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THz spectroscopy of ion-implanted MgO crystals
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 257 (2007) 545–548 www.elsevier.com/locate/nimb
THz spectroscopy of ion-implanted MgO crystals Hisato Ogiso b
a,*
, Masafumi Nakada b, Shizuka Nakano a, Jun Akedo
a
a National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan Fundamental and Environmental Research Laboratories, NEC Corporation, 34 Miyukigakoka, Tsukuba, Ibaraki 305-8501, Japan
Available online 17 January 2007
Abstract The terahertz (THz) spectroscopy of ion-implanted layers was investigated. First, MgO(0 0 1) single crystals were implanted with 3 MeV gold ions at an ion fluence of 1 · 1016 cm2, and annealed in air at 700 K for 1 h, and again at 1100 K for 1 h. Then, the reflectance spectrum ranging from 200 to 700 cm1, and transmittance spectrum ranging from 200 to 1500 nm were measured. Results showed that the MgO had a high reflectance (’1) region from 400 to 500 cm1. The ion-implantation reduced this reflectance to 0.9, and the annealing process restored it. Analysis of the reflectance spectra yielded the oscillation parameters of the optical phonon modes of MgO. The ionimplantation increased the damping constant of the phonon mode at 400 cm1 from 1.31 to 18.9 cm1, whereas the annealing process reduced it to 8.2 cm1. The absorption peak at 580 nm due to the ion-implantation was reduced by the annealing process. 2007 Elsevier B.V. All rights reserved. PACS: 77.22.d; 61.80.Jh Keywords: THz spectroscopy; Ion-implantation; Dielectric constant; Optical phonon; Defect
1. Introduction Ion-implantation into ionic crystals has recently attracted significant interest due to its beneficial role in the formation of nano-structures [1–11]. One target of recent research has been to modify the optical properties of ionic crystals. Ion-implantation followed by thermal annealing generates embedded nano-clusters, which in turn can generate non-linear optical properties. Optical properties are responsible for properties of ion-implanted crystals such as defects in the crystal lattice as well as properties of embedded clusters such as their size, and electric conductivity. Ion-implantation and annealing affects all such properties related to the optical properties. Therefore, evaluation of the lattice structure, and the number of defects in ion-implanted layers is crucial. Several methods have been used for such evaluation, including X-ray diffraction (XRD), transparent electron microcopy (TEM), electron
*
Corresponding author. Tel.: +81 29 861 2436; fax: +81 29 861 7091. E-mail address: [email protected] (H. Ogiso).
0168-583X/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.01.057
diffraction, Rutherford backscattering spectroscopy (RBS), and Raman spectroscopy. Although these are excellent methods, they have disadvantages, such as limitations on the material of the object, destruction of the sample itself, and indirect information. In this study, terahertz (THz) spectroscopy was used as an evaluation method for ion-implanted ionic crystals because this method is non-destructive, and yields direct information. THz spectroscopy can quantitatively clarify the oscillation parameters of the optical phonons, and the dispersion of the dielectric constant [12,13], both of which are closely related to the lattice structure, and important basic properties for designing optical and electrical devices.
2. Experimental procedure MgO(1 0 0) single crystal samples (20 · 20 · 0.5 mm3) were prepared, and implanted with 3.1 MeV Au ions at an ion fluence of 1 · 1016 cm1. The temperature during implantation was maintained at 100 K by adjusting an electric heater and liquid nitrogen supplied to the chamber.
