Nano Letters最新文献

The ion permeability and selectivity of membranes are crucial in nanofluidic behavior, impacting industries ranging from traditional to advanced manufacturing. Herein, we demonstrate the engineering of ion-conductive membranes featuring angstrom-scale ion-transport channels by introducing ionic polyamidoamine (PAMAM) dendrimers for ion separation. The exterior quaternary ammonium-rich structure contributes to significant electrostatic charge exclusion due to enhanced local charge density; the interior protoplasmic channels of PAMAM dendrimer are assembled to provide additional degrees of free volume. This facilitates the monovalent ion transfer while maintaining continuity and efficient ion screening. The dendrimer-assembled hybrid membrane achieves high monovalent ion permeance of 2.81 mol m^-2 h^-1 (K⁺), reaching excellent mono/multivalent selectivity up to 20.1 (K⁺/Mg²⁺) and surpassing the permselectivities of state-of-the-art membranes. Both experimental results and simulating calculations suggest that the impressive ion selectivity arises from the significant disparity in transport energy barrier between mono/multivalent ions, induced by the "exterior-interior" synergistic effects of bifunctional membrane channels.

Strain can modulate bandgap and carrier mobilities in two-dimensional (2D) materials. Conventional strain-application methodologies relying on flexible/patterned/nanoindented substrates are limited by low thermal tolerance, poor tunability, and/or scalability. Here, we leverage the converse piezoelectric effect to electrically generate and control strain transfer from a piezoelectric thin film to electromechanically coupled 2D MoS₂. Electrical bias polarity change across the piezo film tunes the nature of strain transferred to MoS₂ from compressive (∼0.23%) to tensile (∼0.14%) as verified through Raman and photoluminescence spectroscopies and substantiated by density functional theory calculations. The device architecture, on silicon substrate, integrates an MoS₂ field-effect transistor on a metal-piezoelectric-metal stack enabling strain modulation of transistor drain current (130×), on/off ratio (150×), and mobility (1.19×) with high precision, reversibility, and resolution. Large, tunable tensile (1056) and compressive (-1498) strain gauge factors, electrical strain modulation, and high thermal tolerance promise facile integration with silicon-based CMOS and micro-electromechanical systems.

Rare-earth diantimondes exhibit coupling between structural and electronic orders, which are tunable under pressure and temperature. Here we present the discovery of a new polymorph of LaSb₂ stabilized in thin films synthesized using molecular beam epitaxy. Using diffraction, electron microscopy, and first-principles calculations we identify a YbSb₂-type monoclinic lattice as a yet-uncharacterized stacking configuration. The material hosts superconductivity with a T_c = 2 K, which is enhanced relative to the bulk ambient phase, and a long superconducting coherence length of 1730 Å. This result highlights the potential thin film growth has in stabilizing novel stacking configurations in quasi-two-dimensional compounds with competing layered structures.

The controlled vapor-phase synthesis of two-dimensional (2D) transition metal dichalcogenides (TMDs) is essential for functional applications. While chemical vapor deposition (CVD) techniques have been successful for transition metal sulfides, extending these methods to selenides and tellurides often faces challenges due to uncertain roles of hydrogen (H₂) in their synthesis. Using CVD growth of MoSe₂ as an example, this study illustrates the role of a H₂-free environment during temperature ramping in suppressing the reduction of MoO₃, which promotes effective vaporization and selenization of the Mo precursor to form MoSe₂ monolayers with excellent crystal quality. As-synthesized MoSe₂ monolayer-based field-effect transistors show excellent carrier mobility of up to 20.9 cm²/(V·s) with an on-off ratio of 7 × 10⁷. This approach can be extended to other TMDs, such as WSe₂, MoTe₂, and MoSe₂/WSe₂ in-plane heterostructures. Our work provides a rational and facile approach to reproducibly synthesize high-quality TMD monolayers, facilitating their translation from laboratory to manufacturing.

Maxwell's equations are solved when the amplitude and phase of the electromagnetic field are determined at all points in space. Generally, the Stokes parameters can only capture the amplitude and polarization state of the electromagnetic field in the radiation (far) zone. Therefore, the measurement of the Stokes parameters is, in general, insufficient to solve Maxwell's equations. In this Letter, we solve Maxwell's equations for a set of objects widely used in Nanophotonics using the Stokes parameters alone. These objects are lossless, axially symmetric, and well described by a single multipolar order. Our method for solving Maxwell's equations endows the Stokes parameters an even more fundamental role in the electromagnetic scattering theory.