Planar Metal Surface Research Articles

Dispersive surface-response formalism to address nonlocality in extreme plasmonic field confinement

Abstract The surface-response formalism (SRF), where quantum surface-response corrections are incorporated into the classical electromagnetic theory via the Feibelman parameters, serves to address quantum effects in the optical response of metallic nanostructures. So far, the Feibelman parameters have been typically obtained from many-body calculations performed in the long-wavelength approximation, which neglects the nonlocality of the optical response in the direction parallel to the metal–dielectric interface, thus preventing to address the optical response of systems with extreme field confinement. To improve this approach, we introduce a dispersive SRF based on a general Feibelman parameter d ⊥(ω, k ‖), which is a function of both the excitation frequency, ω, and the wavenumber parallel to the planar metal surface, k ‖. An explicit comparison with time-dependent density functional theory (TDDFT) results shows that the dispersive SRF correctly describes the plasmonic response of planar and nonplanar systems featuring extreme field confinement. This work thus significantly extends the applicability range of the SRF, contributing to the development of computationally efficient semiclassical descriptions of light–matter interaction that capture quantum effects.

A modified multi-exposure fusion method for laser measurement of specular surfaces

Line laser is widely used in structural light three-dimensional (3D) measurement of metal parts; however, the laser stripes are severely disturbed when measuring complex surfaces. In the process of laser plaSignal sent for page signal is not returning for this article, hence not possible to proceed. Please do the needful, also return the task only after solving the issue. ne calibration, the laser stripe will be damaged by the pattern on the calibration board; when measuring metal surfaces, the laser stripe will be exposed unevenly. Overexposed parts show highlights and artifacts, while underexposed stripes appear burrs, high noise, or even undetectable due to material absorption, which will greatly affect the accuracy of stripe center extraction. In this paper, a modified multi-exposure fusion (MMEF) method is proposed to improve the dynamic range of laser stripe images by enhancing underexposed regions and reducing saturation. The MMEF method uses a “smoothness” index and a “validity” index to give more weight to smooth, Gaussian-like laser stripe patterns and extract reliable modulation information. To evaluate the effectiveness of our method, the performance of the MMEF method is tested for laser plane calibration and metal surface reconstruction, and the high dynamic range (HDR) method, retrieval fusion (RF) method, and exposure fusion (EF) method are introduced for comparison. Measurement experimental results show that the MMEF method proposed in this paper improves the laser plane calibration accuracy by 86.0% and the 3D measurement accuracy of metal surface by 12.5%.

Enhancement and Saturation of Near-Field Radiative Heat Transfer in Nanogaps between Metallic Surfaces.

Near-field radiative heat transfer (NFRHT) between planar metallic surfaces was computationally explored over five decades ago by Polder and van Hove [Phys. Rev. B 4, 3303 (1971)PLRBAQ0556-280510.1103/PhysRevB.4.3303]. These studies predicted that, as the gap size (d) between the surfaces decreased, the radiative heat flux first increases by several orders of magnitude until d is ∼100 nm after which the heat flux saturates. However, despite both the fundamental and practical importance of these predictions, the combined enhancement and saturation of NFRHT at small gaps in metallic surfaces remains experimentally unverified. Here, we probe NFRHT between planar metallic (Pt, Au) surfaces and show that RHT rates can exceed the far-field rate by over a thousand times when d is reduced to ∼25 nm. More importantly, we show that for small values of d RHT saturates due to the dominant contributions from transverse electric evanescent modes. Our results are in excellent agreement with the predictions of fluctuational electrodynamics and are expected to inform the development of technologies such as near-field thermophotovoltaics, radiative heat-assisted magnetic recording, and nanolithography.

Biochemical Sensing with Nanoplasmonic Architectures: We Know How but Do We Know Why?

Here, the research field of nanoplasmonic sensors is placed under scrutiny, with focus on affinity-based detection using refractive index changes. This review describes how nanostructured plasmonic sensors can deliver unique advantages compared to the established surface plasmon resonance technique, where a planar metal surface is used. At the same time, it shows that these features are actually only useful in quite specific situations. Recent trends in the field are also discussed and some devices that claim extraordinary performance are questioned. It is argued that the most important challenges are related to limited receptor affinity and nonspecific binding rather than instrumental performance. Although some nanoplasmonic sensors may be useful in certain situations, it seems likely that conventional surface plasmon resonance will continue to dominate biomolecular interaction analysis. For detection of analytes in complex samples, plasmonics may be an important tool, but probably not in the form of direct refractometric detection.