H. Ogiso et al. / Nucl. Instr. and Meth. in Phys. Res. B 257 (2007) 545–548
The implanted sample was annealed first at 700 K for 1 h, and then again at 1100 K for 1 h. Before and after the implantation and before and after each annealing, the optical spectra in two frequency ranges were measured: the transmittance T spectrum with a wavelength ranging from 200 to 1500 nm, and the reflectance R spectrum with a wave number ranging from 200 to 700 cm1. The T spectra was used to verify metal nano-cluster formation induced by the ion-implantation, and the R spectra was used to clarify the effect of the ion-implantation on optical phonon modes. 3. Results Fig. 1 shows the T spectra of the MgO ion-implanted ionic crystal samples. The as ion-implanted sample (i.e. no annealing) clearly showed an absorption peak at about 580 nm. The peak disappeared with increasing annealing temperature, indicating that the annealing process suppressed the origin of the absorption. Fig. 2 shows the R spectra. Particularly the untreated MgO sample (i.e. no ion-implantation or annealing) showed a high R region from 400 to 500 cm1 (’1). The ion-implantation reduced the R up to about 0.9, whereas the subsequent annealing process restored the R to its initial level. The spectrum of this frequency range mainly is responsible for ionic polarization, indicating that the lattice structure of an ionic crystal strongly affects this spectrum. To evaluate the effect of ion-implantation on the lattice structure, the dielectric function (m) of MgO and ionimplanted layers were evaluated from the R spectra as follows. The relationship between the complex dielectric
-1
Wave number [cm ] 200
400
500
600
700
MgO (001) 1100 K 700 K As implanted
0.8
0.6
untreated MgO (001) as-implanted annealed (700 K 1 h) annealed (1100 K 1 h)
0.4
6
8
10
12
14
16
18
20
Frequency [THz] Fig. 2. Reflectance R spectra in the THz range for untreated MgO(0 0 1), as-implanted, annealed at 700 K, and annealed at 1100 K.
function (m) = 1(m) + i2(m) and the complex refractive index n = n1 + in2 is given by: 1 ¼ n21 n22 ;
2 ¼ 2n1 n2 :
ð1Þ
For an ionic crystal, based on the classical damping harmonic oscillator model (Lorentian model), (m) is expressed as: ðmÞ ¼ 1 þ
0.9
300
1.0
Reflectance, R
546
X j
S 2j ; m2j m2 icj m
ð2Þ
MgO (001)
0.8
1100 K
Transmittance, T
700 K
untreated MgO (001) as-implanted annealed (700 K 1 h) annealed (1100 K 1 h)
0.7
0.6
as-implanted
0.5 400
600
800
1000
1200
1400
Wavelength [nm] Fig. 1. Transmittance T spectra in the visible and near IR range for untreated MgO(0 0 1), as-implanted, annealed at 700 K, and annealed at 1100 K.
where mj is the frequency of the jth optical phonon mode, Sj is the oscillation strength, and cj is the damping constant. The optical spectrum therefore, can be derived from the oscillation parameters mj, Sj, cj, and conversely, these oscillation parameters can be obtained by fitting the experimental spectrum with a calculated spectrum. In the fitting, we assumed a two-layer model, as shown in Fig. 3, where the thickness of the ion-implanted layer was 2 lm determined by TEM analysis (Fig. 3(a)). The complex dielectric constant of MgO is a(m) and that of the ion-implanted layer is b(m), where the assumed value of b was uniform in the ion-implanted layer. In the fitting procedure, six optical phonon modes (105, 125, 175, 295, 405, 652 cm1) were used as initial values [13]. First, the fitting process was applied to untreated MgO(0 0 1). Fig. 4 shows the best fit result, the calculated R spectrum of MgO(0 0 1) agrees well with the experimental R spectrum. Next, the fitting was applied to ion-implanted MgO by only varying the ci. Fig. 4 shows the fit result, indicating that again, the calculated spectrum agrees well with the experimental spectrum. Together, these two results
H. Ogiso et al. / Nucl. Instr. and Meth. in Phys. Res. B 257 (2007) 545–548 200
1000
Real part of dielectric constant, ε1
547
untreated MgO (001) as-implanted annealed 700 K annealed 1100 K
500
100 0 -100 -200 11.0
12.0
13.0
m in
zoo
0
-500
Imaginary part of dielectric constant, ε2
-1000
1000
Ion-implanted layer 0.5 mm
MgO
Fig. 3. (a) TEM profile of 3 MeV Au ion-implanted MgO, and electron diffraction pattern in the implanted region. (Reprint from Nuclear Instruments and Method B 206, H. Ogiso, S. Nakano, J. Akedo ‘‘Abnormal distribution of defects introduced into MgO single crystals by MeV ion-implantation’’, p. 158 copyright (2003) with permission from Elsevier). (b) Schematic of the two-layer model used for spectrum analysis.
