Dielectric materials are eternal jewels in the view of research due to their strong dissipation ability, low density and higher stability compared to those of magnetic materials. Regarding the ...significance of permittivity to characterize the dielectric properties of dielectrics, an in-depth and systematical investigation of dielectric polarization process has become quite necessary. Updated and critical surveys of the key factors determining permittivity, dielectric polarization in single-component system, dielectric polarization in multi-component system and related polarization relaxation are all highlighted. In addition, the challenges for dielectric polarization and polarization relaxation, the prospects for further exploration in electromagnetic wave absorption are also discussed. In short, this review provides a brief but systematic introduction to dielectric polarization and related polarization relaxation in electromagnetic wave absorption, which motivates further study of dielectric absorbers in microwave absorption field.
•Key factors determining permittivity are discussed.•Dielectric polarizations in single-component system are discussed.•Dielectric polarizations in multi-component system are discussed.•Related polarization relaxations are also highlighted.•The prospects for further exploration in electromagnetic wave absorption are proposed.
It is challenging yet promising to design highly accessible N‐doped carbon skeletons to fully expose the active sites inside single‐atom catalysts. Herein, mesoporous N‐doped carbon hollow spheres ...with regulatable through‐pore size can be formulated by a simple sequential synthesis procedure, in which the condensed SiO2 is acted as removable dual‐templates to produce both hollow interiors and through‐pores, meanwhile, the co‐condensed polydopamine shell is served as N‐doped carbon precursor. After that, Fe─N─C hollow spheres (HSs) with highly accessible active sites can be obtained after rationally implanting Fe single‐atoms. Microstructural analysis and X‐ray absorption fine structure analysis reveal that high‐density Fe─N4 active sites together with tiny Fe clusters are uniformly distributed on the mesoporous carbon skeleton with abundant through‐pores. Benefitted from the highly accessible Fe─N4 active sites arising from the unique through‐pore architecture, the Fe─N─C HSs demonstrate excellent oxygen reduction reaction (ORR) performance in alkaline media with a half‐wave potential up to 0.90 V versus RHE and remarkable stability, both exceeding the commercial Pt/C. When employing Fe─N─C HSs as the air‐cathode catalysts, the assembled Zn–air batteries deliver a high peak power density of 204 mW cm−2 and stable discharging voltage plateau over 140 h.
Using two types of orthosilicates with different hydrolysis rates as dual‐silica sources and dopamine as the N‐doped carbon sources, a sequential synthesis procedure referred to the classic Stöber method is developed to fabricate N‐doped carbon hollow spheres with abundant unusual through‐pores. The formed N‐doped carbon hollow spheres can act as a favorable host to isolate Fe single‐atoms.
Abstract
Neuro-inspired vision systems hold great promise to address the growing demands of mass data processing for edge computing, a distributed framework that brings computation and data storage ...closer to the sources of data. In addition to the capability of static image sensing and processing, the hardware implementation of a neuro-inspired vision system also requires the fulfilment of detecting and recognizing moving targets. Here, we demonstrated a neuro-inspired optical sensor based on two-dimensional NbS
2
/MoS
2
hybrid films, which featured remarkable photo-induced conductance plasticity and low electrical energy consumption. A neuro-inspired optical sensor array with 10 × 10 NbS
2
/MoS
2
phototransistors enabled highly integrated functions of sensing, memory, and contrast enhancement capabilities for static images, which benefits convolutional neural network (CNN) with a high image recognition accuracy. More importantly, in-sensor trajectory registration of moving light spots was experimentally implemented such that the post-processing could yield a high restoration accuracy. Our neuro-inspired optical sensor array could provide a fascinating platform for the implementation of high-performance artificial vision systems.
