Integrated Ferroelectrics An International Journal
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Near-field optical characteristics of Ag nanoparticle within the near-field scope of a metallic AFM tip irradiated by SNOM laser Jianlei Cui, Jianwei Zhang, Xuewen Wang, Theogene Barayavuga, Xiaoqiao He, Xuesong Mei, Wenjun Wang, Gedong Jiang & Kedian Wang To cite this article: Jianlei Cui, Jianwei Zhang, Xuewen Wang, Theogene Barayavuga, Xiaoqiao He, Xuesong Mei, Wenjun Wang, Gedong Jiang & Kedian Wang (2017) Near-field optical characteristics of Ag nanoparticle within the near-field scope of a metallic AFM tip irradiated by SNOM laser, Integrated Ferroelectrics, 178:1, 117-124, DOI: 10.1080/10584587.2017.1325212 To link to this article: http://dx.doi.org/10.1080/10584587.2017.1325212
Published online: 22 Jun 2017.
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Date: 22 June 2017, At: 19:07
INTEGRATED FERROELECTRICS , VOL. , – https://doi.org/./..
Near-field optical characteristics of Ag nanoparticle within the near-field scope of a metallic AFM tip irradiated by SNOM laser Jianlei Cuia,b,c,d , Jianwei Zhanga , Xuewen Wanga , Theogene Barayavugaa , Xiaoqiao Hed,e , Xuesong Meia , Wenjun Wanga , Gedong Jianga , and Kedian Wanga a
State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi’an, P. R. China; State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan, P. R. China; c State Key Laboratory of High Performance Complex Manufacturing, Central South University, Changsha, P. R. China; d Department of Architecture and Civil Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong; e Center for Advanced Structural Materials, City University of Hong Kong Shenzhen Research Institute, Shenzhen, P. R. China b
ABSTRACT
ARTICLE HISTORY
Based on the near-field optical theory, the near-field characteristics of Ag nanoparticle within the near-field scope of a metallic AFM tip irradiated by optical fiber probe laser are carried out with finite element method. As the laser transmits in optical fiber probe, the light of the various modes is gradually turned off, remaining the HE11 mode laser. Meanwhile, the evanescent field can be produced at the confined aperture, which will also stimulate the near-field enhancement phenomenon of metallic AFM tip and Ag nanoparticle with those extrema appearing in the apex of AFM tip, the upper and lower parts of Ag nanoparticle, and the upper and lower sharp boundary positions at the end of the tapered fiber probe. The related mechanism is revealed and nearfield optical characteristics are also analyzed.
Received August Accepted March KEYWORDS
Near-field; laser; SNOM probe; AFM tip; Ag nanoparticle
1. Introduction With the development of near-field optical technique, scanning near-field optical microscope (SNOM) has been developed and more widely used in surface imaging detection with finer resolution than the classical diffraction limit. The tip enhanced Raman scattering (TERS) with the scanning probe microscope (SPM) has been gradually proved to be a powerful and promising tool for optical detection. Thus the innovative applications of SNOM and TERS appear in trapping nanoparticles, molecules and atoms [1–6]. Currently, some researchers have mainly allocated attention to surface modification and nanostructure creation, etc. Chimmalgi et al., using the SNOM fiber probe to transmit high power pulse laser, performed nanoscale rapid melting and CONTACT Jianlei Cui
[email protected]; Xiaoqiao He
[email protected] Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/ginf. © Taylor & Francis Group, LLC
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crystallization of semiconductor thin film with near-field enhancement effect at the aperture of SNOM fiber probe [7]. They also reported the femtosecond laser nearfield nanomachining of metals assisted by SPM probe [8]. Geshev et al. theoretically calculated the near-field enhancement effect between the sample surface and SPM probe tip [9]. Cui et al. also simulated the near-field optical characteristics and distribution of SPM tip irradiated laser [10, 11]. Additionally, Atomic force microscope (AFM) as one of SPM is applied to nanofabrication with additional scanning and imaging function [12–17]. So by means of the near-field optical advantages of both SNOM and SPM, Cui et al. carried out the nanoscale soldering of polystyrene nanoparticles with the near-field enhancement effect of metallic AFM probe tip irradiated by SNOM laser [18]. However, related near-field optical mechanism was not deeply revealed. If it is explained theoretically, it will provide a powerful guidance for nanofabrication [19–27]. Consequently, as for the near-field composite technology of SNOM laser irradiating the metallic AFM probe tip, the near-field optical characteristics of metal nanoparticle is studied within the near-field scope of a metallic AFM tip irradiated by SNOM laser in this paper. 2. Computational modeling Figure 1 gives the computational model about near-field optics of metal nanoparticle within the near-field scope of a metallic AFM tip irradiated SNOM near-field laser. Considering the actual situation, the profile of AFM probe tip is controlled by the following formula [28]. ⎛ ⎞ 2 R z = Rt cot θt ⎝ 1 + − 1⎠ (1) Rt Here, the Rt and θ t is the curvature radius and semi-angle of AFM probe tip, respectively. According to the reports about near-field optical distribution of AFM illuminated by spatial focusing laser, the near-field enhancement effect mainly appears near the AFM tip. So the height size of AFM probe tip is close to the following Rayleigh length.