-1
Wave number [cm ] 200
300
400
500
600
700
100
10
1
0.1 5
15
20
Frequency [THz] Fig. 5. Calculated complex dielectric function (m) = 1(m) + i2(m) for untreated MgO(0 0 1), as-implanted, annealed at 700 K, and annealed at 1100 K.
Table 1 Fitting result of cp
untreated MgO (001)
1.0
10
cp (cm1)
Untreated MgO(0 0 1)
As-implanted
700 K 1 h
1100 K 1 h
1.31
18.9
15.1
8.2
as-implanted
Reflectance, R
0.8
phonon mode at 400 cm1 (12 THz) dominantly contributed to the dispersion of the (m). Therefore, ci at 400 cm1 phonon mode (hereafter called cp) can be regarded as a representative value showing the effect of ion-implantation on the MgO lattice. Table 1 summarizes the fitting result for cp, revealing that the ion-implantation increased cp from 1.31 to 18.9, and that the annealing process reduced it with increasing annealing temperature.
0.6
experimental calculated
0.4
4. Discussion 0.2 6
8
10
12
14
16
18
20
Frequency [THz] Fig. 4. Fitting results of the experimental with calculated THz spectra.
indicate that the effect of the ion-implantation on optical phonon modes is mainly responsible for the change in ci. Fig. 5 shows the (m) calculated from the oscillation parameters, revealing that the resonance of the optical
The THz spectroscopy analysis results indicate that ionimplantation significantly increased cp. Although the resonance was significantly suppressed, the wave number of the principal optical phonon mode (400 cm1) was apparently unaffected by ion-implantation, suggesting that the main lattice structure should be preserved after ion-implantation. This expectation is supported by the result of electron diffraction analysis, as shown in Fig. 3(a). The increase in cp suggests that discontinuities in the lattice bond should
548
H. Ogiso et al. / Nucl. Instr. and Meth. in Phys. Res. B 257 (2007) 545–548
increase with ion-implantation. Therefore, the increase in cp with ion-implantation corresponds to the introduction of defects, and the decrease in cp with annealing corresponds to the recovery from these defects. In the T spectra (Fig. 1), the absorption peak at 580 nm for the ion-implanted MgO diminished with increasing annealing temperature, similar to trend observed for cp. The peak therefore, could be due to defects. Several studies have reported an opposite trend for metal ion-implanted MgO single crystals, however, namely that the absorption peak near 580 nm increases in intensity with increasing annealing temperature [3,4]. This increase in peak intensity is said to be due to formation of metal nano-clusters in the implanted layer, because the surface plasmon resonance (SPR) causes absorption. The reason for the difference in the results between our study and the study by Zimmerman and Fedorov might be the difference in the ion fluence. The ion fluence used here was 1 · 1016 cm2 lower than that used by Zimmerman and Fedorov. The Au concentration in the implanted layer in our study was probably not high enough to form Au clusters, because if Au clusters were formed in the implanted layer, not only the Lorentian model but also the Drude model would be required to explain the R spectrum in Fig. 2. Thus, the origin of the peak cannot be explained by SPR, although the wavelength of the peak was almost identical with that of the peak by SPR. 5. Conclusions THz spectroscopy analysis of Au-ion implanted MgO quantitatively shows that ion-implantation and subsequent annealing significantly affect the damping constant cp of the principal optical phonon mode, and that the absorption peak at 580 nm is caused by defects introduced by ion-
