Search for: All records

Today’s challenges with sustainability are driven by complexity, lack necessary information, resist straightforward solutions, span multiple scales, and encompass diverse or sometimes conflicting perspectives. To tackle these issues effectively, research organizations need tools that support and accelerate the integration of disciplinary knowledge across both natural and social sciences so that they can explore and execute workable solutions. Boundary objects are tools that can bring diverse perspectives together through a shared point of focus that is meaningful across different groups and perspectives, enhancing communication between them. Here, we introduce a framework to develop Triple Bottom Line Scenario Sites (TBL Sites) as “convergence” boundary objects and intervention testbeds to support a holistic approach to sustainability research within multidisciplinary and multi-institutional organizations. We describe four key criteria used to identify a potential TBL Site: (1) proximity to researchers, (2) a bounded geographic location encompassing a particular ecosystem, (3) an integrated stakeholder network, and (4) access to existing resources. We explain how TBL Sites may be used to assess research impacts on environmental, economic, and social sustainability goals. Finally, we provide examples of aquatic, agricultural, and urban TBL Sites used by the Science and Technologies for Phosphorus Sustainability (STEPS) Center, demonstrating how these boundary objects facilitate convergence across a large multidisciplinary research team to tackle sustainable phosphorus management. 

The solid-state synthesis of perovskite BiFeO3 has been a topic of interest for decades. Many studies have reported challenges in the synthesis of BiFeO3 from starting oxides of Bi2O3 and Fe2O3, mainly associated with the development of persistent secondary phases such as Bi25FeO39 (sillenite) and Bi2Fe4O9 (mullite). These secondary phases are thought to be a consequence of unreacted Fe-rich and Bi-rich regions, that is, incomplete interdiffusion. In the present work, in situ high-temperature X-ray diffraction is used to demonstrate that Bi2O3 first reacts with Fe2O3 to form sillenite Bi25FeO39, which then reacts with the remaining Fe2O3 to form BiFeO3. Therefore, the synthesis of perovskite BiFeO3 is shown to occur via a two-step reaction sequence with Bi25FeO39 as an intermediate compound. Because Bi25FeO39 and the γ-Bi2O3 phase are isostructural, it is difficult to discriminate them solely from X-ray diffraction. Evidence is presented for the existence of the intermediate sillenite Bi25FeO39 using quenching experiments, comparisons between Bi2O3 behavior by itself and in the presence of Fe2O3, and crystal structure examination. With this new information, a proposed reaction pathway from the starting oxides to the product is presented. 

Abstract The solid‐state synthesis of perovskite BiFeO₃has been a topic of interest for decades. Many studies have reported challenges in the synthesis of BiFeO₃from starting oxides of Bi₂O₃and Fe₂O₃, mainly associated with the development of persistent secondary phases such as Bi₂₅FeO₃₉(sillenite) and Bi₂Fe₄O₉(mullite). These secondary phases are thought to be a consequence of unreacted Fe‐rich and Bi‐rich regions, that is, incomplete interdiffusion. In the present work, in situ high‐temperature X‐ray diffraction is used to demonstrate that Bi₂O₃first reacts with Fe₂O₃to form sillenite Bi₂₅FeO₃₉, which then reacts with the remaining Fe₂O₃to form BiFeO₃. Therefore, the synthesis of perovskite BiFeO₃is shown to occur via a two‐step reaction sequence with Bi₂₅FeO₃₉as an intermediate compound. Because Bi₂₅FeO₃₉and the γ‐Bi₂O₃phase are isostructural, it is difficult to discriminate them solely from X‐ray diffraction. Evidence is presented for the existence of the intermediate sillenite Bi₂₅FeO₃₉using quenching experiments, comparisons between Bi₂O₃behavior by itself and in the presence of Fe₂O₃, and crystal structure examination. With this new information, a proposed reaction pathway from the starting oxides to the product is presented. 

The impact of the high-power impulse magnetron sputtering (HiPIMS) pulse width on the crystallization, microstructure, and ferroelectric properties of undoped HfO2 films is investigated. HfO2 films were sputtered from a hafnium metal target in an Ar/O2 atmosphere, varying the instantaneous power density by changing the HiPIMS pulse width with fixed time-averaged power and pulse frequency. The pulse width is shown to affect the ion-to-neutral ratio in the depositing species with the shortest pulse durations leading to the highest ion fraction. In situ x-ray diffraction measurements during crystallization demonstrate that the HiPIMS pulse width impacts nucleation and phase formation, with an intermediate pulse width of 110 μs stabilizing the ferroelectric phase over the widest temperature range. Although the pulse width impacts the grain size with the lowest pulse width resulting in the largest grain size, the grain size does not strongly correlate with the phase content or ferroelectric behavior in these films. These results suggest that precise control over the energetics of the depositing species may be beneficial for forming the ferroelectric phase in this material. 

Ferroelectric hafnium-zirconium oxide (HZO) is an excellent candidate for low-power non-volatile memory applications due to its demonstrated ferroelectricity at the nanoscale and compatibility with silicon-based technologies. The interface of HZO in contact with its electrode, typically TiN in a metal–ferroelectric–metal (MFM) capacitor configuration, is of particular interest because factors, such as volume confinement, impurity concentration, interfacial layers, thermal expansion mismatch, and defect trapping, are believed to play a crucial role in the ferroelectric performance of HZO-based devices. Processing variables, such as precursor type, oxygen source, dose duration, and deposition temperature, are known to strongly affect the quality of the oxide–metal interface. However, not many studies have focused on the effect of breaking or maintaining vacuum during MFM deposition. In this study, sequential, no-atmosphere processing (SNAP) is employed to avoid atmospheric exposure, where electrode TiN and ferroelectric HZO are deposited sequentially in the atomic layer deposition chamber without breaking vacuum. The effect of breaking vacuum during the sequential deposition steps is elucidated by fabricating and characterizing MFM capacitors with and without intentional vacuum breaks prior to the deposition of the HZO and top TiN. Using x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS), we reveal that breaking vacuum after bottom TiN electrode deposition leads to interfacial oxidation and increased carbon contamination, which preferentially stabilizes the non-ferroelectric tetragonal phase and lead to diminished remanent polarization. Avoiding carbon impurities and interfacial TiOx at the HZO and TiN interface using SNAP leads to heightened remanent polarization, reduced leakage current density, and elimination of the wake-up effect. Our work highlights the effect of vacuum breaking on the processing-structure-properties of HZO-based capacitors, revealing that maintaining vacuum can significantly improve ferroelectric properties.