Vacancies play a pivotal role in determining the physical and chemical properties of materials. Introducing vacancies into two-dimensional (2D) materials offers a promising strategy for developing high-performance electrode materials for electrochemical energy storage. Herein, a facile top-down strategy is employed to create V-based MXenes with tunable vacancy concentrations, achieved by designing the precursor (V1-xCrx)2AlC (x = 0.05, 0.1, 0.3) MAX phase and precisely controlling the etching process. Systematic investigations reveal that introducing a moderate concentration of Cr-induced vacancies significantly enhances both the capacitance and rate performance of V-based MXenes. Specifically, V1.9CTz achieves a capacitance of 760 F g-1, far exceeding the 420 F g-1 of vacancy-free V2CTz MXene. In contrast, an excessively high vacancy concentration leads to deteriorated electrochemical performance and compromised structural stability. This work illustrates that defect engineering is a powerful approach to tailor the electrochemical properties of MXenes, offering a framework for designing next-generation MXene-based energy storage systems.

Low-dimensional materials are critical for enabling next-generation applications that are central to addressing critical global challenges. Titanium dioxide (TiO2) nanostructures stand out because of their structural versatility and relevance to catalysis, energy conversion, and environmental remediation. Here, we employ a combination of advanced electron microscopy, spectroscopy, and first-principles theoretical calculations to investigate the structural and chemical properties of one- and two-dimensional lepidocrocite-type TiO2. Special emphasis is placed on the one-dimensional material, which exhibits anisotropic growth, extending exclusively along a single-crystallographic direction. Our analysis suggests that this unusual growth behavior can be attributed to light-element impurities, such as carbon, that are incorporated during bottom-up synthesis. The results extend the understanding of these unexplored low-dimensional TiO2 materials and offer fundamental insights into their structure and chemistry.

Acute respiratory infections are the most common cause of acute illness globally and have a severe impact on human health and productivity. There is robust evidence of airborne transmission of many respiratory viruses via direct or indirect contact with droplets and aerosol produced by infected individuals, and this transmission route becomes crucial in crowded indoor spaces. Heating, ventilating and air conditioning (HVAC) systems filters can reduce the concentration of virus-carrying droplets, but HVAC systems able to directly inactivate bacteria and viruses are highly desirable to preserve safe indoor air.The aim of the present work was to assess the antibacterial and antiviral properties of silver nanoclusters/silica or zirconia composite coatings deposited onto polymeric air filters against Staphylococcus epidermidis, Staphylococcus aureus and a panel of representative members of human respiratory viruses, such as human coronavirus OC43 (HCoV-OC43), human rhinovirus A1 (HRV-A1), influenza virus type A (IFVA-H3N2) and adenovirus type -5 (AdV-5) according to standard protocols ISO.Results evidenced that both coatings showed a significant antimicrobial and antiviral activity at variable extent and a good cytocompatibility on all the examined cell lines, demonstrating a broad-spectrum action against selected bacteria and respiratory viruses.

One-dimensional (1D) lepidocrocite titanium dioxide (TiO2) filaments are investigated with respect to their thermal and aqueous stability. Structural and phase evolution are examined by in situ heating in vacuum using (scanning) transmission electron microscopy combined with electron energy loss spectroscopy and under ambient conditions using Raman spectroscopy. The filaments retain their lepidocrocite structure up to ∼300 °C, above which localized sintering and amorphization occur at filament overlap junctions. With further heating, the amorphous regions crystallize into anatase TiO2, with Raman spectroscopy corroborating the onset of structural disorder. Long-term aqueous storage (>100 days) under ambient conditions induces transformation into flake-like anatase nanoparticles. This process is strongly suppressed under refrigerated storage, where no structural changes are observed over the same period. These results establish critical thermal and environmental stability thresholds that define operational advantages and limits for emerging applications of 1D lepidocrocite TiO2 filaments.

