MXenes, an emerging class of two-dimensional transition-metal carbides, nitrides, and carbonitrides, have received increasing attention for electrochemical energy-storage owing to their abundant surface terminations and tunable surface chemistry. This article provides a comprehensive overview of recent advances in MXene surface chemistry engineering for energy-storage applications, with particular emphasis on understanding how surface chemistry regulates electrochemical processes. We first summarize major strategies for tailoring MXene surface chemistry, including in situ termination control during synthesis, post-synthetic inorganic modification, and organic surface functionalization. Subsequently, we discuss how engineered surface chemistry influences key materials properties, including interlayer spacing, ion adsorption and diffusion, charge transport, pseudocapacitive charge storage, electrical and ionic conductivity, wettability, and electrode–electrolyte interfacial reactions. The roles of surface-functionalized MXenes in regulating electrochemical performance in supercapacitors and various battery systems, including lithium-, sodium-, potassium-, and zinc-based batteries, are critically discussed. Finally, future perspectives are presented on rational surface chemistry design strategies to guide the development of MXene-based next-generation electrochemical energy-storage devices.
MXenes, a growing class of two-dimensional transition-metal carbides, nitrides, and carbonitrides, have become increasingly relevant in many fields, ranging from energy storage to biology and tribology, due to their excellent mechanical and surface properties. MXenes are synthesized by selective etching processes, resulting in surface terminations, usually –O, –OH, and –F, whose relative abundance depends on the etching procedure adopted. In this article, we examine the effect of MXenes’ surface terminations on their stability and tribological performance, with a particular emphasis on recent advances in the synthesis routes, allowing for better control over the terminations’ composition and uniformity. We then discuss the stability of MXenes under different conditions, such as in solution or within coatings, summarizing experimental evidence for oxidation and hydrolysis in air and aqueous media, focusing on how surface and edge passivation influences degradation pathways and long-term stability. Subsequently, we focus on tribological applications, exploring MXenes behavior under tribological conditions, for which contact pressure, shear, and local temperature can activate tribochemical reactions, promote termination redistribution, and drive the formation of protective tribofilms that can reduce wear of the substrate. Finally, we analyze how surface terminations affect lubricity by modifying interlayer interactions, adhesion, and shear strength. By reviewing the most relevant results and clearly addressing the existing knowledge gaps, this article aims at summarizing the key design principles and outlining the remaining challenges to develop MXene-based solid lubricants and lubricant additives.
This study proposes a vibration energy-harvesting system that integrates an acoustic black hole (ABH) structure, piezoelectric materials, and a nonlinear coupled-beam configuration. A double elastic steel sheet (DESS) model is developed to describe the interaction between a primary beam and an ABH beam connected through a position-adjustable elastic coupling. The ABH mechanism induces wave slowing and energy localization, providing a favorable region for converting localized mechanical deformation into electrical output. Both theoretical predictions and experimental measurements indicate that the coupling location plays an important role in governing energy transfer. Under the excitation condition investigated in this study, the highest voltage output among the tested locations is obtained when the coupling element is placed near the mid-span of the beam. To accelerate response prediction and parameter mapping, machine-learning surrogate models, including DNN, LSTM, and XGBoost, are trained using a dataset generated from nonlinear RK4 simulations. Among them, XGBoost provides the best balance between prediction accuracy and computational efficiency. The surrogate-assisted parameter map identifies a favorable coupling region that is consistent with the experimental trend. This work suggests that combining ABH-based structural design with physics-based simulation and data-driven surrogate modeling can support efficient design exploration of vibration energy-harvesting systems. This work introduces a materials-enabled design approach that integrates acoustic black hole (ABH) structures, piezoelectric energy harvesting, and machine-learning-assisted surrogate modeling. First, it shows that the performance of ABH-based energy-harvesting systems is influenced not only by geometric tapering and piezoelectric placement, but also by the coupling pathway between structural components. The use of a position-adjustable elastic coupling provides an additional design variable for controlling energy transfer from the primary structure to the ABH–PZT region. Second, this study demonstrates that data-driven surrogate models can be used to accelerate response prediction and parameter mapping in nonlinear coupled systems. Compared with repeated direct numerical simulations, the surrogate-assisted approach reduces computational effort while maintaining high prediction accuracy within the investigated design space. Finally, the combination of physics-based modeling, experimental comparison, and machine-learning surrogate modeling provides a design insight into how global vibration transfer and local ABH-induced energy localization jointly affect piezoelectric voltage output. The results indicate that, under the tested excitation condition, mid-span coupling is the most favorable configuration among the investigated locations. Overall, this work bridges structural dynamics, functional material placement, and data-driven modeling, offering a practical strategy for the design exploration of ABH-based piezoelectric energy-harvesting systems. Future extensions to frequency-dependent and multi-parameter design spaces will be needed to establish broader optimization guidelines for multifunctional energy-localization and energy-harvesting structures.
