Intermediate multidomain state in single-crystalline Mn-doped BiFeO3 thin films during ferroelectric polarization switching.

A intermediate multidomain state and large crystallographic tilting of 1.78° for the (hh0)pc planes of a (001)pc-oriented single-domain Mn-doped BiFeO3 (BFMO) thin film were found when an electric field was applied along the [110]pc direction. The anomalous crystallographic tilting was caused by ferroelastic domain switching of the 109° domain switching. In addition, ferroelastic domain switching occurred via an intermediate multidomain state. To investigate these switching dynamics under an electric field, we used in situ fluorescent X-ray induced Kossel line pattern measurements with synchrotron radiation. In addition, in situ inverse X-ray fluorescence holography (XFH) experiments revealed that atomic displacement occurred under an applied electric field. We attributed the atomic displacement to crystallographic tilting induced by a converse piezoelectric effect. Our findings provide important insights for the design of piezoelectric and ferroelectric materials and devices.

Development of Cu2Se/Ag2(S,Se)-Based Monolithic Thermoelectric Generators for Low-Grade Waste Heat Energy Harvesting.

With the ongoing climate and energy crises, thermoelectric conversion has slowly emerged as a clean and reliable alternative energy source for small Internet of Things (IoT) devices. Commercially available thermoelectric generators (TEGs) are typically composed of expensive and toxic Bi2Te3-based thermoelectric materials and require complicated and energy-intensive device assembly processes. As an alternative solution, we have developed a Ag- and Cu-chalcogenide-based monolithic TEG using simple, quick, and low-energy-cost device fabrication processes for low-grade waste heat recovery for energy harvesting. We used ductile Ag2S0.55Se0.45 and overstoichiometric Cu2.075Se, both possessing excellent transport properties around room temperature, with a zT value of ∼0.5 at 300 K. By optimizing the device fabrication process, we were successfully able to assemble the monolithic TEGs without any significant Ag- or Cu-ion migration and obtained a dense and robust device. Strategic optimization of the device structure was able to reduce the electrical contact resistance of the device, which resulted in increased power output. A maximum power density of 0.68 mW/cm2 at a ΔT = 30 K was obtained, which is comparable to a similar Bi2Te3-based monolithic TEG. These results show the potential of chalcogenide-based monolithic TEG as a simple and low-cost alternative to Bi2Te3-based TEGs for energy harvesting applications.

Development of serial X-ray fluorescence holography for radiation-sensitive protein crystals.

X-ray fluorescence holography (XFH) is a powerful atomic resolution technique capable of directly imaging the local atomic structure around atoms of a target element within a material. Although it is theoretically possible to use XFH to study the local structures of metal clusters in large protein crystals, the experiment has proven difficult to perform, especially on radiation-sensitive proteins. Here, the development of serial X-ray fluorescence holography to allow the direct recording of hologram patterns before the onset of radiation damage is reported. By combining a 2D hybrid detector and the serial data collection used in serial protein crystallography, the X-ray fluorescence hologram can be directly recorded in a fraction of the measurement time needed for conventional XFH measurements. This approach was demonstrated by obtaining the Mn Kα hologram pattern from the protein crystal Photosystem II without any X-ray-induced reduction of the Mn clusters. Furthermore, a method to interpret the fluorescence patterns as real-space projections of the atoms surrounding the Mn emitters has been developed, where the surrounding atoms produce large dark dips along the emitter-scatterer bond directions. This new technique paves the way for future experiments on protein crystals that aim to clarify the local atomic structures of their functional metal clusters, and for other related XFH experiments such as valence-selective XFH or time-resolved XFH.

X-ray fluorescence holography of biological metal sites: Application to myoglobin.

X-ray fluorescence holography (XFH) is a relatively new technique capable of providing unique three-dimensional structural information around specific atoms that act as a light source in crystalline samples. So far, XFH has typically been applied to inorganic materials such as dopants in metals and semiconductors. Here, we investigate the possibility of using XFH to visualize the metal active site in sperm whale myoglobin (Mb), a monomeric oxygen storage heme protein. We demonstrate that the atomic images reconstructed from the hologram data of crystals of carbonmonoxy myoglobin (MbCO) are moderately consistent with the crystal structure, which is also determined in this study by X-ray crystallography in the near-atomic resolution, as well as simulation results. These results open up a new avenue for the application of XFH to local atomic and electronic structure imaging of metal-sites in biomolecules.

Enhanced Performance of Monolithic Chalcogenide Thermoelectric Modules for Energy Harvesting via Co-optimization of Experiment and Simulation.

With the development of application of wireless sensor nodes (WSNs), the need for energy harvesting is rapidly increasing. In this study, we designed and fabricated a robust monolithic thermoelectric generator (TEG) using a simple, low-energy, and low-cost device fabrication process. Our monolithic device consists of Ag2S0.2Se0.8 and Bi0.5Sb1.5Te3 as n-type and p-type legs, respectively, while the empty space between the legs was filled with highly dense, flexible, and thin Ag2S that serves as both an insulating spacer and a shock absorber, which potentially augments the robustness of preventing from damage from an external mechanical force. From the optimization of the device structure via finite element method (FEM) simulations, a three-pair device with dimensions of 12 mm × 10 mm × 10 mm was found to have a theoretical maximum power density of 8.2 mW cm-2 at a ΔT of 50 K. For considering this inevitable contact resistance, experimental measurement and FEM simulation were combined for quantifying the junction resistance; a power density of 2.1 mW cm-2 was established with the consideration of the contact resistance at the p-n junctions. Using these optimized structural parameters, a device was fabricated and was found to have a maximum power density of 2.02 mW cm-2 at a ΔT of 50 K, which is in good agreement with our simulations. The results from our monolithic TEG show that despite the simple, low-energy, and low-cost device fabrication process, the power generation is still comparable to other reported TEGs. It is worth mentioning that our design could be extended to other chalcogenide materials of appropriate temperature regions and/or better zT. Besides, the quantification of contact resistance also exhibited reference value for the enhancement of thermoelectric conversion application. These results provide a convenient, economic, and efficient strategy for waste energy harvesting close to room temperature, which can broaden the applications of waste heat harvesting.