implantation when the ion fluence is low (1 · 1016 cm2). These results demonstrate that THz spectroscopy yields crucial information about ion-implanted ionic crystals that can then be applied to the design of optical and electrical devices. Acknowledgements This work is supported by the NEDO Project ‘‘NanoStructure Forming for Advanced Ceramic Integration Technology’’ in the Japan Nanotechnology Program. References [1] A. Turos, O. Meyer, Hj. Matzke, Appl. Phys. Lett. 38 (11) (1981) 910. [2] R.H. Magruder III, L. Yang, R.F. Haglund Jr., C.W. White, L. Yang, et al., Appl. Phys. Lett. 62 (15) (1993) 1730. [3] R.L. Zimmerman, D. Ila, E.K. Williams, S. Sarkisv, D.B. Poker, et al., Nucl. Instr. and Meth. B 141 (1998) 308. [4] A.V. Fedorov, M.A. van Huis, A. van Veen, H. Schut, Nucl. Instr. and Meth. B 166–167 (2000) 215. [5] M.A. van Huis, A.V. Fedorov, A. van Veen, P.J.M. Smulders, B.J. Kooi, et al., Nucl. Instr. and Meth. B 166–167 (2000) 225. [6] Y. Takeda, C.G. Lee, N. Kishimoto, Nucl. Instr. and Meth. B 190 (2002) 797. [7] M.A. van Huis, A.V. Fedorov, A. van Veen, C.V. Falub, S.W.H. Eijt, et al., Nucl. Instr. and Meth. B 191 (2002) 442. [8] H. Ogiso, S. Nakano, J. Akedo, Nucl. Instr. and Meth. B 206 (2003) 157. [9] H. Ogiso, S. Nakano, Surf. Coat. Tech. 196 (2005) 15. [10] E. Alves, R.C. da Silva, J.V. Pinto, T. Monteiro, B. Savoini, et al., Nucl. Instr. and Meth. B 206 (2003) 148. [11] N. Kishimoto, O.A. Plaksin, K. Masuo, N. Okubo, N. Umeda, Y. Takeda, Nucl. Instr. and Meth. B 242 (2006) 186. [12] M. Nakada, K. Ohashi, J. Akedo, Jpn. J. Appl. Phys. 44 (9B) (2005) 6918. [13] S. Cunsolo, P. Dore, S. Lupi, P. Maselli, C.P. Varsamis, Infrared Phys. 33 (6) (1992) 539.
Nuclear Instruments and Methods in Physics Research B 257 (2007) 545–548 www.elsevier.com/locate/nimb
THz spectroscopy of ion-implanted MgO crystals Hisato Ogiso b
a,*
, Masafumi Nakada b, Shizuka Nakano a, Jun Akedo
a
a National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan Fundamental and Environmental Research Laboratories, NEC Corporation, 34 Miyukigakoka, Tsukuba, Ibaraki 305-8501, Japan
Available online 17 January 2007
Abstract The terahertz (THz) spectroscopy of ion-implanted layers was investigated. First, MgO(0 0 1) single crystals were implanted with 3 MeV gold ions at an ion fluence of 1 · 1016 cm2, and annealed in air at 700 K for 1 h, and again at 1100 K for 1 h. Then, the reflectance spectrum ranging from 200 to 700 cm1, and transmittance spectrum ranging from 200 to 1500 nm were measured. Results showed that the MgO had a high reflectance (’1) region from 400 to 500 cm1. The ion-implantation reduced this reflectance to 0.9, and the annealing process restored it. Analysis of the reflectance spectra yielded the oscillation parameters of the optical phonon modes of MgO. The ionimplantation increased the damping constant of the phonon mode at 400 cm1 from 1.31 to 18.9 cm1, whereas the annealing process reduced it to 8.2 cm1. The absorption peak at 580 nm due to the ion-implantation was reduced by the annealing process. 2007 Elsevier B.V. All rights reserved. PACS: 77.22.d; 61.80.Jh Keywords: THz spectroscopy; Ion-implantation; Dielectric constant; Optical phonon; Defect
1. Introduction Ion-implantation into ionic crystals has recently attracted significant interest due to its beneficial role in the formation of nano-structures [1–11]. One target of recent research has been to modify the optical properties of ionic crystals. Ion-implantation followed by thermal annealing generates embedded nano-clusters, which in turn can generate non-linear optical properties. Optical properties are responsible for properties of ion-implanted crystals such as defects in the crystal lattice as well as properties of embedded clusters such as their size, and electric conductivity. Ion-implantation and annealing affects all such properties related to the optical properties. Therefore, evaluation of the lattice structure, and the number of defects in ion-implanted layers is crucial. Several methods have been used for such evaluation, including X-ray diffraction (XRD), transparent electron microcopy (TEM), electron
*
Corresponding author. Tel.: +81 29 861 2436; fax: +81 29 861 7091. E-mail address: [email protected] (H. Ogiso).
