Ming Yang

Two-dimensional (2D) ferroelectric semiconductors offer unique opportunities for ultrathin non-volatile memory and neuromorphic devices, yet the role of stacking order in intrinsic ferroelectric systems remains largely unexplored. Here we report the stacking-controlled growth of large-area 2D β′- and α-In₂Se₃ with distinct 2H and 3R configurations through chemical vapour deposition by regulating selenium kinetics and strain relaxation. By combining atomic-resolution microscopy, non-linear optical characterization and first-principles calculations, we uncover a strong correlation between stacking order and ferroelectric behaviour: β′-In₂Se₃ undergoes an antiferroelectric-to-paraelectric transition when switching from 2H to 3R stacking, whereas in α-In₂Se₃, in-plane ferroelectric polarization vanishes during the 3R-to-2H transition. We further achieve the controlled synthesis of 2H/3R ferroelectric homojunctions and directly visualize polarization-dependent interfacial potential barriers using differential phase-contrast scanning transmission electron microscopy. The engineered homojunctions exhibit switchable band alignment and tunable carrier transport, yielding memristors with significantly reduced switching voltages and an on/off ratio of ∼2.6 × 10⁴, approximately one order of magnitude higher than devices based on single-stacking α-In₂Se₃. These findings establish stacking order as a powerful structural parameter for tailoring ferroelectricity in 2D materials and introduce stacking-engineered polymorphic heterogeneity as a versatile platform for high-performance ferroelectric electronics and memory technologies.

Infrared (IR) spectroscopy probes the hydrogen-bond structure of electrolyte solutions, yet relating spectra to molecular mechanisms is challenging. We combine machine-learning molecular dynamics with a deep Wannier model to compute concentration-dependent IR spectra of aqueous NaCl with strongly constrained and appropriately normed (SCAN)-level accuracy. The spectra semiquantitatively reproduce the experimental blue shift, intensity enhancement, band narrowing, and isosbestic point of the O–H stretching band. Dipole-current decomposition reveals two ionic effects. First, ions reshape the water IR response: by disrupting the hydrogen-bond network of first-shell water, they blue-shift the stretching band and suppress its intensity, with Na+ more disruptive than Cl–. Second, ions themselves carry an IR response: the electronic polarization of Cl–, driven by O–H stretching of its hydrogen-bonded waters, adds high-frequency intensity essential for the isosbestic point. Because both effects are local and additive, spectra at any concentration can be reconstructed from hydration-shell and ionic contributions, a transferable framework for electrolyte IR spectra.

The International Roadmap for Devices and Systems (IRDS) has identified the tunnel field-effect transistor (TFET) as the most promising next-generation logic device that enables sustainable downscaling in driving voltage and power consumption. Demonstrating an acceptable sub–Boltzmann-limit ON current (namely I ₆₀ , the current level when a TFET switches to a subthreshold swing level of 60 millivolts per decade) and current-switching ratio has presented a formidable challenge. We report a TFET based on a bismuth/indium selenide (Bi/InSe) heterostructure that exhibits an I ₆₀ of up to ~10 microamperes per micrometer and a current-switching ratio of >10 ⁷ . We attribute such promising TFETs to precise material design, clean interfaces fabricated under vacuum, and band engineering based on subthreshold swing physics. Our results demonstrate a high-performance basic building block that meets the IRDS requirements for next-generation integrated circuits.

Two‐dimensional (2D) semiconductors directly grown on metal substrates can enable pristine and low‐defect interfaces that are difficult to achieve through transfer‐based fabrication. Although monolayer transition metal dichalcogenides (TMDs) have been widely synthesized on metals, controllable bilayer growth remains challenging owing to distinct thermodynamics and kinetics of second‐layer growth on inert first‐layer surfaces—a significant hurdle given their importance for interlayer‐coupled functionalities like sliding ferroelectricity. Low‐symmetry rhenium dichalcogenides (ReX ₂ , X = S, Se) are especially attractive because their weak interlayer coupling and multiple thermodynamically stable stacking configurations support low sliding barriers. Here, by optimizing precursor flux and growth kinetics, we achieved controlled chemical vapor deposition (CVD) growth of bilayer ReS ₂ with well‐defined parallel and antiparallel stacking directly on Au(111). As‐grown parallel‐stacked bilayers exhibit a large piezoelectric response (effective d _{33, eff} = 9.84 pm V ⁻¹ ) and sliding ferroelectricity with an ultralow coercive voltage of approximately 2 V. Tip‐defined ferroelectric tunnel junction and ferroelectric field‐effect transistor measurements further support the ferroelectric interpretation. Comparative studies of as‐grown, transferred, and exfoliated bilayers reveal that the cleaner, more conformal interface of the as‐grown bilayers is associated with a lower coercive bias. This work establishes a scalable route for stacking‐specific bilayer TMD growth on metal toward low‐coercive sliding ferroelectricity.

