Gold Layer Research Articles

Computational Investigation of Advanced Refractive Index Sensor Using 3-Dimensional Metamaterial Based Nanoantenna Array.

Photonic researchers are increasingly exploiting nanotechnology due to the development of numerous prevalent nanosized manufacturing technologies, which has enabled novel shape-optimized nanostructures to be manufactured and investigated. Hybrid nanostructures that integrate dielectric resonators with plasmonic nanostructures are also offering new opportunities. In this work, we have explored a hybrid coupled nano-structured antenna with stacked multilayer lithium tantalate (LiTaO3) and Aluminum oxide (Al2O3), operating at wavelength ranging from 400 nm to 2000 nm. Here, the sensitivity response has been explored of these nano-structured hybrid arrays. It shows a strong electromagnetic confinement in the separation gap (g) of the dimers due to strong surface plasmon resonance (SPR). The influences of the structural dimensions have been investigated to optimize the sensitivity. The designed hybrid coupled nanostructure with the combination of 10 layers of gold (Au) and Lithium tantalate (LiTaO3) or Aluminum oxide (Al2O3) (five layers each) having height, h1 = h2 = 10 nm exhibits 730 and 660 nm/RIU sensitivity, respectively. The sensitivity of the proposed hybrid nanostructure has been compared with a single metallic (only gold) elliptical paired nanostructure. Depending on these findings, we demonstrated that a roughly two-fold increase in the sensitivity (S) can be obtained by utilizing a hybrid coupled nanostructure compared to an identical nanostructure, which competes with traditional sensors of the same height, (h). Our innovative novel plasmonic hybrid nanostructures provide a framework for developing plasmonic nanostructures for use in various sensing applications.

Probe type TFBG-excited SPR fiber sensor for simultaneous measurement of multiple ocean parameters assisted by CFBG.

The tilted fiber Bragg grating(TFBG), chirped fiber Bragg grating(CFBG), Vernier effect and metal surface plasmon resonance(SPR) effect are effectively combined to form a probe type fiber sensor for simultaneous measurement of seawater salinity, temperature and depth(STD). The SPR effect excited by the TFBG is achieved by covering a gold layer around the TFBG, which is used to measure the refractive index (RI) of seawater. The core mode of TFBG is used to detect the change of seawater temperature and the measurement of TFBG reflection spectrum is realized by inscribing a CFBG after the TFBG, which makes the sensor have a probe type design and more beneficial to practical applications. The fusion of quartz micro-spheres on the end face of the sensing fiber and the parallel connection of an Fabry Perot(F-P) interference cavity enables the use of Vernier effect to detect the depth of the ocean. Femtosecond laser line-by-line method is used to the inscribing of TFBG, which allows the grating parameters to be changed flexibly depending on the desired spectrum. The experimental results show that the temperature sensitivity is 10.82pm/°C, the salinity sensitivity is 0.122nm/g/Kg, the depth sensitivity is 116.85 pm/m and the depth can be tested to 1000 m or even deeper.

Strong Coupling between Surface Plasmon Resonance and Exciton of Labeled Protein-Dye Complex for Immunosensing Applications.

In this study, we present an analysis of the optical response of strong coupling between SPR and labeled proteins. We demonstrate a sensing methodology that allows to evaluate the protein mass adsorbed to the gold's surface from the Rabi gap, which is a direct consequence of the strong light-matter interaction between surface plasmon polariton and dye exciton of labeled protein. The total internal reflection ellipsometry optical configuration was used for simulation of the optical response for adsorption of HSA-Alexa633 dye-labeled protein to a thin gold layer onto the glass prism. It was shown that Rabi oscillations had parabolic dependence on the number of labeled proteins attached to the sensor surface; however, for photonic-plasmonic systems in real experimental conditions, the range of the Rabi energy is rather narrow, thus it can be linearly approximated. This approach based on the strong coupling effect paves the alternative way for detection and monitoring of the interaction of the proteins on the transducer surface through the change of coupling strengths between plasmonic resonance and the protein-dye complex.

