Optical property changes of silica glass and sapphire induced by Cu and O implantation

Optical property changes of silica glass and sapphire induced by Cu and O implantation

Nuclear Instruments and Methods in Physics Research B 175±177 (2001) 652±657 www.elsevier.nl/locate/nimb Optical property changes of silica glass an...

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Nuclear Instruments and Methods in Physics Research B 175±177 (2001) 652±657

www.elsevier.nl/locate/nimb

Optical property changes of silica glass and sapphire induced by Cu and O implantation M. Ikeyama a

a,*

, S. Nakao a, M. Tazawa a, K. Kadono b, K. Kamada

b

National Industrial Research Institute of Nagoya, Hirate-cho, Kita-ku, Nagoya 462-8510, Japan b Osaka National Research Institute, AIST, Midorigaoka, Ikeda, Osaka 563-8577, Japan

Abstract Single- and multi-energy O and Cu ions were implanted into silica glass (or sapphire) changing the ratios of O and Cu doses as like Cu only (0:1), 1=2O ‡ Cu (0.5:1) and O ‡ Cu (1:1). Optical property changes induced by the ion implantations and successive heat treatments have been studied. Speci®c optical absorption was clearly observed at about 570 nm, which attributed to Cu nano-particles for the samples of Cu, 1=2O ‡ Cu and Cu ‡ 1=2O implantations. Multi-energy implantation at 300 K enhanced the absorption. With the increase of annealing temperature, the size and concentration of Cu particles are increased. The sequence of ion implantation between Cu and O a€ects the optical absorption and nano-particle formation. Third-order non-linear optical susceptibility, v…3† , has been measured for sapphire samples. The values of v…3† were 6:5  10 9 esu and 4:0  10 9 esu for Cu and 1=2O ‡ Cu implantation, respectively. Ó 2001 Elsevier Science B.V. All rights reserved. PACS: 68.55.L; 61.46; 78.66.J; 61.43.Fs Keywords: Ion implantation; Optical absorption; Third-order non-linear optical susceptibility; Nano-particles; Silica glass; Sapphire

1. Introduction Nano-particles have attracted much attention recently because of the possibility of the application for luminescent and non-linear optical devices. Ion implantation is one of the useful techniques for the formation of nano-particles. Many studies have been done to make nano-par-

*

Corresponding author. Tel.: +81-52-911-3452; fax: +81-52911-2141. E-mail address: [email protected] (M. Ikeyama).

ticles by ion implantation and have revealed their luminescent [1] and non-linear optical properties [2±5]. We have studied the formation of metal or metal-oxide nano-particles by metal implantation or co-implantation of metal and oxygen into silica glass or sapphire [6,7]. In this study, optical property changes of silica glass and sapphire induced by Cu and O implantation and successive annealing, have been studied, paying attention to the formation of copper or copper oxide nanoparticles. In order to increase the thickness of the layers of nano-particles, multi-energy implantation was also performed for silica glass samples.

0168-583X/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 0 ) 0 0 6 5 4 - 6

M. Ikeyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 175±177 (2001) 652±657

2. Experiment Optically ¯at silica glass and sapphire samples were implanted with 1:0 MeV O‡ and 1.8 MeV (for silica glass) or 2.1 MeV (for sapphire) Cu‡ ions (hereafter we call this implantation as singleenergy implantation). The energies are chosen in order to obtain the same projection range of O and Cu. The dose of Cu was the same for all samples as 1  1017 ions=cm2 , but the doses of O ions were changed as 0 (Cu only), 0:5  1017 …1=2O ‡ Cu† 2 and 1  1017 …O ‡ Cu† ions=cm . The sample was cooled by liquid nitrogen (about 100 K) in ion implantation. After the implantation, samples were annealed at 1270 K for 1 h in vacuum. For silica glass samples, multi-energy implantation was also performed with 1.2, 1.7 and 2.4 MeV Cu‡ and 0.4, 0.7 and 1.2 MeV O‡ ions, in order to have ¯at and wider pro®les of implanted ions. The dose of each Cu implantation was 2 1  1017 ion=cm . The dose of O ions and implantation sequence between Cu and O were changed as Cu; Cu ‡ 1=2O; 1=2O ‡ Cu; Cu ‡ O and O ‡ Cu. On the energy, we adopted energy increase mode, that is lowest energy implantation is the ®rst, the second is the middle energy and the last is the highest energy implantation. The implantation was performed at room temperature (about 300 K). After the implantation, each sample was cut into four pieces and three pieces of the sample were annealed at 770, 1070 and 1270 K in air, respectively. Optical absorption was measured by a spectrophotometer (JASCO V-570). Glancing angle X-ray di€raction (G-XRD) measurement was performed with the angle of 3° using a RIGAKU RAD-1C system. On the non-linear optical properties, third-order non-linear optical susceptibility, v…3† , has been measured for sapphire samples by the phase-conjugation-type degenerate four-wave mixing method with 532 nm laser of 35 ps pulse duration. As a calibration standard, CS2 was used. 3. Results and discussion Firstly, the results of optical absorption measurement for single-energy implantation of Cu and