Figure . Computational model about near-field optics of Ag nanoparticle within the near-field scope of a metallic AFM tip irradiated SNOM near-field laser.
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Table . Calculation parameters for computational model of Ag nanoparticle within the near-field scope of a metallic AFM tip irradiated SNOM near-field laser. Parameters Values
λ
θt
Rt
ht
T
α
ϕ
ϕ
rp
nm
°
nm
nm
nm
°
nm
nm
nm
R∗ = λl /(2π )
(2)
Here the λl represents the incident laser wavelength. In this computational model, the incident laser with polarization direction of zaxis is transmitted along the x-axis direction of SNOM optical fiber probe. The SiO2 core of optical fiber probe is coated by aluminum film for ensuring the limitation of scattering and transmitting light field. According to the actual situation, some related parameter values are shown in Table 1. Simultaneously, in order to stimulate near-field of AFM probe tip irradiated by laser, the AFM is coated by Pt thin film with the thickness of ∼100 nm. Silver was selected as the material of metal nanoparticle. And the laser wavelength is set to 808 nm combining the actual situation of incident pulse laser. Then, to study the near-field optical characteristics at the corresponding laser wavelength, the refractive permittivity ε SiO2 , ε Al , ε Pt , ε Ag is set 3.9, −34.5 + 8.5i, −17.179 + 29.609i, −10.546 + 0.839i, which depends on the corresponding refractivity n and extinction coefficient k of different materials, respectively [29]. Additionally, for showing the near-field enhancement effect, the field enhancement factor (FEF) is defined as follow FEF =
Ep E0
(3)
Here, Ep shows the enhanced electric field amplitude, E0 gives the initial electric field amplitude of the incident laser. To clearly and simply express the near-field enhancement effect, the initial electric field amplitude of incident laser E0 was set to 1 V/m, so the FEF is equal to Ep value at the corresponding position in the near-field region. In addition, when the Ag nanoparticle is positioned in the near-field region of metallic AFM tip irradiated by SNOM laser, the near-field characteristics mainly depends on the distance l between SNOM probe and the AFM probe, the gap dt-p between AFM tip and Ag nanoparticle and the angle β between polarization direction of the incident laser and the axial direction of AFM probe. For observing the angle β, the polarization direction of incident laser remains unchanged by only changing the axial direction of AFM probe. So the angle β is given as follow β = βl − 90◦
(4)
Here, β l represents the transmission direction of incident laser and the axial direction of AFM probe.
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Figure . (a) Ichnography and (b) -D height image about near-field distribution of silver nanoparticle within near-field scope of AFM tip irradiated by optical fiber probe laser.
