
containing 3 mM PtCl42-. After the sample throughly
washed with conc. H2SO4 and ultra-pure water and dried
with a nitrogen flow, the cyclic voltammetry (CV), angleresolved x-ray photoelectron spectroscopy (ARXPS), andRSXS measurements were carried out. In the RSXS
measurements, incident x-ray energy was employed
between 11.35 and 11.8 keV, which include the PtLIII
absorption. RSXS measurements were carried out at
BL3A/BL4C beamlines in Photon Factory.

3 Results and Discussion
Based on the CV and ARXPS results, it was
found Pt coverage, prepared by a single-potential step anddouble-potential step self-termination, was ca 0.5 ML and1.0 ML, respectively. From the structure analyses of theRSXS results by fitting the data with the theoreticalequation [11,12], while a half Pt monolayer, in which Pt
atoms exist at the three-fold hollow cubic close packed(ccp) and hexagonal close packed (hcp) sites with a ratioof 1:1, forms on the Au(111)-(1×1) surface by a singlestep self-termination, a pseudomorphic Pt full monolayer,
in which all the Pt atoms exist at the three-fold hollow
ccp site, forms on Au(111) by a double-step selftermination.
4 Conclusion
Results of the CV, ARXPS, and RSXS
measurements showed that a half Pt monolayer and a fullpseudomorphic Pt monolayer form on the Au(111)-(1×1)
surface by self-terminated electrochemical deposition.
Acknowledgements
This work was partially supported by Grants-in-Aid for
Scientific Research C (KAKENHI, No. 26410008) andfor Priority Area of "3D Active Sites" (No. 15H01045)
from the Ministry of Education, Culture, Sports, Science,and Technology (MEXT). TK acknowledges an open-lab
program at the Global Research Center for Environment
and Energy based on Nanomaterials Science (GREEN) in
National Institute for Materials Science (NIMS). We wish
to thank to Dr. Tamura of the Japan Atomic Energy
Agency for his help with the RSXS analysis program.
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* kondo.toshihiro@ocha.ac.jp