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Optical response of anisotropic silver nanostructures on polarized light
Materials Letters 137 (2014) 72–74
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Optical response of anisotropic silver nanostructures on polarized light Robert Krajcar n, Jakub Siegel, Oleksiy Lyutakov, Petr Slepička, Václav Švorčík Department of Solid State Engineering, Institute of Chemical Technology, 166 28 Prague, Czech Republic
art ic l e i nf o
a b s t r a c t
Article history: Received 8 July 2014 Accepted 20 August 2014 Available online 28 August 2014
Treatment of absorbing polymer (polyethyleneterephthalate) with pulse KrF excimer laser causes formation of laser induced periodic surface structures (LIPSS). Silver nanowires were prepared on the surface of laser treated polymer using vacuum evaporation at glancing angle geometry (701). The wires were observed with Scanning Electron Microscope equipped with Focused Ion Beam module (FIB-SEM). Relations between size and spacing of wires and morphology of polymer template were observed from those images. Optical response of prepared wires with different cross-sections and spatial parameters was investigated. The effect of polarizer on measured UV–vis absorption spectra showed anisotropy in optical properties of 1D metal nanostructures. The excitation of Localized Surface Plasmon Resonance (LSPR) was achieved only with an appropriate arrangement of the wire axis to the plane of polarization. Influence of wire width on position of absorption band was detected. Wire thickness was found to be a crucial parameter resulting in plasmon peak intensity. & 2014 Elsevier B.V. All rights reserved.
Keywords: Polymer laser treatment LIPSS LSPR Silver nanostructures Optical properties
1. Introduction Noble metal nanostructures smaller than the wavelength of light have attracted great attention of physicists, chemists and material engineers due to their Localized surface plasmon resonance (LSPR). LSPR is the way of response during interaction between incident light and electrons in a conduction band of material. The incoming electromagnetic field of the light induces collective oscillations of electrons in resonance with frequency of radiation. The resonance frequency highly depends on material composition, size, shape, dielectric environment [1] and grating constant (in case of periodically patterned systems) [2]. The occurrence of LSPR results in selective photon absorption, scattering and local electromagnetic field enhancement. Tuning the absorption properties allows obtaining materials of various colors. Such materials are especially gold and silver, which exhibit LSPR in the visible range of spectrum due to the energy levels of d–d transitions [3]. Surface modes in spherical particles depend mostly upon their size. If the particle is small enough (compared to the wavelength of incident light), all scattered waves are approximately in phase and only dipole Plasmon resonance occurs. As the particle size increases, number of possibilities for mutual enhancement or cancellation of scattered waves increases [4]. The phase-retardation effects in the inner region of the particle lead to excitation of higher multipole modes (quadrupole,
n
Corresponding author. E-mail address: [email protected] (R. Krajcar).
http://dx.doi.org/10.1016/j.matlet.2014.08.113 0167-577X/& 2014 Elsevier B.V. All rights reserved.
octupole, etc.). So, more peaks can be observed in spectra of bigger particles, even though they have spherical shape. Splitting of the dipole resonance into two distinct modes can be seen at elongated particles (up to three modes for ellipsoids) due to frequency difference between longitudinal and transverse electron oscillations [5,6]. Positions of plasmon peaks of silver can be strongly influenced by interband transitions, especially from the 4d to the 5sp hybridized band. Usual approach for interpretation of rodded medium optical properties is to introduce several amendments in the traditional Drude model, related to effective electron mass, electron density and damping constant. The effective electron density is diluted because the free electrons are restricted within the physical boundaries of the wires. In case of nanowires with irregular cross-section the position of plasmon frequency maximum depends on wire width to height ratio [7]. Geometry of spherical nanoparticles allows polarization independent plasmon excitation, while plasmon resonance in nanowires can only be excited by an electric field oriented perpendicularly to the wire axis (only in this direction, the sufficient spatial confinement for electrons occurs) [2]. In this work we present response of silver nanowire arrays to linearly polarized light. Silver nanowires were prepared by vacuum evaporation on polymer substrate after its nano-patterning with KrF excimer laser.
