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The rapid development of mixed‐halide perovskites has established a versatile optoelectronic platform owing to their extraordinary physical properties, but there remain challenges toward achieving highly reliable synthesis and performance, in addition, post‐synthesis approaches for tuning their photoluminescence properties after device fabrication remain limited. In this work, an effective approach is reported to leveraging hot electrons generated from plasmonic nanostructures to regulate the optical properties of perovskites. A plasmonic metasurface composed of Au nanoparticles can effectively tailor both photoluminescence and location‐specific phase segregation of mixed‐halide CsPbI2Br thin films. The ultrafast transient absorption spectroscopy measurements reveal hot electron injection on the timescale of hundreds of femtoseconds. Photocurrent measurements confirm the hot‐electron‐enhanced photon‐carrier conversion, and in addition, gate‐voltage tuning of phase segregation is observed because of correlated carrier injection and halide migration in the perovskite films. Finally, the characteristics of the gate‐modulated light emission are found to conform to a rectified linear unit function, serving as nonlinear electrical‐to‐optical converters in artificial neural networks. Overall, the hot electron engineering approach demonstrated in this work provides effective location‐specific control of the phase and optical properties of halide perovskites, underscoring the potential of plasmonic metasurfaces for advancing perovskite technologies. [ABSTRACT FROM AUTHOR]

Gradient‐index (GRIN) lenses have long been recognized for their importance in optics as a result of their ability to manipulate light. However, traditional GRIN lenses are limited on a scale of tens of microns, impeding their integration into nanoscale optical devices. This study presents a groundbreaking self‐assembled method that overcomes this limitation, allowing for constructing GRIN lenses at an extremely small dimension. The self‐assembly process offers several advantages, including creating highly precise, scalable, cost‐effective, and complex structures that eliminate the need for intricate and time‐consuming manual assembly. By engineering densely packed arrays of metallic nanoparticles, exceptional control over the local refractive index has been achieved. This is accomplished by layer‐by‐layer assembly of gold nanoparticles of different sizes over silica beads. A GRIN lens light‐sink is built where light is preferentially directed toward the center, which is corroborated by measuring the fluorescence of Rhodamine B (RhB) in the inside. Unlike traditional bulky macroscopic GRIN lenses, light‐sinks boast a size under 2.5 µm. Notably, the self‐focusing effects of this design allowed us to track the growth of single‐nanoparticle layers using SERS (Surface‐Enhanced Raman Spectroscopy). These results pave the way for designing and developing lens‐like devices at the nanoscale, allowing unprecedented light manipulation. [ABSTRACT FROM AUTHOR]

Semiconductor‐based surface‐enhanced Raman spectroscopy (SERS) substrates, as a new frontier in the field of SERS, are hindered by their poor electromagnetic field confinement and weak light‐matter interaction. Metasurfaces, a class of 2D artificial materials based on the electromagnetic design of nanophotonic resonators, enable strong electromagnetic field enhancement and optical absorption engineering for a wide range of semiconductors. However, the engineering of semiconductor substrates into metasurfaces for improving SERS activity remains underexplored. Here, an improved SERS metasurface platform is developed that leverages the combination of titanium oxide (TiO2) and the emerging physical concept of optical bound states in the continuum (BICs) to boost the Raman emission. Moreover, fine‐tuning of BIC‐assisted resonant absorption offers a pathway for maximizing the photoinduced charge transfer effect (PICT) in SERS. High values of BIC‐assisted electric field enhancement (|E/E0|2 ≈103) are achieved, challenging the preconception of weak electromagnetic (EM) field enhancement on semiconductor SERS substrates. The BIC‐assisted TiO2 metasurface platform offers a new dimension in spectrally‐tunable SERS with earth‐abundant and bio‐compatible semiconductor materials, beyond the traditional plasmonic ones. [ABSTRACT FROM AUTHOR]

High‐index Mie‐resonant dielectric nanostructures provide a new framework to manipulate light at the nanoscale. In particular their local field confinement together with their inherently low losses at frequencies below their bandgap energy allows to efficiently boost and control linear and nonlinear optical processes. Here, nanoantennas composed of a thin indium‐tin oxide (ITO) layer in the center of a dielectric gallium phosphide (GaP) nanodisc are investigated. While the linear response is similar to that of a pure GaP nanodisc, it is shown that second harmonic generation is enhanced across a broadband wavelength range. On the other hand, third harmonic generation is only marginally enhanced around the epsilon‐near‐zero wavelength of ITO. Linear and nonlinear finite‐difference time‐domain simulations show that despite the high refractive index contrast leading to strong field confinement inside the antenna's ITO layer, the nanogap enhancement effect is mitigated by the low nonlinear volume of the nanogap layer and the antenna's behavior at the harmonic wavelength. Measurement of ITO and GaP nonlinear susceptibilities additionally show a comparative advantage for harmonic generation in GaP. These investigations deliver insights on the mechanisms at play in nonlinear nanogap antennas and their potential applications as nanoscale devices. [ABSTRACT FROM AUTHOR]

