Evanescent Electric Field Research Articles

Influence of the configuration of metal sensing layers on the performance of a bimetallic (Ag–Cu) surface plasmon resonance biosensor

Bimetallic surface plasmon resonance (SPR) sensors have the potential to overcome the drawbacks of individual metals, but the effect of the configuration of the two metallic layers on the performance of the sensors has not been explored. This study examines the influence of different positions of a thin layer of silver in relation to a copper layer on the sensitivity of such a bimetallic SPR sensor. The design of this configuration aims to improve the SPR reflectance curve and strengthen the evanescent electric field to improve the sensor efficiency. Our findings indicate that, by optimizing the architectures of SPR sensors and using a silver–copper bimetallic structure, we can achieve superior performance compared to devices that utilize only silver or copper. The optimized Ag (5 nm)/Cu (55 nm) sensor design, with the best sensitivity of 299.09° RIU−1, can detect a change of 0.43°/(g dl−1) for hemoglobin in blood, 0.35°/(g dl−1) for glucose in urine, and 0.1°/(%) for methanol in ethanol. We also demonstrate the importance of signal quality by introducing two new parameters that offer a better quantitative indication of the efficiency of a sensor than is obtained by using only sensitivity.

S-band acoustoelectric amplifier in an InGaAs-AlScN-SiC architecture

Here, we report on an acoustoelectric slab waveguide heterostructure for phonon amplification using a thin Al0.58Sc0.42N film grown directly on a 4H-SiC substrate with an ultra-thin In0.53Ga0.47As epitaxial film heterogeneously integrated onto the surface of the Al0.58Sc0.42N. The aluminum scandium nitride film grown directly on silicon carbide enables a thin (∼850 nm thick) piezoelectric film to be deposited on a thermally conductive bulk substrate (370 W/m K for 4H-SiC); the high thermal conductivity of the substrate, large mobility of the semiconductor (∼7000 cm2/V s), and low carrier concentration (∼5 × 1015 cm−3) yield low self-heating. A Sezawa mode with optimal overlap between the peak of its evanescent electric field and the semiconductor charge carriers is supported. The high velocity of the heterostructure materials allows us to operate the Sezawa mode amplifier at 3.05 GHz, demonstrating a gain of 500 dB/cm (40 dB in 800 μm). Additionally, a terminal end-to-end radio frequency gain of 7.7 dB and a nonreciprocal transmission of 52.6 dB are achieved with a dissipated DC power of 2.3 mW. The power added efficiency and acoustic noise figure are also characterized.

Mode Coupling and Sensing in Plasmonic Layered Structures

Optical sensors based on a plasmonic multilayer stack, such as metal-insulator-metal (MIM), have attracted considerable attention over the past decades owing to their high resolution and high performance compared to conventional surface plasmon resonance (CSPR) sensors for bulk sensing (BS) applications. In this paper we show that CSPR is better than MIM sensors for thin film sensing, i.e. when a dielectric sensing layer (SL) is deposited on the outermost metal layer of the structure. We demonstrate that the deposition of a thin film SL on the top of the outermost-layer of an optimized multilayer structure, i.e. MIM, strongly decreases the evanescent electric field and the field enhancement at metal-SL interface and decreases the sensor’s sensitivity for MIM versus CSPR. By considering the theoretical and experimental results we demontrated that CSPR is more suitable than MIM for thin films sensing applications.

Light‐Induced Virtual Electrodes for Microfluidic Droplet Electro‐Coalescence

AbstractElectro‐coalescence is the fusion phenomenon between a pair or more microfluidic droplets that are immersed in an immiscible medium under an electric field. This technique is frequently used to merge confined droplets in surfactant‐stabilized microfluidic emulsions using local electric fields. Despite the necessity of miniaturized electrodes, this method has proven highly successful in microfluidics and lab‐on‐a‐chip applications. Miniaturized electrodes severely curtail the spatial and temporal flexibility of the electric potential, thus hindering real‐time and flexible operation and leading to high production costs. The current study addresses this problem with reconfigurable electric field potential by light‐driven functional virtual electrodes. These electrodes are light‐induced on a non‐centrosymmetric ferroelectric photovoltaic crystal placed below a microfluidic droplet channel. The photovoltaic effect in the crystal is responsible for the space charge distributions that act as virtual electrodes, whose evanescent field is screened by free charges into the two liquids inside the channel. A numerical model is developed to describe the evolution of the evanescent electric field causing electro‐coalescence. Based on this prediction, two coalescence processes occur at two different timescales and with different numbers of droplets involved. Controlled exposure time modulation allows either rapid on‐demand coalescence of droplet pairs or breakup of the entire emulsion.