Monte-Carlo Modeling of Plasmon-Mediated Ion-Ion Energy Transfer

Energy transfer between donor and acceptor ions is an important phenomenon in phosphor applications. In a quantum electrodynamic formulation of the energy transfer process, the donor-acceptor interaction is mediated by photons. In the presence of a metal, however, donor-acceptor interactions may also be mediated by surface plasmons. For donor-acceptor pairs near a smooth planar metallic surface, the probability of surface plasmon-mediated transfer has been estimated, and depends on both the donor-acceptor distance and the distance of each ion from the metallic surface. With the goal of designing an experiment to directly observe surface plasmon-mediated energy transfer, we simulated plasmon-mediated energy transfer in a solid using Monte Carlo methods. Using MatLab, we constructed a solid doped with randomly placed acceptors and donors, simulated the energy transfer process, and plotted the donor decay curves. We show that the plasmon-mediated transfer rate can be comparable to the radiative decay rate, and that the shape of the donor decay curves in plasmon-mediated transfer differs greatly from those resulting from Foerster-Dexter energy transfer. Thus, for a well-designed experiment, it should be possible to unambiguously identify the role of surface plasmons in the energy transfer process.

Activated iridium oxide film (AIROF) electrodes for neural tissue stimulation

Objective. Iridium oxide films are commonly used as a high charge-injection electrode material in neural devices. Yet, few studies have performed in-depth assessments of material performance versus film thickness, especially for films grown on three-dimensional (instead of planar) metal surfaces in neutral pH electrolyte solutions. Further, few studies have investigated the driving voltage requirements for constant-current stimulation using activated iridium oxide (AIROF) electrodes, which will be a key constraint for future use in wirelessly powered neural devices. Approach. In this study, iridium microwire probes were activated by repeated potential pulsing in room temperature phosphate buffered saline (pH 7.1–7.3). Electrochemical measurements were recorded in three different electrolyte conditions for probes with different geometric surface areas (GSAs) as the AIROF thickness was increased. Main results. Maintaining an anodic potential bias during the inter-pulse interval was required for AIROF electrodes to deliver charge levels considered necessary for neural stimulation. Potential pulsing for 100–200 cycles was sufficient to achieve charge injection levels of 2.5 mC cm−2 (50 nC/phase in a biphasic pulse) in PBS with 2000 µm2 iridium probes. Increasing the electrode surface area to 3000 µm2 and 4000 µm2 significantly increased charge-injection capacity, reduced the driving voltage required to deliver a fixed amount of charge, and reduced polarization of the electrodes during constant-current pulsing. Significance. This study establishes methods for choosing an activation protocol and a desired GSA for three-dimensional iridium electrodes suitable for neural tissue insertion and stimulation, and provides guidelines for evaluating electrochemical performance of AIROF using model saline solutions.

Surface-Plasmon- and Green-Light-Induced Polymerization in Mesoporous Thin Silica Films.

The near-field of surface plasmon resonances at planar metal surfaces is confined to the nanoscale, but its resonance wavelength is located in the visible light range, making it interesting for confining polymer functionalization of surfaces but incompatible with the majority of polymerization reactions. Here, fluorescein as a polymerization initiator allowing dye-sensitized polymerization with green light (438-540 nm) is demonstrated to allow polymer functionalization of mesoporous films deposited onto planar silver metal layers. The fluorescein-induced polymer functionalization of mesoporous silica films is investigated with respect to the influence of irradiation power and irradiation time and its potential to generate polymer gradients. Finally, the polymer functionalization of mesoporous films upon surface-plasmon-initiated polymerization is demonstrated. Polymer functionalization thereby determines pH-responsive ionic mesopore accessibility. Consequently, these results present a sound basis for further nanoscale near-field-induced polymer functionalization of porous films.

