10.1021/acs.langmuir.9b00176.s008 Kei Yamaguchi Kei Yamaguchi Eiji Yamamoto Eiji Yamamoto Ryo Soma Ryo Soma Bokusui Nakayama Bokusui Nakayama Masashi Kuwahara Masashi Kuwahara Toshiharu Saiki Toshiharu Saiki Rapid Assembly of Colloidal Crystals under Laser Illumination on a GeSbTe Substrate American Chemical Society 2019 chalcogenide characteristics  of quasi-two-dimensional chamber distance chalcogenide phase-change material laser intensity Marangoni-like flow causes crystal GeSbTe Substrate Optical techniques micrometer 2019-04-22 00:00:00 Media https://acs.figshare.com/articles/media/Rapid_Assembly_of_Colloidal_Crystals_under_Laser_Illumination_on_a_GeSbTe_Substrate/8070149 Optical 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.