Ag Strips Research Articles

The electromigration study of thin-film structured Sn3.5Ag and Ag using continuous observation and reliability enhancement approach

Thin-film materials have been widely used in advanced technologies because of their flexible structure and superior working performance. However, the reliability of thin films that are employed in electronic devices has become an increasing concern. In this study, thin-film-structured Ag and Sn3.5Ag samples were prepared to observe their reliability behaviors during electromigration (EM) tests at low and high current densities. Under a low current density (8.89 × 104 A/cm2), the Ag stripe shows good resistance to EM, and microstructural changes are only observed in the Sn3.5Ag sample. In the high current density test (8.89 × 105 A/cm2), the microstructures of both samples undergo a significant change; however, the Ag sample shows superior performance than the Sn3.5Ag sample in terms of total experimental duration. Ag exhibits a better EM resistivity than Sn3.5Ag owing to the difference in EM activation energy causing the difference in atomic diffusivity. Moreover, it shows that pre-heating is an efficient method to enhance the EM resistivity of thin-film metals. The findings of this study provide a criterion for manufacturers to select suitable thin-film metals as far as EM is concerned and how to minimize the impact due to EM.

Plasmonic Perfect Absorber Utilizing Polyhexamethylene Biguanide Polymer for Carbon Dioxide Gas Sensing Application.

In this paper a perfect absorber with a photonic crystal cavity (PhC-cavity) is numerically investigated for carbon dioxide (CO2) gas sensing application. Metallic structures in the form of silver are introduced for harnessing plasmonic effects to achieve perfect absorption. The sensor comprises a PhC-cavity, silver (Ag) stripes, and a host functional material-Polyhexamethylene biguanide polymer-deposited on the surface of the sensor. The PhC-cavity is implemented within the middle of the cell, helping to penetrate the EM waves into the sublayers of the structure. Therefore, corresponding to the concentration of the CO2 gas, as it increases, the refractive index of the host material decreases, causing a blue shift in the resonant wavelength and vice versa of the device. The sensor is used for the detection of 0-524 parts per million (ppm) concentration of the CO2 gas, with a maximum sensitivity of 17.32 pm (pico meter)/ppm achieved for a concentration of 366 ppm with a figure of merit (FOM) of 2.9 RIU-1. The four-layer device presents a straightforward and compact design that can be adopted in various sensing applications by using suitable host functional materials.

Plasmon-driven methanol oxidation on PtAg nanoalloys prepared by improved pulsed laser deposition.

The methanol oxidation reaction (MOR) is crucial in many energy-conversion devices. Although intensive efforts have been devoted to improving the MOR catalytic activity of Pt-based catalysts by treatment or alloying, enhancing the MOR catalyst performance utilizing solar energy has been less investigated. PtAg nanoalloys, combining the intrinsic catalytic activity of Pt toward the MOR with the visible spectrum plasmonic response of Ag, are expected to be a good MOR catalyst for solar energy, however, it remains challenging to incorporate these immiscible elements into a nanoalloy in a controlled way using conventional synthetic techniques. Herein, we proposed a general strategy for alloying silver and platinum elements into single-phase solid-solution nanoparticles with arbitrarily desired composition by bonding pure Pt targets with pure Ag strips in an improved pulsed laser deposition. The as-prepared PtAg nanoalloys show two crystalline phases and an average particle size of about 4 nm. To prove utility, we use the PtAg nanoalloys as support-free MOR catalysts anchored on the surface of a glassy carbon electrode solidly and uniformly. The PtAg nanoalloys exhibit a mass catalytic activity of 3.6 A mg-1, which is 4.5 times higher than that of the commercial Pt/C catalyst. Besides, the PtAg nanoalloys exhibit a promising regenerability after reactivation by cyclic voltammetry. Furthermore, the MOR catalytic activity of PtAg nanoalloys increased by 16% under irradiation by simulated sunlight, which is attributed to the surface plasmon resonance as ascertained from the UV-vis absorption spectra and photocurrent response experiments. These studies are believed to provide a new strategy for the enhancement of MOR catalytic activity with visible light as the driving force.