2. Experimental Materials, apparatus and procedures: Periodic nanostructures (Ripples) were produced with KrF excimer laser (COMPexPro 50F, Coherent, Inc., wavelength 248 nm, pulse duration 20–40 ns,
R. Krajcar et al. / Materials Letters 137 (2014) 72–74
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repetition rate 10 Hz) on biaxially oriented polyethyleneterephthalate (PET) foils (Goodfellow Ltd., thickness 50 mm). The laser light was linearly polarized with UV-grade fused silica prism (model PBSO – 248 -100). The aperture with an area of 5 10 mm2 was used. Samples were irradiated under three different angles of incidence (0, 22.5 and 451) with 6000 laser pulses (fluence of 7 mJ cm 2) [8]. Nano-patterned PET substrate was used as a template for deposition of silver (SAFINA, a.s., purity 99.99%) by vacuum evaporation on LEYBOLD-Heraeus, Univex 450 device (room temperature, pressure of 3.10 4 Pa). Deposition in glancing angle geometry (φ ¼701 with respect to the substrate surface normal) enabled growth of wires predominantly on the ridges of periodic polymer lines (shadow deposition) [9]. Analytical methods: Effective thickness of evaporated silver was determined by scratch method on a glass substrate (coated simultaneously with the PET template) using Atomic Force Microscopy (AFM) Digital Instruments CP II device. The “contact mode” with line scanning rate of 0.4 Hz was chosen. Measurements were performed with Bruker Antimony-doped Silicon probe CONT20ACP (spring constant 0.9 N m 1). Optical properties were studied using Perkin-Elmer Lambda 25 UV–vis spectrometer. The device was equipped with wire grid polarizer WP25L-UB (250–4000 nm, Thorlabs). The absorption spectra were recorded stepwise with the step in the wavelength of 1 nm and in the wavelength range of 200–1100 nm. For visual representation of nanowire arrays the Focused Ion Beam Scanning Electron Microscope (FIB-SEM, LYRA3 GMU, Tescan, Czech Republic) was chosen. The FIB cuts were made with a Gallium ion beam. The polishing procedure was performed to clean and flatten the investigated surfaces. The images were taken under an angle of 54.81. Applied voltage was 5 kV.
3. Results and discussion Periodicity of linear polymer nanostructures increases with angle of incidence of laser light (01/Λ ¼ 230 nm, 22.51/Λ ¼345 nm and 451/Λ ¼427 nm) [8]. Besides, width of the wires increases with periodicity of ripple structures (see Fig. 1). Angle of incidence can also influence distance between individual wires. Occurrence and location of silver are most noticeable in Fig. 1a for angle 451/ Λ ¼ 427 nm. Whereas the wires with lower periodicity are pretty close to each other, the spacing of polymer ripples modified under angle of 451 is so high, that prerequisites for shadow deposition are no longer fulfilled. Thus, deposited silver can be found not only on the ridges of ripple structures, but sometimes also in between them (see Fig. 1). Polymer nano-patterning by excimer laser treatment is in detail described in previous papers published by our group [10–12]. We started our investigation of absorption properties of silver nanowires taking into account mutual orientation of wire axis and vector of light polarization. Comparative measurements without polarizer were acquired to obtain counterpart data. Curves in Fig. 2 denoted as TM (transverse magnetic polarization) and TE (transverse electric polarization) clearly show, that when the electric field of incident light is perpendicular to the wire axis (TM), Localized Surface Plasmon Resonance (LSPR) can be excited and strong dipolar peak at 680 nm is observed. Contrary to that, when the light polarization is parallel (TE) to wire axis, no absorption peak occurs. There are no boundaries for motion of electrons in this direction (no selective photon absorption), because these wires are almost infinitely long (approximately 1 cm) in comparison with other dimensions. So the TE spectrum is similar to that, obtained with silver layer of same effective thickness on non-irradiated PET (pristine in Fig. 2). Data measured with non-polarized light in longitudinal (L) and in
Fig. 1. FIB-SEM analysis of silver metalized ripple structures with different periodicities. Different grating parameters are: (a) Λ ¼427 nm, (b) Λ ¼ 345 nm and (c) Λ ¼ 230 nm. Displayed area is 5 2.5 mm2.
