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A ferroelectric is a material with a polar structure whose polarity can be reversed (switched) by applying an electric field 1 , 2 . In metals, itinerant electrons screen electrostatic forces between ions, which explains in part why polar metals are very rare 3 – 7 . Screening also excludes external electric fields, apparently ruling out the possibility of ferroelectric switching. However, in principle, a thin enough polar metal could be sufficiently penetrated by an electric field to have its polarity switched. Here we show that the topological semimetal WTe 2 provides an embodiment of this principle. Although monolayer WTe 2 is centro-symmetric and thus non-polar, the stacked bulk structure is polar. We find that two- or three-layer WTe 2 exhibits spontaneous out-of-plane electric polarization that can be switched using gate electrodes. We directly detect and quantify the polarization using graphene as an electric-field sensor 8 . Moreover, the polarization states can be differentiated by conductivity and the carrier density can be varied to modify the properties. The temperature at which polarization vanishes is above 350 kelvin, and even when WTe 2 is sandwiched between graphene layers it retains its switching capability at room temperature, demonstrating a robustness suitable for applications in combination with other two-dimensional materials 9 – 12 . Two- and three-layer WTe 2 exhibits spontaneous out-of-plane electric polarization that can be switched electrically at room temperature and is sufficiently robust for use in applications with other two-dimensional materials.

The family of III-V materials revolutionized the optoelectronics space, particularly in nitride-based light-emitting diodes (LEDs). LED efficiency has been limited, however, by the Green Gap, which is a drop in efficiency in the green and amber regions, arising from issues with the InGaN material used to reach those light colors. ZnGeN2 has recently been studied as a potential replacement for InGaN within GaN-based LEDs, due to its structural similarly to GaN (0.12% lattice mismatch), and theorized emission in the green wavelength region. ZnGeN2 is predicted to have different optical and structural properties when cation-ordered or cation-disordered. The ordered structure has a theory-predicted band gap of 3.4 eV and an orthorhombic crystal structure. As disorder is introduced to the cation sublattice, the band gap is expected to shrink, and the crystal structure becomes wurtzite. This thesis explores the growth of ZnGeN2 by molecular beam epitaxy (MBE) and then extends that growth to ZnGeN2/GaN superlattices. Next, the valence band offset of ZnGeN2, which lacks consensus in literature, is studied by XPS. Finally, the growth and characterization of ZnGeN2-based LEDs is explored, although the LEDs did not exhibit electroluminescence. ZnGeN2-based LEDs present an opportunity reduce the Green Gap, and assist with the adoption of solid-sate lighting.The first two chapters explore growth of ZnGeN2 by MBE. First, two publications published prior to this thesis are discussed. In the first paper, ZnGeN2 is heteroepitaxially grown on non lattice-matched AlN, allowing for determination of physical and optical properties separately from GaN. The second paper demonstrates commensurate ZnGeN2/GaN double heterojunctions. Abrupt interfaces are seen, but GeZn or ZnGe antisite impurities are also inferred from defect luminescence, motivating more optimization of ZnGeN2/GaN heterostructures. This leads to the next chapter, which investigates improving the luminescence response in ZnGeN2/GaN superlattices. Five-repeating ZnGeN2/GaN superlattices are grown, and through composition control defect reduction is observed.The next chapter presents valence band offset (VBO) exploration of ZnGeN2 on GaN and GaN on ZnGeN2 heterostructures by X-ray spectroscopy (XPS). First the Kraut method is applied to two core levels, which finds band bending at the interface between ZnGeN2 and GaN. By measuring from the most surface sensitive buried core level (2p) to the least surface sensitive top core level (3d) an apparent VBO is found of 1.21 eV for both heterostructure orientations. To measure the VBO while considering band bending, the Kraut method is applied to a single common core level present across the interface (N 1s). That method finds an upper bound on the valence band offset, 2.68 eV. The band gap of ZnGeN2 is still unknown, so the band offset type and magnitude cannot be confirmed. The final chapter of this thesis reports on the growth and characterization of a ZnGeN2-based LED. There is some rectification in the LEDs, but no electroluminescence is observed. Ultimately, this thesis provides a guide for growth of ZnGeN2 by MBE and provides suggestions for future work which could be explored to further asses the potential of ZnGeN2/GaN LEDs to close the Green Gap.