Transparent photovoltaics (TPVs) offer a promising pathway for integrating solar energy harvesting into windows, façades, greenhouses, and wearable electronics while preserving visible-light transmission. However, achieving a balance between power-conversion efficiency, transparency, color neutrality, and long-term stability remains a major challenge. This article critically examines the role of atomic layer deposition (ALD) as an enabling technology for addressing these limitations in organic, perovskite, dye-sensitized, silicon-based, and tandem transparent photovoltaic systems. Particular emphasis is placed on ALD-enabled transport layers, interface engineering, defect passivation, carrier-selective contacts, and encapsulation strategies. The mechanisms by which ALD suppresses interfacial recombination, improves band alignment, mitigates ion migration, and enhances environmental stability are critically discussed. The advantages and limitations of ALD are evaluated through comparative analysis with other thin-film deposition techniques, highlighting its suitability for ultrathin functional layers and interface engineering. Finally, remaining challenges related to cost, throughput, precursor development, and scalability are evaluated, together with emerging opportunities offered by plasma-enhanced, spatial, atmospheric-pressure, and roll-to-roll ALD for large-area TPVs commercialization.
Pair distribution function (PDF) analysis provides a quantitative framework for resolving short- and medium-range order in glasses. This article summarizes recent advances that extend PDF methods from bulk x-ray and neutron-diffraction methods to local electron microscopy-based characterization for metallic glasses. High-energy x-rays and neutrons offer robust structural averages, while electron-based approaches such as electron PDF (ePDF) enable nanoscale mapping of local order and heterogeneity in metallic glasses. Validated PDF techniques, supported by molecular dynamics simulations, allow direct correlation between real-space pair correlations and the underlying atomic configurations. In particular, ePDF mapping visualizes nanoscale variations in short-range order (SRO), interfacial amorphous phases, and deformation-induced structural changes. Machine learning-assisted analysis enhances the extraction of meaningful structural motifs from large ePDF data sets. Complementary three-dimensional (3D) imaging methods, including atomic electron tomography and ptychography, allow to reconstruct coordinate-resolved 3D atomic models, which can be directly compared with atomistic simulations and can be evaluated locally via PDF analysis. This article provides an overview over recent methodology advances and further introduces possibilities to link multiscale PDF-derived structural information with properties and functionality in metallic glasses. Pair distribution function (PDF) analysis to characterize short- and medium range order based on bulk X-ray and neutron diffraction, nanometer level resolved employing 4D scanning transmission electron microscopy (STEM) based electron PDF (ePDF) and by employing atomic electron tomography (AET).
Cancer remains one of the leading causes of death worldwide and requires new and targeted approaches for early detection and treatment. Covalent organic frameworks (COFs) are emerging as promising nanostructured materials for cancer applications. With remarkable properties such as tunable pore size and high specific surface area, chemical stability, and good biocompatibility, COFs can effectively encapsulate and release drugs, reducing drug toxicity while targeting tumor tissues. In this article, we overview recent breakthroughs in design and biomedical applications of COFs as smart drug carriers with a particular focus on their potential in cancer imaging and therapy. This manuscript also explores the potential of COFs to synergistically enhance the immune response and be coupled with emerging immunotherapy. Further research and translation of these materials offer exciting prospects for next-generation cancer theranostics.