Rapid fabrication of interdigitated electrodes by laser ablation with application to electrokinetically enhanced surface plasmon resonance imaging

SignificanceDielectrophoresis, electro-osmosis, and other electrokinetic effects are frequently used in a variety of applications but necessitate patterning of electrodes on sensor surfaces. This typically requires a cleanroom and time-consuming, expensive, and arcane lithography and etching procedures. AimTo demonstrate the applicability of commercial laser direct writing equipment for rapid patterning of electrodes into gold layers on glass substrates, particularly with application to producing electrokinetically active plasmonic sensors. ApproachA commercial printed circuit board prototyper was used to pattern interdigitated electrode (IDE) arrays into the surface of gold-coated slides and off-the-shelf surface plasmon resonance (SPR) prisms. The electrode geometries resulting from different patterning parameters were characterized by profilometry and electron microscopy. The patterned surfaces were then employed for trapping and electro-kinetic manipulation of bacteria, and finally for sensing of bacteria by SPR imaging. ResultsFabrication of an IDE array can be completed in as little as 12 s, with longer fabrication times permitting superior geometry and minimum feature size of 15 µm. The patterned IDEs were capable of concentrating bacteria and controlling their position on the sensor surface as a function of applied frequencies. SPR was demonstrated to detect specific interactions between bacteria and immobilized antimicrobial peptides. ConclusionsLaser direct writing is demonstrated as a feasible, cleanroom-free alternative to more lengthy lithography methods, permitting very rapid fabrication and prototyping of IDEs, which are compatible with active plasmonic sensing and bacterial detection.

Effect of 2-D nanomaterials on sensitivity of plasmonic biosensor for efficient urine glucose detection

This paper presents a multi-layered Kretschmann configuration-based Surface Plasmon Resonance (SPR) biosensor for the detection of urine glucose. The modelling, simulation, and analysis have been done by using Silver (Ag) and Gold (Au) layer on the low refractive index prism BK-7 separately, which created two structures: structure-I (BK7/Ag/Bio-sample) and structure-II (BK7/Au/Bio-sample). Urine samples from a non-diabetic person (0–15 mg/dL) and a diabetic person (.625 gm/dL, 1.25 gm/dL, 2.5 gm/dL, 5 gm/dL, and 10 gm/dL) with the corresponding refractive indices of 1.335, 1.336, 1.337, 1.338, 1.341, and 1.347, respectively, have been used as a bio-sample that has been put on the top layer of the sensor. An investigation was conducted to improve the performance parameters of the proposed plasmonic biosensor by layering different 2-D nanomaterials (graphene, BP) and TMDC materials (MoS2, MoSe2, WS2, and WSe2) over the silicon (Si) layer in both structures at a visible wavelength of 633 nm, using Transfer Matrix Method (TMM). With layer thickness optimization, Structure-I (BK7/Ag (56 nm/Si (3 nm)/WS2 (.8 nm)/Bio-sample) shows a sensitivity of 200 °/RIU which is enhanced up to 1.7 times that of the conventional biosensor (BK7/Ag/Bio-sample) and 1.3 times that of the BK7/Ag (56 nm)/Si (3 nm)/Bio-sample based biosensor. Whereas in Structure-II (BK7/Au (50 nm)/Si (3 nm)/BP (.53 nm)/Bio-sample) with optimised layer thickness, we obtained a sensitivity of 273.4°/RIU, which is enhanced up to 2.2 times that of the conventional biosensor (BK7/Au/Bio-sample) and 1.3 times that of the BK7/Au (50 nm)/Si (3 nm)/Bio-sample. Other performance parameters such as detection accuracy for Structure-I and Structure-II are .5617 degree−1 and .134 degree−1 respectively. The Figure of merit for Structure-I and Structure-II are 112.35/RIU and 36.89/RIU respectively. Therefore, we expect Structure-I (BK7/Ag (56 nm/Si (3 nm)/WS2 (.8 nm)/Bio-sample) and Structure-II (BK7/Au (50 nm)/Si (3 nm)/BP (.53 nm)/Bio-sample) have the potential to detect the glucose concentration with quick response and high sensitivity in terms of the resonance angle shift in SPR curves.

A Non-Perturbative, Low-Noise Surface Coating for Sensitive Force-Gradient Detection of Electron Spin Resonance in Thin Films.

