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Deposition of thin composite films consisting of fluoropolymer and silver nanoparticles having surface plasmon resonance
Deposition of thin composite films consisting of fluoropolymer and silver nanoparticles having surface plasmon resonance Alexey I. Safonov, VeronicaS. Sulyaeva, Nikolay I. Timoshenko, Sergey V. Starinskiy PII: DOI: Reference:
S0040-6090(16)00128-0 doi: 10.1016/j.tsf.2016.02.030 TSF 35030
To appear in:
Thin Solid Films
Received date: Revised date: Accepted date:
11 August 2015 9 February 2016 16 February 2016
Please cite this article as: Alexey I. Safonov, VeronicaS. Sulyaeva, Nikolay I. Timoshenko, Sergey V. Starinskiy, Deposition of thin composite films consisting of fluoropolymer and silver nanoparticles having surface plasmon resonance, Thin Solid Films (2016), doi: 10.1016/j.tsf.2016.02.030
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Deposition of thin composite films consisting of fluoropolymer and silver nanoparticles having surface plasmon resonance Alexey I. Safonov a, *, Veronica S. Sulyaeva b, Nikolay I. Timoshenko a, Sergey V. Starinskiy a a
Kutateladze Institute of Thermophysics SB RAS, Lavrentyev Ave. 1, 630090, Novosibirsk,
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Nikolaev Institute of Inorganic Chemistry SB RAS, Lavrentyev Ave. 3, 630090, Novosibirsk,
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Russia.
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* Corresponding author: Tel.: +007 383 3356245; fax: +007 383 3308018; E-mail address: [email protected] (A.I. Safonov).
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Abstract
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This paper describes the method of obtaining composite coatings consisting of silver nanoparticles covered by a fluoropolymer film. The morphology and optical properties of resulting coatings are given within. The presence of a surface plasmon resonance (SPR) minimum of silver nanoparticles deposited on glass and fused silica surfaces has been revealed. The paper describes a shift towards the infrared (IR) region when the average size of deposited silver nanoparticles is changed. However, coating the nanoparticles in a fluoropolymer film does not significantly shift their resonance. 1. Introduction
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It has been shown that composition and structure of thin films determine their optical properties [1, 2]. Furthermore, the presence of nano-sized elements on the surface often cause effects that change the optical properties [3-5]. Recently great interest has been placed on nanosized elements of noble metals due to their specific response to infrared (IR) and visible radiation which excite localized plasmons. This effect is the most noticeable in silver nanostructures [6]. The incorporation of these nanostructures within biosensors [7] for the visualization of cell structures [8, 9], targeted delivery of medicines [10, 11], photothermolysis of cancer cells [12], higher efficiency of solar elements [13-16] has triggered the development of new methods to obtain and study structures with plasmonic properties. The usage of thin nanostructured silver films is hindered due to their quick surface contamination [17]. Oxidation, sulfidation and nanoparticle coalescence in the coatings are likely to cause its properties to change. It is possible to solve these problems by encapsulating metal nanoparticles inside a polymer matrix. Furthermore, the dielectric layer created by the polymer matrix provides the possibility of preserving of the plasmonic effects. The given investigation presents the results of developing the method to obtain metal nanoparticles in a fluorine-polymer matrix and studies the properties of these films.
ACCEPTED MANUSCRIPT 2. Experimental 2.1. Deposition of silver nanoparticles
2.2. Deposition of fluoropolymer films
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The silver nanoparticles of various sizes were deposited on glass, silicon and fused silica substrates by the vacuum gas-jet method. This method causes the formation of nanoparticles before surface impact. The metal vapor aggregates within the high-speed flow of inert gasses. The size and structure of the nanoparticles formed depends upon the dynamic parameters of the source such as temperature, pressure and type of inert gas. The source construction and synthesis method are described in detail in [18]. The deposition parameters are as follows: the temperature of a source crucible was 900 °C – 980 °C, the pressure of the gas mixture within the crucible was 4 Torr, the diameter of the source critical cross section was 3 mm the inert gas flow rate in the source was 85 90 sccm, the deposition time was 8 minutes, and the distance from the source to the target was 55 mm (Table 1).
