Construction of Hierarchical Yolk-Shell Co/N-Dope C@void@C@MoS2 Composites with Multiple Heterogeneous Interfaces toward Broadband Electromagnetic Wave Absorption.

The synthesis of materials with a multicomponent hierarchical structure is an essential strategy for achieving high-performance electromagnetic wave (EMW) absorption. However, conventional design strategies face challenges in terms of the rational construction of specific architecture. In this study, we employ a combined space-restricted and hierarchical construction strategy to surface-plant MoS2 nanosheets on yolk-shell structural carbon-modified Co-based composites, leading to the development of high-performance Co/NC@void@C@MoS2 absorbers with advanced architecture. The surface-planted MoS2 nanosheets, the Co/NC magnetic yolk, and the dielectric carbon shell work together to enhance the impedance matching characteristics and synergistic loss capabilities in the composites. Experimental results indicate that Co/NC@void@C-700@MoS2 exhibited the best absorption performance with an effective absorption bandwidth of 7.54 GHz (at 2.05 mm) and a minimum reflection loss of -60.88 dB (at 1.85 mm). Furthermore, radar cross-section simulation results demonstrate that Co/NC@void@C-700@MoS2 effectively suppresses the scattering and transmission of EMWs on perfect electric conductor substrates, implying its superior practical application value. This study provides inspiration and experimental basis for designing and optimizing EMW absorption materials with hierarchical yolk-shell architecture.

Yolk-shell construction of Co0.7Fe0.3 modified with dual carbon for broadband microwave absorption.

The rational and effective combination of multicomponent materials and the design of subtle microstructure for efficient microwave absorption are still challenging. In this study, carbon-coated CoFe with heterogeneous interfaces was space-restricted in the void space of hollow mesoporous carbon spheres through a facile approach involving electrostatic adsorption and annealing, and a high-performance microwave absorber (MAs) (denoted as Co0.7Fe0.3@C@void@C) was successfully prepared. The heterostructure, three-dimensional lightweight porous morphology, and electromagnetic synergy strategy enabled the Co0.7Fe0.3@C@void@C material with yolk-shell structure to exhibit surprising microwave absorption properties. When the annealing temperature and filler loading were 550° C and 15 wt%, respectively, the composites exhibited an effective absorption bandwidth (EAB) of 7.16 GHz at 2.48 mm and a minimum reflection loss of -24.1 dB at 2.11 mm. A maximum EAB of 7.21 GHz at 2.37 mm could be achieved for the composite prepared with an annealing temperature of 650° C. In addition, radar cross-section experiments demonstrated, the potential practical applicability of Co0.7Fe0.3@C@void@C. This work expands a new avenue to develop high-performance and lightweight MAs with ingenious microstructure.

Twist angle and electric gating controllable electronic structure of the two-dimensional stacked BP homo-structure.

The boron phosphide (BP) van der Waals (vdW) homostructure is designed to construct high-performance nano-optoelectronic devices due to its distinctive photoelectric properties. Using density functional theory, the electronic properties of twisted and untwisted BP bilayer structures are systematically calculated. We found that the 0° structure is a direct band gap semiconductor with a type II band alignment, the carrier mobility of which is increased to 104, and its photoelectric conversion efficiency is 17.3%. By analyzing the band structure and exciton binding energy calculated at 0° under an electric field, it is further found that 0° is a superior photoelectric material. As for the twist BP bilayer, the band gap changes with torsional structures under the applied electric field, which generates the Stark effect. The twist angles of bilayer BP, specifically 13.17°, 21.79°, 38.21°, and 46.83°, always maintain a direct band gap under the influence of an electric field. While 60° is an indirect band gap, the structure exhibits high resistance to the electric field. Our results reveal that bilayer BP is a potential application prospect in photovoltaic and optoelectronic fields and can provide more insights into optoelectronic devices.

Graphene-like structure of bio-carbon with CoFe Prussian blue derivative composites for enhanced microwave absorption.

Traditional carbon materials such as graphene are often applied in the field of electromagnetic wave (EMW) absorption but they have unbalanced impedance matching and high conductivity. Bio-carbon with graphene-like structure derived from apples has many advantages over graphene: it can be prepared in large quantities and the abundant heteroatoms present in the lattice can provide many polarization phenomena. Herein, Prussian blue analogue (PBA) as a source of magnetic component was combined with bio-carbon or reduced graphene oxide (rGO) to study the EMW absorption properties. The fabricated BC/CFC-12-7 displayed performance with a minimum reflection loss (RLmin) of -72.57 dB and a wide effective absorption bandwidth (EAB) of 5.25 GHz with an ultra-thin and nearly equal matching thickness at 1.61 mm. The results show that the good EMW absorption property of bio-carbon composites comes from good conduction loss, large relaxation polarization loss especially from pyridinic-N, and better impedance matching. The optimized radar cross section is found to be -33.55 dB m2 in the far-field condition using CST. This work explored the advantages of bio-carbon as a novel EMW absorbing material compared with graphene and provided ideas for realizing high-performance EMW absorbing materials in the future.

