Double-layer Metal Films Research Articles

Wideband VHF/UHF Wing Conformal Vertical Polarized Omnidirectional Antenna

This letter proposes a novel wideband wing conformal vertical polarized omnidirectional antenna for the very high frequency&#x002F;ultrahigh frequency band. The antenna adopts symmetrical radiation and feed structures to obtain quasi-omnidirectional radiation. To be conformal with the ultrathin body of the wing, this construction is realized using double-layer flexible metal films that cover the surface of the wing. Moreover, there are several symmetric grooves on the upper metal film that are beneficial to improve the efficiency of radiation. The upper and lower metal films are connected by two shorting plates with same exponential gradual outline for vertical polarization and wideband potential. The ultrawide operating band can be realized by loading resistors and inductors. A conformal prototype of the antenna was fabricated and validated. The wing thickness determines the profile, which is only 0.013 <i>&#x03BB;_L</i>, where <i>&#x03BB;_L</i> is the wavelength at the lowest operating frequency. Its acquired bandwidth ranges from 100 to 600 MHz; high radiation efficiency and vertically polarized quasi-omnidirectional characters are also obtained in this band.

Multi-Characteristic Integration of Double-Layer Metal Film Grating with Composite Periodic Structure

Multi-Characteristic Integration of Double-Layer Metal Film Grating with Composite Periodic Structure

A narrowband dual-polarization filter based on photonic crystal fiber with Au-Ag double-layer films

A narrowband dual-polarization filter based on photonic crystal fiber (PCF) with Au-Ag double-layer films is proposed. The cladding of PCF is composed of three layers of air holes, and Au-Ag double-layer films are coated on two symmetrical air holes to excite surface plasmon resonance (SPR) effect. The special mechanism of the Au-Ag double-layer films takes advantage of the narrower full width at half maximum (FWHM) of silver. On the other hand, gold is used to protect the silver from oxidation and improve the stability of the filter, and can also enhance SPR effect. The simulation results show that the dual-polarization filter with double-layer metal films has higher resonance absorption and better spectra than that with the single-layer metal film. When the thickness of the double-layer metal films is 22.5 nm (the thickness of silver film is 18 nm), the confinement loss of dual-polarization filter at 1430 nm is achieved to 64.08 dB/cm (y-pol core mode) and at 1530 nm is achieved to 37.26 dB/cm (x-pol core mode). The wavelength range of crosstalk (CT) greater than 20 dB and less than −20 dB are 1410–1450 nm and 1510–1550 nm for the device length of 10 mm, respectively. The CT is achieved 555.07 dB and −321.54 dB at the wavelength of 1430 nm and 1530 nm, respectively. These characteristics show that the filter has excellent performance, and will become a suitable candidate for a narrowband polarization filter.

Femtosecond laser selective ablation of Cu/Ag double-layer metal films for fabricating high-performance mesh-type transparent conductive electrodes and heaters

With the ultrashort timescale and high-power density, femtosecond laser is a powerful tool for localized material ablation with high processing accuracy and cleanliness. In this work, femtosecond laser direct writing was used to selectively ablate and remove the copper/silver (Cu/Ag) double-layer metal films on glass substrates for fabricating mesh-type transparent conductive electrodes (TCEs). In particular, the effects of laser fluence and laser scanning speed on surface morphology and photoelectric properties of the TCEs were studied. By using a laser fluence of 1.1 J/cm2 and a laser scanning speed of 400 mm/s, the optimal removal result of the Cu/Ag double-layer metal film was achieved with the minimal damage to the glass substrate. The as-obtained TCE showed a high average transmittance of 87.89% and a low sheet resistance of 1.36 Ω/sq. As an application, a transparent heater based on the as-obtained TCE exhibited an efficient, rapid and stable heating performance, being confirmed by achieving a high temperature of ∼144 °C under a low applied voltage of 2.0 V. The femtosecond laser selective ablation strategy for laser patterning of metal-based films provides a unique scheme for the rapid fabrication of metal mesh-type TCEs under the mask-free condition and room temperature.

