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XPS and optical studies of Xe+-implanted and annealed YSZ single crystals
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 250 (2006) 382–385 www.elsevier.com/locate/nimb
XPS and optical studies of Xe+-implanted and annealed YSZ single crystals X. Xiang a, X.T. Zu a,b,*, S. Zhu c, C.F. Zhang a, Z.G. Wang a, L.M. Wang c, R.C. Ewing c,d a
c
Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, PR China b International Center for Material Physics, Chinese Academy of Sciences, Shenyang 110015, PR China Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109-2104, USA d Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1005, USA Available online 27 June 2006
Abstract Xe+ ion implantation with 200 keV was completed at room temperature up to a fluence of 1 · 1017 ion/cm2 in yttria-stabilized zirconia (YSZ) single crystals. Optical absorption and X-ray photoelectron spectroscopy (XPS) were used to characterize the changes of optical properties and charge state in the as-implanted and annealed crystals. A broad absorption band centered at 522 or 497 nm was observed in the optical absorption spectra of samples implanted with fluences of 1 · 1016 ion/cm2 and 1 · 1017 ion/cm2, respectively. These two absorption bands both disappeared due to recombination of color centers after annealing at 250 C. XPS measurements showed two Gaussian components of O1s spectrum assigned to hZr–Oi and hY–Oi, respectively, in YSZ single crystals. After ion implantation, these two peaks merged into a single peak with the increasing etching depth. However, this single peak split into two Gaussian components again after annealing at 250 C. The concentration of Xe decreased drastically after annealing at 900 C. And the XPS measurement barely detected the Xe. There was no change in the photoluminescence of YSZ single crystals with a fluence of 1 · 1017 ion/cm2 after annealing up to 900 C. 2006 Elsevier B.V. All rights reserved. PACS: 42.88.+h; 61.82.d Keywords: Optical absorption; XPS; Ion implantation; Annealing
1. Introduction YSZ (yttria-stabilized zirconia) has been demonstrated to exhibit exceptional radiation resistance, for both fast neutron [1,2] and ion irradiation [3,4]. YSZ is a candidate material for use as an inert fuel matrix for ‘‘burning’’ excess plutonium in light water nuclear reactors, and also an excellent nuclear waste form for direct geologic disposal [5]. Xenon is a major inert gas fission product, and its behavior in YSZ is a concern. The irradiation damage behavior of *
Corresponding author. Address: Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, PR China. Tel./fax: +86 28 83201939. E-mail address: [email protected] (X.T. Zu). 0168-583X/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.04.142
YSZ induced by Xe+ ion irradiation has been studied extensively in recent years [6–8]. Xe+ ion irradiation-induced defects have been studied by optical measurements and transmission electron microscopy (TEM) [9]. However, the thermal annealing effects on the irradiation-induced defects have not been previously reported. In this paper, the annealing effects on damage evolution induced by Xe+ implantation and the optical properties of point defects in YSZ single crystals have been studied by X-ray photoelectron spectroscopy (XPS) and optical spectroscopy. 2. Experimental Optically polished (1 0 0) faces of YSZ (9.5 mol% Y2O3) single crystals, 10 · 10 · 0.5 mm in size, were implanted at
X. Xiang et al. / Nucl. Instr. and Meth. in Phys. Res. B 250 (2006) 382–385
room temperature with 200 keV Xe+ ion to nominal fluences of 1 · 1016 and 1 · 1017 ion/cm2, respectively. After implantation all the crystals turned purple. The asimplanted crystals were first annealed isochronally for 0.5 h at temperatures from 100 to 300 C in increments of 50 C, then annealed up to 900 C in increments of 100 C in ambient atmosphere in a quartz tube furnace. The heating rate was controlled at 10 C/min. After each annealing step, the crystals were monitored using optical absorption spectroscopy. X-ray photoelectron spectra of as-implanted and annealed samples were obtained at room temperature with a KRATOS X SAM 800 X-ray photoelectron spectrometer with monochromatic AlKa (hm = 1486 eV). The Ar+ ion beam etching of the samples was conducted at an energy of 3 keV and a current density of 10 lA/cm2. The etching rate was approximately 1 nm/min. The optical absorption spectra were measured by a SHIMADZU UV-2550 spectrophotometer at room temperature, with a deuterium lamp for UV and a tungsten halogen lamp for visible region. The wavelength used in the experiment ranged from 300 to 800 nm. Photoluminescence spectra were obtained with a SHIMADZU RF-5301PC photoluminescence spectrophotometer at room temperature, using a 150 W Xe lamp as the excitation source, and the wavelength ranged from 220 to 750 nm.
