- Email: [email protected]
Optical properties of SiO2 thin layers with Ag nanoparticles
Vacuum 69 (2003) 321–325
Optical properties of SiO2 thin layers with Ag nanoparticles Y. Sarova, M. Nikolaevab,*, M. Sendova-Vassilevab, D. Malinovskab, J.C. Pivinc a
Central Laboratory of Optical Storage and Processing of Information, Bulgarian Academy of Sciences, ‘‘Akad. G. Bonchev’’ Str. bl. 101, PO Box 95, Sofia 1113, Bulgaria b Central Laboratory for Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72 ‘‘Tzangradsko Chaussee’’, Sofia 1784, Bulgaria c CSNSM, IN2P3-CNRS, Batiment 108, 91405 Orsay Campus, France
Abstract Ag nanoclusters in a SiO2 matrix prepared by RF magnetron co-sputtering and subsequent irradiation with heavy 4.5 MeV Au+ ions were formed. The refractive index and optical absorption spectra of the films were studied. The method of the disappearing diffraction pattern was used for the refractive index determination. The refractive index enhances with increasing Ag concentration, as expected from the light scattering theory. SiO2:Ag thin films exhibit a plasmon resonance in the visible region. In the as-deposited films the Ag nanoclusters are less than 1 nm and are formed during the deposition. The intensity of the plasmon peak is low. After irradiation with 4.5 MeV Au+ ions the intensity of the peak increases and the peak becomes narrower. The TEM study shows that this is related to the change in the size of the Ag nanoclusters. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Absorption; Plasmon resonance; Nanoclusters; Ion irradiation; Refractive index
1. Introduction The formation of metallic nanoclusters in a dielectric medium provides it with interesting nonlinear optical properties, due to an enhanced thirdorder susceptibility, and with potential applications in optoelectronics, e.g. non-linear wave guide devices. These systems are used for passive optical elements such as filters as well [1]. The investigation of structural and optical properties of granular silver in an insulator prepared by cosputtering was done in 1973 by Cohen et al. [2]. *Corresponding author. Tel.: +359-2-778-448; fax: +359-2754-016. E-mail address: [email protected] (M. Nikolaeva).
Now one of the most popular methods for fabricating nanoclusters of any nature (even compounds or alloys) is ion implantation [3–6]. Nanometer-sized clusters of free electron metals in a dielectric medium exhibit a strong characteristic extinction peak, due to plasmon resonance. The shape, intensity and position of the peak depend on the size and shape of the nanoclusters and the possible interaction between them. The refractive index ðnÞ of the materials is an important optical characteristic. Its exact value is needed for material optical behaviour prediction. Ellipsometry is traditionally used for n determination. An alternative approach is the method of the disappearing diffraction pattern (MDDP), which gives a volume n value. The error in the n value is smaller than
0042-207X/03/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 2 - 2 0 7 X ( 0 2 ) 0 0 3 5 2 - 4
Y. Sarov et al. / Vacuum 69 (2003) 321–325
1 103. In this paper we study the optical extinction spectra and changes of the refractive index n of SiO2 thin films containing Ag nanoclusters prepared by RF magnetron co-sputtering and subsequent irradiation with heavy 4.5 MeV Au+ ions. We also estimated the average radius of Ag clusters using simulations of resonances for isolated clusters in silica, based on a Mie theory presented in [7].
