Search Results (209)

This review explores the variety of diamond-based sensing applications, emphasizing their material properties, such as high Young’s modulus, thermal conductivity, wide bandgap, chemical stability, and radiation hardness. These diamond properties give excellent performance in mechanical, pressure, thermal, magnetic, optoelectronic, radiation, biosensing, quantum, and other applications. In vibration sensing, nano/poly/single-crystal diamond resonators operate from MHz to GHz frequencies, with high quality factor via CVD growth, diamond-on-insulator techniques, and ICP etching. Pressure sensing uses boron-doped piezoresistive, as well as capacitive and Fabry–Pérot readouts. Thermal sensing merges NV nanothermometry, single-crystal resonant thermometers, and resistive/diode sensors. Magnetic detection offers FeGa/Ti/diamond heterostructures, complementing NV. Optoelectronic applications utilize DUV photodiodes and color centers. Radiation detectors benefit from diamond’s neutron conversion capability. Biosensing leverages boron-doped diamond and hydrogen-terminated SGFETs, as well as gas targets such as NO₂/NH₃/H₂ via surface transfer doping and Pd Schottky/MIS. Imaging uses AFM/NV probes and boron-doped diamond tips. Persistent challenges, such as grain boundary losses in nanocrystalline diamond, limited diamond-on-insulator bonding yield, high temperature interface degradation, humidity-dependent gas transduction, stabilization of hydrogen termination, near-surface nitrogen-vacancy noise, and the cost of high-quality single-crystal diamond, are being addressed through interface and surface chemistry control, catalytic/dielectric stack engineering, photonic integration, and scalable chemical vapor deposition routes. These advances are enabling integrated, high-reliability diamond sensors for extreme and quantum-enhanced applications. Full article

Sluggish oxygen reduction reaction (ORR) remains a critical barrier to advancing intermediate-temperature electrochemical energy devices. Here, we demonstrate that strain engineering in two platforms, epitaxial thin films and freestanding membranes, systematically tunes ORR kinetics in Ruddlesden-Popper LaSrCoO₄. In epitaxial films, film thickness is varied to control in-plane tensile strain, whereas in freestanding membranes strain relaxation during the release step using water-soluble sacrificial layers produces flat or wrinkled architectures. Electrochemical impedance spectroscopy analysis reveals more than an order of magnitude increase in the oxygen surface exchange coefficient for tensile-strained films relative to relaxed films, together with a larger oxygen vacancy concentration. Wrinkled freestanding membranes provide a further increase in oxygen surface exchange kinetics and a lower activation energy, which are attributed to increased active surface area and local strain variation. These results identify epitaxial tensile strain and controlled wrinkling as practical design parameters for optimizing ORR activity in Ruddlesden-Popper oxides. Full article

We report a defect-selective luminescence response in calcium-deficient hydroxyapatite (HAp) induced by electron and ion irradiation. Compacted HAp pellets prepared from hydrothermally grown nanofibers were investigated to analyze defect-related luminescence using photoluminescence (PL) and cathodoluminescence (CL) techniques, both before and after compaction. Low-energy electron beam irradiation (15 keV) produced a two-stage luminescent response, an initial enhancement arising from field-assisted activation of OH-channel vacancies (V_OH and V_OH + H_i), followed by an exponential decay attributed to defect annealing. Monochromatic transient CL measurements show that this rise–decay behavior is selective to the OH-related bands at 2.57 and 2.95 eV, whereas the 3.32 and 3.67 eV emissions exhibit only a monotonic exponential decay. The corresponding decay constants further indicate that the activated OH-channel vacancies anneal more rapidly than the other centers, consistent with their higher electron-capture probability and lower structural stability. In contrast, ${\mathrm{Ga}}^{+}$ ion irradiation (30 keV, 1.4 × 10⁻¹³ A/µm²) induced progressive monotonic luminescence quenching, primarily driven by selective annealing of oxygen vacancies in $\mathrm{P}{\mathrm{O}}_4^{3-}$ groups. These complementary pathways, electron-induced activation and ion-driven suppression, demonstrate that irradiation serves as a versatile tool for defect engineering in hydroxyapatite. Beyond providing fundamental insights into vacancy stability, these results open new routes for tailoring the optical, sensing, and bioimaging functionalities of HAp through controlled irradiation. Full article