383
Xe3d5/2
O1s
as-received
as-implanted etching depth 0 nm
8 nm
30 nm
3. Results and discussion 47 nm
The depth profile for the Xe+ ion concentration in YSZ single crystals was calculated using TRIM 96 [10] (Fig. 1). We used a density of 6.0 g/cm3 for yttria-cubic-stabilized zirconia and a threshold displacement energy of 40 eV for all target elements [6,7,11]. According to the calculation, 1 · 1017 ion/cm2 Xe+ implantation causes a maximum concentration level of 21 at.% at 45 nm in YSZ.
20
Concentration (at.%)
670
665 536
532
528
524
Binding energy/eV Fig. 2. XPS spectra of Xe and O at different etching depths before and after ion implantation.
25
15
10
5
0
675
0
20
40
60
80
100
120
Depth (nm) Fig. 1. Depth profile of Xe+ ion concentration in YSZ single crystals calculated by TRIM 96.
The XPS spectra of Xe3d5/2 and O1s energy levels at different etching depths before and after Xe+ ion implantation at a fluence of 1 · 1017 ion/cm2 are shown in Fig. 2. The intensities of Xe3d5/2 peaks at about 670 eV increase with the increasing etching depth. The intensities of O1s spectra do not change but the shapes of the peak clearly do change. Before ion implantation, the O1s spectra can be deconvoluted into two peaks, i.e. hZr–Oi and hY–Oi. However, the two peaks merge into one peak with the increasing etching depth after ion implantation. This indicates that the chemical surroundings of the two types of oxygen anions become more similar due to the irradiation damage. These results are similar to the O1s XPS spectra of Gd2Ti2O7 single crystal after 1.5 MeV Xe+ ion irradiation at 1.7 · 1014 ions/cm2. The electron binding energy of hTi–Oi and hGd–Oi are similar, due to the shortening of hTi–Oi bond length [12].
384
X. Xiang et al. / Nucl. Instr. and Meth. in Phys. Res. B 250 (2006) 382–385
Table 1 The concentrations of elements determined at different depths Depth (nm)
Xe (%)
O (%)
Zr (%)
Y (%)
0 8 30 47 70
0 0.17 0.31 0.41 0.29
68.54 68.89 69.26 69.58 69.51
21.24 20.49 19.91 19.72 19.75
10.22 10.45 10.52 10.29 10.45
0.4 (a)
0.3
as-implanted
There is no clear change for the XPS spectra of Y3d and Zr3d energy levels (not shown). In Table 1, the concentrations of elements determined from the XPS spectra at different depths are listed as atomic ratios. The Xe ion concentration increases with the increasing etching depth and attains the maximum 0.41 at.% at about 45 nm. Then the concentration of Xe ion decreases. This trend is consistent with the results calculated by TRIM 96 in Fig. 1. However, the experimental concentration of Xe calculated from XPS results is lower than the calculated one. Two possible reasons can cause this result. The fluences of 1 · 1016 and 1 · 1017 ion/cm2 should be taken as nominal values. In addition, the substrates were tilted 70 relative to the ion beam in order to avoid ion channeling effects during the ion implantation. The optical absorption spectra of as-implanted and annealed crystals at fluences of 1 · 1016 (a) and 1 · 1017 ion/cm2 (b), respectively, are shown in Fig. 3. A broad absorption band centered at 522 or 497 nm was observed in the as-implanted crystals with fluences of 1 · 1016 ion/cm2 and 1 · 1017 ion/cm2, respectively [9]. The intensities of these two absorption bands decrease with