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O ions at 100 K into silica glass and sapphire samples are shown in Fig. 1. After the annealing at 1270 K for 1 h, an optical absorption band was clearly observed at about 560 nm and 590 nm for Cu only implanted silica glass and sapphire samples, respectively. This absorption originates from the surface plasmon resonance of Cu nano-particles [2,5±7]. It must be emphasized that the

Fig. 1. Optical absorptions for (a) silica glass and (b) sapphire samples induced by 1.0 MeV O and 1.8 MeV Cu for silica glass or 1.0 MeV O and 2.1 MeV Cu for sapphire (single-energy) implantation at 100 K and successive annealing at 1270 K for 1 h. The indications of Cu; 1=2O ‡ Cu and O ‡ Cu in the ®gure show the dose of O is 0, 5  1016 or 1  1017 ions=cm2 , respectively, and the dose of Cu is 1  1017 ions=cm2 for all samples.

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M. Ikeyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 175±177 (2001) 652±657

Fig. 2. Optical absorptions of silica glass samples induced by multi-energy (1.2, 1.7 and 2.4 MeV) Cu ion implantation at room temperature (300 K) and successive annealing. The dose is 1  1017 ions=cm2 for each implantation. Annealing conditions are shown in the ®gure.

absorption band did not appear up to the annealing of 770 K for 1 h [6,7]. On the other hand, co-implantation with Cu and O ions reduced the absorption as a whole and in the case of O ‡ Cu implantation, there was almost no absorption band attributed to Cu nano-particles. Microstructures of these samples are presented in another paper [8]. The results for multi-energy Cu implantation into silica glass are shown in Fig. 2. Clearly, the absorption band at about 570 nm, which attributed to Cu nano-particles, is observed even asimplanted sample and the absorption increased with the increase of annealing temperature. Fig. 3 shows the results of G-XRD measurement for multi-energy Cu implantation into silica glass. Two peaks at 53.3° and 50.4° are observed for all pieces even for the as-implanted one, and they correspond to Cu(1 1 1) and Cu(2 0 0) planes, respectively. This result ensures the formation of Cu nano-particles, which was caused by the optical absorption at about 570 nm. The peak intensity increased and bandwidth decreased with the increase of annealing temperature. This behavior

Fig. 3. Results of G-XRD measurement for the same samples of Fig. 2.

indicates both the size and concentration of Cu nano-particles increase with the annealing temperature. The results of G-XRD measurement agree with the results of optical absorption measurement. Fig. 4 shows the results of optical absorption measurement of as-implant and 1270 K annealed samples for multi-energy Cu; Cu ‡ 1=2O; 1=2O ‡ Cu; Cu ‡ O and O ‡ Cu implantation. The results for 770 K annealed and 1070 K annealed samples are almost the same as the results for as-implanted and 1270 K annealed ones, respectively. Obviously, the increase of O dose leads to reduce the optical absorption in general, however, ®rst O and subsequent Cu implantation leads to larger absorption than the ®rst Cu and subsequent O implantation for the same total doses of Cu and O ions. On the absorption band attributed to Cu nano-particles, besides the Cu implantation, the as-implanted Cu ‡ 1=2O sample shows a weak peak at about 570 nm and the as-implanted Cu ‡ O sample shows a very weak peak in Fig. 4(a). On the other hand, 1=2O ‡ Cu and

M. Ikeyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 175±177 (2001) 652±657

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Fig. 5. Results of G-XRD measurement for the 1270 K annealed silica glass samples with multi-energy Cu; Cu ‡ 1=2O; 1=2O ‡ Cu; Cu ‡ O and O ‡ Cu implantations.

Fig. 4. Optical absorptions of as-implanted and 1270 K annealed silica glass samples for multi-energy Cu; Cu ‡ 1=2O; 1=2O ‡ Cu; Cu ‡ O and O ‡ Cu implantations. The energies of Cu ions are 1.2, 1.7 and 2.4 MeV, and the dose is 1  1017 ions=cm2 for the label of Cu. The energies of O ions are 0.4, 0.7 and 1.2 MeV, and the dose is 5  1016 or 1  1017 ions=cm2 for the label of 1/2O or O, respectively.

