1：Experimental Design and Method Selection:

The study employed a combined approach of focused ion beam (FIB) milling for mould fabrication and nanoimprinting for pattern transfer to polydimethylsiloxane (PDMS). The design rationale was to create sub-micrometre diffractive patterns that enable structural coloration and colour tuning with strain. Theoretical models included the diffraction equation for strain calculation.

2：Sample Selection and Data Sources:

A silicon wafer was used as the mould substrate. PDMS was prepared by mixing Sylgard 184 silicon elastomer base and curing agent at a 10:1 weight ratio, with a black silicon pigment added at 1:50 weight ratio. Samples were 50 mm × 50 mm in size with pattern periods of 520 nm.

3：List of Experimental Equipment and Materials:

Equipment included FIB system (COBRA column, Orsayphysics; UST-5100 stage, FEI), atomic force microscope (AFM; NX-10, Park Systems), field emission-scanning electron microscope (FE-SEM; MERLIN, Zeiss), optical microscope, spectrometer (FLAME-S-XR1, Ocean Optics Inc.), and sample manipulator. Materials included silicon wafer, PDMS (Sylgard 184, Dow Corning), and black silicon pigment.

4：Experimental Procedures and Operational Workflow:

The process involved FIB milling of a nanoscale mould on silicon wafer under varying beam currents (150 pA, 300 pA) and dwell times (0.1 s, 0.2 s, 0.4 s, 0.8 s). PDMS mixture was degassed, poured into the mould, cured at 80°C for 2 h under low vacuum, and ejected. AFM and FE-SEM were used for geometry evaluation. Optical measurements involved irradiating light at 45° incident angle and detecting reflected light at normal angle.

5：1 s, 2 s, 4 s, 8 s). PDMS mixture was degassed, poured into the mould, cured at 80°C for 2 h under low vacuum, and ejected. AFM and FE-SEM were used for geometry evaluation. Optical measurements involved irradiating light at 45° incident angle and detecting reflected light at normal angle. Data Analysis Methods:

5. Data Analysis Methods: Data analysis included measuring geometry parameters (period, depth, diameter, height) via AFM and FE-SEM, and analyzing reflected light intensity and wavelength using spectrometer. Strain was calculated from wavelength changes using linear approximation.