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Tunable potential well for plasmonic trapping of metallic particles by bowtie nano-apertures

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ABSTRACT

In this paper, the tunable optical trapping dependence on wavelength of incident beam is theoretically investigated based on numerical simulations. The Monte Carlo method is taken into account for exploring the trapping characteristics such as average deviation and number distribution histogram of nanoparticles. It is revealed that both the width and the depth of potential well for trapping particles can be flexibly adjusted by tuning the wavelength of the incident beam. In addition, incident wavelengths for the deepest potential well and for the strongest stiffness at bottom are separated. These phenomena are explained as the strong plasmon coupling between tweezers and metallic nanoparticles. In addition, required trapping fluence and particles’ distributions show distinctive properties through carefully modifying the incident wavelengths from 1280 nm to 1300 nm. Trapping with lowest laser fluence can be realized with1280 nm laser and trapping with highest precision can be realized with 1300 nm laser. This work will provide theoretical support for advancing the manipulation of metallic particles and related applications such as single-molecule fluorescence and surface enhanced Raman spectroscopy.

No MeSH data available.


Schematic model for FEM simulation and e-field enhancement distribution.(a) The scheme of the plasmonic tweezers and the nanoparticle. The blue arrow denotes the incident direction and the red one demotes the polarization direction. The direction of the incident laser is vertical to the surface of the gold film where the bowtie nano-aperture (BNA) is milled. The incident light is polarized along the direction where the bowtie dimmer arranges. The diameter of the gold nanparticle is 50 nm. (b) The geometry of the BNA, the thickness of the gold film is 100 nm, A = 180 nm, B = 280 nm, D = 70 nm. (c–f) The e-field distribution under different incident wavelength with the distance between the nanoparticle and the tweezers of (c) 10 nm, (d) 20 nm, (e) 40 nm, (f) 60 nm.
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f1: Schematic model for FEM simulation and e-field enhancement distribution.(a) The scheme of the plasmonic tweezers and the nanoparticle. The blue arrow denotes the incident direction and the red one demotes the polarization direction. The direction of the incident laser is vertical to the surface of the gold film where the bowtie nano-aperture (BNA) is milled. The incident light is polarized along the direction where the bowtie dimmer arranges. The diameter of the gold nanparticle is 50 nm. (b) The geometry of the BNA, the thickness of the gold film is 100 nm, A = 180 nm, B = 280 nm, D = 70 nm. (c–f) The e-field distribution under different incident wavelength with the distance between the nanoparticle and the tweezers of (c) 10 nm, (d) 20 nm, (e) 40 nm, (f) 60 nm.

Mentions: The scheme of the bowtie nano-aperture has been shown in Fig. 1(b), in which the detailed geometry parameter has been given. It has been proved by the previous work that the great localized and enhanced e-field exists in the center of bowtie dimmers, enabling to generate enough e-field gradients to trap nanoparticles within nanoscales. The plasmon resonance modes in metallic nano-apertures, proved as Fabry-Pérot-like interfering of TE10 mode propagation wave, strongly depend on the aperture geometry20. Through modifying apertures sizes or shapes, the wavelength for plasmonic trapping can be flexibly tuned. The e-field enhancement distribution with respect to the spatial arrangement of the particle-tweezers system and the incident wavelength is shown in Fig. 1(c–f). When the displacement of the nanoparticle to the center of the tweezers is 10 nm and 20 nm,shown in Fig. 1(c,d), the maximum e-field enhancement is acquired at the wavelength of 1300 nm. When the displacement increases from 40 nm to 60 nm, the wavelength with respect to the maximum e-field enhancement exhibits a shift from 1280 nm to 1260 nm. The displacement dependence of resonance wavelength could be attributed to the coupling between the metallic nanoparticle and the optical tweezers. The strongly enhanced plasmon coupling, which exists when the nanoparticle is in vicinity of the center of tweezers, leads to the increase of the resonance wavelength of the entire particle-tweezers system and highly enhanced e-field under longer incident wavelength. Correspondingly, as the nanoparticle get away from the tweezers, the strength of the coupling decreases, leading to prominent blue shift of the resonance wavelength of the particle-tweezers system. As a result, highly enhancede-field could be acquired with shorter wavelength.


