Deep-learning-augmented microscopy for super-resolution imaging of nanoparticles.

Conventional optical microscopes generally provide blurry and indistinguishable images for subwavelength nanostructures. However, a wealth of intensity and phase information is hidden in the corresponding diffraction-limited optical patterns and can be used for the recognition of structural features, such as size, shape, and spatial arrangement. Here, we apply a deep-learning framework to improve the spatial resolution of optical imaging for metal nanostructures with regular shapes yet varied arrangement. A convolutional neural network (CNN) is constructed and pre-trained by the optical images of randomly distributed gold nanoparticles as input and the corresponding scanning-electron microscopy images as ground truth. The CNN is then learned to recover reversely the non-diffracted super-resolution images of both regularly arranged nanoparticle dimers and randomly clustered nanoparticle multimers from their blurry optical images. The profiles and orientations of these structures can also be reconstructed accurately. Moreover, the same network is extended to deblur the optical images of randomly cross-linked silver nanowires. Most sections of these intricate nanowire nets are recovered well with a slight discrepancy near their intersections. This deep-learning augmented framework opens new opportunities for computational super-resolution optical microscopy with many potential applications in the fields of bioimaging and nanoscale fabrication and characterization. It could also be applied to significantly enhance the resolving capability of low-magnification scanning-electron microscopy.

Plasmoelectric Potential in Plasmon-Mediated Electrochemistry.

Plasmon-mediated chemical reactions have attracted intensive research interest as a means of achieving desirable reaction yields and selectivity. The energetic charge carriers and elevated local temperature induced by the nonradiative decay of surface plasmons are thought to be responsible for improving reaction outcomes. This study reports that the plasmoelectric potential is another key contributor in plasmon-mediated electrochemistry. Additionally, we disclose a convenient and reliable method for quantifying the specific contributions of the plasmoelectric potential, hot electrons, and photothermal heating to the electroreduction of oxygen at the plasmonic Ag electrode, revealing that the plasmoelectric potential is the dominating nonthermal factor under short-wavelength illumination and moderate electrode bias. This work elucidates novel mechanistic understandings of plasmon-mediated electrochemistry, facilitating high-performance plasmonic electrocatalyst design optimization.

Plasmonic Nanocavity Induced Coupling and Boost of Dark Excitons in Monolayer WSe2 at Room Temperature.

Spin-forbidden excitons in monolayer transition metal dichalcogenides are optically inactive at room temperature. Probing and manipulating these dark excitons are essential for understanding exciton spin relaxation and valley coherence of these 2D materials. Here, we show that the coupling of dark excitons to a metal nanoparticle-on-mirror cavity leads to plasmon-induced resonant emission with the intensity comparable to that of the spin-allowed bright excitons. A three-state quantum model combined with full-wave electrodynamic calculations reveals that the radiative decay rate of the dark excitons can be enhanced by nearly 6 orders of magnitude through the Purcell effect, therefore compensating its intrinsic nature of weak radiation. Our nanocavity approach provides a useful paradigm for understanding the room-temperature dynamics of dark excitons, potentially paving the road for employing dark exciton in quantum computing and nanoscale optoelectronics.

Long-Range Directional Routing and Spatial Selection of High-Spin-Purity Valley Trion Emission in Monolayer WS2.

Valley-dependent excitation and emission in transition metal dichalcogenides (TMDCs) have recently emerged as a new avenue for optical data manipulation, quantum optical technologies, and chiral photonics. The valley-polarized electronic states can be optically addressed through photonic spin-orbit interaction of excitonic emission, typically with plasmonic nanostructures, but their performance is limited by the low quantum yield of neutral excitons in TMDC multilayers and the large Ohmic loss of plasmonic systems. Here, we demonstrate a valleytronic system based on the trion emission in high-quantum-yield WS2 monolayers chirally coupled to a low-loss microfiber. The integrated system uses the spin properties of the waveguided modes to achieve long-range directional routing of valley excitations and also provides an approach to selectively address valley-dependent emission from different spatial locations around the microfiber. This valleytronic interface can be integrated with fiber communication devices, allowing for merging valley polarization and chiral photonics as an alternative mechanism for optical information transport and manipulation in classical and quantum regimes.

A Flexible Plasmonic-Membrane-Enhanced Broadband Tin-Based Perovskite Photodetector.