Fig. 2. Absorption spectra of silver nanowires measured with linearly polarized light in compare with results obtained without polarizer. Sample with grating parameter Λ ¼ 345 nm and effective nanowire thickness of 40 nm was studied. The scheme next to spectra shows movement of electrons with respect to the vector of polarization.
transversal (T) orientation indicate the inherent polarization of spectrometer itself. Tuning the wavelength of primary beam via optical grating and its subsequent splitting into signal and reference beam by multiple reflection cause that signal beam is partially polarized in horizontal plane. When the wire is wider, the mean free path of electrons grows larger, which reduce the frequency of Plasmon oscillations and lead to obvious red-shift in absorption spectra (Fig. 3). Moreover, increasing wire width can results in quadrupole Plasmon excitation (Fig. 3b, dashed curve – 450 nm). In Fig. 3c (dashed and solid) even higher resonance modes occur (555 nm – quadrupole,
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R. Krajcar et al. / Materials Letters 137 (2014) 72–74
Fig. 3. Absorption spectra of TM polarized silver nanowires of different thicknesses and widths (periodicity). Different grating parameters are: (a) Λ ¼ 230 nm, (b) Λ ¼ 345 nm and (c) Λ¼ 427 nm.
405 nm – octupole). Excitation of such multipoles is caused by size dependent interference of retarded electromagnetic scattering fields in the inner region of wires. This phenomenon is proportional to volume of examined material. Commonly used model for description of metal wires array optical behavior with the size smaller then probing wavelength is so-called Bruggeman approximation. According to the Bruggeman theory the position of plasmon related absorption peak is proportional to the plasma frequency of free electron in metal. On the other hand, plasma frequency of electron in the rodded medium is the function of lattice constant. As followed from Pendry calculation, plasma frequency is inversely proportional to the square of the lattice constant [13]. Thus, increasing of lattice constant will lead to decreasing of plasma frequency and red-shifting of plasmon absorption band. This situation is apparent in Fig. 3, where increasing of lattice constant leads to appropriate changes in the position of plasmon related absorption maximum. Intensity of individual peaks in the spectrum depends on thickness of wires (see Fig. 3). Sample with effective thickness of 20 nm always possesses lowest intensity, because there is the lowest number of electrons able to participate in collective oscillations. Ripple structures with 40 nm of silver have stronger dipolar peak than sample with 30 nm, until quadrupole and octupole peaks are excited. Higher multipole peaks are rising at the expense of the intensity of dipolar one. Amount of evaporated metal influences not only thickness of wires, but also their width and spacing (increasing amount of metal leads to wider wires, which are closer to each other and they also show more oblate cross-section) [9]. So the slight blue-shift observed with increase of wire thickness is caused by combination of several effects of different nature. Peaks between 320–350 nm may be attributed to interband transitions. Positions of these peaks do not exhibit high degree of variability, because it is mostly influenced by chemical composition of material. The larger the amount of deposited metal, the higher peak intensity is achieved, because more electrons can undergo transitions to higher energy levels.