MXenes, two-dimensional transition-metal carbides and nitrides, are typically obtained from MAX phases, yet historical reports suggest a broader, largely unexplored chemical space. Here we combine machine-learning-assisted database mining with experiments to uncover overlooked multilayer (ml) MXenes. Screening of repositories reveals a "Treasure Chest" of 38 previously synthesized but unrecognized ml-MXene candidates. Guided by these findings, we rediscover five MXenes using a rapid, scalable self-propagating high-temperature synthesis that requires no sustained external heating and completes within minutes. Inspired by the identified chemistries, we further realize 11 previously unexplored rare-earth-based M2CT2 MXenes (M= Pr, Nd, Sm, Gd, Tb, Ho, and Tm). Experiments and theory reveal semiconducting behavior and diverse magnetic states across this family. Together, these results expand the MXene family and demonstrate a data-driven strategy for accelerating materials discovery through sustainable methods.

Understanding how electrochemically active sites are utilized under high-rate conditions remains a fundamental challenge for MXene-based energy storage systems. In particular, the dynamic interplay between proton transport and surface redox reactions, which governs the accessibility and effective utilization of active sites, is still poorly understood. Herein, we investigate the charge-storage mechanism of Ti3CNTx MXene in acidic electrolytes by systematically tuning surface terminations and structural features via thermal annealing. The optimized sample (annealing at 300 °C) delivers a high specific capacitance of 470 F g−1 at 2 A g−1 and maintains excellent rate capability. Comprehensive characterization reveals that annealing induces coupled modifications in surface chemistry (reduction of F terminations and increase in O groups), electronic structure (increased Ti valence state), and porosity (formation of mesoporous channels), collectively facilitating proton transport and surface redox kinetics. More importantly, we introduce the concept of dynamic saturation of active sites, defined as a rate-dependent steady-state condition in which the occupation of active sites is governed by a dynamic balance between proton insertion and extraction processes. In situ EQCM measurements, together with electrochemical analysis, demonstrate that the progressive activation of active sites during initial cycling evolves into a stable dynamic equilibrium, enabling efficient utilization of active sites even at high rates. This work provides a mechanistic framework linking structural evolution, proton transport, and redox kinetics in MXenes, offering new insights for the rational design of high-rate pseudocapacitive materials.

A new family of nanostructured ternary intermetallic compounds - named the ZIP phases - is introduced in this work. The ZIP phases exhibit dualistic atomic ordering, i.e., they form two structural variants: one with the fcc diamond cubic structure (space group Fd 3 ¯ $\bar 3$ m) and one with the hexagonal structure (space group P63/mmc). They are also characterized by metallic behavior, ionic bonding, and atomic zigzagging. Powder metallurgical routes involving pressure-assisted densification are adopted to demonstrate ZIP phase synthesis in the Nb-Si-Ni, Nb-Si-Co, Ta-Si-Ni, V-Si-Ni, and Nb-Si-Fe ternary systems. Crucially, reactive hot pressing is capable of producing high-purity ZIP phase materials after the judicious, elemental system-specific optimization of the processing route. Synthesis of phase-pure materials - demonstrated in the Nb-Si-Ni ternary system by the synthesis of quasi phase-pure Nb3SiNi2 and Ni3SiNb2 ZIP phase-based materials - is a steppingstone to the prospective exploitation of the ZIP phases. Characterization of Nb3SiNi2 and Ni3SiNb2 involves crystal structure determination, spatially resolved chemical analysis, and determination of select thermal, electrical, magnetic, mechanical, and physical properties. Density functional theory is used to assess the stability of Nb3SiNi2 & Ni3SiNb2 and derivative binary compounds at different temperatures, also exploring the exfoliation of these two ZIP phases along specific surfaces to produce 2D derivatives.

In situ polymerization of conductive polymers (CPs) represents a transformative approach in bioelectronics, by enabling the controlled growth of electrically active materials right at the tissue or device surface to create seamless biotic-abiotic interfaces. Traditional CP deposition techniques often use high anodic potentials, non-physiological electrolytes, or strong oxidants, making them harmful to adjacent tissues. A possible solution is enzymatic polymerization which operates under milder conditions, but it is limited by the stability and activity window of the enzyme catalysts, low throughput, and challenges in spatially confining polymer growth. To resolve these issues, here we developed one-dimensional porous Au-coated Ag nanowires with horseradish peroxidase (HRP)-like catalytic properties, thereby for the first time enabling mild in situ enzyme-free polymerization of conductive polymers near neutral pH. The enzyme-free polymerization is demonstrated both in aqueous dispersions at pH=6 and in situ onto porous Au coated Ag nanowire based stretchable electrodes. Following enzyme-free catalytic polymerization, the electrically conducting polymer coating on the electrode greatly improves the impedance and achieves an impedance of 2.6 kOhm at 1 kHz for 50x50 um large electrodes.