The sensitivity of magnetic resonance force microscopy (MRFM) is limited by surface noise. Coating a thin-film polymer sample with metal has been shown to decrease, by orders of magnitude, sample-related force noise and frequency noise in MRFM experiments. Using both MRFM and inductively detected measurements of electron-spin resonance, we show that thermally evaporating a 12 nm gold layer on a 40 nm nitroxide-doped polystyrene film inactivates the nitroxide spin labels to a depth of 20 nm, making single-spin measurements difficult or impossible. We introduce a "laminated sample" protocol in which the gold layer is first evaporated on a sacrificial polymer. The sample is deposited on the room-temperature gold layer, removed using solvent lift-off, and placed manually on a coplanar waveguide. Electron spin resonance (ESR) of such a laminated sample was detected via MRFM at cryogenic temperatures using a high-compliance cantilever with an integrated 100-nm-scale cobalt tip. A 20-fold increase of spin signal was observed relative to a thin-film sample prepared instead with an evaporated metal coating. The observed signal is still somewhat smaller than expected, and we discuss possible remaining sources of signal loss.

Superimposed multilayer randomly distributed graphene quantum dots and broadband terahertz perfect absorber

For investigating broadband perfect absorption in the Terahertz region, a multilayer structure using superimposed Graphene quantum dots with Gaussian distribution radius is proposed. At first, a three-layer metamaterial structure, which is composed of graphene quantum dots at the top layer, dielectric material at the middle layer, and finally gold layer at the bottom is considered and investigated. The radius Gaussian distribution for three radii 400, 450, and 500 nm is considered. Results for the proposed structure including 3, 5, and 7 layers are extracted and compared. Simulation results for the 7-layer case show a broadband absorption range of (4.2 to 8.1 THz), and (4.3 to 8.71 THz) absorption value above 70%. The dielectric material is Si3N4 in the proposed structure.

Probing the Gold/Water Interface with Surface-Specific Spectroscopy.

Water is an integral component in electrochemistry, in the generation of the electric double layer, and in the propagation of the interfacial electric fields into the solution; however, probing the molecular-level structure of interfacial water near functioning electrode surfaces remains challenging. Due to the surface-specificity, sum-frequency-generation (SFG) spectroscopy offers an opportunity to investigate the structure of water near working electrochemical interfaces but probing the hydrogen-bonded structure of water at this buried electrode-electrolyte interface was thought to be impossible. Propagating the laser beams through the solvent leads to a large attenuation of the infrared light due to the absorption of water, and interrogating the interface by sending the laser beams through the electrode normally obscures the SFG spectra due to the large nonlinear response of conduction band electrons. Here, we show that the latter limitation is removed when the gold layer is thin. To demonstrate this, we prepared Au gradient films on CaF2 with a thickness between 0 and 8 nm. SFG spectra of the Au gradient films in contact with H2O and D2O demonstrate that resonant water SFG spectra can be obtained using Au films with a thickness of ∼2 nm or less. The measured spectra are distinctively different from the frequency-dependent Fresnel factors of the interface, suggesting that the features we observe in the OH stretching region indeed do not arise from the nonresonant response of the Au films. With the newfound ability to probe interfacial solvent structure at electrode/aqueous interfaces, we hope to provide insights into more efficient electrolyte composition and electrode design.

Plasmonic vortices for tunable manipulation of target particles, using arrays of elliptical holes in a gold layer

Here, we numerically prove that light with linear polarization can be coupled to surface plasmon polaritons at an elliptical hole perforated in a gold layer to generate plasmonic vortex (PV). Benefiting from the smooth variation of the minor to major ellipse axes, a gradual variation in the phase profile of the generated PV is achieved. Regarding this, three types of independent arrays of elliptical holes are presented, which can produce uniform and high quality PVs with different topological charges at the center of the arrays. The first array can produce PV with topological charges of + 1 and − 1, depending on the polarization orientation of the incident light. In the second one, the topological charge of the PV can be switched between 0 and + 2, by switching the polarization direction of the incident light. In the third array, a robust PV with topological charge of + 1 is generated independent of possible tolerances in the polarization orientation. In order to use the generated PVs for plasmonic tweezing application, there are side fringes around the central vortex of the arrays that should be eliminated. To produce a single vortex, we propose metal-insulator-metal (MIM) structures, screening excessive fringes and allowing the central PVs to leak out. It is also demonstrated by simulation that target particles, such as gold and polystyrene spheres of subwavelength dimensions, can be efficiently manipulated by our MIM designs, suitable for different applications including local mixing, and applying switchable torque or force to target particles to explore their complete elastic characteristics.

