Charge separation at a semiconductor nano-heterointerface is switched between an on and an off state based on a combination of lattice strain, coulomb interaction, and interface trap states.

The process of symmetry breaking that leads to the formation of anisotropic, colloidal semiconductor nanocrystals is an important issue for understanding the physical mechanism of nucleation and growth. One-dimensional growth of nanorods is assumed to occur under reaction-limited control at a high concentration of monomer, which preferentially reacts at the crystal facet that has the highest energy and least passivation by surface ligands. In this study, it is shown that instead of assuming a homogeneous distribution of monomer in the reaction solution, the seeded growth of CdS nanorods on CdSe particles is driven by the formation of one-dimensional reaction intermediates that act as local monomer reservoirs. These result in heterogeneously distributed hotspots of the nucleating species that guarantees fast deposition and one-dimensional growth of the nanorod exclusively in one direction. Thus, performing anisotropic particle growth reactions under conditions that favor formation of transient, metastable intermediates lead to particles with a higher aspect ratio and better mechanistic reaction control.

Pairing ZnSe/CdS and CdS/ZnSe core/shell quantum dots with NiO thin film photocathodes enhances the photoelectrochemical water reduction.

Complex, anisotropic nanocrystals made from two or more components are extremely interesting functional materials that can drive directional, light-activated processes like charge separation and photocatalysis. However, while some synthetic protocols exist, little is known about the reaction mechanism for regioselective, heterogeneous nucleation of a second semiconductor material onto nanocrystal seeds. This paper presents the mechanism that leads to growth of a single tip at one end of CdS nanorods with yields between 50 and 80%. It is shown that the growth of only one tip is a result of tight control of the available, nucleating monomer in the reaction solution by working at a large chalcogenide excess. Conditions that facilitate this reaction pathway are characterized by a kinetic barrier to homogeneous growth. These match those for the formation of metastable magic-size clusters. Through this boundary condition, it can be understood why the formation of telluride tips is favored in comparison to selenides and sulfides, for which the regimes for cluster formation and nucleation on surfaces do not overlap.

Nanoparticle gradient materials combine a concentration gradient of nanoparticles with a macroscopic matrix. This way, specific properties of nanoscale matter can be transferred to bulk materials. These materials have great potential for applications in optics, electronics, and sensors. However, it is challenging to monitor the formation of such gradient materials and prepare them in a controlled manner. In this study, we present a novel universal approach for the preparation of this material class using diffusion in an analytical ultracentrifuge. The nanoparticles diffuse into a molten thermoreversible polymer gel and the process is observed in real-time by measuring the particle concentrations along the length of the material to establish a systematic understanding of the gradient generation process. We extract the apparent diffusion coefficients using Fick’s second law of diffusion and simulate the diffusion behavior of the particles. When the desired concentration gradient is achieved the polymer solution is cooled down to fix the concentration gradient in the formed gel phase and obtain a nanoparticle gradient material with the desired property gradient. Gradients of semiconductor nanoparticles with different sizes, fluorescent silica particles, and spherical superparamagnetic iron oxide nanoparticles are presented. This method can be used to produce tailored nanoparticle gradient materials with a broad range of physical properties in a simple and predictable way.