John S. Mangum

Battery research increasingly relies on advanced imaging, yet open access to such data remains rare, scattered across various sources, and difficult to find.

Crystalline orientation and offcut angle are non‐trivial for low‐symmetry β‐Ga ₂ O ₃ , where anisotropy impacts bulk and thin film synthesis, material properties, and power device fabrication and performance. Scalable (100)‐oriented β‐Ga ₂ O ₃ wafers are desirable for electronic devices but are not typically used as substrates due to 10–30x slower epitaxial growth rates compared to other orientations. Here we report molecular beam epitaxy (MBE) growth rates equal to the fast growth direction by using (100) Ga ₂ O ₃ wafers with large grown‐in offcuts. Offcuts up to 13.4° (β‐angle minus 90°), with vertically aligned (001) planes, are directly grown by Edge‐defined Film‐fed Growth (EFG) of 2D ribbons with rotated seed crystals, avoiding material loss from crystal boule offcut methods while maintaining high crystalline quality. Chemical‐mechanical polishing produces epitaxy‐ready substrates, and step flow growth is observed across offcuts. We measure an unintentional n‐type doping density < 2 × 10 ¹⁵ cm ⁻³ , one of the lowest values reported for MBE. Planar Schottky barrier diodes on these epilayers without edge termination have an on/off ratio ∼10 ⁵ and an average breakdown field of 1.56 MV/cm, comparable to or exceeding similar devices fabricated on other orientations. Overall, these results illustrate the importance of orientation and offcut, validating the use of the scalable (100)‐oriented β‐Ga ₂ O ₃ wafers.

Low defect, single polarity aluminum nitride layers grown by halide vapor phase epitaxy (HVPE) methods have classically needed growth temperatures well exceeding 1100°C with many of the best results being grown in the range of 1400°C. These high temperatures have typically been required to obtain Al-polar AlN films with smooth morphologies and high crystalline quality. However, these elevated temperatures make the use of quartz reactor chambers difficult, as quartz begins to soften at 1200°C, and requires specially designed reactors. This study examines the use of anhydrous hydrogen chloride (HCl) gas, injected directly to the growth surface, to suppress inverted polarity grains that form at low growth temperatures. This method allows for high quality, single crystal AlN layers with a growth temperature of just 1000°C in a quartz reactor chamber. With this method, AlN layers of 5 µm thickness were grown on c-plane (0 0 0 1) sapphire, with a growth rate of 20 µm/hour, and a resulting full-width at half-maximum (FWHM) of symmetric (0 0 0 2) rocking curve reflection under 400 arcsec and asymmetric (1 0 -1 2) reflection under 1000 arcsec. Electron backscatter diffraction measurements showed the suppression of inversion domains with increasing free HCl, resulting in smoother and higher quality films.

Organic photovoltaics (OPVs) demonstrate great potential for low‐cost and low‐energy intensity electricity production. Progress in OPVs historically arises from discovery of new organic semiconductors. However, the molecular and polymeric organic semiconductor design space is vast and performance evaluation in new materials is slow. Adding to the challenge, device optimization has been overly focused only on highest efficiency, generally incorporating processes at odds with scale‐up and durability efforts that precede commercialization. We have developed a framework to address this problem, named HOOPS (high‐throughput optimization of OPVs for performance and stability), where device fabrication variables that affect both performance and stability are equally weighted in an iterative feedback loop while optimizing device fabrication processes. Applicable to all layers of the OPV, PTQ‐10:Y6‐BO, and ZnO are used as an exemplary materials in an inverted architecture OPV where HOOPS reveals that a performance and stability optimum is not always achieved by the same fabrication methods used to achieve exclusively top initial performance. The results underscore the importance of both high‐throughput methods as well as an equal focus on performance and stability, especially early in research as OPVs continue to transition from lab to market.

Beta-Ga2O3 has emerged as a leading candidate for next-generation power electronics, radio frequency (RF) switches, and extreme environment electronics due to a wide band gap (4.6 - 4.9 eV), high dopability (approximately 40 meV activation energy for an isolated silicon donor), and melt growth characteristics resulting in commercially available 4-inch substrates and commercial demonstrations of 6-inch substrates by multiple techniques. The (100) surface of Ga2O3 is highly desirable from a device and epitaxy standpoint - bulk growth of (100) material is more scalable than (010), the surface is nearly lattice-matched to p-type partner NiO, and Al2O3 incorporates at higher concentrations without phase separation. However, the epitaxial growth rate on (100) surfaces is less than 10% of other faces due to weak bonding and favorable desorption. Recent demonstrations have shown growth rate improvements from 0.4 nm/min to 1.5 nm/min by growing on (100) wafers that are offcut 6 degrees in the -c direction.1 These films show step-flow growth from (-201) step-edges and high electron mobility. Despite these exciting results, offcuts greater than 6 degrees have not been explored due to the waste associated with grinding and polishing large offcuts. In this talk we will discuss the molecular beam epitaxy (MBE) growth and properties of Beta-Ga2O3 grown on (100) substrates offcut in the -c direction up to 13.4 degrees. These large offcuts are enabled by edge-fed film-defined growth (EFG) where the offcut is grown into the surface by pulling the crystal through the EFG die with the seed crystal rotated by the desired offcut angle. We will demonstrate that 13.4 degrees offcut substrates still exhibit a terraced (100) surface, and that a >10x increase (4.8 nm/min) in growth rate is achieved. As previously reported on lower offcuts, we observe 100% reversal of substrate twin domains around the (001) direction at the substrate-epilayer interface. We will discuss electrical properties including record-low (by MBE) unintentional doping densities of < 5E15 cm-3.