A tunable wide-angle narrowband perfect absorber based on an optical cavity containing hyperbolic metamaterials.

We demonstrate that wide-angle narrowband absorption can be achieved from a microcavity where a hyperbolic metamaterial and a dielectric layer are sandwiched between two metal reflectors. As the incident angle changes, the phase-shift variation in the hyperbolic metamaterial can compensate that in the dielectric layer and, consequently, result in the angle-insensitive Fabry-Perot resonance in the proposed cavity. Silicon, indium tin oxide (ITO), and gold layers are used to construct the microcavity to produce a narrow absorption band in the near-infrared region. Our device exhibits good absorption stability over a wide angle range of incidence from 0° to 70°. Moreover, the absorption wavelength can be tuned by changing the thickness of the resonator. The presented absorber may find potential applications in the design of narrowband thermophotovoltaic emitters, sensitive detectors, filters, etc.

Theoretical study on mechanical evolution process of interface between gold electrode and pyridyl anchor group

Pyridyl-ended molecular junctions show high and low breaking forces successively in formation process and at the same time exhibit intriguing conductance switching behaviors. To understand the forming process of pyridyl-ended molecular junctions, the interaction between 4,4′-bipyridine molecule and gold electrode is studied by the <i>ab initio</i>-based adiabatic simulation method. The processes that the molecule moves away from electrode tip with different contact configurations are simulated, and the molecule-electrode interface evolutions, energy of the molecule-electrode system and the force between molecules and electrode are calculated in the simulations. The numerical results show that during the molecule moving away from the pyramid-shaped electrode, the pyridyl is easy to vertically adsorb on the second gold layer of the electrode tip. In this contact configurations, the tip Au atom deviates from the original position due to the lateral pushing force of the pyridyl. It needs about 1.3–1.5 nN stretching force for the pyridyl breaking from the second gold layer and switching to the tip Au atom, which is evidently larger than the force of 0.8–1.0 nN for the molecule breaking from the tip Au atom. This result is well consistent with the experimental observations, which thus reveals the relationship between the interface structures and the stretching force in the formation process of bipyridyl molecular junction in the experiment. The interaction between 4,4′-bipyridine molecule and plane-shaped gold electrode is very weak. It needs no more than 0.5 nN for the molecule breaking from the plane-shaped gold electrode. However, when the molecule adsorbs on the single Au atom which is adsorbed on the surface of plane-shaped electrode, the molecule can sustain 1.7 nN stretching force. Our study shows that the <i>ab initio</i>-based adiabatic stretching simulation method can not only reveal the geometric evolution process of molecule-electrode systems, but also identify the specific contact configurations between molecule and electrode.

The revelation of glucose adsorption mechanisms on hierarchical metal-organic frameworks using a surface plasmon resonance sensor.

The gold layer on the surface plasmon resonance (SPR) sensor chip cannot detect small molecules, such as glucose without the use of specific receptors. Metal-organic frameworks (MOFs) are useful in biosensing technologies for capturing and co-localizing enzymes and receptors with the target biomolecule. In many previous studies, the properties of the MOFs were often ignored, with these studies focusing on the selection of appropriate receptors. To take advantage of the unique properties of MOFs in biosensors, one must also consider the technique and transducer used because these aspects will strongly influence the detection mechanism. In this work, we have investigated for the first time, the applications of hierarchical metal-BDC (M-BDC) MOFs for glucose detection using the SPR technique without the use of specific receptors. The underlying interactions and adsorption mechanisms were analyzed using adsorption isotherm and kinetic models. The sensing measurements show that the SPR chips functionalized with M-BDC MOFs exhibit higher sensitivity and lower limit of detection (LOD). Specifically, the sensitivity follows the order of Zr-BDC > Cu-BDC > Mn-BDC > Ni-BDC > bare Au SPR chips with the LOD in the order of Zr-BDC < Mn-BDC < Ni-BDC < Cu-BDC < bare Au SPR chips. The selectivity test results reveal that Zr-BDC exhibits a decent selectivity to glucose in the presence of other interfering compounds, such as ascorbic acid, uric acid, maltose, and urea. These results demonstrate the promising potential of MOFs for SPR biosensing.