Due to their broken symmetry, chiral plasmonic nanostructures have unique optical properties and numerous applications. However, there is still a lack of comprehension regarding how chirality transfer occurs between circularly polarized light (CPL) and these structures. Here, we thoroughly investigate the plasmon‐assisted growth of chiral nanoparticles from achiral Au nanocubes (AuNCs) via CPL without the involvement of any chiral molecule stimulators. We identify the structural chirality of our synthesized chiral plasmonic nanostructures using circular differential scattering (CDS) spectroscopy, which is correlated with scanning electron microscopy imaging at both the single‐particle and ensemble levels. Theoretical simulations, including hot‐electron surface maps, reveal that the plasmon‐induced chirality transfer is mediated by the asymmetric distribution of hot electrons on achiral AuNCs under CPL excitation. Furthermore, we shed light on how this plasmon‐induced chirality transfer can also be utilized for chiral growth in bimetallic systems, such as Ag or Pd on AuNCs. The results presented here uncover fundamental aspects of chiral light‐matter interaction and have implications for the future design and optimization of chiral sensors and chiral catalysis, among others. [ABSTRACT FROM AUTHOR]

Bound states in the continuum (BICs) are localized electromagnetic modes within the continuous spectrum of radiating waves. Due to their infinite lifetimes without radiation losses, BICs are driving research directions in lasing, non‐linear optical processes, and sensing. However, conventional methods for converting BICs into leaky resonances, or quasi‐BICs, with high‐quality factors typically rely on breaking the in‐plane inversion symmetry of the metasurface and often result in resonances that are strongly dependent on the angle of the incident light, making them unsuitable for many practical applications. Here, an emerging class of BIC‐driven metasurfaces is numerically analyzed and experimentally demonstrated, where the coupling to the far field is controlled by the displacement of individual resonators. In particular, both all‐dielectric and metallic as well as positive and inverse displacement‐mediated metasurfaces sustaining angular‐robust quasi‐BICs are investigated in the mid‐infrared spectral region. Their optical behavior with regard to changes in the angle of incidence is investigated and experimentally shows their superior performance compared to two conventional alternatives: silicon‐based tilted ellipses and cylindrical nanoholes in gold. These findings are anticipated to open exciting perspectives for bio‐sensing, conformal optical devices, and photonic devices using focused light. [ABSTRACT FROM AUTHOR]

Metallic nanoparticles possess strong photothermal responses, especially when illuminated as ensembles due to collective effects. However, accurately quantifying the temperature increase remains a significant challenge, impeding progress in several applications. Anti Stokes thermometry offers a promising solution by enabling direct and non‐invasive temperature measurements of the metal without the need for labeling or prior calibration. While Anti Stokes thermometry is successfully applied to individual nanoparticles, its potential to study light‐to‐heat conversion with plasmonic ensembles remains unexplored. In this study, the theoretical framework and the conditions that must be fulfilled for applying Anti Stokes thermometry to ensembles of nanoparticles are discussed. Then, this technique is implemented to measure the light‐induced heating of square arrays of Au nanodisks. The obtained temperature measurements are validated using wavefront microscopy, demonstrating excellent agreement between the two thermometry methods. These results showcase the extension of Anti Stokes thermometry to plasmonic ensembles, highlighting its potential for implementation in the diverse photothermal applications involving these systems. [ABSTRACT FROM AUTHOR]

Hot electron photodetection based on metallic nanostructures is attracting significant attention due to its potential to overcome the limitation of the traditional semiconductor bandgap. To enable efficient hot electron photodetection for practical applications, it is necessary to achieve broadband and perfect light absorption within extremely thin plasmonic nanostructures using cost‐effective fabrication techniques. In this study, an ultrahigh optical absorption (up to 97.3% in average across the spectral range of 1200−2400 nm) is demonstrated in the ultrathin plasmonic nanoneedle arrays (NNs) with thickness of 10 nm, based on an all‐wet metal‐assisted chemical etching process. The efficient hot electron generation, transport, and injection at the nanoscale apex of the nanoneedles facilitate the photodetector to achieve a record low noise equivalent power (NEP) of 4.4 × 10−12 W Hz−0.5 at the wavelength of 1300 nm. The hot‐electron generation and injection process are elucidated through a transport model based on a Monte Carlo approach, which quantitatively matches the experimental data. The photodetector is further integrated into a light imaging system, as a demonstration of the exceptional imaging capabilities at the near‐IR regime. The study presents a lithography‐free, scalable, and cost‐effective approach to enhance hot electron photodetection, with promising prospects for future imaging systems. [ABSTRACT FROM AUTHOR]

