Fig. 3: Mechanism of the anti-friction Au-RPU device.

a Schematic (top) of the surface dense Au layer, the diffused Au layer and the WPU substrate at the interface and the corresponding atomic concentration from XPS (bottom) show Au grains at the Au-WPU interface are diffused into WPU. Shaded color with dashed black lines indicate the diffusion region. b, c Au 4f (b) and C 1s (c) XPS spectra of the Au layer on flat WPU substrate at different Ar⁺ ion etching levels. d, e O 1s XPS spectra of flat PU film e before and d after surface cleaning by Ar⁺ ion. f O 1s XPS spectra of the Au layer on flat WPU substrate after the 12th etching. g, h Temperature-dependent FTIR spectra of WPU upon heating from 30 °C (purple curve) to 100 °C (crimson curve): g 3500–3150 cm⁻¹; h 1800–1620 cm⁻¹. i Schematic illustration of the DIC mechanism for strong interfacial binding between Au layer and WPU substrate, including the diffusion of molecular glues, construction of hydrogen bonding, and cohesion deposition to achieve tight interfacial adhesion. Light blue and red color indicates the diffusion region and stretchable substrate, respectively. The abbreviated AR number in Fig. 3 is the number of times by Ar⁺ ion etching.