Research on the Action Mechanism of Antibacterial Chinese Medicine Based on SPR Sensing Technology

A detection method based on SPR sensor is proposed to detect the interaction between antimicrobial agents and cytokines and receptors. A bimetallic optical fiber SPR biosensor was fabricated by double layer metal film by vacuum thermal evaporation. The mechanism of Chinese medicine was detected by direct method. The sensor has the function of rapid, objective, accurate and efficient detection of the mechanism of action of Chinese medicine, and the corresponding data are obtained. The application of optical fiber SPR biosensor makes the detection of the mechanism of action of traditional Chinese medicine have the advantages of real-time and high efficiency. It is expected to make new breakthroughs in the study of the target and molecular mechanism of the antibacterial effect of traditional Chinese medicine. Introduction

Femtosecond pulse laser irradiation of gold/chromium double-layer metal film: The role of interface boundary resistance in two-temperature model simulations

In this work, the results of computational single-shot laser pulse irradiation of gold/chromium metal film using two-temperature model are presented. The optical properties of first Au layer are studied based on critical point model and temperature-dependent reflectivity and absorption coefficient are considered in model simulations with and without the effect of ballistic motion of hot electrons. The thermal response of Au/Cr double-layer film is investigated after femtosecond laser pulse irradiation with pulse duration 30fs and 800nm laser wavelength in submelting condition by introducing the influence of thermal boundary resistance. First, the ideal interface between gold and chromium is considered and the two-temperature model results for various thicknesses of gold layer are demonstrated. Then, the time and position dependence of interface resistance is calculated based on Diffuse Mismatch Model. By including the thermal boundary resistance at interface, the electron and lattice temperature distributions and the lattice overheating from chromium side are compared with the ideal interface. The results show that, in the presence of Kapitza resistance, the chromium side lattice overheating at interface is lower than the case of zero interface boundary resistance. Moreover, the two-temperature model simulations for various snapshot times and heat flow distribution for Au/Cr double-layer structure are studied. The simulated results provide more information about femtosecond laser irradiation for double-layer metal films.

High Polaried Transmission Effects for Double-Layer Metallic Grating Films on GaN Substrate

Highly polarized light transmission from GaN based light emitting diode is proposed using a double-layer metallic grating film and a dielectric transition layer. TM mode transmission and the polarized extinction ratio (ER) are calculated using commercial software, based on a full vector implementation of Rigorous Coupled Wave Analysis (RCWA) algorithm. Such a thin-film double-layer grating with subwavelength metallic stripes are designed and simulated by perfect parameters of period, thickness and filling factor for achieving good polarization properties. It is found that TM transmission and ER are almost stable and flat under different slit arrays of the double-layer grating. The polarized structure shows larger width of incident wavelength with a transition layer of a low refractive index than that of a high refractive index, but higher TM transmission and ER can be obtained for low refractive index transition layer. Flat sensitivity and high transmission of the TM mode on the double-layer metal grating thickness have been achieved. Up to 100nm range of the grating height can be employed to achieve TM transmission more than 92% while ER&gt; 20dB. The results provide guidance in designing, optimizing and fabricating the integrated GaN-based and polarized photonic devices.

Thermal analysis of double-layer metal films during femtosecond laser heating

In this paper, the primary interest is the heat effect of the bottom-layer metal on thetemperature distribution of the top-layer metal in a double-layer metal structure duringfemtosecond laser irradiation. The evolution of the surface electron and lattice temperaturedepends a lot on the thermal parameters of the substrate. The damage threshold can beincreased by using a substrate material with high electron–lattice coupling factor. Next, wechoose chrome as the bottom-layer material. The results of modeling show that the surfacelattice temperature of top-layer gold can be reduced remarkably. For a fixed entirethickness of the double-layer film, there is an optimal proportion of top and bottomlayers for which the damage threshold is the highest possible. Also, for increasingthe damage threshold, a substrate with higher melting temperature should bechosen.

Optical transmission through double-layer, laterally shifted metallic subwavelength hole arrays

We measure the transmission of IR radiation through double-layer metal films with periodic arrays of subwavelength holes. When the two metal films are placed in sufficiently close proximity, two types of transmission resonances emerge. For the surface plasmon mode, the electromagnetic field is concentrated on the outer surface of the entire metallic layer stack. In contrast, for the guided mode, the field is confined to the gap between the two metal layers. Our measurements indicate that, as the two layers are laterally shifted from perfect alignment, the peak transmission frequency of the guided mode decreases significantly, while that of the surface plasmon mode remains largely unchanged, in agreement with numerical calculations.

Role of localised surface plasmon polaritons coupling in optical transmission through double-layer metal apertures

In this paper, we investigate the optical properties of the double-layer metal films perforated with single apertures by analysing the coupling of localized surface plasmon polaritons (LSPPs). It is found that the amplitude and the wavelength of transmission peak in such a structure can be adjusted by changing the longitudinal interval D between two films and the lateral displacements dx and dy which are parallel and perpendicular to the polarization direction of incident light, respectively. The variation of longitudinal interval D results in the redshift of transmission peak due to the change of coupling strength of LSPPs near the single apertures. The amplitude of transmission peak decreases with the increase of dy and is less than that in the case of dx, which originates from the difference in coupling manner between LSPPs and the localized natures of LSPPs.

