Mask-Assisted Seeded Growth of Segmented Metallic Heteronanostructures

Abstract

Controlling the deposition of exotic metals in the seeded growth of multimetal nanostructures is challenging. This work describes a seeded growth method assisted by a mask for synthesis of segmented binary or ternary metal nanostructures. Silica is used as a mask to partially block the surface of a seed and a second metal is subsequently deposited on the exposed area, forming a bimetallic heterodimer. The initial demonstration was carried out on a Au seed, followed by deposition of Pd or Pt on the seed. It was found that Pd tended to spread out laterally on the seed while Pt inclined to grow vertically into branched topology on Au. Without removal of the SiO 2 mask, Pt could be further deposited on the unblocked Pd of the Pd−Au dimer to form a Pt−Pd−Au trimer. Mask-assisted seeded growth provides a general strategy to construct segmented metallic nanoarchitectures. ■ INTRODUCTIONHeterostructures of two or more metals with interfaces at the nanoscale is of particular significance because they exhibit unique properties and multifunctions distinctly different from the individual components. 1−4 The diverse surface chemistry of these heteronanostructures enables new applications that are not possible with each component alone. For example, multisegmented metal nanorods have been demonstrated for applications in synergistic heterogeneous catalysis, 5,6 selfelectrophoretic nanomotors/nanobatteries, 7,8 multifunctional biomedicine, 9,10 and multiplexed detections. 11,12 To fabricate the heteronanostructures, sequential electrochemical deposition of metal ions into templates has been the most common method since the 1990s. 13,14 In this approach, commercially available alumina or polycarbonate membranes with uniform pores are often used as templates, yielding segmented metal rods. 15 This method could be further extended to selective growth of additional metals within the templates in solution after the initial electrochemical deposition of rod-shaped seeds. 16,17 To generate heterostructures with other configurations, cost-intensive and time-consuming lithography techniques are usually required. 18 In this work, a site-selective seeded growth method, termed mask-assisted seeded growth (MASG), is developed to expand the library of metal heterostructures with complex nanoarchitectures.Seeded growth has emerged as a compelling method to create a wide variety of novel metal nanostructures. 19−24 Conditions that yield heteronanostructures depend on a number of factors such as the structural characteristics of constituent components, the reduction kinetics of metal precursors, and the capping agents. For example, a high degree of lattice mismatch between the seed and the second metal prevents conformal growth of core@shell structures and yields heteronanostructures of Au on CoPt 3 , 25 Au rods on Pt cubes, 21 and Cu on Au. 24 Controlling the reduction kinetics can selectively direct the nucleation and subsequent growth of the second metal on the seed to form dimers of Au on Pd 26 or other nonconformal structures such as Ag/...

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