Advanced Operando Electron Microscopy for Disentangling Stability and Orbital Transport at Metallic Interfaces

Résumé fourni par la source

Spin–orbit–enabled transport in dilute alloys is highly sensitive to nanoscale chemistry and microstructure [1], yet device operation necessarily couples these variables to Joule heating and bias-driven mass transport. Bi-doped Cu nanowires are a particularly interesting test case: sub-at.% Bi can generate a giant spin Hall effect (SHE) response [2], while Bi’s surfactant character and large size mismatch favor segregation to free surfaces and grain boundaries. Here, spectroscopy and spectral imaging in aberration-corrected scanning transmission electron microscopy (STEM) are applied to quantify when and where Bi remains substitutional versus redistributes under thermal loads relevant to operation. Electron energy-loss spectroscopy (EELS) is combined with four-dimensional STEM (4D-STEM) to correlate Bi distribution with crystallinity, including grain-boundary density, domain size, and local strain signatures. By deliberately tuning crystalline domain size from the few-hundred-nanometer regime to micron scale, microstructure-dependent segregation pathways are isolated [3]. Variable-temperature measurements reveal an onset of Bi de-incorporation at certain temperatures, while a residual Bi fraction remains stabilized at higher temperatures [4], providing an experimentally grounded window for sustaining spin–orbit functionality. Current-driven orbital phenomena will be also addressed at the Cu/Cu-oxide interface. Using electron magnetic chiral dichroism measured by EELS (EMCD-EELS) acquisition geometries under in situ electrical bias, practical conditions are delineated for maximizing sensitivity while rejecting artifacts, including momentum-transfer selection [5,6]. Together, the results establish a structure–chemistry–temperature framework for interpreting spin–orbit transport in CuBi nanowires and define a transferable measurement strategy for probing orbital responses in broader 3d transition-metal systems. This framework is extended to self-supported metallic Cr-based films, enabling conventional Hall measurements and EMCD-EELS on the same device area. Microfabricated chip designs improve film stability and reproducibility under bias, allowing transport readouts to be directly correlated with nanometer-scale dichroic signatures. Establishing this benchmark in simple metals provides a controlled route to more subtle charge-neutral Hall responses, including orbital-current–related phenomena, in broader 3d transition-metal films and heterointerfaces [7]. (a) Annular bright field low magnification image of the heating (green)-biasing (red) electrodes of the geometry of the in situ chip. The boxed region indicates the device set-up probed in the microscope while a current is driven through the metallic nanostructure (inset: simplified biasing circuit). (b) Conceptual STEM/EMCD-EELS geometry used to detect current-driven orbital responses: a scanning probe rasters across the biased sample while EELS is acquired with momentum-transfer (⁠→⇀q⁠) selection at collection positions (A and B) in reciprocal space, alongside simultaneous annular dark field detector imaging.

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