la9b00176_si_008.mpg (2.29 MB)
Rapid Assembly of Colloidal Crystals under Laser Illumination on a GeSbTe Substrate
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posted on 2019-04-22, 00:00 authored by Kei Yamaguchi, Eiji Yamamoto, Ryo Soma, Bokusui Nakayama, Masashi Kuwahara, Toshiharu SaikiOptical
techniques have been actively studied for manipulating
nano- to microsized objects. However, long-range attraction and rapid
transport of particles within thin quasi-two-dimensional systems are
difficult because of the weak thermophoretic forces. Here, we introduce
an experimental system that can rapidly generate quasi-two-dimensional
colloidal crystals in deionized water, sandwiched between two hard
plates. When a pulsed laser is irradiated on a chalcogenide phase-change
material spattered on one side of the plates, the induced Marangoni-like
flow causes a colloidal self-assembly in the order of tens of micrometers
within the laser spot, with a transport velocity of a few tens of
micrometers per second. This is due to the large thermal gradient
induced by chalcogenide characteristics of high laser absorption
and low thermal conductivity, and a strong hydrodynamic slip flow
at the hydrophobic chalcogenide interface. Moreover, the colloidal
crystals exhibit various lattice structures, depending on the laser
intensity and chamber distance. For a certain range of the chamber
distance, the colloidal crystal phases can be alternated by tuning
the laser intensity in real time. Our system forms and deforms quasi-two-dimensional
colloidal crystals at an on-demand location on a GeSbTe substrate.