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The silver nanoparticles were coated by a fluoropolymer film immediately after their deposition without removal from the vacuum. The deposited nanoparticles were covered by a fluoropolymer film of 40 nm thickness by Hot-Wire Chemical Vapor Deposition (HWCVD) [19-21]. This method flows the precursor gas through a heated wire catalyst which activates the gas before deposition. The method enables control of the resulting film structure by changing the deposition parameters. Hexafluoropropylene oxide (C3F6O) was used as a precursor of fluoropolymer films. This method gives a uniform deposition of polymer films without cavities, voids and bubbles [22]. The deposition process parameters were as follows: the pressure in the chamber was 0.5 Torr, the activator wire temperature was 550 °C, the wire diameter was 0.5 mm, the substrate temperature was 30 °C, the precursor flow rate was 100 sccm, the wire-substrate distance was 50 mm, and the deposition time was 70 seconds. 2.3. Characterization techniques The surface morphology and the elemental composition of composite coatings were observed by scanning electron microscope (SEM) JEOL JSM6700F equipped with an EX-23000BU analyzer for the element composition determination by X-ray energy dispersive spectroscopy (EDX). During EDX the field emission electron gun (W) was operated at 15 keV energy (the excitation volume radius ~1 μm) and 1 nA current. The X-ray detector EX 64165JNH is characterized by 133 eV resolution at Mn Kα line (5.9 keV) at a count rate of 2000 cps (measuring time is 200 s) giving a dead time loss of about 20%. The spectra were evaluated by means of the program “Analysis Station 3.30.06” of the JEOL Engineering Co., Ltd. using ratio correction. The optical properties of coatings obtained were investigated using a DFS-485S spectrograph with a tungsten filament lamp as the radiation source. The spectral range of device measurements is from 380 to 730 nm with 0.01 nm resolution. The scheme and measurement parameters were described elsewhere [23, 24]. The transmittance of the coatings was calculated using the formula: T=I/I0
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ACCEPTED MANUSCRIPT where I0 is an incident radiation intensity and I is a transmitted radiation intensity through the produced sample. 2.4. Materials
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The silver used for the nanoparticles and argon carrier gas were of 99.99 % and 99.999 % purity respectively. The mixture of gaseous hexafluoropropylene oxide (98.7 % purity) produced by LLC “Polymer Plant Kirov-Chepetsk Chemical Plant” and high purity (1.3 %) argon was used as a precursor of a fluoropolymer film. The hot catalytic filament was made of NiCr wire with the diameter of 0.5 mm. 3. Results and discussion
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3.1. Deposited silver nanoparticles
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The average size of deposited silver nanoparticles was determined by analysis of the SEM images via Image J graphics editor. Typical SEM-images of samples are shown in Fig. 1. Size distribution functions of silver nanoparticles are shown in Fig. 2. It was found that increasing the source temperature increases the average size of the deposited nanoparticles which vary from 18 to 32 nm. The transmittance spectra of silver nanoparticle coatings on glass and fused silica substrates are shown in Fig. 3. It can be seen that there are SPR minimums within the range from 450 to 650 nm which shift according to the size of the nanoparticle. The dielectric properties of a substrate material slightly affect the position of the SPR minimum. The resonance curve is wider and shifted towards the IR in the case of fused silica in comparison with the samples synthesized on the glass (Fig. 3). A similar effect was observed in several papers [25-27]. Usually the silver nanoparticles have a SPR minimum around 400 nm, for example, prepared in solution [28] or deposited via annealing [29]. In our case, the SPR minimums of samples are within the range from 450 to 650 nm. This is likely due to the close proximity of our nanoparticles as they have a high surface concentration. It is known that closely located particles can excite additional oscillations of conduction electrons by themselves, and this can be the reason for the displacement of SPR minimum position that was noted earlier in [30]. The transmittance spectrums of particles with average size 20 and 25 nm are relatively similar and quite different from 18 and 32 nm particles. In papers [31, 32] was shown that peak position and the bandwidth dependence on particles size is significantly nonlinear and has a plateau. We suggest that size and position of this plateau are determined by surrounding medium permittivity and surface concentration of particles. The dispersion distribution function does not shift SPR into the IR region, and allows only a minor broadening of a transmission spectrum. High surface concentrations of the deposited nanoparticles may be the cause of this resonant response.