Metallic Structures Based on Zinc Oxide Film for Enzyme Biorecognition

Two structures (Ag/ZnO/ITI/glass: #1 sample and Ag/ZnO/SiO2/Si: #2 sample) are investigated, on the one hand, from the point of view of the formation of evanescent waves in the gratings of metal strips on the structures when the incident TEz wave in the radio frequency range is used. The simulation of the formation of evanescent waves at the edge of the Ag strips, with thicknesses in the range of micrometers, was carried out before the test in the subwavelength regime, with the help of a new improved transducer with metamaterial (MM) lenses. By simulation, a field snapshot was obtained in each sequence of geometry. The evanescent waves are emphasized in the plane XY, due to the scattering of the field on the edge of the strips. On the other hand, ZnO nanoparticles are investigated as a convenient high-efficiency biodetection material, where these structures were used as a biosensitive element to various enzymes (glucose, cholesterol, uric acid, and ascorbic acid). The obtained results demonstrate that the investigated structures based on ZnO nanostructures deposited on different supports are fast and sensitive for enzyme detection and can be successfully incorporated into a device as a biosensing element.

Shape-stable Bi-Sn-In alloy/Ag/copper foam composite phase change material for thermal storage and management

With the increasing challenge of heat dissipation in electronic device, the development of rapid thermal storage and management materials with high thermal conductivity becomes an important topic. This study developed a novel low melting point metal composite phase change material composed of Bi-Sn-In alloy, Ag particles (1–4 wt%) and copper foam (apertures 0.25–0.64 mm) using high thermal conductivity synergetic enhanced effect. The Ag particles were uniformly distributed in Bi-Sn-In alloy and they changed to Ag strips with high Ag content, and Bi-Sn-In alloy/Ag can be evenly filled in apertures of copper foam. Bi-Sn-In alloy/Ag/copper foam composite with optimal aperture of 0.42 mm exhibited highest shape stability, because it avoided molten alloy leakage for larger apertures and residual alloy which was not pressed into copper foam for small apertures. As Ag content increases, the melting points of Bi-Sn-In alloy/Ag and Bi-Sn-In alloy/Ag/copper foam with Ag content of 4 wt% respectively increased by 4.91 % and 2.46 %, while their enthalpy slightly decreases by 10.9 % and 2.49 %. More importantly, the synergistic effect of Ag strips and copper skeleton addition formed continuous channels for heat transfer. The thermal conductivities of alloy/Ag (4 wt%) and alloy/Ag (4 wt%)/copper foam were respectively 22.4 and 42.7 Wm−1 °C−1, and they were remarkably higher than that of Bi-Sn-In alloy (16.4 Wm−1 °C−1). Furthermore, thermal management test showed that Bi-Sn-In alloy/Ag/foam copper had the most prominent endothermic and exothermic properties. The outstanding performance of present Bi-Sn-In alloy/Ag/copper foam demonstrates a promising prospect for solving the thermal management problems of contemporary electronic devices.

Directional coupling with parity-time symmetric Bragg gratings.

Parity-time symmetric Bragg gratings produce unidirectional reflection around the exceptional point. We propose and explore directional coupling of gain and loss modulated waveguide Bragg gratings operating at around 880 nm with long-range surface plasmon polaritons. Step-in-width modulation of a Ag stripe supporting long-range plasmons combined with a periodic modulation of the cladding were used to balance the real and imaginary index perturbation of the gratings. IR140 dye molecules in solvent forms a portion of the uppercladding, providing gain under optical pumping. We investigate directional coupling between a pair of parity-time symmetric waveguide Bragg gratings operating near their exceptional point, arranged in various configurations - duplicate, duplicate-shifted and duplicate-flipped. We also investigate coupling to a bus waveguide and to a conventional waveguide Bragg grating. Unidirectional multi-wavelength reflection and coupled supermode conversion are predicted.

Smart Thermal Management Textiles with Anisotropic and Thermoresponsive Electrical Conductivity

AbstractOutdoor heat stress can cause health hazards for workers and reduce labor productivity, thus leading to an annual burden of US $6.2 billion for the Australian workforce. Because the outdoor temperature fluctuates within a day, self‐regulating textiles are urgently needed to keep the temperature of the human body stable. Smart textiles are able to sense their surrounding environment and can respond by adapting their behaviors accordingly. However, there are a number of challenges in utilizing functional materials to achieve smart thermal radiation management for outdoor comfort and energy saving without using an external power supply. Here, a smart textile with thermal radiation management is designed by combining vanadium dioxide (VO2) and silver (Ag) strips on polyester (PET). This well‐designed VO2/Ag–PET exhibits high thermal management efficiency with a decrease of 13.9 °C at in‐box temperature under intense radiation while remaining transparent to thermal radiation at low temperature. Moreover, the VO2/Ag–PET shows good thermoresponsive and anisotropic electrical conductivity. In addition, it maintains 95% of its performance after bending. The proposed VO2/Ag–PET textile has the potential to be used for thermal management, for wearable and flexible communication devices, and for energy saving applications.

