Photon Factory Activity Report 2005 #23Part B (2006)
Surface and Interface

7A/2004G305

XAFS Study of 17,19-Hexatriacontadiyne Monolayers on Au(111)
Osamu Endoa, Taro Furutaa, Hiroyuki Ozakia,*, Yasuhiro Mazakib
Department of Organic and Polymer Materials Chemistry, Faculty of Technology, Tokyo Universityof Agriculture and Technology, Koganei, Tokyo 184-8588, Japanb
Department of Chemistry, School of Science, Kitasato University, Sagamihara, Kanagawa 228-8555,
Japan
aResults & Discussion
In Fig. 1(a), we show the polarization dependent C Kedge NEXAS spectra of HTDY on Au(111) before UVirradiation. A peak dominantly observed in a NI spectrum,
which corresponds to the σ*CC resonance, indicates thatthe carbon zigzag plane of the HTDY molecule is parallelto the surface (flat-on orientation). Another peak assigned
to the M* resonance proves that there exists an mixing ofthe σ*CH or pseudo-π* orbitals of the alkyl chains withmetal d-bands, which is consistent with the flat-onorientation and the soft mode of the CH stretching(a)(b)
σ*CH, pseudo-π*/R
σ*CCπ*

M*

multilayerMImonolayerGIMINI280pseudo-π*/R
290 300 310

Photon Energy / eV

Intensity (arb. units)Experimental
XAFS measurement was performed at a soft X-ray
beam line BL-7A of Photon Factory in Institute ofMaterials Structure Science. A flame-annealed Au(111)
surface cooled in pure acetone was immersed into an
HTDY acetone solution for a short period of time andsubsequently rinsed with the pure solvent. The monolayer
was irradiated with UV light from a deuterium lump.
After each specimen was introduced into a UHV chamber,
C K-edge NEXAFS spectra were measured at 1 × 10-6 Pawith a partial electron yield method using a microchannel
plate. The spectra were collected at three X-ray incidence
angle: grazing (GI), magic angle (MI), and normal
incidence (NI).

vibration observed by infrared reflection absorption
spectrscopy[3]. The peak position of the π* resonance forthe monolayer is almost the same as that for a multilayer.
This means that there is little mixing between the π*
orbital of HTDY in the monolayer and the metal d-bands.
Changes occurring in the GI spectrum upon UV
irradiation are shown in Fig. 1(b). The polarizationdependence of the spectra is diminished and the π*
resonance shifts to a lower energy. These results indicatethat the molecular orientation becomes random owing to
the formation of oligomeric species resembling red phase
PDs in LB films[4].

Intensity (arb. units)

Introduction
Conjugatedalkadiyne
17,19-hexatriacontadiyne(HTDY) molecules physisorbed on a graphite (0001)
surface form self-assembled columns or lamellae with
their carbon planes parallel to the surface. Each column isconverted into a single sheet of sashlike polydiacetylene(PD) -atomic sash (AS)- upon UV irradiation[1,2]. The
AS molecules having one-dimensional π electronicsystems serve for a detailed study on organic nanowires
and it is desirable to construct the AS nanowires onalternative surfaces including semiconductors and metals.
We have recently reported that HTDY forms flat-lying
columns in a monolayer prepared by a wet process onAu(111)[3]. However, it was also revealed that theproducts obtained by UV irradiation on HTDY/Au(111)are somewhat different from those on HTDY/graphite(0001). In this work, we intend to study the nature of theproducts and a possible cause of the difference in thereaction using carbon K-near edge X-ray absorption finestructure (C K-NEXAFS).

σ*CH, pseudo-π*/R
σ*CC

380 s
80 s
20 s
0s

π*

M*
pseudo-π*/R

280

290

300

310

Photon Energy / eVFig. 1 (a) C K-edge NEXAFS spectra for a mono- and amultilayer of HTDY on Au(111); GI, MI, and NI meangrazing, magic angle, and normal incidence of X-ray,respectively. (b) Changes of C K-edge NEXAFS spectra(GI) for an HTDY monolayer on Au(111) upon UVirradiation.
References[1] H. Ozaki, T. Funaki, Y. Mazaki, S. Masuda, Y.
Harada, J. Am. Chem. Soc. 117 (1995) 5596.
[2] O. Endo, H. Ootsubo, N. Toda, M. Suhara, H. Ozaki,
Y. Mazaki, J. Am. Chem. Soc. 126 (2004) 9894.
[3] O. Endo, T. Furuta, H. Ozaki, M. Sonoyama, Y.
Mazaki, J. Phys. Chem. B, in press.
[4] A. Fujimori, M. Ishitsuka, H. Nakahara, E. Ito, M.
Hara, K. Kanai, Y. Ouchi, K. Seki, J. Phys. Chem. B 108(2004) 13153.
*hiroyuki@cc.tuat.ac.jp

Users' Report63