Tailoring critical light‐matter coupling is a fundamental challenge of nanophotonics, impacting fields from higher harmonic generation and energy conversion to surface‐enhanced spectroscopy. Plasmonic perfect absorbers (PAs), where resonant antennas couple to their mirror images in adjacent metal films, excel at obtaining different coupling regimes by tuning the antenna‐film gap size. However, practical PA applications require constant gap size, making it impossible to maintain critical coupling beyond singular wavelengths. Here, a new approach for plasmonic PAs is introduced by combining mirror‐coupled resonances with the unique loss engineering capabilities of plasmonic quasi‐bound states in the continuum. This novel combination allows to tailor the light–matter interaction within the under‐coupling, over‐coupling, and critical coupling regimes using flexible tuning knobs including asymmetry parameter, dielectric gap, and geometrical scaling factor. The study demonstrates a pixelated PA metasurface with optimal absorption over a broad range of mid‐infrared wavenumbers (950–2000 cm−1) using only a single gap size and applies it for multispectral surface‐enhanced molecular spectroscopy. Moreover, the asymmetry parameter enables convenient adjustment of the quality factor and resonance amplitude. This concept expands the capabilities and flexibility of traditional gap‐tuned PAs, opening new perspectives for miniaturized sensing platforms towards on‐chip and in situ detection. [ABSTRACT FROM AUTHOR]

Gallium phosphide (GaP) is a promising material for nanophotonics, given its large refractive index and a transparency over most of the visible spectrum. However, since easy phase‐matching is not possible with bulk GaP, a comprehensive study of its nonlinear optical properties for harmonic generation, especially when grown as thin films, is still missing. Here, second harmonic generation is studied from epitaxially grown GaP thin films, demonstrating that the absolute conversion efficiencies are comparable to a bulk wafer over the pump wavelength range from 1060 to 1370 nm. Furthermore, the results are compared to nonlinear simulations, and the second order nonlinear susceptibility is extracted, showing a similar dispersion and magnitude to that of the bulk material. Furthermore, the third order nonlinear susceptibility of amorphous GaP thin films is extracted from third harmonic generation to be more than one order of magnitude larger than that of the crystalline material, and generation of up to the fifth harmonic is reported. The results show the potential of crystalline and amorphous thin films for nonlinear optics with nanoantennas and metasurfaces, particularly in the visible to near infrared part of the spectrum. [ABSTRACT FROM AUTHOR]

Electrocatalysis plays a crucial role in realizing the transition toward a zero‐carbon future, driving research directions from green hydrogen generation to carbon dioxide reduction. Surface‐enhanced infrared absorption spectroscopy (SEIRAS) is a suitable method for investigating electrocatalytic processes because it can monitor with chemical specificity the mechanisms of the reactions. However, it remains difficult to detect many relevant aspects of electrochemical reactions such as short‐lived intermediates. Herein, an integrated nanophotonic‐electrochemical SEIRAS platform is developed and experimentally realized for the in situ investigation of molecular signal traces emerging during electrochemical experiments. A platinum nano‐slot metasurface featuring strongly enhanced electromagnetic near fields is implemented and spectrally targets the weak vibrational mode of the adsorbed carbon monoxide at ≈2033 cm−1. The metasurface‐driven resonances can be tuned over a broad range in the mid‐infrared spectrum and provide high molecular sensitivity. Compared to conventional unstructured platinum films, this nanophotonic‐electrochemical platform delivers a 27‐fold improvement of the experimentally detected characteristic absorption signals, enabling the detection of new species with weak signals, fast conversions, or low surface concentrations. By providing a deeper understanding of catalytic reactions, the nanophotonic‐electrochemical platform is anticipated to open exciting perspectives for electrochemical SEIRAS, surface‐enhanced Raman spectroscopy, and other fields of chemistry such as photoelectrocatalysis. [ABSTRACT FROM AUTHOR]

