Physics

Abstract In-situ electrochemical spectroscopic ellipsometry (EC-SE) can enable real-time monitoring of optical properties and thickness changes of surfaces and thin films. This method can provide a broad range of information on the evolution of the microenvironment of an electrode during electrochemical reactions. However, to avoid modeling artifacts, accurate data analysis is critical. Here, we outline key steps in data analysis that can help prevent overfitting and misinterpretation of results. For example, determining the refractive index of the electrolyte at the air/electrolyte interface, along with measurements of the electrode’s dielectric data in dry conditions, can yield more accurate results than simultaneous fitting of all parameters for the electrolyte and electrode. We also present detailed modeling strategies tailored to fitting in-situ cyclic voltammetry (CV) data on various types of thin films, by providing two distinct examples: the thickness change of catalyst polymer films due to swelling by the electrolyte, and the simultaneous change in thickness and optical properties of Ti3C2Tx MXene films due to both reversible (electrochromic effect) and irreversible (degradation) processes. These details can help guide the informed selection of models in similar conditions by providing practical guidelines. The step-by-step approach to modeling can be more broadly adopted to enhance the accuracy and reproducibility of EC-SE experiments for interfacial studies relevant to energy conversion and storage, as well as other electrochemical reactions.

Abstract The inherent flexibility and processability of polymers make them indispensable for next-generation flexible electronics, yet their intrinsic electrical properties remain critical bottlenecks. A powerful workaround lies in hybrid materials that challenge this bottleneck by merging organic and inorganic components to unlock unprecedented functionalities through synergies. Beyond composition, area-selective functionalization is equally critical to the practical construction of electronic devices. Here, we demonstrate infiltration of ZnO into a lithographically patterned poly(ethylene terephthalate) (PET) matrix, locally transferring the pattern to the polymer subsurface. Following our approach of area-selective vapor-phase infiltration (AS-VPI), both the region and the depth of infiltration become controllable, even to the micrometer scale. With linear patterns, we demonstrate anisotropic electrical conductivity, showing a difference in resistance of more than 7 orders of magnitude between directions parallel and perpendicular to the infiltrated pattern. The benefit of using VPI to embed ZnO within the polymeric matrix rather than simply coating the surface is demonstrated by the preservation of electrical resistance after bending and deliberate scratching of the sample, as conductive pathways in the subsurface maintain current flow. AS-VPI is therefore demonstrated as an effective strategy for producing electrically functionalized polymers suitable for the design of flexible and wearable electronic devices.

Abstract Hexagonal boron nitride (hBN) is a van der Waals material with excellent insulating properties that make it well-suited as a gate dielectric in 2D electronic devices. In recent years, the discovery of an ever-increasing list of properties has led to a much broader range of potential applications, including quantum photonics, memristive devices, and extreme-environment coatings. However, current growth methods for hBN films are characterized by a narrow selection of substrates and high temperatures that require transfer and limit scale-up. Here, we report a remote plasma-activated approach to directly synthesize large-area hBN films on a diverse range of representative metallic, semiconducting, and amorphous insulating substrates. Specifically, we employ the spatial afterglow of an Ar/H2 plasma to activate ammonia borane, which enables the growth of thick (>30 nm), uniform, and stoichiometric films on substrates such as Si, SiO2, glass, fused silica, Mo, and Al. Systematic spectroscopic characterization reveals that hBN films can be grown as low as 300 °C. Furthermore, plasma afterglow-grown hBN films exhibit mechanical, electrical, and thermal properties on par with or exceeding those reported by alternate synthesis methods. These results establish plasma afterglow growth for the direct integration of hBN into a wide range of emerging technologies.

Abstract Reversible and wavelength-selective luminescence modulation is essential for advanced optical encryption, anticounterfeiting, and adaptive photonic devices. However, conventional photochromism-induced luminescence regulation is usually governed by a reabsorption effect, leading to nonselective intensity modulation. Herein, PbWO4:Yb3+/Er3+ inverse opal photonic crystals were fabricated through a template-assisted stepwise infiltration strategy, in which W- and Pb-containing precursor sols were sequentially introduced to avoid precipitation and ensure the formation of ordered photonic architectures. The obtained PbWO4:Yb3+/Er3+ inverse opals exhibit tunable photonic stop-bands and distinct structural colors. By matching the photonic bandgap with Er3+ emission bands, wavelength-selective inhibition and band-edge-enhanced upconversion luminescence were achieved, enabling the regulation of the red-to-green emission ratio. X-ray-induced photochromism originates from the synergistic effect of oxygen vacancy-related color center formation and polaron hopping associated with W6+/W5+ mixed-valence states, providing a reversible route for overall emission intensity modulation. Benefiting from the structural-color masking effect and coloration-induced upconversion luminescence modulation, concealed information writing and 980 nm laser-readable optical patterns were demonstrated. This work provides an effective strategy for integrating photonic bandgap engineering with photochromism toward upconversion luminescence modulation and advanced optical anticounterfeiting applications.