A flexible electrochemical glucose sensing platform based on an electrospun PVA mat covered with in situ grown silver nanoparticles and a mixed self-assembled monolayer of glucose oxidase and ferrocene.

An electrochemical glucose sensor based on flexible materials is significant for wearable devices used for real-time health monitoring and diagnosis. However, applying flexible electrodes involves complex fabrication processes and might reduce detection sensitivity. To overcome these obstacles, we herein report a novel strategy for preparing a highly flexible enzyme electrode based on an electrospun poly(vinyl alcohol) (PVA) mat decorated with in situ grown silver nanoparticles (nano-Ag) for electrochemical glucose sensing. Ferrocene (Fc) was selected as an electron acceptor for glucose oxidase (GOD) in order to minimize the influence of oxygen. Electron transfer between GOD and Fc was facilitated by confining them within a mixed self-assembled monolayer (SAM) formed on a thin layer of gold deposited on top of the PVA/nano-Ag film. Nano-Ag was found to significantly increase the surface area of the electrode and improve the stability of electrode conductivity during tensile deformation. Electrochemical glucose detection was performed by chronoamperometry in the electroactivity domain of ferrocene, and good linearity (R2 = 0.993) was obtained in the range of 0.2-7 mM with a detection limit of 0.038 mM and a relative standard deviation (RSD) of 1.45% (n = 6). After being stuck to a bendable PDMS slice and bent, respectively, at 30° and 60° 50 times, the electrode showed slight changes in detection results (<4.78%), which remained within 8% when the bending angle increased to 90°. With its high flexibility, good detection performance, and convenient fabrication process, the proposed enzyme electrode showed good potential as a flexible platform for wearable glucose sensing systems.

A cold-responsive liquid crystal elastomer provides visual signals for monitoring a critical temperature decrease.

Critical temperature indicators have been extensively utilized in various fields, ranging from healthcare to food safety. However, the majority of the temperature indicators are designed for upper critical temperature monitoring, indicating when the temperature rises and exceeds a predefined limit, whereas stringently demanded low critical temperature indicators are scarcely developed. Herein, we develop a new material and system that monitor temperature decrease, e.g., from ambient temperature to the freezing point, or even to an ultra-low temperature of -20 °C. For this purpose, we create a dynamic membrane which can open and close during temperature cycles from high temperature to low temperature. This membrane consists of a gold-liquid crystal elastomer (Au-LCE) bilayer structure. Unlike the commonly used thermo-responsive LCEs which actuate upon temperature rise, our LCE is cold-responsive. This means that geometric deformations occur when the environmental temperature decreases. Specifically, upon temperature decrease the LCE creates stresses at the gold interface by uniaxial deformation due to expansion along the molecular director and shrinkage perpendicular to it. At a critical stress, optimized to occur at the desired temperature, the brittle Au top layer fractures, which allows contact between the LCE and material on top of the gold layer. Material transport via cracks enables the onset of the visible signal for instance caused by a pH indicator substance. We apply the dynamic Au-LCE membrane for cold-chain applications, indicating the loss of the effectiveness of perishable goods. We anticipate that our newly developed low critical temperature/time indicator will be shortly implemented in supply chains to minimize food and medical product waste.

