Ultrahigh UV Responsivity Quasi-Two-Dimensional BixSn1-xO2 Films Achieved through Surface Reaction.

In this study, quasi-two-dimensional BixSn1-xO2 (BTO) thin films were fabricated using a liquid metal transfer method. The ultraviolet (UV) photodetector based on BTO thin films was constructed, and the ultrahigh responsivity of 589 A/W was observed at 300 nm UV light illumination. Interestingly, by dropping ethanol during light-off period, the recovery time induced by the persistent photoconductivity (PPC) effect is reduced from 1.65 × 103 s to 5.71 s. Furthermore, the recovery time can also be reduced by dropping methanol, propylene glycol, NaNO2, and Na2SO3 after light termination. The working mechanisms are attributed to the rapid consumption of holes stored in BTO thin films by reaction with those solutions. This work demonstrates that the BTO thin films have potential applications in high-performance UV detectors and present an innovation route to weaken the PPC effects in semiconductors by introducing chemical liquids on their surface.

Synergistic Enhancement of Near-Infrared Emission in CsPbCl3 Host via Co-Doping with Yb3+ and Nd3+ for Perovskite Light Emitting Diodes.

Perovskite nanocrystals (PeNCs) have emerged as a promising class of luminescent materials offering size and composition-tunable luminescence with high efficiency and color purity in the visible range. PeNCs doped with Yb3+ ions, known for their near-infrared (NIR) emission properties, have gained significant attention due to their potential applications. However, these materials still face challenges with weak NIR electroluminescence (EL) emission and low external quantum efficiency (EQE), primarily due to undesired resonance energy transfer (RET) occurring between the host and Yb3+ ions, which adversely affects their emission efficiency and device performance. Herein, we report the synergistic enhancement of NIR emission in a CsPbCl3 host through co-doping with Yb3+/Nd3+ ions for perovskite LEDs (PeLEDs). The co-doping of Yb3+/Nd3+ ions in a CsPbCl3 host resulted in enhanced NIR emission above 1000 nm, which is highly desirable for NIR optoelectronic applications. This cooperative energy transfer between Yb3+ and Nd3+ can enhance the overall efficiency of energy conversion. Furthermore, the PeLEDs incorporating the co-doped CsPbCl3/Yb3+/Nd3+ PeNCs as an emitting layer exhibited significantly enhanced NIR EL compared to the single doped PeLEDs. The optimized co-doped PeLEDs showed improved device performance, including increased EQE of 6.2% at 1035 nm wavelength and low turn-on voltage. Our findings highlight the potential of co-doping with Yb3+ and Nd3+ ions as a strategy for achieving synergistic enhancement of NIR emission in CsPbCl3 perovskite materials, which could pave the way for the development of highly efficient perovskite LEDs for NIR optoelectronic applications.

Laser-Induced Graphene-based Flexible Substrate with Photothermal Conversion and Photoresponse Performance on Polyimide Film.

Graphene-based flexible electronic devices are widely used in photoelectric components and photodetectors. However, it remains a huge challenge to fabricate graphene-based flexible devices efficiently and economically. Compared with the flexible electronic devices made by combining the flexible film with metal and semiconductor materials, the graphene-based flexible substrate (GFS) can be efficiently and conveniently induced by laser direct writing on the flexible film. In this paper, the GFS with a resistance of as low as 15 Ω was successfully induced by CO2 laser on a polyimide (PI) film in one step, and the GFS surface covered with carbon nanoparticles (GFSC) with a resistance of 25 Ω was further induced by femtosecond (fs) laser reprocessing. Benefiting from the laser-induced porous graphene structure, the absorptivity of GFS is up to 90% in the wavelength range of 200-2000 nm. The formation of carbon nanoparticles on the GFSC surface further improves the absorptivity to 97.5% in a wide spectral range. Under white light irradiation of 1 sun, the surface temperature of GFS reaches 65.7 °C and that of GFSC is up to 70.8 °C within 2 min. Under the irradiation of a light-emitting diode (LED) with a central wavelength of 365 nm, the highest photoresponsivity of GFS and GFSC was 8.8 and 1.3 mA/W, respectively. The response time and recovery time of GFS are 8 and 7.3 s, and those of GFSC are 8.3 and 6.7 s, respectively. Importantly, GFSC has a more stable photoresponse performance due to the better electron capture and transfer capability of carbon nanoparticles. It is believed that GFS and GFSC have great application potential in flexible photodetectors and sensors.

High-intensity first near-infrared emission through energy migration in multilayered upconversion nanoparticles.

