Reconfigurable optoelectronic transistors for multimodal recognition.

Biological nervous system outperforms in both dynamic and static information perception due to their capability to integrate the sensing, memory and processing functions. Reconfigurable neuromorphic transistors, which can be used to emulate different types of biological analogues in a single device, are important for creating compact and efficient neuromorphic computing networks, but their design remains challenging due to the need for opposing physical mechanisms to achieve different functions. Here we report a neuromorphic electrolyte-gated transistor that can be reconfigured to perform physical reservoir and synaptic functions. The device exhibits dynamics with tunable time-scales under optical and electrical stimuli. The nonlinear volatile property is suitable for reservoir computing, which can be used for multimodal pre-processing. The nonvolatility and programmability of the device through ion insertion/extraction achieved via electrolyte gating, which are required to realize synaptic functions, are verified. The device's superior performance in mimicking human perception of dynamic and static multisensory information based on the reconfigurable neuromorphic functions is also demonstrated. The present study provides an exciting paradigm for the realization of multimodal reconfigurable devices and opens an avenue for mimicking biological multisensory fusion.

Interface-type tunable oxygen ion dynamics for physical reservoir computing.

Reservoir computing can more efficiently be used to solve time-dependent tasks than conventional feedforward network owing to various advantages, such as easy training and low hardware overhead. Physical reservoirs that contain intrinsic nonlinear dynamic processes could serve as next-generation dynamic computing systems. High-efficiency reservoir systems require nonlinear and dynamic responses to distinguish time-series input data. Herein, an interface-type dynamic transistor gated by an Hf0.5Zr0.5O2 (HZO) film was introduced to perform reservoir computing. The channel conductance of Mott material La0.67Sr0.33MnO3 (LSMO) can effectively be modulated by taking advantage of the unique coupled property of the polarization process and oxygen migration in hafnium-based ferroelectrics. The large positive value of the oxygen vacancy formation energy and negative value of the oxygen affinity energy resulted in the spontaneous migration of accumulated oxygen ions in the HZO films to the channel, leading to the dynamic relaxation process. The modulation of the channel conductance was found to be closely related to the current state, identified as the origin of the nonlinear response. In the time series recognition and prediction tasks, the proposed reservoir system showed an extremely low decision-making error. This work provides a promising pathway for exploiting dynamic ion systems for high-performance neural network devices.

Magnetoelectric coupling in multiferroics probed by optical second harmonic generation.

Magnetoelectric coupling, as a fundamental physical nature and with the potential to add functionality to devices while also reducing energy consumption, has been challenging to be probed in freestanding membranes or two-dimensional materials due to their instability and fragility. In this paper, we report a magnetoelectric coupling probed by optical second harmonic generation with external magnetic field, and show the manipulation of the ferroelectric and antiferromagnetic orders by the magnetic and thermal fields in BiFeO3 films epitaxially grown on the substrates and in the freestanding ones. Here we define an optical magnetoelectric-coupling constant, denoting the ability of controlling light-induced nonlinear polarization by the magnetic field, and found the magnetoelectric-coupling was suppressed by strain releasing but remain robust against thermal fluctuation for freestanding BiFeO3.

Reversible fatigue-rejuvenation procedure and its mechanism in Hf0.5Zr0.5O2epitaxial films.

HfO2-based ferroelectrics, such as Hf0.5Zr0.5O2, arouse great attention in recent years because of their CMOS compatibility and robust nano-scale ferroelectricity. However, fatigue is one of the toughest problems for ferroelectric applications. The fatigue mechanism of HfO2-based ferroelectrics is different from conventional ferroelectric materials, and research on the fatigue mechanism in HfO2-based epitaxial films have been rarely reported. In this work, we fabricate 10 nm Hf0.5Zr0.5O2epitaxial films and investigate the fatigue mechanism. The experimental data show that the remanent ferroelectric polarization value decreased by 50% after 108cycles. It is worth noting that the fatigued Hf0.5Zr0.5O2epitaxial films can be recovered through applying electric stimulus. Combined with the temperature-dependent endurance analysis, we propose that fatigue of our Hf0.5Zr0.5O2films comes from both phase transition between ferroelectric Pca21and antiferroelectric Pbca as well as defects generation and dipole pinned. This result offers a fundamental understanding of HfO2-based film system, and could provide an important guideline for subsequent studies and future applications.

Photo-induced non-volatile VO2 phase transition for neuromorphic ultraviolet sensors.

