Controlling Equilibrium Morphologies of Bimetallic Nanostructures Using Thermal Dewetting via Phase-Field Modeling

Herein, we report a computational model for the morphological evolution of bimetallic nanostructures in a thermal dewetting process, with a phase-field framework and superior optical, physical, and chemical properties compared to those of conventional nanostructures. The quantitative analysis of the simulation results revealed nano-cap, nano-ring, and nano-island equilibrium morphologies of the deposited material in thermal dewetting, and the morphologies depended on the gap between the spherical patterns on the substrate, size of the substrate, and deposition thickness. We studied the variations in the equilibrium morphologies of the nanostructures with the changes in the shape of the substrate pattern and the thickness of the deposited material. The method described herein can be used to control the properties of bimetallic nanostructures by altering their equilibrium morphologies using thermal dewetting.

Construction of Lattice Strain in Bimetallic Nanostructures and Its Effectiveness in Electrochemical Applications

Bimetallic nanocrystals (NCs), associated with various surface functions such as ligand effect, ensemble effect, and strain effect, exhibit superior electrocatalytic properties. The stress-induced surface strain effect can alter binding strength between the surface active sites and reactants as well as their intermediates, and the electrochemical performance of bimetallic NCs can be significantly facilitated by the lattice-strain modification via their morphologies, sizes, shell-thickness, surface defectiveness as well as compositions. In this review, an overview of fundamental principles, characterization techniques, and quantitative determination of the surface lattice strain is provided. Various strategies and synthesis efforts on creating lattice-strain-engineered bimetallic NCs, including the de-alloying process, atomic layer-by-layer deposition, thermal treatment evolution, one-pot synthesis, and other efforts are also discussed. It is further outlined how the lattice strain effect promotes electrochemical catalysis through the selected case studies. The reactions on oxygen reduction reaction, small molecular oxidation, water splitting reaction, and electrochemical carbon dioxide reduction reactions are focused. In particular, studies of lattice strain arisen from core-shell nanostructure and defectiveness are highlighted. Lastly, the potential challenges are summarized and the prospects of lattice-strain-based engineering on bimetallic nanocatalysts with suggestion and guidance of the future electrocatalyst design are envisioned.

Three-Dimensional Nanoporous Metal Structures from Poly(2-vinylpyridine)-block-Poly(4-vinylpyridine) Copolymer Thin Film

We fabricated 3D nanoporous metal structures from poly(2-vinylpyridine)-block-poly(4-vinylpyridine) copolymer (P24VP) thin film with vertically oriented lamellar nanodomains by coordinating corresponding metal precursors followed by reduction to metals. Although metal precursors are coordinated with both P2VP and P4VP blocks, the metal coordination power toward P4VP block is much greater than that toward P2VP block. Thus, most of the metal precursors are located in the P4VP block, while a few exist in the P2VP block. After the metal precursors were reduced to corresponding metals by reactive ion etching, metals located in P4VP regions became continuous main frames. However, metals in P2VP regions could not be continuous because of smaller amounts, resulting in nanoporous structures. Using these 3D nanoporous structures, we measured the electrocatalytic activity for hydrogen evolution reaction. 3D nanoporous platinum (Pt) showed enhanced catalytic activity compared with Pt flat film due to the large surface area. Moreover, 3D nanoporous Pt/cobalt bimetallic structures showed better catalytic activity than 3D nanoporous Pt structures.

Preparation of Ag/Au bimetallic nanostructures and their application in surface-enhanced fluorescence

An effective substrate for surface-enhanced fluorescence, which consists of cluster Ag/Au bimetallic nanostructures on a copper surface, was synthesized via a multi-stage galvanic replacement reaction of a Ag cluster in a chlorauric acid (HAuCl4) solution at room temperature. The fabricated silver/gold bimetallic cluster were found to yield large surface-enhanced fluorescence (SEF) enhancement factors for rhodamine 6G probe molecules deposited on the substrate, and also the fluorescence efficiency is critically dependent on the period of nanostructure growth. With the help of proper control reaction conditions, such as the reaction time, and concentration of reaction solutions, the maximum fluorescence enhanced effect was obtained. Therefore, the bimetallic nanostructure substrate also can be adapted to studies in SEF, which will expand the application of SEF.