2D multifunctional devices:from material preparation to device fabrication and neuromorphic applications

Neuromorphic computing systems,which mimic the operation of neurons and synapses in the human brain,are seen as an appealing next-generation computing method due to their strong and efficient computing abilities.Two-dimensional (2D) materials with dangling bond-free surfaces and atomic-level thicknesses have emerged as promising candidates for neuromorphic computing hardware.As a result,2D neuromorphic devices may provide an ideal platform for developing multifunctional neuromorphic applications.Here,we review the recent neuromorphic devices based on 2D material and their multifunctional applications.The synthesis and next micro–nano fabrication methods of 2D materials and their heterostructures are first introduced.The recent advances of neuromorphic 2D devices are discussed in detail using different operating principles.More importantly,we present a review of emerging multifunctional neuromorphic applications,including neuromorphic visual,auditory,tactile,and nociceptive systems based on 2D devices.In the end,we discuss the problems and methods for 2D neuromorphic device developments in the future.This paper will give insights into designing 2D neuromorphic devices and applying them to the future neuromorphic systems.

Low-temperature crystalline lead-free piezoelectric thin films grown on 2D perovskite nanosheet for flexible electronic device applications

A monolayer of Sr2Nb3Oio(SNO)is deposited on the Pt/Ti/SiCWSi(Pt?Si)or Pt/Ti/polyimide(Pt-Pl)substrate by using the Langmuir-Blodgett method and employed as a seed-layer for the growth of a crystalline(Nai_xKx)NbO3(NKN)film at 350℃.The crystalline NKN film is grown along the[001]direction on the SNO/Pt-Si(or SNO/Pt-PI)substrate.Due to the presence of oxygen vacancies in the SNO seed-layer,the NKN film exhibits low ferroelectric properties and large leakage current.To ameliorate these properties,the SNO/Pt-Si substrate is annealed in a 50 Torr oxygen atmosphere at 300℃,which removes the oxygen vacancies.Consequently,the NKN film deposited on this substrate exhibits promising electrical properties,namely a dielectric constant of 278,dissipation factor of 1.7%,a piezoelectric 8nstant of 175 pm`V^-1,and a leakage current density of 6.47 x 10^-7 A cm^-2 at-0.2 MV crrT1.Similar electrical properties are obtained from the NKN film grown on the flexible SNO/Pt-PI substrate at 350°C.Hence,the NKN films grown on the SNO seed-layer at 350°C can be applied to electronic devices with flexible polymer substrates.

Enhancing light-matter interaction in 2D materials by optical micro/nano architectures for high-performance optoelectronic devices

Two-dimensional materials are a promising solution for next-generation electronic and optoelectronic devices due to their unique properties.Owing to the atomic thickness of 2D materials,the light-matter interaction length in 2D materials is much shorter than that in bulk materials,which limits the performance of optoelectronic devices composed of 2D materials.To improve the light-matter interactions,optical micro/nano architectures have been introduced into 2D material optoelectronic devices.In this review,we present a concise introduction and discussion of various strategies for the enhancement of lightmatter interaction in 2D materials,namely,the plasmonic effect,waveguide,optical cavity,and reflection architecture.We have outlined the current advances in high-performance 2D material optoelectronic devices(eg,photodetectors,electrooptic modulators,light-emitting diodes,and molecular sensors)assisted by these enhancement strategies.Finally,we have discussed the future challenges and opportunities of micro/nano photonic structure designs in 2D material devices.

Organophosphine ligand derived sandwich-structural electrocatalyst for oxygen evolution reaction

The synchronous construction of metal phosphate and phosphorus-doped carbon structures is of great significance to innovate the design,synthesis,and application of catalysts,as these phosphoruscontaining composite materials have shown a remarkable contribution to electrocatalysts.However,their preparation procedure generally involves using large amounts of excess phosphorus sources for phosphorization,which inevitably release poisonous PH_(3) or dangerous phosphorus vapor.Here,a strategy for in-situ formation of FePO_(4) embedded in P-doped carbon 2D nano film(FePO_(4)/PdC)is developed using a highly integrated precursor,which is a small molecular organophosphine ligand,1,1’bis(diphenylphosphine)ferrocene(DPPF).The multi-source precursor DPPF that contains Fe,P,and C is molecular-vapor-deposited on the nickel foam(NF)supported ZIF-67 nanosheets to obtain the composite catalyst,namely DPPF-500/ZIF-67/NF.FePO_(4)/PdC encapsulated the ZIF-67 derived Co/N-doped carbon matrix(Co NC)to form a sandwich structure FePO_(4)/PdC@CoNC.The constructed catalyst shows good performance for OER,requiring an overpotential of only 297 m V to deliver 600 m A/cm^(2) with a Tafel slope of 42.7 m V dec^(-1).DFT calculations demonstrate that the synergistic effects between the metal active center and P-doped carbon film reduce the energy barriers and improve electron transport.This method of constructing P-containing catalysts overcomes the demand for additional P sources to realize eco-friendly fabrication and yields a unique structure with good catalytic activity.

Layer-by-layer assembly of long-afterglow self-supporting thin films with dual-stimuli-responsive phosphorescence and antiforgery applications

The assembly of thin films （TFs） having long-lasting luminescence can be expected to play an important role in the development of new-generation smart sensors, anti-counterfeiting materials, and information-encryption systems. However, such films are limited compared with their powder and solution counterparts. In this study, by exploiting the self-organization of phosphors in the two-dimensional （2D） galleries between clay nanosheets, we developed a method for the ordered assembly of long-afterglow TFs by utilizing a hydrogen-bonding layer-by-layer （LBL） process. Compared with the pristine powder, the TFs exhibit high polarization and up-conversion room-temperature phosphorescence （RTP）, as well as enhanced quantum yields and luminescence lifetimes, allowing them to be used as room-temperature phosphorescent sensors for humidity and oxygen. Moreover, modified clay-based hybrids with multicolor RTP can serve as anti-counterfeiting marks and triple-mode 2D barcode displays. We anticipate that the LBL assembly process can be extended to the fabrication of other inorganic--organic room-temperature phosphorescent hybrids with smart luminescent sensor and antiforgery applications.