increasing annealing temperature. After annealing at 250 C for 0.5 h, the two bands disappeared. The optical absorption spectrum of 1 · 1016 ion/cm2 crystal after annealing at 250 C is the same as that of the as-received crystal. As for the absorption spectrum of 1 · 1017 ion/cm2 crystal at annealing temperature of 250 C, there is still strong background absorption between 400 and 600 nm. Immediately after annealing at 400 C, the absorption disappears completely in the visible region. There are no changes for the absorption spectra for the two fluences after annealing at higher temperatures. From the previous study [9], the two absorption bands centered at 522 or 497 nm are associated with two defect types: oxygen vacancies with trapped electrons (F-type centers) nearest to zirconium cations, and hole-trapped oxygen ions (V-type centers) adjacent to yttrium cations. The annealed spectra indicate that the two defect types are unstable and disappear due to the recombination of color centers after annealing at 250 C for 0.5 h. In addition, the density of the defect clusters with a fluence of 1 · 1016 ion/cm2 (1 · 1016 cm3) is smaller than that with 1 · 1017 ion/cm2 (4 · 1016 cm3) [9]. Thus, the absorption spectrum with a fluence of 1 · 1016 ion/cm2 is easily recovered. XPS spectra of Xe3d5/2 and O1s energy levels of crystals at a fluence of 1 · 1017 ion/cm2 at etching depth of 30 nm after annealing at temperatures of 250 and 900 C, respectively, are shown in Fig. 4. The XPS spectra of O1s core level elec-
100 ºC
0.2
150 ºC 200 ºC 250 ºC
0.1 300
400
500
600
700
800
Wavelength/nm
0.5 (b)
0.4 as-implanted 0.3
100 ºC 150 ºC 200 ºC 250 ºC
0.2
400 ºC
0.1 300
400
500
600
700
800
Wavelength/nm Fig. 3. Optical absorption spectra of as-implanted and annealed crystals at fluences of 1 · 1016 (a) and 1 · 1017 ion/cm2 (b), respectively.
trons shows that the single peak induced by ion implantation splits into two Gaussian components after annealing at 250 C. This result reflects the recovery of irradiation damage and is consistent with the absence of the absorption band due to the recombination of color centers. From the XPS spectra, the Xe concentration as an atomic ratio is estimated to be 0.49 at.% at an etching depth of 30 nm after annealing at 250 C. The implanted Xe ions migrate to the surface of crystals during thermal annealing. After annealing at 900 C, the XPS measurement barely detects the Xe. This indicates that the implanted Xe ions have been almost completely removed from the YSZ matrix. A broad photoluminescence emission band from 400 to 700 nm had been observed in the Xe+-implanted YSZ with a fluence of 1 · 1016 ion/cm2. However, no luminescence
X. Xiang et al. / Nucl. Instr. and Meth. in Phys. Res. B 250 (2006) 382–385
O1s
Xe3d5/2
250 ºC
900 ºC
675
385
split into two Gaussian components after annealing at 250 C. The concentration of Xe decreased drastically after annealing at 900 C. And the XPS measurement barely detected the Xe. There was no change in the photoluminescence of the YSZ single crystals which had experienced a fluence of 1 · 1017 ion/cm2 after annealing up to 900 C. Acknowledgements
670
665 536
532
528
524
Binding energy / eV Fig. 4. XPS spectra of Xe and O after annealing at 250 and 900 C, respectively.
