A new class of castable cerium strengthened aluminum alloys has phenomenal high temperature properties without the need for heat treatment.

Functional porous materials are of increasing importance in energy conversion and catalysis. Improved analysis is needed to guide optimization. Four-dimensional (4D) imaging [chemical mapping in three-dimensional (3D) by spectro-tomography] of an Al 2 O 3 aerogel coated with ZnO by atomic layer deposition was performed using soft X-ray ptychography at the Zn L-edge. A two-dimensional spatial resolution of 14(2) nm was achieved. Visualizations of the 3D chemical structure are provided. The degree of ZnO coverage of the surface of the Al 2 O 3 aerogel framework in two different samples was estimated and found to be both thicker and less homogeneous than expected. Other analyses of the 4D results, including the degree of contact between Al 2 O 3 and ZnO, were extracted from the reconstructed 3D data. This pioneering soft X-ray spectro-ptycho-tomography study will anchor further studies of functional porous materials.

Above room temperature, the accumulation of radiation damage in 3C-SiC is strongly influenced by dynamic defect interaction processes and remains poorly understood. Here, we use a combination of ion channeling and transmission electron microscopy to study lattice disorder in 3C-SiC irradiated with 500 keV Ar ions in the temperature range of 25–250 °C. Results reveal sigmoidal damage buildup for all the temperatures studied. For 150 °C and below, the damage level monotonically increases with ion dose up to amorphization. Starting at 200 °C, the shape of damage–depth profiles becomes anomalous, with the damage peak narrowing and moving to larger depths and an additional shoulder forming close to the ion end of range. As a result, damage buildup curves for 200 and 250 °C exhibit an anomalous two-step shape, with a damage saturation stage followed by rapid amorphization above a critical ion dose, suggesting a nucleation-limited amorphization behavior. Despite their complexity, all damage buildup curves are well described by a phenomenological model based on an assumption of a linear dependence of the effective amorphization cross section on ion dose. In contrast to the results of previous studies, 3C-SiC can be amorphized by bombardment with 500 keV Ar ions even at 250 °C with a relatively large dose rate of ∼2×1013 cm−2 s−1, revealing a dominant role of defect interaction dynamics at elevated temperatures.

Fluctuation electron microscopy can reveal the nanoscale order in amorphous materials via the statistical variance in the scattering intensity as a function of position, scattering vector, and resolution. However, several sources of experimental artifacts can seriously affect the magnitude of the variance peaks. The use of a scanning transmission electron microscope for data collection affords a convenient means to check whether artifacts are present. As nanodiffraction patterns are collected in serial, any spatial or temporal dependence of the scattering intensity across the series can easily be detected. We present examples of the major types of artifact and methods to correct the data or to avoid the problem experimentally. We also re-cast the statistical formalism used to identify sources of noise in view of the present results. The present work provides a basis on which to perform fluctuation electron microscopy with a high level of reliability and confidence in the quantitative magnitude of the data.

We analyze the evolution of subcritical nuclei as a function of nitrogen alloying and thermal annealing in the amorphous phase change material Ge2Sb2Te5. The existence of subcritical nuclei is inferred through measurement of the nucleation time in pulsed laser annealing, and is detected more directly using fluctuation transmission electron microscopy measurements that are sensitive to topological order on the nanoscale. In samples that are pre-annealed before crystallization experiments, the nanoscale order consistently increases and the nucleation times consistently decrease, in agreement with the interpretation that the nanoscale order corresponds to a population of subcritical nuclei that ripens upon annealing. However, this correlation is less obvious in as-deposited samples across a range of nitrogen contents: The quantity of nanoscale order diminishes only slightly with increased nitrogen alloying, whereas the nucleation times increase by nearly two orders of magnitude. We therefore interpret that nitrogen must affect either the critical size in order for a nucleus to be stable (the thermodynamics) or the rate at which nucleation and growth take place (the kinetics).

Sputter deposited amorphous Ge thin films had their nanostructure altered by irradiation with high-energy Ar+ ions. The change in the structure resulted in a reduction in medium range order (MRO) characterized using fluctuation electron microscopy. The pulsed laser crystallization kinetics of the as-deposited versus irradiated materials were investigated using the dynamic transmission electron microscope operated in the multi-frame movie mode. The propagation rate of the crystallization front for the irradiated material was lower; the changes were correlated to the MRO difference and formation of a thin liquid layer during crystallization.

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