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Vacancy-Driven Robust Metallicity of Structurally Pinned Monoclinic Epitaxial VO <sub/>2</sub> Thin Films
摘要： Vanadium dioxide (VO2) is a strongly-correlated material with 3d-electrons, which exhibits temperature-driven insulator-to-metal transition with a concurrent change in the crystal symmetry. Interestingly, even modest changes in stoichiometry-induced orbital occupancy dramatically affect the electrical conductivity of the system. Here, we report a successful transformation of epitaxial monoclinic VO2 thin films from a conventionally insulating to permanently metallic behavior by manipulating the electron-correlations. These ultrathin (~10 nm) epitaxial VO2 films were grown on NiO (111)/Al2O3 (0001) pseudomorphically, where the large misfit between NiO and Al2O3 were fully relaxed by domain matching epitaxy. Complete conversion from an insulator to permanent metallic phase is achieved through injecting oxygen vacancies (x~0.20±0.02) into the VO2-x system via annealing under high vacuum (~5x10-7 Torr) and elevated temperature (450 oC). Systematic introduction of oxygen vacancies partially converts V4+ to V3+ and generates unpaired electron charges which result in the emergence of donor states near Fermi level. Through the detailed study of the vibrational modes by Raman spectroscopy, hardening of the V-V vibrational modes and stabilization of V-V dimers are observed in vacuum-annealed VO2 films providing conclusive evidence for stabilization of monoclinic phase. This ultimately leads to convenient free-electron transport through the oxygen-deficient VO2-x thin films resulting in the metallic character at room temperature. With these results, we propose a defect engineering driven pathway through the control of oxygen vacancies to tune electrical and optical properties in epitaxial monoclinic VO2.
关键词： Defect engineering,Oxygen Vacancy,Metallicity,Mott transition,Metallic monoclinic VO2,Charge doping
更新于2025-09-23 15:23:52
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Bandgap Tuning of C3N monolayer: A First-Principles Study
摘要： The newly found graphene-like material C3N exhibits great potential in a variety of important applications, due to its unique topological and electronic structures. To extend the utilization, a crucial challenge is to make its intrinsic bandgap (1.03 eV) tunable. Here we performed first-principles calculations to investigate the band structure variations of C3N monolayer under various surface modification treatments, including defect engineering, surface decoration and substitutional doping. Results show that those treatments can induce impurity states, orbital rehybridization, and n- or p-type doping simultaneously, and therefore enable effective band structure adjustment. Importantly, some linear relationships between the bandgap and doping concentration are revealed, paving the way for precise control of C3N bandgap.
关键词： Bandgap tuning,substitutional doping,defect engineering,surface decoration,g-C3N
更新于2025-09-23 15:23:52
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Nanoscale Light Sources for Optical Interconnects
摘要： This editorial is aimed at addressing two key aspects of nanoscale light sources: (1) low-power optical communication and (2) crystallographic defect engineering for monolithic integration with silicon. We will further discuss opportunities and challenges for nanoscale light sources for next generation, high density optical interconnect. Designing and prototyping light sources with sub light wavelength dimensions has been the topic of keen interest because of their versatility in optical communication. For example, nano light sources can operate at hundreds of GHz [1,2] which is not possible with conventional light sources [3]. In addition, power consumption in interconnects with these light sources can be reduced by omitting the modulator and using direct source modulation to encode optical data [4]. There are a number of nano light sources under investigation: (i) small photonic mode laser [5-9], (ii) plasmonic lasers [10,11] (iii) photonic-plasmonic hybrid lasers [12-15] and (iv) nanoscale LEDs [16,17]. Pros and cons of these nano light sources are discussed below.