A ferroelectric is a material with a polar structure whose polarity can be reversed (switched) by applying an electric field.sup.1,2. In metals, itinerant electrons screen electrostatic forces between ions, which explains in part why polar metals are very rare.sup.3-7. Screening also excludes external electric fields, apparently ruling out the possibility of ferroelectric switching. However, in principle, a thin enough polar metal could be sufficiently penetrated by an electric field to have its polarity switched. Here we show that the topological semimetal WTe.sub.2 provides an embodiment of this principle. Although monolayer WTe.sub.2 is centro-symmetric and thus non-polar, the stacked bulk structure is polar. We find that two- or three-layer WTe.sub.2 exhibits spontaneous out-of-plane electric polarization that can be switched using gate electrodes. We directly detect and quantify the polarization using graphene as an electric-field sensor.sup.8. Moreover, the polarization states can be differentiated by conductivity and the carrier density can be varied to modify the properties. The temperature at which polarization vanishes is above 350 kelvin, and even when WTe.sub.2 is sandwiched between graphene layers it retains its switching capability at room temperature, demonstrating a robustness suitable for applications in combination with other two-dimensional materials.sup.9-12.

A ferroelectric is a material with a polar structure whose polarity can be reversed (switched) by applying an electric field.sup.1,2. In metals, itinerant electrons screen electrostatic forces between ions, which explains in part why polar metals are very rare.sup.3-7. Screening also excludes external electric fields, apparently ruling out the possibility of ferroelectric switching. However, in principle, a thin enough polar metal could be sufficiently penetrated by an electric field to have its polarity switched. Here we show that the topological semimetal WTe.sub.2 provides an embodiment of this principle. Although monolayer WTe.sub.2 is centro-symmetric and thus non-polar, the stacked bulk structure is polar. We find that two- or three-layer WTe.sub.2 exhibits spontaneous out-of-plane electric polarization that can be switched using gate electrodes. We directly detect and quantify the polarization using graphene as an electric-field sensor.sup.8. Moreover, the polarization states can be differentiated by conductivity and the carrier density can be varied to modify the properties. The temperature at which polarization vanishes is above 350 kelvin, and even when WTe.sub.2 is sandwiched between graphene layers it retains its switching capability at room temperature, demonstrating a robustness suitable for applications in combination with other two-dimensional materials.sup.9-12.

A ferroelectric is a material with a polar structure whose polarity can be reversed (switched) by applying an electric field.sup.1,2. In metals, itinerant electrons screen electrostatic forces between ions, which explains in part why polar metals are very rare.sup.3-7. Screening also excludes external electric fields, apparently ruling out the possibility of ferroelectric switching. However, in principle, a thin enough polar metal could be sufficiently penetrated by an electric field to have its polarity switched. Here we show that the topological semimetal WTe.sub.2 provides an embodiment of this principle. Although monolayer WTe.sub.2 is centro-symmetric and thus non-polar, the stacked bulk structure is polar. We find that two- or three-layer WTe.sub.2 exhibits spontaneous out-of-plane electric polarization that can be switched using gate electrodes. We directly detect and quantify the polarization using graphene as an electric-field sensor.sup.8. Moreover, the polarization states can be differentiated by conductivity and the carrier density can be varied to modify the properties. The temperature at which polarization vanishes is above 350 kelvin, and even when WTe.sub.2 is sandwiched between graphene layers it retains its switching capability at room temperature, demonstrating a robustness suitable for applications in combination with other two-dimensional materials.sup.9-12.

In 1987, Gerda Lerner reviewed three books about women of the nineteenth century who subverted the social and political status quo by way of an ideologically radical and therefore supremely “disorderly” choice: to remain unmarried.¹ In addition to a common interest in the socially subversive nature of rejecting marriage as a defining life choice, the books under review also share a conceptual framework provided by Carroll Smith-Rosenberg’s (1975) article “The Female World of Love and Ritual: Relations between Women in Nineteenth-Century America,” in which she locates and describes women-only organizations that were not only separate from, but acted to transform,

