Directed Assembly of Au-Tipped 1D Inorganic Nanostructures via Nanolithographic Docking.

Controlled assembly of nanostructures is a key challenge in nanotechnology. In this work, we introduce an approach for the controlled assembly of 1D nanodumbbells-Au-tipped semiconductor nanorods-into arbitrary 2D higher architectures, by their chemical docking to nanopatterned functionalities. We realized the docking functionalities via nanoimprinted metallic nanodots functionalized with an organic monolayer, whose terminal thiol groups chemically bind the nanodumbbell tips. We demonstrated that the functional nanopattern encodes the nanodumbbell assembly and can be designed to deterministically position nanodumbbells in two possible modes. In the single-docking mode, the nanodot arrays are designed with a spacing that exceeds the nanodumbbell length, restricting each nanodumbbell to dock with one edge and physically connect with its free edge to one of the neighboring nanodumbbells. Alternatively, in the double-docking mode, the nanodots are spaced to exactly fit the nanodumbbell length, allowing nanodumbbell docking with both edges. We found that the docking kinetics can be described by a random attachment model, and verified that for the used docking chemistry, nanodumbbells that are docked to the same dot do not interact with each other. Our work demonstrates the possibility for massively parallel positioning of sub-100 nm 1D semiconductor nanostructures, and can potentially enable their future integration into functional nanodevices and nanosystems.

Electrophoretic deposition of single-source precursors as a general approach for the formation of hybrid nanorod array heterostructures.

HYPOTHESIS: Subjecting colloids to electric fields often results in (electrophoretic) deposition on conductive substrates. Dispersing a single-source precursor (SSP) of choice in an appropriate solvent, should allow its deposition on different substrates. The SSP-solvent interaction might play a role in the deposition (e.g., direction, rate, coverage). After thermal decomposition, the SSPs convert to the designed material, thus allowing formation of thin films or hybrid nanostructures. EXPERIMENTS: Electrophoretic deposition (EPD) was applied on two representative SSPs in different solvents. These SSPs were deposited onto substrates covered with vertically-aligned ZnO nanorod (NR) arrays. After thermal decomposition, hybrid nanostructures were obtained and their morphology and interfaces were characterized by electron microscopy, X-ray diffraction, UV-vis, and electrochemistry. FINDINGS: Tuning the organic dispersant-SSP interaction allows control over the final film morphology, which can result in coating and filling of NRs with metal-sulfides or metal-oxides after thermal decomposition of the SSP. These findings introduce a new facile method for a fast and large-scale uniform deposition of different (nanostructured) thin film semiconductors on a variety of substrates. We discuss the influence of the dispersant medium on the deposition of metallo-organic SSPs. As an example, the formed ZnO-CdS interface supports charge transfer upon illumination.

Ternary hybrid nanostructures of Au-CdS-ZnO grown via a solution-liquid-solid route using Au-ZnO catalysts.

Multi-component nanostructures of Au-CdS-ZnO with a novel morphology were synthesized by a non-conventional strategy where seeded growth is combined with solution-liquid-solid (SLS) growth. Each of these synthetic routes is used for growing a different domain of the final heterostructure, where ZnO rods are grown first on Au nanoparticles via heterogeneous nucleation while CdS is later grown between these two domains via SLS, using the Au tip of the preformed Au-ZnO as a catalyst. The in situ alloying of the Au tip with Cd enabled the metal tip to function as an SLS catalyst at a relatively mild reaction temperature which is lower than the melting point of pure Au.

Organic phase synthesis of noble metal-zinc chalcogenide core-shell nanostructures.

Multi-component nanostructures have been attracting tremendous attention due to their ability to form novel materials with unique chemical, optical and physical properties. Development of hybrid nanostructures that are composed of metal-semiconductor components using a simple approach is of interest. Herein, we report a robust and general organic phase synthesis of metal (Au or Ag)-Zinc chalcogenide (ZnS or ZnSe) core-shell nanostructures. This synthetic protocol also enabled the growth of more compositionally complex nanostructures of Au-ZnSxSe1-x alloys and Au-ZnS-ZnSe core-shell-shell. The optical and structural properties of these hybrid nanostructures are also presented.

Photocatalytic hybrid Au/ZnO nanoparticles assembled through a one-pot method.

Growth of metal domains on semiconductor nanoparticles is known to enhance their photocatalytic properties. We prepared ZnO nanoparticles decorated with metallic Au domains through a new one-pot microwave-based strategy. The synthetic route utilized microwave-heating of a mixture of only three components: Zn(2+) salt, Au(SCN)4(-) which served as a precursor for metallic gold, and Tris base. The Tris molecules had a dual role in the process, both shaping the morphology of the ZnO particles, as well as constituting docking and nucleation sites for the Au(SCN)4(-) ions. The Au complex subsequently underwent spontaneous crystallization/reduction without co-addition of reducing or stabilizing agents, yielding Au nanoparticles attached to the ZnO surface. We show that the hybrid Au/ZnO nanoparticles exhibited enhanced photocatalytic properties compared to the plain ZnO nanoparticles.

Coating and enhanced photocurrent of vertically aligned zinc oxide nanowire arrays with metal sulfide materials.

Hybrid nanostructures combining zinc oxide (ZnO) and a metal sulfide (MS) semiconductor are highly important for energy-related applications. Controlled filling and coating of vertically aligned ZnO nanowire arrays with different MS materials was achieved via the thermal decomposition approach of single-source precursors in the gas phase by using a simple atmospheric-pressure chemical vapor deposition system. Using different precursors allowed us to synthesize multicomponent structures such as nanowires coated with alloy shell or multishell structures. Herein, we present the synthesis and structural characterization of the different structures, as well as an electrochemical characterization and a photovoltaic response of the ZnO-CdS system, in which the resulting photocurrent upon illumination indicates charge separation at the interface.

Selective growth of metal particles on ZnO nanopyramids via a one-pot synthesis.

Hybrid nanostructures of metal (Cu, Au, Ag)-ZnO nanopyramids were synthesized. These hybrid nanostructures possess two distinct morphologies where the metal can be selectively attached to either the base or the tip of the ZnO pyramids. This is the first time that such morphologies are reported for Cu-ZnO and Ag-ZnO hybrid nanostructures.