A type-II NGyne/GaSe heterostructure with high carrier mobility and tunable electronic properties for photovoltaic application.

The two-dimensional heterostructures with type-II band alignment and super-high carrier mobility offer an updated perspective for photovoltaic devices. Here, based on the first-principles calculation, a novel vertical NGyne/GaSe heterostructure with an intrinsic type-II band alignment, super-high carrier mobility (104cm2V-1s-1), and strong visible to ultraviolet light absorption (104-105cm-1) is constructed. We investigate the electronic structure and the interfacial properties of the NGyne/GaSe heterostructure under electric field and strain. The band offsets and band gap of the NGyne/GaSe heterostructure can be regulated under applied vertical electric field and strain efficiently. Further study reveals that the photoelectric conversion efficiency of the NGyne/GaSe heterostructure is vastly improved under a negative electric field and reaches up to 25.09%. Meanwhile, near-free electron states are induced under a large applied electric field, leading to the NGyne/GaSe heterostructure transform from semiconductors to metal. Our results indicate that the NGyne/GaSe heterostructure will have extremely potential in optoelectronic devices, especially solar cells.

Twistronics in tensile strained bilayer black phosphorus.

In this work, by performing state-of-the-art first-principles methods combined with molecular dynamic (MD) simulation, we theoretically investigate the electronic and mechanical behaviours of small-angle twisted bilayer black phosphorus (tbBP) under uniaxial tensile deformation. Twistronics, namely the regulation of electronic properties by Moiré physics, is demonstrated as the gene - the most crucial factor dominating not only electronic behaviour but also mechanical behaviour of tensile deformed tbBP. Compared to untwisted few-layer black phosphorus (utBP) with strong electronic sensitivity to geometric deformation, the existence of Moiré patterns in tbBP leads to spatial electronic localization, giving rise to the conservation of direct band gaps and stability of phonon limited carrier mobility under tensile deformation along the armchair direction. Moreover, during the fracture failure process, the nucleation of micro-cracks is preferentially detected at the transitional pattern boundary areas in tbBP, which could be attributed to the intra-layer maldistribution of mechanical strengths in Moiré superlattices. The explorations of twistronics in tensile strained bilayer black phosphorus contribute to the better understanding of such Moiré superlattice structures and provide insights for the design of new 2D van der Waals heterostructures in flexible nano-electronic devices.

Enhanced Optical Absorption and Interfacial Carrier Separation of CsPbBr3/Graphene Heterostructure: Experimental and Theoretical Insights.

Controlling effective separation of carriers at the interface is a key element to realize highly efficient halogenated perovskite-based optoelectronic devices. Here, a comprehensive study of interfacial properties for CsPbBr3 nanocrystals (NCs)/graphene heterostructure is performed by the combination of theoretical and experimental methods. Enhanced visible light absorption is observed experimentally in the CsPbBr3 NCs/graphene heterostructure. The strong photoluminescence quenching phenomenon and improved photoresponse prove the efficient interfacial charge transfer from the perovskite CsPbBr3 NC layer to the graphene side. Significantly, theoretical calculations suggest that an intrinsic built-in electric field, pointing from graphene toward CsPbBr3, promotes the separation of photoinduced carriers at the CsPbBr3 NCs/graphene interface and simultaneously inhibits the recombination of electron-hole pairs. Thus, the high optoelectronic performance can be obtained in the CsPbBr3 NCs/graphene heterostructure, as shown in our experiment. Moreover, the CsPbBr3 NCs/graphene heterostructure exhibits smaller effective mass than that of CsPbBr3 NCs, indicating that the heterostructure does possess a high carrier mobility, which can further accelerate the separation of photogenerated carriers. Furthermore, the calculated results reveal that, accounting for the presence of the stronger built-in electric field, larger band bending value, and smaller effective mass, the PbBr2/graphene interface can realize the separation of the photoinduced carriers more effectively than the CsBr/graphene interface and thus more efficiently facilitate electron transfer from the perovskite optical absorber side to the graphene electronic transport side. Our findings provide valuable insight into perovskite/graphene-based photodetector devices via the interface engineering project.