4. Conclusions Treatment of polyethyleneterephthalate with pulse excimer laser light leads to creation of well-defined linear periodic nanostructures. Preparation of separated metallic wires on the ridges of polymer
lines can be achieved by vacuum evaporation under glancing angle geometry. Width of wires and distance between them depends on morphology of polymer template. Plasmon resonance of anisotropic metallic nanostructures is highly sensitive to polarization of incident light. Resonance effect in wires only occurs, when the electric component of light is perpendicular to wire axis. Perceptible redshift in the spectra with increasing wire width occurs which reflects spatial parameters of prepared nanowires. Larger amounts of deposited metal causes occurrence of higher multipolar peaks in their absorption spectra. Acknowledgments Financial support from specific university research, Ministry of Education of Czech Republic (MSMT No. 20/2014) (R.K.) and Grant Agency of Czech Republic (P108/12/G108). References [1] Kelly KL, Coronado E, Zhao LL, Schatz GC. The optical properties of metal nanoparticles: the influence of size, shape and dielectric environment. J Phys Chem B 2003;107:668–77. [2] Schider G, Krenn JR, Gotschy W, Lamprecht B, Ditlbacher H, Leitner A, et al. Optical properties of Ag and Au nanowire gratings. J Appl Phys 2001;90:3825–30. [3] Petryayeva E, Krull UJ. Localized surface plasmon resonance: nanostructures, bioassays and biosensing – A review. Anal Chim Acta 2011;706:8–24. [4] Bohren CF, Huffman DR. Absorption and Scattering of Light by Small Particles. Nex York: Wiley; 1983. [5] Cao J, Sun T, Grattan KTV. Gold nanorod-based localized surface plasmon resonance biosensors: a review. Sens Actuators B 2014;195:332–51. [6] Kreibig U, Vollmer M. Optical Properties of Metal Clusters. Berlin: SpringerVerlag; 1995. [7] Xu Q, Bao J, Capasso F, Whitesides GM. Surface plasmon resonances of freestanding gold nanowires fabricated by nanoskiving. Angew Chem Int Ed 2006;45:3631–5. [8] Krajcar R, Siegel J, Slepička P, Fitl P, Švorčík V. Silver nanowires prepared on PET structured by laser irradiation. Mater Lett 2014;117:184–7. [9] Siegel J, Heitz J, Řezníčková A, Švorčík V. Preparation and characterization of fully separed gold nanowire arrays. Appl Surf Sci 2013;264:443–7. [10] Slepička P, Neděla O, Siegel J, Krajcar R, Kolská Z, Švorčík V. Ripple polystyrene nano-pattern induced by KrF laser. Express Polym Lett 2014;8:459–66. [11] Slepička P, Rebollar E, Heitz J, Švorčík V. Gold coatings on polyethyleneterephthalate nano-patterned by F2 laser irradiation. Appl Surf Sci 2008;254:3585–90. [12] Siegel J, Heitz J, Švorčík V. Self-organized gold nanostructures on laser patterned PET. Surf Coat Technol 2011;206:517–21. [13] Pendry JB, Holden AJ, Robbins DJ, Stewart WJ. Low frequency plasmons in thin-wire structures. J Phys Condens Matter 1998;10 (4785-09).
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Optical response of anisotropic silver nanostructures on polarized light Robert Krajcar n, Jakub Siegel, Oleksiy Lyutakov, Petr Slepička, Václav Švorčík Department of Solid State Engineering, Institute of Chemical Technology, 166 28 Prague, Czech Republic
art ic l e i nf o
a b s t r a c t
Article history: Received 8 July 2014 Accepted 20 August 2014 Available online 28 August 2014
Treatment of absorbing polymer (polyethyleneterephthalate) with pulse KrF excimer laser causes formation of laser induced periodic surface structures (LIPSS). Silver nanowires were prepared on the surface of laser treated polymer using vacuum evaporation at glancing angle geometry (701). The wires were observed with Scanning Electron Microscope equipped with Focused Ion Beam module (FIB-SEM). Relations between size and spacing of wires and morphology of polymer template were observed from those images. Optical response of prepared wires with different cross-sections and spatial parameters was investigated. The effect of polarizer on measured UV–vis absorption spectra showed anisotropy in optical properties of 1D metal nanostructures. The excitation of Localized Surface Plasmon Resonance (LSPR) was achieved only with an appropriate arrangement of the wire axis to the plane of polarization. Influence of wire width on position of absorption band was detected. Wire thickness was found to be a crucial parameter resulting in plasmon peak intensity. & 2014 Elsevier B.V. All rights reserved.
Keywords: Polymer laser treatment LIPSS LSPR Silver nanostructures Optical properties
1. Introduction Noble metal nanostructures smaller than the wavelength of light have attracted great attention of physicists, chemists and material engineers due to their Localized surface plasmon resonance (LSPR). LSPR is the way of response during interaction between incident light and electrons in a conduction band of material. The incoming electromagnetic field of the light induces collective oscillations of electrons in resonance with frequency of radiation. The resonance frequency highly depends on material composition, size, shape, dielectric environment [1] and grating constant (in case of periodically patterned systems) [2]. The occurrence of LSPR results in selective photon absorption, scattering and local electromagnetic field enhancement. Tuning the absorption properties allows obtaining materials of various colors. Such materials are especially gold and silver, which exhibit LSPR in the visible range of spectrum due to the energy levels of d–d transitions [3]. Surface modes in spherical particles depend mostly upon their size. If the particle is small enough (compared to the wavelength of incident light), all scattered waves are approximately in phase and only dipole Plasmon resonance occurs. As the particle size increases, number of possibilities for mutual enhancement or cancellation of scattered waves increases [4]. The phase-retardation effects in the inner region of the particle lead to excitation of higher multipole modes (quadrupole,
n
Corresponding author. E-mail address: [email protected] (R. Krajcar).