Formation controllable two-dimensional surface optical lattices

The evanescent light field created by total internal reflection at a dielectric-vacuum interface has tight spatial confinement and high local intensity. These properties become more robust when a dual layer of dielectric thin films with different thicknesses is deposited on a planar dielectric surface. Optical construction is promising in nanoscale trapping of absorbed atoms congregating at extreme light field intensity distribution regions on the dielectric surface. Here, we theoretically demonstrate the controllable two-dimensional surface optical lattices based on the evanescent electric field generated by the Hermite-Gaussian light beam. By considering the coupling of lattice to quadrupole-active atomic transitions, we show that the topologies cannot just have high stability, but also the optical potential deep, and thus the dynamic trapping can be governed by changing the design parameters of the optical construction. We expect that this study may contribute to providing another unique method for fabricating spatially complicated two-dimensional nanostructures.

Fiber Optic Sensor with a Gold Nanowire Group Array for Broad Range and Low Refractive Index Detection

To achieve high performance and wide range detection, we propose an ultra-wide range high sensitivity plasmonic fiber optic sensor with a gold (Au) nanowire group array, which has both propagating surface plasmon resonance (PSPR) and local surface plasmon resonance (LSPR) sensing characteristics. The PSPR, LSPR, and PSPR+LSPR are presented as Au thin layers, Au spheres (or Au nanowires), and Au nanowire group arrays, respectively, and their respective properties are analyzed from theoretical, simulated, and numerical aspects. When detection is performed, the presence of both evanescent wave and electric field forces in the Au nanowire group array combines to significantly improve the sensor’s detection capability. Detection simulation analysis was performed using COMSOL Multiphysics software. The range of refractive indices that can be detected is 1.08 to 1.37 in the optical band from 1210 nm to 2140 nm. In the detection range, the maximum sensitivity of the detected wavelength is 13,000 nm/RIU. Our proposed sensor has a broad range, high sensitivity, and low refractive index detection, and has good research value and application prospects.

Determination of the Dielectrophoretic Force Induced by the Photovoltaic Effect on Lithium Niobate.

The actuation of droplets on a surface is extremely relevant for microfluidic applications. In recent years, various methodologies have been used. A promising solution relies on iron-doped lithium niobate crystals that, when illuminated, generate an evanescent electric field in the surrounding space due to the photovoltaic effect. This field can be successfully exploited to control the motion of water droplets. Here, we present an experimental method to determine the attractive force exerted by the evanescent field. It consists of the analysis of the elongation of a pendant droplet and its detachment from the suspending syringe needle, caused by the illumination of an iron-doped lithium niobate crystal. We show that this interaction resembles that obtained by applying a voltage between the needle and a metallic substrate, and a quantitative investigation of these two types of actuation yields similar results. Pendant droplet tensiometry is then demonstrated to offer a simple solution for quickly mapping out the force at different distances from the crystal, generated by the photovoltaic effect and its temporal evolution, providing important quantitative data for the design and characterization of optofluidic devices based on lithium niobate crystals.

Substrate-Induced Growth of Micro/Nanostructured Zn(OH)F Arrays for Highly Sensitive Microfluidic Fluorescence Assays.

