Photon Factory Activity Report 2005 #23 Part B (2006)
Chemistry

11B/2004G062

X-ray Absorption Near Edge Structure (XANES) Studies of Silver salt and its
Photochemical Products

Takeshi Miyamoto1, Hironobu Niimi2, Wang-Jae Chun2, 3, Yoshinori Kitajima4, Hideyuki Sugawara5,Tamotsu Inabe5, and Toshio Naito5, 6, Kiyotaka Asakura*1, 3
1
Department of Quantuam Science and Engineering, Hokkaido Unversity 21-10,Sapporo,001-0021
2
CREST JST, 21-10 Sapporo 001-0021
3CRC,Hokkaido University, 21-10, Sapporo,001-0021
4
PF-IMSS-KEK, Oho1-1, Tsukuba,305-0801
5Division of Chemistry, Graduate School of Science, Hokkaido University, 10- 8, Sapporo, 060-0810.
6CRIS, Hokkaido University, 21-10, Sapporo, Hokkaido 001-0021

(f)
(e)

Intensity / A.U.

Introduction
A silver salt Ag(DM)2 (DM=2,5-dimethyl-N,N’dicyanoquionediimine) shows one dimensional(1D) metallic
conductivity due to 1D π-electronic band of the DM anion
column. This salt also shows photosensitivity; theconductivity dramatically changes from metallic tosemiconducting and insulating ones only by UV-VIS lightillumination under different conditions. This property canbe utilized to fabricate 1D electronic devices directly byphotolithography. Further investigation has revealed thatfour different kinds of product are created by theillumination of Ag(DM)2. Their properties aresummarized in Table1. We characterized the Ag chemical
state by measuring Ag L3-edge XANES spectra of pristineand four photochemical products of Ag(DM)2, andproposed the photo-indcued conduction changing
mechanism.
Experimental
XANES measurements were carried out at BL11B in asample current mode. The sample powder was put on theconductive carbon tape and was loaded in a UHVchamber.
Result and discussion
Fig. 1 shows the L3-edge XANES spectra of pristine
Ag(DM)2, its four photochemical products and Ag foil forreference. The spectrum shows that the photo products
classify into two according to the Ag chemical state. α,βand γ gave similar spectra which showed a peak around3352 eV. These peaks could be assigned to a 2p → 4d+
dipole transition. Since the Ag in α was usually thought
10
to be d , the d vacancy might be created by the back+donation from Ag to DM . The occurrence of the edge
peak in α, β, and γ meant that the Ag should have thebond with ligands and be cationic. β almost the samechemical state and structure of α. But γ is amorphousstate from XRD. The changing conductivity mechanismof γ is as follows. The energy brought in through the(d)(c)
(b)
(a)

3300

3350

3400

12

Users' Reportα (pristine)
BlackNeedle
2
Ag(DM)2
metallic

3500

Fig. 1. Normalized Ag L3-edge XANES spectra forAg(DM)2 and its light induced products. (a)α, (b)β, (c)γ,(d)δ, (e)ε and (f) silver foil.

photoexcitation is used to break the stacking structure of
the DM column. Consequently, the conduction path isdisrupted.
On the other hand, δ and ε gave the same spectra asthat of Ag foil, indicating the formation of Ag metal in δ+and ε due to the redox reactions between Ag and DM .
DM molecules were neutralized and sublimated andhence the conductivity was lost in δ.
These findings are important to control thephotoprocesses and to create a new device from Ag(DM)2.
References
1. A. Aumüller et al. Angew. Chem. Int. Ed. Engl. 25,740 (1986)
2. T. Naito et al. Adv. Mater. 16, 1786 (2004)*askr@cat.hokuai.ac.jp

Table 1. The properties of the pristine Ag(DM)2 and photo-induced products β, γ, δ, and ε.
productcolor
appearance
stoichiometry [DM/Ag]
XRD
conductivity

3450

X-ray energy / eVβBlackNeedle
2Ag(DM)2
semiconducting

γBrownNeedle2amorphous
InsulatingδBlackpowder
1.5
Ag foilInsulatingεSilver White
powder~0
Ag foil
metallic