http://dx.doi.org/10.1016/j.matlet.2014.08.113 0167-577X/& 2014 Elsevier B.V. All rights reserved.
octupole, etc.). So, more peaks can be observed in spectra of bigger particles, even though they have spherical shape. Splitting of the dipole resonance into two distinct modes can be seen at elongated particles (up to three modes for ellipsoids) due to frequency difference between longitudinal and transverse electron oscillations [5,6]. Positions of plasmon peaks of silver can be strongly influenced by interband transitions, especially from the 4d to the 5sp hybridized band. Usual approach for interpretation of rodded medium optical properties is to introduce several amendments in the traditional Drude model, related to effective electron mass, electron density and damping constant. The effective electron density is diluted because the free electrons are restricted within the physical boundaries of the wires. In case of nanowires with irregular cross-section the position of plasmon frequency maximum depends on wire width to height ratio [7]. Geometry of spherical nanoparticles allows polarization independent plasmon excitation, while plasmon resonance in nanowires can only be excited by an electric field oriented perpendicularly to the wire axis (only in this direction, the sufficient spatial confinement for electrons occurs) [2]. In this work we present response of silver nanowire arrays to linearly polarized light. Silver nanowires were prepared by vacuum evaporation on polymer substrate after its nano-patterning with KrF excimer laser.
2. Experimental Materials, apparatus and procedures: Periodic nanostructures (Ripples) were produced with KrF excimer laser (COMPexPro 50F, Coherent, Inc., wavelength 248 nm, pulse duration 20–40 ns,
R. Krajcar et al. / Materials Letters 137 (2014) 72–74
73
repetition rate 10 Hz) on biaxially oriented polyethyleneterephthalate (PET) foils (Goodfellow Ltd., thickness 50 mm). The laser light was linearly polarized with UV-grade fused silica prism (model PBSO – 248 -100). The aperture with an area of 5 10 mm2 was used. Samples were irradiated under three different angles of incidence (0, 22.5 and 451) with 6000 laser pulses (fluence of 7 mJ cm 2) [8]. Nano-patterned PET substrate was used as a template for deposition of silver (SAFINA, a.s., purity 99.99%) by vacuum evaporation on LEYBOLD-Heraeus, Univex 450 device (room temperature, pressure of 3.10 4 Pa). Deposition in glancing angle geometry (φ ¼701 with respect to the substrate surface normal) enabled growth of wires predominantly on the ridges of periodic polymer lines (shadow deposition) [9]. Analytical methods: Effective thickness of evaporated silver was determined by scratch method on a glass substrate (coated simultaneously with the PET template) using Atomic Force Microscopy (AFM) Digital Instruments CP II device. The “contact mode” with line scanning rate of 0.4 Hz was chosen. Measurements were performed with Bruker Antimony-doped Silicon probe CONT20ACP (spring constant 0.9 N m 1). Optical properties were studied using Perkin-Elmer Lambda 25 UV–vis spectrometer. The device was equipped with wire grid polarizer WP25L-UB (250–4000 nm, Thorlabs). The absorption spectra were recorded stepwise with the step in the wavelength of 1 nm and in the wavelength range of 200–1100 nm. For visual representation of nanowire arrays the Focused Ion Beam Scanning Electron Microscope (FIB-SEM, LYRA3 GMU, Tescan, Czech Republic) was chosen. The FIB cuts were made with a Gallium ion beam. The polishing procedure was performed to clean and flatten the investigated surfaces. The images were taken under an angle of 54.81. Applied voltage was 5 kV.