2. Experimental The SiO2 thin films were prepared by magnetron co-sputtering from a complex target in an Ar atmosphere. Ag chips were placed on the surface of the SiO2 target. The Ag concentration in the films was varied between 0.3 and 2 at% by changing the Ag quantity on the target. Some of the samples were irradiated with incremented fluences of 4.5 MeV Au+ ions delivered by the ARAMIS accelerator (CNRS Orsay, France). The thin films were deposited on glass substrates for transmission measurements, heavy glass for MDDP and silicon substrates for RBS measurements. The thickness of the layers is below 1000 nm. RBS spectra show that Ag nanoclusters are homogeneously distributed in the matrix. The optical transmittance of the films was measured in the range of 200–800 nm with a CARY UV–VIS– NIR spectrophotometer. The MDDP was used to measure the real part of the refractive index n of the films. It is a critical angle type of method [8,9] and gives a volume n value, averaged in the penetration depth of the evanescent field. The substrate with the SiO2:Ag layer deposited on it is placed between a glass prism and a binary metal diffraction grating by an index matching liquid with the layer toward the grating. The laser light passes through the prism, the liquid layer, the substrate and reaches the investigated layer, which is expected to be the one with the smallest refractive index. When the angle of incidence with respect to the substrate/SiO2:Ag layer interface is smaller than the angle of total internal reflection, part of the beam refracted into the layer is reflected from the diffraction grating, creating diffraction orders. If the angle is equal or beyond the critical
jcr there is no refracted light, all diffraction orders disappear and only totally reflected light remains. The layer’s n is calculated from the jcr value [10].
3. Results and discussion 3.1. Optical absorption The optical extinction spectra of the plasmon resonance of samples with different Ag concentrations between 0.7 and 2 at% were studied. Fig. 1 shows the absorption for 2 at% Ag. A constant background has been subtracted from these raw optical extinction spectra. The as-deposited SiO2:Ag films exhibit a plasmon resonance, the intensity of which increases with the Ag concentration. The extinction peak is broad as it can be seen from the figure. After irradiation the intensity of the peak becomes higher than that of the asdeposited film. The position of the plasmon peaks is at a constant mean energy (3.1 eV), independent of the Ag concentration and treatment. The changes are only in the full-width at half-maximum (FWHM) of the plasmon band. The variations of the FWHM depend also on the Ag concentration [10]. The peaks become narrower with increasing Ag content. These alterations can be related to the variation of the cluster size. To ni 1e14 2e14 4e14 6e14 1e15
Extinction, [a.u.]
322
0
2
4
R=0.5nm R=0.7nm R=0.8nm R=1.05nm R=1.2nm R=1.5nm
6
8
Photon energy, [eV] Fig. 1. Extinction spectra of SiO2 thin films with 2 at% Ag irradiated with increasing ion fluences. Lines are experimental spectra and symbols are simulation spectra.
Y. Sarov et al. / Vacuum 69 (2003) 321–325
estimate the average radius R of Ag nanoparticles we used the programme based on the Mie formula [7] since the filling factor of our films is relatively low and the shape of the nanoparticles is nearly spherical. As can be seen from Fig. 1 there is a good agreement between experimental (lines) and calculated (symbols) resonances in the region of the peaks and slight discrepancies in the region of the interband absorption edge, which are probably due to the modification of the band structure in very small clusters [7]. The results of the radii of the clusters calculated by this simulation are shown in Fig. 2. It is shown that there is an enhancement of R of the clusters with increasing ion fluence. The saturation with fluences higher than 4 1014 ions/cm2 is observed for the smallest Ag concentrations. 3.2. Refractive index measurements We estimated the changes of the real part of the refractive index of samples with different Ag concentrations and also the changes after irradiation with 1 1014 and 1 1015 cm2 ion fluence. n of the samples is calculated according to the equation [8] sin jcr n ¼ npr sin A arcsin ; ð1Þ npr where jcr is the critical angle at which there is no refracted light, npr is the refractive index of the
heavy glass substrates. The main error source in the MDDP is the error in jcr determination [9]. The calculated critical angle quadratic deviation for every sample during repeated measurements was estimated to be Djcr ¼ 70 : This value leads to an error in the n value smaller than 1 103. n values calculated from experimental data of the investigated layers for different Ag concentrations ðNÞ are presented in Fig. 3. A linear n increase with Ag concentration can be observed for small N values (up to about 1 at%). Such a behaviour can be predicted according to the Mie theory for a disperse system. The scattering process plays an important role in it. If the multiple scattering could be neglected (satisfied for small concentration of the disperse phase) the refraction is regarded as an interference between non-scattered transmitted light and the light scattered in the forward direction by individual particles [11]. In summary this affects the n increase [12,13]. In the case of spherical particles with negligible size (smaller than 10 nm), the considerations significantly simplifies [14] and the disperse system n is expressed as ! n2Ag n20 3 n ¼ n0 þ n0 v Re 2 ; ð2Þ 2 nAg þ 2n20 where n0 and nAg are the SiO2 and Ag refractive indexes, respectively, and v is the Ag volume concentration. The latter is calculated using the atomic masses and densities of Ag and SiO2.