Plasmon enhanced light scattering into semiconductors by aperiodic metal nanowire arrays.

Light scattering from nanostructures is an essential ingredient in several optical technologies, and experimental verification of simulations of light scattering is important. In particular, solar cells may benefit from light-trapping due to scattering. However, light that is successfully trapped in an absorbing media such as e.g. Si necessarily escapes direct detection. We present in this paper a technique for direct measurement and analysis of light scattering from nanostructures on a surface, exemplified with aperiodic patterns of Ag strips placed on a GaAs substrate. By placing the structures on the flat face of a half-cylinder, the angular distribution of light scattered into the azimuth plane can be directly detected, including directions above the critical angle that would be captured if the substrate had the form of a slab. Modelling of the scattered light by summing up contributions from each strip agrees with the experimental results to a very detailed level, both for scattering backward and into the substrate.

Propagation Properties of Nanoscale Three-Dimensional Plasmonic Waveguide Based on Hybrid of Two Fundamental Planar Optical Metal Waveguides

In this paper, a nanoscale three-dimensional plasmonic waveguide (TDPW), created by depositing an Ag stripe on a SiO2 layer with an Ag substrate, is introduced and theoretically investigated at visible and telecom wavelengths. By applying the effective index method and finite-difference time-domain numerical simulations, the authors find that the propagation properties of surface plasmon polaritons (SPPs) in the TDPW, including the propagation length and beam width, are mainly decided by the core (the SiO2 layer just under the Ag stripe) itself, due to the much stronger localization of SPPs in the core than in the two side claddings (the SiO2 layer without the covered Ag stripe). And propagating SPPs in the TDPW are strongly confined in the core region, even with a very small waveguide cross section. Furthermore, based on the stronger localization of propagation SPPs in the TDPW, two kinds of bending waveguides, oblique bending and 90° circular bending waveguides, are also investigated. For wavelength of 1550 nm, the 90° circular bending guide with a minimum radius as small as 2.6 μm show nearly zero radiation loss, even with a small waveguide cross section of 70 × 80 nm2. The proposed TDPW is suitable for planar integration and provides a possible way for constructing various nanoscale counterparts of conventional integrated devices such as splitter, resonator, sensor, and optical switch.

Low-loss and wide-band polarization converter based on a hybrid plasmonic waveguide with symmetric Ag strips

We propose a polarization converter (PC) based on mode coupling in a hybrid plasmonic waveguide (HPW), comprising a Si waveguide, SiO2 layers surrounding the Si core, and two symmetrically arranged metal strips with respect to the optical axes. In this HPW structure, the surface-plasmon-polariton modes at the metal and SiO2 interfaces are hybridized with traditional optical modes within the SiO2 layer Two orthogonal hybrid polarization modes are thus excited. By exploiting the mode characteristics of these two hybrid polarization modes, a compact polarization converter is realized. Simulations indicate that polarization conversion is achieved with a polarization conversion efficiency (PCE) of 99.9%, an insertion loss (IL) of 0.82 dB and an extinction ratio (ER) of 30.4 dB at a wavelength of 155 nm for a conversion length of 4.58μm. For the C-band, in a wavelength range of 1530–1565 nm the PCE is greater than 99.6% the IL is below 1 dB and the ER is larger than 24 dB. These performance values are an improvement over those reported HPW-based PCs

Study of Ag induced bimetallic (Au–Ag) nanowires on silicon (5 5 12) surfaces: Experiment and theoretical aspects

The reconstructed vicinal (high index) silicon surfaces, such as, Si (5 5 12) composes row-like structures that can be used as templates for growing aligned nanowires. By using a sub-monolayers of Ag, prior to Au deposition on reconstructed Si (5 512) surface, intermixing of Au and Ag, enhancement of aspect ratio of bimetallic Au–Ag nanowires with tunable morphology is reported. This is attributed to a combined effect of pre-grown Ag strips as nucleation centers for incoming Au ad-atoms and anisotropic Au–Ag intermixing. To achieve optimum conditions for the growth of larger aspect ratio Au–Ag nanostructures, the growth kinetics have been studied by varying growth and annealing temperatures. At ≈400 °C, the Ag diffused into silicon substrate and the inter-diffusion found to inhibit the formation of Au–Ag bimetallic nanostructures. Controlled experiments under ultra-high vacuum condition in a molecular beam epitaxy system and in-situ scanning tunneling microscopy measurements along with ex-situ scanning transmission and secondary electron microscopy measurements have been carried out to understand the bimetallic nanostructure growth. Kinetic Monte Carlo (KMC) simulations based on kinematics of ad-atoms on an anisotropic template with a solid on solid model in which the relative ratios of binding energies (that are obtained from the Density Functional Theory) have been used and the KMC simulations results agree with the experimental observations. Advantage of having bimetallic structures as effective substrates for Surface enhanced Raman spectroscopy application is demonstrated by detecting Rhodamine 6G (R6G) molecule at the concentration of 10−7M.

