Nano Letters最新文献

Hybrid superconductor–topological insulator (TI)nanostructuresconstitute a promising material platform for exploring proximity-inducedsuperconductivity in systems with topologically protected surfacestates. A key obstacle has been the realization of clean and well-controlledsuperconductor–TI interfaces, as TI surfaces rapidly degradeunder ambient conditions. Here, we introduce a fully in situ, multi-angle stencil lithography technique that enables the fabricationof proximitized charge islands in TIs. The approach combines selectivearea growth of (Bi,Sb)₂Te₃ nanoribbons withangle-controlled deposition of diffusion barriers, superconductingAl, and ultrathin oxide tunnel barriers, allowing scalable fabricationof hybrid nanostructures without post-growth processing. Low-temperaturetransport measurements reveal robust Coulomb blockade and a pronouncedsuppression of low-energy conductance, which vanishes with a magneticfield, consistent with proximity-induced superconductivity in theisland. These results establish a versatile nanofabrication platformthat enables access to previously unexplored TI-based hybrid quantumdevices and opens new routes for investigating superconductivity intopological nanostructures.

Spectrally isolated,electrically driven emission fromlocalizedstates in two-dimensional semiconductors remains challenging in scalableplanar devices. Here, we report narrow-line-width alternating-currentelectroluminescence (ACEL) from localized states in monolayer WSe₂ using a lithographically defined sub-5 nm Au/Pt nanogap onSiO₂/Si at 3.5 K. The curved nanogap geometry producesa nonuniform strain landscape and regions of enhanced electric fieldthat may influence the local electronic environment. Under square-wavegate excitation, the device exhibits a spectrally isolated ACEL lineat 1.652 eV with an apparent fitted line width of approximately 2meV, in contrast to broad, multipeak photoluminescence from the samedevice. Spectral decomposition identifies dominant ZPL-like and weakerred-shifted sideband-like contributions. This nanogap architectureprovides a scalable planar platform for narrow-line-width, electricallydriven localized emission in two-dimensional materials.

The recent discovery that double-stranded DNA standsverticallyon graphene has transformed graphene from a passive quenching surfaceinto an active platform for axial single-molecule readout, openingopportunities in biosensing, molecular materials, and nanoscale devices.Here, we use graphene energy transfer with vertical nucleic acids(GETvNA) to resolve how partially single- and double-stranded DNAconstructs interact with graphene at the molecular level. Single-moleculefluorescence lifetime measurements show that dsDNA adopts both verticaland parallel orientations on graphene and reveal rare 1–3 base-pairzipping and unzipping events. We further show that the ssDNA anchorlength regulates dsDNA conformation by controlling the availabilityof graphene binding sites for exposed nucleotides, thereby modulatingpartial unzipping. Finally, we demonstrate programmable axial motionusing DNA hybridization and strand-displacement reactions, realizinga single-molecule DNA nanoelevator with nanometer precision. Theseresults establish GETvNA as a platform for probing molecular interfacesand engineering DNA-based nanodevices on graphene.

Photoexcited quantum dot (QD)–chromophorehybrid systemshold great promise for photon upconversion, a process that could significantlyboost the efficiency of solar energy technologies and be useful forspintronics and quantum information science. However, the magneticinteractions that govern the generation and transfer of spin polarizationin these systems are not well understood. Here, we report the firsttime-resolved electron paramagnetic resonance (EPR) study of tripletenergy transfer (TET) in colloidal Si QDs conjugated with two anthracene-basedorganic molecules: 9-ethylanthracene and 9-vinylanthracene. Tripletformation and spin dynamics monitored with time-resolved continuous-waveand pulsed EPR spectroscopy reveal Dexter-type TET from Si QDs tothe anthracene moiety. Notably, the electron spin polarization ofthese conjugates displayed unusual fully emissive patterns, a surprisingresult that cannot be explained by the conventional spin-orbit orradical-pair mechanisms typically seen in purely organic donor–acceptorsystems. The mechanism of this novel TET is discussed.

Plasma-driven solutionelectrochemistry (PDSE) offers an additive-freeapproach to nanomaterial synthesis but has not been widely implementedbecause of the current lack of control strategies, rooted in the limitedmechanistic understanding of nucleation and growth that has been inaccessibleto direct observation. We report on the real-time visualization ofgold nanoparticle nucleation, growth, and coalescence in a thin ionicliquid film using a newly developed in situ plasma–liquidtransmission electron microscopy platform. Monomer attachment is identifiedas the dominant growth process, and the measured growth rates suggesta nucleation-limited regime. Trajectory analysis reveals enhancednucleation near the film edge, likely due to an increased monomerconcentration caused by plasma-induced solvent evaporation. The reportedobservations provide critical insights into mechanisms and rate-limitingprocesses and can provide guidance for PDSE-enabled process developmentto achieve the rapid synthesis of colloidal nanomaterials with a narrowsize distribution.