This study was supported by the NSAF Joint Foundation of China (10376006), the Sichuan Young Scientists Foundation (03ZQ026-059), the Program for New Century Excellent Talents in University (NCET-04-0899), Ph.D. Funding Support Program of Education Ministry of China (20050614013) and the K.C. Wong Education Foundation, Hong Kong. References
was observed in the as-implanted YSZ with a fluence of 1 · 1017 ion/cm2 [9]. After annealing, the intensity of the broad emission band of 1 · 1016 ion/cm2 YSZ decreased gradually with the increasing annealing temperature and disappeared after annealing at 250 C (not shown). This is just consistent with the optical absorption spectra. However, there was no change in the photoluminescence of YSZ single crystals that had a fluence of 1 · 1017 ion/cm2 after annealing at temperatures up to 900 C. 4. Conclusion A broad absorption band centered at 522 or 497 nm was observed for the Xe+-implanted YSZ with fluences of 1 · 1016 ion/cm2 and 1 · 1017 ion/cm2, respectively. These two absorption bands disappeared due to the recombination of color centers after isochronal annealing at 250 C for 0.5 h in an ambient atmosphere. There were two Gaussian components of O1s XPS spectrum assigned to Zr–O and Y–O, respectively, in the YSZ single crystals. After ion implantation, these two peaks merged into a single peak with increasing etching depth. However, this single peak
[1] B. Savoini, D. Ca´ceres, I. Vergara, R. Gonza´lez, J.E. Mun˜oz Santiuste, J. Nucl. Mater. 277 (2000) 199. [2] J. Fradin, T. Thome´, R.I. Grynszpan, L. Thome´, W. Anwand, G. Brauer, Nucl. Instr. and Meth. B 175–177 (2001) 516. [3] S.X. Wang, L.M. Wang, R.C. Ewing, Phys. Rev. B 63 (2000) 024105. [4] L. Thome´, J. Jagielski, A. Gentils, F. Garrido, Nucl. Instr. and Meth. B 175–177 (2001) 453. [5] L.M. Wang, S.X. Wang, S. Zhu, R.C. Ewing, J. Nucl. Mater. 289 (2001) 122. [6] C. Degueldre, M. Pouchon, M. Do¨beli, K. Sickafus, K. Hojou, G. Ledergerber, S. Abolhassani-Dadras, J. Nucl. Mater. 289 (2001) 115. [7] K.E. Sickafus, C.J. Wetteland, N.P. Baker, N. Yu, R.D. Devanathan, M. Nastasi, N. Bordes, Mater. Sci. Eng. A 253 (1998) 78. [8] L.M. Wang, S.X. Wang, R.C. Ewing, Philos. Mag. Lett. 80 (2000) 341. [9] S. Zhu, X.T. Zu, X. Xiang, Z.G. Wang, L.M. Wang, R.C. Ewing, Nucl. Instr. and Meth. B 206 (2003) 1092. [10] J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Pergamon Press, New York, 1985. [11] K.E. Sickafus, Hj. Matzke, Th. Hartmann, K. Yasuda, J.A. Valdez, P. Chodak III, M. Nastasi, R.A. Verrall, J. Nucl. Mater. 274 (1999) 66. [12] J. Chen, J. Lian, L.M. Wang, R.C. Ewing, L.A. Boatner, Appl. Phys. Lett. 79 (2001) 1989.
Nuclear Instruments and Methods in Physics Research B 250 (2006) 382–385 www.elsevier.com/locate/nimb
XPS and optical studies of Xe+-implanted and annealed YSZ single crystals X. Xiang a, X.T. Zu a,b,*, S. Zhu c, C.F. Zhang a, Z.G. Wang a, L.M. Wang c, R.C. Ewing c,d a
c
Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, PR China b International Center for Material Physics, Chinese Academy of Sciences, Shenyang 110015, PR China Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109-2104, USA d Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1005, USA Available online 27 June 2006
Abstract Xe+ ion implantation with 200 keV was completed at room temperature up to a fluence of 1 · 1017 ion/cm2 in yttria-stabilized zirconia (YSZ) single crystals. Optical absorption and X-ray photoelectron spectroscopy (XPS) were used to characterize the changes of optical properties and charge state in the as-implanted and annealed crystals. A broad absorption band centered at 522 or 497 nm was observed in the optical absorption spectra of samples implanted with fluences of 1 · 1016 ion/cm2 and 1 · 1017 ion/cm2, respectively. These two absorption bands both disappeared due to recombination of color centers after annealing at 250 C. XPS measurements showed two Gaussian components of O1s spectrum assigned to hZr–Oi and hY–Oi, respectively, in YSZ single crystals. After ion implantation, these two peaks merged into a single peak with the increasing etching depth. However, this single peak split into two Gaussian components again after annealing at 250 C. The concentration of Xe decreased drastically after annealing at 900 C. And the XPS measurement barely detected the Xe. There was no change in the photoluminescence of YSZ single crystals with a fluence of 1 · 1017 ion/cm2 after annealing up to 900 C. 2006 Elsevier B.V. All rights reserved. PACS: 42.88.+h; 61.82.d Keywords: Optical absorption; XPS; Ion implantation; Annealing