The development of Tm3+ 807 nm first near-infrared (NIR-I, 700-1000 nm) emission with second near-infrared (NIR-II, 1000-1700 nm) excitation is urgently needed, due to its potential application in biomedicine. In this work, a range of NaErF4:Yb@NaYF4:Yb@NaYF4:Yb,Tm@NaYF4 multilayer core-shell structure upconversion nanoparticles (UCNPs) were successfully prepared by a co-precipitation method. The strongest UC emissions can be obtained by changing the concentration of Yb3+ in the core and the first shell, and the proposed UC process was discussed in detail. The analysis shows that high-intensity NIR-I emission (807 nm) from Tm3+ and visible light from Er3+ were achieved through the energy migration among Yb3+ and the energy back transfer from Yb3+ to Er3+ under 1532 nm excitation. Besides, compared to bilayer UCNPs, multilayer core-shell UCNPs display superior optical performance. The high-intensity NIR-I emission at 807 nm (Tm3+:3H4 → 3H6) under 1532 nm NIR-II excitation demonstrates huge advantages in bioimaging.

Criticality and Neuromorphic Sensing in a Single Memristor.

Resistive random access memory (RRAM) is an important technology for both data storage and neuromorphic computation, where the dynamics of nanoscale conductive filaments lies at the core of the technology. Here, we analyze the current noise of various silicon-based memristors that involves the creation of a percolation path at the intermediate phase of filament growth. Remarkably, we find that these atomic switching events follow scale-free avalanche dynamics with exponents satisfying the criteria for criticality. We further prove that the switching dynamics are universal and show little dependence on device sizes or material features. Utilizing criticality in memristors, we simulate the functionality of hair cells in auditory sensory systems by observing the frequency selectivity of input stimuli with tunable characteristic frequency. We further demonstrate a single-memristor-based sensing primitive for representation of input stimuli that exceeds the theoretical limits dictated by the Nyquist-Shannon theorem.

Sr2+doped CsPbBrI2perovskite nanocrystals coated with ZrO2for applications as white LEDs.

Perovskite nanocrystals (NCs) feature adjustable bandgap, wide absorption range, and great color purity for robust perovskite optoelectronic applications. Nevertheless, the absence of lasting stability under continues energization, is still a major hurdle to the widespread use of NCs in commercial applications. In particular, the reactivity of red-emitting perovskites to environmental surroundings is more sensitive than that of their green counterparts. Here, we present a simple synthesis of ultrathin ZrO2coated, Sr2+doped CsPbBrI2NCs. Introducing divalent Sr2+may significantly eliminate Pb° surface traps, whereas ZrO2encapsulation greatly improves environmental stability. The photoluminescence quantum yield of the Sr2+-doped CsPbBrI2/ZrO2NCs was increased from 50.2% to 87.2% as a direct consequence of the efficient elimination of Pb° surface defects. Moreover, the thickness of the ZrO2thin coating gives remarkable heat resistance and improved water stability. Combining CsPbSr0.3BrI2/ZrO2NCs in a white light emitting diode (LED) with an excellent optical efficiency (100.08 lm W-1), high and a broad gamut 141% (NTSC) standard. This work offers a potential method to suppress Pb° traps by doping with Sr2+and improves the performance of perovskite NCs by ultrathin coating structured ZrO2, consequently enabling their applicability in commercial optical displays.

Strong Plasmon-Mie Resonance in Si@Pd Core-Ω Shell Nanocavity.

The surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) can be used to enhance the generation of the hot electrons in plasmon metal nanocavity. In this paper, Pd nanomembrane (NMB) is sputtered on the surface of Si nanosphere (NS) on glass substrate to form the Si@Pd core-Ω shell nanocavity. A plasmon-Mie resonance is induced in the nanocavity by coupling the plasmon resonance with the Mie resonance to control the optical property of Si NS. When this nanocavity is excited by near-infrared-1 (NIR-1, 650 nm-900 nm) femtosecond (fs) laser, the luminescence intensity of Si NS is dramatically enhanced due to the synergistic interaction of plasmon and Mie resonance. The generation of resonance coupling regulates resonant mode of the nanocavity to realize multi-dimensional nonlinear optical response, which can be utilized in the fields of biological imaging and nanoscale light source.

Resonance Coupling in Si@WS2Core-Ω Shell Nanostructure.

