Facet to Facet Linking of Shape Anisotropic Inorganic Nanocrystals with Site Specific and Stoichiometric Control.

Nonclassical growth mechanisms such as self-assembly and oriented attachment are effective ways to build complex nanostructures from simpler ones. In the latter case, the nanoparticle components are electronically coupled; however, control over the attachment between nanoparticles is highly challenging and generally requires a delicate balance between dipole-, ligand-, and solvent-based interactions. To this end, we perform incomplete cation exchange with Ag+ (Cu+) on CdSe-seeded CdS nanorods and tetrapods to exclusively convert their tips into small Ag2S (Cu2S) domains. Selective removal of the ligands from these inorganic domains results in spontaneous, site-specific bridging of the nanoparticles. Using this method, we demonstrate the fabrication of polymer-like linear and branched nanoparticles with enhanced electrical properties, as well as the stoichiometric formation of nanoparticle homo- and heterodimers and tetramers. We show that linked structures can then be completely cation exchanged with Pb2+ to generate PbSe/PbS-based nanostructured photodetector media with enhanced properties.

Wet-Chemically Synthesized Colloidal Semiconductor Nanostructures as Optical Gain Media.

An overview on the development of wet-chemically synthesized semiconductor nanostructures as optical gain materials is presented in this Review, beginning with the first demonstration of amplified spontaneous emission in zero-dimensional quantum dots and evolving to more sophisticated heterostructures such as one-dimensional core-seeded nanorods, branched core-seeded tetrapods and two-dimensional nanoplatelets. The advantages and challenges of utilizing strongly quantum-confined colloidal semiconductor materials as gain media are discussed, and a concerted effort is made to elaborate on how the progression towards more structurally complex architectures has allowed for dramatic improvements in performance and stability over the archetypal quantum dot.

Thermochromism from Ultrathin Colloidal Sb2 Se3 Nanowires Undergoing Reversible Growth and Dissolution in an Amine-Thiol Mixture.

Liquid-based thermochromics can be incorporated into an arbitrarily shaped container and provide a visual map of the temperature changes within its volume. However, photochemical degradation, narrow temperature range of operation, and the need for stringent encapsulation processes are challenges that can limit their widespread use. Here, a unique solution-based thermochromic comprising ultrathin colloidal Sb2 Se3 nanowires in an amine-thiol mixture is introduced. The nanowires undergo reversible growth and dissolution with repeated cycles of heating and cooling between 20 and 160 °C, exhibiting intense and contrasting color changes during these processes. Furthermore, the transition temperature in which a change in color first appears can be continuously tuned over a range larger than 100 °C by introducing controlled amounts of Sn2+ . The colloidal nanowire dispersion in the amine-thiol mixture retains its thermochromic properties over hundreds of temperature cycles, continuous heating at 80 °C over months, and shelf life of up to 2 years in an open container under ambient conditions. To illustrate its utility as a robust liquid thermochromic, the nanowire solution is coated onto standard filter paper and its uses as a rewritable surface by thermal scribing, as well as an inexpensive means of visualizing the temperature distribution of an anisotropically heated block are demonstrated.

Facet-to-facet Linking of Shape-anisotropic Colloidal Cadmium Chalcogenide Nanostructures.

Here, we describe a protocol that allows for shape-anisotropic cadmium chalcogenide nanocrystals (NCs), such as nanorods (NRs) and tetrapods (TPs), to be covalently and site-specifically linked via their end facets, resulting in polymer-like linear or branched chains. The linking procedure begins with a cation-exchange process in which the end facets of the cadmium chalcogenide NCs are first converted to silver chalcogenide. This is followed by the selective removal of ligands at their surface. This results in cadmium chalcogenide NCs with highly reactive silver chalcogenide end facets that spontaneously fuse upon contact with each other, thereby establishing an interparticle facet-to-facet attachment. Through the judicious choice of precursor concentrations, an extensive network of linked NCs can be produced. Structural characterization of the linked NCs is carried out via low- and high-resolution transmission electron microscopy (TEM), as well as energy-dispersive X-ray spectroscopy, which confirm the presence of silver chalcogenide domains between chains of cadmium chalcogenide NCs.