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

12C/2005G031

Local structures of Co implanted in α-Al2O3 single crystal IIKaoru IJIMA*1, Takeshi NARUSAWA1,Kiyotaka ASAKURA2, Yukinori SAITO1
1
Department of Electronic Engineering, University of Yamanashi
Takeda, Kofu 400-8511, Yamanashi, Japan.
2Catalysis Research Center Hokkaido University, Sapporo 001-0021, Japan
Introduction
Implantation of metal ion brings about the colour of acolourless single crystal oxide, which can be used for thesynthesis of new optical materials. Since the structure ofthe metal species is unclear at moment, two origins forthe coloration have been proposed: surface plasmon of theimplanted metal particles in dielectric material andelectron transitions between valence and conduction
orbitals of the metal ionic species. We found the various
Co structures implanted in the α-Al2O3. depending on theimplanted energies (around 20 keV) [1]
We have carried out the structure analysis of cobalt ion
implanted in the α-Al2O3 which fabricated by high energy(3MeV) ion implantation and post thermal annealing. The
colour of the as-implanted Co species is dark grey and itchanges to light grey after(during ) annealing. The
purpose of this study is to unveil the origin of thedifferent colours in two different implantation energies
and annealing treatment.
Experiment
A 0.5 mm thick α-Al2O3 single crystal was cleaned
162+
with acetone. 3×10 atom/cm of Co ion was implanted+
by Ar plasma assisted ion source(operated at 3MeV).
Post annealing was carried out for 1 hour at 1073K,
1273K and 1773K respectively in air. XAFS wasmeasured at BL12C in a fluorescence mode at room
temperature in air. The fluorescence X-ray was detectedusing a 19-elements SSD.
Results and discussion
3Fig.1 shows Fourier transform of the k -weighted
EXAFS oscillations. Co-O(0.19nm) peak appears in theFourier transform of the as-implanted sample, indicating
the presence of oxidized Co dispersed in the α-Al2O3.
This result is different from the case of low energy
implantation.
During the annealing process, Co-O peak decreased
and disappeared at 1273 K accompanied by theappearance of Co-Co peak. The peak increases with theannealing temperature, indicating the reduction of Cooxide and the creation and growth of the Co metal
particles in the α-Al2O3. From the curve fitting for thesample annealed at 1773K, coordination number of CoCo(0.25nm) bond is 9.6, and Co metal particle size is
1.8nm.
However, in low energy implantation, Co species of as
implanted sample is metal particle while it is reacted with
Al oxide after the annealing to form cobalt aluminates.

The difference of Co behavior against Co beam energy
can be explained as follows. The implantation depths forthe low (20keV) and high (3 MeV) energy Co beam into
α-Al2O3 are about 10nm and 1600 nm, respectivelycalculated from the TRIM code calculation. In the low
energy implantation Co species is concentrated at thesurface region and Co metal cluster is formed. During theannealing process the Co ions can be reactive with thesurface active oxygen and to produce the surface Coaluminate.
In the high energy implantation the Co
species widely dispersed in the Al2O3 lattice which wasdefected by the high energy ion implantation. During theannealing process, the Al2O3 lattice was recovered and Cospecies was removed from the lattice to create the large
Co particles. To the best of our knowledge, this is thefirst example that clearly shows the annealing effect ofcoloration by the ion implantation.
References[1] K. Ijima et al., PF activity report(2003)193* ijima@es.yamanashi.ac.jp

4540

353025

1773K
201273K

15101073K
as implanted

5001

2

3

456

R / 0.1nm
Figure 1 Fourier transforms of the k3weighted EXAFS oscillations.

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