Plasmon‐Induced Sub‐Bandgap Photodetection with Organic Schottky Diodes

Organic materials for near‐infrared (NIR) photodetection are in the focus for developing organic optical‐sensing devices. The choice of materials for bulk‐type organic photodetectors is limited due to effects like high nonradiative recombination rates for low‐gap materials. Here, an organic Schottky barrier photodetector with an integrated plasmonic nanohole electrode is proposed, enabling structure‐dependent, sub‐bandgap photodetection in the NIR. Photons are detected via internal photoemission (IPE) process over a metal/organic semiconductor Schottky barrier. The efficiency of IPE is improved by exciting localized surface plasmon resonances, which are further enhanced by coupling to an out‐of‐plane Fabry–Pérot cavity within the metal/organic/metal device configuration. The device allows large on/off ratio (>1000) and the selective control of individual pixels by modulating the Schottky barrier height. The concept opens up new design and application possibilities for organic NIR photodetectors.     

Enhanced Spin Seebeck Effect in Monolayer Tungsten Diselenide Due to Strong Spin Current Injection at Interface

The spin current is significantly limited by the spin‐orbit interaction strength, material quality, and spin‐mixing conductance at material interfaces. Such limitations lead to spin current decay at the interfaces, which severely hinders potential applications in spin‐current‐generating thermoelectric devices. Thus, methodical studies on the enhancement of spin currents are indispensable. Herein, a novel approach for enhancing the spin current injected into a normal metal, Pt, using interface effects with a ferromagnetic insulator, yttrium iron garnet (YIG), is demonstrated. This is accomplished by inserting atomically thin monolayer (ML), tungsten diselenide (WSe₂) between Pt and YIG layers. A comparative study of longitudinal spin Seebeck effect (LSSE) measurements is conducted. Two types of ML WSe₂ (continuous and large‐area ML WSe₂ and isolated ML WSe₂ flakes) are used as intermediate layers on YIG film. Notably, the insertion of ML WSe₂ between the Pt and YIG layers significantly enhances the thermopower, V_LSSE/ΔT by a factor of approximately 5.6 compared with that of the Pt/YIG reference sample. This enhancement in the measured LSSE voltages in the Pt/ML WSe₂/YIG trilayer can be explained by the increased spin‐to‐charge conversion at the interface owing to the large spin‐orbit coupling and improved spin mixing conductance with the ML WSe₂ intermediate layer.     

Plasmon‐Enhanced Blue Upconversion Luminescence by Indium Nanocrystals

Numerous endeavors have been undertaken to gain enhanced upconversion luminescence via surface plasmon resonance (SPR) generated by specially designed nanostructures of noble metals (e.g., Au, Ag). However, the SPR response of these metals is usually weak in the ultraviolet (UV) region because of their intrinsic electronic configurations; thus, only green and red upconversion emissions can undergo significant plasmonic enhancement yet without selectivity, while an efficient approach to selectively enhancing the blue upconversion luminescence has been lacking. Herein, by integrating the pronounced UV SPR of silica‐coated indium nanocrystals (InNCs) with blue‐emission upconversion nanoparticles (UCNPs) of NaYbF₄:Tm, an up to tenfold selective luminescence enhancement at 450 nm is obtained upon 980 nm laser excitation. Precise manipulation of the silica shell thickness suggests an optimal working distance of 3 nm between InNCs and UCNPs. This study has, for the first time, realized selective blue upconversion luminescence enhancement by using an inexpensive, non‐noble metal material, which will not only enrich the fundamental investigations of SPR‐enhanced upconversion emission, but also widen the applications of blue light‐emitting nanomaterials, for example, in therapeutics.     

Magnetic Field‐Enhanced Thermoelectric Performance in Dirac Semimetal Cd3As2 Crystals with Different Carrier Concentrations

The magneto‐thermoelectric figure of merit (ZT) in crystals of the topological Dirac semimetal Cd₃As₂ with different carrier concentrations is studied. The ZTs for all the crystals increase with the temperature and show maxima at high temperatures. Meanwhile, the temperatures corresponding to the ZT maxima increase with the carrier concentration. The limit to the improvement in ZT(T) at high temperature could be related to the unusual large enhancement in thermal conductivity at elevated temperatures. The bipolar effect and Dirac liquid behavior are presented as processes possibly responsible for the peculiar behavior of the thermal conductivity. Applying a transverse magnetic field initially leads to a dramatic enhancement and, subsequently, to a slight reduction in ZT for all the crystals. The maximum ZT achieved in a magnetic field increases with the carrier concentration and reaches 1.24 at 450 K in a magnetic field of 9 T for the crystal with the highest carrier concentration. It is expected that this work will be beneficial to the current interests in optimizing the thermoelectric properties of quantum topological materials.     