0168-583X/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.01.057
diffraction, Rutherford backscattering spectroscopy (RBS), and Raman spectroscopy. Although these are excellent methods, they have disadvantages, such as limitations on the material of the object, destruction of the sample itself, and indirect information. In this study, terahertz (THz) spectroscopy was used as an evaluation method for ion-implanted ionic crystals because this method is non-destructive, and yields direct information. THz spectroscopy can quantitatively clarify the oscillation parameters of the optical phonons, and the dispersion of the dielectric constant [12,13], both of which are closely related to the lattice structure, and important basic properties for designing optical and electrical devices.
2. Experimental procedure MgO(1 0 0) single crystal samples (20 · 20 · 0.5 mm3) were prepared, and implanted with 3.1 MeV Au ions at an ion fluence of 1 · 1016 cm1. The temperature during implantation was maintained at 100 K by adjusting an electric heater and liquid nitrogen supplied to the chamber.
H. Ogiso et al. / Nucl. Instr. and Meth. in Phys. Res. B 257 (2007) 545–548
The implanted sample was annealed first at 700 K for 1 h, and then again at 1100 K for 1 h. Before and after the implantation and before and after each annealing, the optical spectra in two frequency ranges were measured: the transmittance T spectrum with a wavelength ranging from 200 to 1500 nm, and the reflectance R spectrum with a wave number ranging from 200 to 700 cm1. The T spectra was used to verify metal nano-cluster formation induced by the ion-implantation, and the R spectra was used to clarify the effect of the ion-implantation on optical phonon modes. 3. Results Fig. 1 shows the T spectra of the MgO ion-implanted ionic crystal samples. The as ion-implanted sample (i.e. no annealing) clearly showed an absorption peak at about 580 nm. The peak disappeared with increasing annealing temperature, indicating that the annealing process suppressed the origin of the absorption. Fig. 2 shows the R spectra. Particularly the untreated MgO sample (i.e. no ion-implantation or annealing) showed a high R region from 400 to 500 cm1 (’1). The ion-implantation reduced the R up to about 0.9, whereas the subsequent annealing process restored the R to its initial level. The spectrum of this frequency range mainly is responsible for ionic polarization, indicating that the lattice structure of an ionic crystal strongly affects this spectrum. To evaluate the effect of ion-implantation on the lattice structure, the dielectric function (m) of MgO and ionimplanted layers were evaluated from the R spectra as follows. The relationship between the complex dielectric
-1
Wave number [cm ] 200
400
500
600
700
MgO (001) 1100 K 700 K As implanted
0.8
0.6
untreated MgO (001) as-implanted annealed (700 K 1 h) annealed (1100 K 1 h)
0.4
6
8
10
12
14
16
18
20
Frequency [THz] Fig. 2. Reflectance R spectra in the THz range for untreated MgO(0 0 1), as-implanted, annealed at 700 K, and annealed at 1100 K.
function (m) = 1(m) + i2(m) and the complex refractive index n = n1 + in2 is given by: 1 ¼ n21 n22 ;
2 ¼ 2n1 n2 :
ð1Þ
For an ionic crystal, based on the classical damping harmonic oscillator model (Lorentian model), (m) is expressed as: ðmÞ ¼ 1 þ
0.9
300
1.0
Reflectance, R
546
X j
S 2j ; m2j m2 icj m
ð2Þ
MgO (001)
0.8
1100 K
Transmittance, T
700 K
untreated MgO (001) as-implanted annealed (700 K 1 h) annealed (1100 K 1 h)
0.7
0.6
as-implanted
0.5 400
600
800
1000
1200
1400
Wavelength [nm] Fig. 1. Transmittance T spectra in the visible and near IR range for untreated MgO(0 0 1), as-implanted, annealed at 700 K, and annealed at 1100 K.