Semiconducting MoSe ₂ is susceptible to photon reabsorption, while metallic NbSe ₂ yields low optical damage thresholds, each limiting their nonlinear optical (NLO) performance. Combining these contrasting traits, this study demonstrates that equimolar heterometallic Mo _(1−x) Nb _x Se ₂ , undergoes structural reconfiguration that substantially enhances NLO responses, as revealed by second harmonic generation (SHG) and nonlinear optical absorption (NOA) measurements. Pronounced SHG is observed in odd‐layer samples across 840–1020 nm, with a 32.5% higher optical damage threshold than NbSe ₂ . Further, anomalous SHG persists in even layers, attributed to strain‐induced symmetry breaking and emergence of non‐zero Berry curvature under substantial alloying. This rare behavior distinguishes the alloy from its binaries and enables integration into piezoelectric, ferroelectric, and spin‐valley‐coupling platforms. Furthermore, straindriven bandstructure modifications also yield prominent saturable absorption (SA) at 1 µm, as demonstrated by the generation of ultrafast‐ultrashort laser pulses of 2.292 ps with repetition rate of 11.21 MHz in Yb‑doped fiber laser system and exceptional reverse‐SA (RSA) at 1.5 µm, exhibiting intrinsic “selftriggered” optical‐limiting (10.21% and 18.15% improvements over respective binaries), suitable for laserprotection devices. Overall, the study provides a systematic strategy to engineer and enhance NLO functionalities in binary 2D materials, facilitating the development of functional NLO photonics devices.

Large-area high-quality dielectrics are essential for the integration of two-dimensional (2D) transistors. However, this integration remains challenging, especially for conventional dielectrics that require deposition processes. Adopting van der Waals (vdW) dielectrics is attractive. Molybdenum trioxide (α-MoO ₃ ) has been demonstrated as a vdW dielectric in 2D field-effect transistors (FETs), but previous demonstrations showed limited performance and small size. Here, we grow large-area single-crystalline MoO ₃ with uniform thickness and explore its properties as a dielectric. Single-crystalline MoO ₃ reaches the millimeter scale and maintains a high dielectric constant of ~ 18.5, low gate leakage of approximately 10 ⁻² A cm ⁻² at 3.0 MV cm ^−1, and a large breakdown field of ~ 26.75 MV cm ⁻¹ . Top-gated molybdenum disulfide (MoS ₂ ) transistors exhibit an average subthreshold swing of ~ 71 mV dec ⁻¹ , and an on/off current ratio exceeding 10 ⁸ . Furthermore, we demonstrate MoO ₃ -based integrated circuits and low-power complementary metal-oxide-semiconductor (CMOS) inverters.

Recently, the demand for high‐energy‐density batteries in high‐end consumer electronics has driven the iterative advancement of LiCoO ₂ (LCO) cathodes. For LCO, under conventional charging voltages (≤4.5 V vs. Li/Li ⁺ ), its reversible capacity is only 140–180 mAh g ⁻¹ , far below its theoretical capacity of 274 mAh g ⁻¹ . Increasing the charging voltage (to 4.6 V or even higher) is expected to achieve reversible capacity exceeding 220 mAh g ⁻¹ . However, LCO faces significant issues, including deep phase transitions, lattice O oxidation, severe side reactions, etc., resulting in rapid capacity decay. To solve these issues, a series of breakthroughs were attempted via tuning bulk phase, near‐surface structure, and surface coating aspects, enabling the transition of high‐capacity LCO from lab research toward practical application. This work aims to systematically summarize the intrinsic connections between failure mechanisms and modification strategies, and further refine the design principles for high‐capacity LCO cathodes. By doing so, we provide insights for the next‐generation LCO cathodes, thereby reinforcing the dominance of LCO not only in consumer electronics, but also in emerging fields such as drones and solid‐state batteries.

Alloying two-dimensional semiconductors holds great promise to tailor electronic and optical properties for device applications. In this study, we report the synthesis of monolayer Mo1−xWxS2 alloys with a laterally gradient composition using an improved one-step chemical vapor deposition method. With increasing W composition, the intensity of exciton peak A exhibits a slow increase followed by a near-exponential enhancement, resulting in a significantly enhanced photoluminescence efficiency and a nonlinear blueshift of the peak. First-principles calculations reveal that this nonlinear blueshift is due to the predominant regulation of the conduction band by the Mo atom over a broad composition range. Furthermore, the asymmetry evolution within the conduction band can be attributed to the Mo-dz2 and W-dz2 orbital hybridizations in Mo1−xWxS2 alloys. At high W composition, the Raman spectra exhibit four peaks. The newly emerged A1g-mixed peak originates from the splitting of A1g peak in monolayer MoS2, corresponding to other out-of-plane vibrational modes of S atoms induced by W atoms. Furthermore, the evolution of Raman spectra is driven by lattice distortions and alterations in atomic vibrational modes. This work unravels the mechanism of composition-gradient-tuned electronic and optical properties of 2D Mo1−xWxS2 alloys, which could facilitate the development of next-generation electronic and optoelectronic devices.