Tunable potential well for plasmonic trapping of metallic particles by bowtie nano-apertures
Schematic model for FEM simulation and e-field enhancement distribution.(a) The scheme of the plasmonic tweezers and the nanoparticle. The blue arrow denotes the incident direction and the red one demotes the polarization direction. The direction of the incident laser is vertical to the surface of the gold film where the bowtie nano-aperture (BNA) is milled. The incident light is polarized along the direction where the bowtie dimmer arranges. The diameter of the gold nanparticle is 50 nm. (b) The geometry of the BNA, the thickness of the gold film is 100 nm, A = 180 nm, B = 280 nm, D = 70 nm. (c–f) The e-field distribution under different incident wavelength with the distance between the nanoparticle and the tweezers of (c) 10 nm, (d) 20 nm, (e) 40 nm, (f) 60 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036050&req=5

f1: Schematic model for FEM simulation and e-field enhancement distribution.(a) The scheme of the plasmonic tweezers and the nanoparticle. The blue arrow denotes the incident direction and the red one demotes the polarization direction. The direction of the incident laser is vertical to the surface of the gold film where the bowtie nano-aperture (BNA) is milled. The incident light is polarized along the direction where the bowtie dimmer arranges. The diameter of the gold nanparticle is 50 nm. (b) The geometry of the BNA, the thickness of the gold film is 100 nm, A = 180 nm, B = 280 nm, D = 70 nm. (c–f) The e-field distribution under different incident wavelength with the distance between the nanoparticle and the tweezers of (c) 10 nm, (d) 20 nm, (e) 40 nm, (f) 60 nm.
Mentions: The scheme of the bowtie nano-aperture has been shown in Fig. 1(b), in which the detailed geometry parameter has been given. It has been proved by the previous work that the great localized and enhanced e-field exists in the center of bowtie dimmers, enabling to generate enough e-field gradients to trap nanoparticles within nanoscales. The plasmon resonance modes in metallic nano-apertures, proved as Fabry-Pérot-like interfering of TE10 mode propagation wave, strongly depend on the aperture geometry20. Through modifying apertures sizes or shapes, the wavelength for plasmonic trapping can be flexibly tuned. The e-field enhancement distribution with respect to the spatial arrangement of the particle-tweezers system and the incident wavelength is shown in Fig. 1(c–f). When the displacement of the nanoparticle to the center of the tweezers is 10 nm and 20 nm,shown in Fig. 1(c,d), the maximum e-field enhancement is acquired at the wavelength of 1300 nm. When the displacement increases from 40 nm to 60 nm, the wavelength with respect to the maximum e-field enhancement exhibits a shift from 1280 nm to 1260 nm. The displacement dependence of resonance wavelength could be attributed to the coupling between the metallic nanoparticle and the optical tweezers. The strongly enhanced plasmon coupling, which exists when the nanoparticle is in vicinity of the center of tweezers, leads to the increase of the resonance wavelength of the entire particle-tweezers system and highly enhanced e-field under longer incident wavelength. Correspondingly, as the nanoparticle get away from the tweezers, the strength of the coupling decreases, leading to prominent blue shift of the resonance wavelength of the particle-tweezers system. As a result, highly enhancede-field could be acquired with shorter wavelength.

View Article: PubMed Central - PubMed

ABSTRACT

In this paper, the tunable optical trapping dependence on wavelength of incident beam is theoretically investigated based on numerical simulations. The Monte Carlo method is taken into account for exploring the trapping characteristics such as average deviation and number distribution histogram of nanoparticles. It is revealed that both the width and the depth of potential well for trapping particles can be flexibly adjusted by tuning the wavelength of the incident beam. In addition, incident wavelengths for the deepest potential well and for the strongest stiffness at bottom are separated. These phenomena are explained as the strong plasmon coupling between tweezers and metallic nanoparticles. In addition, required trapping fluence and particles’ distributions show distinctive properties through carefully modifying the incident wavelengths from 1280 nm to 1300 nm. Trapping with lowest laser fluence can be realized with1280 nm laser and trapping with highest precision can be realized with 1300 nm laser. This work will provide theoretical support for advancing the manipulation of metallic particles and related applications such as single-molecule fluorescence and surface enhanced Raman spectroscopy.

No MeSH data available.