Fig. 1. (a) Schematic of creating Au/SLG HSFL via FLPL enabling chromotropic color printing. The violet and green arrows represent the direction of sample scanning (S) and the direction of polarization (E) of the incident fs-laser beam, respectively. (b) Scanning electron microscopy (SEM) images of Au/SLG HSFL created with different values of F (N=1408), corresponding to the red, green, and brown colors in (a). Scale bar: 200 nm. (c) 2D-FFT spectrum of the fabricated Au/SLG HSFL (F=2.37  J cm−2, N=1408). Cross-sectional TEM images of (d) pristine a-Au/SLG and (e) c-Au/SLG HSFL (F=2.37  J cm−2, N=1408, the SLG is too thin to be observed). The top layer of deposited carbon as shown in (d) and (e) serves as a protection layer during the preparation and measurement of TEM.

Fig. 2. Operation mechanism of Au HSFL. (a) Schematic of the HSFL formation process in terms of N, depicting impacts of coupled SPP with “seed” pre-structure (relief on Si surface) and fs-laser-induced crystallization. The shaded areas in the cross-sectional schematic indicate thermal distributions. (b) Cross-sectional TEM images of the sample irradiated by fs-laser with (b1) N=0, (b2) N=88, and (b3) N=1408 (F=2.37  J cm−2). (c1)–(c3) High-resolution TEM images of the rectangular regions in (b1)–(b3), respectively. (d1)–(d3) Inverse fast Fourier transform (IFFT) images of the square regions in (c1)–(c3), respectively. The white arrows in (d3) indicate dislocations and stacking faults in the lattice structures. “⊥” and “∥” indicate the direction of excited SPP perpendicular and parallel to the polarization (E) of the used fs-laser, respectively. The top layer of deposited carbon as shown in (b) serves as a protection layer during the preparation and measurement of TEM.

Fig. 3. (a) Standard CIE-1931 chromaticity diagram, (b) optical microscope images of color squares of 15  μm×15  μm, and (c) SEM image of Au/SLG HSFL with F ranging from 0 to 3.4  J cm−2 (N=1408). (d) Optical reflection spectra of Au/SLG HSFL corresponding to (a).

Fig. 4. Complex refractive index (n2 and k) of (a) pristine a-Au measured by an ellipsometer and (b) typical Au. Simulated optical reflection spectra of (c) a-Au/SLG/SiO2/Si (F=N=0) without HSFL and (d) c-Au/SLG/SiO2/Si with HSFL (F=2.37  J cm−2, N=1408) using the refractive indices as derived from (a) and (b). Simulated total electric field distributions of (e) Au surface and (f) cross-section along x=0 of c-Au/SLG HSFL with F=2.37  J cm−2 and N=1408 in response to a plane wave with λ=550  nm (n2 and k of typical Au were used).

Fig. 5. (a) Large-area (2  mm×2.5  mm) color printing based on fs-laser-induced Au/SLG HSFL with a 0.25-NA objective lens. (b) Enlarged optical micrograph and SEM image of the rectangular region in (a). (c) Optical micrograph and SEM image of a single line fabricated by FLPL accompanied by a 0.85-NA objective lens.

Fig. 6. Schematics of remotely controlling the background color through drop-wise aqua regia treatment (a1) without and (b1) with isolation zones. Optical micrographs of “PRL,” an abbreviation of “Photonics Research Lab,” with the background color varying from (a2) yellow to (a3) green after the aqua regia treatment when isolation zones are absent. (b2) Optical micrographs of the game “Tetris” keeping yellow background after the drop-wise treatment with the isolation zones. (c) SEM images of the pristine a-Au (c1) before aqua regia etching, subject to aqua regia (c2) without and (c3) with the isolation zones. (d) SEM images of the Au/SLG HSFL (F=2.15  J cm−2, N=1408) (d1) before aqua regia etching, subject to aqua regia (d2) without and (d3) with the isolation zones. (e) SEM images of the Au/SLG HSFL (F=3.07  J cm−2, N=1408) (e1) before aqua regia etching, subject to aqua regia (e2) without and (e3) with the isolation zones. (f) SEM images of the Au/SLG HSFL (F=3.4  J cm−2, N=1408) (f1) before aqua regia etching, under the aqua regia treatment (f2) without and (f3) with the isolation zones. Scale bar: 200 nm.