Radiation of a charge moving along a corrugated surface with a relatively small period

We consider electromagnetic radiation of a charged particle bunch moving uniformly along a corrugated planar metallic surface. It is assumed that the wavelengths under consideration are much larger than the period and the depth of corrugation. Using the method of the equivalent boundary conditions we obtain the Fourier-transform of the Hertz vector. It is demonstrated that the ultra-relativistic bunch excites the surface waves, whereas the volume radiation is absent. Fourier-transforms of the surface wave components and spectral density of energy losses are obtained and analyzed.

Planar Aperiodic Arrays as Metasurfaces for Optical Near-Field Patterning

Plasmonic metasurfaces have spawned the field of flat optics using nanostructured planar metallic or dielectric surfaces that can replace bulky optical elements and enhance the capabilities of traditional far-field optics. Furthermore, the potential of flat optics can go far beyond far-field modulation and can be exploited for functionality in the near-field itself. Here, we design metasurfaces based on aperiodic arrays of plasmonic Au nanostructures for tailoring the optical near-field in the visible and near-infrared spectral range. The basic element of the arrays is a rhomboid that is modulated in size, orientation, and position to achieve the desired functionality of the micron-size metasurface structure. Using two-photon-photoluminescence as a tool to probe the near-field profiles in the plane of the metasurfaces, we demonstrate the molding of light into different near-field intensity patterns and active pattern control via the far-field illumination. Finite element method simulations reveal that the near-field modulation occurs via a combination of the plasmonic resonances of the rhomboids and field enhancement in the nanoscale gaps in between the elements. This approach enables optical elements that can switch the near-field distribution across the metasurface via wavelength and polarization of the incident far-field light and provides pathways for light matter interaction in integrated devices.

Design and Simulation of the Bifacial III-V-Nanowire-on-Si Solar Cell

ABSTRACTRigorous coupled wave analysis (RCWA) simulation was used to model the absorption in periodic arrays of GaAs0.73P0.27 nanowires (NWs) on Si substrates dependent upon the diameter (D), length (L), and spacing (center-to-center distance, or pitch, P) of the NWs. Based on this study, two resonant arrangements for a top NW array sub-cell having the highest limiting short-circuit current densities (Jsc) were found to be close to D = 150 nm, P = 250 nm and D = 300 nm, P = 500 nm, both featuring the same packing density of 0.28. Even though a configuration with thinner NWs exhibited the highest Jsc = 19.46 mA/cm2, the array with D = 350 nm and P = 500 nm provided current matching with the underlying Si sub-cell with Jsc = 18.59 mA/cm2. Addition of a rear-side In0.81Ga0.19As nanowire array with D = 800 nm and P = 1000 nm was found to be suitable for current matching with the front NW sub-cell and middle Si. However, with thinner and sparser In0.81Ga0.19As NWs with D = 700 nm and P = 1000 nm, the Jsc of the bottom sub-cell was increased from 17.35 mA/cm2 to 18.76 mA/cm2 using a planar metallic back surface reflector, thus achieving a current matching with the top and middle cells.

Coupled harmonic oscillator model to describe surface-mode mediated heat transfer

When two objects made of a material that supports surface modes are brought in close proximity to each other such that the vacuum gap between them is less than the thermal wavelength of radiation, then the coupling between the surface modes provides an important channel for the heat transfer to occur, which is different from that mediated by long range propagating electromagnetic waves. Indeed, the heat transfer then exceeds Planck’s blackbody limit by several orders of magnitude and consequently has been used for several energy applications, such as near-field thermophotovoltaic systems. This near-field radiative heat exchange has been traditionally and successfully described using fluctuational electrodynamics principles. Here, we describe an alternate coupled harmonic oscillator model approach, which can be used to model the coupling between surface modes and hence the resultant near-field heat transfer. We apply this theory to estimate the near-field heat transfer for the configurations of two metallic nanoparticles and two planar metal surfaces and compare the result with predictions from fluctuational electrodynamics theory.