O ‡ Cu samples do not show the peak. It is clear that the sequence of ion implantation a€ects the optical absorption or the formation of Cu nanoparticles. For 1270 K annealing (Fig. 4(b)), the increase of the absorption at the Cu nano-particle band is obvious for Cu; Cu ‡ 1=2O and 1=2O ‡ Cu implantation, as shown in Fig. 2. For Cu; Cu ‡ O and O ‡ Cu implantations, decreases

of absorption in UV region are shown clearly but the absorption increased for Cu ‡ 1=2O and 1=2O ‡ Cu implantations, especially at about 210 nm and 340 nm. Fig. 5 shows the results of G-XRD measurement for the 1270 K annealed samples. Peaks from Cu(1 1 1) and Cu(2 0 0) planes are found for Cu; Cu ‡ 1=2O and 1=2O ‡ Cu implantations, although they are not found for Cu ‡ O and O ‡ Cu implantations. With the increase of the O dose, several peaks are found at about 36.6° and 42.4° attributed to Cu2 O…1 1 1† and Cu2 O…2 0 0†, and 35.6°, 38.6° and 48.8° attributed to CuO()1 1 1), CuO(1 1 1) and CuO()2 0 2) planes, respectively. These peaks became apparent after the 1070 K annealing. However, the intensities were weaker than the 1270 K annealing. Very weak peaks attributed to Cu2 O planes can be seen even for the Cu-implanted samples as like our previous study [6]. This suggests the oxidization of Cu during the annealing. Indeed, color of the sample changed in some regions and the

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M. Ikeyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 175±177 (2001) 652±657

surface became very rough after the 1270 K annealing. For multi-energy Cu implantation, the area of absorptions attributed to Cu nano-particles increases continuously with the temperature, as 21.4, 25.2, 33.7 and 36.5 for as-implanted, 770, 1070 and 1270 K annealing, respectively. The areas are 3±5 times larger than that of single-energy implantation (7.6). We must remember that the total amount of implanted ions for multi-energy implantation is three times larger than that for single-energy implantation, and the temperatures in implantation are di€erent. Estimated radius of Cu nano-particles, according to Arnold [9], for single-energy Cu implanted sample is 6.56 nm and agrees very well with the peak diameter of Cu nano-particles (13 nm) evaluated from TEM observation for the same sample [8]. For multi-energy Cu implantation, the radius increases with the annealing temperature, as 5.6, 5.9 and 6.1 nm for as-implanted, 770 and 1070 K annealing, respectively. The decrease of the radius for 1270 K annealing (5.8 nm) might be a€ected by oxidization. There is also a tendency that the peak position shifts toward longer wavelengths with the increase of annealing temperature. It must be related to the growth of Cu nano-particles like Au nano-particles [3]. Third-order non-linear optical susceptibility, v…3† , was evaluated with the thickness of nanoparticle layers as 250 nm from the straggling of implanted ions calculated by SRIM code [10]. The values of v…3† were 6:5  10 9 and 4:0  10 9 esu for Cu and 1=2O ‡ Cu implantation, respectively. For O ‡ Cu implantation, the phase-conjugate beam could not be detected. From Fig. 1(b), the formation of Cu nano-particles by the Cu and 1=2O ‡ Cu implantation and successive annealing very clear, and the formation was con®rmed by XRD measurement (not shown). The XRD measurement also revealed the formation of Cu2 O nano-particles for 1=2O ‡ Cu implantations, and Cu2 O and very small amount of CuO nano-particle but almost no Cu nano-particles for O ‡ Cu implantation, as like silica glass shown in Fig. 5. It can be said that the origin of the measured nonlinear optical properties is Cu nano-particles formed in sapphire samples.

In order to consider the inherent strength of non-linear process, a ®gure of merit [4], v…3† =a532 , is useful. The values of v…3† =a532 are 3:3  10 13 and 7:4  10 13 esu cm for Cu and 1=2O ‡ Cu implantation, respectively. The value of v…3† for Cu implantation is about 1.5 times larger than that for 1=2O ‡ Cu implantation, but the value of v…3† =a532 for Cu implantation is less than one-half for 1/ 2O+Cu implantation. It can be said that the reduction of optical absorption, a532 , by O implantation is very e€ective. To optimize the ratio between Cu and O doses, it might be possible to increase the value of v…3† =a532 . Our values of v…3† and v…3† =a532 of 4:0±6:5  10 9 esu and 3:3±7:4  10 13 esu cm measured with a 35-ps-pulse laser, are smaller than those of Uchida et al. [2] and Takeda et al. [5] with 7-ns-pulse lasers, by the factor of ten or more. Ando et al. [4] have revealed that the v…3† obtained by using a 35ps-pulse laser is 10±30 times smaller than that by a 7-ns-pulse laser.

4. Summary Optical property changes of silica glass and sapphire, which were implanted with the singleand multi-energy O and Cu by changing the dose ratios of O and Cu, and the e€ect of successive heat treatments, have been studied. Speci®c optical absorption was clearly observed at about 570 nm, which is attributed to Cu nano-particles for the samples of Cu; 1=2O ‡ Cu and Cu ‡ 1=2O implantations. Multi-energy implantation at 300 K enhanced the absorption. With the increase of annealing temperature, the size and concentration of Cu particles are increased. The sequence of ion implantation between Cu and O a€ects the optical absorption and nanoparticle formation. Third-order non-linear optical susceptibility, v…3† , has been measured for sapphire samples. The values of v…3† were 6:5  10 9 and 4:0  10 9 esu for Cu and 1=2O ‡ Cu implantation, respectively. It can be said that the origin of the measured non-linear optical properties is caused by the Cu nano-particles in sapphire.

M. Ikeyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 175±177 (2001) 652±657

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