\\(Al_xGa_{1-x}N\\) is a critical ultra-wide bandgap material for optoelectronics, but the deposition of thick, high quality epitaxial layers has been hindered by a lack of lattice-matched substrates. Here we identify the (111) face of transition metal carbides as a suitable class of materials for substrates lattice matched to (0001) \\(Al_xGa_{1-x}N\\) and demonstrate the growth of thin film TaC which has an effective hexagonal lattice constant matched to \\(Al_{0.45}Ga_{0.55}N\\). We explore growth conditions for sputtered TaC on sapphire substrates and investigate the effects of sputter power, layer thickness and incident plasma angle on film structure and in- and out-of-plane strain. We then show critical improvements to film quality by annealing films in a face-to-face configuration at 1600 \\(^\\circ\\)C, which significantly reduces full width at half max (FWHM) of in- and out-of-plane diffraction peaks and results in a step-and-terrace surface morphology. This work presents a path toward electrically conductive, lattice matched, thermally compatible substrates for \\(Al_xGa_{1-x}N\\) heteroepitaxy, a critical step for vertical devices and other power electronics applications.

A ferroelectric is a material with a polar structure whose polarity can be reversed by applying an electric field. In metals, the itinerant electrons tend to screen electrostatic forces between ions, helping to explain why polar metals are very rare. Screening also excludes external electric fields, apparently ruling out the possibility of polarity reversal and thus ferroelectric switching. In principle, however, a thin enough polar metal could be penetrated by an electric field sufficiently to be switched. Here we show that the layered topological semimetal WTe2 provides the first embodiment of this principle. Although monolayer WTe2 is centrosymmetric and thus nonpolar, the stacked bulk structure is polar. We find that two- or three-layer WTe2 exhibits a spontaneous out-of-plane electric polarization which can be switched using gate electrodes. We directly detect and quantify the polarization using graphene as an electric field sensor. Moreover, the polarization states can be differentiated by conductivity, and the carrier density can be varied to modify the properties. The critical temperature is above 350 K, and even when WTe2 is sandwiched in graphene it retains its switching capability at room temperature, demonstrating a robustness suitable for applications in combination with other two-dimensional materials.

Cigarette smoking is undoubtedly a risk factor for lung cancer. Moreover, smokers with genetic mutations on chromosome 3p21.3, a region frequently deleted in cancer and notably in lung cancer, have a dramatically higher risk of aggressive lung cancer. The RNA binding motif 5 (RBM5) is one of the component genes in the 3p21.3 tumour suppressor region. Studies using human cancer specimens and cell lines suggest a role for RBM5 as a tumour suppressor. Here we demonstrate, for the first time, an in vivo role for RBM5 as a tumour suppressor in the mouse lung. We generated Rbm5 loss-of-function mice and exposed them to a tobacco carcinogen NNK. Upon exposure to NNK, Rbm5 loss-of-function mice developed lung cancer at similar rates to wild type mice. As tumourigenesis progressed, however, reduced Rbm5 expression lead to significantly more aggressive lung cancer i.e. increased adenocarcinoma nodule numbers and tumour size. Our data provide in vivo evidence that reduced RBM5 function, as occurs in a large number of patients, coupled with exposure to tobacco carcinogens is a risk factor for an aggressive lung cancer phenotype. These data suggest that RBM5 loss-of-function likely underpins at least part of the pro-tumourigenic consequences of 3p21.3 deletion in humans.

A primary barrier to translation of clinical research discoveries into care delivery and population health is the lack of sustainable infrastructure bringing researchers, policymakers, practitioners, and communities together to reduce silos in knowledge and action. As National Institutes of Healthʼs (NIH) mechanism to advance translational research, Clinical and Translational Science Award (CTSA) awardees are uniquely positioned to bridge this gap. Delivering on this promise requires sustained collaboration and alignment between research institutions and public health and healthcare programs and services. We describe the collaboration of seven CTSA hubs with city, county, and state healthcare and public health organizations striving to realize this vision together. Partnership representatives convened monthly to identify key components, common and unique themes, and barriers in academic–public collaborations. All partnerships aligned the activities of the CTSA programs with the needs of the city/county/state partners, by sharing resources, responding to real-time policy questions and training needs, promoting best practices, and advancing community-engaged research, and dissemination and implementation science to narrow the knowledge-to-practice gap. Barriers included competing priorities, differing timelines, bureaucratic hurdles, and unstable funding. Academic–public health/health system partnerships represent a unique and underutilized model with potential to enhance community and population health.