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Abstract Next-generation semiconductor devices are adopting three-dimensional (3D) architectures with feature sizes in the few-nanometer regime, creating a need for atomic-scale metrology to identify and resolve performance-limiting fabrication challenges. X-ray methods provide 3D information but lack atomic resolution, while conventional electron microscopy offers limited depth sensitivity. Here we show how multislice electron ptychography, a computational microscopy technique with sub-Ångström lateral and nanometer-scale depth resolution, enables 3D imaging of buried device structures. We image prototype gate-all-around transistors and directly quantify roughness, strain, and defects at the interface of the 3D gate oxide wrapped around the channel. We find that silicon in the 5-nm-thick channel relaxes away from the interfaces, leaving only ~60% of atoms in a bulk-like structure. From a single dataset, ptychography provides quantitative metrology of atomic-scale interface roughness in 3D, previously accessible only through indirect inference, along with strain and other structural parameters needed for device modeling and process development. 

When hydrogen atoms occupy interstitial sites in metal lattices, they form metal hydrides (MHx), whose structural and electronic properties can differ significantly from those of the host metals. Determining where the hydrogen is located within the MHx is crucial for predicting and understanding the resultant unique physical and electronic properties of the hydride. Yet, directly imaging hydrogen within a host material remains a major challenge due to its weak signal in conventional X-ray and electron imaging techniques. Here, we employ electron ptychography, a scanning transmission electron microscopy (STEM) technique, to image the three-dimensional (3D) distribution of H atoms in palladium hydride (PdHx) nanocubes, one of the most studied and industrially relevant MHx materials. We observe an unexpected one-dimensional superlattice ordering of hydrogen within the PdHx nanocubes and 3D hydrogen clustering in localized regions within the PdHx nanocubes, revealing spatial heterogeneity in metal hydride nanoparticles previously inaccessible by other methods. 

Developments in the design and fabrication of the high saturation magnetization magnetic nanoparticles in the single-domain size regime are highly desirable due to their significant potential for various near-future applications. In this work, we present an in-depth investigation of iron cobalt (Fe65Co35) nanocubes with different sizes covering magnetization configurations from flower to vortex to multidomain states. We synthesized Fe65Co35 nanocubes with tunable edge lengths by adjusting reaction parameters in a liquid-phase reduction reaction. Scanning electron microscope (SEM) images confirm a narrow size distribution. Measured hysteresis loops indicate the size dependence of coercivity and remanence, showing a peak at a size of 17 nm. To explain this phenomenon, a finite element micromagnetic model was used to predict the magnetic properties of Fe65Co35 nanocubes, ranging in size from 10 to 100 nm. Simulation results reveal that the flower-to-vortex transition occurs at around 20 nm, coinciding with the highest coercivity. Larger nanoparticle sizes exhibit a decrease in remanence, with the most significant drop observed between 40 and 60 nm. By combining chemical synthesis and micromagnetic calculations, we have experimentally elucidated the size-dependent spin configurations in Fe65Co35 nanocubes. These findings offer insights for the accurate design and control of spin texture, magnetic remanence, and coercivity in high magnetization nanoparticles. Such advancements can greatly enhance contrast agents for bioimaging, actuators for microelectromechanical (MEMS) systems, and magnetic composites for various applications. 

The development of large-wafer single-crystal AlN substrates has expanded their role beyond UV photonics to enable next-generation integrated electronics. In this study, we investigated δ-doped AlN/GaN/AlN heterostructures, where an n-type δ-doping layer is introduced to suppress the undesired two-dimensional hole gas at the bottom GaN/AlN interface, thereby enhancing the conductivity of the two-dimensional electron gas at the top AlN/GaN interface. We began by systematically identifying epitaxial growth conditions to achieve high crystalline quality, as confirmed by cross-sectional transmission electron microscopy images. To understand the impact of δ-doping density on transport properties, we combined theoretical modeling with experimental measurements, revealing that an optimal δ-doping density of ∼5×1013cm−2 minimizes interface roughness scattering and enhances mobility. Finally, we demonstrated scalability by extending the growth to large-area wafers, supported by structural and transport characterization. A sheet resistance of 246.8 ± 38.1 Ω/□ measured across a 3-in. (75 mm) wafer highlights the uniformity and performance potential of δ-doped AlN/GaN/AlN heterostructures for high-power, high-frequency electronic applications. 

Recently, superconductivity was discovered with a superconducting transition temperature (Tc) of 2 K in strained (110)-oriented RuO2 films grown on TiO2(110) single-crystal substrates. In this work, we predict and realize superconductivity in strained (100)-oriented RuO2 thin films grown on TiO2(100) single-crystal substrates. We show that while density functional theory predicts the Tc of strained RuO2(100) films to be even higher than the RuO2(110) films, our transport and angle-resolved photoemission spectroscopy measurements find the Tc to be about 1 K in strained RuO2(100) films grown on TiO2(100) substrates. Nonetheless, the thickness dependence of the Tc follows a similar trend in both cases. Our scanning SQUID measurements reveal a local superfluid response, indicating a 100 mK inhomogeneity in Tc over a 100 μm scale. 

The Josephson junction is a crucial element in superconducting devices, and niobium is a promising candidate for the superconducting material due to its large energy gap relative to aluminum. AlOx has long been regarded as the highest quality oxide tunnel barrier and is often used in niobium-based junctions. Here, we propose ZrOx as an alternative tunnel barrier material for Nb electrodes. We theoretically estimate that zirconium oxide has excellent oxygen retention properties and experimentally verify that there is no significant oxygen diffusion leading to NbOx formation in the adjacent Nb electrode. We develop a top–down, subtractive fabrication process for Nb/Zr–ZrOx/Nb Josephson junctions, which enables scalability and large-scale production of superconducting electronics. Using cross-sectional scanning transmission electron microscopy, we experimentally find that depending on the Zr thickness, ZrOx tunnel barriers can be fully crystalline with chemically abrupt interfaces with niobium. Further analysis using electron energy loss spectroscopy reveals that ZrOx corresponds to tetragonal ZrO2. Room temperature characterization of fabricated junctions using Simmons’ model shows that ZrO2 exhibits a low tunnel barrier height, which is promising in merged-element transmon applications. Low temperature transport measurements reveal sub-gap structure, while the low-voltage sub-gap resistance remains in the megaohm range.