关键词： crystallographic defect engineering,optical interconnects,low-power optical communication,Nanoscale light sources,monolithic integration
更新于2025-09-23 15:21:01
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Engineering Point Defect States in Monolayer WSe <sub/>2</sub>
摘要： Defect engineering is a key approach for tailoring the properties of the emerging two-dimensional semiconductors. Here, we report an atomic engineering of the W vacancy in monolayer WSe2 by single potassium atom decoration. The K decoration alters the energy states and reshapes the wave-function such that previously hidden mid-gap states become visible with well-resolved multiplets in scanning tunneling spectroscopy. Their energy levels are in good agreement with first principle calculations. More interestingly, the calculations show that an unpaired electron donated by the K atom can lead to a local magnetic moment, exhibiting an on-off switching by the odd-even number of electron filling. Experimentally the Fermi level is pinned above all defect states due to the graphite substrate, corresponding to an off state. The close agreement between theory and experiment in the off state, on the other hand, suggest a possibility of gate-programmable magnetic moments at the defects.
关键词： mid-gap defect states,spin splitting,defect engineering,local magnetic moment,transition metal dichalcogenides
更新于2025-09-19 17:15:36
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Bismuth mediated defect engineering of epitaxial graphene on SiC(0001)
摘要： Structural defects are commonly undesirable in materials, however, atomic-level defect engineering is promising to improve the electronic, mechanical and chemical properties of graphene, if the density and types of defects could be well controlled. Herein, bismuth-mediated defect engineering method for epitaxial graphene (EG) grown on SiC(0001) is demonstrated. It is found that single defects and defect clusters could be facilitated by evaporating Bi atoms on SiC(0001) substrate before the standard EG preparation and, Bi atoms could be thoroughly cleaned away from the EG and the unwanted doping effects of Bi will be avoided by post-annealing at higher temperature. Scanning tunneling microscopy/spectroscopy characterization reveals the atomic structures, the electronic states and the Fermi level shift of flower-like, tube-like and point defects. This study sheds light on the metal-mediated formation of defects in graphene, and provides a practical defect engineering method.
关键词： Defect engineering,Scanning tunneling microscopy/spectroscopy.,Epitaxial graphene (EG)
更新于2025-09-19 17:15:36
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ZnO Nanosheets Abundant in Oxygen Vacancies Derived from Metal-Organic Frameworks for ppb-Level Gas Sensing
摘要： Surmounting the inhomogeniety issue of gas sensors and realizing their reproducible ppb-level gas sensing are highly desirable for widespread deployments of sensors to build networks in applications of industrial safety and indoor/outdoor air quality monitoring. Herein, a strategy is proposed to substantially improve the surface homogeneity of sensing materials and gas sensing performance via chip-level pyrolysis of as-grown ZIF-L (ZIF stands for zeolitic imidazolate framework) films to porous and hierarchical zinc oxide (ZnO) nanosheets. A novel approach to generate adjustable oxygen vacancies is demonstrated, through which the electronic structure of sensing materials can be fine-tuned. Their presence is thoroughly verified by various techniques. The sensing results demonstrate that the resultant oxygen vacancy-abundant ZnO nanosheets exhibit significantly enhanced sensitivity and shortened response time toward ppb-level carbon monoxide (CO) and volatile organic compounds encompassing 1,3-butadiene, toluene, and tetrachloroethylene, which can be ascribed to several reasons including unpaired electrons, consequent bandgap narrowing, increased specific surface area, and hierarchical micro–mesoporous structures. This facile approach sheds light on the rational design of sensing materials via defect engineering, and can facilitate the mass production, commercialization, and large-scale deployments of sensors with controllable morphology and superior sensing performance targeted for ultratrace gas detection.
关键词： metal-organic frameworks,oxygen vacancies,ppb-level gas sensing,defect engineering,ZnO nanosheets
更新于2025-09-19 17:15:36
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Micropatterning and defect engineering of colloidal photonic crystals <i>via</i> laser direct writing
摘要： Micropatterning and defect engineering of colloidal photonic crystals (CPCs) play a significant role in the functionality of photonic crystals as they are crucial for optical chip integration, microcavity lasing, chemical sensing, etc. However, obstacles have arisen in recent years especially due to the lack of a general, cost-effective and versatile strategy to make these functional structures in one step. Traditional micro-/nanofabrication techniques may work for one structure but fail for another and the fabrication process is mostly complicated, which potentially incurs reproducibility issues. Here, point defects, waveguides and micropatterns with variable feature sizes (4B500 nm) can be easily created in polystyrene (PS)/SiO2 CPC films via laser direct writing, which is based on selective photodegradation of PS beads. By applying different laser powers or irradiation times, different coloured micropatterns and images with high resolution can be generated, which has great implications for image displays and anti-counterfeiting.