where mj is the frequency of the jth optical phonon mode, Sj is the oscillation strength, and cj is the damping constant. The optical spectrum therefore, can be derived from the oscillation parameters mj, Sj, cj, and conversely, these oscillation parameters can be obtained by fitting the experimental spectrum with a calculated spectrum. In the fitting, we assumed a two-layer model, as shown in Fig. 3, where the thickness of the ion-implanted layer was 2 lm determined by TEM analysis (Fig. 3(a)). The complex dielectric constant of MgO is a(m) and that of the ion-implanted layer is b(m), where the assumed value of b was uniform in the ion-implanted layer. In the fitting procedure, six optical phonon modes (105, 125, 175, 295, 405, 652 cm1) were used as initial values [13]. First, the fitting process was applied to untreated MgO(0 0 1). Fig. 4 shows the best fit result, the calculated R spectrum of MgO(0 0 1) agrees well with the experimental R spectrum. Next, the fitting was applied to ion-implanted MgO by only varying the ci. Fig. 4 shows the fit result, indicating that again, the calculated spectrum agrees well with the experimental spectrum. Together, these two results
H. Ogiso et al. / Nucl. Instr. and Meth. in Phys. Res. B 257 (2007) 545–548 200
1000
Real part of dielectric constant, ε1
547
untreated MgO (001) as-implanted annealed 700 K annealed 1100 K
500
100 0 -100 -200 11.0
12.0
13.0
m in
zoo
0
-500
Imaginary part of dielectric constant, ε2
-1000
1000
Ion-implanted layer 0.5 mm
MgO
Fig. 3. (a) TEM profile of 3 MeV Au ion-implanted MgO, and electron diffraction pattern in the implanted region. (Reprint from Nuclear Instruments and Method B 206, H. Ogiso, S. Nakano, J. Akedo ‘‘Abnormal distribution of defects introduced into MgO single crystals by MeV ion-implantation’’, p. 158 copyright (2003) with permission from Elsevier). (b) Schematic of the two-layer model used for spectrum analysis.
-1
Wave number [cm ] 200
300
400
500
600
700
100
10
1
0.1 5
15
20
Frequency [THz] Fig. 5. Calculated complex dielectric function (m) = 1(m) + i2(m) for untreated MgO(0 0 1), as-implanted, annealed at 700 K, and annealed at 1100 K.
Table 1 Fitting result of cp
untreated MgO (001)
1.0
10
cp (cm1)
Untreated MgO(0 0 1)
As-implanted
700 K 1 h
1100 K 1 h
1.31
18.9
15.1
8.2
as-implanted
Reflectance, R
0.8
phonon mode at 400 cm1 (12 THz) dominantly contributed to the dispersion of the (m). Therefore, ci at 400 cm1 phonon mode (hereafter called cp) can be regarded as a representative value showing the effect of ion-implantation on the MgO lattice. Table 1 summarizes the fitting result for cp, revealing that the ion-implantation increased cp from 1.31 to 18.9, and that the annealing process reduced it with increasing annealing temperature.
0.6
experimental calculated
0.4
4. Discussion 0.2 6
8
10
12
14
16
18
20
Frequency [THz] Fig. 4. Fitting results of the experimental with calculated THz spectra.