Light‐Induced Plasmon‐Assisted Phase Transformation of Carbon on Metal Nanoparticles

Highly localized light‐induced phase transformation of electron beam induced deposited carbon nanostructures (dots and squares) on noble metal surfaces is reported. The phase transformation from the amorphous phase to the disordered graphitic phase is analyzed using the characteristic Raman signatures for amorphous and graphitized carbon and conductive force microscopy. The extent of the transformation is found to be largely dependent on the plasmon absorption properties of the underlying metal film. It is observed that the amorphous carbon deposits on the silver films consisting of 12 nm particles with the plasmon absorption near the laser excitation wavelength (514 nm), undergo fast graphitization to a nanocrystalline or a disordered graphitic phase. This transformation results in the formation of a highly conductive carbon/metal interface with at least seven orders of magnitude lower electrical resistivity than the initial insulating interface. It is suggested that the fast graphitization of nanoscale carbon deposits might serve as an efficient path for the formation of complex patterned nanoscale metal‐carbon interconnects with high electrical conductivity.     

Efficient Ag@AgCl Cubic Cage Photocatalysts Profit from Ultrafast Plasmon‐Induced Electron Transfer Processes

Photon‐coupling and electron dynamics are the key processes leading to the photocatalytic activity of plasmonic metal‐semiconductor nanohybrids. To better utilize and explore these effects, a facile large‐scale synthesis route to form Ag@AgCl cubic cages with well‐defined hollow interiors is carried out using a water‐soluble sacrificial salt‐crystal‐template process. Theoretical calculations and experimental probes of the electron transfer process are used in an effort to gain insight into the underlying plasmonic properties of the Ag@AgCl materials. Efficient utilization of solar energy to create electron‐hole pairs is attributed to the significant light confinement and enhancement around the Ag/AgCl interfacial plasmon hot spots and multilight‐reflection inside the cage structure. More importantly, an ultrafast electron transfer process (≤150 fs) from Ag nanoparticles to the AgCl surface is detected, which facilitates the charge separation efficiency in this system, contributing to high photocatalytic activity and stability of Ag@AgCl photocatalyst towards organic dye degradation.     

Plasmon‐Enhanced Fluorescent Sensor based on Aggregation‐Induced Emission for the Study of Protein Conformational Transformation

The alteration in protein conformation not only affects the performance of its biological functions, but also leads to a variety of protein‐mediated diseases. Developing a sensitive strategy for protein detection and monitoring its conformation changes is of great significance for the diagnosis and treatment of protein conformation diseases. Herein, a plasmon‐enhanced fluorescence (PEF) sensor is developed, based on an aggregation‐induced emission (AIE) molecule to monitor conformational changes in protein, using prion protein as a model. Three anthracene derivatives with AIE characteristics are synthesized and a water‐miscible sulfonate salt of 9,10‐bis(2‐(6‐sulfonaphthalen‐2‐yl)vinyl)anthracene (BSNVA) is selected to construct the PEF–AIE sensor. The sensor is nearly non‐emissive when it is mixed with cellular prion protein while emits fluorescence when mixed with disease‐associated prion protein (PrP^Sc). The kinetic process of conformational conversion can be monitored through the fluorescence changes of the PEF–AIE sensor. By right of the amplified fluorescence signal, this PEF–AIE sensor can achieve a detection limit 10 pM lower than the traditional AIE probe and exhibit a good performance in human serum sample. Furthermore, molecular docking simulations suggest that BSNVA tends to dock in the β‐sheet structure of PrP by hydrophobic interaction between BSNVA and the exposed hydrophobic residues.     