Herein, we report the synthesis of two-dimensional Ta2Se2C (2D-Ta2Se2C) nanosheets using electrochemical lithiation in multilayer Ta2Se2C followed by sonication in deionized water. Multilayer Ta2Se2C was obtained via solid-state synthesis of FexTa2Se2C followed by chemical etching of Fe. 2D-Ta2Se2C exhibited promising electrocatalytic activity for the hydrogen evolution reaction from water compared to multilayer Ta2Se2C and 2D-TaSe2. 2D-Ta2Se2C showed an overpotential at 10 mA·cm-2 (η10) of 264 mV, a Tafel slope of 91 mV·dec-1, and an electrochemically active surface area of 17.61 mECSA2·gcatalyst-1. The high performance could be attributed to the large surface area of single sheets which hence maximizes the number of exposed catalytic sites and increased density of vacancies, observed with transmission electron microscopy, during synthesis and processing.

We report on the formation of the Cr2C compound using chemical etching-free methodology to extract Al from a Cr2AlC MAX phase thin film. Cr2AlC/Cu assemblies were deposited on sapphire substrates, using magnetron sputtering, and were subsequently annealed in vacuum. The Al from the MAX phase was shown to diffuse into Cu resulting in the formation of Al4Cu9 and causing the MAX phase to collapse into Cr2C grains. These carbide grains were characterized by transmission electron microscopy and the interatomic distances extracted were in good agreement with ab initio calculations predicting the equilibrium volume of the Cr2C phase.

Defect engineering in the form of the intentional creation of defects has been shown to enhance the properties of two-dimensional materials in various applications. Herein, we systematically explore a simple and reproducible method for introducing random vacancies and pores in Mo-based MXenes by combining first-principles calculations and experiments. The process is based on alloying Mo2Ga2C with Cr, which is an element that, together with Ga, is selectively etched in hydrofluoric acid, resulting in vacancies and vacancy clusters in the MXene sheets. The limit of Cr incorporation on the metal site was found to be approximately 60 atom % in the precursor powder Mo2-x Cr x C. Lower concentrations, up to 25 atom %, were used in the subsequent synthesis of Mo2-x Cr x Ga2C, since an increasing Cr content promoted the formation of another MAX phase (Mo2-x Cr x GaC). A Mo1.87CT z MXene derived from Mo1.87Cr0.13Ga2C (6.5 atom % Cr) exhibited excellent electrochemical behavior, reaching a volumetric capacitance of 1117 Fcm-3 at 2 mVs-1 scan rate, and suggested that defect concentration can be used to tune the rate capability. Overall, we have demonstrated that using Cr as a sacrificial element in the MAX phase is a simple and effective strategy for the defect engineering of MXenes. Moreover, this method can likely be extended to include other sacrificial elements and MAX phases, making MXene defect engineering a viable pathway for property enhancement across various applications, including energy storage and catalysis.

The unique attributes of carbon nanotubes (CNTs) establish them as the preferred material for fabricating sophisticated membrane architectures. However, CNT membranes are also susceptible to degradation under harsh environmental conditions, necessitating protective measures to maintain their functionalities. This study presents deposition of boron carbide (B4C) thin films as protective coatings on CNT membranes using chemical vapor deposition. Electron microscopy shows that B4C films were uniformly deposited on the CNTs. Raman spectroscopy shows the preservation of the G and D bands, with a notable stability in the RBM bands, while XPS measurements show sp2 hybridized C-C bonds and an additional shoulder characteristic of the deposited B4C film. This suggests that the CVD process does not degrade the CNTs, but merely adds a layer of B4C to their outer surface. This deposition process also allows for precise control over the membrane's pore size, offering the potential to fine-tune the properties of CNT membranes.