2.0
1.70 SiO2:Ag (0.7at% Ag) SiO2:Ag (1.5at% Ag) SiO2:Ag (2at% Ag)
Experimental Theoretical
1.65 Refractive index
1.6 Radius R, [nm]
323
1.2 0.8 0.4
1.60 1.55 1.50 1.45
0
2
4
6
8
10
12
Au+fluence, [1014ions/cm2] Fig. 2. Dependence of the average radius of the clusters on the ion fluence.
1.40
0.0
1.0 1.5 0.5 Ag concentration, at.%
2.0
Fig. 3. Refractive index dependence on Ag concentration. Dashed line is the theoretical dependence.
Y. Sarov et al. / Vacuum 69 (2003) 321–325
324
The theoretical dependence according to Eq. (2) is also presented in Fig. 3 by a dashed line. The observed saturation for higher concentrations (more than 1 at%) could be explained with an increasing multiple scattering possibility. It leads to a decrease in forward-scattered light. The single scattering approximation is valid in the case when the photon leaving the layer is scattered not more than once, i.e. for a Ag distribution when the clusters’ projections on the layer’s surface do not overlap. Since the right cylinder is projected on to its base, the above condition is satisfied when one Ag particle with radius R is situated in a SiO2 cylinder with a cross-section pR2 and height d (the layer’s thickness). If we substitute RB122 nm and dB600 nm the linear n behaviour with a volume concentration of 0.2–0.4 vol% can be estimated and a deviation for 2 times larger concentrations could be expected. The influence of the Au+ irradiation fluence on the layers n is also examined. The refractometric data for two fluences and different Ag concentrations are presented in Fig. 4. The results show a small enhancement of n with increasing ion fluence. This is probably related to the formation of new Ag nanoclusters from segregation of atoms and of very small particles (less than 0.3 nm) in the matrix during the irradiation with these two ion fluences.
1.60
4. Conclusion A plasmon resonance extinction peak is observed in as-deposited and ion irradiated cosputtered SiO2 films with homogeneously distributed Ag clusters. The metal clusters formed in asdeposited films are less than 0.5 nm in size and their resonance peak is broad. After irradiation the size of the metal clusters increases. The intensity of the plasmon resonance extinction peak grows with the irradiation ion fluence. The FWHM of the plasmon peak corresponds to an increasing mean radius with the ion fluence. There is a good agreement between experimental and simulated spectra using the Mie formula. A refractive index saturation for higher Ag concentration is observed. It is explained by an increase of the multiple scattering probability. The increase of the refractive index is related to the formation of new nanoclusters. These SiO2:Ag thin films with Ag nanoclusters prepared by the proposed technology can be used for optical filters.
Acknowledgements This work has been financially supported by the Bulgarian National Science Fund—Project X-903 and partially supported by a cooperation project between the BAS and CNRS, France. We acknowledge Dr. M.A. Garcia for providing us with the fitting program.
Refractive index
1.58
References 1.56
1.54 0.7 Ag at.% 1.5 Ag at.% 2.0 Ag at.%
1.52 1.50 0.0
5.0×1014
1.0×1015
Au+ fluence, [ions/cm2] Fig. 4. Refractive index of the samples after irradiation with different Au doses.
