A 3nm-thick, quasi-single crystalline Cu layer with ultralow optoelectrical losses and exceptional durability

An ultrathin, highly crystalline, two-dimensional Cu layer is necessary for simultaneously achieving ultralow electrical and optical losses in transparent electrodes. However, perfect Cu wetting on heterogeneous oxide substrates has not yet been achieved. Herein, we report the Ge-mediated fabrication of an ultrathin, highly crystalline, complexly continuous Cu layer. The unique surfactant-like segregation of atomic Ge towards the outermost boundaries of the Cu geometries remarkably enhanced Cu wetting on the ZnO substrate. Numerical simulation indicated that the enhanced wetting can be attributed to the simultaneous decreases in the thermodynamic cohesive and formation energies at the surface and interface of the Cu nanostructures owing to Ge segregation. This enabled the fabrication of an ultrathin (similar to 3 nm), highly crystalline, two-dimensional Cu layer in a ZnO/Cu/ZnO configuration, which exhibited a recordlow average optical loss at a near-bulk resistivity (8 x 10(-8) Omega m) comparable to those of conventional Ag electrodes; it also showed exceptional durability in water, ozone, and high-temperature (up to 400 degrees C) environments. These unique features would ensure the development of highly reliable optoelectrical devices employing Cu superstructure-based transparent electrodes as inexpensive alternatives to Ag-based transparent electrodes. (C) 2021 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc.

Automated summary

This study reports a method for fabricating an ultrathin, highly crystalline, complexly continuous Cu layer mediated by Ge. The segregation of Ge remarkably enhances the wetting of Cu layer on ZnO substrate. The Cu layer fabricated by this method exhibits a record-low optical loss at near-bulk resistivity and exceptional durability in water, ozone, and high-temperature environments.