Coupled colloidal quantum dot (CQD) dimers represent a new class of artificial molecules composed of fused core/shell semiconductor nanocrystals. The electronic coupling and wave function hybridization are enabled by the formation of an epitaxial connection with a coherent lattice between the shells of the two neighboring quantum dots where the shell material and its dimensions dictate the quantum barrier characteristics for the charge carriers. Herein we introduce a colloidal approach to control the neck formation at the interface between the two CQDs in such artificial molecular constructs. This allows the tailoring of the neck barrier in prelinked homodimers formed via fusion of multifaceted wurtzite CdSe/CdS CQDs. The effects of reaction time, temperature, and excess ligands are studied. The neck filling process follows an intraparticle ripening mechanism at relatively mild reaction conditions while avoiding interparticle ripening. The degree of surface ligand passivation plays a key role in activating the surface atom diffusion to the neck region. The degree of neck filling strongly depends also on the initial relative orientation of the two CQDs, where homonymous plane attachment allows for facile neck growth, unlike the case of heteronymous plane attachment. Upon neck filling, the observed red-shift of the absorption and fluorescence measured both for ensemble and single dimers is assigned to enhanced hybridization of the confined wave function in CQD dimer molecules, as supported by quantum calculations. The fine-tuning of the particle interface introduced herein provides therefore a powerful tool to further control the extent of hybridization and coupling in CQD molecules.

Robust control over the carrier type is fundamental for the fabrication of nanocrystal‐based optoelectronic devices, such as the p–n homojunction, but effective incorporation of impurities in semiconductor nanocrystals and its characterization is highly challenging due to their small size. Herein, InAs nanocrystals (NCs), post‐synthetically doped with Cd, serve as a model system for successful p‐type doping of originally n‐type InAs nanocrystals, as demonstrated in field effect transistors (FETs). Advanced structural analysis, using atomic resolution electron microscopy and synchrotron X‐ray absorption fine structure spectroscopy reveal that Cd impurities reside near and on the nanocrystal surface acting as substitutional p‐dopants replacing Indium. Commensurately, Cd‐doped InAs FETs exhibit remarkable stability of their hole conduction, mobility, and hysteretic behavior over time when exposed to air, while intrinsic InAs NCs FETs are easily oxidized and their performance quickly declines. Therefore, Cd plays a dual role acting as a p‐type dopant, and also protects the nanocrystals from oxidation, as evidenced directly by X‐ray photoelectron spectroscopy measurements of air exposed samples of intrinsic and Cd‐doped InAs NCs films. This study demonstrates robust p‐type doping of InAs nanocrystals, setting the stage for implementation of such doped nanocrystal systems in printed electronic devices.

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Using dichroic electrostatic mirrors, which can reflect a fast ion beam while transmitting a counterion beam, allows extending the field of electrostatic ion trapping. We present the design and simulations of a hybrid electrostatic ion beam trap that allows simultaneous trapping of velocity matched cation and anion beams. The possible merged beam ion-ion, ion-neutral, and ion-laser experiments are discussed.

Synopsis A new hybrid electrostatic ion beam trap (HEIBT) is designed and simulated for low-energy ion-ion, ion-neutral merged beam collision studies as well as ion-laser interaction experiments. The HEIBT is made possible by the design of dichroic electrostatic mirrors that reflect or transmit ion beams of different charge and energy. The experimental setup allows fragment imaging detection of the investigated reaction products ejected outside the trap.