Large scale and ultra-thin conductive two-dimensional metal films (<3.5 nm) for fast flexible electronics

Pushing the thickness of two-dimensional (2D) metal films to below 10 nm means higher transparency and better flexibility, which will help improve the response sensitivity of flexible electronic devices based on 2D metals. However, lattice distortion and void cracks are facile occurred in the 2D metal film due to the island structure growth mechanism on the traditional solid substrates, which greatly weakens the transparency and conductivity of ultra-thin 2D metal films. Here, we innovatively proposed an air–liquid interface deposition (ALID) method to address this dilemma, in which ultrathin 2D metal films with continuous conductivity were deposited on liquid substrates. Thanks to the shallow injection and the Brownian motion of the liquid substrate, 2D metal (Au, Ag, Cu, Bi, Pt, etc.) films with dimensions up to φ 90 mm × 3.5 nm were obtained through the above method with continuous conductivity in only 5 s. More importantly, compared with the metal film prepared by traditional air–solid interface deposition method, the metal film prepared through ALID has lower surface roughness (0.207 nm), better transparency (85 %), and stronger wear resistance since metal atoms can be arranged almost freely on the isotropic liquid surface. Furthermore, the fabricated resistance sensor based on these 2D metal films can realize flexible sensing such as bending, hitting and stretching motions with ultrafast response time (t = 60 ms) and robust response sensitivity (△R/R₀ = 800 %). On the one hand, it provides a new solution for the large scale preparation of ultra-thin continuous conductive films, and on the other hand, it enriches the growth mechanism of thin films on the liquid surface.