3. Results and discussion To reveal the near-field optical characteristics, the corresponding simulations were performed with the finite element method (FEM) which is now regarded as an effective tool for solving electromagnetic problems. Figure 2 gives the ichnography and 3-D height image about near-field distribution of Ag nanoparticle within near-field scope of AFM tip irradiated by optical fiber probe laser. When incident laser enters into the optical fiber probe, the transmission problem will be transformed into the waveguide propagation situation based on the waveguide theory. If the laser is transmitted to the tip part of optical fiber probe, part of laser will be reflected by the inner side of the cladding layer and superimposed with the incident laser to form the strong standing wave field along the x-axis direction. And the laser of the various modes is gradually turned off due to the cut-off radius which is related to the diameter of the tapered section of optical fiber probe, remaining the HE11 mode laser in the subsequent transmission process. If the diameter of the tapered section reduces to the cut-off diameter of HE11 mode light, the HE11 laser will also be cut-off with the light vector becoming imaginary. So the evanescent field can be produced at the confined aperture of optical fiber probe, which will also stimulate the near-field enhancement phenomenon of metallic AFM tip and Ag nanoparticle. Due to the size effect and superimposed effect, those extrema appear in the apex of AFM tip (marked with word “A”), the upper and lower positions of Ag nanoparticle (marked with words “B” and “C”), and the upper and lower sharp boundary positions at the end of the tapered fiber probe (marked with words “D” and “E”). However, the near-field enhancement effect at the five positions mainly depends on the parameters of l, dt-p and β. To study the impact of the gap dt-p between AFM tip and Ag nanoparticle, the incident laser direction is set to be perpendicular to the axial direction of AFM probe tip i.e. angle β is equal to 0, and the distance l is also set to 60 nm for ensuring the AFM tip and Ag nanoparticle in the near-field region of SNOM probe tip. Figure 3 shows the effect of the gap between AFM tip and Ag nanoparticle on the near-field enhancement. Obviously, when the gap is 2 nm, the values of A and B are close to 10. However, when the dt-p value is less than 10 nm, the field enhancement dramatically decreases with the increase of gap at the positions of AFM tip apex and the upper point of Ag nanoparticle. Subsequently, the FEF values of A and B positions decrease slowly, which is mainly related to the near-field superimposed effect of AFM tip
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Figure . Effect of the gap between AFM tip and Ag nanoparticle on the near-field enhancement.
apex and Ag nanoparticle, possessing smaller proportion of superimposed effect between SNOM tip and AFM tip/Ag nanoparticle. Increasing the gap, the mutual superimposed effect can be gradually weakened between A and B points. As for the lower C position of Ag nanoparticle, far away from the AFM tip apex, the FEF value decreases very slowly with small near-field superimposed effect. In addition, the FEF values at the sharp D and E positions of SNOM probe tip are almost constant, which is independent of the gap value dt-p without suffering the superimposed effect from the near-field of AFM tip and Ag nanoparticle due to the larger distance between SNOM probe and AFM probe tip. If the distance l between SNOM probe and the AFM tip and the gap dt-p between AFM tip and Ag nanoparticle is set 60 nm and 10 nm, respectively, the effect of the angle β on the near-field enhancement is shown in Figure 4. When the polarization
Figure . Effect of the angle between polarization direction of the incident laser and the axial direction of AFM probe on the near-field enhancement.
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Figure . Effect of the distance between SNOM probe and the AFM probe on the near-field enhancement.
direction is parallel to the axial direction of AFM probe, the FEF of the AFM tip apex has the largest value. Increasing the angle, the FEF value gradually decreases, which indicates that matching characteristics between laser polarization and the axial direction of AFM probe plays an important role in the near-field enhancement. Owing to the superimposed effect of decreasing evanescent field, the nearfield enhancement of the upper B position of Ag nanoparticle also decreases subsequently. As for the D and E positions of SNOM probe tip, the FEF values gradually become larger and finally tend to be stable. As the FEF value at the E position is almost constant with keeping the similar situation changed with the gap value dt-p . For analyzing the effect of the distance between SNOM probe and the AFM probe on the near-field enhancement, the gap value dt-p and angle β is set to10 nm and 30°, respectively, with the corresponding results in Figure 5. The evanescent field at the outlet of SNOM probe tip gradually dies down with the increases of l value, which can lead to smaller near-field enhancement effect of AFM tip apex and Ag nanoparticle. When the AFM probe and Ag nanoparticle are far away from the outlet of SNOM probe tip, the electric field values at the sharp D and E positions are gradually independent of the evanescent field effect of AFM tip and Ag nanoparticle, finally keeping the same FEF values with the increases of l. In addition, the second near-field enhancement effect lessens gradually at the positions of AFM tip and Ag nanoparticle. According to the above near-field characteristics of Ag nanoparticle, the nearfield effect can be controlled through adjusting the parameters of dt-p , β and l. It is possible to decrease the values of dt-p , β and l for obtaining the high near-field enhancement effect during the nanofabrication.