First-principles calculations and experimental investigation on SnO2@ZnO heterojunction photocatalyst with enhanced photocatalytic performance.

In this study, branch-like SnO2@ZnO heterojunction photocatalyst was successfully fabricated via a simple two-step hydrothermal process. The optical and electronic properties were characterized in detail and the results indicated that SnO2@ZnO nanocomposites (TZNCs) exhibited superior photocatalytic performance under visible light irradiation as compared to pure SnO2 and ZnO. The excellent photocatalytic performance of TZNCs can be ascribed to the heterojunction structure between ZnO and SnO2 which depresses the recombination of photogenerated electron-hole pairs. In addition, the branch-like morphology can provide large specific surface. Moreover, the density functional theory (DFT) computation on the Fermi level results confirmed that heterojunction structure between ZnO and SnO2 is more favor of the transfer of photogenerated eletrons from ZnO to SnO2, effectively improving separation of photogenerated electron-hole pairs. Noteworthy, this work would pave the route for the two semiconductor materials with a big work function difference which would lead to the high contact potential difference, surely contributing to improving the performance of photocatalysts.

Tunable band gap of graphyne-based homo- and hetero-structures by stacking sequences, strain and electric field.

A comprehensive investigation was carried out on graphyne/graphyne (Gyne/Gyne), graphyne-like BN/graphyne-like BN (BNyne/BNyne) and graphyne/graphyne-like BN (Gyne/BNyne) bilayer structures using van der Waals (vdW)-corrected density functional theory. These bilayers exhibited distinct stacking-dependent characteristics in their ground state electronic structure and also had different responses to external strain and a vertical electric field. For the Gyne/Gyne and Gyne/BNyne bilayers, the application of biaxial tensile strain led to an increase in the band gap, while the application of biaxial compressive strain in addition to uniaxial strain, either under tension or compression, induced a reduction in the band gap. However, in the case of the BNyne/BNyne bilayer, the application of biaxial tensile strain led to a decrease in the band gap, but an increase in the band gap occurred under biaxial compressive strain, which could be explained by a change in the ionic nature of the B-N bonds. Under a vertical electric field, the band gaps of the homo-bilayers (Gyne/Gyne and BNyne/BNyne) decreased and were symmetrical. However, the hetero-bilayer (Gyne/BNyne) exhibited a decreased band gap under a positive electric field, but an almost constant band gap under a negative electric field. The physical origin of the band gap variation under an electric field was unraveled using energy-band theory. Our findings pave the way for experimental research and provide valuable insight into two-dimensional vdW layered structures for use in next generation flexible nanoelectronics and optoelectronic devices.

Photoluminescence and Growth Mechanism of Oriented Hierarchical Fibrous-Like ZnO Nanowires.

Oriented hierarchical fibrous-like ZnO nanowires with the diameter of about 30­50 nm and the length of about 15­30 um were successfully synthesized on the seed-coated Zn substrates by a simple two-step process. The morphology and structure of the obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It is shown that fibrous-like ZnO nanowires with the aspect ratio of about 500˜1000 present the dense reticular structure, which are grown on ZnO nanowire arrays. But beyond that, as-prepared samples are found to be good single crystalline with hexagonal wurtzite structure and preferential grow along the c-axis. A possible growth mechanism of oriented hierarchical fibrous-like ZnO nanowires is presented in detail, revealing that the synthesis of fibrous-like ZnO nanowires should be attributed to differences in the growth rate of the different crystallographic planes and the two growth ways. The photoluminescence (PL) spectra of oriented hierarchical fibrous-like ZnO nanowires grown at 240 min shows the 5 nm blue-shift and enhanced intensity property in the UV emission.

Effect of intrinsic point defect on the magnetic properties of ZnO nanowire.

The effect of intrinsic point defect on the magnetic properties of ZnO nanowire is investigated by the first-principles calculation based on the density functional theory (DFT). The calculated results reveal that the pure ZnO nanowire without intrinsic point defect is nonmagnetic and ZnO nanowire with V(O), Zn(i), O(i), O(Zn), or Zn(O) point defect also is nonmagnetic. However, a strong spin splitting phenomenon is observed in ZnO nanowire with V(Zn) defect sitting on the surface site. The Mulliken population analysis reveals that the oxygen atoms which are close to the V(Zn) defect do major contribution to the magnetic moment. Partial density states calculation further suggests that the appearance of the half-metallic ferromagnetism in ZnO nanorod with V(Zn) originates from the hybridization of the O2p states with Zn 3d states.