Dawei Li

Sensitive linear temperature and photo-thermo-electric dual function detection on the micro/nano scale was achieved by constructing a flexible probe based on C@VO ₂ nanocoils.

Developing zero-power humidity sensors is critical to overcoming battery limitations in wearable health monitoring. Here, we report a high-performance self-powered humidity sensor based on MXene/MoS2 van der Waals heterostructures. A thickness gradient in the chemical vapor deposition-grown MoS2 film creates a stable in-plane built-in electric field, while the work function difference between MXene and MoS2 forms a Schottky junction that suppresses dark current and boosts the signal-to-noise ratio. In a humid environment, the super-hydrophilicity of MXene induces moisture-mediated charge transfer and electron injection. The vertical interfacial field efficiently pumps electrons into the MoS2 channel, where they subsequently undergo directional drift driven by the in-plane built-in field, generating a stable direct current output. The sensor exhibits excellent linearity (R2 > 0.99) and ultrafast response/recovery. It enables high-sensitivity monitoring of human respiration and voiceprint characteristics. This dual-field synergistic mechanism offers a promising strategy for next-generation low-power, high-sensitivity environmental and health-monitoring microsystems.

A comprehensive understanding of interfacial physics including electron/phonon transport and coupling at graphene/MoS2 heterojunctions is critical for thermoelectric conversion and sensing, yet remains insufficiently explored. Here, we comprehensively investigate its electrical transport, thermal transport, and thermoelectric properties using a well-designed micro-heater device and a photo-thermal Raman technique. Electrical transport measurements reveal opposite resistance dependence on gate voltage in individual MoS2 and graphene/MoS2 regions, based on which a low-voltage 0–1 logic device is demonstrated. The graphene/MoS2 heterojunction exhibits strong (maximum 1.03 mV/K in our experiment) and asymmetric thermoelectric characteristics, which are attributed to a synergistic mechanism involving interface energy filtering and graphene-doping. The thermoelectric response can be effectively tuned through modulation of interfacial Schottky barrier and electrical coupling. Additionally, we observe electrically tunable interfacial thermal conductance at the interface, which may arise from combined phonon coupling and electron–phonon interaction. Our study provides a promising platform for developing intelligent thermoelectric devices applications.

Sliding ferroelectricity in 2D β-InSe has been confirmed, but its intrinsic electrical and photo-response under ferroelectric polarization remain unclear. Here, graphene/β-InSe/graphene heterostructures were fabricated using graphene electrodes, avoiding the destruction of InSe intrinsic ferroelectric polarization from interface defects in conventional metal contacts. Electrical measurements show robust in-plane and out-of-plane ferroelectric polarizations with synergistic regulation, ultralow switching voltage (<6 V), and a four-order resistance window. The device exhibits high specific detectivity (∼1011 Jones) across the visible range, with photo-response effectively modulated by polarizations, unaffected by photocarriers. This system holds great promise for low-power nonvolatile electronics and intelligent optoelectronics.

Layered niobium oxide dihalides NbOX2 (X = I, Cl), as a new family of van der Waals (vdW) ferroelectrics, have attracted extensive attention, but achieving nonvolatile modulation of their optical and electrical properties remains challenging, thereby limiting their integration into next-generation nanoelectronics and optoelectronics. Here, we report the controlled fabrication of highly crystalline NbOI2−xClx vdW alloys with composition-driven tunable optical and electrical properties via a chemical vapor transport method. Comprehensive experimental characterization combined with first-principles calculation shows that the crystal lattices, phonon modes, and band structures of NbOI2−xClx can be well tailored, which are distributed between NbOI2 and NbOCl2. Both the amplitude and polarization of the second harmonic generation optical signal in NbOI2−xClx exhibit pronounced compositional dependence, offering optical evidence for tunable in-plane ferroelectric characteristics. Moreover, field-effect transistors based on NbOI2−xClx display robust n-type semiconducting behavior, with threshold voltage and carrier mobility precisely modulated through adjustment of I/Cl molar ratio. Furthermore, 2D NbOI2−xClx photodetectors across all compositions exhibit exceptional gate-tunable current on/off ratio and strong polarization-sensitive photo-response. This study thus provides a new vdW ferroelectric material platform with tunable optical and electrical properties, paving the path for its implementation in modern nanophotonics and nanoelectronics.

