Electroplating of conformal electrodes for vacuum nanogap tunnel junction

TL;DR

This paper presents a method for electroplating conformal Cu electrodes with controlled curvature and nanogaps, enabling applications in energy conversion and cooling through vacuum nanogap tunneling.

Contribution

It introduces a novel electroplating process to produce large-area, conformal electrodes with precise nanogaps and curvature control for vacuum tunneling devices.

Findings

Achieved 40 nm/mm curvature on 12-mm diameter electrodes.

Fabricated electrodes with less than 5 nm nanogap over 7 mm² area.

Demonstrated potential for energy conversion and cooling applications.

Abstract

In this study, we electroplate Cu electrode on Si substrate to realize a large-area vacuum nanogap for electron tunneling. We used cathode coating, cathode rotation, asymmetric current regime, and electrolyte temperature stabilization to obtain the regular geometry of the Cu electrode and reduce its internal tension. Subsequently, internal tension was altered to achieve the predefined surface curvature (concave or convex). For 12-mm diameter Ag/Cu electrode, we achieve the curvature of 40 nm/mm from the Ag side. Reduction of the electrode diameter to 3 mm allowed curvature as low as of 2.5 nm/mm. It also allowed fabrication of two conformal electrodes having a nanogap of less than 5 nm wide, over the area of 7 mm2. Such electrodes can be used for efficient energy conversion and cooling in the mixed thermionic and thermotunneling regime.