indicate that the effect of the ion-implantation on optical phonon modes is mainly responsible for the change in ci. Fig. 5 shows the (m) calculated from the oscillation parameters, revealing that the resonance of the optical
The THz spectroscopy analysis results indicate that ionimplantation significantly increased cp. Although the resonance was significantly suppressed, the wave number of the principal optical phonon mode (400 cm1) was apparently unaffected by ion-implantation, suggesting that the main lattice structure should be preserved after ion-implantation. This expectation is supported by the result of electron diffraction analysis, as shown in Fig. 3(a). The increase in cp suggests that discontinuities in the lattice bond should
548
H. Ogiso et al. / Nucl. Instr. and Meth. in Phys. Res. B 257 (2007) 545–548
increase with ion-implantation. Therefore, the increase in cp with ion-implantation corresponds to the introduction of defects, and the decrease in cp with annealing corresponds to the recovery from these defects. In the T spectra (Fig. 1), the absorption peak at 580 nm for the ion-implanted MgO diminished with increasing annealing temperature, similar to trend observed for cp. The peak therefore, could be due to defects. Several studies have reported an opposite trend for metal ion-implanted MgO single crystals, however, namely that the absorption peak near 580 nm increases in intensity with increasing annealing temperature [3,4]. This increase in peak intensity is said to be due to formation of metal nano-clusters in the implanted layer, because the surface plasmon resonance (SPR) causes absorption. The reason for the difference in the results between our study and the study by Zimmerman and Fedorov might be the difference in the ion fluence. The ion fluence used here was 1 · 1016 cm2 lower than that used by Zimmerman and Fedorov. The Au concentration in the implanted layer in our study was probably not high enough to form Au clusters, because if Au clusters were formed in the implanted layer, not only the Lorentian model but also the Drude model would be required to explain the R spectrum in Fig. 2. Thus, the origin of the peak cannot be explained by SPR, although the wavelength of the peak was almost identical with that of the peak by SPR. 5. Conclusions THz spectroscopy analysis of Au-ion implanted MgO quantitatively shows that ion-implantation and subsequent annealing significantly affect the damping constant cp of the principal optical phonon mode, and that the absorption peak at 580 nm is caused by defects introduced by ion-
implantation when the ion fluence is low (1 · 1016 cm2). These results demonstrate that THz spectroscopy yields crucial information about ion-implanted ionic crystals that can then be applied to the design of optical and electrical devices. Acknowledgements This work is supported by the NEDO Project ‘‘NanoStructure Forming for Advanced Ceramic Integration Technology’’ in the Japan Nanotechnology Program. References [1] A. Turos, O. Meyer, Hj. Matzke, Appl. Phys. Lett. 38 (11) (1981) 910. [2] R.H. Magruder III, L. Yang, R.F. Haglund Jr., C.W. White, L. Yang, et al., Appl. Phys. Lett. 62 (15) (1993) 1730. [3] R.L. Zimmerman, D. Ila, E.K. Williams, S. Sarkisv, D.B. Poker, et al., Nucl. Instr. and Meth. B 141 (1998) 308. [4] A.V. Fedorov, M.A. van Huis, A. van Veen, H. Schut, Nucl. Instr. and Meth. B 166–167 (2000) 215. [5] M.A. van Huis, A.V. Fedorov, A. van Veen, P.J.M. Smulders, B.J. Kooi, et al., Nucl. Instr. and Meth. B 166–167 (2000) 225. [6] Y. Takeda, C.G. Lee, N. Kishimoto, Nucl. Instr. and Meth. B 190 (2002) 797. [7] M.A. van Huis, A.V. Fedorov, A. van Veen, C.V. Falub, S.W.H. Eijt, et al., Nucl. Instr. and Meth. B 191 (2002) 442. [8] H. Ogiso, S. Nakano, J. Akedo, Nucl. Instr. and Meth. B 206 (2003) 157. [9] H. Ogiso, S. Nakano, Surf. Coat. Tech. 196 (2005) 15. [10] E. Alves, R.C. da Silva, J.V. Pinto, T. Monteiro, B. Savoini, et al., Nucl. Instr. and Meth. B 206 (2003) 148. [11] N. Kishimoto, O.A. Plaksin, K. Masuo, N. Okubo, N. Umeda, Y. Takeda, Nucl. Instr. and Meth. B 242 (2006) 186. [12] M. Nakada, K. Ohashi, J. Akedo, Jpn. J. Appl. Phys. 44 (9B) (2005) 6918. [13] S. Cunsolo, P. Dore, S. Lupi, P. Maselli, C.P. Varsamis, Infrared Phys. 33 (6) (1992) 539.