Fig. 4: Mechanism for orientation control of PS/Au Janus particles.

a Schematic illustration of a PS/Au Janus particle rotating under a focused green laser beam. b Simulated temperature profile and c force analysis of a 2.7 µm PS/Au rotating under a focused green laser beam. The orientation is parallel to the Y axis, and the offset between the centre of the particle and the centre of the beam is equal to 0.8 R. The laser beam propagates along the negative Z direction. The power of the green laser beam is set as 2 mW. d Calculated X and Y components of the thermoelectric force and optical force as a function of the offset (the origin is at the centre of the beam). The red dashed lines indicate the balance position X = 0.8 R. e Calculated thermoelectric torques in the balance position (X = 0.8 R) as a function of θ, which is the angle of the PS/Au interface relative to the substrate (X–Y plane). The insets of e depict the corresponding configurations and temperature profiles at certain θ (indicated by dashed lines or arrows)