Fig. 1. Schematic of the experimental setup. L1, lens; M1-M2, mirrors; DM, dichroic mirror; Ltube, tube lens; MO, microscope objective; CMOS, CMOS camera. Inset: top view of the circular trough. ‘+’ indicates the optical trap center.

Fig. 2. Two-dimensional self-assembly accelerated at the water–air interface by optical tweezers. The NA of the objective is 1.25. The white lines mark the water–air interface at the upper left. The black arrow indicates the direction of the particles’ movement. Scale bar, 10 μm; ‘+’ indicates the optical trap center.

Fig. 3. Particles’ velocities dependence of laser power at the pupil of the objective lens. Error bars are the standard deviations of velocity. NA=1.25. The line is a linear fit to the whole data.

Fig. 4. Gap at the growing front is filled up by the incoming particles. The steep peak is created by optical tweezers. Scale bar, 10 μm; ‘+’ indicates the optical trap center.

Fig. 5. Smoothing process for a steep peak at the growing front. The particles at the peak are pulled down by the Marangoni flow, resulting in a reduction of the local roughness. Scale bar, 10 μm; ‘+’ indicates the optical trap center. The black arrows indicate the direction of the particles’ movement.

Fig. 6. Integration of particle aggregation into the crystal. (a) and (b) The aggregation is created by the optical tweezers. (c) and (d) The wide peak growing. Black lines mark the shape of the peak. Scale bar, 10 μm; ‘+’ indicates the optical trap center.