Abstract
Plasmon-mediated coalescence of two nearby gold nanorods (NRs) suspended in water induced by the illumination of a linearly polarized (LP) light was studied theoretically. We analyzed the coupled optical forces and torques in terms of Maxwell’s stress tensor upon two identical NRs irradiated by a LP plane wave using the multiple multipole method to estimate the optomechanical outcome. Numerical results show that the light-matter interaction can perform attraction or repulsion, depending on their initial configurations. For the attraction, the end-to-end or side-by-side coalescence of the two gold NRs could be caused by the LP light, depending on the wavelength. For example, the side-by-side coalescence of two adjacent NRs of r = 15 nm and L = 120 nm is most likely induced by 800-nm LP laser beam, whereas the end-to-end coalescence by 1064-nm or 1700-nm LP laser. These distinct phenomena are attributed to the perpendicular or parallel alignment of NR to the polarization of LP light in different wavelength ranges. The magnitude of optical force, proportional to the light’s fluence, could be stronger than van der Waals force. The estimation based on quasi-static model without considering the fluid dynamics may provide an insight to optical manipulation on the self-assembly of gold colloid.
Highlights
The growth mechanism of natural crystal has been studied for several centuries
We assume that two adjacent gold NRs lying on the xy plane are irradiated by a normal-incident plane wave, propagating along the z axis with x-polarization; the configuration is shown in Fig. 1(a), where the surrounding medium is water
Numerical results illustrate that the end-to-end or side-by-side coalescence of two nearby and coupled NRs could be induced under the illumination of linearly polarized (LP) light, beside the repulsion
Summary
The growth mechanism of natural crystal has been studied for several centuries. A classical theory of Ostwald ripening was proposed first based on thermodynamics to explain this mechanism[1]; smaller particles tend to detach and diffuse toward another larger one spontaneously. The plasmon-mediated optical forces between two gold bipyramids or NRs have been investigated numerically[20,21,22] In these studies the corresponding optical torque could play critical role in the alignment for these NPs’ coalescence[23,24,25]. The study of light-matter interaction of two coupled NRs with LP plane wave will provide an insight into the plasmon-mediated optomechanics on the self-assembly of NPs and the OA of elongated NRs or NWs under the irradiation of a continuous-wave (CW) LP laser beam
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