Preparation and test on mechanical characteristics of W/Al bilayer films

A W/Al double-layer metal film sample has been prepared by the magnetron sputtering method on glass substrates. The membrane-substrate system sample was measured by using nano-indentation test for investigating the mechanical characteristics. Based on the analysis of the data from the indentation experiments, the elastic modulus, hardness of the system and other mechanical properties as well as the mechanical parameters were investigated. The results lay an experimental basis for future work.

Two resonances effect for light transmission assisted with surface plasmon through perforated metal film

Abstract When light is incident on a nonplanar metal surface, an oscillating dipole is excited at the entrance openings. We show that the enhanced transmission assisted with surface plasmon (SP) through a perforated metal film results from two different SP resonances effects: (i) zero-order Fabry–Perot resonance effect where each air hole can be considered as a section of metallic waveguide, forming a low-quality-factor resonator, and many dipoles are arranged inside the nanoholes region; and (ii) structure-factor-induced charges self-tunnelling effect due to the well-recognized surface structure periodicity, where the positive or negative charges can respectively tunnel into the right surface through the metal walls. Furthermore, when light transmits through the double-layer perforated metal films, the different transport behaviors are also clearly shown, which convinces the existence of dual SP resonances effect.

Analytical expressions of the electrical conductivity and the temperature coefficient of resistivity of two thin coaxial metallic wires

Assuming, that the sources of scattering act independently in the two thin coaxial metallic wires, and introducing the mean free path describing the Fuchs–Sondheimer effect, an apparent size effect is then defined. The aim of this paper is to show that the size effects in the thin coaxial metallic wires can be examined as well by using initially the theoretical formulations proposed in the case of a single wire and of the thin double-layer metal films. Simple analytical expressions of the electrical conductivity and the temperature coefficient of resistivity are therefore proposed.

Oscillation galvanomagnetic effect in double-layer metal films

A semiclassical approximation has been used to analyze theoretically the dependence of the conductivity σ (resistivity ρ) of a double-layer film consisting of plane-parallel single-crystal metal layers of different thickness dj ≠ dn and grade lj ≠ ln on the layer thickness ratio d2,1 = d2/d1 and on the magnitude of the magnetic field normal to the layer interface. A general expression (for any d2,1) and asymptotic expressions (for thick and thin (compared to the electron free path lj) metal layers in a weak and a strong magnetic field) for the conductivity of a double-layer specimen have been obtained. A nonmonotonic relation between the conductivity of a double-layer film and the layer thickness ratio at weak magnetic fields has been predicted which is sensitive to the character of the interaction of charge carriers with the conductor boundaries. At strong magnetic fields, ρ becomes an oscillating function of magnetic field (layer thickness). A detailed numerical analysis of the resistivity of a double-layer film on the layer thickness ratio and on the magnetic field strength has been performed for arbitrary values of the parameters that describe the character of the interaction of charge carriers with the specimen boundaries.

Theory of electrical transport and scattering at a metal-metal interface

The Schrodinger equation for an electron near a randomly rough metal-metal (or metal-vacuum) interface is approximately solved. The wavefunction and probability currents are averaged over all realisations of the interface characterised by its root-mean-square departure from flatness and the extent of its lateral correlation, and the results are used to set up simple boundary conditions for the Boltzmann transport equation. These are in the form of angle-dependent transmission and reflection coefficients, generalising Fuch's reflectivity parameter, but given as explicit functions of observable properties of the interface. These results are further applied to the calculation of the electrical conductivity of thin films and foils, and of double-layer metallic films.

Electronic transport properties of double layer metallic films

Size effect modifications of the normal and Hall resistivities for copper and copper-ferromagnetic amorphous double layer metallic films are studied vs. the thickness of copper deposited on the top of the amorphous substrate. Experimental data are compared with calculations derived from the Fuchs-Sondheimer theory, as developed by Bergmann. For copper, one can see that the size effect on the resistivity tends to approach the theoretical behaviour when the deposition of the copper film on the substrate is uniform, as on an amorphous metallic film. The calculation of the Hall resistivities for the double layer samples reproduces quite well the experimental values obtained in correspondence to a magnetic field higher than the saturation induction of the samples. These results suggest that the theory could achieve better results than those found by Bergmann if certain simplifications are avoided.

