Abstract
Through the light-driven geometrically oriented attachment (OA) and self-assembly of Au nanorods (NRs) or nanoparticles (NPs), single-crystalline Au nanowires (NWs) were synthesized by the irradiation of a linearly-polarized (LP) laser. The process was conducted in a droplet of Au colloid on a glass irradiated by LP near-infrared (e.g. 1064 nm and 785 nm) laser beam of low power at room temperature and atmospheric pressure, without any additive. The FE-SEM images show that the cross sections of NWs are various: tetragonal, pentagonal or hexagonal. The EDS spectrum verifies the composition is Au, and the pattern of X-ray diffraction identifies the crystallinity of NWs with the facets of {111}, {200}, {220} and {311}. We proposed a hypothesis for the mechanism that the primary building units are aligned and coalesced by the plasmon-mediated optical torque and force to form the secondary building units. Subsequently, the secondary building units undergo the next self-assembly, and so forth the tertiary ones. The LP light guides the translational and rotational motions of these building units to perform geometrically OA in the side-by-side, end-to-end and T-shaped manners. Consequently, micron-sized ordered mesocrystals are produced. Additionally, the concomitant plasmonic heating causes the annealing for recrystallizing the mesocrystals in water.
Highlights
Two-photon[20], electron beam[21], X ray22) or surface tension[23,24] have been proposed to enhance the oriented attachment (OA) process of NPs for forming a micron-sized crystal
With an exposure time of 40 min, Au NR was produced in a droplet of 0.8 μl; Fig. 4b shows a FE-SEM image indicating one Au NR with pentagonal cross section accompanied with one Au NR
We do not have enough evidences yet, we propose a hypothesis for the light-driven OA that at the beginning the primary building units (Au NRs or NPs) are driven to perform geometrically OA by the optical force and torque induced by linearly polarized (LP) light to assemble and form larger secondary building units in an end-to-end or side-by-side manner for the subsequent self-assembly, and so forth the tertiary building units are formed
Summary
Two-photon[20], electron beam[21], X ray22) or surface tension (capillary force)[23,24] have been proposed to enhance the OA process of NPs for forming a micron-sized crystal. Via the irradiation of a CW linearly polarized (LP) near-infrared (NIR) laser beam, the plasmon-mediated optical force and torque are induced upon coupled Au NRs or NPs for providing the directionality for the light-driven geometrically OA of these building blocks and the growth of Au NW, as well as the concomitant plasmonic heating is generated for the recrystallization of Au NW. Using the light-driven OA of primary building blocks (e.g. nanocrystals: NRs or NPs) to form larger structures, we can fabricate 3D micron-sized anisotropic mesocrystals and even single-crystalline Au NWs. Without any surfactant, ligand, DNA, polymeric binder or other additive, Au NWs can be fabricated in an aqueous solution at room temperature and atmospheric pressure by the irradiation of LP light alone. This simple method can be applied for the process of plasmonic waveguide in PIC or conducting channel in opto-electronic devices
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