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ABSTRACT In this work, failure of a magnesium aluminate spinel (MgAl₂O₄) is investigated at the microscale by concurrent in situ imaging and loading within a transmission electron microscope. The goal of the effort is to quantitively measure the grain boundary fracture toughness of a spinel bi‐crystal and study the toughness property disparity between the grain boundary and lattice (measured in an earlier effort). Additionally, the mode mixity dependence of the grain boundary fracture properties is measured as the applied loading configuration is varied. By placing a notch aligned with the grain boundary at the top or bottom edge of a bi‐crystal beam sample, bending experiments can generate grain boundary failure with different mode mixites. Critical energy release rates and mode mixity indicators for each sample were extracted through three‐dimensional finite element analysis (FEA), validated by comparison of particle tracking measurements with the FEA results. For opening‐dominated fracture, the grain boundary exhibited a lower fracture energy when compared to the single crystal lattice. Alternatively, shear‐dominated modes exhibit much larger toughness. 

Charge transfer is a fundamental interface process that can be harnessed for light detection, photovoltaics, and photosynthesis. Recently, charge transfer was exploited in nanophotonics to alter plasmon polaritons by involving additional non-polaritonic materials to activate the charge transfer. Yet, direct charge transfer between polaritonic materials has not been demonstrated. We report the direct charge transfer in pure polaritonic van der Waals (vdW) heterostructures of α-MoO3/graphene. We extracted the Fermi energy of 0.6 eV for graphene by infrared nano-imaging of charge transfer hyperbolic polaritons in the vdW heterostructure. This unusually high Fermi energy is attributed to the charge transfer between graphene and α-MoO3. Moreover, we have observed charge transfer hyperbolic polaritons in multiple energy–momentum dispersion branches with a wavelength elongation of up to 150%. With the support from the density functional theory calculation, we find that the charge transfer between graphene and α-MoO3, absent in mechanically assembled vdW heterostructures, is attributed to the relatively pristine heterointerface preserved in the epitaxially grown vdW heterostructure. The direct charge transfer and charge transfer hyperbolic polaritons demonstrated in our work hold great promise for developing nano-optical circuits, computational devices, communication systems, and light and energy manipulation devices. 

The Student Pathways in Engineering and Computing for Transfers (SPECTRA) program is a newly funded S-STEM program in South Carolina, expected to run through 2026. The program is envisioned to provide a streamlined academic pathway for transfer students from 2-year programs within South Carolina into Clemson University, and provide programming to aid their academic success and social integration. To achieve this, SPECTRA will create cohorts of students at two community/technical colleges (Spartanburg Community College and Trident Technical College) and then support that cohort as they transitioned together into Clemson University. This cohort would then be mentored in how to navigate Clemson University’s academic environment, utilizing available programming such as academic tutoring, field trips to see local engineering companies, etc. A unique component of the SPECTRA program is the requirement that scholarship recipients at Clemson University enroll in two semesters of research, in addition to their participation in social and academic programing. Through this Work in Progress paper, the experience in designing and facilitating these research courses while matriculating through their graduate programs is documented by the authors. Specifically, the design constraints of the research courses, the topics developed for the 2021-2022 cohorts and the envisioned assessment are discussed.