Point Defect Engineering of High‐Performance Bismuth‐Telluride‐Based Thermoelectric Materials

Developing high‐performance thermoelectric materials is one of the crucial aspects for direct thermal‐to‐electric energy conversion. Herein, atomic scale point defect engineering is introduced as a new strategy to simultaneously optimize the electrical properties and lattice thermal conductivity of thermoelectric materials, and (Bi,Sb)₂(Te,Se)₃ thermoelectric solid solutions are selected as a paradigm to demonstrate the applicability of this new approach. Intrinsic point defects play an important role in enhancing the thermoelectric properties. Antisite defects and donor‐like effects are engineered in this system by tuning the formation energy of point defects and hot deformation. As a result, a record value of the figure of merit ZT of ≈1.2 at 445 K is obtained for n‐type polycrystalline Bi₂Te_2.3Se_0.7 alloys, and a high ZT value of ≈1.3 at 380 K is achieved for p‐type polycrystalline Bi_0.3Sb_1.7Te₃ alloys, both values being higher than those of commercial zone‐melted ingots. These results demonstrate the promise of point defect engineering as a new strategy to optimize thermoelectric properties.     

Enhanced Thermoelectric Performance in 18‐Electron Nb0.8CoSb Half‐Heusler Compound with Intrinsic Nb Vacancies

Typical 18‐electron half‐Heusler compounds, ZrNiSn and NbFeSb, are identified as promising high‐temperature thermoelectric materials. NbCoSb with nominal 19 valence electrons, which is supposed to be metallic, is recently reported to also exhibit thermoelectric properties of a heavily doped n‐type semiconductor. Here for the first time, it is experimentally demonstrated that the nominal 19‐electron NbCoSb is actually the composite of 18‐electron Nb_0.8+δCoSb (0 ≤ δ < 0.05) and impurity phases. Single‐phase Nb_0.8+δCoSb with intrinsic Nb vacancies, following the 18‐electron rule, possesses improved thermoelectric performance, and the slight change in the content of Nb vacancies has a profound effect on the thermoelectric properties. The carrier concentration can be controlled by varying the Nb deficiency, and the optimization of the thermoelectric properties can be realized within the narrow pure phase region. Benefiting from the elimination of impurity phases and the optimization of carrier concentration, thermoelectric performance is remarkably enhanced by ≈100% and a maximum zT of 0.9 is achieved in Nb_0.83CoSb at 1123 K. This work expands the family of half‐Heusler thermoelectric materials and opens a new avenue for searching for nominal 19‐electron half‐Heusler compounds with intrinsic vacancies as promising thermoelectric materials.     

High‐Performance Dibenzoheteraborin‐Based Thermally Activated Delayed Fluorescence Emitters: Molecular Architectonics for Concurrently Achieving Narrowband Emission and Efficient Triplet–Singlet Spin Conversion

Thermally activated delayed fluorescence (TADF) materials, which enable the full harvesting of singlet and triplet excited states for light emission, are expected as the third‐generation emitters for organic light‐emitting diodes (OLEDs), superseding the conventional fluorescence and phosphorescence materials. High photoluminescence quantum yield (Φ_PL), narrow‐band emission (or high color purity), and short delayed fluorescence lifetime are all strongly desired for practical applications. However, to date, no rational design strategy of TADF emitters is established to fulfill these requirements. Here, an epoch‐making design strategy is proposed for producing high‐performance TADF emitters that concurrently exhibiting high Φ_PL values close to 100%, narrow emission bandwidths, and short emission lifetimes of ≈1 µs, with a fast reverse intersystem crossing rate of over 10⁶ s^?1. A new family of TADF emitters based on dibenzoheteraborins is introduced, which enable both doped and non‐doped TADF‐OLEDs to achieve markedly high external electroluminescence quantum efficiencies, exceeding 20%, and negligible efficiency roll‐offs at a practical high luminance. Systematic photophysical and theoretical investigations and device evaluations for these dibenzoheteraborin‐based TADF emitters are reported here.     

