Stacked single-crystalline field-effect transistors
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Analyzing long-period structural evolution of biaxially stretched ultra-high molecular weight polyethylene films
Ultra-high molecular weight polyethylene (UHMWPE) films are widely used in high-performance applications due to their excellent mechanical properties. However, understanding the structural evolution, particularly the long-period structure under tensile fields, remains a challenge in both practical use and processing. Here, we investigate the long-period structural evolution of biaxially stretched UHMWPE films under tensile fields using time-resolved small-angle X-ray scattering. Our results reveal distinct changes in the long-period structure during the stretching process. Initially, the isotropic crystalline regions of UHMWPE align along the stretching direction, transitioning from a diffuse scattering pattern to an ellipsoidal one. As stretching progresses, fibrillar crystals form, dominating the scattering pattern with sharp, oriented features. In the later stages, fragmentation of the fibrillar structure leads to smaller crystalline regions and a butterfly-shaped scattering pattern due to rearranged lamellar structures. Based on these findings, we propose a new model that suggests a reverse transformation from fibrillar crystals to lamellar crystals, contrasting with the traditional “shish-kebab” model. The reduced crystallinity, as shown by differential scanning calorimetry data, further supports this structural transformation.
Switching on and off the spin polarization of the conduction band in antiferromagnetic bilayer transistors
Antiferromagnetic conductors with suitably broken spatial symmetries host spin-polarized bands, which lead to transport phenomena commonly observed in metallic ferromagnets. In bulk materials, it is the given crystalline structure that determines whether symmetries are broken and spin-polarized bands are present. Here we show that, in the two-dimensional limit, an electric field can control the relevant symmetries. To this end, we fabricate a double-gate transistor based on bilayers of van der Waals antiferromagnetic semiconductor CrPS4 and show how a perpendicular electric displacement field can switch the spin polarization of the conduction band on and off. Because conduction band states with opposite spin polarizations are hosted in the different layers and are spatially separated, these devices also give control over the magnetization of the electrons that are accumulated electrostatically. Our experiments show that double-gated CrPS4 transistors provide a viable platform to create gate-induced conductors with near unity spin polarization at the Fermi level, as well as devices with a full electrostatic control of the total magnetization of the system.
Array of micro-epidermal actuators for noninvasive pediatric flexible conductive hearing aids
Corrective surgeries and implantable aids are highly invasive for pediatric patients with conductive hearing loss. Flexible hearing aids are a noninvasive solution to address pediatric hearing loss. These aids generate vibrations on epidermal layer of skin behind the ear using micro-epidermal actuators to bypass the auditory canal. However, the major challenge is to generate a strong level of vibrations that can reach cochlea. Here, we designed, fabricated, and characterized arrays of micro-epidermal actuators to increase the vibration level from the flexible aids, improve frequency response and control the directionality of vibrations. Our human subject study showed that the flexible hearing aid with an array of actuators improved the hearing threshold by an average of 13.8 dB at 500 Hz, compared to a device with a single actuator. Also, the flexible aid with two actuators enhanced the hearing threshold by 30.5 dB at 1 kHz and 20.5 dB across 0.25–8 kHz versus unaided hearing.
Development of accessible and scalable maize pollen storage technology
The inherent short lifespan of Zea mays (maize, corn) pollen hinders crop improvement and challenges the hybrid seed production required to produce food, fuel, and feed. Decades of scientific effort on maize pollen storage technology have been unable to deliver a widely accessible protocol that works for liters of pollen at a hybrid seed production scale. Here we show how suppressing the pollen cellular respiration rate through refrigeration and optimizing gas exchange within the storage environment are the critical combination of factors for maintaining pollen viability in storage. The common practice of preserving maize pollen by mixing the pollen with talcum powder is critically examined using pollen tube germination testing, electron microscopy of pollen-silk (stigma) interaction, and test pollinations in production environments. These techniques lead to mixing maize pollen collected for storage with anti-clumping carrier compounds, including microcrystalline cellulose. These carriers improve stored pollen flowability during pollination and enable increased seed sets to be obtained from stored pollen. Field testing in maize seed production demonstrates that a wide range of pollen volumes can be stored for up to seven days using low-cost, globally available materials and that stored pollen can achieve seed-set equivalency to fresh pollen.
Discovery of giant unit-cell super-structure in the infinite-layer nickelate PrNiO2+x
The discovery of unconventional superconductivity often triggers significant interest in associated electronic and structural symmetry breaking phenomena. For the infinite-layer nickelates, structural allotropes are investigated intensively. Here, using high-energy grazing-incidence x-ray diffraction, we demonstrate how in-situ temperature annealing of the infinite-layer nickelate PrNiO2+x (x ≈ 0) induces a giant superlattice structure. The annealing effect has a maximum well above room temperature. By covering a large scattering volume, we show a rare period-six in-plane (bi-axial) symmetry and a period-four symmetry in the out-of-plane direction. This giant unit-cell superstructure—likely stemming from ordering of diffusive oxygen—persists over a large temperature range and can be quenched. As such, the stability and controlled annealing process leading to the formation of this superlattice structure provides a pathway for novel nickelate chemistry.
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