Complex face-centered-cubic (FCC) alloys frequently display chemical short-range ordering (CSRO), which can be detected through the analysis of diffuse scattering. However, the interpretation of diffuse scattering is complicated by the presence of defects and thermal diffuse scattering, making it extremely challenging to distinguish CSRO using conventional scattering techniques. This complexity has sparked intense debates regarding the origin of specific diffuse-scattering signals, such as those observed at 1/3{422} and 1/2{311} positions. To address this challenge, we introduce the method of spatial fluctuation and correlation (FluCor) analysis of local diffuse scattering captured using Four-Dimensional Scanning Transmission Electron Microscopy (4D-STEM). We demonstrate our methodology using a solution-treated (CrCoNi)93Al4Ti2Nb medium-entropy alloy (MEA) and show that the FluCor analysis can differentiate diffuse scattering of different origins. The results reveal two sets of overlapping diffuse-scattering signals at the 1/3{422} and 1/2{311} positions in the studied MEA and link both to non-CSRO origins. Specifically, the heterogeneous-domain diffuse-scattering signals are attributed to nanoscale planar defects, while the homogeneous diffuse-scattering of the matrix is best explained by thermal-diffuse scattering. The principles underlying our fluctuation and correlation analysis of diffuse scattering are general and broadly applicable to order-disordered crystals, including various complex alloy systems. This versatility promises to yield valuable insights into the interplay between microstructural characteristics and CSRO behavior in a wide range of materials, potentially resolving long-standing debates in the field.

Monochromators are essential components in electron microscopy and spectroscopy for improving spatial and energy resolution. Their use in scanning electron microscopes (SEMs), however, remains limited due to high cost and operational complexity. Using a thin-deflector analysis of a homogeneous electrostatic deflector, we show that conventional monochromators exhibit extreme sensitivity to power-supply drift and mechanical imperfections. Meeting these stringent tolerances typically requires additional correction elements, which further increase system complexity and cost. We demonstrate that fringe-field deflectors are inherently less sensitive to these limitations. Based on this insight, we propose a simple and cost-effective monochromator architecture relying solely on fringe fields. The design achieves optimal energy resolution by incorporating short-range deceleration lenses surrounding the main deflector, eliminating the need for auxiliary correction elements. Such a fully electrostatic configuration is compatible with MEMS fabrication, offering a compact, robust, and accessible pathway for high-performance energy filtering in SEMs.

The preparation of ultra-thin PtSn-alloyed layers by molecular beam epitaxy was studied using low-energy electron microscopy (LEEM) and micro-diffraction (μ-LEED). Deposition at a sample temperature of 435 °C initially results in the formation of a Pt3Sn/Pt(111) layer showing a (2 × 2) reconstruction. With continued Sn deposition, a Pt2Sn/Pt(111) layer develops, showing a (3×3)R30° reconstruction. An ultra-thin tin oxide was formed from the (2 × 2) surface by exposure to molecular oxygen at temperatures of 500 °C and 590 °C, respectively. LEED shows the evolution of a new surface structure, which could be identified as an incommensurate rectangular 2.301.83.6 reconstruction with lattice parameters of a = (6.4 ± 0.1)Å and b = (8.6 ± 0.1)Å present in three domains rotated by 120° with respect to each other. This structure can be related to the zigzag reconstructions found for similar ultra-thin oxide systems. Contrarily, the (3×3)R30° structure showed no oxide formation even after extensive exposure to molecular oxygen. The usage of atomic oxygen, however, allows for oxidation of this surface and the growth of thicker oxides on both types of overlayers. At 500 °C this process is accompanied by substantial roughening of the surface.

The framework to determine the morphology of nano particles from atomically resolved electron microscopy images and atom counting data is introduced. Focus is placed on electron microscopy data avoiding advanced geometry optimization of the particle. The problem is solved by simulated annealing with different fitness functions assessed. Even for small particles the solution space rapidly becomes too large to be exhausted. The concept of site occupation probabilities, pi, is then used to analyze a subset, typically very few hundred solutions. This is shown to be sufficient to reach a relative error of below 10% for pi>0.5 already with 100 solutions allowing to determine with high confidence and low statistical error realistic average shapes also for nano particles of a few thousand atoms. These particles typically exhibit a well defined core covered by a layer of sites that are not occupied in each solution. It is further demonstrated that sites with high probability to contain a vacancy can be identified assuming the presence of a vacancy. If a vacancy is actually present in a particle its position can be identified with rather high fidelity. Finally, it is shown that the procedure can cope with the statistical error or ambiguities inherent in atom counting data based on noisy, low dose electron microscopy images.