Circular dichroism (CD) in plasmonic metamaterials canbe strengthenedby engineering three-dimensional (3D) chiral geometry and electromagneticcoupling. We report 3D helical-shaped plasmonic metamaterials assembledfrom colloidal Au nanocrystal/bulk Au bilayer heterostructures. Arraysof planar spiral patterns defined by nanoimprint lithography are transformedinto 3D helical metamaterials through strain-driven, out-of-planefolding induced by ligand exchange and annealing. Compared with multiple-short-arm(4C) references having the same total arm length, single-helical (1H)structures exhibit stronger differential transmittance between left-and right-handed circularly polarized light (ΔT). Adding a second helical arm to form double-helical (2H) structuresfurther increases ΔT to nearly 70% in the mid-infraredrange. Electromagnetic simulations reveal that intra-meta-atom coupling,antenna loading, and mode hybridization reshape the resonances andamplify CD beyond the response of isolated components. This work demonstratesthat 3D helical architectures can significantly strengthen plasmonicCD responses and provides a scalable nanocrystal-based platform fordesigning compact mid-infrared chiroptical devices.

Theorbital Hall conductivity (OHC) is central to orbitronics,yet its microscopic control remains largely unexplored. Here we identifya general mechanism in which tilted Weyl crossings formed by orbitallydistinct bands generate a strongly asymmetric orbital Berry curvature(OBC) distribution, whose imbalance survives Brillouin-zone integrationand yields a sizable OHC already at zeroth order. Using first-principlescalculations, we show that monolayer PtBi₂ realizes thismechanism and hosts a giant OHC dominated by a type-II Weyl point.A small biaxial tensile strain drives a type-II → type-I →type-II Weyl-cone tilting transition, reversibly switching the signof the OHC through the chiral orbital texture of the crossing bands,assisted by a strain-induced structural phase transition. Our resultsestablish Weyl engineering of orbital quantum geometry as a routeto generating and reversibly controlling OHC in polar multi-orbitalmaterials.

Theoretically,defect-free monolayer graphene grown bychemicalvapor deposition can block nearly all gases and moisture, making ita promising material for large-scale flexible encapsulation in futurephotonic and electronic applications. However, the lack of reliabletransfer and fabrication methods that suppress the formation of transfer-inducedcracks and interlayer transport of water molecules in stacked graphenefilms severely limits the barrier performance of current graphene-basedbarrier films. In this work, we employed a dopant-incorporated polyvinylidenedifluoride with a concentration gradient as a transfer medium to suppresscrack formation during transfer through conformal graphene–polymercontact and to dope graphene, thereby hindering water diffusion throughenhanced water–graphene interactions. Consequently, the as-fabricatedbarrier film achieved an ultralow water vapor transmission rate valueof 9.3 × 10^–5 g m^–2 day^–1. In addition, a home-built roll-to-roll transfersystem for continuous fabrication of graphene barrier films demonstratesthe scalability of this strategy and its potential for large-scaleflexible and transparent encapsulation.

Miniaturized weak-light detection is constrained by therelianceon external amplification and signal-accumulation circuitry. Here,we report a time-integrated phototransistor (TIPT) based on γ-InSephotoactive gate architecture that enables intrinsic signal amplificationand temporal accumulation within a single device. This architectureenables continuous integration and amplification of weak optical signals,achieving ultra-low-power detection with high photosensitivity, withdetection limits down to 29 fW at 520 nm and 4.2 pW at 980 nm. Theaccumulation process is dynamically tunable and resettable via gatecontrol. A single-device sequential scanning reconstruction furthervalidates improved image contrast through temporal integration dueto the robustness and repeatability of TIPT. These results establishtime-integrated photogating as a strategy for ultra-low-power photodetection,offering a compact and energy-efficient platform for miniaturizedweak-light imaging.

Battery-free wireless energy delivery is highly desiredfor implantablemedical devices (IMDs). Although triboelectric nanogenerators (TENGs)show promise, they often face challenges in delivering high powerdensity under small loads, limiting their capability to drive extracorporealtransmitters. Herein, we propose a self-circulating instantaneous-dischargeTENG (SCID-TENG) that decouples charge accumulation from instantaneousrelease. The SCID-TENG delivers 144.6 V and 20.9 W at 1 kΩ whilemaintaining a load-insensitive output from 1 kΩ to 1 MΩ.Integrating electrowetting-assisted charge injection (EWCI) with theSCID-TENG further boosts the output, yielding a peak power densityof 3922 W/m². With incorporation into a wireless transmissionsystem, the device achieves a subcutaneous peak-to-peak voltage of145.8 V, 1.9 times that before EWCI. The SCID-TENG generates negligibleenergy per pulse, confirming its safety for direct contact. Collectively,this work achieves ultrahigh power density under small loads, providinga viable pathway toward wireless energy delivery of IMDs.