Large Area Freestanding Au Nanoporous Ultrathin Films Transfer Printed on Bendable Substrates and 3D Surfaces for Flexible Electronics

Abstract

Conductive films based on metal nanomaterials have been studied as electrical interconnects for flexible electronics. Among them, freestanding ultrathin films are flexible, making them ideal candidates for integration onto 3D surfaces with complex shapes. Nevertheless, obtaining self-supported films of a few tens of nm with an area of several cm 2 without breaking them is difficult. The solution proposed in this work is to get the films floating on the water surface before transferring them to 3D flexible surfaces by a water transfer printing process. Herein, we report the fabrication of stable and homogeneous Au nanoporous films with a thickness range of 6−60 nm and a floating surface area of several tens of cm 2 on the water surface. The process combines Au and Cu magnetron sputtering deposition, Cu dealloying, and etching in acid vapor. We show that the transfer of such ultrathin films with a large area from the water surface onto the surface of flat flexible substrates or 3D surfaces is possible, maintaining conformability without significant electrical conductivity degradation. The thinnest films have a sheet resistance of about 10 Ω/□ with a transparency of about 50% at 550 nm. Because of their specific nanostructuration consisting of nanopores and interconnected nanoligaments, these films transferred to flexible flat surfaces can withstand bending for at least 3000 cycles with a curvature radius of 1 mm. Moreover, we show that a transfer of a design to a complex curved surface of 3D objects is possible using a 6 nm layer, whose role is to keep the geometry of the design during the transfer process.