Spoof Surface Plasmon Polariton-Based Reconfigurable Band-Pass Filter Using Planar Ring Resonator

In this paper, we report the design, analysis, and development of spoof surface plasmon polariton (SSPP)-based reconfigurable band-pass filter using a planar ring resonator. A transition from quasi-transverse electromagnetic (QTEM) mode of microstrip to SSPP mode was implemented which has been subsequently used to develop a reconfigurable band-pass filter. Trapezoidal shape periodically corrugated metallic grooves etched on the planar metallic surface have been used in the implementation of this transition. In the designed transition, impedance and mode matching between QTEM mode and SSPP mode have been achieved using gradient grooves. The developed transition has been used in the characterization of a ring resonator corrugated with the periodical array of the trapezoidal shape grooves. This SSPP ring resonator shows multiple passbands at different frequencies within the specified frequency range. Varactor diodes have been incorporated in the SSPP ring resonator to obtain tunable passband. Three types of varactor-tuned circuits have been experimentally implemented and characterized using SMV2019-079LF diode package. These circuits will pave the path for development of other front-end circuit elements using the concept of spoof SPP.

Taming parasitic thermal emission by Tamm plasmon polaritons for the mid-infrared

We investigated the concept of a 1D layered structure for resonant selective thermal emission by excitation Tamm plasmon polaritons (TPPs). The modeled and simulated TPP structures for the mid-IR spectral region yield a promising approach for integrated sensing applications. In particular, the TPP structure is composed of an aperiodic multilayer stack of dielectric layers (silicon and silica) on a planar metallic surface acting as a heater and thus emitter for thermal radiation. By varying the layer depths, this design is highly optimizable for individual specifications, such as for enhancing the thermal emittance near to unity around a target wavelength and achieving a resonance with high Q-factor. Here, for demonstration purposes we chose λ=4.26 μm as the target emission wavelength (corresponding to a major CO2 absorption line). However, considering a larger spectral range within the mid-IR region, parasitic resonances emerge in a more or less unpredictable manner and lead to multiband emission. A transfer matrix approach and genetic algorithm (GA) optimization were used to identify feasible stack configurations and characterize the behavior of parasitic resonances. In order to analyze and control the emergence of parasitic emission, different parameters characterizing the stack–metal composition were set. In particular, we found that keeping constraints on the number of dielectric layers and their individual thicknesses allows effective control of parasitic emission while also facilitating modern microlayer fabrication processes. Even though those constraints can hamper the enhancement of the Q-factor at the target resonance, highly performant configurations and parameters for the TPP structures could be identified. Each configuration corresponds to a particular choice of substrate metals (Ag or W), number of layers, and individual layer thicknesses. The behavior of the target and the parasitic resonances was discussed by using concepts of topological photonics and lumped parameter models.

Tools 4.0 – Intelligence starts on the cutting edge

Predominantly milling tools with indexable inserts, so-called inserted-tooth cutters, are used to produce plane metal surfaces. The remarkable features of efficient milling tools are that great production qualities can be attained at large material removal rates and that they are very reliable in use. Hence, it is important for the user that the cutting process is performed at the greatest possible material removal rate with the best possible surface quality. An important cost factor here is the tool life, i.e. the service life of the tool until the cutting edge has to be replaced.Today under Industry 4.0, production is combined with cutting-edge information and communication technology. The goal of a joint project initiated by industry is to increase reliability and save costs by a continuous predictive analysis of the milling process. In this project, the relevant information of the cutting process were permanently established directly in the milling tool during cutting, then processed with intelligent algorithms and displayed to the operator. The physical parameters here are the cutting force directly on the cutting edge, the rotational speed of the tool, the hardness of the machining as well as the temperature close to the cutting edge. An integrated accelerometer is used to determine the rotational speed and also serves as an on/off switching function of the electronics.The measuring data already prefiltered are received by an intelligent tool changer for indexable inserts, which is located right in the middle of several machines. This tool changer functions as charging station and tool for indicating worn indexable inserts. Moreover, it serves as a base for up to five milling tools and as a transmitting terminal for transferring process data to various terminals. Critical system states and necessary changes of indexable inserts can be displayed on terminals, such as computers, smartphones, tablets or smartwatches.This paper presents a functional information chain with the main focus on the design of an intelligent and sensitive tool.

Electrochemical THz-SERS Observation of Thiol Monolayers on Au(111) and (100) Using Nanoparticle-assisted Gap-Mode Plasmon Excitation.

