Shape-controlled Nanocrystals Research Articles

Tunable Size and Shape Control of Platinum Nanocrystals from a Single Peptide Sequence

Nanoscale platinum architectures have been extensively studied as potential materials for applications in catalysis and fuel cells. Due to the high cost of platinum, much of the research has been geared toward developing methods to obtain monodisperse, monomorphic nanocrystals smaller than 10 nm. Peptide-mediated synthesis of inorganic materials is an attractive alternative to colloidal synthesis because it can be performed under ambient conditions and the peptides can be removed from the metal surfaces at mild pH or in the presence of enzymes. As a first step to achieve size and shape-controlled nanocrystals using peptides, we demonstrate here (a) the isolation of peptides that bind to specific crystal planes of platinum and (b) that a single peptide can produce structures ranging from sub-2 nm seed crystals to monodisperse 4 nm platinum polyhedra to 7 to 8 nm platinum cubes simply by changing the rates of metal reduction. This work demonstrates the first steps toward achieving biochemical control of platinum nanocrystal synthesis.

End‐to‐End Assembly of Shape‐Controlled Nanocrystals via a Nanowelding Approach Mediated by Gold Domains

[*] Dr. A. Figuerola, I. R. Franchini, A. Fiore, Dr. S. Kudera, Prof. R. Cingolani, Dr. L. Manna National Nanotechnology Laboratory of CNR-INFM, Unita di Ricerca IIT Distretto Tecnologico ISUFI, via per Arnesano km 5, I-73100 Lecce (Italy) Fax: (þ39) 0832298237 E-mail: liberato.manna@unile.it Dr. A. Figuerola, A. Fiore, R. Mastria, Prof. R. Cingolani Scuola Superiore ISUFI; University of Salento Distretto Tecnologico ISUFI, via per Arnesano km 5, I-73100 Lecce (Italy)

Probe Tips Functionalized with Colloidal Nanocrystal Tetrapods for High‐Resolution Atomic Force Microscopy Imaging

Probe Tips Functionalized with Colloidal Nanocrystal Tetrapods for High‐Resolution Atomic Force Microscopy Imaging

Fatty Acid Salts as Stabilizers in Size- and Shape-Controlled Nanocrystal Synthesis: The Case of Inverse Spinel Iron Oxide

Various oleic acid salts are demonstrated to act as stabilizers for high-quality iron oxide nanocrystals, synthesized by thermal decomposition of ferric oleate. Changing the cation species in oleic acid salts allows different degrees of dissociation at high temperatures to be obtained, resulting in various stabilizer performances: Sodium oleate as stabilizer results in monodisperse iron oxide nanocrystals of cubic shape with precisely adjustable edge lengths between 7 and 23 nm. Dibutylammonium oleate and oleic acid, in contrast, induce growth of spherical nanocrystals in the same size range. Further adjustment of the growth conditions leads to {100}-bound bipyramidal nanocrystals with a single, (111) oriented twin plane. While the nanocrystal size is related to their superparamagnetic blocking temperature, the shape influences their magnetization hysteresis properties observed at low temperatures.

Shape Control of Semiconductor and Metal Oxide Nanocrystals Through Nonhydrolytic Colloidal Routes

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Mechanisms for Photogeneration and Recombination of Multiexcitons in Semiconductor Nanocrystals: Implications for Lasing and Solar Energy Conversion

One consequence of strong spatial confinement of electronic wave functions in ultrasmall semiconductor nanocrystals is a great enhancement of carrier-carrier interactions, which has a dramatic effect on the spectral and dynamical properties of both single and multiexciton states. Strong carrier-carrier interactions open new nanocrystal-specific energy relaxation and recombination channels associated, e.g., with electron-hole energy transfer and ultrafast nonradiative Auger recombination. Further, they lead to extremely efficient direct photogeneration of multiple electron-hole pairs (excitons) by single photons known as carrier (or exciton) multiplication. This review focuses on the effect of Coulomb interactions on carrier recombination and photogeneration mechanisms in nanocrystals based on II-VI (e.g., CdSe) and IV-VI (e.g., PbSe) compounds. The specific topics discussed here include the fine structure of the band-edge optical transitions and its effect on temperature-dependent single-exciton recombination dynamics, Auger recombination of multiexcitons in size- and shape-controlled nanocrystals with a specific emphasis on optical-gain properties of nanocrystalline materials (including quantum rods and multicomponent core-shell heterostructures), and the direct generation of multiple excitons via carrier multiplication and its implications in photovoltaic technologies.