Electrochemical CO₂ reduction (CO₂RR) is a promising route to transform a major greenhouse gas into value-added fuels and chemicals. However, its deployment is still hindered by the sluggish activation of CO₂, poor selectivity toward multielectron products, and competition with the hydrogen evolution reaction (HER). Single-atom catalysts (SACs) have emerged as powerful materials to address these challenges because they combine maximal metal utilization with well-defined coordination environments whose electronic structure can be precisely tuned through metal–support interactions. This minireview summarizes current understanding of how structural, electronic, and chemical features of SAC supports (e.g., porosity, heteroatom doping, vacancies, and surface functionalization) govern the adsorption and conversion of key CO₂RR intermediates and thus control product distributions from CO to CH₄, CH₃OH and C₂⁺ species. Particular emphasis is placed on selectivity descriptors (e.g., coordination number, d-band position, binding energies of *COOH and *OCHO) and on rational design strategies that exploit curvature, microenvironment engineering, and electronic metal–support interactions to direct the reaction along desired pathways. Representative SAC systems based primarily on N-doped carbons, complemented by selected examples on oxides and MXenes are discussed in terms of Faradaic efficiency (FE), current density and operational stability under practically relevant conditions. Finally, the review highlights remaining bottlenecks and outlines future directions, including operando spectroscopy and data-driven analysis of dynamic single-site ensembles, machine-learning-assisted DFT screening, scalable mechanochemical synthesis, and integration of SACs into industrially viable electrolyzers for carbon-neutral chemical production. Full article

Ga₂O₃ and In₂O₃ are vital semiconductors with current and future electronic device applications. Here, we study the alloying of In₂O₃ and Ga₂O₃ (IGO) and the associated changes in structure, morphology, band gap, and electrical transport properties. Undoped films of IGO were deposited on sapphire substrates with varying indium (In) percentage from zero to 100% by metal-organic chemical vapor deposition (MOCVD). Some films were annealed in H₂ to induce electrical conductivity. The measurements showed the optical band gap decreased by adding In; this was confirmed by density functional (DFT) calculations, which revealed that the nature of the valence band maximum and conduction band minimum strongly relate to the chemistry and that the band gap drops by adding In. The as-grown films were highly resistive except for pure In₂O₃, which possesses p-type conductivity, likely arising from In vacancy-related acceptor states. N-type conductivity was induced in all films after H-anneal. DFT calculations revealed that the presence of In decreases the electron effective mass, which is consistent with the electrical transport measurements that showed higher electron mobility for higher In percentage. The work revealed the successful band gap engineering of IGO and the modification of its band structure while maintaining high-quality films by MOCVD. Full article

ABO₃ perovskite oxides are a versatile class of materials whose surfaces and interfaces play essential roles in sustainable energy technologies, including catalysis, solid oxide fuel and electrolysis cells, thermoelectrics, and energy-relevant oxide electronics. The interplay between point defects and surface reconstructions strongly affects interfacial stability, charge transport, and catalytic activity under operating conditions. This review summarizes recent progress in understanding how oxygen vacancies, cation nonstoichiometry, and electronic defects couple to atomic-scale surface rearrangements in representative perovskite systems. We first revisit Tasker’s classification of ionic surfaces and clarify how defect chemistry provides compensation mechanisms that stabilize otherwise polar or metastable terminations. We then discuss experimental and theoretical insights into defect-mediated reconstructions on perovskite surfaces and how they influence the performance of energy conversion devices. Finally, we conclude with a perspective on design strategies that leverage defect engineering and surface control to enhance functionality in energy applications, aiming to connect fundamental surface science with practical materials solutions for the transition to sustainable energy. Full article

Defect engineering in semiconductor heterojunctions offers a promising route for enhancing the selectivity of photocatalytic CO₂ conversion. In this work, a ZnS/gel-derived TiO₂ photocatalyst featuring sulfur vacancies introduced via hydrazine hydrate (N₂H₄) treatment is developed. XRD, HRTEM, and XPS analyses confirm the formation of a crystalline heterointerface and a defect-rich ZnS surface, enabling effective interfacial electronic modulation. The optimized ZnS/gel-derived TiO₂-0.48 composite achieves CH₄ and CO yields of 6.76 and 14.47 μmol·g⁻¹·h⁻¹, respectively, with a CH₄ selectivity of 31.8% and an electron selectivity of 65.1%, clearly outperforming pristine TiO₂ and the corresponding single-component catalysts under identical conditions. Photoluminescence quenching, enhanced photocurrent response, and reduced charge-transfer resistance indicate significantly improved interfacial charge separation. Mott–Schottky analysis combined with optical bandgap measurements reveals pronounced interfacial charge redistribution in the composite system. Considering the intrinsic band structure of ZnS and gel-derived TiO₂, a Z-scheme-compatible interfacial charge migration model is proposed, in which photogenerated electrons with strong reductive power are preferentially retained on ZnS, while holes with strong oxidative capability remain on gel-derived TiO₂. This charge migration pathway preserves high redox potentials, facilitating multi-electron CO₂ methanation and water oxidation. Density functional theory calculations further demonstrate that sulfur vacancies stabilize *COOH and *CO intermediates and reduce the energy barrier for *COOH formation from +0.51 eV to +0.21 eV, thereby promoting CO₂ activation and CH₄ formation. These results reveal that sulfur vacancies not only activate CO₂ molecules but also regulate interfacial charge migration behavior. This work provides a synergistic strategy combining defect engineering and interfacial electronic modulation to enhance selectivity and mechanistic understanding in CO₂-to-CH₄ photoconversion. Full article