[1] Haglund RF, Li Yang, Magruder III R, White C, Zuhr R, Yang L, Dorsinville R, Alfano R. Nucl Instrum Methods B 1994;91:493. [2] Cohen RW, Cody GD, Coutts MD, Abeles B. Phys Rev B 1973;8:3689. [3] White CW, Budai JD, Withrow SP, Zhu JG, Sonder E, Zuhr RA, Meldrum A, Hembree Jr DM, Henderson DO, Prawer S. In: McHargues CJ, Weber WJ, editors. Proceedings of the Ninth International Conference on Radiation Effects in Insulators (1997), Nucl Instrum Methods B 1998;141:228. [4] Ila D, Williams EK, Sarkisov S, Smith C, Poker DB, Hensley DK. IN: McHargues CJ, Weber WJ, editors.
Y. Sarov et al. / Vacuum 69 (2003) 321–325
[5]
[6] [7] [8] [9]
Proceedings of the Ninth International Conference on Radiation Effects in Insul (’97). Nucl Instrum Methods B 1998;141:289. Mazzoldi P, Tramontin L, Boscolo-Boscoletto A, Dattaglin G, Arnold GW. Nucl Instrum Methods Phys Res 1993;B80/81:1192. Stepanov AL, Hole OE, Townsend PD. J Non-Cryst Solids 1999;244:275. Kreibig U, Genzel L. Surf Sci 1985;156:678. Sainov S, Dushkina N. Appl Opt 1990;29:1046. Sainov S. Rev Sci Instrum 1991;62:3106.
325
[10] Nikolaeva M, Sendova-Vassileva M, Malinovska D, Sarov Y, Pivin JC. Nucl Instrum Methods B, submitted for publication. [11] Alexander K, Killey A, Meeten G, Senior M. J Chem Soc Faraday Trans 1981;77(2):361. [12] Kovatchev M, Sainov V, Mateeva C. Quant Electron 1976;3:2399 (in Russian). [13] Sainov V, Mazakova M, Koleva N. C R Acad Bulg Sci 1981;34:1241. [14] van de Hulst H. Light scattenng by small particles. New York: Wiley, 1957.
Optical properties of SiO2 thin layers with Ag nanoparticles Y. Sarova, M. Nikolaevab,*, M. Sendova-Vassilevab, D. Malinovskab, J.C. Pivinc a
Central Laboratory of Optical Storage and Processing of Information, Bulgarian Academy of Sciences, ‘‘Akad. G. Bonchev’’ Str. bl. 101, PO Box 95, Sofia 1113, Bulgaria b Central Laboratory for Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72 ‘‘Tzangradsko Chaussee’’, Sofia 1784, Bulgaria c CSNSM, IN2P3-CNRS, Batiment 108, 91405 Orsay Campus, France
Abstract Ag nanoclusters in a SiO2 matrix prepared by RF magnetron co-sputtering and subsequent irradiation with heavy 4.5 MeV Au+ ions were formed. The refractive index and optical absorption spectra of the films were studied. The method of the disappearing diffraction pattern was used for the refractive index determination. The refractive index enhances with increasing Ag concentration, as expected from the light scattering theory. SiO2:Ag thin films exhibit a plasmon resonance in the visible region. In the as-deposited films the Ag nanoclusters are less than 1 nm and are formed during the deposition. The intensity of the plasmon peak is low. After irradiation with 4.5 MeV Au+ ions the intensity of the peak increases and the peak becomes narrower. The TEM study shows that this is related to the change in the size of the Ag nanoclusters. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Absorption; Plasmon resonance; Nanoclusters; Ion irradiation; Refractive index
1. Introduction The formation of metallic nanoclusters in a dielectric medium provides it with interesting nonlinear optical properties, due to an enhanced thirdorder susceptibility, and with potential applications in optoelectronics, e.g. non-linear wave guide devices. These systems are used for passive optical elements such as filters as well [1]. The investigation of structural and optical properties of granular silver in an insulator prepared by cosputtering was done in 1973 by Cohen et al. [2]. *Corresponding author. Tel.: +359-2-778-448; fax: +359-2754-016. E-mail address: [email protected] (M. Nikolaeva).