Realizing strong laser-matter interaction in a heterostructure consisting of two-dimensional transition metal dichalcogenides (TMDCs) and an optical nanocavity is a potential strategy for novel photonic devices. In this paper, two core-Ω shell nanostructures, Si@WS2 core-Ω shell nanostructure on glass/Si substrates, are briefly introduced. A strong laser-matter interaction occurred in the Si@WS2 core-Ω shell nanostructure when it was excited by femtosecond (fs) laser in the near-infrared-1 region (NIR-1, 650 nm-950 nm), resulting in a resonance coupling between the electric dipole resonance (EDR) of the Si nanosphere (NS) and the exciton resonance of the WS2 nanomembrane (NMB). The generation of resonance coupling regulates the resonant mode of the nanostructure to realize the multi-dimensional nonlinear optical response, which can be utilized in the fields of biological imaging and nanoscale light source.

Charge Carrier Recombination Dynamics in MAPb(BrxCl1-x)3 Single Crystals.

Understanding carrier recombination processes in MAPb(BrxCl1-x)3 crystals is essential for their photoelectrical applications. In this work, carrier recombination dynamics in MAPb(BrxCl1-x)3 single crystals were studied by steady-state photoluminescence (PL), time-resolved photoluminescence (TRPL), and time-resolved microwave photoconductivity (TRMC). By comparing TRPL and TRMC, we find TRPL of MAPb(BrxCl1-x)3 (x < 0.98) single crystals is dominated by a hole trapping process while the long-lived component of TRMC is dominated by an electron trapping process. We also find both electron and hole trapping rates of MAPb(BrxCl1-x)3 (x < 0.98) crystals decrease with an increase in Br content. A temperature-dependent PL study shows there are shallow trap states besides the deep level trap states in the MAPb(Br0.82Cl0.18)3 crystal. The activation energy for holes in shallow trap states detrapped into the valence band is ∼0.1 eV, while the activation energy for free holes to be trapped into deep trap states is ∼0.4 eV. This work provides insight into carrier recombination processes in MAPb(BrxCl1-x)3 single crystals.

Surface Engineering in SnO2/Si for High-Performance Broadband Photodetectors.

Silicon-based photodetectors are important optoelectronic devices in many fields. Many investigations have been conducted to improve the performance of silicon-based photodetectors, such as spectral responsivity and sensitivity in the ultraviolet band. In this study, we combine the surface structure engineering of silicon with wide-bandgap semiconductor SnO2 films to realize textured Si-based heterojunction photodetectors. The obtained SnO2/T-Si photodetectors exhibit high responsivity ranging from ultraviolet to near-infrared light. Under a bias voltage of 1 V, SnO2/T-Si photodetectors (PDs) with an inverted pyramid texture show the best performance, and the typical responsivities to ultraviolet, visible, and near-infrared light are 0.512, 0.538, 1.88 (800 nm, 67.7 µW/cm2) A/W@1 V, respectively. The photodetectors exhibit short rise and decay times of 18.07 and 29.16 ms, respectively. Our results demonstrate that SnO2/T-Si can serve as a high-performance broadband photodetector.

NaCdSb: An Orthorhombic Zintl Phase with Exceptional Intrinsic Thermoelectric Performance.

Many Zintl phases are promising thermoelectric materials owning to their features like narrow band gaps, multiband behaviors, ideal charge transport tunnels, and loosely bound cations. Herein we show a new Zintl phase NaCdSb with exceptional intrinsic thermoelectric performance. Pristine NaCdSb exhibits semiconductor behaviors with an experimental hole concentration of 2.9×1018  cm-3 and a calculated band gap of 0.5 eV. As the temperature increases, the hole concentration rises gradually and approaches its optimal one, leading to a high power factor of 11.56 µW cm-1 K-2 at 673 K. The ultralow thermal conductivity is derived from the small phonon group velocity and short phonon lifetime, ascribed to the structural anharmonicity of Cd-Sb bonds. As a consequence, a maximum zT of 1.3 at 673 K has been achieved without any doping optimization or structural modification, demonstrating that NaCdSb is a remarkable thermoelectric compound with great potential for performance improvement.

Analog Tunnel Memory Based on Programmable Metallization for Passive Neuromorphic Circuits.