Parametric infrared (IR) upconversion is a process in which low‐frequency IR photons are upconverted into high‐frequency ultraviolet/visible photons through a nonlinear optical process. It is of paramount importance for a wide range of security, material science, and healthcare applications. However, in general, the efficiencies of upconversion processes are typically extremely low for nanometer‐scale materials due to the short penetration depth of the excitation fields. Here, parametric IR upconversion processes, including frequency doubling and sum‐frequency generation, are studied in layered van der Waals NbOCl2. An upconversion efficiency of up to 0.004% is attained for the NbOCl2 nanosheets, orders of magnitude higher than previously reported values for nonlinear layered materials. The upconverted signal is sensitive to layer numbers, crystal orientation, excitation wavelength, and temperature, and it can be utilized as an optical cross‐correlator for ultrashort pulse characterization. [ABSTRACT FROM AUTHOR]

Plasmon‐driven dehalogenation of brominated purines has been recently explored as a model system to understand fundamental aspects of plasmon‐assisted chemical reactions. Here, it is shown that divalent Ca2+ ions strongly bridge the adsorption of bromoadenine (Br‐Ade) to Ag surfaces. Such ion‐mediated binding increases the molecule's adsorption energy leading to an overlap of the metal energy states and the molecular states, enabling the chemical interface damping (CID) of the plasmon modes of the Ag nanostructures (i.e., direct electron transfer from the metal to Br‐Ade). Consequently, the conversion of Br‐Ade to adenine almost doubles following the addition of Ca2+. These experimental results, supported by theoretical calculations of the local density of states of the Ag/Br‐Ade complex, indicate a change of the charge transfer pathway driving the dehalogenation reaction, from Landau damping (in the lack of Ca2+ ions) to CID (after the addition of Ca2+). The results show that the surface dynamics of chemical species (including water molecules) play an essential role in charge transfer at plasmonic interfaces and cannot be ignored. It is envisioned that these results will help in designing more efficient nanoreactors, harnessing the full potential of plasmon‐assisted chemistry. [ABSTRACT FROM AUTHOR]

The hot carriers generated from the nonradiative decay of surface plasmons in metallic nanostructures can inject into the conduction band of a semiconductor, allowing for the sub‐bandgap photodetection under room temperature. By the controllable interfacial barrier height between the plasmonic and semiconductor/insulator materials, the hot carrier photodetectors working from ultraviolet to infrared bands are extensively demonstrated with significant progress. In this review, hot carrier dynamics are briefly discussed from generation, transport, and emission perspectives. The state‐of‐the‐art progress of hot carrier photodetectors with various configurations, material constitutions, and plasmonic nanostructures are surveyed. To further promote hot carrier extraction efficiency toward the practical applications, the thermodynamic loss analysis, and the potential strategies from the optical, electrical, and material perspectives are addressed. The performances of the developed hot carrier photodetectors are also summarized, particularly addressing the novel functionalities, challenges, and future opportunities. [ABSTRACT FROM AUTHOR]

Optofluidic sensors integrate photonics with micro/nanofluidics to realize compact devices for the label‐free detection of molecules and the real‐time monitoring of dynamic surface binding events with high specificity, ultrahigh sensitivity, low detection limit, and multiplexing capability. Nanophotonic structures composed of metallic and/or dielectric building blocks excel at focusing light into ultrasmall volumes, creating enhanced electromagnetic near‐fields ideal for amplifying the molecular signal readout. Furthermore, fluidic control on small length scales enables precise tailoring of the spatial overlap between the electromagnetic hotspots and the analytes, boosting light‐matter interaction, and can be utilized to integrate advanced functionalities for the pre‐treatment of samples in real‐world‐use cases, such as purification, separation, or dilution. In this review, the authors highlight current trends in nanophotonics‐enabled optofluidic biosensors for applications in the life sciences while providing a detailed perspective on how these approaches can synergistically amplify the optical signal readout and achieve real‐time dynamic monitoring, which is crucial in biomedical assays and clinical diagnostics. [ABSTRACT FROM AUTHOR]

Tailoring optical properties in photocatalysts by nanostructuring them can help increase solar light harvesting efficiencies in a wide range of materials. Whereas plasmon resonances are widely employed in metallic catalysts for this purpose, latest advances of nonradiative, dielectric nanophotonics also enable light confinement and enhanced visible light absorption in semiconductors. Here, a design procedure for large‐scale nanofabrication of semiconductor photoelectrodes using imprint lithography is developed. Anapole excitations and metasurface lattice resonances are combined to enhance the absorption of the model material, amorphous gallium phosphide (a‐GaP), over the visible spectrum. It is shown that cost‐effective, high sample throughput is achieved while retaining the precise signature of the engineered photonic states. Photoelectrochemical measurements under hydrogen evolution reaction conditions and sunlight illumination reveal the contributions of the respective resonances and demonstrate an overall photocurrent enhancement of 5.7, compared to a planar film. These results are supported by optical and numerical analysis of single nanodisks and of the upscaled metasurface. [ABSTRACT FROM AUTHOR]