Large Area Artificial Spin Ice and Anti‐Spin Ice Ni80Fe20 Structures: Static and Dynamic Behavior

Artificial spin ice has been the subject of extensive investigation in the last few years due to advances in nanotechnology and characterization techniques. So far, most of the studies have been limited to local probe of small area magnetic elements due to limitations with lithographic techniques used. In this study, large area spin ice and anti‐spin ice Ni₈₀Fe₂₀ structures with three lattice configurations have been fabricated using deep ultraviolet lithography at 193 nm exposure wavelength. The static and dynamic properties are systematically characterized using vibrating sample magnetometer, magnetic force microscopy, and broadband ferromagnetic resonance spectroscopy. Intriguing static and dynamic behaviors are observed due to the geometrical arrangement of the nanomagnets in the lattice. When the nanomagnets are saturated at high field, multiple resonance peaks whose frequencies are strongly dependent on the orientation of the applied magnetic field are observed. The experimental results are in qualitative agreement with the micromagnetic simulations. These findings may find application in the design of magnetically controlled tunable microwave filters.     

Enhanced Light‐Harvesting by Integrating Synergetic Microcavity and Plasmonic Effects for High‐Performance ITO‐Free Flexible Polymer Solar Cells

In this work, a high‐performance ITO‐free flexible polymer solar cell (PSC) is successfully described by integrating the plasmonic effect into the ITO‐free microcavity architecture. By carefully controlling the sizes of embedded Ag nanoprisms and their doping positons in the stratified device, a significant enhancement in power conversion efficiency (PCE) is shown from 8.5% (reference microcavity architecture) to 9.4% on flexible substrates. The well‐manipulated plasmonic resonances introduced by the embedded Ag nanoprisms with different LSPR peaks allow the complementary light‐harvesting with microcavity resonance in the regions of 400–500 nm and 600–700 nm, resulting in the substantially increased photocurrent. This result not only signifies that the spectral matching between the LSPR peaks of Ag nanoprisms and the relatively low absorption response of photoactive layer in the microcavity architecture is an effective strategy to enhance light‐harvesting across its absorption region, but also demonstrates the promise of tailoring two different resonance bands in a synergistic manner at desired wavelength region to enhance the efficiency of PSCs.     

Localized Surface Plasmon Enhanced All‐Inorganic Perovskite Quantum Dot Light‐Emitting Diodes Based on Coaxial Core/Shell Heterojunction Architecture

This work presents a strategy of combining the concepts of localized surface plasmons (LSPs) and core/shell nanostructure configuration in a single perovskite light‐emitting diode (PeLED) to addresses simultaneously the emission efficiency and stability issues facing current PeLEDs' challenges. Wide bandgap n‐ZnO nanowires and p‐NiO are employed as the carrier injectors, and also the bottom/upper protection layers to construct coaxial core/shell heterostructured CsPbBr₃ quantum dots LEDs. Through embedding plasmonic Au nanoparticles into the device and thickness optimization of the MgZnO spacer layer, an emission enhancement ratio of 1.55 is achieved. The best‐performing plasmonic PeLED reaches up a luminance of 10 206 cd m^?2, an external quantum efficiency of ≈4.626%, and a current efficiency of 8.736 cd A^?1. The underlying mechanisms for electroluminescence enhancement are associated with the increased spontaneous emission rate and improved internal quantum efficiency induced by exciton–LSP coupling. More importantly, the proposed PeLEDs, even without encapsulation, present a substantially improved operation stability against water and oxygen degradation (30‐day storage in air ambient, 85% humidity) compared with any previous reports. It is believed that the experimental results obtained will provide an effective strategy to enhance the performance of PeLEDs, which may push forward the application of such kind of LEDs.     

Antisite Defect‐Enhanced Thermoelectric Performance of Topological Crystalline Insulators

As the first experimentally established topological crystalline insulator (TCI), SnTe also exhibits superior thermoelectricity upon proper doping; yet to date, whether such doping will preserve or destroy the salient topological properties in achieving outstanding thermoelectric (TE) performance remains elusive. Using first‐principles calculations combined with Boltzmann transport theory, here the elegant role of antisite defect in optimally enhancing the thermopower of SnTe while simultaneously preserving its topological nature is uncovered. It is first shown that Sn_Te antisite defect effectively induces pronounced variations in the low‐energy density of states rather than rigidly shifting the chemical potential, resulting in a higher Seebeck coefficient and power factor. Next, it is demonstrated that in a wide temperature range, the Seebeck coefficient of antisite‐doped SnTe distinctly outperforms previously identified systems invoking extrinsic dopants. It is further confirmed that such intrinsic antisite doping preserves the nontrivial topology, which in turn favors high electrical conductivity and thermoelectricity. These central findings not only identify an effective and powerful knob in future studies of TE materials, but also help to resolve standing controversies between theory and experiment surrounding the TE performances of both TCIs and topological insulators.     