Defect engineering has been demonstrated to be an attractive strategy to improve the catalytic performance of g−C₃N₄−based catalysts. Herein, three graphite carbon nitrides (labeled “CN”) containing a certain number of cyano groups and nitrogen vacancies are prepared successfully by calcination of the dicyandiamide−based CN in the presence of KOH, and the performances of the corresponding Pd−based catalysts are evaluated by using the formic acid (FA) dehydrogenation as a probe reaction. The characterizations of X−ray diffraction (XRD), scanning transmission electron microscopy (STEM), X−ray photoelectron spectra (XPS), hydrogen temperature−programmed desorption (H₂−TPD), and hydrogen spillover experiments indicate that the high catalytic activity of Pd/CNK−0.5 is mainly attributed to its high efficient hydrogen spillover, relatively high dispersity of Pd species, and basicity due to the introduction of a proper amount of cyano groups and nitrogen vacancies. The low initial activity of Pd/CNK−0.75 may mainly be ascribed to its low hydrogen spillover ability and the strongly chemisorbed hydrogen on Pd single atoms or small clusters. Full article

A deterministic platform for engineering epitaxial strain in CaMnO_3-δ (CMO) thermoelectric thin films is demonstrated using pulsed laser deposition, enabling precise control of the interplay between strain state and oxygen vacancy formation. High-quality epitaxial CMO films are grown on four different single crystalline substrates, which impose fully relaxed, partially relaxed, low tensile, and high tensile strain states, respectively. Increasing tensile strain induces a monotonic expansion of the unit cell volume and a systematic rise in oxygen vacancy concentration. Oxygen vacancies increase carrier concentration but decrease mobility due to enhanced scattering. Reducing tensile strain suppresses scattering of electrons by oxygen vacancies and increases both electrical conductivity (σ) and the Seebeck coefficient (S), mitigating the conventional inverse relationship between S and σ. Fully relaxed films exhibit σ approximately four orders of magnitude higher at room temperature than highly tensile strained films. These relaxed films also show the highest power factor (PF = S²·σ), exceeding strained films by up to six orders of magnitude. Strain-controlled oxygen vacancies thus provide a direct route to optimize charge transport and maximize the thermoelectric performance of CMO thin films. Full article

Methanol fuel engines can effectively reduce emissions of carbon monoxide and particulate matter, but they cause a substantial increase in emissions of unregulated pollutants like methanol and formaldehyde. In this study, Ag/CeO₂ catalysts were prepared from metal–organic framework (MOF) and silver acetate precursors using different methods and applied to the deep oxidation of methanol. The influence of preparation conditions on the types of active oxygen, surface chemical state, and oxygen vacancies was revealed by changing the calcination conditions and compared with the Ag/CeO₂ catalyst prepared by traditional methods. At the same time, the low-temperature reaction pathway of methanol was explored. The results showed that calcination conditions greatly affected the structure of the catalyst. Among them, Ag/CeO₂-A500 obtained by calcining Ag/Ce BTC in air at 500 °C had the best catalytic performance for methanol oxidation. The surface chemical state, overall oxygen vacancies, and the proportion of metallic silver may be key factors for its superior catalytic performance. Full article

The development of highly efficient and stable non-noble metal catalysts for volatile organic compound (VOCs) abatement remains a pressing challenge. Mn-based perovskites exhibit superior thermal stability as redox catalysts but suffer from limited activity in light alkane combustion. This study systematically investigates the performance of SmMnO₃ (SMO) perovskite catalysts for propane oxidation through selective etching of Sm species. By precisely controlling the etching process, the removal of surface Sm exposes more active sites and significantly increases the specific surface area from 22.05 m²·g⁻¹ for pristine SMO to 66.15 m²·g⁻¹. SEM and N₂ adsorption–desorption analysis revealed that prolonged etching induces surface roughening and pore channel expansion. XPS and XANES measurements confirmed that an increased Mn⁴⁺/Mn³⁺ ratio enhances reactant adsorption and accessibility to active sites. The etched catalysts exhibited markedly improved activity for propane oxidation, achieving a ~50 °C reduction in light-off temperature compared to the raw SMO. This performance enhancement is attributed to the synergistic effects of enhanced oxygen mobility, elevated Mn⁴⁺ content, and abundant oxygen vacancies. Further characterization via Raman spectroscopy and H₂-TPR revealed weakened Jahn–Teller distortion and lower reduction temperatures, reflecting optimized Mn–O interactions and superior redox properties. Among the samples, SMO-20 demonstrated exceptional stability. Moreover, the SMO-20/cordierite monolithic catalyst maintained outstanding catalytic performance over 1000 h of operation. This work offers a facile and effective approach to engineer perovskite catalysts and provides new insights into structure–activity relationships in VOC oxidation. Full article