Metallic nanogaps with metal–metal separations of less than 10 nm have many applications in nanoscale photonics and electronics. However, their fabrication remains a considerable challenge, especially for applications that require patterning of nanoscale features over macroscopic length‐scales. Here, some of the most promising techniques for nanogap fabrication are evaluated, covering established technologies such as photolithography, electron‐beam lithography (EBL), and focused ion beam (FIB) milling, plus a number of newer methods that use novel electrochemical and mechanical means to effect the patterning. The physical principles behind each method are reviewed and their strengths and limitations for nanogap patterning in terms of resolution, fidelity, speed, ease of implementation, versatility, and scalability to large substrate sizes are discussed. [ABSTRACT FROM AUTHOR]

Metasurfaces based on quasi‐bound states in the continuum (quasi‐BICs) constitute an emerging toolkit in nanophotonic sensing as they sustain high quality factor resonances and substantial near‐field enhancements. It is demonstrated that silicon metasurfaces composed of crescent shaped meta‐atoms provide tailored light‐matter interaction controlled by the crescent geometry. Significantly, this metasurface not only exhibits a fundamental quasi‐BIC resonance, but also supports a higher‐order resonance with tunable electromagnetic field enhancement and advantageous properties for sensing. The higher‐order resonance shows twice the sensitivity of the fundamental one for bulk refractive index sensing. It is further demonstrated that both the fundamental and higher‐order resonances can be exploited for sensing ultrathin layers of biomolecules in air and buffer solutions. Specifically, when measuring in buffer solution, the figure of merit of the sensor, defined as the change in the spectral position of the resonance normalized to its full width at half maximum, is a factor of 2.5 larger for the higher‐order resonance when compared to the fundamental one. Due to its high sensitivity and potential for straightforward microfluidic integration, the silicon crescent metasurface is ideally suited for real‐time and in situ biosensing, enabling compact sensing devices for a wide range of diagnostic applications. [ABSTRACT FROM AUTHOR]

The bonding nature between chalcogenides and rare‐earth‐elements is typically described as ionic in the spirit of the Zintl‐Klemm formalism; yet, recent efforts showed that lanthanides also act as d‐metals in transition‐metal‐post‐transition‐metal‐element bonding. Hence, how can we describe the bonding nature between chalcogen and europium atoms, which have frequently acted as electron‐donors like group‐I/II‐elements? To answer this question, we prototypically explored the electronic structure of Eu2CuSe3, which was obtained in considerable yields from solid‐state reactions of the pure elements at 600 °C. The crystal structure of Eu2CuSe3 was determined based on X‐ray diffraction experiments and it is composed of diverse types of linear chains of selenium polyhedra enclosing the copper and europium atoms. These chains are condensed into ∞2 [EuCuSe3] layers, which are separated by additional europium atoms. From analyses of the crystal structure and electronic structure of Eu2CuSe3, it is clear that there are two different europium valence states, whose nature controls if europium acts as an electron‐donor like a group‐I/II‐element or as a d‐metal. [ABSTRACT FROM AUTHOR]

Efficient manipulation of nanoparticles and single molecules has always been of great interest and potential in nanotechnology. However, many challenges still remain in effectively functionalizing structures for this purpose. In this work, taking advantage of graphene's Dirac plasmon for its extreme confinement and tunability, a monolayer conveyor along which the position of optical potential well can be dynamically controlled is theoretically proposed. It is shown that by tuning a single voltage, one can manipulate the resonance along the graphene nanoribbon by changing graphene's effective surface plasmons wavelength. A configuration of monolayer graphene conveyor is proposed and Langevin dynamics reveals that a prototypical nanoparticle (1 nm size) can be effectively confined and transported along the device with proper external bias voltage. Hence, this work successfully proposes a promising avenue toward reconfigurable nanomanipulation of sub‐1 nm nanoparticles, and goes beyond the current state‐of‐the‐art of optical micrometer/nanometer‐sized particles manipulation with optical tweezers and nanoplasmonic tweezers. [ABSTRACT FROM AUTHOR]

