Pulsed Laser-Induced Dewetting for The Formation of Monometallic and Bimetallic Nanoparticle Arrays on Patterned Dimpled Tantalum Substrates and Their Electrochemical Properties

Highly ordered metal nanoparticle (NP) arrays have attracted great research interest due to their unique electronic, optical and magnetic properties, leading to their diverse applications as model electrodes for electrocatalysis in fuel cells, sensors, in magnetic memory arrays and catalyst arrays for the growth of semiconductor nanowires. Here in this work, we report the use of pulsed laser-induced dewetting (PLiD) for the fabrication of metallic NP arrays, including monometallic (Au, Pt) and bimetallic Au-Pt, on a pre-patterned dimpled Ta substrate. In PLiD, the metal is quickly heated to above its melting point within a short duration of the incident laser irradiation and the molten film breaks up to form metal NPs to reduce the free energy of the film-substrate-ambient system. The highly ordered dimpled Ta substrate, formed by anodization of polycrystalline Ta in a H₂SO₄ + HF solution, consists of a self-assembled array of inverted hemispherical caps, or nanodimples. It has been shown that highly ordered Au, Pt, and Au-Pt NP arrays can be produced on the dimpled Ta substrate with excellent monodispersity, long-range order and good dimple coverage. Compared with thermal dewetting, which is a solid-state dewetting method driven mainly by surface diffusion, PLiD is more efficient and better suited for metals of high melting point. The size of monometallic Au and Pt NPs can be controlled by the initial film thickness as the dewetting process is shown to follow the spinodal dewetting mechanism. For the bimetallic Au-Pt NPs, the total bilayer metallic film thickness plays a determining role. We have also shown that the metallic NPs formed by PLiD are more spherical in shape than those by thermal dewetting. The produced bimetallic Au-Pt NPs have a configuration of a Pt-rich core and Au-rich shell. Finally, characterization of the electrochemical properties of the Pt-rich core/Au-rich shell NPs reveals strong Pt-O bonding on the bimetallic NP surfaces. In addition, while Au is enriched on the bimetallic NP surfaces, a significant Pt content, ranging from 10% to close to 40%, is still present on the NP surfaces, which makes the produced Au-Pt NPs useful for bifunctional electrocatalytic reactions.