Fermi's golden rule, a remarkable concept for the transition probability involving continuous states, is applicable to the interfacial electron‐transporting efficiency via correlation with the ...surface density of states (SDOS). Yet, this concept has not been reported to tailor single‐molecule junctions where gold is an overwhelmingly popular electrode material due to its superior amenability in regenerating molecular junctions. At the Fermi level, however, the SDOS of gold is small due to its fully filled d‐shell. To increase the electron‐transport efficiency, herein, gold electrodes are modified by a monolayer of platinum or palladium that bears partially filled d‐shells and exhibits significant SDOS at the Fermi energy. An increase by 2–30 fold is found for single‐molecule conductance of α,ω‐hexanes bridged via common headgroups. The improved junction conductance is attributed to the electrode self‐energy which involves a stronger coupling with the molecule and a larger SDOS participated by d‐electrons at the electrode‐molecule interfaces.
The conductance of molecular junctions bridged in Pt‐ or Pd‐adlayer modified Au electrodes was investigated. The conductance on bimetallic electrodes was found 2–30 fold higher than that on Au electrodes. This was attributed to the increase in the local density of states by partially‐filled d shells of the adlayer.
With the rapid development of artificial intelligence, the simulation of the human brain for neuromorphic computing has demonstrated unprecedented progress. Photonic artificial synapses are strongly ...desirable owing to their higher neuron selectivity, lower crosstalk, wavelength multiplexing capabilities, and low operating power compared to their electric counterparts. This study demonstrates a highly transparent and flexible artificial synapse with a two‐terminal architecture that emulates photonic synaptic functionalities. This optically triggered artificial synapse exhibits clear synaptic characteristics such as paired‐pulse facilitation, short/long‐term memory, and synaptic behavior analogous to that of the iris in the human eye. Ultraviolet light illumination‐induced neuromorphic characteristics exhibited by the synapse are attributed to carrier trapping and detrapping in the SnO2 nanoparticles and CsPbCl3 perovskite interface. Moreover, the ability to detect deep red light without changes in synaptic behavior indicates the potential for dual‐mode operation. This study establishes a novel two‐terminal architecture for highly transparent and flexible photonic artificial synapse that can help facilitate higher integration density of transparent 3D stacking memristors, and make it possible to approach optical learning, memory, computing, and visual recognition.
An inorganic CsPbCl3 perovskite artificial photonic synapse is demonstrated for the first time. This work shows the promising potential of multilevel storage capacity devices that can emulate synaptic functionalities via tuning of light intensity and frequency. The two‐terminal architecture synapse device exhibits the potential of dual‐mode operation, high transparency, and flexibility, which enable optical learning, memory, computing, and visual recognition.
Biodegradable electronic systems represent an emerging class of technology with unique application possibilities, from temporary biomedical implants to “green” consumer gadgets. This paper introduces ...materials and processing methods for 3D, heterogeneously integrated devices of this type, with various functional examples in sophisticated forms of silicon‐based electronics. Specifically, techniques for performing multilayer assembly by transfer printing and for fabricating layer‐to‐layer vias and interconnects by lithographic procedures serve as routes to biodegradable, 3D integrated circuits composed of functional building blocks formed using specialized approaches or sourced from commercial semiconductor foundries. Demonstration examples range from logic gates and analog circuits that undergo functional transformation by transience to systems that integrate multilayer resistive sensors for in situ, continuous electrical monitoring of the processes of transience. The results significantly expand the scope of engineering options for biodegradable electronics and other types of transient microsystem technologies.
Transient 3D electronic systems follow from use of biodegradable materials and deterministic assembly of foundry‐compatible microelectronic components. Physical and electrical transience allow functional transformation upon system dissolution and disintegration, thereby expanding the scope of engineering options for biodegradable electronics and other types of transient microsystem technologies.
