Fig. 1. Stainless steel micro-nano structure surface via femtosecond laser. (a) Laser energy density is 0.4 J/cm²; (b) laser energy density is 1.2 J/cm²

Fig. 2. Contact angle. (a) Contact angle of the original surface of stainless steel; (b) contact angle of stainless steel surface processed via femtosecond laser with laser energy density of 0.4 J/cm²

Fig. 3. Contact angle of S_L-Air and S_L-NaOH changes with time. (a) Surface morphology of S_L-Air after 60 days; (b)surface morphology of S_L-NaOH after 60 days

Fig. 4. Infiltration time of S_H-Air and S_H-NaOH. (a) Start time of measuring the infiltration time; (b) end time of measuring the infiltration time; (c) surface morphology of S_H-Airafter 40 days; (d)surface morphology of S_H-NaOH after 40 days

Fig. 5. XPS high-resolution spectra of S_L-Air-1 surface

Fig. 6. Energy spectrum peak results of different surfaces. (a) S_L-Air-1 and (b) S_L-Air-60 of C 1s peak; (c)S_L-Air-1 and (d) S_L-Air- 60 of O 1s peak

Fig. 7. Changes in the content of C and O

Fig. 8. O 1s split peak fitting situation and the content of oxygen-containing groups. (a) Peak splitting results of S_L-NaOH-1; (b) peak splitting results of S_L-NaOH-60; (c) content of oxygen-containing groups