Abstract: Extracting plasmon‐induced hot carriers over a metal–semiconductor Schottky barrier enables photodetection below the semiconductor bandgap energy. However, interfacial carrier recombination hinders the efficiency and stability of this process, severely limiting its implementation in telecommunication. This study proposes and demonstrates the use of epitaxially grown lattice‐matched SrTiO3 for interfacial passivation of silicon‐based plasmonic Schottky devices. The devices are activated by an electrical soft‐breakdown of the interfacial SrTiO3 layer, resulting in reproducible rectified Schottky characteristics. The transition to a low resistance state of the SrTiO3 layer boosts the extraction efficiency of hot holes upon resonant plasmonic excitation, giving rise to a two orders of magnitude higher photocurrent compared to devices with a native oxide layer. Photoresponse, tunability, and barrier height studies under reverse biases as high as 100 V present superior stability with the incorporation of the SrTiO3 layer. The investigation paves the way toward plasmon‐induced photodetection for practical applications including those under challenging operating conditions. [ABSTRACT FROM AUTHOR]

Abstract: Synthesis of low‐dimensional metallic nanoparticles with a clean surface, high dispersibility, and enhanced atomic surface distribution is extremely important, as these factors strongly influence the electrocatalytic properties of the nanoparticles. In this study, the early stage electrochemical nucleation and growth of palladium nanoparticles (Pd NPs) under potentiostatic control has been investigated on a Au(111) textured substrate. The size distribution and structural characterization of the ex situ as‐deposited Pd NPs by means of high‐resolution field emission gun‐scanning electron microscopy (FEG‐SEM) at different stages combined with electrochemical measurements revealed that the cluster of nuclei grew independently through the reduction of metal ions. The electrodeposited Pd NPs were very pure, as confirmed by X‐ray photoelectron spectroscopy (XPS), owing to the surfactant‐free green electrodeposition process, and they exhibited a highly dispersed average particle size of 2–5 nm. The average nanoparticle size becomes smaller with higher overpotentials for the same deposition time. The synthesized Pd NPs demonstrated the largest specific surface area (four times that of commercial Pd−C) and electrocatalytic activity in ferrocyanide/ferricyanide redox and ethanol electrooxidation processes (35 times that of commercial Pd−C). This work represents an important step in achieving the fundamental understanding of nucleation and growth of nanoparticles correlating the electrocatalytic performances. [ABSTRACT FROM AUTHOR]

Positioning probe molecules at electromagnetic hot spots with nanometer precision is required to achieve highly sensitive and reproducible surface-enhanced Raman spectroscopy (SERS) analysis. In this article, molecular positioning at plasmonic nanogaps is reported using a high aspect ratio (HAR) plasmonic nanopillar array with a controlled surface energy. A large-area HAR plasmonic nanopillar array is generated using a nanolithography-free simple process involving Ar plasma treatment applied to a smooth polymer surface and the subsequent evaporation of metal onto the polymer nanopillars. The surface energy can be precisely controlled through the selective removal of an adsorbed self-assembled monolayer of low surface-energy molecules prepared on the plasmonic nanopillars. This process can be used to tune the surface energy and provide a superhydrophobic surface with a water contact angle of 165.8° on the one hand or a hydrophilic surface with a water contact angle of 40.0° on the other. The highly tunable surface wettability is employed to systematically investigate the effects of the surface energy on the capillary-force-induced clustering among the HAR plasmonic nanopillars as well as on molecular concentration at the collapsed nanogaps present at the tops of the clustered nanopillars. [ABSTRACT FROM AUTHOR]

Plasmon hybridization between closely spaced nanoparticles yields new hybrid modes not found in individual constituents, allowing for the engineering of resonance properties as well as field enhancement capabilities of metallic nanostructure. Experimental verifications of plasmon hybridization have been thus far mostly limited to optical frequencies, as metals cannot support surface plasmons at longer wavelengths. Here, we introduce the concept of 'spoof plasmon hybridization' in highly conductive metal structures and investigate experimentally the interaction of localized surface plasmon resonances (LSPR) in adjacent metal disks corrugated with subwavelength spiral patterns. We show that the hybridization results in the splitting of spoof plasmon modes into bonding and antibonding resonances analogous to the molecular orbital rule and plasmonic hybridization in optical spectrum. These hybrid modes can be manipulated to produce enormous field enhancement (>5000) by tuning the separation between disks or alternatively, the disk size, which effectively changes the relative gap size. The impact of the radiation loss is considered to find out the optimum disk size that maximizes field enhancement capabilities. Our investigation not only extends the range of applicability of the hybridization model, but also provides insightful guidance to exporting the exciting applications associated with plasmon hybridization to lower spectral range. [ABSTRACT FROM AUTHOR]

Macrocycles with quaterthiophene subunits were obtained by cyclooligomerization by direct oxidative coupling of unsubstituted dithiophene moieties. The rings were closed with high selectivity by an α,β ′-connection of the thiophenes as proven by NMR spectroscopy. The reaction of the precursor with terthiophene moieties yielded the symmetric α,α ′-linked macrocycle in low yield together with various differently connected isomers. Blocking of the β-position of the half-rings yielded selectively the α,α ′-linked macrocycle. Selected cyclothiophenes were investigated by scanning tunneling microscopy, which displayed the formation of highly ordered 2D crystalline monolayers. [ABSTRACT FROM AUTHOR]

