Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

9A, 12C/2001G326

Ion beam irradiation effects of Niobium oxide thin films
formed by oxygen cluster ion beam assisted deposition
Yutaka SHIMIZUGAWA1, Hiroyuki KGEYAMA*2, Kohei KADONO2, Tomonari TAKEUCHI2,23
3
Tatsuya ASANUMA , Toshio SEKI , and Jiro MATSUO
1
Hyogo Science and Technology Association,
3-1-1 Koto, Kamigori, Ako-gun, Hyogo 678-1205, Japan
2
National Institute of Advanced Industrial Science and Technology (AIST), Kansai-Center,
1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan3Ion Beam Engineering Experimental Laboratory, Faculty of Engineering, Kyoto University,Sakyo, Kyoto 606-8501, Japan
Introduction
The thin films metal oxides, for example Nb2O5 will be
used for multi-layer thin films for optical devices
combined with SiO2 thin films. It is necessary for theimprovement of the optical properties to control
accurately the refractive index and the opticaltransparency of the Nb2O5 layer, i.e. high stoichiometry
and so-called ‘amorphous’ structure.
The fluorescence XAFS analysis is one of powerfultools to analyses the valence state and the structure of the‘amorphous’ thin films at the atomic level instead of theconventional X-ray diffraction technique. In this study
we made the fluorescence XAFS measurement of Nboxide thin films, which were obtained by the oxygen gas
cluster ion beam assisted deposition techniques.
Experimental
The Nb K-XAFS spectra of Nb oxide thin films with
200nm thickness, which were formed by both the oxygengas cluster ion beam assisted deposition and an electron
beam deposition only, were measured in fluorescence
XAFS mode by a Lytle type ionization chamber usingincident X-ray beam monochromatized by double Si(111)crystals at beam line 12C. Also the Nb K-XAFS spectraof various Nb oxide samples including Nb oxide
deposition target material were measured as reference.
Results and Discussion
Fig. 1 shows the comparison of the Nb K-XANES ofthe samples. The XANES spectra of the Nb oxide thinfilms obtained by the oxygen gas cluster ion beam(GCIB) assisted deposition were closer to stoichiometricNb2O5 than that by the electron beam deposition only.
Table 1 shows the results of the curve-fitting analysisfor the first shell Nb-O peaks. Coordination numbers N,interatomic distances R and mean-square-relative
displacements σ are listed. Also this indicated that theNb oxide thin films obtained by the GCIB assisted
deposition were more similar to stoichiometric Nb2O5
than that by the electron beam deposition only comparing
with the Nb-O distances and their distribution.

Absorption Coefficient (Normalized)

Nb oxide film
(GCIB, 9kV,-25µAcm )Nb oxide film
(GCIB, 7kV,-25µAcm )Nb K-edge
Nb oxide film
(Electron beam)
Depositiontarget material
NbO2
StoichiometricNb2O5

18.98019.00019.02019.040
Photon Energy/keV

Fig. 1. Nb K-XANES of Nb oxide thin films, which wereformed by the GCIB assisted deposition and electron beam
deposition together with those of various Nb oxides.
Table 1. The results of the curve-fitting analysis.
R [Å]
N
σ[Å]

SampleStoichiometric
Nb2O5

NbO2
Deposition
target material
Nb oxide film,(Electron beam)
Nb oxide film
(GCIB 7 kV,5µAcm-2)
Nb oxide film
(GCIB 9 kV,5µAcm-2)

2 (fixed)
2 (fixed)
2 (fixed)
6 (fixed)
6 (fixed)

1.854(5)2.010(6)2.166(1)2.05
2.05

0.076(8)0.062(4)0.131(16)
0.09
0.08

6 (fixed)

2.11

0.13

2.5
3.5

1.99
2.16

0.09
0.09

2.7
3.3

1.99
2.16

0.10
0.10

New Energy and Industrial Technology Development
Organization (NEDO) support this work.
*h-kageyama@aist.go.jp

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