Pulse electroplating of ultra-fine grained Au films with high compressive strength

• Micro-mechanical properties of electrodeposited pure Au films were evaluated.
• The Au film obtained by pulse electroplating (PE) showed strength of 800 MPa.
• The high strength is a result of the Hall–Petch relationship.
• Grain size of 10.5 nm was achieved by applying the PE.
• The Au film obtained by PE showed fewer defects and lower roughness.

Grain refinement, surface smoothening, and compressive strength enhancement of Au films were achieved by pulse electroplating using non-toxic sulfite-based electrolyte. The estimated grain size of the Au film prepared by pulse electroplating was 10.5 nm, and it was much smaller than the grain size of the Au film prepared by constant-current electroplating, which was 22.8 nm. This can be attributed to the increase in the nucleation rate during the on-time period. The mechanical strength of the Au films in micro-scale was also evaluated. The pulse electroplated Au micro-pillar acquired a high compressive strength of 800 MPa, and it was larger than the constant-current electroplated micro-pillar, which was 600 MPa. The high strength is presumably due to the grain-boundary strengthening known as the Hall–Petch effect. The compression test also revealed that the pulse electroplated Au micro-pillar possesses better ductility and malleability than that fabricated by constant-current electroplating.

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