3.2. Produced composites and their optical properties EDX analysis revealed that prepared composite samples consisted of Ag (60 – 72 at.%), F (14 – 26 at.%), and C (7 – 13 at.%) depending on growth conditions, i.e. they were composite materials.
ACCEPTED MANUSCRIPT After six months, EDX analysis of the obtained samples kept on air was repeated. It did not show any significant changes in the composition or external impurities.
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The transmittance spectra of obtained silver nanoparticle samples in the fluoropolymer film are presented in Fig. 3. There is a slight shift of the SPR minimum towards the ultraviolet (UV) region relative to the minimum position characteristic of silver nanoparticles without a fluoropolymer film. This is likely due to the change in dielectric constant of the polymer which now occupies the space normally filled by air. As mentioned above, the interaction of particles with each other at high density results in shifting the SPR minimum to the IR region. Filling the space among silver particles by a fluoropolymer matrix weakens their interaction because the fluoropolymer refractive index (n = 1.4) is higher than that of air (n = 1) and causes a reverse shift of a resonance absorption to the UV region. This resonant response confirms that Ag nanoparticle coatings had a lower density without a fluoropolymer film [33]. 4. Conclusions
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Using the methods of vacuum gas-jet deposition and HWCVD, the composite coatings consisting of silver nanoparticles and a fluoropolymer matrix have been deposited. Studying optical properties of coatings has revealed the plasmon resonance present in the system and the possibility to control its frequency in the wavelength range from 450 to 650 nm by changing sizes of silver nanoparticles. The deposition of a polymer matrix has resulted in a slight shift of SPR minimum to the shortwave region of a spectrum. The main result of our investigation is the possibility to protect the silver nanostructures by fluoropolymer thin film without significant changing of their optical properties. Acknowledgements
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This work was funded by RFBR, according to the research projects No. 15-38-20411A, No. 1408-00534 and No. 15-08-01949. The depositions were performed at a vacuum gas-dynamic complex IT SB RAS. The authors would like to thank Mr. Nathan Goodfriend for editing this article. References [1] X. F. Wang, M. Zhao, K. P. Chen, D. D. Nolte, X. Wang, K. Chen, M. Zhao, and D. D. Nolte, Refractive index and dielectric constant evolution of ultra-thin gold from clusters to films Refractive index and dielectric constant evolution of ultra-thin gold from clusters to films, Opt. Express, 18 (2010), 24858-24867. [2] K. Tanaka, Y. Fukui, N. Moritake, and H. Uchiki, Chemical composition dependence of morphological and optical properties of Cu2ZnSnS4 thin films deposited by sol-gel sulfurization and Cu2ZnSnS4 thin film solar cell efficiency, Sol. Energy Mater. Sol. Cells. 95 (2011) 838–842. [3] A. Janotta, Y. Dikce, M. Schmidt, C. Eisele, M. Stutzmann, M. Luysberg, and L. Houben, Lightinduced modification of a-SiOx II: Laser crystallization, J. Appl. Phys. 95 (2004) 4060–4068. [4] Y. Tian and T. Tatsuma, Mechanisms and Applications of Plasmon-Induced Charge Separation at TiO 2Films Loaded with Gold Nanoparticles, J. Am. Chem. Soc. 127 (2005) 7632–7637.