3. Results and discussion Periodicity of linear polymer nanostructures increases with angle of incidence of laser light (01/Λ ¼ 230 nm, 22.51/Λ ¼345 nm and 451/Λ ¼427 nm) [8]. Besides, width of the wires increases with periodicity of ripple structures (see Fig. 1). Angle of incidence can also influence distance between individual wires. Occurrence and location of silver are most noticeable in Fig. 1a for angle 451/ Λ ¼ 427 nm. Whereas the wires with lower periodicity are pretty close to each other, the spacing of polymer ripples modified under angle of 451 is so high, that prerequisites for shadow deposition are no longer fulfilled. Thus, deposited silver can be found not only on the ridges of ripple structures, but sometimes also in between them (see Fig. 1). Polymer nano-patterning by excimer laser treatment is in detail described in previous papers published by our group [10–12]. We started our investigation of absorption properties of silver nanowires taking into account mutual orientation of wire axis and vector of light polarization. Comparative measurements without polarizer were acquired to obtain counterpart data. Curves in Fig. 2 denoted as TM (transverse magnetic polarization) and TE (transverse electric polarization) clearly show, that when the electric field of incident light is perpendicular to the wire axis (TM), Localized Surface Plasmon Resonance (LSPR) can be excited and strong dipolar peak at 680 nm is observed. Contrary to that, when the light polarization is parallel (TE) to wire axis, no absorption peak occurs. There are no boundaries for motion of electrons in this direction (no selective photon absorption), because these wires are almost infinitely long (approximately 1 cm) in comparison with other dimensions. So the TE spectrum is similar to that, obtained with silver layer of same effective thickness on non-irradiated PET (pristine in Fig. 2). Data measured with non-polarized light in longitudinal (L) and in
Fig. 1. FIB-SEM analysis of silver metalized ripple structures with different periodicities. Different grating parameters are: (a) Λ ¼427 nm, (b) Λ ¼ 345 nm and (c) Λ ¼ 230 nm. Displayed area is 5 2.5 mm2.
Fig. 2. Absorption spectra of silver nanowires measured with linearly polarized light in compare with results obtained without polarizer. Sample with grating parameter Λ ¼ 345 nm and effective nanowire thickness of 40 nm was studied. The scheme next to spectra shows movement of electrons with respect to the vector of polarization.
transversal (T) orientation indicate the inherent polarization of spectrometer itself. Tuning the wavelength of primary beam via optical grating and its subsequent splitting into signal and reference beam by multiple reflection cause that signal beam is partially polarized in horizontal plane. When the wire is wider, the mean free path of electrons grows larger, which reduce the frequency of Plasmon oscillations and lead to obvious red-shift in absorption spectra (Fig. 3). Moreover, increasing wire width can results in quadrupole Plasmon excitation (Fig. 3b, dashed curve – 450 nm). In Fig. 3c (dashed and solid) even higher resonance modes occur (555 nm – quadrupole,
74
R. Krajcar et al. / Materials Letters 137 (2014) 72–74
Fig. 3. Absorption spectra of TM polarized silver nanowires of different thicknesses and widths (periodicity). Different grating parameters are: (a) Λ ¼ 230 nm, (b) Λ ¼ 345 nm and (c) Λ¼ 427 nm.