1. Introduction YSZ (yttria-stabilized zirconia) has been demonstrated to exhibit exceptional radiation resistance, for both fast neutron [1,2] and ion irradiation [3,4]. YSZ is a candidate material for use as an inert fuel matrix for ‘‘burning’’ excess plutonium in light water nuclear reactors, and also an excellent nuclear waste form for direct geologic disposal [5]. Xenon is a major inert gas fission product, and its behavior in YSZ is a concern. The irradiation damage behavior of *
Corresponding author. Address: Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, PR China. Tel./fax: +86 28 83201939. E-mail address: [email protected] (X.T. Zu). 0168-583X/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.04.142
YSZ induced by Xe+ ion irradiation has been studied extensively in recent years [6–8]. Xe+ ion irradiation-induced defects have been studied by optical measurements and transmission electron microscopy (TEM) [9]. However, the thermal annealing effects on the irradiation-induced defects have not been previously reported. In this paper, the annealing effects on damage evolution induced by Xe+ implantation and the optical properties of point defects in YSZ single crystals have been studied by X-ray photoelectron spectroscopy (XPS) and optical spectroscopy. 2. Experimental Optically polished (1 0 0) faces of YSZ (9.5 mol% Y2O3) single crystals, 10 · 10 · 0.5 mm in size, were implanted at
X. Xiang et al. / Nucl. Instr. and Meth. in Phys. Res. B 250 (2006) 382–385
room temperature with 200 keV Xe+ ion to nominal fluences of 1 · 1016 and 1 · 1017 ion/cm2, respectively. After implantation all the crystals turned purple. The asimplanted crystals were first annealed isochronally for 0.5 h at temperatures from 100 to 300 C in increments of 50 C, then annealed up to 900 C in increments of 100 C in ambient atmosphere in a quartz tube furnace. The heating rate was controlled at 10 C/min. After each annealing step, the crystals were monitored using optical absorption spectroscopy. X-ray photoelectron spectra of as-implanted and annealed samples were obtained at room temperature with a KRATOS X SAM 800 X-ray photoelectron spectrometer with monochromatic AlKa (hm = 1486 eV). The Ar+ ion beam etching of the samples was conducted at an energy of 3 keV and a current density of 10 lA/cm2. The etching rate was approximately 1 nm/min. The optical absorption spectra were measured by a SHIMADZU UV-2550 spectrophotometer at room temperature, with a deuterium lamp for UV and a tungsten halogen lamp for visible region. The wavelength used in the experiment ranged from 300 to 800 nm. Photoluminescence spectra were obtained with a SHIMADZU RF-5301PC photoluminescence spectrophotometer at room temperature, using a 150 W Xe lamp as the excitation source, and the wavelength ranged from 220 to 750 nm.
383
Xe3d5/2
O1s
as-received
as-implanted etching depth 0 nm
8 nm
30 nm
3. Results and discussion 47 nm
The depth profile for the Xe+ ion concentration in YSZ single crystals was calculated using TRIM 96 [10] (Fig. 1). We used a density of 6.0 g/cm3 for yttria-cubic-stabilized zirconia and a threshold displacement energy of 40 eV for all target elements [6,7,11]. According to the calculation, 1 · 1017 ion/cm2 Xe+ implantation causes a maximum concentration level of 21 at.% at 45 nm in YSZ.
20
Concentration (at.%)
670
665 536
532
528
524
Binding energy/eV Fig. 2. XPS spectra of Xe and O at different etching depths before and after ion implantation.
25
15
10
5
0
675
0
20
40
60
80
100
120
Depth (nm) Fig. 1. Depth profile of Xe+ ion concentration in YSZ single crystals calculated by TRIM 96.
The XPS spectra of Xe3d5/2 and O1s energy levels at different etching depths before and after Xe+ ion implantation at a fluence of 1 · 1017 ion/cm2 are shown in Fig. 2. The intensities of Xe3d5/2 peaks at about 670 eV increase with the increasing etching depth. The intensities of O1s spectra do not change but the shapes of the peak clearly do change. Before ion implantation, the O1s spectra can be deconvoluted into two peaks, i.e. hZr–Oi and hY–Oi. However, the two peaks merge into one peak with the increasing etching depth after ion implantation. This indicates that the chemical surroundings of the two types of oxygen anions become more similar due to the irradiation damage. These results are similar to the O1s XPS spectra of Gd2Ti2O7 single crystal after 1.5 MeV Xe+ ion irradiation at 1.7 · 1014 ions/cm2. The electron binding energy of hTi–Oi and hGd–Oi are similar, due to the shortening of hTi–Oi bond length [12].