Shape Control of Semiconductor and Metal Oxide Nanocrystals through Nonhydrolytic Colloidal Routes

Inorganic nanocrystals with tailored geometries exhibit unique shape-dependent phenomena and subsequent utilization of them as building blocks for the fabrication of nanodevices is of significant interest. Herein, we review the recent developments in the shape control of colloidal nanocrystals with a focus on the scientifically and technologically important semiconductor and metal oxide nanocrystals obtained by nonhydrolytic synthetic methods. Many structurally unprecedented motifs have been discovered including polyhedrons, rods and wires, plates and prisms, and other advanced shapes such as branched rods, stars, inorganic dendrites, and dumbbells. The currently proposed shape-guiding mechanisms are presented and the important pioneering studies on the assembly of shape-controlled nanocrystals into ordered superlattices and the fabrication of prototype advanced nanodevices are discussed.

Direct growth of shape-controlled nanocrystals on nanotubes via biological recognition.

The new biological approach was examined to fabricate shape-controlled Ag nanocrystals grown directly on surfaces, inspired by nature that various shapes of nanocrystals are produced accurately and reproducibly in biological systems. Here we demonstrate the direct growth of hexagon-shaped Ag nanocrystals on sequenced peptide-coated nanotubes via biological recognition. When the peptide, Asn-Pro-Ser-Ser-Leu-Phe-Arg-Tyr-Leu-Pro-Ser-Asp, recognizing and effecting the Ag nanocrystal growth on the (111) face, was sequenced and incorporated onto template nanotube surfaces, the biomineralization of Ag ions on the nanotubes led the isotropic hexagon-shaped Ag nanocrystal coating under pH control of the growth solution. Multiple Ag nanocrystal shapes were observed when the peptide mineralized Ag ions without the template nanotubes, and therefore the template nanotube has a significant influence on regulating the majority of Ag nanocrystals into the hexagonal shape. This biological approach, using specific peptide sequences on surfaces to control nanocrystal shapes, may be developed as a simple and economical method to produce building blocks with desired physical properties for new generation of electronics, sensors, and optical devices.

Mechanisms for the Shape‐Control and Shape‐Evolution of Colloidal Semiconductor Nanocrystals

AbstractThe shape of CdSe and other semiconductor nanocrystals is controlled, producing dots, rods, rice‐shaped particles, tetrapods, or other elongated shapes. Monomer concentration in the growth solution is the determining factor in shape‐control and shape‐evolution. The elongated shapes could be transformed into more spherical shapes if the monomer concentration in the solution was lowered to a certain level, and spherically shaped nanocrystals could grow to elongated shapes by simply increasing the monomer concentration. The precursors are stable, inexpensive, and relatively non‐toxic, and therefore good choices for the growth of nearly monodisperse and shape‐controlled nanocrystals.

Self-assembly of shape-controlled nanocrystals and their in-situ thermodynamic properties

Size and shape selected nanocrystals behave like molecular matter that can be used as fundamental building blocks for constructing nanocrystal assembled superlattices. The nanocrystals form a new class of materials that have orders in both atomic and nanocrystal length-scales. The nanocrystals are passivated with organic molecules (called thiolates) that not only protect them from coalescence but act as the molecular bonds for forming the superlattice structure. The interparticle distance is adjustable, possibly resulting in tunable electric, optical and transport properties. This paper reviews our current progress in nanocrystal self-assembled materials and their thermodynamic properties probed by in-situ transmission electron microscopy (TEM). The studies mainly focused on size and shape-controlled nanocrystals to understand the role played by particle shape in determining their physical and chemical properties. Recent studies on photonic crystals and mesoporous materials such as silica and titania are also presented.

Transmission Electron Microscopy of Shape-Controlled Nanocrystals and Their Assemblies

The physical and chemical properties of nanophase materials rely on their crystal and surface structures. Transmission electron microscopy (TEM) is a powerful and unique technique for structure characterization. The most important application of TEM is the atomic-resolution real-space imaging of nanoparticles. This article introduces the fundamentals of TEM and its applications in structural determination of shape-controlled nanocrystals and their assemblies. By forming a nanometer size electron probe, TEM is unique in identifying and quantifying the chemical and electronic structure of individual nanocrystals. Electron energy-loss spectroscopy analysis of the solid-state effects and mapping the valence states are even more attractive. In situ TEM is demonstrated for characterizing and measuring the thermodynamic, electric, and mechanical properties of individual nanostructures, from which the structure−property relationship can be registered with a specific nanoparticle/structure.