In the quest for emerging in-sensor computing, materials that respond to optical stimuli in conjunction with non-volatile phase transition are highly desired for realizing bioinspired neuromorphic vision components. Here, we report a non-volatile multi-level control of VO2 films by oxygen stoichiometry engineering under ultraviolet irradiation. Based on the reversible regulation of VO2 films using ultraviolet irradiation and electrolyte gating, we demonstrate a proof-of-principle neuromorphic ultraviolet sensor with integrated sensing, memory, and processing functions at room temperature, and also prove its silicon compatible potential through the wafer-scale integration of a neuromorphic sensor array. The device displays linear weight update with optical writing because its metallic phase proportion increases almost linearly with the light dosage. Moreover, the artificial neural network consisting of this neuromorphic sensor can extract ultraviolet information from the surrounding environment, and significantly improve the recognition accuracy from 24% to 93%. This work provides a path to design neuromorphic sensors and will facilitate the potential applications in artificial vision systems.

Large-Scale Hf0.5 Zr0.5 O2 Membranes with Robust Ferroelectricity.

Hafnia-based compounds have considerable potential for use in nanoelectronics due to their compatibility with complementary metal-oxide-semiconductor devices and robust ferroelectricity at nanoscale sizes. However, the unexpected ferroelectricity in this class of compounds often remains elusive due to the polymorphic nature of hafnia, as well as the lack of suitable methods for the characterization of the mixed/complex phases in hafnia thin films. Herein, the preparation of centimeter-scale, crack-free, freestanding Hf0.5 Zr0.5 O2 (HZO) nanomembranes that are well suited for investigating the local crystallographic phases, orientations, and grain boundaries at both the microscopic and mesoscopic scales is reported. Atomic-level imaging of the plan-view crystallographic patterns shows that more than 80% of the grains are the ferroelectric orthorhombic phase, and that the mean equivalent diameter of these grains is about 12.1 nm, with values ranging from 4 to 50 nm. Moreover, the ferroelectric orthorhombic phase is stable in substrate-free HZO membranes, indicating that strain from the substrate is not responsible for maintaining the polar phase. It is also demonstrated that HZO capacitors prepared on flexible substrates are highly uniform, stable, and robust. These freestanding membranes provide a viable platform for the exploration of HZO polymorphic films with complex structures and pave the way to flexible nanoelectronics.

Accurately Regulating the Electronic Structure of Nix Sey @NC Core-Shell Nanohybrids through Controllable Selenization of a Ni-MOF for pH-Universal Hydrogen Evolution Reaction.

N-doped carbon-encapsulated transition metal selenides (TMSs) have garnered increasing attention as promising electrocatalysts for hydrogen evolution reaction (HER). Accurately regulating the electronic structure of these nanohybrids to reveal the underlying mechanism for enhanced HER performances is still challenging and thus requires deep excavation. Herein, a series of pomegranate-like Nix Sey @NC core-shell nanohybrids (including Ni0.85 Se @ NC, NiSe2 @NC, and NiSe@NC) through controllable selenization of a Ni-MOF precursor is reported. The component of the nanohybrids can be fine-tuned by tailoring the selenization temperature and feed ratio, through which the electronic structure can be synchronously regulated. Among these nanohybrids, the Ni0.85 Se @ NC exhibits the optimum pH-universal HER performance with overpotentials of 131, 135, and 183 mV in 0.5 m H2 SO4 , 1.0 m KOH, and 1.0 m PBS, respectively, at 10 mA cm-2 , which are attributed to the increased partial density of state at the Fermi level and effective van der Waals interactions between Ni0.85 Se and NC matrix explained by density functional theory calculations.

Unveiling the thermolysis natures of ZIF-8 and ZIF-67 by employing in situ structural characterization studies.

The thermolysis routes of two isostructural metal-organic framework compounds (Zn-based ZIF-8 and Co-based ZIF-67) are investigated based on temperature-dependent and time-dependent in situ Fourier transform infrared (FTIR) spectroscopy and in situ X-ray diffraction data, as well as thermogravimetric-differential scanning calorimetry (TG-DSC) analyses and density functional theory (DFT) calculations. These data highlight thermolysis effects on different vibrations and dissociations within specific atomic moieties. The coordination differences between Zn-N and Co-N lead to the distinct thermolysis routes of ZIF-8 and ZIF-67. ZIF-8 is easily deformed during heating while decomposes at a higher temperature due to the saturated Zn-N coordination. ZIF-67, however, does not deform during heating due to the stronger Co-N bonds, but easily reacts with oxygen due to the unsaturated Co-N bonds. Our results demonstrate that in situ FTIR paired with in situ XRD is a powerful technique for MOF thermolysis investigation, and we suggest that the thermolysis mechanisms of MOFs may be unveiled by investigating a series of MOFs having different coordination types using in situ characterisation methods.