Lead-free perovskite quantum dots (QDs) have been widely investigated for optoelectronic devices because of their excellent electrical and optical properties. However, optoelectronic devices based on such lead-free perovskites still have much lower performance than those made of Pb-based counterparts. Herein, we developed a lead-free photodetector with an enhanced broadband spectral response ranging from 300 to 630 nm. By balancing plasmonic near-field enhancement and surface energy quenching through precisely controlling the thickness of Al2O3 spacer between the CsSnBr3 QDs and silver nanoparticle membrane, the photodetector with 5 nm thick Al2O3 experiences a maximum photocurrent enhancement of 6.5-fold at 410 nm, with a responsivity of 62.3 mA/W and detectivity of 4.27 × 1011 Jones. Moreover, its photocurrent shows a negligible decrease after 100 cycles of bending, which is ascribed to the tension-offset induced by the self-assembled nanoparticle membrane. The proposed plasmonic membrane enhancement provides a great potential for high-performance perovskite optoelectronic devices.

Two-dimensional ferroelasticity in van der Waals ß'-In2Se3.

Two-dimensional (2D) materials exhibit remarkable mechanical properties, enabling their applications as flexible and stretchable ultrathin devices. As the origin of several extraordinary mechanical behaviors, ferroelasticity has also been predicted theoretically in 2D materials, but so far lacks experimental validation and investigation. Here, we present the experimental demonstration of 2D ferroelasticity in both exfoliated and chemical-vapor-deposited ß'-In2Se3 down to few-layer thickness. We identify quantitatively 2D spontaneous strain originating from in-plane antiferroelectric distortion, using both atomic-resolution electron microscopy and in situ X-ray diffraction. The symmetry-equivalent strain orientations give rise to three domain variants separated by 60° and 120° domain walls (DWs). Mechanical switching between these ferroelastic domains is achieved under ≤0.5% external strain, demonstrating the feasibility to tailor the antiferroelectric polar structure as well as DW patterns through mechanical stimuli. The detailed domain switching mechanism through both DW propagation and domain nucleation is unraveled, and the effects of 3D stacking on such 2D ferroelasticity are also discussed. The observed 2D ferroelasticity here should be widely available in 2D materials with anisotropic lattice distortion, including the 1T' transition metal dichalcogenides with Peierls distortion and 2D ferroelectrics such as the SnTe family, rendering tantalizing potential to tune 2D functionalities through strain or DW engineering.

Two-Dimensional Antiferroelectricity in Nanostripe-Ordered In_{2}Se_{3}.

Two-dimensional (2D) layered materials have been an exciting frontier for exploring emerging physics at reduced dimensionality, with a variety of exotic properties demonstrated at 2D limit. Here, we report the first experimental discovery of in-plane antiferroelectricity in a 2D material ß^{'}-In_{2}Se_{3}, using optical and electron microscopy consolidated by first-principles calculations. Different from conventional 3D antiferroelectricity, antiferroelectricity in ß^{'}-In_{2}Se_{3} is confined within the 2D layer and generates the unusual nanostripe ordering: the individual nanostripes exhibit local ferroelectric polarization, whereas the neighboring nanostripes are antipolar with zero net polarization. Such a unique superstructure is underpinned by the intriguing competition between 2D ferroelectric and antiferroelectric ordering in ß^{'}-In_{2}Se_{3}, which can be preserved down to single-layer thickness as predicted by calculation. Besides demonstrating 2D antiferroelectricity, our finding further resolves the true nature of the ß^{'}-In_{2}Se_{3} superstructure that has been under debate for over four decades.

Thermal and Nonthermal Effects in Plasmon-Mediated Electrochemistry at Nanostructured Ag Electrodes.

Hot carriers (HCs) and thermal effects, stemming from plasmon decays, are crucial for most plasmonic applications. However, quantifying these two effects remains extremely challenging due to the experimental difficulty in accurately measuring the temperature at reaction sites. Herein, we provide a novel strategy to disentangle HCs from photothermal effects based on the different traits of heat dissipation (long range) and HCs transport (short range), and quantitatively uncover the dominant and potential-dependent role of photothermal effect by investigating the rapid- and slow-response currents in plasmon-mediated electrochemistry at nanostructured Ag electrode. Furthermore, the plasmoelectric surface potential is found to contribute to the rapid-response currents, which is absent in the previous studies.