Now one of the most popular methods for fabricating nanoclusters of any nature (even compounds or alloys) is ion implantation [3–6]. Nanometer-sized clusters of free electron metals in a dielectric medium exhibit a strong characteristic extinction peak, due to plasmon resonance. The shape, intensity and position of the peak depend on the size and shape of the nanoclusters and the possible interaction between them. The refractive index ðnÞ of the materials is an important optical characteristic. Its exact value is needed for material optical behaviour prediction. Ellipsometry is traditionally used for n determination. An alternative approach is the method of the disappearing diffraction pattern (MDDP), which gives a volume n value. The error in the n value is smaller than
0042-207X/03/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 2 - 2 0 7 X ( 0 2 ) 0 0 3 5 2 - 4
Y. Sarov et al. / Vacuum 69 (2003) 321–325
1 103. In this paper we study the optical extinction spectra and changes of the refractive index n of SiO2 thin films containing Ag nanoclusters prepared by RF magnetron co-sputtering and subsequent irradiation with heavy 4.5 MeV Au+ ions. We also estimated the average radius of Ag clusters using simulations of resonances for isolated clusters in silica, based on a Mie theory presented in [7].
2. Experimental The SiO2 thin films were prepared by magnetron co-sputtering from a complex target in an Ar atmosphere. Ag chips were placed on the surface of the SiO2 target. The Ag concentration in the films was varied between 0.3 and 2 at% by changing the Ag quantity on the target. Some of the samples were irradiated with incremented fluences of 4.5 MeV Au+ ions delivered by the ARAMIS accelerator (CNRS Orsay, France). The thin films were deposited on glass substrates for transmission measurements, heavy glass for MDDP and silicon substrates for RBS measurements. The thickness of the layers is below 1000 nm. RBS spectra show that Ag nanoclusters are homogeneously distributed in the matrix. The optical transmittance of the films was measured in the range of 200–800 nm with a CARY UV–VIS– NIR spectrophotometer. The MDDP was used to measure the real part of the refractive index n of the films. It is a critical angle type of method [8,9] and gives a volume n value, averaged in the penetration depth of the evanescent field. The substrate with the SiO2:Ag layer deposited on it is placed between a glass prism and a binary metal diffraction grating by an index matching liquid with the layer toward the grating. The laser light passes through the prism, the liquid layer, the substrate and reaches the investigated layer, which is expected to be the one with the smallest refractive index. When the angle of incidence with respect to the substrate/SiO2:Ag layer interface is smaller than the angle of total internal reflection, part of the beam refracted into the layer is reflected from the diffraction grating, creating diffraction orders. If the angle is equal or beyond the critical
jcr there is no refracted light, all diffraction orders disappear and only totally reflected light remains. The layer’s n is calculated from the jcr value [10].
3. Results and discussion 3.1. Optical absorption The optical extinction spectra of the plasmon resonance of samples with different Ag concentrations between 0.7 and 2 at% were studied. Fig. 1 shows the absorption for 2 at% Ag. A constant background has been subtracted from these raw optical extinction spectra. The as-deposited SiO2:Ag films exhibit a plasmon resonance, the intensity of which increases with the Ag concentration. The extinction peak is broad as it can be seen from the figure. After irradiation the intensity of the peak becomes higher than that of the asdeposited film. The position of the plasmon peaks is at a constant mean energy (3.1 eV), independent of the Ag concentration and treatment. The changes are only in the full-width at half-maximum (FWHM) of the plasmon band. The variations of the FWHM depend also on the Ag concentration [10]. The peaks become narrower with increasing Ag content. These alterations can be related to the variation of the cluster size. To ni 1e14 2e14 4e14 6e14 1e15
Extinction, [a.u.]
