Electric-field control of single-molecule tautomerization.

The electric field is an important parameter to vary in a single-molecule experiment, because it can directly affect the charge distribution around the molecule. Yet, performing such an experiment with a well-defined electric field for a model chemical reaction at an interface has proven to be extremely difficult. Here, by combining a graphene field-effect transistor and a gate-tunable scanning tunneling microscope (STM), we reveal how this strategy enables the intramolecular H atom transfer of a metal-free macrocycle to be controlled with an external field. Experiments and theory both elucidate how the energetic barrier to tautomerization decreases with increasing electric field. The consistency between the two results demonstrates the potential in using electric fields to engineer molecular switching mechanisms that are ubiquitous in nanoscale electronic devices.

The effect of atomic disorder at the core-shell interface on stacking fault formation in hybrid nanoparticles.

On the atomic scale, the exact engineering of interfaces affects the overall properties of functional nanostructures. One factor that is considered both fundamental and practical in determining the structural features of interfaces is the lattice mismatch, but zooming into the atomic scale reveals new data, which suggest that this paradigm should be reconsidered. Here, we used advanced transmission electron microscopy techniques to image, with atomic resolution, the core-shell interfaces of a strain-free system (CdSe@CdSe) and of a strain-induced system (CdSe@CdS). Then, we analyzed the pattern of stacking fault formation in these particles and correlated the location of the stacking faults with the synthetic procedure. We found that, in the strain-free system, the formation of stacking faults is substantial and the faults are located mostly at the core-shell interface, in a pattern that was surprisingly similar to that observed in the strain-induced system. Therefore, we conclude that the formation of faults within the nanoparticles results mainly from the interaction between the last atomic layer and the growth solution, and it is only weakly correlated with lattice mismatch. This finding is important for the design of defect-engineering in multi-step syntheses.

Designing Bimetallic Co-Catalysts: A Party of Two.

The enhanced catalytic properties of bimetallic particles has made them the focus of extensive research. We compare the photocatalytic activity for hydrogen production of core-shell structures of Au@Pd and Au@(Au/Pd alloy) on seeded rods of CdSe@CdS and show that Au@alloy was superior toward hydrogen production. Our finding reveals that the promotion effects of Au in Pd originate both from the alteration of the electronic structure by the Au core as well as by the atomic rearrangement of the surface. Long-term monitoring of the activity of the photocatalysts offered insights into the dynamic processes during the illumination showing that the tip morphology influenced the stability of the hybrid structures. The Au core served as a physical barrier, protecting the CdS rod against cation exchange reactions with the Pd. The coupling of these factors to achieve synergistic effects is therefore a prime aspect in the rational design of efficient cocatalysts.

Atomic-scale evolution of a growing core-shell nanoparticle.

Understanding the atomic-scale growth at solid/solution interfaces is an emerging frontier in molecular and materials chemistry. This is particularly challenging when studying chemistry occurring on the surfaces of nanoparticles in solution. Here, we provide atomic-scale resolution of growth, in a statistical approach, at the surfaces of inorganic nanoparticles by state-of-the-art aberration-corrected transmission electron microscopy (TEM) and focal series reconstruction. Using well-known CdSe nanoparticles, we unfold new information that, for the first time, allows following growth directly, and the subsequent formation of CdS shells. We correlate synthetic procedures with resulting atomic structure by revealing the distribution of lattice disorder (such as stacking faults) within the CdSe core particles. With additional sequential synthetic steps, an ongoing transformation of the entire structure occurs, such that annealing takes place and stacking faults are eliminated from the core. The general strategy introduced here can now be used to provide equally revealing atomic-scale information concerning the structural evolution of inorganic nanostructures.