Fig. 7. Large-area SEM image of Au/SLG HSFL created by FLPL (N=1408, F=2.37  J cm−2).

Fig. 8. Impact of SLG on the formation of Au HSFL (N=1408). SEM images of (a) Au/SiO2/Si and (b) Au/SLG/SiO2/Si surfaces irradiated by fs-laser with F=2.37  J cm−2; (c) Au/SiO2/Si and (d) Au/SLG/SiO2/Si surfaces irradiated by fs-laser with F=3.07  J cm−2.

Fig. 9. SEM images of the sample irradiated by fs-laser with (a) N=0, (b) N=88, and (c) N=1408 (F=2.37  J cm−2). (d)–(f) Cross-sectional high-resolution TEM images of the SEM images in (a)–(c), respectively. (g)–(i) 2D-FFT spectral images of (d)–(f), respectively.

Fig. 10. Instability of the irradiation of 520 nm fs-laser on a-Au/SiO2. (a) Schematic of the treatment of a-Au on SiO2 substrate by 520 nm fs-laser. (b) SEM image of a-Au/SiO2 surface with identical fabrication conditions, where different surface morphologies are formed. High-resolution SEM images of (c) periodic structures and (d) irregular damages corresponding to the marked region in green and yellow in (b), respectively.

Fig. 11. Distributions of the absorbed optical power in the yz-plane with a single surface inhomogeneity (hemisphere with a radius of 30 nm) corresponding to increased N for (a) a-Au/SiO2/Si without Si reliefs, (b) a-Au/SiO2/Si with Si reliefs, (c) Inter-Au/SiO2/Si with Si reliefs, and (d) c-Au/SiO2/Si with Si reliefs.

Fig. 12. Total electric-field distributions in the xy-plane with a single surface inhomogeneity (hemisphere with radius of 30 nm) corresponding to an increase in N for (a) a-Au/SiO2/Si without Si reliefs (i.e., “seed” pre-structure), (b) a-Au/SiO2/Si with Si reliefs, (c) Inter-Au/SiO2/Si with Si reliefs, and (d) c-Au/SiO2/Si with Si reliefs.

Fig. 13. Part of SEM images of Inter-Au surface irradiated by fs-laser with (a) N=6, (b) N=11, (c) N=22, and (d) N=44 (F=2.31  J cm−2).

Fig. 14. (a) SEM image of fs-laser-induced Au/SLG HSFL with F=2.37  J cm−2 and N=1408. (b) Image imported into FDTD simulations from the SEM image shown in (a). The rectangular region indicates the effective simulation area.

Fig. 15. Simulations of the absorption spectra according to the FLPL and complex refractive indices of Au. (a) Schematic of the cases identifying the mechanism responsible for the spectral characteristics. The geometry of the Au/SLG HSFL layer in (a3) and (a4) is identified using the SEM images (Fig. 9). The thicknesses of Au, SLG, and SiO2 layers are 50, 0.34, and 340 nm, respectively. The absorption spectra related to the pristine surface morphologies were calculated with (b) a-Au and (c) c-Au. The absorption spectra based on fs-laser induced Au/SLG HSFL (F=2.37  J cm−2, N=1408) were calculated with (d) a-Au and (e) c-Au. The absorption spectra in (b)–(e) correspond to the schematics in (a1)–(a4), respectively.

Fig. 16. Schematics of (a) the recovery of crystal structures from a-Au to c-Au due to fs-laser-induced crystallization and the reflected colors for the cases of (b) pristine a-Au/SLG and (c) c-Au/SLG HSFL after immersion in an etching solution of aqua regia, where the background color related to a-Au was changed from yellow to green while the printed colors based on c-Au/HSFL were preserved due to the reinforced corrosion resistance of c-Au. The black vertical lines in a-Au and c-Au indicate the lattice structures.

Fig. 17. Remote control of pristine background color based on the capillarity of SLG. (a) Optical microscopic image of the Au/SLG surface of the sample 3 min after dropping 2 μL aqua regia on it. Zoomed-in images of the Au/SLG surface (b) with and (c), (d) without aqua regia covering.

Fig. 18. (a) Raman spectra of SLG in the isolation zone and preserved background area, marked P1 and P2 in (b), respectively.