To date, ZnO array-based microfluidic fluorescence assays have been widely investigated and have exhibited excellent performance in the detection of cancer biomarkers. However, the requirements of highly sensitive detection necessitate further improvement of current Zn-based fluorescence detection devices. Here, a rhombus-like Zn(OH)F array-based microfluidic fluorescence detection device is proposed. Construction of Zn(OH)F arrays on the inner wall of a microchannel is carried out via a microfluidic chemical method. A substrate-induced growth strategy for Zn(OH)F arrays is proposed, and various micro/nanostructured Zn(OH)F arrays are successfully obtained. Zn(OH)F nanorod arrays with a high aspect ratio can be constructed on the columnar ZnO nanorod arrays, and the results indicate that the fluorescence enhancement factor (EF) of the Zn(OH)F arrays toward Cy3 is approximately 4-fold that of the ZnO nanorod arrays, which can be attributed to the higher excitation light absorption and evanescent electric field. In human epididymis-specific protein 4 (HE4) detection, the limit of detection (LOD) reaches 9.3 fM, and the dynamic linear range is 10 fM to 100 pM. It has been demonstrated that Zn(OH)F nanorod array-based microfluidic devices are excellent fluorescence assay platforms that also provide a new design and construction strategy for fluorescence enhancement substrates for the detection of biomarkers.

The effect of gold quantum dots/grating-coupled surface plasmons in inverted organic solar cells.

We studied the effect of gold quantum dots (AuQDs)/grating-coupled surface plasmon resonance (GC-SPR) in inverted organic solar cells (OSCs). AuQDs are located within a GC-SPR evanescent field in inverted OSCs, indicating an interaction between GC-SPR and AuQDs' quantum effects, subsequently giving rise to improvement in the performance of inverted OSCs. The fabricated solar cell device comprises an ITO/TiO2/P3HT : PCBM/PEDOT : PSS : AuQD/silver grating structure. The AuQDs were loaded into a hole transport layer (PEDOT : PSS) of the inverted OSCs to increase absorption in the near-ultraviolet (UV) light region and to emit visible light into the neighbouring photoactive layer, thereby achieving light-harvesting improvement of the device. The grating structures were fabricated on P3HT:PCBM layers using a nanoimprinting technique to induce GC-SPR within the inverted OSCs. The AuQDs incorporated within the strongly enhanced GC-SPR evanescent electric field on metallic nanostructures in the inverted OSCs improved the short-circuit current and the efficiency of photovoltaic devices. In comparison with the reference OSC and OSCs with only green AuQDs or only metallic grating, the developed device indicates enhancement of up to 16% power conversion efficiency. This indicates that our light management approach allows for greater light utilization of the OSCs because of the synergistic effect of G-AuQDs and GC-SPR.

Acoustic cavitation at low gas pressures in PZT-based ultrasonic systems

The generation of cavitation-free radicals through evanescent electric field and bulk-streaming was reported when micro-volumes of a liquid were subjected to 10 MHz surface acoustic waves (SAW) on a piezoelectric substrate [Rezk et al., J. Phys. Chem. Lett. 2020, 11, 4655–4661; Rezk et al., Adv. Sci. 2021, 8, 2001983]. In the current study, we have tested a similar hypothesis with PZT-based ultrasonic units (760 kHz and 2 MHz) with varying dissolved gas concentrations, by sonochemiluminescence measurement and iodide dosimetry, to correlate radical generation with dissolved gas concentrations. The dissolved gas concentration was adjusted by controlling the over-head gas pressure. Our study reveals that there is a strong correlation between sonochemical activity and dissolved gas concentration, with negligible sonochemical activity at near-vacuum conditions. We therefore conclude that radical generation is dominated by acoustic cavitation in conventional PZT-based ultrasonic reactors, regardless of the excitation frequency.

Highly sensitive plasmonic sensor fabricated with multilayer Ag/Si3N4/Au nanostructure for the detection of glucose in glucose/water solutions

The surface plasmon resonance (SPR) sensors are well-known for their high sensitivity and resolution, for example in the detection of a change in the refractive index of materials due to variations in the physical conditions (e. g., temperature, relative concentration) and/or impurities. In the majority of the cases, SPR sensors are made by using a thin film of a single metal, like gold. Here, we introduce a new type of SPR sensor fabricated by using a multi-layer nanostructure Ag/Si3N4/Au. This sensor has shown excellent performance in monitoring relative concentration of glucose in glucose/water solutions. The results presented in this work show that the sensor can resolve relative concentrations of glucose in glucose/water solutions down to a limit of about a percent. The performance of the sensor is enhanced significantly by high strength of the evanescent electric fields associated with the surface plasmon resonance. Computer simulations show that the electric field at the surface of this multilayer sensor is stronger by as much as 50 % compared to the field at the surface of a gold film sensor. Additionally, the evanescent electric fields persist above the sensor surface to much longer distances with decay lengths of as large as approximately 300 nms. Strong evanescent fields with long decay lengths add to the performance of the sensor and facilitate detection of the changes in the optical properties of materials up to large distances from the sensor.