Although experimental implementations of memristive crossbar arrays have indicated the potential of these networks for in-memory computing, their performance is generally limited by an intrinsic variability on the device level as a result of the stochastic formation of conducting filaments. A tunnel-type memristive device typically exhibits small switching variations, owing to the relatively uniform interface effect. However, the low mobility of oxygen ions and large depolarization field result in slow operation speed and poor retention. Here, we demonstrate a quantum-tunneling memory with Ag-doped percolating systems, which possesses desired characteristics for large-scale artificial neural networks. The percolating layer suppresses the random formation of conductive filaments, and the nonvolatile modulation of the Fowler-Nordheim tunneling current is enabled by the collective movement of active Ag nanocrystals with high mobility and a minimal depolarization field. Such devices simultaneously possess electroforming-free characteristics, record low switching variabilities (temporal and spatial variation down to 1.6 and 2.1%, respectively), nanosecond operation speed, and long data retention (>104 s at 85 °C). Simulations prove that passive arrays with our analog memory of large current-voltage nonlinearity achieve a high write and recognition accuracy. Thus, our discovery of the unique tunnel memory contributes to an important step toward realizing neuromorphic circuits.

Integrated CuO/Pd Nanospike Hydrogen Sensor on Silicon Substrate.

A large area of randomly distributed nanospike as nanostructured template was induced by femtosecond (fs) laser on a silicon substrate in water. Copper oxide (CuO) and palladium (Pd) heterostructured nanofilm were coated on the nanospikes by magnetron sputtering technology and vacuum thermal evaporation coating technology respectively for the construction of a p-type hydrogen sensor. Compared with the conventional gas sensor based on CuO working at high temperature, nanostructured CuO/Pd heterostructure exhibited promising detection capability to hydrogen at room temperature. The detection sensitivity to 1% H2 was 10.8%, the response time was 198 s, and the detection limit was as low as 40 ppm, presenting an important application prospect in the clean energy field. The excellent reusability and selectivity of the CuO/Pd heterostructure sensor toward H2 at room temperature were also demonstrated by a series of cyclic response characteristics. It is believed that our room-temperature hydrogen sensor fabricated with a waste-free green process, directly on silicon substrate, would greatly promote the future fabrication of a circuit-chip integrating hydrogen sensor.

Reliable Memristor Based on Ultrathin Native Silicon Oxide.

Memristors based on two-dimensional (2D) materials can exhibit great scalability and ultralow power consumption, yet the structural and thickness inhomogeneity of ultrathin electrolytes lowers the production yield and reliability of devices. Here, we report that the self-limiting amorphous SiOx (∼2.7 nm) provides a perfect atomically thin electrolyte with high uniformity, featuring a record high production yield. With the guidance of physical modeling, we reveal that the atomic thickness of SiOx enables anomalous resistive switching with a transition to an analog quasi-reset mode, where the filament stability can be further enhanced using Ag-Au nanocomposite electrodes. Such a picojoule memristor shows record low switching variabilities (C2C and D2D variation down to 1.1 and 2.6%, respectively), good retention at a few microsiemens, and high conductance-updating linearity, constituting key metrics for analog neural networks. In addition, the stable high-resistance state is found to be an excellent source for true random numbers of Gaussian distribution. This work opens up opportunities in mass production of Si-compatible memristors for ultradense neuromorphic and security hardware.

Numerical demonstration of low-reflective wire grid polarizers with a patterned Fe2O3 absorptive layer.

Absorptive polarizers are pivotal components for realizing a low ambient reflection in liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs). Different types of absorptive polarizers have been proposed. Nevertheless, the realization of compact and efficient absorptive polarizers remains challenging. Wire grid polarizers (WGPs) are a promising solution because of their high durability and relatively thin thickness. In this paper, two structures of absorptive-WGPs have been proposed and optimized at the target wavelength of 532 nm: one is based on a patterned F e 2 O 3/A l bi-layer on top of a S i O 2 substrate, and the second one builds on the first one by depositing a S i O 2 layer in the gaps of Al. The optimal solutions exhibit a reflectance less than 5%, a transmittance over 45%, and an extinction ratio over 40 dB. To evaluate the manufacturing feasibility, their sensitivity to the wire's dimensional parameters is investigated. Their great spectral performance and large acceptance angles demonstrate that such polarizers have the potential to significantly promote the development of current display technologies.

Solution-processed inorganic δ-phase CsPbI3 electronic synapses with short- and long-term plasticity in a crossbar array structure.

