Electroless Plating of Stacked, Single-Crystalline Silver Nanoplatelets and Dendrites
Authors: Münch Falk , Vaskevich Alexander , Bendikov Tatyana , Popovitz-Biro Ronit , Feldman Yishay , Rubinstein Israel 
Published: February 2020

Electroless plating has been developed primarily for the deposition of continuous, polycrystalline films [1]; yet, the morphological control in electroless plating of nanostructured materials is underdeveloped compared to bulk nanoparticle synthesis [2]. Complex product morphologies can be realized by applying electroless plating to nano- or microstructured templates [3, 4]. However, the reliance on templates interferes with the favorable characteristics of electroless plating for the preparation of functional metal nanomaterials (quick, conformal, autocatalytic deposition on various substrate materials, sizes and shapes without complex instrumentation).
Our aim is to develop strategies for electroless plating with intrinsic shape control, enabling the direct deposition of films composed of high aspect ratio nanostructures [5]. In the present work we show that silver crystal nucleation and growth during electroless plating can be adjusted to induce the formation of different one- and two-dimensional nanomaterials, which are structurally related.
The morphological evolution and the deposition kinetics are investigated over the course of the plating reaction, and are supplemented by analysis of the crystallinity and chemical composition of the materials. We show that introduction of an iron-tartrate complex is essential for anisotropic growth. It strongly adsorbs onto the silver deposit, which is confirmed by cyclic voltammetry and X-ray photoelectron spectroscopy. This interaction favors the formation of structures terminated by (111) surfaces. Preferred metal deposition on the nanostructure edges results in highly anisotropic in-plane growth and a strong (111) texture, as verified by X-ray diffraction. The typically obtained micron-sized platelets (Fig. 1 a) consist of silver sheets of nanoscale thickness. The two-dimensional geometry is defined at the very beginning of the reaction, when small sheets are formed from elongated, triangle-based structures (Fig. 1 b). Due to the suppression of random three-dimensional nucleation, this structural motif is preserved during all stages of the deposition. Thickness growth occurs via branching of new, separate silver sheets, which form stacks and are aligned with the underlying ones. As the deposition progresses, becoming increasingly diffusion-limited, these structures turn into parallel arrays of dendrites (Fig. 1 c). By pH adjustment, platelet stacks with a well-defined outline of hexagonal symmetry can be obtained (Fig. 1 d), all belonging to a single crystal system (Fig. 1 e).
In summary, the outlined reactions provide a facile wet-chemical route for coating substrates with plate-like silver nanostructures of tunable morphology.
F. M. acknowledges funding by a Research Fellowship of the German Research Foundation (MU 4125/1-1).
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Figure 1