Multiplexed Long-Range Electrohydrodynamic Transport and Nano-Optical Trapping with Cascaded Bowtie Photonic Crystal Nanobeams

Sen Yang, Joshua A. Allen, Chuchuan Hong, Kellen P. Arnold, Sharon M. Weiss, and Justus C. Ndukaife

Phys. Rev. Lett. 130, 083802 – Published 23 February 2023

Abstract

Photonic crystal cavities with bowtie defects that combine ultrahigh $Q$ and ultralow mode volume are theoretically studied for low-power nanoscale optical trapping. By harnessing the localized heating of the water layer near the bowtie region, combined with an applied alternating current electric field, this system provides long-range electrohydrodynamic transport of particles with average radial velocities of $30 μ m / s$ towards the bowtie region on demand by switching the input wavelength. Once transported to a given bowtie region, synergistic interaction of optical gradient and attractive negative thermophoretic forces stably trap a 10 nm quantum dot in a potential well with a depth of $10 k_{B} T$ using a mW input power.

Received 7 March 2022
Accepted 19 January 2023

DOI:https://doi.org/10.1103/PhysRevLett.130.083802

Physics Subject Headings (PhySH)

Electrokinetic flows Fluid-particle interactions Microfluidics Nanophotonics Photonic crystals

Optical tweezers

Atomic, Molecular & OpticalFluid Dynamics

Authors & Affiliations

Sen Yang ^1,3,*, Joshua A. Allen^1,3,*, Chuchuan Hong ^2,3, Kellen P. Arnold ^1,3, Sharon M. Weiss ^2,1,3, and Justus C. Ndukaife ^2,1,3,†

¹Interdisciplinary Materials Science, Vanderbilt University, Nashville, Tennessee 37235, USA
²Department of Electrical and Computer Engineering, Vanderbilt University, Nashville, Tennessee 37235, USA
³Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, Nashville, Tennessee 37235, USA

^*These authors contribute equally to this work.
^†justus.ndukaife@vanderbilt.edu

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Issue

Vol. 130, Iss. 8 — 24 February 2023

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Images

Figure 1
Schematic of the PhC-based multiplexed long-range electrohydrodynamic transport and trapping system. The inset shows the forces experienced by a particle trapped at the bowtie. Optical force (opt), electrothermal force (et), and thermophoretic force (th).
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Figure 2
(a) Electric field enhancement distribution of the BPCN cavity on resonance in the absence of the particle. The field enhancement is calculated by normalization to the amplitude of the electric field of the input fundamental TE mode in the bus waveguide. Inset: Zoom-in view of the bowtie region. (b) Transmission spectra for the three BPCNs, demonstrating the multiresonant property of the system. The resonant wavelengths are $λ_{1} = 1635.33, λ_{2} = 1623.65, λ_{3} = 1647.28 nm$ .
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Figure 3
Optical trapping characterization for a 10 nm PbSe quantum dot placed 21 nm above the bowtie surface. (a) Trapping force spectra for the quantum dot. (b)–(d) Trapping potential as well as trapping forces when moving the quantum dot along the $x$ , $y$ , and $z$ directions, respectively. The vertical dashed lines in (b) and (c) denote the center of the bowtie.
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Figure 4
(a) Depth of the trapping potential well along the $y$ direction ( $U_{y}^{opt}$ ) due to $F_{y}^{opt}$ and (b) the maximum absolute value of the pulling force $F_{z}^{opt}$ at different distances $z$ from the bowtie surface [shown in the inset of (b)]. $z$ is varied as 3, 9, 15, and 21 nm. Both $y$ axes are in log scale. (c) Transverse thermophoretic trapping potential for a 10 nm quantum dot at $z = 21 nm$ . (d) Transverse trapping potential for the optical trapping and thermophoretic trapping potentials along the $y$ direction [red dash line in (c), $z = 21 nm$ ].
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Figure 5
(a) Temperature field distribution of the $x y$ plane 300 nm above the bowtie surface. The radial velocity vector plot of the electrothermal flow induced around the resonant BPCN is superimposed on the temperature profile. Arrow length represents the magnitude of the flow velocity. (b) Temperature field distribution of the $x z$ plane and (c) the $y z$ plane. (d) Illustration of three cascaded BPCNs placed beside a bus waveguide. The right three panels show corresponding radial velocity profiles of the induced electrothermal flow along $x$ and $y$ directions (300 nm above the bowtie surface) around the three BPCNs in different states. The electrothermal flow shows a long-range characteristic ( $\sim 50 μ m$ ); (a) to (c) corresponds to the $Λ_{1}$ panel.
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