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[5] S. Meskinis, A. Ciegis, A. Vasiliauskas, A. Tamuleviciene, K. Slapikas, R. Juskenas, G. Niaura, S. Tamulevicius, Plasmonic properties of silver nanoparticles embedded in diamond like carbon films: Influence of structure and composition, Applied Surface Science 317 (2014) 1041–1046. [6] R. Kuladeep, L. Jyothi, K. S. Alee, K. L. N. Deepak, and D. N. Rao, Laser-assisted synthesis of Au-Ag alloy nanoparticles with tunable surface plasmon resonance frequency, Opt. Mater. Express, 2 (2012) 161-172. [7] D.A. Stuart, A.J. Hacs, C.R. Yonzon, E.M. Hicks, R.P. Van Duyne, Biological applications of localised surface plasmonic phenomenae, IEE Proc. Nanobiotechnol. 152 (2005) 13-32. [8] M.E. Stewart, C.R. Anderton, L.B. Thompson, S.K. Gray, J.A. Rogers, R.G. Nuzzo, Nanostructured plasmonic sensors, Chem. Rev. 108 (2008) 494-521 [9] S. Kumar, N. Harrison, R. Richards-Kortum, K. Sokolov, Plasmonic nanosensors for imaging intracellular biomarkers in live cells, Nano. Lett. 7 (2007) 1338-1343. [10] G.F. Paciotti, D.G.I. Kingston, L. Tamarkin, Colloidal gold nanoparticles: a novel nanoparticle platform for developing multifunctional tumor-targeted drug delivery vectors, Drug Dev. Res. 67 (2006) 47-54. [11] W. Zhou, X. Gao, D. Liu, and X. Chen, Gold Nanoparticles for In Vitro Diagnostics, Chem. Rev. 115 (2015) 10575–10636. [12] P.K. Jain, I.H. El-Sayed, M.A. El-Sayed, Au nanoparticles target cancer, Nano Today 2 (2007) 1829. [13] W. Jiang, S.C. Mangham, B.D. Weaver, Surface plasmon enhanced intermediate band based quantum dots solar cell, Sol. Energy Mater. Sol. Cells 102 (2012) 44–49. [14] S. Pillai, M.A. Green, Sol. Plasmonics for photovoltaic applications, Sol. Cells 94 (2010) 1481– 1486. [15] S. Pillai, K.R. Catchpole, M.A. Green, Surface plasmon enhanced silicon solar cells, J. Appl. Phys. 101 (2007) 0931051–0931058. [16] S. Linic, P. Christopher, D.B. Ingram, Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy, Nature Materials 10 (2011) 911–921. [17] S. Maier, Plasmonics: Fundamentals and Applications. Springer, 2007, P. 224. [18] M.N. Andreev, A.K. Rebrov, N.I. Timoshenko, Synthesis of silver nanoparticles using gas-jet deposition method, Nanotechnologies in Russia 6 (2011) 587–592. [19] K. Lau, J. Caulfield, K. Gleason, Structure and Morphology of Fluorocarbon Films Grown by Hot Filament Chemical Vapor Deposition, Chem. Mater. 12 (2000) 3032–3037. [20] K.S. Lau, Yu Mao, H.G.P. Lewis, S.K. Murthy, B.D. Olsen, L.S. Loo, K.K. Gleason, Polymeric nanocoatings by hot-wire chemical vapor deposition (HWCVD), Thin Solid Films 501 (2006) 211–215. [21] M. Takachi, H. Yasuoka, K. Ohdaira, T. Shimoda, H. Matsumura, A novel patterning technique using super-hydrophobic PTFE thin films by Cat-CVD method, Thin Solid Films 517 (2009) 3622–3624. [22] M.E. Alf, A. Asatekin, M.C. Barr, S.H. Baxamusa, H. Chelawat, G. Ozaydin-Ince, C.D. Petruczok, R. Sreenivasan, W.E. Tenhaeff, N.J. Trujillo, S. Vaddiraju, J. Xu, K.K. Gleason, Chemical Vapor Deposition of Conformal, Functional, and Responsive Polymer Films, Adv. Mater. 22(18) (2010) 1993–2027. [23] M.N. Andreev, I.S. Bespalov, A.I. Safonov, Gas-jet method for deposition of metal nanoparticles into the fluorine-polymer matrix, Thermophysics and Aeromechanics 20(3) (2013) 375–379. [24] M.N. Andreev, A.I. Aliferov, and N.I. Timoshenko, Gas jet synthesis of nano-sized polymer-silver composites, Journal of Engineering Thermophysics 23(3) (2014) 194–200.