Interfacial engineering of perovskite solar cells (PSCs) is attracting intensive attention owing to the charge transfer efficiency at an interface, which greatly influences the photovoltaic ...performance. This study demonstrates the modification of a TiO2 electron‐transporting layer with various amino acids, which affects charge transfer efficiency at the TiO2/CH3NH3PbI3 interface in PSC, among which the l‐alanine‐modified cell exhibits the best power conversion efficiency with 30% enhancement. This study also shows that the (110) plane of perovskite crystallites tends to align in the direction perpendicular to the amino‐acid‐modified TiO2 as observed in grazing‐incidence wide‐angle X‐ray scattering of thin CH3NH3PbI3 perovskite film. Electrochemical impedance spectroscopy reveals less charge transfer resistance at the TiO2/CH3NH3PbI3 interface after being modified with amino acids, which is also supported by the lower intensity of steady‐state photoluminescence (PL) and the reduced PL lifetime of perovskite. In addition, based on the PL measurement with excitation from different side of the sample, amino‐acid‐modified samples show less surface trapping effect compared to the sample without modification, which may also facilitate charge transfer efficiency at the interface. The results suggest that appropriate orientation of perovskite crystallites at the interface and trap‐passivation are the niche for better photovoltaic performance.
The (110) plane of CH3NH3PbI3 crystallites adjacent to the amino‐acid‐modified TiO2 surface tends to align in the direciton perpendicular to the TiO2 surface. Such crystalline orientation significantly enhances charge transfer efficiency at the TiO2/CH3NH3PbI3 interface and greatly improves the photovotaic performance of perovskite solar cells.
Photodegradation of organic pollutants in aqueous solution is a promising method for environmental purification. Photocatalysts capable of promoting this reaction are often composed of noble metal ...nanoparticles deposited on a semiconductor. Unfortunately, the separation of these semiconductor‐metal nanopowders from the treated water is very difficult and energy consumptive, so their usefulness in practical applications is limited. Here, a precisely controlled synthesis of a large‐scale and highly efficient photocatalyst composed of monolayered Au nanoparticles (AuNPs) chemically bound to vertically aligned ZnO nanorod arrays (ZNA) through a bifunctional surface molecular linker is demonstrated. Thioctic acid with sufficient steric stabilization is used as a molecular linker. High density unaggregated AuNPs bonding on entire surfaces of ZNA are successfully prepared on a conductive film/substrate, allowing easy recovery and reuse of the photocatalysts. Surprisingly, the ZNA‐AuNPs heterostructures exhibit a photodegradation rate 8.1 times higher than that recorded for the bare ZNA under UV irradiation. High density AuNPs, dispersed perfectly on the ZNA surfaces, significantly improve the separation of the photogenerated electron‐hole pairs, enlarge the reaction space, and consequently enhance the photocatalytic property for degradation of chemical pollutants. Photoelectron, photoluminescence and photoconductive measurements confirm the discussion on the charge carrier separation and photocatalytic experimental data. The demonstrated higher photodegradation rates demonstrated indicate that the ZNA‐AuNPs heterostructures are candidates for the next‐generation photocatalysts, replacing the conventional slurry photocatalysts.
The chemically conjugated hybrid system, composed of Au nanoparticles (AuNPs) and single‐crystal ZnO nanorod arrays (ZNA), shows spiked club‐like morphology and possesses several advantages, such as large‐scale production, high fabrication efficiency, long durability, and ease of separation from reaction solution for environmental purification. Higher photodegradation rates of organic pollutants indicate that the ZNA‐AuNPs are candidates for the next‐generation photocatalysts, replacing the conventional slurry photocatalysts.
