Multiferroic oxide BFCNT/BFCO heterojunction black silicon photovoltaic devices

An adjustable multistage resistance switching behavior of a photoelectric artificial synaptic device with a ferroelectric diode effect for neuromorphic computing

Neuromorphic computing, which mimics biological neural networks, is widely regarded as the optimal solution for addressing the limitations of traditional von Neumann computing architecture. In this work, an adjustable multistage resistance switching ferroelectric Bi2FeCrO6 diode artificial synaptic device was fabricated using a sol-gel method with a simple process. The device exhibits nonlinearity in its electrical characteristics, demonstrating tunable multistage resistance switching behavior and a strong ferroelectric diode effect through the manipulation of ferroelectric polarization. One of its salient advantages resides in its capacity to dynamically regulate its polarization state in response to an external electric field, thereby facilitating the fine-tuning of synaptic connection strength while maintaining synaptic stability. The device is capable of accurately simulating the fundamental properties of biological synapses, including long/short-term plasticity, paired-pulse facilitation, and spike-timing-dependent plasticity. Additionally, the device exhibits a distinctive photoelectric response and is capable of inducing synaptic plasticity by light signal activation. The utilization of a femtosecond laser for the scrutiny of carrier transport mechanisms imparts profound insights into the intricate dynamics governing the optical memory effect. Furthermore, utilizing a convolutional neural network (CNN) architecture, the recognition accuracy of the MNIST and fashion MNIST datasets was improved to 95.6% and 78%, respectively, through the implementation of improved random adaptive algorithms. These findings present a new opportunity for utilizing Bi2FeCrO6 materials in the development of artificial synapses for neuromorphic computation.

Colossal Ferroelectric Photovoltaic Effect in Inequivalent Double-Perovskite Bi2FeMnO6 Thin Films

Double perovskite films have been extensively studied for ferroelectric order, ferromagnetic order, and photovoltaic effects. The customized ion combinations and ordered ionic arrangements provide unique opportunities for bandgap engineering. Here, a synergistic strategy to induce chemical strain and charge compensation through inequivalent element substitution is proposed. A-site substitution of the barium ion is used to modify the chemical valence and defect density of the two B-site elements in Bi2FeMnO6 double perovskite epitaxial thin films. We dramatically increased the ferroelectric photovoltaic effect to ∼135.67 μA/cm2 from 30.62 μA/cm2, which is the highest in ferroelectric thin films with a thickness of less than 100 nm under white-light LED irradiation. More importantly, the ferroelectric polarization can effectively improve the photovoltaic efficiency of more than 5 times. High-resolution HAADF-STEM, synchrotron-based X-ray diffraction and absorption spectroscopy, and DFT calculations collectively demonstrate that inequivalent ion plays a dual role of chemical strain (+1.92 and -1.04 GPa) and charge balance, thereby introducing lattice distortion effects. The reduction of the oxygen vacancy density and the competing Jahn-Teller distortion of the oxygen octahedron are the main phenomena of the change in electron-orbital hybridization, which also leads to enhanced ferroelectric polarization values and optical absorption. The inequivalent strategy can be extended to other double perovskite systems and applied to other functional materials, such as photocatalysis for efficient defect control.

Tuneable Schottky contact of MoSi2N4/TaS2 van der Waals heterostructure

The two-dimensional M o S i 2 N 4 monolayer is an emerging semiconductor material that offers considerable promise due to its ultra-thin profile, tuneable mechanical properties, excellent optoelectronic properties and exceptional environmental stability. The van der Waals (vdW) heterostructure formed by stacking such two-dimensional monolayers has demonstrated superior performance across various domains. In this study, a vdW heterostructure combining the two-dimensional M o S i 2 N 4 and T a S 2 monolayers is examined using first-principles density functional theory. In its ground state, this van der Waals heterostructure establishes an ohmic contact with an exceptionally low potential barrier height. By modulating the vdW heterostructure with an applied electric field of -0.1 V/Å and under vertical stress, we discovered that M o S i 2 N 4 and T a S 2 can transition from an ohmic contact to a p-type Schottky with an ultra-low Schottky barrier height (SBH). Our observations may give valuable insights for designing reconfigurable, tuneable Schottky nano-devices with enhanced electronic and optical properties based on M o S i 2 N 4 / T a S 2 .

Unexpected Phonon Behaviour in BiFexCr1-xO3, a Material System Different from Its BiFeO3 and BiCrO3 Parents

The dielectric function and the bandgap of BiFe0.5Cr0.5O3 thin films were determined from spectroscopic ellipsometry and compared with that of the parent compounds BiFeO3 and BiCrO3. The bandgap value of BiFe0.5Cr0.5O3 is lower than that of BiFeO3 and BiCrO3, due to an optical transition at ~2.27 eV attributed to a charge transfer excitation between the Cr and Fe ions. This optical transition enables new phonon modes which have been investigated using Raman spectroscopy by employing multi-wavelengths excitation. The appearance of a new Raman mode at ~670 cm-1 with a strong intensity dependence on the excitation line and its higher order scattering activation was found for both BiFe0.5Cr0.5O3 thin films and BiFexCr1-xO3 polycrystalline bulk samples. Furthermore, Raman spectroscopy was also used to investigate temperature induced structural phase transitions in BiFe0.3Cr0.7O3.