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[25] W.A. Weimer and M.J. Dyer, Tunable surface plasmon resonance silver films, Applied Physics Letters 79, (2001) 3164–3166. [26] G. Xu, M. Tazawa, P. Jin, S. Nakao, and K. Yoshimura, Wavelength tuning of surface plasmon resonance using dielectric layers on silver island films, Applied Physics Letters 82 (2003) 3811–3813. [27] H. Acharya, Y.J. Park, Y.S. Choi, J. Sung, T. Kim, D.H. Kim, C. Park, Control over the surface plasmon band of block copolymer/Ag/Au nanoparticles composites by the addition of single walled carbon nanotubes, Reactive & Functional Polymers 71 (2011) 1195–1201. [28] M.G. Sreenivasan, S. Malik, S. Thigulla, B.R. Mehta, Dependence of Plasmonic Properties of Silver Island Films on Nanoparticle Size and Substrate Coverage, Journal of Nanomaterials (2013) Article ID 247045, 8 pages. [29] D. Evanoff and G. Chumanov, Synthesis and optical properties of silver nanoparticles and arrays, Chem. Phys. Chem. 6 (2005) 1221–1231. [30] T. Menegotto, F. Horowitz, Anisotropic effective medium properties from interacting Ag nanoparticles in silicon dioxide, Appl. Opt. 53 (2004) 2853–2859. [31] S. Link and M.A. El-Sayed, Spectral properties and relaxation dynamics of surface plasmon electronic oscillations in, J. Phys. Chem. B. 103 (1999) 8410–8426. [32] U. Kreibig and C.V. Fragstein, The Limitation of Electron Mean Free Path in Small Silver Particles, Z. Phys. 224, (1969) 307–323. [33] Y.H. Ko, J.S. Yu, Silver nanoparticle decorated ZnO nanorod arrays on AZO films for light absorption enhancement, Phys. Status Solidi A 209 (2012) 297–301.
Fig. 1. SEM image of Ag NPs coating on silicon: planar (a), cross-section (b).
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Fig. 2. Size distribution of deposited nanoparticles: (a) 18 nm, (b) 20 nm, (c) 25 nm and (d) 32 nm.
Fig. 3. Transmittance spectra of silver nanoparticles deposited on glass, fused silica and into a fluoropolymer film on glass with sizes: (a) 18 nm, (b) 20 nm, (c) 25 nm and (d) 32 nm.
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Mass-flow (sccm)
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Sample 1
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Sample 3
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Sample 4
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Pressure (Torr)
ACCEPTED MANUSCRIPT Highlights
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Optical properties and film structure dramatically depend on synthesis condition. Ag NPs films were covered by fluoropolymer for protection from the surroundings. Changings of surface plasmon resonance position are discussed.
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Ag thin films were synthesized by vacuum gas-jet method.
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S0040-6090(16)00128-0 doi: 10.1016/j.tsf.2016.02.030 TSF 35030
To appear in:
Thin Solid Films
Received date: Revised date: Accepted date:
11 August 2015 9 February 2016 16 February 2016
Please cite this article as: Alexey I. Safonov, VeronicaS. Sulyaeva, Nikolay I. Timoshenko, Sergey V. Starinskiy, Deposition of thin composite films consisting of fluoropolymer and silver nanoparticles having surface plasmon resonance, Thin Solid Films (2016), doi: 10.1016/j.tsf.2016.02.030
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Deposition of thin composite films consisting of fluoropolymer and silver nanoparticles having surface plasmon resonance Alexey I. Safonov a, *, Veronica S. Sulyaeva b, Nikolay I. Timoshenko a, Sergey V. Starinskiy a a
Kutateladze Institute of Thermophysics SB RAS, Lavrentyev Ave. 1, 630090, Novosibirsk,
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Russia.
