Photon Factory Activity Report 2017 #35 (2018)

BL-27B/2017G520/2016G534

EXAFS study on clustering of Fe atoms implanted in silica glass
Kengo FUKUDA1, Masaaki OCHI1, Yoshihiro OKAMOTO2, Yuichi SAITOH3, Toshiyuki MATSUI1,Fuminobu HORI1, and Akihiro IWASE1,*
1Osaka Prefecture University, Sakai, Osaka, 599-8531, Japan
2
Japan Atomic Energy Agency, Sayo, Hyogo, 679-5148, Japan
3
National Institutes for Quantum and Radiological Science and Technology, Takasaki, 370-1292,
Japan
1 Introduction
In our previous report[1], we have shown through theXANES measurements that during the energetic Fe ion
implantation in silica glass, the valence of Fe ions tends
to decrease, and becomes close to zero (pure Fe) when Feion fulence is large. In other words, when focused on one
Fe nanoparticle implanted in silica glass, more Fe atoms
exist around the Fe nanoparticle with increasing ion
fluence. In the present report, we will show the change inEXAFS spectra for various Fe ion fluences and will
discuss the structure of Fe nano-particles in silica glass.
2 Experiment
Target samples were SiO2 sheets with the dimension of5mmx5mmx1mm. They were implanted with 380keV Feions at the fluences of 3x1016, 1.4x1017 and 2.1x1017/cm2
at room temperature by using an ion-implanter atTakasaki Advanced Radiation Research Institute, QST.
The effect of the implantation on magnetic properties wasstudied by using a SQUID magnetometer. In order toinvestigate the atomic arrangement of the implanted Feions, the extended x-ray absorption fine structure(EXAFS) measurements around the Fe-K edge (7.11keV) were performed at a synchrotron radiation facility ofHigh Energy Accelerator Research Organization (KEKPF). For comparison, the EXAFS spectra for ironoxide(Fe2O3) and pure iron (-Fe) were also measured.
3 Results and Discussion
Fig. 1 shows the EXAFS-FT spectra for silica glass
implanted with Fe ions. For comparison, the spectra for
Fe2O3 and pure iron are also plotted in the figure. Thespectrum for Fe2O3 shows a clear peak at 1.4 A
corresponding to oxygen atoms as nearest neighbors of Featoms. Other peaks for the regular atomic arrangementsof iron and oxygen atoms around iron atoms are alsoobserved in the spectrum for Fe2O3. The spectrum forsilica glass implanted with 3x1016/cm2 Fe ions has also apeak at 1.4A. This peak can be identified as due tooxygen atoms which are nearest neighbors of iron atoms.
However, we can not see any other clear peaks in thespectrum. The result implies that in silica glass implantedwith 3x1016/cm2 Fe ions, amorphous iron oxide clusters
are produced. With increasing the Fe implantation fluence,

Fe2O3

3x1016Fe/ cm2FT

1.4x1017Fe/cm2
2.1x1017Fe/cm2

Pure iron (-Fe)01

2345678R(A)Fig. 1 EXAFS-FT spectra for silica glass implanted with
Fe ions. Spectra for Fe2O3 and pure iron are also shown.

Photon Factory Activity Report 2017 #35 (2018)the shape of the spectrum changes, and for the Fe
implantation with the fluence of 2.1x10 17/cm2, the shapeof the spectrum is almost the same as that for pure iron.
Therefore, we can conclude that Fe iron implantation withthe fluence of 2.1x1017/cm2 produces pure iron (-Fe)clusters in silica glass. The existence of -Fe clusters canbe confirmed by means of SQUID measurement. Figs. 2and 3 show the magnetization, M, as a function of
external magnetic field, H, (M-H curves) for silica glass
implanted with various fluences.
32.1x1017/cm2

21.4x1017/cm2

As can be seen in the figures, the magnetization increases
with increasing the Fe ion fluence. In the M-H curves for
3x1016 and 1.4x1017/cm2 Fe ion implantation, thehysteresis can hardly be found, meaning that the Feclusters in such silica glass samples show the(super)paramagnetic character. On the other hand, for theFe implantation with the fluence of 2.1x1017/cm2, a clear
hysteresis can be observed in the M-H curve. This result
is consistent with the result of EXAFS measurement; theFe ion implantation with the fluence of 2.1x10 17/cm2
produces ferromagnetic -Fe clusters in silica glass.
References[1] K. Fukuda et al., Photon Factory Activity Report2016 #34(2017)B.

1M

016

Acknowledgement
The authors thank the technical staff of QST-Takasaki
accelerators and KEK-PF for their help.

23x10 /cm-1-2* iwase@mtr.osakafu-u.ac.jp-3-10000-500005000

10000

H(Oe)
Fig. 2 Magnetization-external magnetic filed (M-H)
curves for silica glass samples Fe-implanted with fuencesof 3x1016, 1.4x1017 and 2.1x1017/cm2.
3M

2

2.1x1017/cm2
1.4x1017/cm2

1

1.4x1017/cm2

0

3x1016/cm2-1-2-3-2000-1500-1000 -500

0500 1000 1500 2000

H (Oe)
Fig. 3 Magnification of Fig.2 near the origin.