Growth and reductive transformation of a gold shell around pyramidal cadmium selenide nanocrystals

Abstract

We report the growth of an unstable shell-like gold structure around dihexagonal pyramidal CdSe nanocrystals in organic solution and the structural transformation to spherical domains by two means: i) electron beam irradiation (in situ) and (ii) addition of a strong reducing agent during synthesis. By varying the conditions of gold deposition, such as ligands present or the geometry of the CdSe nanocrystals, we were able to tune the gold domain size between 1.4 nm to 3.9 nm and gain important information on the role of surface chemistry in hetero nanoparticle synthesis and seed reactivity, both of which are crucial points regarding the chemical design of new materials for photocatalysis and optoelectronic applications.Recent developments in materials physics and chemistry allow the synthesis of colloidal nanocrystals (NCs) with unique optical and electrical properties [1,2]. However, it remains a grand challenge to prepare multicomponent or hybrid structures in which two or more NC domains of different materials with individually tailored properties and controlled composition are integrated into one nanostructure in core-shell or oligomertype configurations. These new hybrid NCs (HNCs) with a higher level of structural complexity are expected to exhibit modified physicochemical properties [3, 4] and provide systems which allow site-specific functionalization with biomolecules [5,6] and their use in photocatalysis and optoelectronic applications. The most common strategy for the synthesis of these HNCs is the seedmediated method in which one material is used as seed particle and a different material is grown around (coreshell HNCs [7,8]) or forming domains on their surface (oligomer-like HNCs). Examples of the latter case are metal-semiconductor heterodimers made of spherical domains [9][10][11][12], dumbbell-like [13,14], peanut-like [15] and matchstick-shaped [13,16,17] structures. Several reviews on heterostructured nanocrystals summarize the progress and the perspectives on this emerging field [3,4]. Additionally, these systems are unique platforms to study nucleation, growth, dissolution and reshaping of HNCs. In this context, Banin's group reported how dumbbelllike structures, formed by preferential nucleation of gold on crystal facets with high reactivity, evolved into a hetero structure with only one end covered due to a ripening process [13,17] while a recent publication of Manna and coworkers investigated the structural and morphological evolution of as-synthesized CdSe-Au HNCs subjected to thermal annealing [18]. The reactivities of crystal facets are closely associated to particle geometry and the degree of surface passivation. Thus, the use of NCs with * Electronic address: klinke@chemie.uni-hamburg.de a different topology as substrates for the Au growth can provide new insights not only into the formation of hybrid structures but also to the role of the NCs ligand density on the final hybrid structure.

Metal Domain Size Dependent Electrical Transport in Pt-CdSe Hybrid Nanoparticle Monolayers

“…Quasi-spherical chalcogenide nanoparticles with crystallographically exposed sites proved to be excellent 4 materials for metal deposition. 52,53 For this reason, hexagonal pyramidal CdSe NPs were synthesized as seeds. 54 Pt(acac) 2 was dissolved in toluene and oleylamine was added to act both as ligand and reducing agent.…”

Phase transformation of PbSe/CdSe nanocrystals from core-shell to Janus structure studied by photoemission spectroscopy

“…7,8 By increasing the electron energy that is released to an atomic lattice, even more fascinating structural changes have been obtained: Metaltipped semiconductor nanorods have been converted into shell-like structures, for instance. 9,10 Irradiated nanomaterials, thus, provide an interesting playground for studying how direct atomic displacements and electronic excitations lead to the formation of defects, chemical disordering, phase segregation/ordering, or spinodal decomposition, in an effort to gain control over the fabrication of more and more complex nanostructures. Although radiation-induced phenomena can also be observed with intense fluxes in photons, the disordering effects are generally much reduced and are limited to the surfaces of the nanomaterials.…”

The Reactivity of Colloidal Inorganic Nanoparticles

“…In the case of semiconductor materials with anisotropic shapes (such as rods, tetrapods or even pyramids), the higher reactivity of the polar facets opens up the possibility of nucleating a second material exclusively at these locations. This idea has been clearly demonstrated for the growth of Au domains onto CdSe NCs (Mokari et al, 2004;Meyns et al, 2010).…”