The effect of linear thermal expansion on the temperature coefficient of resistance of double-layer thin metallic films

A general theoretical expression for the temperature coefficient of resistance of double-layer thin metallic films, based on the well known Fuchs-Sondheimer model, is derived. This expression includes the linear thermal expansion coefficients and Poisson's ratios of the double layers and the substrate, also the film dimensions and temperature coefficient of resistance of the double-layer thin film, with and without the thermal expansion of both the film layers and the substrate. Numerical calculations are carried out for gold-silver double-layer films deposited on a glass substrate, where variations in the temperature coefficient of resistance depending on thermal expansion are studied as a function of reduced film thickness. The computed numerical results, using the derived new expression for the temperature coefficient of resistance of the double-layer thin metallic films, show that the thermal expansion decreases the value of the temperature coefficient of resistance.

Thickness dependence of the work function in double-layer metallic films

The work function of metallic thin films limited by symmetric surfaces is expected to be thickness dependent at a level of 0.1 eV and a thickness range of about 5 nm. Recent experiments, however, demonstrated that Cu films on glass or Ni substrates show a long ranging (10–20 nm) increase of the work function with increasing film thickness [1]. This effect was attributed to a violation of local charge neutrality in films with unlike surfaces. In this paper we show that the barrier height of thin film diodes like metal-insulator-metal (MIM)-, metal-semiconductor (Schottky contacts)-and metal-vacuum-metal (Kelvin capacitors) structures decreases with increasing thickness of one metal electrode. This metal electrode consists of a double layer whose single layer thicknesses are of the order of few tens of nm. The observed effect can be attributed to a decrease of the work function at the counter limiting interface not exposed to the evaporation beam. A possible explanation can be found again in the violation of the local charge neutrality in films with unlike surfaces.

Dependence of the temperature coefficient of the strain coefficients of resistance of double-layer thin metallic films on thermal strains

General theoretical expressions for βγFITS and βγFtTs (temperature coefficient of the longitudinal and transverse strain coefficients of resistance) of double-layer thin metallic films are derived, based on the Fuchs-Sondheimer theory for conduction, on the one hand, and on the other hand, on the assumption that the differential variations in resistance with strains are temperature dependent. The variations in βγFITS and βγFITS as a function of the reduced film thickness K1 are calculated for double-layer thin metallic films of Au/Ag deposited onto glass substrates. Allgemeine theoretische Ausdrucke fur die Temperaturkoeffizienten der longitudinalen und transversalen Spannungskoeffizienten des Widerstands, βγFITS und βγFtTS, werden fur dunne, metallische Doppelschichtfilme abgeleitet, einerseits auf der Grundlage der Fuchs-Sondheimerschen Leitungstheorie, andererseits aufgrund der Annahme von temperaturabhangigen differentiellen Anderungen des Widerstands mit der Spannung. Die Anderungen von βγFITS und βγFtTS mit der reduzierten Filmdicke K1 werden fur dunne Au/Ag Doppelschichtfilme auf Glassubstrat berechnet.

Temperature coefficient of the strain coefficient of electrical resistivity of double-layer thin metallic films

On the basis of the Fuchs-Sondheimer theory, a general theoretical expression for the temperature coefficient of the longitudinal (transverse) strain coefficient of electrical resistance of doublelayer thin metallic films is derived. The derivation is performed upon the assumption that the differential variation in the film resistance with strain is temperature independent. The scattering of the conduction electrons at the surfaces of the film is described by the well known Fuchs specularity parameter P. On the interfaces beside the parameter P, a parameter Q is introduced which characterizes the probability that the conduction electrons are refracted, according to the law of refraction. Numerical calculations are made for an Au/Ag double-layer film. The calculations show that the coefficients exhibit size effects. Auf der Grundlage der Fuchs-Sondheimer-Theorie wird ein allgemeiner theoretischer Ausdruck für den Temperaturkoeffizienten des longitudinalen (transversalen) Spannungskoeffizienten des elektrischen Widerstands von Doppelschicht-Metallfilmen abgeleitet. Die Ableitung erfolgt unter der Annahme, daß die differentielle Änderung des Schichtwiderstandes mit der Spannung temperaturunabhängig ist. Die Streuung der Leitungselektronen an der Oberfläche der Schicht wird sehr gut durch den Fuchsschen Spiegelungsparameter P beschrieben. An den Grenzflächen wird neben dem Parameter P ein Parameter Q eingeführt, der die Wahrscheinlichkeit charakterisiert, daß die Leitungselektronen entsprechend dem Brechungsgesetz gebrochen werden. Numerische Berechnungen werden für Au/Ag-Doppelschichtfilme durehgeführt. Die Rechnungen zeigen, daß die Koeffizienten Gröeneffekte zeigen.