405 nm – octupole). Excitation of such multipoles is caused by size dependent interference of retarded electromagnetic scattering fields in the inner region of wires. This phenomenon is proportional to volume of examined material. Commonly used model for description of metal wires array optical behavior with the size smaller then probing wavelength is so-called Bruggeman approximation. According to the Bruggeman theory the position of plasmon related absorption peak is proportional to the plasma frequency of free electron in metal. On the other hand, plasma frequency of electron in the rodded medium is the function of lattice constant. As followed from Pendry calculation, plasma frequency is inversely proportional to the square of the lattice constant [13]. Thus, increasing of lattice constant will lead to decreasing of plasma frequency and red-shifting of plasmon absorption band. This situation is apparent in Fig. 3, where increasing of lattice constant leads to appropriate changes in the position of plasmon related absorption maximum. Intensity of individual peaks in the spectrum depends on thickness of wires (see Fig. 3). Sample with effective thickness of 20 nm always possesses lowest intensity, because there is the lowest number of electrons able to participate in collective oscillations. Ripple structures with 40 nm of silver have stronger dipolar peak than sample with 30 nm, until quadrupole and octupole peaks are excited. Higher multipole peaks are rising at the expense of the intensity of dipolar one. Amount of evaporated metal influences not only thickness of wires, but also their width and spacing (increasing amount of metal leads to wider wires, which are closer to each other and they also show more oblate cross-section) [9]. So the slight blue-shift observed with increase of wire thickness is caused by combination of several effects of different nature. Peaks between 320–350 nm may be attributed to interband transitions. Positions of these peaks do not exhibit high degree of variability, because it is mostly influenced by chemical composition of material. The larger the amount of deposited metal, the higher peak intensity is achieved, because more electrons can undergo transitions to higher energy levels.
4. Conclusions Treatment of polyethyleneterephthalate with pulse excimer laser light leads to creation of well-defined linear periodic nanostructures. Preparation of separated metallic wires on the ridges of polymer
lines can be achieved by vacuum evaporation under glancing angle geometry. Width of wires and distance between them depends on morphology of polymer template. Plasmon resonance of anisotropic metallic nanostructures is highly sensitive to polarization of incident light. Resonance effect in wires only occurs, when the electric component of light is perpendicular to wire axis. Perceptible redshift in the spectra with increasing wire width occurs which reflects spatial parameters of prepared nanowires. Larger amounts of deposited metal causes occurrence of higher multipolar peaks in their absorption spectra. Acknowledgments Financial support from specific university research, Ministry of Education of Czech Republic (MSMT No. 20/2014) (R.K.) and Grant Agency of Czech Republic (P108/12/G108). References [1] Kelly KL, Coronado E, Zhao LL, Schatz GC. The optical properties of metal nanoparticles: the influence of size, shape and dielectric environment. J Phys Chem B 2003;107:668–77. [2] Schider G, Krenn JR, Gotschy W, Lamprecht B, Ditlbacher H, Leitner A, et al. Optical properties of Ag and Au nanowire gratings. J Appl Phys 2001;90:3825–30. [3] Petryayeva E, Krull UJ. Localized surface plasmon resonance: nanostructures, bioassays and biosensing – A review. Anal Chim Acta 2011;706:8–24. [4] Bohren CF, Huffman DR. Absorption and Scattering of Light by Small Particles. Nex York: Wiley; 1983. [5] Cao J, Sun T, Grattan KTV. Gold nanorod-based localized surface plasmon resonance biosensors: a review. Sens Actuators B 2014;195:332–51. [6] Kreibig U, Vollmer M. Optical Properties of Metal Clusters. Berlin: SpringerVerlag; 1995. [7] Xu Q, Bao J, Capasso F, Whitesides GM. Surface plasmon resonances of freestanding gold nanowires fabricated by nanoskiving. Angew Chem Int Ed 2006;45:3631–5. [8] Krajcar R, Siegel J, Slepička P, Fitl P, Švorčík V. Silver nanowires prepared on PET structured by laser irradiation. Mater Lett 2014;117:184–7. [9] Siegel J, Heitz J, Řezníčková A, Švorčík V. Preparation and characterization of fully separed gold nanowire arrays. Appl Surf Sci 2013;264:443–7. [10] Slepička P, Neděla O, Siegel J, Krajcar R, Kolská Z, Švorčík V. Ripple polystyrene nano-pattern induced by KrF laser. Express Polym Lett 2014;8:459–66. [11] Slepička P, Rebollar E, Heitz J, Švorčík V. Gold coatings on polyethyleneterephthalate nano-patterned by F2 laser irradiation. Appl Surf Sci 2008;254:3585–90. [12] Siegel J, Heitz J, Švorčík V. Self-organized gold nanostructures on laser patterned PET. Surf Coat Technol 2011;206:517–21. [13] Pendry JB, Holden AJ, Robbins DJ, Stewart WJ. Low frequency plasmons in thin-wire structures. J Phys Condens Matter 1998;10 (4785-09).