Abstract Developing high-performance cathode materials is crucial for advancing grid-scale sodium-ion batteries (SIBs). Here, we introduce a P2-type layered oxide cathode material, Na0·67Ni0·33Mn0·51Ru0·16O2, which demonstrates exceptional electrochemical performance through a robust dual cationic–anionic redox mechanism. This material delivers a high discharge capacity of 175.6 mAh g−1 at an average voltage of 3.6 V and maintains remarkable cycling stability with ∼93% capacity retention after 1000 cycles. A key to this performance is the strategic Ru doping, which plays a pivotal role in electronically stabilizing the oxidized oxygen states. By mediating the reversible formation of oxygen holes and preventing oxygen undercoordination, the Ru dopant stabilizes the anionic redox process. Unlike Na-rich layered oxides, this ligand-to-metal charge-transfer mechanism effectively suppresses detrimental oxygen evolution and preserves the structural integrity of the layered Na-deficient P2-type framework. This design strategy enables a synergistic redox landscape, confirmed by ex situ and operando advanced characterizations and theoretical calculations such as Fukui functions, offering critical insights into the rational design of high-capacity cathode for next-generation SIBs.

Abstract The convergence of artificial intelligence and biomedicine is creating opportunities for smart sensing systems in precision medicine. Conventional sensors, however, remain dependent on external power sources. Short battery life, difficult replacement, and potential biological risks limit their use in implantable, wearable, and long-term monitoring applications. Self-powered smart sensing systems offer a promising alternative. These devices harvest ambient energy from mechanical, thermal, chemical, or biological sources and convert it directly into electricity. The result is an integrated sense-and-power unit. This paradigm provides a direction for next-generation medical devices. In this review, we summarized recent progress in the field by focusing on two key healthcare applications. The first is the ultrasensitive detection of biomarkers for early cancer diagnosis. The second is the construction of intelligent closed-loop wound management systems that combine real-time monitoring with precise treatment. We discussed the working mechanisms, core materials, and system architectures of these devices. We also identify current challenges and outline future research directions. We intend this review for a broad interdisciplinary audience, including researchers in materials science, electronic engineering, biomedical engineering, and clinical medicine who are working on self-powered sensing systems for healthcare.

Zinc oxide–titanium dioxide heterostructure phosphors doped with ytterbium and holmium ions were synthesized using a hydrothermal method. The structure, morphology, and upconversion luminescence properties of the prepared heterostructures were investigated. The mixed oxides of ZnO and TiO2 (anatase and rutile) were confirmed by x-ray diffraction. Electron microscopy revealed agglomerated spherical particles with nanoscale dimensions. Diffuse reflectance spectra exhibited several absorption bands at 453, 488, 540, and 647 nm. Optical absorption bands were associated with electronic transitions of holmium ions, and codoping increased the estimated optical bandgap energy. Under excitation at 980 nm, visible emission peaks at 545 and 661 nm were observed. The composition containing 0.1 mol. % holmium and 9 mol. % ytterbium showed the highest emission intensity and good luminescence stability, indicating potential for near infrared to visible light conversion applications. These results demonstrate that zinc oxide–titanium dioxide heterostructures doped with rare earth ions are promising materials for efficient near-infrared to visible light conversion.

This review on experimental magnetic properties of spin glasses is based on static and dynamic magnetic properties derived from low field SQUID magnetometry experiments combined with properties at higher magnetic fields collected from measurements using commercial SQUID and VSM magnetometers. We describe spin glass materials and results from experimental methods designed to probe and allow analysis of their magnetic properties. Important concepts derived from these studies include the relaxation time spectrum of spin glasses, their susceptibility cusp, critical slowing down, and lack of phase transition in a magnetic field; aging, chaos-overlap and memory; the influences of spin and spatial dimensionality; magnetic hysteresis and thermo- and isothermal remanent magnetization; re-entrant spin glasses and other glassy systems such as superspin glasses.

Strain engineering has emerged as a strategic approach for modulating the piezoelectric and ferroelectric properties of thin films. We investigated local piezoelectric properties in clamped and freestanding epitaxial BaTi O 3 films via piezoresponse force microscopy. The freestanding membrane exhibits a ∼ 300 % increase in the effective piezoelectric coefficient compared to the clamped films, driven by increased nonlinearity. Quantitative analysis reveals about fourfold increase in the nonlinearity parameter, originating from enhanced domain wall motion enabled by strain relaxation after removal of substrate-induced clamping. Our molecular dynamics simulations further support about threefold increase in domain-wall velocity in the freestanding film. Additionally, under optical excitation, the membrane exhibits a photoinduced enhancement of the piezoelectric response arising from coupled photostriction effect and light-driven domain wall motion. Density functional theory calculations reveal ∼ 2 % decrease in the out-of-plane lattice parameter of the freestanding membrane under optical excitation, consistent with the observed photoinduced deformation. However, the corresponding change in the clamped film ceases to exist. These results identify substrate clamping as a critical limitation to piezoelectric performance and establish freestanding ferroelectric membranes as promising platforms for low-power electromechanical and optoelectronic devices.