This work reviews recent findings on the dynamics of metallic glasses, focusing on the relationship between mechanical relaxation and microscopic dynamics, the latter explored by means of coherent x-ray scattering experiments. We first summarize the fundamental features of the mechanical relaxation spectrum of metallic glasses, encompassing α relaxation as well as secondary processes (such as β and γ). We examine the specificities and limitations of various characterization methods, and we survey what we currently know about how the relaxation spectrum evolves during cooling—from the supercooled liquid through the glass transition—and during physical aging of the glass. Subsequently, we contrast these macroscopic results with the microscopic dynamics. While macroscopic and microscopic observations appear consistent in the SCL, a notable divergence emerges in the glass state, with the emergence of compressed nonexponential relaxation functions. We discuss the possible origins of these differences in view of recent microscopic observations.
Medium-range structure at a length scale between 0.5 and 3 nm strongly influences the properties and phase transformations of metallic glass alloys. Electron diffraction methods based on four-dimensional scanning transmission electron microscopy are well suited for characterizing such structure using nanodiffraction with beams matched in size to the length scale of interest. Structural characterization using techniques including fluctuation electron microscopy, Ångström-beam electron diffraction, and angular correlation mapping have revealed widespread competition between crystalline and noncrystalline order, structural motifs responsible for crystallization and glass formation, and length scales controlling plasticity. Time-resolved, in situ electron correlation microscopy has demonstrated spatially heterogeneous dynamics in supercooled liquids and glasses and has hinted at connections between structure and atomic motions. Continued advances in techniques, sources, and detectors offer prospects for more discoveries to come.
Developing strategies to control damage and protect vulnerable regions in engineering materials remains a major challenge. Biological materials provide a rich source of inspiration for damage-control based on interfaces, gradients, and hierarchical architectures, principles that have been widely explored also in bioinspired systems. In bone, a lightweight biological material, large canals accommodating delicate blood vessels are found within osteons. These canals are surrounded by a lamellar region and bordered by a thin interface, known to promote crack deflection. Inspired by this construction principle, we investigate whether a circular interlayer can control damage and protect a weak spot (hole) in synthetic systems. Using multimaterial three-dimensional printing, mechanical testing, and numerical simulations, we study how crack propagation is influenced by interlayer properties and crack trajectory. We show that cracks approaching the hole can be redirected either through trapping in a weak interlayer or deflection along a stronger interlayer, with the former being easier to achieve. These results confirm that simple architectural features can program damage pathways. They also provide a controlled model system to examine how interlayer-mediated crack paths may be exploited to protect vulnerable regions, thereby informing the design of damage-tolerant architectured materials. Controlling how material damage develops and propagates is a central challenge for improving the safety and durability of engineering structures. This work shows that damage pathways can be controlled using simple architectural features inspired by the osteons in cortical bone. A single circular interlayer can trap or deflect damage depending on its relative strength compared to the surrounding material, providing design principles for protecting vulnerable regions such as cavities or embedded channels. The results highlight how bioinspired construction principles enable tunable damage, while avoiding overdesigning. These findings are not limited to the model systems studied and prototyped here but are applicable to a broad class of additively manufactured multi-material structures. Local tuning of internal architecture and material contrast between different components shall provide a pathway toward damage-tolerant design, ultimately promoting more resilient and sustainable material systems.
In this article, we discuss the challenges in assessing dynamics and structural changes of metallic glasses as amorphous out-of-equilibrium materials by means of coherent x-ray scattering. We focus on the fundamental understanding of the x-ray photon correlation spectroscopy (XPCS) technique and on how such an experimental probe may facilitate a deeper quantitative understanding of the underlying structural fluctuations occurring within the amorphous solid. Furthermore, we present how atomistic simulations and simulated x-ray photon correlation spectroscopy experiments can guide the interpretation of experimentally measured data. We conclude with a broader perspective on how contemporary advances in modeling, detector technology, and high flux x‑ray sources are transforming the study of glassy dynamics, enabling access to wider time and length scales and thus offering new avenues to probe the broad relaxation spectrum and complex nonequilibrium relaxation processes characteristic of amorphous solids.