The exciplex forming co‐host with phosphorescent dopant system has potential to realize highly efficient phosphorescent organic light emitting didoes (PhOLEDs). However, the exciplex forming co‐host ...for blue phosphorescent OLEDs has been rarely introduced because of higher triplet level of the blue dopant than green and red dopants. In this work, a novel exciplex forming co‐host with high triplet energy level is developed by mixing a phosphine oxide based electron transporting material, PO‐T2T, and a hole transporting material, N,N′‐dicarbazolyl‐3,5‐benzene (mCP). Photo‐physical analysis shows that the exciplexes are formed efficiently in the host and the energy transfer from the exciplex to blue phosphorescent dopant (iridium(III)bis(4,6‐difluorophenyl)‐pyridinato‐N,C2′picolinate; FIrpic) is also efficient, enabling the triplet harvest without energy loss. As a result, an unprecedented high performance blue PhOLED with the exciplex forming co‐host is demonstrated, showing a maximum external quantum efficiency (EQE) of 30.3%, a maximum power efficiency of 66 lm W−1, and low driving voltage of 2.75 at 100 cd m−2, 3.29 V at 1000 cd m−2, and 4.65 V at 10 000 cd m−2, respectively. The importance of the exciton confinement in the exciplex forming co‐host is further investigated which is directly related to the performance of PhOLEDs.
A novel exciplex forming host, composed of mCP and PO‐T2T, is realized. Using the host and efficient energy transfer to FIrpic, unprecedented high performance blue phosphorescent OLED is demonstrated, showing a maximum EQE of 30.3%, power efficiency of 66 lm W−1, and extremely low operating voltages of 2.75 at 100 cd m−2, and 4.65 V at 10 000 cd m−2.
A flexible triboelectric nanogenerator (FTENG) based on wavy‐structured Kapton film and a serpentine electrode on stretchable substrates is presented. The as‐fabricated FTENG is capable of harvesting ...ambient mechanical energy via both compressive and stretching modes. Moreover, the FTENG can be a bendable power source to work on curved surfaces; it can also be adaptively attached onto human skin for monitoring gentle body motions.
Monolayer molybdenum disulfide (MoS2) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the ...electrical and optoelectronic properties of monolayer MoS2 devices. Here, highly crystalline molybdenum diselenide (MoSe2) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS2 and MoSe2 monolayers reveals that the MoSe2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS2. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 and is useful for guiding future designs in 2D material-based optoelectronic devices.
In recent years, bismuth iodide (BiI3), a layered metal halide semiconducting light absorber with a wide bandgap of ≈1.8 eV and strong optical absorption in the visible region, has received greater ...attention for photovoltaic applications. In this study, ultrasensitive visible‐light photodetectors with graphene/BiI3 vertical heterostructures are achieved by van der Waals epitaxies. The BiI3 films deposited on graphene show flatter morphologies and significantly better crystallinities than that of BiI3 films on SiO2 substrates, mainly due to weak van der Waals interactions at the graphene/BiI3 interface. Hybrid photodetectors with highly crystalline graphene/BiI3 heterostructures demonstrate an ultrahigh responsivity of 6 × 106 A W−1, shot‐noise‐limited detectivity of 7 × 1014 Jones, and a relatively short response time of ≈8 ms. Compared to most previously reported graphene‐based hybrid photodetectors, these devices have comparable photosensitivities but a faster response speed and lower operation voltage, which is quite promising for ultralow intensity visible‐light sensors. Moreover, the electronic structure and interfacial chemistry at the graphene/BiI3 heterojunctions are investigated using photoemission spectroscopy. The results give clear evidence that no chemical interactions occur between graphene and BiI3, resulting in the van der Waals epitaxial growth, and the measured band bending consistently illustrates that a photoinduced charge transfer occurs at the graphene/BiI3 interface.
High‐quality crystal growth of layered metal halide BiI3 is demonstrated using van der Waals epitaxies. Compared to BiI3 on SiO2, BiI3 films on graphene produce flatter morphologies and remarkably better crystallinities because of weak van der Waals interactions at the graphene/BiI3 interface. The electronic structures and band bending at the graphene/BiI3 heterojunctions are also investigated using photoemission spectroscopy.
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