384
X. Xiang et al. / Nucl. Instr. and Meth. in Phys. Res. B 250 (2006) 382–385
Table 1 The concentrations of elements determined at different depths Depth (nm)
Xe (%)
O (%)
Zr (%)
Y (%)
0 8 30 47 70
0 0.17 0.31 0.41 0.29
68.54 68.89 69.26 69.58 69.51
21.24 20.49 19.91 19.72 19.75
10.22 10.45 10.52 10.29 10.45
0.4 (a)
0.3
as-implanted
There is no clear change for the XPS spectra of Y3d and Zr3d energy levels (not shown). In Table 1, the concentrations of elements determined from the XPS spectra at different depths are listed as atomic ratios. The Xe ion concentration increases with the increasing etching depth and attains the maximum 0.41 at.% at about 45 nm. Then the concentration of Xe ion decreases. This trend is consistent with the results calculated by TRIM 96 in Fig. 1. However, the experimental concentration of Xe calculated from XPS results is lower than the calculated one. Two possible reasons can cause this result. The fluences of 1 · 1016 and 1 · 1017 ion/cm2 should be taken as nominal values. In addition, the substrates were tilted 70 relative to the ion beam in order to avoid ion channeling effects during the ion implantation. The optical absorption spectra of as-implanted and annealed crystals at fluences of 1 · 1016 (a) and 1 · 1017 ion/cm2 (b), respectively, are shown in Fig. 3. A broad absorption band centered at 522 or 497 nm was observed in the as-implanted crystals with fluences of 1 · 1016 ion/cm2 and 1 · 1017 ion/cm2, respectively [9]. The intensities of these two absorption bands decrease with increasing annealing temperature. After annealing at 250 C for 0.5 h, the two bands disappeared. The optical absorption spectrum of 1 · 1016 ion/cm2 crystal after annealing at 250 C is the same as that of the as-received crystal. As for the absorption spectrum of 1 · 1017 ion/cm2 crystal at annealing temperature of 250 C, there is still strong background absorption between 400 and 600 nm. Immediately after annealing at 400 C, the absorption disappears completely in the visible region. There are no changes for the absorption spectra for the two fluences after annealing at higher temperatures. From the previous study [9], the two absorption bands centered at 522 or 497 nm are associated with two defect types: oxygen vacancies with trapped electrons (F-type centers) nearest to zirconium cations, and hole-trapped oxygen ions (V-type centers) adjacent to yttrium cations. The annealed spectra indicate that the two defect types are unstable and disappear due to the recombination of color centers after annealing at 250 C for 0.5 h. In addition, the density of the defect clusters with a fluence of 1 · 1016 ion/cm2 (1 · 1016 cm3) is smaller than that with 1 · 1017 ion/cm2 (4 · 1016 cm3) [9]. Thus, the absorption spectrum with a fluence of 1 · 1016 ion/cm2 is easily recovered. XPS spectra of Xe3d5/2 and O1s energy levels of crystals at a fluence of 1 · 1017 ion/cm2 at etching depth of 30 nm after annealing at temperatures of 250 and 900 C, respectively, are shown in Fig. 4. The XPS spectra of O1s core level elec-
100 ºC
0.2
150 ºC 200 ºC 250 ºC
0.1 300
400
500
600
700
800
Wavelength/nm
0.5 (b)
0.4 as-implanted 0.3
100 ºC 150 ºC 200 ºC 250 ºC
0.2
400 ºC
0.1 300
400
500
600
700
800
Wavelength/nm Fig. 3. Optical absorption spectra of as-implanted and annealed crystals at fluences of 1 · 1016 (a) and 1 · 1017 ion/cm2 (b), respectively.
