posted on 2021-09-24, 15:33authored byYunxia Wang, Huatian Hu, Jibo Tang, Shuang Meng, Hongxing Xu, Tao Ding
Silver nanowires (Ag NWs) present
prominent waveguiding properties
of subwavelength light due to their nanoconfinement with propagating
surface plasmons, which is of great importance for on-chip integration
of nanophotonic devices and optical computation. Such propagating
plasmons also exert plasmonic forces, which can be utilized to manipulate
nanoparticles (NPs) beyond the diffraction limit. However, such controllability
is spatially limited to the near fields, whereas a large portion of
uncontrolled particles are randomly deposited on the chips, which
could be detrimental to the integrated optical devices. Herein we
shine continuous wave laser at one end of the Ag NW immersed in AgNO3 solution to launch the propagating surface plasmons. The
laser irradiation also induces the photoreduction of Ag+ ions to locally generate tiny Ag NPs, which evolve into large Ag
flake branches closer to the other end of the Ag NW. Such a peculiar
growth is due to the synergistic effect of plasmonic forces and the
thermophoretic/thermo-osmosis forces induced by temperature gradient.
These branched Ag NWs with sharp angles are intrinsically chiral,
which can be partially controlled by changing the irradiation location,
forming plasmonic chiral enantiomers. The circular differential scattering
(CDS) response of these branched Ag NWs can be as large as 40%, which
can be used for chiral enantiomer sensing with spectral dissymmetric
factor up to 4 nm induced by phenylalanine. This plasmon-directed
on-wire growth not only offers a facile approach for generating plasmonic
chiral nanostructures with remote controllability, but also provides
significant insights on the synergistic effect of plasmonic forces
and thermal-induced forces, which has great implications for self-assembly
and integration of on-chip optics.