This work presents analytical, numerical and experimental demonstrations of light diffracted through a logarithmic spiral (LS) nanoslit, which forms a type of switchable and focustunable structure. Owing to a strong dependence on the incident photon spin, the proposed LS-nanoslit converges incoming light of opposite handedness (to that of the LS-nanoslit) into a confined subwavelength spot, while it shapes light with similar chirality into a donut-like intensity profile. Benefitting from the varying width of the LS-nanoslit, different incident wavelengths interfere constructively at different positions, i.e., the focal length shifts from 7.5 μm (at λ = 632.8 nm) to 10 μm (at λ = 488 nm), which opens up new opportunities for tuning and spatially separating broadband light at the micrometer scale. [ABSTRACT FROM AUTHOR]

High carrier mobility and tunability in graphene enable fundamental studies for plasmonics and various applications. Despite its versatility, however, single‐layer graphene (SLG) suffers from poor coupling efficiency to electromagnetic waves, presenting a major challenge for photonic applications. Compared with visible or infrared radiation, terahertz (THz) waves exhibit higher absorption in SLG due to Drude‐like intraband transitions, but the wavelength‐to‐SLG size mismatch becomes even more dramatic. Here, we experimentally demonstrate 99% extinction of THz wave transmission when SLG covers the openings of 2‐nm‐wide (≈λ/1 000 000) slits through a metal film. By resonantly coupling THz waves through annular nanogaps, the extremely localized fields lead to near‐perfect extinction and strong absorption in SLG. Atomic‐layer lithography is used to produce these nanometer‐wide, millimeter‐long gaps over an entire 4‐in. wafer. Furthermore, by integrating these devices with an ionic liquid, enhanced intraband absorption in the SLG leads to 80% modulation of THz waves with an operational voltage as low as 1.5 V. [ABSTRACT FROM AUTHOR]

An essential and so far unresolved factor influencing the evolution of cancer and the clinical management of patients is intratumour clonal and phenotypic heterogeneity. However, the de novo identification of tumour subpopulations is so far both a challenging and an unresolved task. Here we present the first systematic approach for the de novo discovery of clinically detrimental molecular tumour subpopulations. In this proof-of-principle study, spatially resolved, tumour-specific mass spectra were acquired, using matrix-assisted laser desorption/ionization ( MALDI) imaging mass spectrometry, from tissues of 63 gastric carcinoma and 32 breast carcinoma patients. The mass spectra, representing the proteomic heterogeneity within tumour areas, were grouped by a corroborated statistical clustering algorithm in order to obtain segmentation maps of molecularly distinct regions. These regions were presumed to represent different phenotypic tumour subpopulations. This was confirmed by linking the presence of these tumour subpopulations to the patients' clinical data. This revealed several of the detected tumour subpopulations to be associated with a different overall survival of the gastric cancer patients ( p = 0.025) and the presence of locoregional metastases in patients with breast cancer ( p = 0.036). The procedure presented is generic and opens novel options in cancer research, as it reveals microscopically indistinct tumour subpopulations that have an adverse impact on clinical outcome. This enables their further molecular characterization for deeper insights into the biological processes of cancer, which may finally lead to new targeted therapies. Copyright © 2014 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Realizing laterally continuous ultra‐thin gold films on transparent substrates is a challenge of significant technological importance. In the present work, formation of ultra‐thin gold films on fused silica is studied, demonstrating how suppression of island formation and reduction of plasmonic absorption can be achieved by treating substrates with (3‐mercaptopropyl) trimethoxysilane prior to deposition. Void‐free films with deposition thickness as low as 5.4 nm are realized and remain structurally stable at room temperature. Based on detailed structural analysis of the films by specular and diffuse X‐ray reflectivity measurements, it is shown that optical transmission properties of continuous ultra‐thin films can be accounted for using the bulk dielectric function of gold. However, it is important to take into account the non‐abrupt transition zone between the metal and the surrounding dielectrics, which extends through several lattice constants for the laterally continuous ultra‐thin films (film thickness below 10 nm). This results in a significant reduction of optical transmission, as compared to the case of abrupt interfaces. These findings imply that the atomic‐scale interface structure plays an important role when continuous ultra‐thin films are considered, e.g., as semi‐transparent electrical contacts, since optical transmission deviates significantly from the theoretical predictions for ideal films. [ABSTRACT FROM AUTHOR]