Nikolaev Institute of Inorganic Chemistry SB RAS, Lavrentyev Ave. 3, 630090, Novosibirsk,
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Russia.
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* Corresponding author: Tel.: +007 383 3356245; fax: +007 383 3308018; E-mail address: [email protected] (A.I. Safonov).
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Abstract
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This paper describes the method of obtaining composite coatings consisting of silver nanoparticles covered by a fluoropolymer film. The morphology and optical properties of resulting coatings are given within. The presence of a surface plasmon resonance (SPR) minimum of silver nanoparticles deposited on glass and fused silica surfaces has been revealed. The paper describes a shift towards the infrared (IR) region when the average size of deposited silver nanoparticles is changed. However, coating the nanoparticles in a fluoropolymer film does not significantly shift their resonance. 1. Introduction
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It has been shown that composition and structure of thin films determine their optical properties [1, 2]. Furthermore, the presence of nano-sized elements on the surface often cause effects that change the optical properties [3-5]. Recently great interest has been placed on nanosized elements of noble metals due to their specific response to infrared (IR) and visible radiation which excite localized plasmons. This effect is the most noticeable in silver nanostructures [6]. The incorporation of these nanostructures within biosensors [7] for the visualization of cell structures [8, 9], targeted delivery of medicines [10, 11], photothermolysis of cancer cells [12], higher efficiency of solar elements [13-16] has triggered the development of new methods to obtain and study structures with plasmonic properties. The usage of thin nanostructured silver films is hindered due to their quick surface contamination [17]. Oxidation, sulfidation and nanoparticle coalescence in the coatings are likely to cause its properties to change. It is possible to solve these problems by encapsulating metal nanoparticles inside a polymer matrix. Furthermore, the dielectric layer created by the polymer matrix provides the possibility of preserving of the plasmonic effects. The given investigation presents the results of developing the method to obtain metal nanoparticles in a fluorine-polymer matrix and studies the properties of these films.
ACCEPTED MANUSCRIPT 2. Experimental 2.1. Deposition of silver nanoparticles
2.2. Deposition of fluoropolymer films
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The silver nanoparticles of various sizes were deposited on glass, silicon and fused silica substrates by the vacuum gas-jet method. This method causes the formation of nanoparticles before surface impact. The metal vapor aggregates within the high-speed flow of inert gasses. The size and structure of the nanoparticles formed depends upon the dynamic parameters of the source such as temperature, pressure and type of inert gas. The source construction and synthesis method are described in detail in [18]. The deposition parameters are as follows: the temperature of a source crucible was 900 °C – 980 °C, the pressure of the gas mixture within the crucible was 4 Torr, the diameter of the source critical cross section was 3 mm the inert gas flow rate in the source was 85 90 sccm, the deposition time was 8 minutes, and the distance from the source to the target was 55 mm (Table 1).
