Electroplating of Conformal Electrodes for Vacuum Nanogap Tunnel Junction

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 mm 2 . Such electrodes can be used for efficient energy conversion and cooling in the mixed thermionic and thermotunneling regime.

Vacuum nanogap formation in multilayer structures by an adhesion-controlled process

“…These results need further explanation because in other experiments the opposite results have been observed (i.e., buckle delamination dominated over edge delamination) [24]. Our hypothesis is that a much lower value of compressive prestress σ was present in our experiments in comparison to those previously reported (because our work was focused on the reduction of σ [17]). This explanation is in good agreement with an edge delamination model for the compressed films.…”

“…The best results were obtained for T= 306 K and 308 K, respectively. More detailed data on electroplating is presented in reference [17]. Compressive prestress was present in the Ag/Cu electrodes, exhibited by the fact that these electrodes were always more convex than the corresponding Si/Ti electrodes (Fig.…”

“…The practical realization of energy converters and coolers based on thermotunneling has been discussed in the literature [9][10][11][12][13][14][15][16]. Multilayer structures allowing the formation of vacuum nanogaps on a large scale has been reported in reference [17].…”

Thermoelectric energy harvesting with quantum dots

“…Similar to the previously discussed energy harvester, the hybrid microwave cavity heat engine [57] also allows to separate the hot and the cold part of the engine by a macroscopic distance of the order of a centimeter. This suppresses leakage heat currents far more efficiently than vacuum nanogaps that are only a few nanometer wide [187,188]. In addition, the heat engine has the advantage that the cavity helps in efficiently transferring photons from the hot to the cold side whereas otherwise photons just get randomly emitted into all directions and can be lost for the energy harvesting purpose.…”