Ilan Jen-La Plante

A tunable library of substituted thiourea precursors to metal sulfide nanocrystals

Quality manufacture beats quality control For semiconductor nanocrystals, tight control over particle size is needed to obtain particles with uniform properties. However, post-synthesis purification methods can be difficult and costly. Hendricks et al. present a family of substituted thioureas as a class of chalcogen precursors (see the Perspective by Hens). The rate of reactivity is connected to the specific chemistry of the precursor, making it possible to synthesize metal chalcogenide nanocrystals, such as PbS, with a specific size, narrow size distribution, and full conversion of the reactants. Science, this issue p. 1226; see also p. 1211 High-quality quantum dots with tunable particle size and composition are fabricated using inexpensive thioureas. [Also see Perspective by Hens] Controlling the size of colloidal nanocrystals is essential to optimizing their performance in optoelectronic devices, catalysis, and imaging applications. Traditional synthetic methods control size by terminating the growth, an approach that limits the reaction yield and causes batch-to-batch variability. Herein we report a library of thioureas whose substitution pattern tunes their conversion reactivity over more than five orders of magnitude and demonstrate that faster thiourea conversion kinetics increases the extent of crystal nucleation. Tunable kinetics thereby allows the nanocrystal concentration to be adjusted and a desired crystal size to be prepared at full conversion. Controlled precursor reactivity and quantitative conversion improve the batch-to-batch consistency of the final nanocrystal size at industrially relevant reaction scales.

Synthesis of metal sulfide nanomaterials via thermal decomposition of single-source precursors

In this report, we present a synthetic method for the formation of cuprous sulfide (Cu2S) and lead sulfide (PbS) nanomaterials directly on substrates from the thermolysis of single-source precursors. We find that the final morphology and arrangement of the nanomaterials may be controlled through the concentration of the dissolved precursors and choice of solvent. One-dimensional (1-D) morphologies may also be grown onto substrates with the addition of a metal catalyst layer through solution-liquid-solid (SLS) growth. These synthetic techniques may be expanded to other metal sulfide materials.

Studying the chemical, optical and catalytic properties of noble metal (Pt, Pd, Ag, Au)–Cu2O core–shell nanostructures grown via a general approach

We studied the chemical, optical and catalytic properties of metal (Pt, Pd, Ag, Au)–Cu2O core–shell nanoparticles grown via a simple and reproducible approach which utilizes aqueous-phase reactions at room temperature. We were able to control the thickness of the Cu2O shell and examine the effect of the cores shape and size on the structure and properties of the hybrid nanocrystals. We also studied the optical properties of the hybrid nanocrystals, in particular the effect of the Cu2O shell thickness on the frequency of the plasmon of gold nanorods. In addition, the catalytic activity of the hybrid nanostructures was examined by testing the reduction reaction of 4-nitrophenol with NaBH4. Finally, the hybrid metal–Cu2O nanostructures were used as templates to form the yolk–shell of metal–Cu2S materials. The interface and the crystalline structures of the four hybrid nanostructures were extensively characterized by high resolution transmission electron microscopy (HRTEM), energy-filtered TEM (EFTRM) and X-ray diffraction (XRD).

Exciton Quenching Due to Copper Diffusion Limits the Photocatalytic Activity of CdS/Cu2S Nanorod Heterostructures.

The formation of donor/acceptor junctions in hybrid nanomaterials is predicted to enhance photocatalytic activity as compared to single-component semiconductor systems. Specifically, nanomaterials containing a junction of n-type cadmium sulfide (CdS) and p-type copper sulfide (Cu2S) formed via cation exchange have been proposed as potential photocatalysts for reactions such as water splitting. Herein, we study the elemental distribution of Cu within these nanostructures using analytical transmission electron microscopy techniques. The resulting effects of this elemental distribution on photocatalytic activity and charge dynamics were further studied using a model photoreduction reaction and transient absorption spectroscopy. We find that copper diffusion in the hybrid nanostructure quenches the exciton lifetime and results in low photocatalytic activity; however, this effect can be partially mitigated via selective extraction. These results provide a deeper understanding of the physical processes within these hybrid nanostructures and will lead to more rational design of photocatalyst materials.

A facile one-step approach for the synthesis and assembly of copper and copper-oxide nanocrystals

A simple one-step approach for the formation of close packed films of copper and copper oxide nanoparticles is described. Thermal decomposition of copper cupferrate, a single-source precursor, on silicon produces a well-controlled, assembled film of Cu nanocrystals. Upon oxidation, Cu2O is formed with retention of the assembly. Similarly, the thermal decomposition of manganese cupferrate results in the formation of porous MnO nanowires. Various solvents were used to examine their influence on the composition and assembly of the nanoparticles. This approach enables an easy and reproducible process for the synthesis and assembly of metal oxide nanostructures.

Targeted intracellular voltage recordings from dendritic spines using quantum-dot-coated nanopipettes

Dendritic spines are the primary site of excitatory synaptic input onto neurons, and are biochemically isolated from the parent dendritic shaft by their thin neck. However, due to the lack of direct electrical recordings from spines, the influence that the neck resistance has on synaptic transmission, and the extent to which spines compartmentalize voltage, specifically excitatory postsynaptic potentials, albeit critical, remains controversial. Here, we use quantum-dot-coated nanopipette electrodes (tip diameters ∼15-30 nm) to establish the first intracellular recordings from targeted spine heads under two-photon visualization. Using simultaneous somato-spine electrical recordings, we find that back propagating action potentials fully invade spines, that excitatory postsynaptic potentials are large in the spine head (mean 26 mV) but are strongly attenuated at the soma (0.5-1 mV) and that the estimated neck resistance (mean 420 MΩ) is large enough to generate significant voltage compartmentalization. Nanopipettes can thus be used to electrically probe biological nanostructures.

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 sulfide tips onto cadmium chalcogenide nanostructures

We demonstrate a general approach for growing selectively semiconductor nanocrystals onto the edges of elongated Cd–chalcogenide nanostructures. Our approach utilizes the thermal decomposition of metal bisdiethyldithiocarbamate precursors to achieve selective growth onto cadmium chalcogenide nanostructures.

Growth of GaN@InGaN Core-Shell and Au-GaN Hybrid Nanostructures for Energy Applications

We demonstrated a method to control the bandgap energy of GaN nanowires by forming GaN@InGaN core-shell hybrid structures using metal organic chemical vapor deposition (MOCVD). Furthermore, we show the growth of Au nanoparticles on the surface of GaN nanowires in solution at room temperature. The work shown here is a first step toward engineering properties that are crucial for the rational design and synthesis of a new class of photocatalytic materials. The hybrid structures were characterized by various techniques, including photoluminescence (PL), energy dispersive x-ray spectroscopy (EDS), transmission and scanning electron microscopy (TEM and SEM), and x-ray diffraction (XRD).

Harnessing Thermal Expansion Mismatch to Form Hollow Nanoparticles

Nano popcorn: a new formation mechanism for the synthesis of hollow metal oxide nanoparticles through a melt fracture mechanism. The hollow nanoparticles are formed via brittle fracture following the generation of tensile stresses arising due to liquid-phase thermal expansion of a low melting point core metal. The progress of this physical process can be monitored using in situ transmission electron microscopy for a model system of indium/indium oxide.