High‐Density Hotspots Engineered by Naturally Piled‐Up Subwavelength Structures in Three‐Dimensional Copper Butterfly Wing Scales for Surface‐Enhanced Raman Scattering Detection

Very recently, wing scales of natural Lepidopterans (butterflies and moths) manifested themselves in providing excellent three dimensional (3D) hierarchical structures for surface‐enhanced Raman scattering (SERS) detection. But the origin of the observed enormous Raman enhancement of the analytes on 3D metallic replicas of butterfly wing scales has not been clarified yet, hindering a full utilization of this huge natural wealth with more than 175 000 3D morphologies. Herein, the 3D sub‐micrometer Cu structures replicated from butterfly wing scales are successfully tuned by modifying the Cu deposition time. An optimized Cu plating process (10 min in Cu deposition) yields replicas with the best conformal morphologies of original wing scales and in turn the best SERS performance. Simulation results show that the so‐called “rib‐structures” in Cu butterfly wing scales present naturally piled‐up hotspots where electromagnetic fields are substantially amplified, giving rise to a much higher hotspot density than in plain 2D Cu structures. Such a mechanism is further verified in several Cu replicas of scales from various butterfly species. This finding paves the way to the optimal scale candidates out of ca. 175 000 Lepidopteran species as bio‐templates to replicate for SERS applications, and thus helps bring affordable SERS substrates as consumables with high sensitivity, high reproducibility, and low cost to ordinary laboratories across the world.     

Plasmonic‐Assisted Graphene Oxide Films with Enhanced Photothermal Actuation for Soft Robots

Carbon‐based materials are widely used as light‐driven soft actuators relying on their thermal desorption or expansion. However, applying a passive layer in such film construction greatly limits the actuating efficiency, e.g., bending amplitude and speed. In this work, a dual active layer strengthened bilayer composite film made of graphene oxide (GO)–polydopamine (PDA)–gold nanoparticles (Au NPs)/polydimethylsiloxane (PDMS) is developed. In this film, the conventional passive layer is replaced by another AuNPs‐enhanced thermal responsive layer. When applying NIR light exposure, the whole film deforms controllably resulting from the water loss in the GO–PDA–Au NPs layer and thermal expansion in the PDMS layer. Benefiting from the dual active bilayer mechanism, the thin film's actuating efficiency is dramatically improved compared with that of conventional methods. Specifically, the bending amplitude is enhanced up to 173%, and the actuating speed is improved to 3.5‐fold. The soft actuator can act as an artificial arm with high actuating strength and can be used as a wireless gripper. Moreover, the film can be designed as soft robots with various locomotion modes including linear, rolling, and steering motions. The developed composite film offers new opportunities for biomimetic soft robotics as well as future applications.     

Plasmonic Nanowire‐Enhanced Upconversion Luminescence for Anticounterfeit Devices

A novel, efficient, cost‐effective, and high‐level security performance anticounterfeit device achieved by plasmonic‐enhanced upconversion luminescence (UCL) is demonstrated. The plasmonic architecture consists of the randomly dispersed Ag nanowires (AgNWs) network, upconversion nanoparticles (UCNPs) monolayer, and metal film, in which the UCL is enhanced by a few tens, compared to reference sample, becuase the plasmonic modes lead to the concentration of the incident near infrared (NIR) light in the UCNPs monolayer. In the configuration, both the localized surface plasmons (LSPs) around the metallic nanostructures and gap plasmon polaritons (GPPs) confined in the UCNPs monolayer, significantly contribute to the UCL enhancement. The UCL enhancement mechanism resulting from enhanced NIR absorption, boosted internal quantum process, and formation of strong plasmonic hot spots in the plasmonic architecture is analyzed theoretically and numerically. More interestingly, a proof‐of‐concept anticounterfeit device using the plasmonic‐enhanced UCL is proposed, through which a nonreusable and high‐level cost‐effective security device protecting the genuine products is realized.