Monolayer transition metal dichalcogenides (TMDs) and their van der Waals heterostructures have been experimentally and theoretically demonstrated as potential candidates for photovoltaic and ...optoelectronic devices due to the suitable bandgap and excellent light absorption. In this work, we report the observation of photodiode behavior in (both n- and p- type) silicon/monolayer MoS2 vertical heterostructures. The photocurrent and photoresponsivity of heterostructures photodiodes were dependent both on the incident light wavelength and power density, and the highest photoresponsivity of 7.2 A/W was achieved in n-Si/monolayer MoS2 vertical heterostructures photodiodes. Compared with n-Si/MoS2 heterostructures, the photoresponsivity of p-Si/MoS2 heterostructure was much lower. Kelvin probe microscope (KFM) results demonstrated the more efficient separation of photogenerated excitons in n-Si/MoS2 than that in p-Si/MoS2. Coupling KFM results with band alignments of (p-, n-) Si/MoS2 heterostructures, the origins of photodiode-like phenomena of p-Si/MoS2 and n-Si/MoS2 have been unveiled, that is intrinsic built-in electric field in p-n junction, and modulated barrier height and width at the interface in n-n junction. Our work may benefit to the deep understanding of the integration of two-dimensional materials with more conventional three-dimensional semiconductors, and then contribute to the developments in the area of van der Waals heterostructures.
A one‐step synthesis of Li‐rich layered materials with layered/spinel heterostructure has been systematically investigated. The composites are synthesized by a polyol method followed with an ...annealing process at 500–900 °C for 12 h. A spinel to layer phase transition is considered to take place during the heat treatment, and the samples obtained at different temperatures show diverse phase compositions. An “Li‐rich spinel phase decomposition” phase transition mechanism is proposed to explain the formation of such a heterostructure. The electrochemical properties of the heterostructure are found to be associated with the ratio of spinel to layer phases, the leach out of rock salt phase, and the change of crystallinity and particle size. Product with improved cyclic and rate performance is achieved by annealing at 700 °C for 12 h, with a discharge capacity of 214 mA h g−1 remaining at 0.2 C after 60 cycles and discharge capacity of about 200 mA h g−1 at 1 C.
Li‐rich layered materials with layered/spinel heterostructure are prepared through a novel polyol method. With an “Li‐rich spinel phase decomposition” phase transition mechanism, the content of LLO is controllable and the products with moderate content of spinel phase demonstrate superior electrochemical performances with a discharge capacity of about 200 mA h g−1 at 1 C.
Highlights
A flexible and lightweight microwave absorber was prepared by a vacuum filtration method.
The remarkable microwave absorbency makes the absorber paper attractive in wireless wearable ...electronics field.
Developing a flexible, lightweight and effective electromagnetic (EM) absorber remains challenging despite being on increasing demand as more wearable devices and portable electronics are commercialized. Herein, we report a flexible and lightweight hybrid paper by a facile vacuum-filtration-induced self-assembly process, in which cotton-derived carbon fibers serve as flexible skeletons, compactly surrounded by other microwave-attenuating components (reduced graphene oxide and Fe
3
O
4
@C nanowires). Owing to its unique architecture and synergy of the three components, the as-prepared hybrid paper exhibits flexible and lightweight features as well as superb microwave absorption performance. Maximum absorption intensity with reflection loss as low as − 63 dB can be achieved, and its broadest frequency absorption bandwidth of 5.8 GHz almost covers the entire Ku band. Such a hybrid paper is promising to cope with ever-increasing EM interference. The work also paves the way to develop low-cost and flexible EM wave absorber from biomass through a facile method.
Elemental tantalum is a well‐known biomedical metal in clinics due to its extremely high biocompatibility, which is superior to that of other biomedical metallic materials. Hence, it is of ...significance to expand the scope of biomedical applications of tantalum. Herein, it is reported that tantalum nanoparticles (Ta NPs), upon surface modification with polyethylene glycol (PEG) molecules via a silane‐coupling approach, are employed as a metallic photoacoustic (PA) contrast agent for multiwavelength imaging of tumors. By virtue of the broad optical absorbance from the visible to near‐infrared region and high photothermal conversion efficiency (27.9%), PEGylated Ta NPs depict high multiwavelength contrast capability for enhancing PA imaging to satisfy the various demands (penetration depth, background noise, etc.) of clinical diagnosis as needed. Particularly, the PA intensity of the tumor region postinjection is greatly increased by 4.87, 7.47, and 6.87‐fold than that of preinjection under 680, 808, and 970 nm laser irradiation, respectively. In addition, Ta NPs with negligible cytotoxicity are capable of eliminating undesirable reactive oxygen species, ensuring the safety for biomedical applications. This work introduces a silane‐coupling strategy for the surface engineering of Ta NPs, and highlights the potential of Ta NPs as a biocompatible metallic contrast agent for multiwavelength photoacoustic image.
