With the continuous development of science and technology, it is of scientific significance to construct a structural color with a special color effect and good stability based on the nanostructure. At present, various artificially prepared structural color tuning methods are put forward, such as traditional nanoimprint lithography, ultrafast laser direct writing, microfluidics, and inkjet printing. Although it is possible to produce nanostructures with good periodicity and various patterns, the cost and complexity of the process also restrict the development of technology. To this end, two-dimensional ordered templates with planar hexagonal close-packed structures are prepared by the gas-liquid interface assembly method on silicon wafers, and silicon wafers with a certain thickness of SiO₂ in our study, and metal thin films with different thicknesses are prepared by the magnetron sputtering method. Then the deformation degree of the periodic surface is changed by post-treatment of 532 nm pulse laser to realize the modulation of structural color samples. Color modulation is carried out by regulating the changes in microstructure morphology.

The fabrication process of the periodic polystyrene (PS) microsphere substrate is divided into two steps. First, a polymer sphere monolayer is assembled at the gas-liquid interface and then transferred to the Si/SiO₂ substrate. Second, the Au films with different thicknesses are deposited on the above-mentioned PS colloidal crystal template by a radio frequency (RF) magnetron sputtering technique. Then a 532 nm pulsed solid-state laser system (EP10-1, Changchun New Industries Optoelectronics Technology Co., Ltd.,) is employed to post-treatment the ordered surface with metal-coated colloidal crystal by changing different scanning speeds. The laser system generates a train of 5 ns laser pulses at a repetition rate of 1 kHz. The laser beam is focused by a convex lens with a focal length of 160 mm, and the diameter of the focused laser beam is about 180 μm at the focal plane. By adopting such a method, vivid colors such as cyan, orange, and yellow are experimentally obtained, and the saturation is also improved by adding a SiO₂ layer.

With Si as the substrate and the coating time fixed at 20 s, 80s, and 120 s, the peak positions of the reflectance spectrum shift gradually from 609 nm, 602 nm, and 593 nm to 485 nm, 519 nm, and 524 nm in the long-wave band, and from 420 nm, 416 nm, and 401 nm to 394 nm, 375 nm, and 368 nm in the short-wave band respectively, as the laser scanning speed decreases. At a fixed laser scanning speed of 50 mm/s, the peak positions of the reflectance spectrum of the sample first shift to short wavelength from 585 nm to 538 nm with the increasing coating time, and then turn to 559 nm in the long wavelength direction. When the laser scanning speed increases to 200 mm/s, with the rising coating time, the spectrum shows a slight blueshifted trend and Δλ=17 nm (Fig. 6). In addition, by adding the SiO₂ layer, under the scanning speed of 50 mm/s, the spectral reflective ratio is improved significantly and the reflectance peak positions change from 537 nm and 394 nm to 411 nm and 492 nm, showing a clear blueshift. At the same time, the half-peak width becomes narrower and the color saturation is higher (Fig. 8). Observations on the microscopic surface morphology show that under the same substrate, the longer coating time leads to thicker gold films, while the smaller sample scanning speed results in a greater degree of surface deformation of microstructures. When the scanning speed is small enough, the PS microsphere structure is destroyed or even disappears. Under the same scanning speed, the deformation degree of thin gold films without SiO₂ is greater, and nano gold particles stack at the edge of the microsphere to form a metal ring, which also influences the measurement in the macroscopic spectral reflectance of the sample (Fig. 9).

In this paper, a 532 nm pulsed laser system is employed as an efficient method to modulate structural colors on metal-coated PS microsphere surfaces by changing the scanning speed with different substrates. The color turning method is carried out by controlling the deformation degree of the morphology of periodic structures, and thus various colors are obtained. The results show that with the same coating time, the central wavelengths of structural colors shift blue towards the short-wave direction as the laser scanning speed decreases. At the same scanning speed, the peak position of the reflectance spectrum first shifts blue from the long-wave to short-wave directions and then shifts red towards the long-wave direction as the coating time rises. When the laser scanning speed increases, the peak position of the reflectance spectrum presents a gradual blueshifted trend. In addition, when the SiO₂ layer is added to the substrate, besides obvious changes in hue, the color saturation of samples is also significantly improved, while other parameters remain unchanged. Our study proposes a new method of color tuning and explores a low-cost application in green printing and anti-counterfeiting.