We report the synthesis of monodisperse colloidal copper nanocrystals and subsequent solvent-dependent oxidation to form copper(I) oxide nanoparticles. The oxidation process was monitored by optical spectroscopy in the visible spectrum with the Cu nanocrystals exhibiting a surface plasmon feature that was replaced over time by an excitonic feature corresponding to the band gap of the Cu2O nanocrystals. The initial intensity of the copper plasmon was strongly dependent on the properties of the solvent used to form the nanocrystal dispersion; solvents with π-bonds significantly reduced (by >3-fold) the plasmon intensity and this effect was attributed to electron sharing between the solvent and the copper surface. The damped plasmon only recovered to its solvent-independent intensity once the nanocrystal surface oxidized and eliminated the solvent−Cu surface interactions. Solvents without π-bonds induced only a very small damping of the plasmon, and at longer time scales all solvents caused similar changes in the optical properties as oxidation converted the nanocrystals from metallic copper to semiconducting copper oxide.

SummaryWe report the effects of varying specimen thickness on the generation of transmission Kikuchi patterns in the scanning electron microscope. Diffraction patterns sufficient for automated indexing were observed from films spanning nearly three orders of magnitude in thickness in several materials, from 5 nm of hafnium dioxide to 3 μm of aluminum, corresponding to a mass-thickness range of ß5 to 810 μg cm -2 . The scattering events that are most likely to be detected in transmission are shown to be very near the exit surface of the films. The energies, spatial distribution and trajectories of the electrons that are transmitted through the film and are collected by the detector are predicted using Monte Carlo simulations.

Prior investigations into the synthesis of colloidal CdSe nanocrystals with a wurtzite crystal structure (wz-CdSe) have given rise to well-developed methods for producing particles with anisotropic shapes such as rods, tetrapods, and wires; however, the synthesis of other shapes has proved challenging. Here we present a seed-mediated approach for the growth of colloidal, shape-controlled wz-CdSe nanoparticles with previously unobserved morphologies. The synthesis, which makes use of small (2-3 nm) wz-CdSe nanocrystals as nucleation sites for subsequent growth, can be tuned to selectively yield colloidal wz-CdSe nanocubes and hexagonal nanoplatelets in addition to nanorod and bullet-shaped particles. We thoroughly characterize the morphology and crystal structures of these new shapes, as well as discuss possible growth mechanisms in the context of control over surface chemistry and the nucleation stage.

The low‐temperature oxidation of ≈10 nm diameter copper nanocrystals is characterized using in situ UV–vis absorbance spectroscopy and observed to lead to hollow copper oxide shells. The kinetics of the oxidation of solid Cu nanocrystals to hollow Cu2O nanoparticles is monitored in real‐time via the localized surface plasmon resonance response of the copper. A reaction‐diffusion model for the formation of hollow nanoparticles is fit to the measured time for complete Cu nanocrystal oxidation, and is used to quantify the diffusion coefficient of Cu in Cu2O and the activation energy of the oxidation process. The diffusivity measured here in single‐crystalline nanoscale systems is 1–5 orders of magnitude greater than in comparable systems in the bulk, and have an Arrhenius dependence on temperature with an activation energy for diffusion of 37.5 kJ mol−1 for 85 °C ≤ T ≤ 205 °C. These diffusion parameters are measured in some of the smallest metal systems and at the lowest oxidation temperatures yet reported, and are enabled by the unique nanoscale single‐crystalline material and the in situ characterization technique.

Al 2 O 3 atomic layer deposition (ALD) is analyzed on ZrO 2 nanoparticles in a rotary reactor. This rotary reactor allows for static exposures and efficiently utilizes the reactants for ALD on high surface area nanoparticles. The Al 2 O 3 ALD is performed using exposures to Al(CH 3 ) 3 and H 2 O reactants. The pressure transients during these exposures are examined using a sequence of reactant micropulses. These micropulses are less than the required exposures for the ALD surface chemistry to reach completion. The pressure transients during identical sequential Al(CH 3 ) 3 and H 2 O micropulses change as the surface chemistry progresses to completion. These pressure transients allow the required saturation reactant exposure to be determined to maximize reactant usage. The ZrO 2 nanoparticles are coated using various numbers of Al(CH 3 ) 3 and H 2 O reactant exposures. The Al 2 O 3 ALD-coated ZrO 2 nanoparticles are subsequently analyzed using a number of techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Auger electron spectroscopy (AES), scanning AES (SAES), and X-ray photoelectron spectroscopy (XPS