322
0
2
4
R=0.5nm R=0.7nm R=0.8nm R=1.05nm R=1.2nm R=1.5nm
6
8
Photon energy, [eV] Fig. 1. Extinction spectra of SiO2 thin films with 2 at% Ag irradiated with increasing ion fluences. Lines are experimental spectra and symbols are simulation spectra.
Y. Sarov et al. / Vacuum 69 (2003) 321–325
estimate the average radius R of Ag nanoparticles we used the programme based on the Mie formula [7] since the filling factor of our films is relatively low and the shape of the nanoparticles is nearly spherical. As can be seen from Fig. 1 there is a good agreement between experimental (lines) and calculated (symbols) resonances in the region of the peaks and slight discrepancies in the region of the interband absorption edge, which are probably due to the modification of the band structure in very small clusters [7]. The results of the radii of the clusters calculated by this simulation are shown in Fig. 2. It is shown that there is an enhancement of R of the clusters with increasing ion fluence. The saturation with fluences higher than 4 1014 ions/cm2 is observed for the smallest Ag concentrations. 3.2. Refractive index measurements We estimated the changes of the real part of the refractive index of samples with different Ag concentrations and also the changes after irradiation with 1 1014 and 1 1015 cm2 ion fluence. n of the samples is calculated according to the equation [8] sin jcr n ¼ npr sin A arcsin ; ð1Þ npr where jcr is the critical angle at which there is no refracted light, npr is the refractive index of the
heavy glass substrates. The main error source in the MDDP is the error in jcr determination [9]. The calculated critical angle quadratic deviation for every sample during repeated measurements was estimated to be Djcr ¼ 70 : This value leads to an error in the n value smaller than 1 103. n values calculated from experimental data of the investigated layers for different Ag concentrations ðNÞ are presented in Fig. 3. A linear n increase with Ag concentration can be observed for small N values (up to about 1 at%). Such a behaviour can be predicted according to the Mie theory for a disperse system. The scattering process plays an important role in it. If the multiple scattering could be neglected (satisfied for small concentration of the disperse phase) the refraction is regarded as an interference between non-scattered transmitted light and the light scattered in the forward direction by individual particles [11]. In summary this affects the n increase [12,13]. In the case of spherical particles with negligible size (smaller than 10 nm), the considerations significantly simplifies [14] and the disperse system n is expressed as ! n2Ag n20 3 n ¼ n0 þ n0 v Re 2 ; ð2Þ 2 nAg þ 2n20 where n0 and nAg are the SiO2 and Ag refractive indexes, respectively, and v is the Ag volume concentration. The latter is calculated using the atomic masses and densities of Ag and SiO2.
2.0
1.70 SiO2:Ag (0.7at% Ag) SiO2:Ag (1.5at% Ag) SiO2:Ag (2at% Ag)
Experimental Theoretical
1.65 Refractive index
1.6 Radius R, [nm]
323
1.2 0.8 0.4
1.60 1.55 1.50 1.45
0
2
4
6
8
10
12
Au+fluence, [1014ions/cm2] Fig. 2. Dependence of the average radius of the clusters on the ion fluence.
1.40
0.0
1.0 1.5 0.5 Ag concentration, at.%
2.0
Fig. 3. Refractive index dependence on Ag concentration. Dashed line is the theoretical dependence.
Y. Sarov et al. / Vacuum 69 (2003) 321–325
324
The theoretical dependence according to Eq. (2) is also presented in Fig. 3 by a dashed line. The observed saturation for higher concentrations (more than 1 at%) could be explained with an increasing multiple scattering possibility. It leads to a decrease in forward-scattered light. The single scattering approximation is valid in the case when the photon leaving the layer is scattered not more than once, i.e. for a Ag distribution when the clusters’ projections on the layer’s surface do not overlap. Since the right cylinder is projected on to its base, the above condition is satisfied when one Ag particle with radius R is situated in a SiO2 cylinder with a cross-section pR2 and height d (the layer’s thickness). If we substitute RB122 nm and dB600 nm the linear n behaviour with a volume concentration of 0.2–0.4 vol% can be estimated and a deviation for 2 times larger concentrations could be expected. The influence of the Au+ irradiation fluence on the layers n is also examined. The refractometric data for two fluences and different Ag concentrations are presented in Fig. 4. The results show a small enhancement of n with increasing ion fluence. This is probably related to the formation of new Ag nanoclusters from segregation of atoms and of very small particles (less than 0.3 nm) in the matrix during the irradiation with these two ion fluences.