Effect of Au thickness on AuAg bimetallic growth on reconstructed Si(5 5 12) surfaces

Large, stable and single domain unit cell with row-like structures makes reconstructed Si(5 5 12) surface an important one-dimensional growth template of nanostructures. We report on the morphological aspects of the growth of AuAg bimetallic nanostructures on a reconstructed Si(5 5 12) surface that has been deposited with a 0.5 monolayer (ML) Ag and various Au thicknesses (0.5 to 5.0 ML) to determine the optimum gold thickness for a growth of high aspect ratio of AuAg nanostructures. The mean aspect ratio of AuAg nanostructures increases up to Au thickness of 3.0 ML and for larger thickness the mean aspect ratio decreases. The prior growth of 0.5 ML Ag on reconstructed surface result in the formation of one-dimensional Ag strips which are helping for preferential nucleation sites along Si $$\left\langle 1\bar{1}0 \right\rangle$$ to form AuAg bimetallic long aspect ratio structures. Followed by these early processes of growth, for Au thickness >3.0 ML, excess Au ad-atoms begin to accumulate along Si $$\left\langle 66\bar{5} \right\rangle$$ and consequences reduction of mean aspect ratio of bimetallic nanostructures. Nanostructures are grown using molecular beam epitaxy method under ultra-high vacuum conditions and in situ scanning tunneling microscopy has been used to investigate the morphological variations. Determination of structural aspects and compositional analysis has been carried out using Rutherford backscattering spectrometry and high-resolution (scanning) transmission electron microscopy methods.

Behaviour of a ZnO thin film as MSG for biosensing material in sub-wavelength regime

Zinc oxide nanostructured materials, such as films and nanoparticles, could provide a suitable platform for development of high performance biosensing material due to their unique fundamental material properties. In this study, the enzyme biosensing consisting of a zinc oxide (ZnO) nanoparticles were grown on SiO2/Si substrates by vacuum thermal evaporation method and their sensing characteristics are examined in air and investigated. The film morphology is characterized by X-ray diffraction (XRD) the film crystalline quality and by scanning electron microscopy (SEM). Also, the interest in surface waves appeared due to evanescent waves in the metallic strip grating structure (MSG-Ag/ZnO/SiO2/Si) in sub-wavelength regime. Before testing the sensor with metamaterials (MMs) lens in the sub-wavelength regime, a simulation of the evanescent wave's formation has been performed at the edge of Ag strips, with thicknesses in the range of micrometers.

Incoherent Ag islands growth on Ni(100)

Growth of two-dimensional superstructure and island morphologies of silver atoms evaporated on a nickel (100) surface are studied by scanning tunneling microscopy. Near-equilibrium islands form at moderate annealing temperature (lower than 500K) and present two kinds of morphologies. While they share a common monolayer c(2×8) superstructure, two distinct populations of islands coexist: rounded islands grown on the surface and spindle-shaped islands grown inside the Ni surface. The latter present a clear saturation of their density with increasing coverage. These shapes are mostly dominated by boundary energies as confirmed by a simple two-dimensional Wulff model whose parameters are derived using molecular statics simulations. Further annealing to 700K leads to long Ag strips decorating the Ni step edges.

ZnO thin film as MSG for sensitive biosensor

In this paper, we investigate the cholesterol sensors consisting of a mixture of cholesterol oxidase (ChOx) and zinc oxide (ZnO) nanoparticles were grown on ITO/glass substrates by vacuum thermal evaporation method and their sensing characteristics are examined in air. Also, the interest in surface waves appeared due to evanescent waves in the metallic strip grating in sub-wavelength regime. Before testing the transducer with metamaterials lens in the sub-wavelength regime, a simulation of the evanescent wave's formation has been performed at the edge of Ag strips, with thicknesses in the range of micrometers.

