Nano-Micro Letters最新文献

Optical switching of ferroelectric polarization is of interest for wireless and energy-efficient control of logic states. So far, this phenomenon has been widely demonstrated only in ferroelectric perovskites, while studies on other emerging ferroelectrics remain limited. In this regard, the paradigmatic example of a technologically relevant ferroelectric material is HfO₂. However, HfO₂ has a very wide bandgap, limiting light absorption. So far, the proposed strategies to enhance light absorption in HfO₂-based systems are detrimental to ferroelectric properties, i.e., bandgap lowering or on-purpose defect introduction, which reduce switchable polarization and increase the presence of leakage currents. Here, we show that good ferroelectric properties, i.e., sizeable polarization (up to 15 μC cm^-2), low leakage current (under 10^-6 A cm^-2), high endurance (up to 10⁸ cycles) and fast switching (< 50 ns), can be achieved in epitaxial Hf_0.5Zr_0.5O₂ films through an alternative strategy, BaTiO₃ capping. While ferroelectric properties are remarkable, we demonstrate that the presence of BaTiO₃ allows light absorption and the concomitant electric field generation, as supported by density functional theory calculations, which enables optical switching of polarization in Hf_0.5Zr_0.5O₂ under 405 nm illumination. It is observed that optical switching is more efficient in films with thicker BaTiO₃ capping layer. The high polarizability of BaTiO₃ contributes to minimizing degradation in the ferroelectric response of the system. The results presented here indicate that appropriate designs can be followed to obtain optical switching of polarization in ferroelectric HfO₂ while preserving main functional properties.

Aqueous zinc batteries are gaining attention as promising alternatives to Li-ion systems, owing to the increased need for safe and cost-effective energy storage. Aqueous Zn-halogen batteries are particularly important because of their low cost and the abundance of precursors. However, critical challenges, such as the shuttle effect, sluggish redox kinetics, and dendrite growth, impede their practical development. Metal-organic frameworks (MOFs) with high porosity, ease of functionalization, and stability offer a multifunctional approach to overcome these limitations. This review systematically examines the advancements in MOF-based Zn-halogen batteries, focusing on their roles in different components of the battery, including the cathode, anode, and separator. This review also highlights the key design strategies for MOF-based materials and then examines the structure-performance relationships through advanced characterization and computational insights. The remaining challenges and future directions are also outlined. Overall, this review provides a roadmap for developing advanced MOF-based Zn-halogen batteries that combine high energy density and long-term durability for next-generation energy storage applications.

Na₄Fe₃(PO₄)₂P₂O₇ (NFPP) is regarded as a prospective cathode for sodium-ion batteries (SIBs) because of its high structural stability and cost-effectiveness. However, its practical application is hindered by intrinsically low electronic conductivity. Herein, an unconventional electron transfer mechanism from Ni²⁺ to Fe³⁺ ions is unveiled in Ni-doped Na_4.3Fe₃(PO₄)₂P₂O₇ (NFPP-Ni) cathode, which facilitates electronic coupling within the Fe-O-Ni coordination unit and thereby effectively boosts electron transport. Moreover, the redox kinetics and reversibility of NFPP materials are predominantly governed by the degree of Fe-O covalency. The intermediate e_g occupancy of Fe²⁺, modulated by the presence of Ni²⁺, optimizes the overlap between Fe d and O p orbitals. The adjustment of Ni dopant strikes a balance between accelerating Na⁺ diffusion kinetics and mitigating lattice strain during cycling. As a result, the NFPP-Ni electrode displays impressive rate capacity (121.0 mAh g^-1 at 0.1C / 80.9 mAh g^-1 at 10C) and stable cyclability (89.1% capacity retention after 1000 cycles). More importantly, the relationship between Fe e_g orbital occupancy and Fe-O covalency in NFPP as modulated by various transition metal cations (Ni²⁺, Mn²⁺, Zn²⁺, Co²⁺ and Cu²⁺) with different electron configurations are systematically elucidated, thereby providing insights for the commercial development of sodium-ion batteries (SIBs). Tuning the e_g orbital occupancy of Fe in Na_4.3Fe₃(PO₄)₂P₂O₇ cathode can effectively optimize the spatial overlap between Fe d and O p orbitals with excellent rate capability for sodium-ion batteries. The e_g could be a significant descriptor for Fe-O covalency that describes a volcano curve as a function of e_g.

Organic optoelectronic devices demonstrate immense potential in flexible displays, wearable electronics, and artificial skin, needing precise light-field and morphology management strategies to further improve their opto-electric performance. Nanoimprint lithography (NIL) has emerged as a high-resolution, high-efficiency, and low-cost patterning technique that mechanically transferring micro/nanoscale patterns from a template to a substrate to significantly enhance the optoelectronic performance through the precise creation of advanced light-management structures, combined with additional solid-state stacking morphology. This review systematically summarizes recent advances in NIL technology for organic optoelectronics. It begins with an introduction to the fundamental principles, main process variants (thermal, ultraviolet, and electrochemical NIL), as well as key technical issues. Subsequently, through specific applications in organic light-emitting diodes, organic solar cells, and organic field-effect transistors, it highlights the exceptional capabilities of NIL to enhance device performance by controlling crystallization and creating functional micro/nanostructuring. Specific advantages include enabling high-efficiency light management to overcome efficiency bottlenecks, facilitating low-cost, high-throughput manufacturing for industrialization, full compatibility with flexible substrates for emerging applications, enabling multifunctional integration and novel device architectures, and tailoring material microstructures and properties advance fundamental research. Finally, we discuss the remaining challenges and future prospects of NIL in integrated organic optoelectronic systems.

Various metal oxide catalysts have been utilized to enhance the electrode reaction kinetics in vanadium redox flow battery (VRFB). However, the determining factor governing their catalysis is still insufficiently understood. Herein, selectively doping of Sr and Ce at La site of LaMnO₃ perovskite (LSMO and LCMO) was used to modulate chemical environments of Mn ion activity donors, thereby boosting vanadium redox reaction processes. Sr doping increases the valence state of Mn ions, making it easier for Mn ions to take an electron from the electrode and transfer it to V³⁺ ions, which lowers the reaction energy barrier of V³⁺/V²⁺ redox processes. Conversely, Ce doping decreases the Mn valence and increases the oxygen vacancies, boosting the charge transfer and mass transfer of VO²⁺/VO₂⁺ redox processes. Theoretical calculation further demonstrates that doping Sr and Ce enhances the vanadium ion's ability for charge transfer and adsorption. Compared with pristine VRFB, the VRFB with LSMO- and LCMO-modified anode and cathode, respectively, exhibits an excellent energy efficiency (EE) of 67% at a high current density of 300 mA cm^-2 and an increased EE of 15% at 150 mA cm^-2. This study is critical for promoting fundamental understanding and offering a design strategy for achieving superior-performance metal-based electrocatalysts in VRFB.