The BPVE response in the MoS ₂ /CrOCl heterojunction is very strong throughout the visible light region, and the shift photoconductivity reaches −1225.8 µA V ⁻² , which is dozens of times larger than that of traditional bulk BPVE materials.

Layered NbOX₂ (X = Cl, I) materials have recently attracted significant attention owing to their intrinsic in-plane ferroelectricity and anisotropic optical and electronic properties, while the nondestructive modulation of their optical and optoelectronic anisotropy responses remains challenging. In this work, we propose a nondestructive approach to modulate the optical and optoelectronic anisotropy in multilayer NbOX₂ by constructing homo/heterostructures with tunable twist angles. By constructing stacked NbOCl₂ homostructures (or NbOCl₂/NbOI₂ heterostructures) and precisely tuning the twist angle, we achieve giant modulation of both optical reflection anisotropy and Raman scattering anisotropy, ranging from pronounced anisotropy to complete isotropy. The observed modulation can be attributed to optical superposition and is well modeled by linear electromagnetic theory. Moreover, we realize polarization-programmable photodetectors using twisted NbOI₂ homostructures, where distinct anisotropic and isotropic photoresponses are simultaneously achieved within a single device. This study offers an effective strategy for tailoring optical and optoelectronic anisotropy in layered ferroelectrics.

Probing and manipulating the intriguing nonlinear optical responses in new two‐dimensional (2D) van der Waals ferroelectrics are of great significance to the development of 2D material‐based nonlinear optical devices. Herein, the simultaneous detection of second‐harmonic generation (SHG) and third‐harmonic generation (THG) optical responses in a recently discovered 2D in‐plane ferroelectric material, NbOI ₂ is reported, as well as the giant modulation of SHG and THG in NbOI ₂ by integrating with atomically thin MoS ₂ . Both experimental and theoretical results show that NbOI ₂ , ranging from few‐layer to thick‐layer dimensions, exhibits robust SHG and THG responses with pronounced dependence on excitation polarization and wavelength. This behavior is attributed to the anisotropic band structure and excitonic resonance effects in NbOI ₂ . By interfacing a few‐layer NbOI ₂ with a monolayer MoS ₂ , the amplitude and polarization of both SHG and THG signals are effectively modulated, which can be further tailored by excitation wavelength and twist angle. The nonlinear optical control in MoS ₂ /NbOI ₂ heterostructures is correlated with polar symmetry coupling, which is well modeled via nonlinear electromagnetic theory. This study thus provides a new material platform based on van der Waals ferroelectric heterostructures for dynamic control of nonlinear light intensity and polarization, paving the path for developing advanced nonlinear photonic nanodevices.

Ferroelectric oxides, such as Pb(Zr,Ti)O₃ (PZT), have been shown to maintain stable ferroelectricity even in ultrathin film configurations. However, achieving controllable modulation of microstructure and physical responses in these ultrathin films remains challenging, limiting their potential applications in modern nanoelectronics and optoelectronics. Here, we propose a single-pulse femtosecond (fs) laser micromachining technique for high-precision engineering of microstructure and ferroelectric/piezoelectric responses in ultrathin PZT films. The results show that various microstructures can be selectively fabricated through precise control of fs laser fluence. Specifically, nano-concave arrays are formed via low-fluence laser irradiation, which is mainly attributed to the fs laser peening effect. In contrast, nano-volcano (nano-cave) structures are generated when the laser fluence is close to or reaches the ablation threshold. Additionally, applying an fs laser pulse with fluence exceeding a critical threshold enables the formation of nano-cave structures with controlled depth and width in PZT/Pt/SiO₂ multilayers. Piezoresponse force microscopy measurements demonstrate that the laser peening process significantly enhances the piezoelectric response while exerting minimal influence on the coercive field of PZT thin films. This improvement is attributed to the enhanced electromechanical energy transfer and concentrated compressive stresses distribution in PZT thin films resulting from the laser peening effect. Our study not only offers an effective strategy for microstructure and property engineering in ferroelectric materials at the nanoscale but also provides new insights into the underlying mechanism of ultrafast laser processing in ferroelectric thin films.