1.60
4. Conclusion A plasmon resonance extinction peak is observed in as-deposited and ion irradiated cosputtered SiO2 films with homogeneously distributed Ag clusters. The metal clusters formed in asdeposited films are less than 0.5 nm in size and their resonance peak is broad. After irradiation the size of the metal clusters increases. The intensity of the plasmon resonance extinction peak grows with the irradiation ion fluence. The FWHM of the plasmon peak corresponds to an increasing mean radius with the ion fluence. There is a good agreement between experimental and simulated spectra using the Mie formula. A refractive index saturation for higher Ag concentration is observed. It is explained by an increase of the multiple scattering probability. The increase of the refractive index is related to the formation of new nanoclusters. These SiO2:Ag thin films with Ag nanoclusters prepared by the proposed technology can be used for optical filters.
Acknowledgements This work has been financially supported by the Bulgarian National Science Fund—Project X-903 and partially supported by a cooperation project between the BAS and CNRS, France. We acknowledge Dr. M.A. Garcia for providing us with the fitting program.
Refractive index
1.58
References 1.56
1.54 0.7 Ag at.% 1.5 Ag at.% 2.0 Ag at.%
1.52 1.50 0.0
5.0×1014
1.0×1015
Au+ fluence, [ions/cm2] Fig. 4. Refractive index of the samples after irradiation with different Au doses.
[1] Haglund RF, Li Yang, Magruder III R, White C, Zuhr R, Yang L, Dorsinville R, Alfano R. Nucl Instrum Methods B 1994;91:493. [2] Cohen RW, Cody GD, Coutts MD, Abeles B. Phys Rev B 1973;8:3689. [3] White CW, Budai JD, Withrow SP, Zhu JG, Sonder E, Zuhr RA, Meldrum A, Hembree Jr DM, Henderson DO, Prawer S. In: McHargues CJ, Weber WJ, editors. Proceedings of the Ninth International Conference on Radiation Effects in Insulators (1997), Nucl Instrum Methods B 1998;141:228. [4] Ila D, Williams EK, Sarkisov S, Smith C, Poker DB, Hensley DK. IN: McHargues CJ, Weber WJ, editors.
Y. Sarov et al. / Vacuum 69 (2003) 321–325
[5]
[6] [7] [8] [9]
Proceedings of the Ninth International Conference on Radiation Effects in Insul (’97). Nucl Instrum Methods B 1998;141:289. Mazzoldi P, Tramontin L, Boscolo-Boscoletto A, Dattaglin G, Arnold GW. Nucl Instrum Methods Phys Res 1993;B80/81:1192. Stepanov AL, Hole OE, Townsend PD. J Non-Cryst Solids 1999;244:275. Kreibig U, Genzel L. Surf Sci 1985;156:678. Sainov S, Dushkina N. Appl Opt 1990;29:1046. Sainov S. Rev Sci Instrum 1991;62:3106.
325
[10] Nikolaeva M, Sendova-Vassileva M, Malinovska D, Sarov Y, Pivin JC. Nucl Instrum Methods B, submitted for publication. [11] Alexander K, Killey A, Meeten G, Senior M. J Chem Soc Faraday Trans 1981;77(2):361. [12] Kovatchev M, Sainov V, Mateeva C. Quant Electron 1976;3:2399 (in Russian). [13] Sainov V, Mazakova M, Koleva N. C R Acad Bulg Sci 1981;34:1241. [14] van de Hulst H. Light scattenng by small particles. New York: Wiley, 1957.