Evanescent Field Ratio Enhancement of a Modified Ridge Waveguide Structure for Methane Gas Sensing Application

We presented a significant improvement of the evanescent field ratio in a ridge waveguide modified into a dual hybrid plasmonic waveguide by tapering the middle section of the waveguide and placing a gold layer on both sides with a sub-wavelength gap. The waveguide geometry is optimized at 3.392 μm which is an absorption line of methane gas. The proposed waveguide scheme provides a large waveguide cross-section which facilitates a flexible but coupling of light with an enhanced evanescent field in the middle. To validate the study, the evanescent field ratio, propagation loss, confinement factor and electric field distribution of the waveguide is studied via the finite element method. Additionally, the device fabrication steps and optical setup is also proposed. An elevated evanescent field ratio of 0.74 is obtained with a propagation loss of ~0.7 dB/μm. The sensitivity of 0.0715 (mW/gas conc.) is obtained for the proposed waveguide scheme by calculating the decay in transmission power due to absorption by the gas in the medium.

Free Radical Generation from High-Frequency Electromechanical Dissociation of Pure Water.

We reveal a unique mechanism by which pure water can be dissociated to form free radicals without requiring catalysts, electrolytes, or electrode contact by means of high-frequency nanometer-amplitude electromechanical surface vibrations in the form of surface acoustic waves (SAWs) generated on a piezoelectric substrate. The physical undulations associated with these mechanical waves, in concert with the evanescent electric field arising from the piezoelectric coupling, constitute half-wavelength "nanoelectrochemical cells" in which liquid is trapped within the SAW potential minima with vertical dimensions defined by the wave amplitude (∼10 nm), thereby forming highly confined polarized regions with intense electric field strengths that enable the breakdown of water. The ions and free radicals that are generated rapidly electromigrate under the high field intensity in addition to being convectively transported away from the cells by the bulk liquid recirculation generated by the acoustic excitation, thereby overcoming mass transport limitations that lead to ion recombination.

Orientation measurements of clay minerals by polarized attenuated total reflection infrared spectroscopy

The orientation and organization of molecular guests within the interlayer of clay minerals control the reactivity and performance of tailored organo-clay materials. Such a detailed investigation of hybrid structure on the molecular scale is usually provided by computational methods with limited experimental validation. In this study, polarized attenuated total reflection infrared spectroscopy was used to extract quantitative orientation measurements of montmorillonite particles. The validity of the evanescent electric field amplitude calculations necessary to derive the order parameter was critically evaluated to propose a methodology for determining the orientation of the normal to the clay layer relative to a reference axis, enabling comparison with the results obtained from X-ray scattering experiments and molecular dynamic simulations. Subsequently, the orientation of the interlayer water dipole and surface hydroxyls with respect to the normal of the clay layer was experimentally determined, showing good agreement with molecular simulations. This methodology may provide quantitative insights into the molecular-level description of interfacial processes between organic molecules and clay minerals.

4D electron microscopy of T cell activation

T cells can be controllably stimulated through antigen-specific or nonspecific protocols. Accompanying functional hallmarks of T cell activation can include cytoskeletal reorganization, cell size increase, and cytokine secretion. Photon-induced near-field electron microscopy (PINEM) is used to image and quantify evanescent electric fields at the surface of T cells as a function of various stimulation conditions. While PINEM signal strength scales with multiple of the biophysical changes associated with T cell functional activation, it mostly strongly correlates with antigen-engagement of the T cell receptors, even under conditions that do not lead to functional T cell activation. PINEM image analysis suggests that a stimulation-induced reorganization of T cell surface structure, especially over length scales of a few hundred nanometers, is the dominant contributor to these PINEM signal changes. These experiments reveal that PINEM can provide a sensitive label-free probe of nanoscale cellular surface structures.

