Paul Alivisatos

Colloidal quantum dots. From scaling laws to biological applications

Over a twenty-year period, condensed matter physicists and physical chemists have elucidated a series of scaling laws which successfully describe the size dependence of solid state properties [1,2]. Often the experiments were performed under somewhat exotic conditions, for instance on mass-selected clusters isolated in molecular beams or on quantum dots grown by molecular beam epitaxy and interrogated at low temperatures and in high magnetic fields. As a result, we now have an understanding of how thermodynamic, optical, electrical, and magnetic properties evolve from the atomic to the solid state limit. This area of research is presently undergoing a remarkable transformation. The scaling laws, previously the direct subject of research, now provide a tool for the design of advanced new materials. In the case of colloidal quantum dots, or semiconductor nanocrystals, these new insights are poised to have impact in disciplines remote from solid state physics [3].

Novel two-step synthesis of controlled size and shape platinum nanoparticles encapsulated in mesoporous silica

Uniform shape and size platinum nanoparticles encapsulated in mesoporous silica (SBA-15) were prepared in the same solution by a novel two-step method. Platinum nanoparticles were prepared in aqueous solution of K2PtCl4, the reduction was carried out by bubbling hydrogen, the capping material was tri-block poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer. The mesoporous silica was synthesized using the same copolymer as template from tetraethyl orthosilicate by hydrolysis in acidic conditions. The “Pt-nanoparticles-in-mesoporous-silica” system was characterized by a combination of low-angle powder X-ray diffraction, transmission electron microscopy and N2 porosimetry. The platinum nanoparticles are encapsulated in the mesopores and retained their size and morphology. It appears that this hybrid material should be a superior three-dimensional high-surface-area catalyst for selective platinum-catalyzed reactions.

Synthesis and characterization of hyperbranched mesoporous silica SBA-15

Branched mesoporous silica SBA-15 materials have been prepared in a simple process using non-ionic surfactant in acidic conditions in the presence of metal ions.

SYNTHESIS OF PASSIVATED COBALT NANOCRYSTAL ARRAYS WITH CONTROLLED SIZE AND SHAPE

Rapid pyrolysis of cobalt carbonyl in an inert atmosphere was employed to produce magnetic colloids (ferrofluids) of monodispersed, stabilized, cobalt nanocrystals. The size distribution and the shape of the nanocrystals were controlled by varying the surfactant (oleic acid, phosphonic oxides and acids...), its concentration and the reaction temperature. Thus, we systematically synthetised passivated nanocrystals with nearly monodisperse (std. dev.< 5%) size ranging from 3 to 17 nm. The surface tension of the Co crystals were modified during the reaction and cubic and prism-like crystals of size ~20–30 nm were also synthesized. Particles are single crystals with a complex cubic structure related to the beta phase of manganese (e-Co). Thus by controlling the size, the shape and the crystal structure the superparamagnetic transition can be customized. These particles have been observed to produce 2D self-assemblies when evaporated at low rates in a controlled atmosphere. A combination of x-ray powder diffraction, transmission electron microscopy and vibrating sample magnetometer has been used to characterize both the dispersed nanocrystals and the assembled superlattices.