Surface-enhanced Raman scattering (SERS) microscopy using nanoparticle-assisted gap-mode plasmon excitation, which enables us to observe an atomically defined planar metal surface, was combined with THz-Raman spectroscopy to observe ultra-low-frequency vibration modes under electrochemical conditions. This combination helps us to gain deeper insights into electrode/electrolyte interfaces via direct observation of extramolecular vibrations including information on intermolecular and substrate/molecule interactions. Electrochemical reductive desorption of benzenethiol derivatives from Au(111) and (100) was monitored to demonstrate the power of this spectroscopy. Structural differences of the monolayers between these surfaces were seen only in the extramolecular vibration modes such as a large-amplitude hinge-bending motion of the phenyl ring. On the Au(111), where hollow-site and bridge-site adsorption coexisted, the electrochemical reductive desorption was preferentially induced at the hollow sites.

Thermionic field emission of electrons from the paraboloidal metal micropoint

The problem of determining the emission current as a function of voltage, radius of the micropoint curvature, and the distance between the micropoint and a conducting plane is considered on the basis of the theoretical method developed for determining the electric field in the vicinity of a paraboloidal micropoint near a plane metal surface. The universal current–voltage characteristics for a copper micropoint, which are considered for various distances between the micropoint and the plane, can be used for obtaining quantitative estimates of currents in various physics problems.

2D/3D image charge for modeling field emission

Analytic image charge approximations exist for planar and spherical metal surfaces but approximations for more complex geometries, such as the conical and wirelike structures characteristic of field emitters, are lacking. Such models are the basis for the evaluation of Schottky lowering factors in equations for current density. The development of a multidimensional image charge approximation, useful for a general thermal-field emission equation used in space charge studies, is given and based on an analytical model using a prolate spheroidal geometry. A description of how the model may be adapted to be used with a line charge model appropriate for carbon nanotube and carbon fiber field emitters is discussed.

Numerical analysis of terahertz surface plasmon polaritons propagating in a parallel plate configuration

In this paper, we present numerical analysis of terahertz (THz) surface plasmon polaritons propagating in a parallel plate configuration. A planar metal surface has the ability to support loosely bound surface waves, called Zenneck waves at terahertz frequencies. Two parallel metal plates separated by a narrow vacuum region can lead to the highly confined terahertz surface plasmon modes at specific frequencies. The frequency of the terahertz mode can be changed with a change in the gap between the plates. Further, we observed that the carrier concentration of plates strongly effect the frequency of the terahertz mode as well as its properties. We have examined in detail the dispersion properties of the terahertz surface plasmons supported by the parallel plate configuration with a varying gap width as well as carrier density of the plates.

Particle rotational trapping on a floating electrode by rotating induced-charge electroosmosis.

We describe a novel rotating trait of induced-charge electroosmotic slip above a planar metal surface, a phenomenon termed "Rotating induced-charge electro-osmosis" (ROT-ICEO), in the context of a new microfluidic technology for tunable particle rotation or rotational trap. ROT-ICEO has a dynamic flow stagnation line (FSL) that rotates synchronously with a background circularly polarized electric field. We reveal that the rotating FSL of ROT-ICEO gives rise to a net hydrodynamic torque that is responsible for rotating fluids or particles in the direction of the applied rotating electric field either synchronously or asynchronously, the magnitude of which is adjusted by a balance between rotation of FSL and amplitude of angular-direction flow component oscillating at twice the field frequency. Supported by experimental observation, our physical demonstration with ROT-ICEO proves invaluable for the design of flexible electrokinetic framework in modern microfluidic system.

SPR Sensor Platform Based on a Novel Metal Bilayer Applied on D–Shaped Plastic Optical Fibers for Refractive Index Measurements in the Range 1.38–1.42

A surface plasmon resonance sensor based on a D–shaped plastic optical fiber and a palladium/gold (Pd/Au) bilayer was designed, implemented, and characterized. The platform was properly thought to work in the 1.38–1.42 refractive index range, where it exhibits excellent performances. This refractive index range is very important when a thin polymer layer is used on the planar metal surface for bio-chemical sensing applications.