Morphological Control in Solution-Deposited Silver Nanoplatelet Films
Authors: Vaskevich Alexander , Muench Falk , Kaplan-Ashiri Ifat , Rubinstein Israel 
Published: February 2020

Recently we introduced a new electroless plating (EP) strategy based on a plating bath containing Fe(III) tartrate, a metal complex surfactant, which is capable of producing a variety of previously undescribed silver nanoplatelet architectures (Fig. 1a) [1, 2]. Likewise to conventional colloidal syntheses, in-plane growth is promoted by stacking faults, while out-of-plane growth on (111) oriented surfaces is efficiently suppressed by effective passivation with adsorbed layer of Fe(III) tartrate.
In this research we focused on evaluation of parameters which define the formation of nanoplatelet films. We found that morphology of Ag nanoplatelets deposited on variety of materials such as Pt, Ag, Au, highly ordered pyrolytic graphite (HOPG), mica, thermally oxidized silicon, and indium tin oxide is very robust. The general nanoplatelets structure was found in all cases, although the substrate type had some effect on the deposit morphology. The Ag nanoplatelets deposited on Pt grew to much larger size than during EP on other materials, most probably due to contribution of the Pt substrate to tartrate oxidation. EP on Ag substrate resulted in the suppression of the hierarchical layer of small nanostructures, with only large nanoplatelets emerging from the substrate (Fig. 1b). This could be explained by the strong passivating effect of the Fe(III) tartrate complex on Ag surfaces, which could be seen in the absence of any notable deposits apart from the large, spread-out nanoplatelets.
Deposition of metals is generally performed either in conditions of electroless plating or under electrochemical control. Here we studied the influence of electrochemical control on morphology of Ag deposited on Ag electrode from electroless plating bath. We revealed that morphology of Ag deposit could be tuned by change in the applied overpotential. At moderate overpotential formation of nanoplatelets was preserved (Fig. 1c), indicating effective passivation of (111)-
oriented facets by adsorbed Fe(III) tartrate layer (Fig. 1d) while growth proceeded in <211> directions of Ag lattice similarly to EP [2]. Deposition under potential control increased density of of Ag nanoplatelets and their lateral size decreased when compare to EP (Fig. 1b). Increase of the overpotential induced secondary nucleation on (111) surfaces that proceeded simultaneously with 2D growth of nanoplatelets, resulting in radical changes in morphology of Ag nanostructures (Fig. 1e).
Interesting variation of the Ag nanostructure morphology was also obtained when EP combined with potential control was performed using plating solution with decreased concentration of tartrate. These conditions resulted in formation of large well-defined Ag crystals instead of nanoplatelets (Fig. 1f). Remnants of platelet motive were still seen, however, as blade-like protrusions (see arrow in Fig. 1f). We assume that introduction of electrochemical control during electroless (chemical) deposition opens new possibilities of tuning morphology of nanostructured films.
F.M. acknowledges funding by a Research Fellowship of the German Research Foundation (MU 4125/1-1).
Prof. Israel Rubinstein passed away on October 21, 2017.

Figure 1