trons shows that the single peak induced by ion implantation splits into two Gaussian components after annealing at 250 C. This result reflects the recovery of irradiation damage and is consistent with the absence of the absorption band due to the recombination of color centers. From the XPS spectra, the Xe concentration as an atomic ratio is estimated to be 0.49 at.% at an etching depth of 30 nm after annealing at 250 C. The implanted Xe ions migrate to the surface of crystals during thermal annealing. After annealing at 900 C, the XPS measurement barely detects the Xe. This indicates that the implanted Xe ions have been almost completely removed from the YSZ matrix. A broad photoluminescence emission band from 400 to 700 nm had been observed in the Xe+-implanted YSZ with a fluence of 1 · 1016 ion/cm2. However, no luminescence
X. Xiang et al. / Nucl. Instr. and Meth. in Phys. Res. B 250 (2006) 382–385
O1s
Xe3d5/2
250 ºC
900 ºC
675
385
split into two Gaussian components after annealing at 250 C. The concentration of Xe decreased drastically after annealing at 900 C. And the XPS measurement barely detected the Xe. There was no change in the photoluminescence of the YSZ single crystals which had experienced a fluence of 1 · 1017 ion/cm2 after annealing up to 900 C. Acknowledgements
670
665 536
532
528
524
Binding energy / eV Fig. 4. XPS spectra of Xe and O after annealing at 250 and 900 C, respectively.
This study was supported by the NSAF Joint Foundation of China (10376006), the Sichuan Young Scientists Foundation (03ZQ026-059), the Program for New Century Excellent Talents in University (NCET-04-0899), Ph.D. Funding Support Program of Education Ministry of China (20050614013) and the K.C. Wong Education Foundation, Hong Kong. References
was observed in the as-implanted YSZ with a fluence of 1 · 1017 ion/cm2 [9]. After annealing, the intensity of the broad emission band of 1 · 1016 ion/cm2 YSZ decreased gradually with the increasing annealing temperature and disappeared after annealing at 250 C (not shown). This is just consistent with the optical absorption spectra. However, there was no change in the photoluminescence of YSZ single crystals that had a fluence of 1 · 1017 ion/cm2 after annealing at temperatures up to 900 C. 4. Conclusion A broad absorption band centered at 522 or 497 nm was observed for the Xe+-implanted YSZ with fluences of 1 · 1016 ion/cm2 and 1 · 1017 ion/cm2, respectively. These two absorption bands disappeared due to the recombination of color centers after isochronal annealing at 250 C for 0.5 h in an ambient atmosphere. There were two Gaussian components of O1s XPS spectrum assigned to Zr–O and Y–O, respectively, in the YSZ single crystals. After ion implantation, these two peaks merged into a single peak with increasing etching depth. However, this single peak
[1] B. Savoini, D. Ca´ceres, I. Vergara, R. Gonza´lez, J.E. Mun˜oz Santiuste, J. Nucl. Mater. 277 (2000) 199. [2] J. Fradin, T. Thome´, R.I. Grynszpan, L. Thome´, W. Anwand, G. Brauer, Nucl. Instr. and Meth. B 175–177 (2001) 516. [3] S.X. Wang, L.M. Wang, R.C. Ewing, Phys. Rev. B 63 (2000) 024105. [4] L. Thome´, J. Jagielski, A. Gentils, F. Garrido, Nucl. Instr. and Meth. B 175–177 (2001) 453. [5] L.M. Wang, S.X. Wang, S. Zhu, R.C. Ewing, J. Nucl. Mater. 289 (2001) 122. [6] C. Degueldre, M. Pouchon, M. Do¨beli, K. Sickafus, K. Hojou, G. Ledergerber, S. Abolhassani-Dadras, J. Nucl. Mater. 289 (2001) 115. [7] K.E. Sickafus, C.J. Wetteland, N.P. Baker, N. Yu, R.D. Devanathan, M. Nastasi, N. Bordes, Mater. Sci. Eng. A 253 (1998) 78. [8] L.M. Wang, S.X. Wang, R.C. Ewing, Philos. Mag. Lett. 80 (2000) 341. [9] S. Zhu, X.T. Zu, X. Xiang, Z.G. Wang, L.M. Wang, R.C. Ewing, Nucl. Instr. and Meth. B 206 (2003) 1092. [10] J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Pergamon Press, New York, 1985. [11] K.E. Sickafus, Hj. Matzke, Th. Hartmann, K. Yasuda, J.A. Valdez, P. Chodak III, M. Nastasi, R.A. Verrall, J. Nucl. Mater. 274 (1999) 66. [12] J. Chen, J. Lian, L.M. Wang, R.C. Ewing, L.A. Boatner, Appl. Phys. Lett. 79 (2001) 1989.