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The silver nanoparticles were coated by a fluoropolymer film immediately after their deposition without removal from the vacuum. The deposited nanoparticles were covered by a fluoropolymer film of 40 nm thickness by Hot-Wire Chemical Vapor Deposition (HWCVD) [19-21]. This method flows the precursor gas through a heated wire catalyst which activates the gas before deposition. The method enables control of the resulting film structure by changing the deposition parameters. Hexafluoropropylene oxide (C3F6O) was used as a precursor of fluoropolymer films. This method gives a uniform deposition of polymer films without cavities, voids and bubbles [22]. The deposition process parameters were as follows: the pressure in the chamber was 0.5 Torr, the activator wire temperature was 550 °C, the wire diameter was 0.5 mm, the substrate temperature was 30 °C, the precursor flow rate was 100 sccm, the wire-substrate distance was 50 mm, and the deposition time was 70 seconds. 2.3. Characterization techniques The surface morphology and the elemental composition of composite coatings were observed by scanning electron microscope (SEM) JEOL JSM6700F equipped with an EX-23000BU analyzer for the element composition determination by X-ray energy dispersive spectroscopy (EDX). During EDX the field emission electron gun (W) was operated at 15 keV energy (the excitation volume radius ~1 μm) and 1 nA current. The X-ray detector EX 64165JNH is characterized by 133 eV resolution at Mn Kα line (5.9 keV) at a count rate of 2000 cps (measuring time is 200 s) giving a dead time loss of about 20%. The spectra were evaluated by means of the program “Analysis Station 3.30.06” of the JEOL Engineering Co., Ltd. using ratio correction. The optical properties of coatings obtained were investigated using a DFS-485S spectrograph with a tungsten filament lamp as the radiation source. The spectral range of device measurements is from 380 to 730 nm with 0.01 nm resolution. The scheme and measurement parameters were described elsewhere [23, 24]. The transmittance of the coatings was calculated using the formula: T=I/I0
(1)
ACCEPTED MANUSCRIPT where I0 is an incident radiation intensity and I is a transmitted radiation intensity through the produced sample. 2.4. Materials
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The silver used for the nanoparticles and argon carrier gas were of 99.99 % and 99.999 % purity respectively. The mixture of gaseous hexafluoropropylene oxide (98.7 % purity) produced by LLC “Polymer Plant Kirov-Chepetsk Chemical Plant” and high purity (1.3 %) argon was used as a precursor of a fluoropolymer film. The hot catalytic filament was made of NiCr wire with the diameter of 0.5 mm. 3. Results and discussion
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3.1. Deposited silver nanoparticles
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The average size of deposited silver nanoparticles was determined by analysis of the SEM images via Image J graphics editor. Typical SEM-images of samples are shown in Fig. 1. Size distribution functions of silver nanoparticles are shown in Fig. 2. It was found that increasing the source temperature increases the average size of the deposited nanoparticles which vary from 18 to 32 nm. The transmittance spectra of silver nanoparticle coatings on glass and fused silica substrates are shown in Fig. 3. It can be seen that there are SPR minimums within the range from 450 to 650 nm which shift according to the size of the nanoparticle. The dielectric properties of a substrate material slightly affect the position of the SPR minimum. The resonance curve is wider and shifted towards the IR in the case of fused silica in comparison with the samples synthesized on the glass (Fig. 3). A similar effect was observed in several papers [25-27]. Usually the silver nanoparticles have a SPR minimum around 400 nm, for example, prepared in solution [28] or deposited via annealing [29]. In our case, the SPR minimums of samples are within the range from 450 to 650 nm. This is likely due to the close proximity of our nanoparticles as they have a high surface concentration. It is known that closely located particles can excite additional oscillations of conduction electrons by themselves, and this can be the reason for the displacement of SPR minimum position that was noted earlier in [30]. The transmittance spectrums of particles with average size 20 and 25 nm are relatively similar and quite different from 18 and 32 nm particles. In papers [31, 32] was shown that peak position and the bandwidth dependence on particles size is significantly nonlinear and has a plateau. We suggest that size and position of this plateau are determined by surrounding medium permittivity and surface concentration of particles. The dispersion distribution function does not shift SPR into the IR region, and allows only a minor broadening of a transmission spectrum. High surface concentrations of the deposited nanoparticles may be the cause of this resonant response.
3.2. Produced composites and their optical properties EDX analysis revealed that prepared composite samples consisted of Ag (60 – 72 at.%), F (14 – 26 at.%), and C (7 – 13 at.%) depending on growth conditions, i.e. they were composite materials.
