Nanometer size effects in nucleation, growth and characterization of templated CdS nanocrystal assemblies

Mapping Charge Distribution in Single PbS Core - CdS Arm Nano-Multipod Heterostructures by Off-Axis Electron Holography

We synthesized PbS core-CdS arm nanomultipod heterostructures (NMHs) that exhibit PbS{111}/CdS{0002} epitaxial relations. The PbS-CdS interface is chemically sharp as determined by aberration corrected transmission electron microscopy (TEM) and compared to density functional theory (DFT) calculations. Ensemble fluorescence measurements show quenching of the optical signal from the CdS arms indicating charge separation due to the heterojunction with PbS. A finite-element three-dimensional (3D) calculation of the Poisson equation shows a type-I heterojunction, which would prevent recombination in the CdS arm after optical excitation. To examine charge redistribution, we used off-axis electron holography (OAEH) in the TEM to map the electrostatic potential across an individual heterojunction. Indeed, a built-in potential of 500 mV is estimated across the junction, though as opposed to the thermal equilibrium calculations significant accumulation of positive charge at the CdS side of the interface is detected. We conclude that the NMH multipod geometry prevents efficient removal of generated charge carriers by the high energy electrons of the TEM. Simulations of generated electron-hole pairs in the insulated CdS arm of the NMH indeed show charge accumulation in agreement with the experimental measurements. Thus, we show that OAEH can be used as a complementary methodology to ensemble measurements by mapping the charge distribution in single NMHs with complex geometries.

Heterogeneous nucleation of Al melt in symmetrical or asymmetrical confined nanoslits

MD simulations are performed to study the solidification of Al melt in confined nanoslits (NSs) constructed by identical or different substrates, as well as on Fe substrates. Compared to the single substrate, the confined NS could promote the crystallization of Al melt, and its size has a significant impact on the solidified structure. In symmetrical NSs, liquid Al atoms would stack based on the atomic arrangement mode of the substrate, however in asymmetrical confined NSs, the atomic arrangement mode of liquid Al is governed by the constitution of asymmetrical substrates. Specifically, for the NS formed by Fe(110) and Fe(111) substrates, the induced region from the Fe(110) substrate is much bigger than that from Fe(111). Moreover, the freezing of liquid Al in asymmetrical NSs constructed from copper and iron has also been studied. These results throw light on heterogeneous nucleation in confined space.

Effects of crystalline phase and morphology on the visible light photocatalytic H2-production activity of CdS nanocrystals

Optimized multi-armed CdS nanorods with a high percentage of wurtzite, prepared by a simple solvothermal route, exhibited high visible-light photocatalytic H₂-production performance.