4. Conclusions In this paper, the exploration on the near-field characteristics of silver nanoparticle within the near-field scope of a metallic AFM tip irradiated by optical fiber
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probe laser is carried out with finite element method based on the near-field optical theory. In the transmission of laser, the light of the various modes is gradually turned off due to the cut-off radius which is related to the diameter of the tapered section of optical fiber probe, remaining the HE11 mode laser in the subsequent transmission process. The evanescent field can be produced at the confined aperture of optical fiber probe, which will also stimulate the near-field enhancement phenomenon of metallic AFM tip and Ag nanoparticle. Due to the size effect and superimposed effect, those extrema appear in the apex of AFM tip, the upper and lower parts of Ag nanoparticle, and the upper and lower sharp boundary potions at the end of the tapered fiber probe, which mainly depends on the distance between SNOM probe and the AFM probe, the gap between AFM tip and Ag nanoparticle and the angle between polarization direction of the incident laser and the axial direction of AFM probe. It is possible to decrease the variable values for obtaining the high near-field enhancement effect during the nanofabrication.
Funding This project is supported by National Natural Science Foundation of China (51505371, 11372264), Hong Kong Scholars Program (XJ2015038), a research grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (CityU 114013), China Postdoctoral Science Foundation (2014M562397, 2015T81018), Program for Changjiang Scholars and Innovative Research Team in University (IRT_15R54), Open Research Foundation of State Key Lab. of Digital Manufacturing Equipment and Technology in Huazhong University of Science and Technology (DMETKF2016007), Open Research Fund of Key Laboratory of High Performance Complex Manufacturing, Central South University (Kfkt2015-06).
References 1. F. Zenhausern, Y. Martin, & H. K. Wickramasinghe, Scanning interferometric apertureless microscopy: optical imaging at 10 angstrom resolution. Science, 269, 1083–1085 (1995). 2. B. Knoll, & F. Keilmann, Near-field probing of vibrational absorption for chemical microscopy. Nature, 399, 134–137 (1999). 3. L. Novotny, & S. J. Stranick, Near-field optical microscopy and spectroscopy with pointed probes. Annu. Rev. Phys. Chem., 57, 303–331 (2006). 4. L. Novotny, & N. Van Hulst, Antennas for light. Nat. Photonics, 5, 83–90 (2011). 5. J. Cui, L. Yang, Y. Wang, et al., Local field enhancement characteristics in a tapered metalcoated optical fiber probe for nanolithography. Integr. Ferroelectr., 164, 90–97 (2015). 6. J. Cui, L. Yang, H. Xie, et al., New optical near-field nanolithography with optical fiber probe laser irradiating atomic force microscopy probe tip. Integr. Ferroelectr., 169, 124–132 (2016). 7. A. Chimmalgi, D. J. Hwang, & C. P. Grigoropoulos, Nanoscale rapid melting and crystallization of semiconductor thin films. Nano Lett., 5, 1924–1930 (2005). 8. A. Chimmalgi, T. Y. Choi, C. P. Grigoropoulos, et al., Femtosecond laser aperturless nearfield nanomachining of metals assisted by scanning probe microscopy. Appl. Phys. Lett., 82, 1146 (2003). 9. P. I. Geshev, U. Fischer, & H. Fuchs, Calculation of tip enhanced Raman scattering caused by nanoparticle plasmons acting on a molecule placed near a metallic film. Phys. Rev. B, 81, 125441 (2010).
