Structural coloration with two-dimensional nanostructures fabricated by elliptical vibration nanoindentation

Structural color stemming from the two-dimensional (2D) nanostructures that induced light interference attracts more attention than 1D grating due to its higher design flexibility. However, the fast and cost-effective fabrication of pixel-by-pixel 2D nanostructures is challenging. This study prompts nanoindentation as a promising technique for fabricating 2D nanostructure on metallic surfaces by adding an ultrafast elliptical vibration on the nanoindenter. First, the elliptical vibration nanoindentation (EVN) process principle is analyzed. Next, an ultrafast elliptical vibration nanoindentation tool (UEVNT) with a maximum working frequency of 2 kHz is developed. Then, machining experiments were conducted on aluminum to evaluate the performance of EVN, whose results demonstrate the successful fabrication of pyramid-type nanostructures with a depth of hundreds of nanometers and a spacing of 1–3 μm. Based on the unique spatial diffraction characteristic of 2D nanostructures, a high-decoupling optical variable device has also been fabricated on the aluminum surface by rendering two images into two orthogonal observation directions. Finally, the 2D nanostructures on a metallic surface were transferred to the flexible polymer to fabricate a structural color-based bidirectional strain sensor. Stretching tests have been performed with results verifying the potential application of 2D nanostructures-induced structural color in the wireless measurement of mechanical deformation.