Metallic MoO₂ is promising to be one of noble-metal-comparable SERS substrate materials based on the strong electromagnetic mechanism (EM) enhancement. However, the SERS performance is still unable to meet the practical application requirements. Synthesizing large-scale 2D metallic MoO₂ with controllable thickness, even at atomic level is an effective solution, but it has rarely been reported. The enhancement mechanism based on such kind of metallic metal oxide SERS substrates also lacks a more systematic study. Here, submillimeter-scale (~466 μm) atomic-thin (~4 nm) metallic MoO₂ was firstly synthesized by chemical vapor deposition (CVD). What’s more, it shows high sensitivity as SERS substrates with a maximum enhancement factor up to 10⁷ and a limit of detection down to 10^-9 M, which is at a high level among most metal oxide-based SERS substrates and even comparable to the values of noble metal substrates with ‘hot spots’. It was also firstly and systematically found that both the EM (SPR effect) and CM (charge transfer process) enhancements exist simultaneously in such MoO₂ substrate. The key lies in the thickness of MoO₂ that determines the dominant enhancement mechanism. MoO₂ flakes not only possess noble-metal-comparable SERS performance, but also show potential in image security and information encryption.

Artificial tetrachromatic vision significantly enhanced color discrimination by enabling the detection and spectral decoding of ultraviolet (UV) and visible wavelengths. Inspired by the butterfly visual system, we develop a tetrachromatic optoelectronic synapse utilizing monolayer WS₂ as the core element, effectively integrating sensing, memory, and processing capabilities. The constructed device demonstrates wavelength-sensitive synaptic excitatory behaviors under both visible and UV stimuli, successfully emulating key synaptic functions, including short-term potentiation (STP), long-term potentiation (LTP), and long-term depression (LTD), which achieves an ultralow power consumption of 2.28 aJ. An 8 × 8 retinal synapse array was constructed to achieve high-fidelity tetrachromatic image sensing and memory while enabling color discrimination. Furthermore, the image preprocessing is realized in the optoelectronic synapse array based on visual attention for color, which resulted in an enhancement of the recognition accuracy of the tetrachromatic image to over ~ 98%. This work has precipitated the development of next-generation neuromorphic vision systems that require UV–visible spectral intelligence.

Spiking neural network (SNN), widely known as the third-generation neural network, has been frequently investigated due to its excellent spatiotemporal information processing capability, high biological plausibility, and low energy consumption characteristics. Analogous to the working mechanism of human brain, the SNN system transmits information through the spiking action of neurons. Therefore, artificial neurons are critical building blocks for constructing SNN in hardware. Memristors are drawing growing attention due to low consumption, high speed, and nonlinearity characteristics, which are recently introduced to mimic the functions of biological neurons. Researchers have proposed multifarious memristive materials including organic materials, inorganic materials, or even two-dimensional materials. Taking advantage of the unique electrical behavior of these materials, several neuron models are successfully implemented, such as Hodgkin–Huxley model, leaky integrate-and-fire model and integrate-and-fire model. In this review, the recent reports of artificial neurons based on memristive devices are discussed. In addition, we highlight the models and applications through combining artificial neuronal devices with sensors or other electronic devices. Finally, the future challenges and outlooks of memristor-based artificial neurons are discussed, and the development of hardware implementation of brain-like intelligence system based on SNN is also prospected.

To further improve the quantum efficiency of atomically thin transition metal dichalcogenides (TMDs) is crucial for the realization of high-performance optoelectronic applications. To this regard, a few chemical or physical approaches such as superacid treatment, electrical gating, dielectric screening, and laser irradiation have been developed. In particular, the laser irradiation appears to be a more efficient way with good processability and spatial selectivity. However, the underlying mechanism especially about whether chemisorption or physisorption plays a more important role is still debatable. Here, we unravel the mystery of laser irradiation induced photoluminescence enhancement in monolayer WS₂ by precisely controlling irradiation time and environment. It is found that the synergetic effect of physisorption and chemisorption is responsible for the photoluminescence enhancement, where the physisorption dominates with more than 74% contribution. The comprehensive understanding of the adsorption mechanism in laser-irradiated TMDs may trigger the potential applications for patterned light source, effective photosensor and ultrathin optical memory.