Ultra-Broadband Tunable Terahertz Absorber of Graphene and Hierarchical Plasmonic Metamaterials

Broadband metamaterial-based perfect absorbers (MPAs) have significant potential in many applications. However, the design and fabrication of ultra-broadband terahertz MPAs pose considerable challenges. Most terahertz MPAs reported rely on complex, multilayer, or three-dimensional structures that are difficult to fabricate and hard to meet the miniaturization and integration requirements. In this study, we propose and investigate a novel tunable, ultra-broadband terahertz MPA of atomically thin monolayer graphene and hierarchically structured plasmonic metamaterials. The metamaterial MPA consists of alternating T-shaped gold bars, a dielectric layer, and a graphene layer on the bottom gold layer. These near-perfect absorbers exhibit an exceptional absorption of nearly 90% over an ultra-broad frequency range from 20.8 to 39.7 THz; the bandwidth is as high as 18.9 THz. Furthermore, a quantitative analysis of the impact of geometrical parameters on the absorption spectra is conducted. Additionally, the modulation of the absorption window by tuning the Fermi level of graphene is investigated, and the potential applications are discussed.

Reduction of surface charging effects in laser ablation ionisation mass spectrometry through gold coating.

In femtosecond Laser Ablation Ionisation Mass Spectrometry (fs-LIMS) short laser pulses are used to ablate, atomise, and ionise solid sample material shot-by-shot. When ablating non-conductive samples electric charging of the surface can occur. Depending on the geometry of the instrument, the surface charge can influence the spread of the ablation plume and reduce spectral quality. Methods to reduce surface charging were investigated using a non-conductive geological sample and a miniature fs-LIMS system with a co-linear ablation geometry. Pausing five seconds between consecutive laser bursts fired on non-coated material improved the spectral quality by giving surface charges more time to dissipate. However, best mass spectrometric results were achieved after the sample was sputter coated with a thin gold layer, as a conductive sample surface hinders charge build-up. Consequently, gold coating allowed operation of the laser system at much higher laser pulse energies improving sensitivity and reliability. It also removed the need to pause between laser bursts, speeding up the measurement acquisition.

ЧУТЛИВИЙ ЕЛЕМЕНТ СЕНСОРА ПОВЕРХНЕВИХ ПЛАЗМОНІВ З ТЕРМІЧНОЮ МОДИФІКАЦІЄЮ СТРУКТУРНИХ ВЛАСТИВОСТЕЙ ПОЛІМЕРНОЇ ПІДКЛАДКИ

The development of an effective sensing element (ChE) sensor with a prism type of excitation (Kretchman configuration) of surface plasmon resonance (SPR) in a gold film and a mechanical survey of the angle of incidence of monochromatic light based on a polymer substrate is based on a combination of radiation binding schemes using a prism and a lattice to prevent losses in the active metal film. Replacing the glass substrate with a polymer one has reduced the cost of ChE, led to increased sensitivity and simplification of its manufacturing technology, which does not require the use of intermediate adhesion layers. Additionally, we applied a thermal method of modifying the optical and structural properties of the substrate – hot pressing of the matrix, which contained a periodically nanostructured surface relief in the form of a diffraction two-dimensional (2D) lattice. The original 2D lattice was recorded on photoresist-covered (Shepley 1805) glass plates using the method of two-beam interference (He-Cd laser, = 440 nm) at double exposure (time 2040 s, power 20 mW/cm2) of the sample with a rotation of 90. Characteristics of ChE on an optical polycarbonate substrate (d = 2.25 mm, n = 1.58 at ( = 650 nm) after hot pressing, which contained a flat and periodically nanostructured surface in the form of a diffraction 2D lattice, followed by the deposition of a thin (d 40 nm) layer of gold on them was examined using an atomic force microscope (AFM) and the device "Plasmon". AFM studies have shown that the technological technique used made it possible to obtain lateral-ordered structures in the form of pyramids with calculated parameters – a period of 422435 nm (spatial frequency of about 2350 lin/mm) and a relief depth of 7090 nm. However, the preservation of a wave-like relief (about 300 nm) on a flat part of the surface and double ray refraction of the polymer substrate, encourage optimization of the hot pressing process using the resulting matrix on polymer substrates of smaller thickness.

