Harnessing a silicon carbide nanowire photoelectric synaptic device for novel visual adaptation spiking neural networks.

Visual adaptation is essential for optimizing the image quality and sensitivity of artificial vision systems in real-world lighting conditions. However, additional modules, leading to time delays and potentially increasing power consumption, are needed for traditional artificial vision systems to implement visual adaptation. Here, an ITO/PMMA/SiC-NWs/ITO photoelectric synaptic device is developed for compact artificial vision systems with the visual adaption function. The theoretical calculation and experimental results demonstrated that the heating effect, induced by the increment light intensity, leads to the photoelectric synaptic device enabling the visual adaption function. Additionally, a visual adaptation artificial neuron (VAAN) circuit was implemented by incorporating the photoelectric synaptic device into a LIF neuron circuit. The output frequency of this VAAN circuit initially increases and then decreases with gradual light intensification, reflecting the dynamic process of visual adaptation. Furthermore, a visual adaptation spiking neural network (VASNN) was constructed to evaluate the photoelectric synaptic device based visual system for perception tasks. The results indicate that, in the task of traffic sign detection under extreme weather conditions, an accuracy of 97% was achieved (which is approximately 12% higher than that without a visual adaptation function). Our research provides a biologically plausible hardware solution for visual adaptation in neuromorphic computing.

First-principles prediction of ferroelectric Janus Si2XY (X/Y = S/Se/Te, X ≠ Y) monolayers with negative Poisson's ratios.

Nowadays, two-dimensional (2D) materials with Janus structures evoke much attention due to their unique mechanical and electronic properties. In this work, Janus Pma2-Si2XY (X/Y = S/Se/Te, X ≠ Y) ferroelectric monolayers are firstly proposed and systematically investigated by first-principles calculations. These monolayers exhibit remarkable mechanical properties, including small Young's modulus values, negative Poisson's ratios (NPRs) and large critical strains, reflecting their exceptional flexibility and stretchability. More strikingly, the novel structures of Si2STe and Si2SeTe also endow them with in-plane spontaneous polarization (Ps) and low energy barrier for phase transition, with Ps and energy barrier values being 1.632 × 10-10 C m-1 and 159 meV for Si2STe and 1.149 × 10-10 C m-1 and 196.6 meV for Si2SeTe. The ab initio molecular dynamics (AIMD) simulations reveal high Curie temperatures (Tc) for Si2STe and Si2SeTe, ranging between 1300 K and 1400 K. Additionally, Si2XY monolayers exhibit high anisotropic carrier mobility (∼103 cm2 V-1 s-1) and an extraordinary light absorption coefficient (∼105 cm-1). Our research not only broadens the family of 2D Janus ferroelectric materials, but also demonstrates their potential applications in nanomechanical, nanoelectronic and optoelectronic devices.

Janus monolayer PXC (X = As/Sb) for photocatalytic water splitting with a negative Poisson's ratio.

Two-dimensional (2D) Janus materials have attracted considerable attention in photocatalysis owing to their robust redox capability and efficient segregation. In this study, we propose a novel Janus monolayer structure, denoted as PXC (X = As/Sb), exhibiting favorable stability in terms of dynamics, thermal properties, and mechanical characteristics. The PXC monolayers demonstrate a relatively smaller Young's modulus (132.5/119.5 N m-1 for PAsC/PSbC) and large negative Poisson's ratios (-0.15/-0.101 for PAsC/PSbC). Moreover, the HSE06 + SOC functional results show that PAsC/PSbC are indirect semiconductors with a 2.33/1.43 eV band gap, exhibiting a suitable band alignment for photocatalytic water splitting. The calculated high carrier mobility (104 cm2 V-1 s-1), along with a significant discrepancy, determined by the deformation potential theory and the built-up field induced by the large intrinsic dipole, effectively suppresses the recombination of photogenerated carriers. Furthermore, PXC monolayers possess a strong absorption capacity in the visible and ultraviolet light region (105 cm-1). Therefore, our results indicate that PXC monolayers hold great potential for application in the field of photocatalytic water splitting.

Resistive switching modulation by incorporating thermally enhanced layer in HfO2-based memristor.

Oxide-based memristors by incorporating thermally enhanced layer (TEL) have showed great potential in electronic devices for high-efficient and high-density neuromorphic computing owing to the improvement of multilevel resistive switching. However, research on the mechanism of resistive switching regulation is still lacking. In this work, based on the method of finite element numerical simulation analysis, a bilayer oxide-based memristor Pt/HfO2(5 nm)/Ta2O5(5 nm)/Pt with the Ta2O5TEL was proposed. The oxygen vacancy concentrates distribution shows that the fracture of conductive filaments (CF) is at the interface where the local temperature is the highest during the reset process. The multilevel resistive switching properties were also obtained by applying different stop voltages. The fracture gap of CF can be enlarged with the increase of the stopping voltage, which is attributed to the heat-gathering ability of the TEL. Moreover, it was found that the fracture position of oxygen CF is dependent on the thickness of TEL, which exhibits a modulation of device RS performance. These results provide a theoretical guidance on the suitability of memristor devices for use in high-density memory and brain-actuated computer systems.

Electrostatic gating dependent multiple band alignments in ferroelectric VS2/Ga2O3 van der Waals heterostructures.

Two-dimensional (2D) van der Waals (vdW) heterostructures with spontaneous intrinsic ferroelectrics play an essential role in ferroelectric memories. Also, the reversal of polarized directions induces band alignment transitions among different types to provide a new path for multifunctional devices. In this work, the structural and electronic properties of 2D VS2/Ga2O3 vdW heterostructures under different polarizations were investigated using first-principles calculations with the vdW correction of the DFT-D2 method. The results reveal that the polarized direction of a 2D Ga2O3 monolayer can cause a distinct band structure reversion from a metal to a semiconductor due to the shift of band alignment induced by the interlayer charge transfer. Moreover, the VS2/P↑ Ga2O3 heterostructures retain type-I and type-II band alignments in the majority and minority channel, respectively, under an external electric field. Interestingly, applying the external electric field for VS2/P↓ Ga2O3 heterostructures can lead to a transition from type-II to type-I in the majority channel, and from type-II to type-III in the minority channel. Our work provides a feasible way to realize 2D VS2/Ga2O3 vdW heterostructures for potential applications in ferroelectric memories and electrostatic gating dependent multiple band alignment devices.

Robust ferroelectricity in low-dimensional δ-SiX (X = S/Se): a first-principles study.

Low-dimensional ferroelectric materials hold great promise for application in nonvolatile memory devices. In this work, ferroelectricity in two-dimensional monolayers and one-dimensional nanowires based on δ-SiX (X = S and Se) materials with spontaneous polarization and ferroelectric switching energy barriers has been predicted using the first-principles method. The results show that the intrinsic ferroelectric values due to spontaneous polarization of 2D-SiS, 2D-SiSe, 1D-SiS and 1D-SiSe are 3.22 × 10-10 C m-1, 3.00 × 10-10 C m-1, 7.58 × 10-10 C m-1 and 6.81 × 10-10 C m-1, respectively. The Monte Carlo simulations and ab initio molecular dynamics (AIMD) simulations both indicate that 2D-SiX and 1D-SiX exhibit room-temperature ferroelectricity. Moreover, the polarization and ferroelectric switching energy barrier can be tuned by applying a strain. Notably, spontaneous spin polarization can be achieved by hole doping in one-dimensional nanowires. Our findings not only broaden the research field of low-dimensional ferroelectric materials, but also provide a promising platform for the application of novel nano-ferroelectric devices.