Inspired by the idea of combining conventional optical tweezers with plasmonic nanostructures, a technique named plasmonic optical tweezers (POT) has been widely explored from fundamental principles to applications. With the ability to break the diffraction barrier and enhance the localized electromagnetic field, POT techniques are especially effective for high spatial-resolution manipulation of nanoscale or even subnanoscale objects, from small bioparticles to atoms. In addition, POT can be easily integrated with other techniques such as lab-on-chip devices, which results in a very promising alternative technique for high-throughput single-bioparticle sensing or imaging. Despite its label-free, high-precision, and high-spatial-resolution nature, it also suffers from some limitations. One of the main obstacles is that the plasmonic nanostructures are located over the surfaces of a substrate, which makes the manipulation of bioparticles turn from a three-dimensional problem to a nearly two-dimensional problem. Meanwhile, the operation zone is limited to a predefined area. Therefore, the target objects must be delivered to the operation zone near the plasmonic structures. This review summarizes the state-of-the-art target delivery methods for the POT-based particle manipulating technique, along with its applications in single-bioparticle analysis/imaging, high-throughput bioparticle purifying, and single-atom manipulation. Future developmental perspectives of POT techniques are also discussed.
This paper presents a comprehensive theoretical study of the magnetic-tunable near-field radiative heat transfer (NFRHT) between two twisted graphene gratings. As a result of the quantum Hall regime of magneto-optical graphene and the grating effect, three types of graphene surface plasmon polaritons (SPPs) modes are observed in the system: near-zero modes, high-frequency hyperbolic modes, and elliptic modes. The elliptic SPPs modes, which are caused by the combined effect of magnetic field and grating, are observed in the graphene grating system for the first time. In addition, the near-zero modes can be greatly enhanced by the combined effect grating and magnetic field, rendering graphene devices promising for thermal communication at ultra-low frequency. In particular, the near-zero modes result in a unique enhancement region of heat transfer, no matter for any twisted angle between gratings. The combined effect of grating and magnetic field is investigated simultaneously. By changing the strength of magnetic field, the positions and intensities of the modes can be modulated, and hence the NFRHT can be tuned accordingly, no matter for parallel or twisted graphene gratings.The magnetic field endows the grating action (graphene filling factors and twisted angles) with a higher modulation ability to modulate the NFRHT compared with zero-field. Moreover, the modulation ability of twist can be tuned by the magnetic field at different twisted angles. In sum, the combined effect of magnetic field and grating provides a tunable way to realize the energy modulation or multi-frequency thermal communications related to graphene devices.
In this letter, we have demonstrated the possibility to efficiently relay the radiative heat flux between two nanoparticles by opening a smooth channel for heat transfer. By coating the nanoparticles with a silica shell and modifying the substrate with multilayered graphene sheets respectively, the localized phonon polaritons excited near the nanoparticles can couple with the multiple surface plasmon polaritons near the substrate to realize the heat relay in the long distance. The heat transfer can be enhanced by more than six orders of magnitude and the relay distance can be as high as 35 times in the far-field regime. The work may provide a way to realize the energy modulation or thermal communications especially in long distance. 2Since the prediction by Polder and Van Hove [1] that the heat exchange between two objects can be much higher than the blackbody limit at nanoscale separations, numerous nanoscale thermal devices [2-8] and unique phenomena [9, 10] are proposed. Thermal repeater is a device that can help the heat propagate further, acting as a relay. In other words, the key function of it is amplifying the radiative heat transfer (RHT) in long distance. When the two objects are separated at long distance, the RHT decreases dramatically as a result of the deterioration of the evanescent wave channel. Based on that, Dong et al. [11] proposed a method to delay the deterioration between two nanoparticles by placing a substrate near the two nanoparticles to form a channel for propagating surface waves. However, its performance dramatically degrades for metal nanoparticles, due to lack of coupled modes between the nanoparticles and the dielectric substrate. By coating monolayer graphene on the substrate, the performance of the long-distance energy-exchange has been improved [12]. However, the amplification is still limited for the reason that the graphene sheet can only couple with the substrate to form surface modes, but cannot greatly tailor the interplay between the nanoparticles and substrate. Moreover, the amplification is sorely confined near the interface of the substrate, due to the surface characteristics of graphene surface plasmon polaritons (SPPs).The lack of the connecting between the particles and the substrate, and the nature of SPPs both restrict the relay effect.Graphene exhibits intriguing electronic properties including the presence of strongly confined SPPs which can be excited to transport energy in photonic channels [13,14]. This has been exploited for a more efficient RHT between hybrid periodic structures [15] and between nanoparticles [16]. Recently, by using multilayer structures, the RHT between NPs has been shown to be further increased thanks to a resonant coupling between the substrate surface modes and the NPs resonances [17]. In addition, some unique phenomena are observed in multilayered graphene system [15,18,19], and one of the most important features is the multiple SPPs excited by the multilayered graphene. The effect provides the possibility to strengthen the SPPs near ...
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