The influence of heavy atom incorporation (in this case, tungsten, W) into scandium nitride is examined to assess its impact on the electronic structure and associated thermoelectric properties. Incorporating W, with its 5d valence electrons, is expected to shift the Fermi level into the conduction band. A solid solution of Sc1-xWxNy system is also expected to form as ScN exhibits the largest unit cell among the early 3d transition metal nitrides. However, phase separation is initiated at x = 0.10 and results in Sc- and W-rich regions occurring through conventional nucleation and growth. High-temperature nitrogen substoichiometry (at similar to 800 degrees C) and formation of secondary phase is governed by inducing N vacancies in the crystal system. The N/W ratio alters the occupancy of the nonbonding t(2g) states in the valence band and results in phase instability. The Sc1-xWxNy system is found to be less covalent than a ScN reference sample indicating the presence of ionic and metallic bonds as observed through spectroscopic studies. A unique combination of a metal-like Seebeck coefficient with increased electrical resistivity is found for the Sc1-xWxNy system compared to the ScN reference. This study aims to elucidate the structural, microstructural, and electronic properties of the Sc1-xWxNy system and establishing a correlation with thermoelectric properties, through a combined experimental and theoretical approach.

We report on the angle-resolved polarized Raman spectroscopy and estimation of the Raman tensor elements using both classical and quantum treatments to analyse the polarized Raman spectra of single crystal Bismuth Telluride. The observed polar patterns and systematic variations in the relative intensities of four characteristic Raman active modes indicate a higher differential polarizability along the c-axis, accompanied by anisotropic photon-phonon interactions. This interplay of electron-photon-phonon interactions is crucial for understanding the lattice dynamics of Bismuth Telluride, which underpin its thermoelectric performance and topological properties.

The sustainable utilization of natural resources and growing demand for various electronic devices have promoted the development of safe, stable, and rechargeable aqueous zinc-ion batteries (AZIBs). However, a stable cathode material is crucial for ZIBs in an aqueous electrolyte, since it is more difficult for divalent Zn2+ to be reversibly inserted and extracted between active materials than it is for monovalent metal ions. In this work, a tailored multi-defect MXene, Mo1.74CTz, of a complete chemical formula of Mo1.74±0.06CO0.95±0.02(OH)0.63±0.01F0.3±0.03.0.2±0.05H2Oads (Mo1.74CTz), is assembled as cathode in AZIBs. It achieved 75% capacity retention and nearly 100% Coulombic efficiency even after up to 100 000 cycles as the intrinsic structural stability and many vertical holes of the Mo1.74CTz MXene contributed to alleviating the MXene collapse under repeated charge and discharge. Meanwhile, the Mo1.74CTz-based AZIBs exhibited good performance with a specific capacity of 200 mAh g-1 at a current density of 0.2 A g-1, which greatly exceeds previous reports of pure MXene-based cathodes in AZIBs. This work will aid in finding new solutions for sustainable energy development, which will pave the way for AZIBs as an alternative to lithium-ion batteries (LIBs) in the future.

The present work investigates the growth, microstructure, and phase evolution of reactively sputtered Ta-N thin films deposited on Al2O3(0001) substrates with and without a Ta2O5 seed layer using complementary experimental techniques and theoretical calculations. X-ray diffraction (XRD) patterns reveal that without a seed layer, the films predominantly consist of the (111)-oriented cubic delta-TaN phase. In contrast, Ta2O5 seed layers promote the formation of an orthorhombic Ta3N5 phase with preferred orientation along the c-axis. Scanning transmission electron microscopy (STEM) results show the presence of large epitaxial Ta3N5 domains. Thickness-dependent XRD patterns and STEM images, together with fast Fourier transform studies, reveal that the transformations from beta-Ta2O5 to a Ta-N mixed phase and finally to Ta3N5 take place during film growth. This observed phase transformation depicts that the seed layer serves not only as a structural template for the epitaxial growth of Ta3N5 but also as an active participant in the nitridation process during growth. Energy calculations suggest that the Ta-N species play a crucial role in stabilizing Ta3N5 growth. This work elucidates the complex interplay among seed layers, deposition conditions, and precursor energetics, offering a comprehensive understanding of Ta3N5 thin film epitaxial growth mechanisms.

