Nanocrystals with metastable high-pressure phases under ambient conditions.

The ambient metastability of the rock-salt phase in well-defined model systems comprising nanospheres or nanorods of cadmium selenide, cadmium sulfide, or both was investigated as a function of composition, initial crystal phase, particle structure, shape, surface functionalization, and ordering level of their assemblies. Our experiments show that these nanocrystal systems exhibit ligand-tailorable reversibility in the rock salt-to-zinc blende solid-phase transformation. Interparticle sintering was used to engineer kinetic barriers in the phase transformation to produce ambient-pressure metastable rock-salt structures in a controllable manner.

Correlating soil nutrient test lead with bioaccessible lead in highly-contaminated soils receiving lead-immobilizing amendments.

Lead (Pb) is one of the most common metals exceeding human health risk guidelines for soil concentrations worldwide. Pb bioaccessibility is known to vary depending on soil physiochemical characteristics and, as a result, in vitro and in vivo tests exist that are used to estimate bioaccessible Pb in contaminated soils. Although in vitro tests such as the relative bioaccessibility leaching procedure (RBALP) present simpler and more cost-effective risk assessments than in vivo methods, soil tests such as Mehlich-3, Modified Morgan, and ammonium bicarbonate-diethylenetriamine pentaacetate (AB-DTPA) extractions are extremely routine and even more cost-effective.

Macroscale lateral alignment of semiconductor nanorods into freestanding thin films.

This Communication reports that needle-like supercrystalline colloidal particles can be synthesized through anisotropy-driven self-assembly of 1,12-dodecanediamine-functionalized CdSe/CdS core/shell nanorods. The resulting superparticles exhibit both 1D lamellar and 2D hexagonal supercrystalline orders along directions parallel and perpendicular to the long axis of constituent nanorods, respectively. Our results show that the needle-like superparticles can be unidirectionally aligned through capillary forces on a patterned solid surface and further transferred into macroscopic, uniform, freestanding polymer films, which exhibit strong linear polarized PL with an enhanced polarization ratio, and are useful as energy down-conversion phosphors in polarized LEDs.

Colloidal superparticles from nanoparticle assembly.

Colloidal superparticles are size- and shape-controlled nanoparticle assemblies in the form of colloidal particles. Because these superparticles can exhibit physical and chemical properties different from both individual nanoparticles and their bulk assemblies, the development of superparticle synthesis has attracted significant research attention and is emerging as a new frontier in the field of nanotechnology. In this review, we discuss theoretical considerations on the nucleation and growth of colloidal superparticles.

Self-assembled colloidal superparticles from nanorods.

Colloidal superparticles are nanoparticle assemblies in the form of colloidal particles. The assembly of nanoscopic objects into mesoscopic or macroscopic complex architectures allows bottom-up fabrication of functional materials. We report that the self-assembly of cadmium selenide-cadmium sulfide (CdSe-CdS) core-shell semiconductor nanorods, mediated by shape and structural anisotropy, produces mesoscopic colloidal superparticles having multiple well-defined supercrystalline domains.

Shape-controlled synthesis of colloidal superparticles from nanocubes.

This communication reports a shape-controlled synthesis of colloidal superparticles (SPs) from iron oxide nanocubes. Our results show that the formation of SPs is under thermodynamic control and that their shape is determined by Gibbs free energy minimization. The resulting SPs adopt a simple-cubic superlattice structure, and their shape can be tuned between spheres and cubes by varying the relative free energy contributions from the surface and bulk free energy terms.

Formation of heterodimer nanocrystals: UO2/In2O3 and FePt/In2O3.

This Article reports a mechanistic study on the formation of colloidal UO(2)/In(2)O(3) and FePt/In(2)O(3) heterodimer nanocrystals. These dimer nanocrystals were synthesized via the growth of In(2)O(3) as the epitaxial material onto the seed nanocrystals of UO(2) or FePt. The resulting dimer nanocrystals were characterized using X-ray powder diffraction (XRD), energy dispersion spectroscopy, transmission electron microscopy (TEM), scanning transmission electron microscopy, and high-resolution TEM (HRTEM).

Gas-bubble effects on the formation of colloidal iron oxide nanocrystals.

This paper reports that gas bubbles can be used to tailor the kinetics of the nucleation and growth of inorganic-nanocrystals in a colloidal synthesis. We conducted a mechanistic study of the synthesis of colloidal iron oxide nanocrystals using gas bubbles generated by boiling solvents or artificial Ar bubbling. We identified that bubbling effects take place through absorbing local latent heat released from the exothermic reactions involved in the nucleation and growth of iron oxide nanocrystals.