ПЕРСПЕКТИВИ ТА ТЕНДЕНЦІЇ РОЗВИТКУ ПРИЛАДІВ ТА МЕТОДІВ НА ОСНОВІ ЯВИЩА ПОВЕРХНЕВОГО ПЛАЗМОННОГО РЕЗОНАНСУ В ІНФРАЧЕРВОНОМУ ДІАПАЗОНІ (ОГЛЯД)

On the phenomenon of surface plasmon resonance (SPR) and its use for the study of gaseous and liquid substances, more and more papers are published in professional journals. These studies are used in clinical diagnostics, food industry, environmental monitoring. The advantages of SPR sensors include quick results, a small amount of analyte, the possibility of real-time measurement of such reactions as antigen-antibody, protein-protein, enzyme-substrate or inhibitor, protein-DNA, receptor-drug, protein-polysaccharide , virus protein and reactions of external stimulation of a living cell. The high sensitivity of the method is due to the properties of its resonant nature of plasmon-polariton oscillation. SPR devices are used in laboratory conditions and there is a potential possibility of further reduction of overall dimensions for use in field conditions. The use of SPR in the IR region of the spectrum has a number of advantages, namely: the laser light penetrates deeper into the sample, it becomes possible to study substances that are not transparent in the visible region, but transparent in the infrared, which allows working with larger research objects, provides a narrower characteristic of the SPR, which allows to more accurately determine the angle of the minimum of the SPR, and also requires the application of a thinner layer of gold on the glass chip, which reduces the cost of the analysis. The review analyzed literary sources and determined prospects for the development of devices and methods based on IR SPR, considered prospective materials of the sensitive element and prisms of the total internal reflection device according to the Kretchman scheme. It was determined that, in addition to precious metals (gold and silver), conductive metal oxides ITO, ZnO, CdO:Dy have the prospect of being used as materials for manufacturing the sensitive element of the sensor. Their compliance with the requirements for materials for maintaining the SPR was analyzed. It is shown that CdO:Dy has the greatest potential due to sufficient mobility and density of charge carriers. But in practice, the most common use is gold and silver, for which it is necessary to determine the optimal thicknesses for the IR range of SPR. Total internal reflection prisms (hereafter prisms) in SPR devices according to the Kretchman scheme are usually made of glass, but for the IR range it is advisable to consider other materials that are less sensitive to the temperature effect of the IR laser. The paper analyzes the dependence of the plasmon resonance parameters on the prism material. The possibility of using not only different brands of traditional glass, but also glass ceramics with practically zero coefficient of thermal expansion, semiconductor silicon and chalcogenide glass for the manufacture of prisms is shown.

20 dB improvement utilizing custom-designed 3D-printed terahertz horn coupler.

Terahertz band is envisaged to provide substantially higher capacity and much lower latency for wireless communications in contrast to microwave frequencies. Moving to higher frequencies comes with its own unique challenges to be addressed, such as poor coupling efficiency from free space into and out of planar air-core waveguides. Here, we propose a framework for rapid design and low-cost fabrication of terahertz horn couplers. The horn couplers are first designed by maximizing the field overlap integral on apex and aperture interfaces, then fabricated exploiting 3D printing technique, and finally sputtered with a thin layer of gold. A 28~μm standard deviation of the surface roughness height of the 3D printed horn couplers is calculated. Experimental demonstrations show that the proposed horn coupler improves the transmittance of a hybrid photonic crystal waveguide by 20 dB in comparison with the previous pinhole-based coupling configuration. This work provides a fast, convenient and economical approach for design and fabrication of customized couplers for any waveguide size, with a cost of only 5% of commercially available counterparts, and could be integrated in 3D-printed terahertz devices during fabrication.

Study the influence of shell thickness in bimetallic Ag core&Au shell configurations integrated in bare Si PN junction solar cells

The effect of the gold layer thickness of Ag core&Au shell configurations on the performance of the bare Si n-type layer of a PN junction solar cell was explored. The different forms of Ag core&Au shell configurations were formed via pulsed laser ablation method of Ag and Au plate using second harmonic generation (SHG) of Nd:YAG laser wavelength at 530 nm with 0.61 J/cm2 energy flounce and various pluses repetition rate 350-500. The integrating of Ag core&Au shell configurations in n-type of bare PN Si junction was accomplished via pluses laser illumination of bare PN junction substrate. The photovoltaic results of formed solar cells showed strong dependence on Au shell thickness. Tangible enhancement was observed in the performance of bare Si solar cells after inserting core–shell configuration with specific shell thickness owning to the broadband absorption of plasmonics nanoparticles and the high values of specific surface area.