Artificial superlattices exhibit exceptional electronic, magnetic, optical, and mechanical properties which make them unique candidates for applications in a broad range of technologies. A common key feature of superlattices is the need for atomically abrupt interfaces. However, superlattices comprised of materials with different properties, such as melting points and diffusivities, pose large challenges for achieving high crystal quality of both constituents with abrupt interfaces. By employing ion-assisted magnetron sputter epitaxy, we present an innovative solution to this problem with utilizing a unique combination of thermal radiation and kinetic energy that enable sufficient adatom mobility for epitaxial growth of both materials. The research was implemented for the case of CrB2/TiB2 heteroepitaxial superlattices, as neutron interference mirrors, wherein the constituents' melting points differ by 1100 K. Ion-induced intermixing was avoided by commencing growth of each TiB2 and CrB2 layer by up to 3 unit cells (uc) without ion assistance, forming a buffer to protect the interface during the ion-assisted growth of the remainder of each layer. Heteroepitaxial superlattice growth with interface widths sigma(CrB2) similar to 1 uc and sigma(TiB2) similar to 2 uc was confirmed for different modulation periods. More than 3000 uc (similar to 1 mu m) thick superlattices with abrupt interfaces were demonstrated for neutron mirror applications.

Two-dimensional MXenes are emerging as promising materials for electrocatalysts owing to their layered structure, metallic conductivity, and abundant catalytically active basal planes. However, achieving coordinated regulation of both reactivity and the number of active sites through modulation of surface groups remains challenging, which hinders further optimization of the electrocatalytic performance of MXene. Herein, sulfur-functionalized MXene with enhanced HER catalytic activity was achieved through a convenient one-step sulfurization strategy. During the sulfidation process, the surface fluorine atoms of MXene were partially replaced by sulfur atoms, providing enhanced electrocatalytic activity and high stability. The strategy was applied for various MXenes: Mo4/3C, W4/3C, and Nb1.33C, and particularly, S-Mo4/3C delivers a low overpotential, 210 mV for a current density of 10 mA cm-2, with a Tafel slope of 67 mV dec-1, and possesses excellent HER stability with negligible attenuation of the current density after 120 h. In situ Raman spectroscopy shows that sulfur atoms serve as active sites for the hydrogen evolution, confirmed by the appearance of a Raman peak at 2542 cm-1 which is ascribed to the S-H stretching vibration of Mo-S-H moieties. This work promotes further efforts in exploration of efficient catalysts within the large MXene materials family, as well as exploiting their potential toward more versatile applications.

i-MAX phases are quaternary variants of the nanolaminated MAX phases, with additional in-plane ordering of the M atoms. The combination of in-plane and out-of-plane ordering potentially gives rise to complex magnetic behaviour. The i-MAX phase (Mn2/3Sc1/3)2GaC has been synthesized in epitaxial thin film form on three different substrates, SiC-4H(001), MgO(111) and Al2O3(0001), by magnetron sputtering using elemental targets. Structural characterization by x-ray scattering and scanning transmission electron microscopy confirms the phase on all three substrates, although the highest crystal quality is obtained on SiC-4H(001). Highresolution images reveal the distinctive i-MAX structure, which is orthorhombic of space group Cmcm. Magnetic characterization reveals that the ground state is most likely antiferromagnetic. This confirms previous theoretical calculations which predicted an antiferromagnetic ground state and establishes the (Mn2/3Sc1/3)2GaC i-MAX phase as a potential candidate for antiferromagnetic spintronic applications.

We report on the angle-resolved polarized Raman spectroscopy and estimation of the Raman tensor elements using both classical and quantum treatments to analyze the polarized Raman spectra of single crystal Bi2Te3. The observed polar patterns and systematic variations in the relative intensities of four characteristic Raman-active modes indicate a higher differential polarizability along the c axis, accompanied by anisotropic photon-phonon interactions. This interplay of electron-photon-phonon interactions is crucial for understanding the lattice dynamics of Bi2Te3, which underpin its thermoelectric performance and topological properties.