[21a-A307-1~9] 3.1 Basic optics and frontier of optics (merged with formerly 3.2 Equipment optics and materials)

▲ [21a-A307-8] Laser-induced hydrothermal synthesis of VO₂ on gold thin film and in solution

〇Pin Christophe¹, Ryo Kakuta¹, Hideki Fujiwara², Keiji Sasaki¹ (1.RIES, Hokkaido Univ., 2.Hokkai-gakuen Univ.)

Keywords:vanadium dioxide, laser-induced hydrothermal synthesis, optical tweezers

In this study, we investigate the growth of VO₂ nanocrystals and microparticles using a laser-induced hydrothermal synthesis method [2]. First, a 1064 nm-laser beam was focused onto the surface of a gold thin film (30 nm thickness). The synthesis of particles was observed when a critical laser intensity is reached. However, due to the combined light absorption of gold and vanadium oxide, high temperatures are easily reached leading to the formation of microbubbles and to damages of the gold thin film. The synthesis of vanadium oxide was confirmed by EDS measurements performed on nanocrystal structures synthesized at the bottom of a microbubble.
Using a high magnification (100x) and high NA (0.8) microscope objective, synthesized particles were optically trapped in the precursor solution using a Gaussian laser beam (1064 nm, 9 mW). Because of the light absorption, the particles were trapped close to a glass surface. Dark-field microscopy images show that the synthesized particles were trapped at a distance away from the beam center following an orbital trajectory. This phenomenon is a typical feature of the insulator-to-metal phase transition-induced optical force reversal occurring when VO₂ particles are optically trapped. Further analysis of the particle dynamics will be performed to investigate the optical forces acting on the trapped particles during the VO₂ growth process.