Color temperature tuning of white organic light-emitting diodes via spatial control of micro-cavity effects based on thin metal strips

White organic light-emitting diodes (WOLEDs) are one of the most promising technologies to realize future solid-state lighting with high power efficiency, broad and adjustable spectral coverage, and area emission for more effective and natural illumination. In this work, we report a new method of tuning the correlated color temperature (CCT) of WOLEDs via spatially controlling the degree of the micro-cavity effect in an OLED. Varying the width of thin Ag strips deposited on top of a transparent electrode leads to changes in both intensity and phase of reflection at the anode, hence significantly altering emission spectra of proposed WOLEDs. CCT of the implemented WOLEDs span a wide range, from 3000K to 8000K, demonstrating that our proposed approach helps to meet the need for lighting with various CCTs.

Single-mode lasers and parity-time symmetry broken gratings based on active dielectric-loaded long-range surface plasmon polariton waveguides.

Single-mode distributed feedback laser structures and parity-time symmetry broken grating structures based on dielectric-loaded long-range surface plasmon polariton waveguides are proposed. The structures comprise a thin Ag stripe on an active polymer bottom cladding with an active polymer ridge. The active polymer assumed is PMMA doped with IR140 dye providing optical gain at near infrared wavelengths. Cutoff top ridge dimensions (thickness and width) are calculated using a finite element method and selected to guarantee single-mode operation of the laser. Several parameters such as the threshold number of periods and the lasing wavelength are determined using the transfer matrix method. A related structure based on two pairs of waveguides of two widths, which have the same imaginary part but different real part of effective index, arranged within one grating period, is proposed as an active grating operating at the threshold for parity-time symmetry breaking (i.e., operating at an exceptional point). Such "exceptional point" gratings produce ideal reflectance asymmetry as demonstrated via transfer matrix computations.

Optomechanical coupling in phoxonic–plasmonic slab cavities with periodic metal strips

We theoretically investigate the optomechanical (OM) coupling of submicron cavities formed in one-dimensional phoxonic–plasmonic slabs. The phoxonic–plasmonic slabs are structured by depositing periodic Ag strips onto the top surfaces of dielectric GaAs slabs to produce dual band gaps for both electromagnetic and acoustic waves, thereby inducing the coupling of surface plasmons with photons for tailoring the OM coupling. We quantify the OM coupling by calculating the temporal modulation of the optical resonance wavelength with the acoustic phonon-induced photoelastic (PE) and moving-boundary (MB) effects. We also consider the appearance of a uniform Ag layer on the bottom surface of the slabs to modulate the photonic–plasmonic coupling. The results show that the PE and MB effects can be constructive or destructive in the overall OM coupling, and their magnitudes depend not only on the quality factors of the resonant modes but also on the mode area, mode overlap, and individual symmetries of the photonic–phononic mode pairs. Lowering the mode area could be effective for enhancing the OM coupling of subwavelength photons and phonons. This study introduces possible engineering applications to achieve enhanced interaction between photons and phonons in nanoscale OM devices.

The Evanescent Waves in Metallic Strip Gratings and Complex Structures in Subwavelength Regime

The paper investigates the formation of evanescent waves in metallic strip gratings on the Ag/ZnO/SiO2/Si structure with silver strips when TEz incident wave in the radiofrequency range was used. The Ag/ZnO/SiO2/Si structure was fabricated by vacuum thermal evaporation technique and Scanning Electron Microscopy was used to evidenceits high quality structure with parallel silver strips of same width and thickness. Simulation of the evanescent wave formation at the edge of Ag strips, with thicknesses in the range of micrometers, was performed, before performing the test in the subwavelength regime by the mean of a new transducer improved with metamaterials lens. The generation in slits, in air, of the electric evanescent mode, when metallic strip grating was excited with a TEz polarized wave at a frequency of 474MHz, was successfully demonstrated.

Spatially nonreciprocal Bragg gratings based on surface plasmons

Using the concept of parity-time symmetry in optics, we propose a spatially non-reciprocal Bragg grating at near infrared wavelengths, operating with long-range surface plasmon polaritons, by employing balanced modulation of index and gain/loss in a step-in-width configuration. The index perturbation is created by stepping the width of an Ag stripe supporting long-range plasmons. Gain/loss modulation is generated by periodically doping the top polymer cladding of the structure with IR-140 dye molecules and pumping the grating optically from top. Loss exists inherently in the undoped regions due to plasmonic propagation loss. The transmission matrix method was employed as an accurate modeling technique to compute the reflectance and transmittance spectra of the proposed structures. Simulation results exhibit a strong reflectance from one end of the grating at about 880 nm as opposed to nearly no reflectance from the other end at the same wavelength.