PEGylated Ta nanoparticles with surface modification with polyethylene glycol (PEG) molecules via silane‐coupling chemistry are explored as a metallic photoacoustic (PA) contrast agent for multiwavelength imaging of tumors. The PA intensity of the tumor region postinjection is greatly increased by 4.87, 7.47, and 6.87‐fold than that of preinjection under 680, 808, and 970 nm laser irradiation, respectively.
Electric double layer (EDL) devices based on 2D materials have made great achievements for versatile electronic and opto‐electronic applications; however, the ion dynamics and electric field ...distribution of the EDL at the electrolyte/2D material interface and their influence on the physical properties of 2D materials have not been clearly clarified. In this work, by using Kelvin probe force microscope and steady/transient optical techniques, the character of the EDL and its influence on the optical properties of monolayer transition metal dichalcogenides (TMDs) are probed. The potential drop, unscreened EDL potential distribution, and accumulated carriers at the electrolyte/TMD interface are revealed, which can be explained by nonlinear Thomas–Fermi theory. By monitoring the potential distribution along the channel, the evolution of the electric field‐induced lateral junction in the TMD EDL transistor is accessed, giving rise to the better exploration of EDL device physics. More importantly, EDL gate‐dependent carrier recombination and exciton–exciton annihilation in monolayer TMDs on lithium‐ion solid state electrolyte (Li2Al2SiP2TiO13) are evaluated for the first time, benefiting from the understanding of the interaction between ions, carriers, and excitons. The work will deepen the understanding of the EDL for the exploitation of functional device applications.
The ion dynamics and electric field distribution at the electrolyte/2D material interface and their influence on monolayer transition metal dichalcogenides (TMDs) properties are clarified by Kelvin probe force microscope and optical techniques experimentally as well as theoretically in this study. Potential distribution, electric field‐induced junctions, and gate‐dependent photonic dynamics in TMD electric double layer (EDL) transistors are revealed.
2D organic crystals exhibit efficient charge transport and field‐effect characteristics, making them promising candidates for high‐performance nanoelectronics. However, the strong Fermi level pinning ...(FLP) effect and large Schottky barrier between organic semiconductors and metals largely limit device performance. Herein, by carrying out temperature‐dependent transport and Kelvin probe force microscopy measurements, it is demonstrated that the introducing of 2D metallic 1T‐TaSe2 with matched band‐alignment as electrodes for F16CuPc nanoflake filed‐effect transistors leads to enhanced field‐effect characteristics, especially lowered Schottky barrier height and contact resistance at the contact and highly efficient charge transport within the channel, which are attributed to the significantly suppressed FLP effect and appropriate band alignment at the nonbonding van der Waals (vdW) hetero‐interface. Moreover, by taking advantage of the improved contact behavior with 1T‐TaSe2 contact, the optoelectronic performance of F16CuPc nanoflake‐based phototransistor is drastically improved, with a maximum photoresponsivity of 387 A W−1 and detectivity of 3.7 × 1014 Jones at quite a low Vds of 1 V, which is more competitive than those of the reported organic photodetectors and phototransistors. The work provides an avenue to improve the electrical and optoelectronic properties of 2D organic devices by introducing 2D metals with appropriate work function for vdW contacts.
A new approach is reported for contact engineering of 2D F16CuPc nanoflakes by using vdW contacts with 2D metal, 1T‐TaSe2. It is demonstrated that their efficient charge injection reduces Schottky barrier height and contact resistance, but results in superior charge transport, which further enables the significant enhancement of optoelectronic performance.
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