Electrochemical interfaces are dynamic systems, evolving based on their local environment and reactant surface structures. The electrode-electrolyte interface in Li-ion batteries can be protective, limiting parasitic reactions with the electrolyte to passivate the surface [1]. Additionally, this interphase has an impact on the Li-ion transport through that layer based on its composition, bonding environment, and thickness. These parameters are challenging to collect and may vary depending on the electrode surface site investigated relative to its spatial position in a coin cell. This study will detail a multiscale cryogenic electron microscopy approach where millimeter-scale cross-sections through the coin cell batteries were made using a cryogenic stage within a fs-laser plasma focused ion beam (laser PFIB) with complementary energy dispersive X-ray spectroscopy able to detect variations in the composition at electrode interfaces [2]. Microscale cross-sectioning and lamella sample preparation of battery electrodes was conducted at the Center for Integrated Nanotechnologies using a Ga-ion focused ion beam (FIB) with air-free and cryo-transfer [3], followed by nanoscale mapping of composition and bonding within the CEI through cryo-scanning transmission electron microscopy (cryo-STEM) electron energy loss spectroscopy [4]. This multiscale approach enabled identification of millimeter-scale features of a battery stack with visualization of degradation in electrodes such as cracks in cathode particles, gas evolution, and SEI evolution; microscale interfacial characteristics, such as heterogeneity in the SEI or barrier layer and identification of electrolyte networks to the electrode surfaces; and nanoscale measurement of the CEI thickness, mapping of transition metal bonding within the cathode particles to identify loss of active materials, and identification of beneficial electrolyte additives incorporated into the CEI structure. This multiscale approach allows for a statistical understanding of the primary mechanisms and parasitic degradation pathways that impact performance by limiting the ion transport pathways within Li+ batteries.

Thermal energy storage (TES) technology facilitates supply-demand energy management by storing heat in concentrated solar power, waste heat recovery, baseload nuclear plants, and industrial applications. Magnesium chloride (MgCl2) is a promising salt-based phase change material candidate for TES applications due to its favorable thermo-physical properties. However, the highly corrosive nature of this chloride-based salt in the molten state presents challenges for the realization of efficient TES system utilizing this salt. This study evaluates the performance of 304L stainless steel (SS304L) as a structural alloy in contact with MgCl2 under thermal cycling conditions relevant for TES applications. We utilize a multi-modal approach, integrating synchrotron-based sub-micron X-ray fluorescence and electron microscopy, to investigate the microstructural evolution and elemental diffusion at the alloy-salt (SS304L-MgCl2) interface under short- and long-term thermal cycling conditions. The primary corrosion mechanisms are discussed, revealing a shift in the dominant corrosion process between short- and long-term exposure.

Ternary nitride alloys based on wurtzite AlN are a promising platform to realize functional materials, particularly ferroelectrics and optical emitters, that can smoothly integrate with conventional microelectronics. Here, a strategic design is presented to enable multifunctional materials by substituting multiple elements into AlN to create quaternary nitride alloys. By combining computational predictions and combinatorial thin film synthesis, the phase diagram of these quaternary Al–Sc–Gd–N alloys (or pseudo‐ternary heterostructural AlN–ScN–GdN alloys) is successfully predicted as a function of effective temperature, and we experimentally grow thin films for the first time. It is revealed that crystallizes in a wurtzite‐derived structure for , consistent with the calculated phase diagram. The computational investigation explores whether co‐substitution induces cooperative effects on these alloys' piezoelectric and ferroelectric properties, finding that it is beneficial for reducing the polarization switching barrier. We calculate that thin films should display ferroelectric switching. This is supported by our experimental measurements of a high optical bandgap, enhanced piezoelectric coefficient, and a change in the calculated polarization switching mechanism, and we achieve preliminary ferroelectric switching that experimentally realizes the prediction. Overall, our work sets the foundation toward quaternary wurtzite‐nitride‐based multifunctional materials, including piezoelectrics, ferroelectrics, and possibly even multiferroics.