关键词： photodegradation,Micropatterning,colloidal photonic crystals,anti-counterfeiting,defect engineering,laser direct writing,image displays
更新于2025-09-16 10:30:52
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zT = 1.1 in CuInTe <sub/>2</sub> Solid Solutions Enabled by Rational Defect Engineering
摘要： In this study, the synthesis and thermoelectric performance of CuInTe2?In2Te3 and Cu0.85Ag0.15InTe2?In2Te3 solid solutions are reported. The experimental results associated with model fitting reveal that the cation vacancies generated by creating solid solutions with a compound with a smaller cation-to-anion ratio can strongly scatter phonons with high frequency, which remarkably decrease the total as well as lattice thermal conductivity of the CuInTe2 system and finally realize an enhanced thermoelectric properties compared to the pristine sample. Furthermore, substitutional Ag/Cu defects integrated with vacancies lead to a further reduction in lattice thermal conductivity. With the benefit from the rational defect design, a high figure of merit of 1.1 is gained at 840 K for the sample (Cu0.85Ag0.15InTe2)0.98?(In2Te3)0.02. In addition, a 188% improvement on average zT is obtained. This work provides an effective method for boosting thermoelectric performance of chalcopyrite compounds by defect engineering on multiple types of defects.
关键词： defect engineering,thermoelectric performance,vacancy phonon scattering,thermal conductivity,CuInTe2
更新于2025-09-12 10:27:22
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Defect‐Engineering‐Enabled High‐Efficiency All‐Inorganic Perovskite Solar Cells
摘要： The emergence of cesium lead iodide (CsPbI3) perovskite solar cells (PSCs) has generated enormous interest in the photovoltaic research community. However, in general they exhibit low power conversion efficiencies (PCEs) because of the existence of defects. A new all-inorganic perovskite material, CsPbI3:Br:InI3, is prepared by defect engineering of CsPbI3. This new perovskite retains the same bandgap as CsPbI3, while the intrinsic defect concentration is largely suppressed. Moreover, it can be prepared in an extremely high humidity atmosphere and thus a glovebox is not required. By completely eliminating the labile and expensive components in traditional PSCs, the all-inorganic PSCs based on CsPbI3:Br:InI3 and carbon electrode exhibit PCE and open-circuit voltage as high as 12.04% and 1.20 V, respectively. More importantly, they demonstrate excellent stability in air for more than two months, while those based on CsPbI3 can survive only a few days in air. The progress reported represents a major leap for all-inorganic PSCs and paves the way for their further exploration in order to achieve higher performance.
关键词： perovskite solar cells,indium,all-inorganic solar cells,defect engineering,CsPbX3
更新于2025-09-11 14:15:04
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Disorder Engineering in Monolayer Nanosheets Enabling Photothermic Catalysis for Full Solar Spectrum (250 <b>-</b> 2500?nm) Harvesting
摘要： A persistent challenge in classical photocatalyst systems with extended light absorption is the unavoidable trade-off between maximizing light harvesting and sustaining high photoredox capability. Alternatively, cooperative energy conversion through photothermic activation and photocatalytic redox is a promising yet unmet scientific proposition that critically demands a spectrum-tailored catalyst system. Here, we construct a solar thermal-promoted photocatalyst, an ultrathin “biphasic” ordered–disordered D-HNb3O8 junction, which performs two disparate spectral selective functions of photoexcitation by ordered structure and thermal activated conversion via disordered lattice for combinatorial photothermal mediated catalysis. This in situ synthetically immobilized lattice distortion, constrained to a single-entity monolayer structure not only circumvents interfacial incompatibility but also triggers near-field temperature rise at the catalyst–reactant complexes’ proximity to promote photoreaction. Ultimately, a generic full solar conversion improvement for H2 fuel production, organic transformation and water purification is realized.
关键词： redox reaction,photothermic catalysis,defect engineering,order–disorder,full solar spectrum
更新于2025-09-10 09:29:36