Savanna ecosystems comprise 22% of the global terrestrial surface and 25% of Australia (almost 1.9 million km2) and provide significant ecosystem services through carbon and water cycles and the maintenance of biodiversity. The current structure, composition and distribution of Australian savannas have coevolved with fire, yet remain driven by the dynamic constraints of their bioclimatic niche. Fire in Australian savannas influences both the biophysical and biogeochemical processes at multiple scales from leaf to landscape. Here, we present the latest emission estimates from Australian savanna biomass burning and their contribution to global greenhouse gas budgets. We then review our understanding of the impacts of fire on ecosystem function and local surface water and heat balances, which in turn influence regional climate. We show how savanna fires are coupled to the global climate through the carbon cycle and fire regimes. We present new research that climate change is likely to alter the structure and function of savannas through shifts in moisture availability and increases in atmospheric carbon dioxide, in turn altering fire regimes with further feedbacks to climate. We explore opportunities to reduce net greenhouse gas emissions from savanna ecosystems through changes in savanna fire management. [ABSTRACT FROM AUTHOR]

Supersized darkness in three dimensions surrounded by all light in free space is demonstrated theoretically and experimentally in the visible regime. The object staying in the darkness is similar to staying in an empty light capsule because light just bypasses it by resorting to destructive interference. A binary-optical system is designed and fabricated based on achieving antiresolution (AR), by which electromagnetic energy flux avoids and bends smoothly around a nearly perfect darkness region. AR remains an unexplored topic hitherto, in contrast to the super-resolution for realizing high spatial resolution. This novel scheme replies on smearing out the point spread function and thus poses less stringent limitations upon the object's size and position since the created dark (zero-field) area reach 8 orders of magnitude larger than λ2 in cross-sectional size. It functions very well with arbitrarily polarized beams in three dimensions, which is also frequency scalable in the whole electromagnetic spectrum. [ABSTRACT FROM AUTHOR]

Analysis of wildfire extinguishment can help to identify the relative contribution of weather and management to the prevention of fire spread. Here we examine the role of weather, previous fire scars and other fuel interruptions at stopping the spread of nine large (mean 90 000 ha) late dry season fires in Arnhem Land, in the tropical savannas of northern Australia. Daily spread was mapped using Moderate-resolution Imaging Spectroradiometer ( MODIS) satellite imagery with a resolution of 250 m. We sampled points along the boundary of the fires and 1 km inside the boundary and compared conditions between the two sets. Using a combination of binomial regression and regression tree analysis, we found that recent burn scars (from the same year) were very effective at stopping fires. Where there was any recent burning within 500 m of a point, there was a 92% likelihood that it was a boundary. Interruptions such as roads, rivers and topography had small but significant effects. Vegetation type and vegetation greenness also had minor effects. Weather had a small effect via wind speed. This minor role of weather was reinforced by the fact that on most days the fires were both spreading and stopping at different parts of their perimeter. In these savannas, the weather in the late dry season is relatively invariant and is probably always conducive to some degree of fire spread. Here, interruptions to the fuel are critical to stopping fires. Nevertheless, for approximately half of boundary cases, the cause of stopping was not clear. This is probably due to the coarse scale of the analysis that does not reflect fine patterns of fuel arrangements. [ABSTRACT FROM AUTHOR]

We investigate with Raman spectroscopy how gold nanostructures of different shape, size and geometry locally modify a graphene cover layer through strain. The resulting phonon softening translates into frequency downshifts of up to 85 cm-1 for the 2D-mode of graphene. With spatially resolved and excitation dependent Raman measurements we demonstrate that the downshifted Raman peaks exclusively arise from strained graphene subject to plasmonic enhancement by the nanostructures. The signals arise from an area well below the size of the laser spot. They serve as a local probe for the interaction between graphene and intense light fields. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Ultrastrong exciton–photon coupling of Frenkel molecular excitons is demonstrated at room temperature in a metal‐clad microcavity containing a thin film of 2,7‐bis[9,9‐di(4‐methylphenyl)‐fluoren‐2‐yl]‐9,9‐di(4‐methylphenyl)fluorene. A giant Rabi splitting of Ω ∼ 1 eV is measured using angle‐resolved reflectivity and bright photoluminescence is observed from the lower polariton branch. To obtain the virtual photon and exciton content of the polariton ground state, the results are interpreted in terms of the full Hopfield Hamiltonian, including anti‐resonant terms. Also included is an analytical treatment of the often ignored and sometimes misinterpreted TM‐polarized metal–insulator–metal plasmon–polariton. [ABSTRACT FROM AUTHOR]