Electronic synapses based on memristive devices can potentially open a niche area for neuromorphic computing by replicating the function of biological synapses with high fidelity. Recently, two-terminal memristors based on halide perovskites have demonstrated outstanding memristive properties and a variety of synaptic characteristics, combining with their additional advantages such as a solution-processed fabrication method and low crystalline temperature. However, the concerns over the chemical and phase stability of halide perovskites greatly hinder their practical applications. In this study, by using a simple single-step spin-coating method, we report artificial synapses with superior ambient stability (>90 days under ambient conditions) based on fully inorganic nonperovskite δ-phase CsPbI3 in a cross-bar array architecture. The threshold switching memristive device exhibits a moderate ON/OFF ratio, a relatively low operation voltage (0.3 V) and high endurance (>5 × 105). More importantly, the electronic device can emulate synaptic characteristics such as short-term plasticity, paired-pulse facilitation, and the transition from short-term memory to long-term memory with a high output signal-to-noise ratio (>102). This work represents the first record for artificial synapses based on nonperovskite CsPbI3 and will be a step toward achieving low-cost and high-density practical synapse arrays.

Memristive synapses with high reproducibility for flexible neuromorphic networks based on biological nanocomposites.

Memristive synapses from biomaterials are promising for building flexible and implantable artificial neuromorphic systems due to their remarkable mechanical and biological properties. However, these biological devices have relatively poor memristive switching characteristics, and thus fail to meet the requirement of neuromorphic networks for high learning accuracy. Here, memristive synapses based on carrageenan nanocomposites that possess desirable characteristics are demonstrated. These devices show highly reproducible analog resistive switching behaviors with 250 conductance states, low write noise, good write linearity, high retention of more than 104 s and endurance for at least 106 pulses. The enhanced switching properties are attributed to controllable and confined conductive filament growth, owing to the synergistic effect of self-assembled silver nanocluster doping and nanocone-shaped electrode contact. Moreover, the devices exhibit excellent reliability after 1000 bending cycles. Simulations including the non-ideal factors prove that the synaptic device array can operate with an online learning accuracy of 94.3%. These findings enable broader applications of biomaterials in flexible memristive devices and neuromorphic systems.

Flexible artificial nociceptor using a biopolymer-based forming-free memristor.

The development of electronic devices possessing the functionality of a nociceptor is a crucial step toward electronic receptors that can transfer the external stimuli to the internal nerve system. Of the various materials that have been used to realize artificial nociceptors, biopolymers have the advantages of being abundant, inexpensive, biocompatible, and flexible. In this study, nociceptor behaviors are demonstrated by the flexible Ag/carboxymethyl ι-carrageenan/ITO/PET forming-free memristors for the electronic receptors. The flexible carboxymethyl ι-carrageenan-based memristor showed threshold switching characteristics with a high ION/IOFF ratio of ∼104 and good switching endurance (>1.5 × 105 cycles). It also showed high bending endurance over 1000 cycles when measured in both the flat and the maximum bending conditions. More importantly, it differs from other common sensory receptors with its key features and functions, including threshold, relaxation, allodynia and hyperalgesia behaviors. Such nociceptive behaviors are attributed to the formation and spontaneous rupture of the Ag filament with diffusive dynamics. Finally, we built a pressure sensory alarm system by using our artificial nociceptor devices.

Synthesis of naked plasmonic/magnetic Au/Fe3O4 nanostructures by plasmon-driven anti-replacement reaction.

In this study, naked Au(core)/Fe3O4(shell) hybrid nanostructures are rapidly synthesized by a plasmon-driven anti-replacement reaction. The Au nanoparticles are prepared by pulsed laser ablation in water. The mixture of Au nanoparticles and FeCl3 solution is irradiated under a laser with a specific wavelength. The Fe3+ ions are reduced to low valence species by the 'hot electrons' in Au, and form the Fe3O4 spindles on the surface of Au nanoparticles. The Au nanoparticles are synchronously oxidized to Au+ and Au3+ ions by the 'hot holes'. The saturation magnetization and coercivity of Fe3O4 spindles are 48.7 emu g-1 and 218.9 Oe, respectively. Our work provides a facile route to obtain the naked Au/Fe3O4 plasmonic/magnetic nanostructures.

Trap state passivation and photoactivation in wide band gap inorganic perovskite semiconductors.

CsPbCl3 is a promising material to construct future short wavelength optoelectronic devices based on inorganic perovskite semiconductors. In this study, CsPbCl3 microcrystals were synthesized by a solution phase process. It was found that the photoluminescence (PL) intensities of the CsPbCl3 microcrystals can increase by up to five times under persistent irradiation of UV light without peak shifting, accompanied with an increased absorption coefficient above the band gap and decreased PL lifetime. This PL enhancement is a reversible process with excitation light switching on and off. The photoactivation process of the CsPbCl3 microcrystals is attributed to the passivation of the trap states.