Flexible and Transparent Ultrathin Gold Electrodes via Ion Beam Smoothing

Herein, a large-area nanofabrication process is proposed for flexible, ultrathin, and ultrasmooth gold films with extraordinary electro-optical performance, making them competitive as transparent conductive electrodes (TCEs). The approach circumvents the thermodynamic constraints associated with the physical deposition of thin film electrodes, where 3D growth and metal dewetting delay stable percolation until the deposited film thickness exceeds 8-10 nm. It is demonstrated that a postgrowth ion irradiation procedure of compact gold films with Ar⁺ beam at very low energies, around 100 eV, predominantly induces ballistic smoothing and grain boundary restructuring. This process finally leads to the formation of ultrasmooth and ultrathin gold films that remain compact even at a thickness of 4 nm, with a sheet resistance in the range of 60 Ω sq^-1 and an optical transparency around 80%. Remarkably, the films remain percolated even at thicknesses as low as 3 nm, with a transparency exceeding 90% and a sheet resistance of 190 Ω sq^-1. These figures are comparable to those of commercial TCEs and enable simple, scalable, all-metal transparent contacts on both rigid and flexible substrates, with significant potential for optoelectronic applications.