124
J. CUI ET AL.
10. J. Cui, L. Yang, & Y. Wang, Simulation study of near-field enhancement on a laser-irradiated AFM metal probe. Laser Phys., 23, 076003 (2013). 11. L. Yang, J. Cui, Y. Wang et al., Nanospot soldering of carbon nanotubes using near-field enhancement effect of AFM probe irradiated by optical fiber probe laser. RSC Adv., 5, 56677– 56685 (2015). 12. J. E. Sader, J. A. Sanelli, B. D. Adamson et al., Spring constant calibration of atomic force microscope cantilevers of arbitrary shape. Rev. Sci. Instrum., 83, 103705 (2012). 13. J. Cui, L. Yang, X. Mei et al., Nanomanipulation of carbon nanotubes with the vector scanning mode of atomic force microscope. Integr. Ferroelectr., 163, 81–88 (2015). 14. J. Cui, L. Yang, & Y. Wang, Creation and measurement of nanodots with combined-dynamic mode “dip-pen” nanolithography based on atomic force microscope. Micro Nano Lett., 9, 189–192 (2014). 15. N. Gavara, & R. S. Chadwick, Determination of the elastic moduli of thin samples and adherent cells using conical atomic force microscope tips. Nat. Nanotechnol., 7, 733–736 (2012). 16. J. Cui, L. Yang, Y. Wang et al., Experimental study on the creation of nanodots with combineddynamic mode “dip-pen” nanolithography. Integr. Ferroelectr., 151, 1–7 (2014). 17. A. K. Lee, D. M. Lewis, & P. J. Ashman, Force and energy requirement for microalgal cell disruption: an atomic force microscope evaluation. Bioresour. Technol., 128, 199–206 (2013). 18. J. Cui, L. Yang, Y. Wang et al., Nanospot soldering polystyrene nanoparticles with an optical fiber probe laser irradiating a metallic AFM probe based on the near-field enhancement effect. ACS Appl. Mater. Interfaces, 7, 2294–2300 (2015). 19. X. Chen, & X. Wang, Microscale spatially resolved thermal response of Si nanotip to laser irradiation. J Phys. Chem. C, 115, 22207–22216 (2011). 20. M. Borovšak, P. Šutar, E. Goreshnik et al., Topotactic changes on η-Mo4 O11 caused by biased atomic force microscope tip and cw-laser. Appl. Surf. Sci., 354, 256–259 (2015). 21. J. Cui, B. Theogene, X. Wang et al., Molecular dynamics study of nanojoining between axially positioned Ag nanowires. Appl. Surf. Sci., 378, 57–62 (2016). 22. J. Cui, L. Yang, L. Zhou et al., Nanoscale soldering of axially positioned single-walled carbon nanotubes: a molecular dynamics simulation study. ACS Appl. Mater. Interfaces, 6, 2044–2050 (2014). 23. S. Ryu, D. J. Hwang, E. Kim et al., Tip-based nanoscale selective growth of discrete silicon nanowires by near-field laser illumination. Appl. Phys. A, 116, 51–58 (2014). 24. N. Hosoya, M. Tanimura, & M. Tachibana, Effect of laser irradiation on few-layer graphene in air probed by Raman spectroscopy. Trans. Mater. Res. Soc. Jpn., 38, 579–583 (2013). 25. J. Cui, L. Yang, & Y. Wang, Nanowelding configuration between carbon nanotubes in axial direction. Appl. Surf. Sci., 264, 713–717 (2013). 26. J. Cui, X. Wang, T. Barayavuga et al., Nanojoining of Crossed Ag Nanowires: A Molecular Dynamics Study. J. Nanopart. Res., 18, 175 (2016). 27. J. Cui, L. Yang, & Y. Wang, Molecular dynamics study of the positioned single-walled carbon nanotubes with T-, X-, Y- junction during nanoscale soldering. Appl. Surf. Sci., 284, 392–396 (2013). 28. C. D’Andrea, F. Neri, P. M. Ossi et al., Synthesis by pulsed laser ablation in Ar and SERS activity of silver thin films with controlled nanostructure. Laser Phys., 21, 818–822 (2011). 28. F. Demming, J. Jersch, K. Dickmann et al., Calculation of the field enhancement on laserilluminated scanning probe tips by the boundary element method. Appl. Phys. B: Lasers Opt., 66, 593–598 (1998). 29. E. D. Palik, Handbook of optical constants of solids. Academic press (1998).