ACCEPTED MANUSCRIPT After six months, EDX analysis of the obtained samples kept on air was repeated. It did not show any significant changes in the composition or external impurities.
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The transmittance spectra of obtained silver nanoparticle samples in the fluoropolymer film are presented in Fig. 3. There is a slight shift of the SPR minimum towards the ultraviolet (UV) region relative to the minimum position characteristic of silver nanoparticles without a fluoropolymer film. This is likely due to the change in dielectric constant of the polymer which now occupies the space normally filled by air. As mentioned above, the interaction of particles with each other at high density results in shifting the SPR minimum to the IR region. Filling the space among silver particles by a fluoropolymer matrix weakens their interaction because the fluoropolymer refractive index (n = 1.4) is higher than that of air (n = 1) and causes a reverse shift of a resonance absorption to the UV region. This resonant response confirms that Ag nanoparticle coatings had a lower density without a fluoropolymer film [33]. 4. Conclusions
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Using the methods of vacuum gas-jet deposition and HWCVD, the composite coatings consisting of silver nanoparticles and a fluoropolymer matrix have been deposited. Studying optical properties of coatings has revealed the plasmon resonance present in the system and the possibility to control its frequency in the wavelength range from 450 to 650 nm by changing sizes of silver nanoparticles. The deposition of a polymer matrix has resulted in a slight shift of SPR minimum to the shortwave region of a spectrum. The main result of our investigation is the possibility to protect the silver nanostructures by fluoropolymer thin film without significant changing of their optical properties. Acknowledgements
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This work was funded by RFBR, according to the research projects No. 15-38-20411A, No. 1408-00534 and No. 15-08-01949. The depositions were performed at a vacuum gas-dynamic complex IT SB RAS. The authors would like to thank Mr. Nathan Goodfriend for editing this article. References [1] X. F. Wang, M. Zhao, K. P. Chen, D. D. Nolte, X. Wang, K. Chen, M. Zhao, and D. D. Nolte, Refractive index and dielectric constant evolution of ultra-thin gold from clusters to films Refractive index and dielectric constant evolution of ultra-thin gold from clusters to films, Opt. Express, 18 (2010), 24858-24867. [2] K. Tanaka, Y. Fukui, N. Moritake, and H. Uchiki, Chemical composition dependence of morphological and optical properties of Cu2ZnSnS4 thin films deposited by sol-gel sulfurization and Cu2ZnSnS4 thin film solar cell efficiency, Sol. Energy Mater. Sol. Cells. 95 (2011) 838–842. [3] A. Janotta, Y. Dikce, M. Schmidt, C. Eisele, M. Stutzmann, M. Luysberg, and L. Houben, Lightinduced modification of a-SiOx II: Laser crystallization, J. Appl. Phys. 95 (2004) 4060–4068. [4] Y. Tian and T. Tatsuma, Mechanisms and Applications of Plasmon-Induced Charge Separation at TiO 2Films Loaded with Gold Nanoparticles, J. Am. Chem. Soc. 127 (2005) 7632–7637.
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Fig. 1. SEM image of Ag NPs coating on silicon: planar (a), cross-section (b).
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Fig. 2. Size distribution of deposited nanoparticles: (a) 18 nm, (b) 20 nm, (c) 25 nm and (d) 32 nm.
Fig. 3. Transmittance spectra of silver nanoparticles deposited on glass, fused silica and into a fluoropolymer film on glass with sizes: (a) 18 nm, (b) 20 nm, (c) 25 nm and (d) 32 nm.
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Mass-flow (sccm)
Time deposition (min)
Sample 1
4.00
928
90.4
8
Sample 2
4.01
940
87.0
8
Sample 3
3.98
968
86.8
8
Sample 4
3.97
980
86.5
8
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Pressure (Torr)
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Optical properties and film structure dramatically depend on synthesis condition. Ag NPs films were covered by fluoropolymer for protection from the surroundings. Changings of surface plasmon resonance position are discussed.
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Ag thin films were synthesized by vacuum gas-jet method.
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