Wavelength-influenced electrical performance of laser-written flexible copper-based structures

The one-step direct laser writing process has been an efficient strategy for constructing flexible metal structures. However, the effect of laser wavelength on the structuring process remains unclear, thus restricting the universal manufacturing process development. In this work, the feasibility of one-step writing of flexible Cu structures with different wavelength continuous diode lasers has been verified. Here, photothermal reactions dominate in the decomposition of the reducing agent to form copper structures. Differences in the wavelength primarily affect the photothermal reaction amplitude for structuring, resulting in a variation in the formation of Cu structures. Under our processing conditions, the photothermal reaction induced by 532 nm laser is higher than 808 nm laser, a higher reduced-joining degree of the Cu structure can be achieved by 532 nm laser. This results in a superior conductivity, adhesion, and bendability of Cu structures fabricated by 532 nm laser than that of 808 nm laser. Furthermore, strain sensors that can detect different bending angles and bending frequencies have been fabricated by 532 nm laser-written structures to demonstrate their practical applications.