Efficient oxidation of refractory sulfides, such as dibenzothiophene (DBT) and its derivatives, provides a promising strategy to produce fuel oils with ultra-low sulfur content, or even completely sulfur-free. In this study, a series of non-stoichiometric molybdenum oxides (MoO_x) were synthesized via a facile procedure and employed as efficient catalysts. These catalysts can effectively oxidize DBT and its derivatives into insoluble sulfones, which subsequently precipitate from the oil phase, achieving efficient sulfur removal. In this system, molecular oxygen from air can be activated by the MoO_x catalysts with oxygen vacancies into superoxide radicals, which act as active oxygen species to efficiently oxidize refractory sulfides. Under atmospheric pressure at 120 °C, complete sulfur removal (100%) was achieved for both DBT and its derivatives, representing significantly milder conditions compared to conventional hydrodesulfurization. The aerobic oxidation system could be reused for up to 12 consecutive cycles without any significant decline in sulfur removal. And complete desulfurization (100%) was regained after a simple washing of the separated solid phase. Then, a possible reaction procedure was subsequently proposed to describe the desulfurization route. The remarkable catalytic performance, together with the facile synthesis strategy, indicates the potential of this approach for constructing other transition metal oxides used in various advanced aerobic oxidation reactions. Full article

Denitrification catalysts are essential for reducing NO_x emissions from combustion and protecting air quality. This study introduces and validates an Oxygen Vacancy Index (OVI) that quantifies redox-active vacancies and guides defect engineering in fly ash-derived catalysts. We apply a simple cascade strategy to tune defect types; procedural details are reported in Methods rather than in the abstract. The optimized catalyst shows an over-twofold increase in OVI compared with raw fly ash. Surface-related changes and point/line defects contribute comparably (≈one-third each) to the explained variance. OVI positively correlates with NO conversion, and the optimized material delivers high NO conversion at 400 °C. These results establish a quantitative process–structure–performance link. Looking ahead, the OVI framework can guide defect design in other waste-derived catalysts and support scale-up to monolith coatings and pilot-scale units. This OVI-guided route provides a simple, low-cost path to robust fly ash catalysts for industrial NO_x control. Full article

The practical application of vanadium-based cathode materials in aqueous zinc-ion batteries (AZIBs) is severely hindered by vanadium dissolution, low electronic conductivity, and sluggish reaction kinetics in aqueous electrolytes. In this work, a three-dimensional confined V₂O₅@ nitrogen-doped carbon (V₂O₅@NC) composite was rationally designed and constructed through a dual-regulation strategy combining oxygen-vacancy engineering and conductive network enhancement. In this architecture, the nitrogen-doped carbon framework provides a highly conductive network and robust structural support, while in situ carbonization induces the generation of oxygen vacancies within V₂O₅. These oxygen vacancies cause lattice distortion and expand the interlayer spacing, thereby accelerating Zn²⁺ diffusion and improving reaction kinetics. Benefiting from this synergistic effect, the V₂O₅@NC electrode exhibits an excellent specific capacity of 437 mAh g⁻¹ at 0.1 A g⁻¹ and maintains a remarkable 89.3% capacity retention after 2000 cycles at 3 A g⁻¹, demonstrating outstanding rate performance and cycling stability. This study provides new insights and an effective design strategy for developing high-performance cathode materials for next-generation aqueous zinc-ion batteries. Full article

The morphology, structure, and composition of CVD-grown molybdenum disulfide (${\mathrm{MoS}}_2$) films were investigated under varying precursor vapor pressures. Increasing sulfur vapor pressure transformed the film morphology from well-defined triangular domains to structures dominated by sulfur-terminated zigzag edges. These morphological changes were accompanied by notable variations in both structural and electrical properties. Non-uniform precursor vapor distribution promoted the formation of intrinsic point defects. To elucidate this behavior, a thermodynamic model was developed to link growth parameters to native defect formation. The analysis considered molybdenum and sulfur vacancies in both neutral and charged states, with equilibrium concentrations determined from the corresponding defect formation reactions. Sulfur vapor pressure emerged as the dominant factor controlling defect concentrations. The model validated experimental observations, with films grown under optimum and sulfur-rich conditions, yielding a carrier concentration of $9.6\times {10}^{11}$ ${\mathrm{cm}}^{-2}$ and $7.5\times {10}^{11}$ ${\mathrm{cm}}^{-2}$, respectively. The major difference in the field-effect transistor (FET) performance of devices fabricated under these two conditions was the degradation of the field-effect mobility and the current switching ratio. The degradation observed is attributed to increased carrier scattering at charged vacancy defect sites. Full article