Surface Plasmon Resonance Based Temperature Sensors in Liquid Environment.

The aim of this work is to measure the temperature variations by analyzing the plasmon signature on a metallic surface that is periodically structured and immersed in a liquid. A change in the temperature of the sample surface induces a modification of the local refractive index leading to a shift of the surface plasmon resonance (SPR) frequency due to the strong interaction between the evanescent electric field and the metallic surface. The experimental set-up used in this study to detect the refractive index changes is based on a metallic grating permitting a direct excitation of a plasmon wave, leading to a high sensibility, high-temperature range and contactless sensor within a very compact and simple device. The experimental set-up demonstrated that SPR could be used as a non-invasive, high-resolution temperature measurement method for metallic surfaces.

Long-range surface plasmon polariton detection with a graphene photodetector.

We present an integration of a single Ag nanowire (NW) with a graphene photodetector and demonstrate an efficient and compact detection of long-range surface plasmon polaritons (SPPs). Atomically thin graphene provides an ideal platform to detect the evanescent electric field of SPPs extremely bound at the interface of the Ag NW and glass substrate. Scanning photocurrent microscopy directly visualizes a polarization-dependent excitation and detects the SPPs. The SPP detection responsivity is readily controlled up to ∼17 mA/W by the drain-source voltage. We believe that the graphene SPP detector will be a promising building block for highly integrated photonic and optoelectronic circuits.

Composite layer based plasmon waveguide resonance for label-free biosensing with high figure of merit

A plasmon waveguide resonance (PWR) sensing structure was presented based on composite waveguide layer in this article. This composite layer based PWR (CLPWR) could provide stronger evanescent electric field and sharper resonance curve than surface plasmon resonance (SPR). Owing to these, the CLPWR sensor could provide up to 20 times higher resolution than the conventional SPR technology under ideal conditions. The vacuum coating techniques and optimal optical arrangements were developed for the realization of CLPWR sensor, and the residual analysis was introduced to quantify the effect of experimental system noise on measurement accuracy. In the label free biosensing experiment, it was demonstrated that the CLPWR sensor could provide more accurate measurement results than conventional SPR sensor for label free biomolecular interaction analysis in complex media.

Massive ordering and alignment of cylindrical micro-objects by photovoltaic optoelectronic tweezers.

Optical tools for manipulation and trapping of micro- and nano-objects are a fundamental issue for many applications in nano- and biotechnology. This work reports on the use of one such method, known as photovoltaic optoelectronics tweezers, to orientate and organize cylindrical microcrystals, specifically elongated zeolite L, on the surface of Fe-doped LiNbO3 crystal plates. Patterns of aligned zeolites have been achieved through the forces and torques generated by the bulk photovoltaic effect. The alignment patterns with zeolites parallel or perpendicular to the substrate surface are highly dependent on the features of light distribution and crystal configuration. Moreover, dielectrophoretic chains of zeolites with lengths up to 100μm have often been observed. The experimental results of zeolite trapping and alignment have been discussed and compared together with theoretical simulations of the evanescent photovoltaic electric field and the dielectrophoretic potential. They demonstrate the remarkable capabilities of the optoelectronic photovoltaic method to orientate and pattern anisotropic microcrystals. The combined action of patterning and alignment offers a unique tool to prepare functional nanostructures with potential applications in a variety of fields such as nonlinear optics or plasmonics.

Dynamical Control over the Confinement of Spatially Indirect Excitons in Electrostatic Traps Composed of Coupled GaAs Quantum Wells

Exploring collective quantum phenomena is aided by model systems of cold gases of (quasi)particles, such as spatially indirect excitons in a semiconductor---but a proper control system is needed. This study provides a technique to manipulate the confinement energy of indirect excitons, relying only on dipolar coupling to the evanescent electric field inside a field-effect device, with no need for impedance matching. A microscopic trap offers control with nanosecond precision at subkelvin temperatures, without incidental heating, for direct application in studying excitonic Bose-Einstein condensates, and in tuning excitonic transition energies in semiconductor quantum optics.