Metal Layer Thickness Research Articles

Design of Planar Reconfigurable, Tunable, and Wide Angle Resonant Absorbers for Applications in the IR Spectrum

AbstractA hybrid resonant absorber Fabry Perot—FP tunable from a simple stack of planar layers of ultra‐thin films of phase change material is proposed, designed, and demonstrated numerically. This work shows that properly designed metal–dielectric–metal) structures comprising thin films of titanium (Ti), germanium telluride (GeTe) on a silver (Ag) substrate produce a dynamic modulation of light in the near IR with almost perfect absorption (A > 93%). It is demonstrated that the resonant peaks of the hybrid absorber can be tuned in two different ways for any wavelength, with the crystallization fractions and the thickness of the dielectric. The influence of the metallic top layer thickness is also analyzed and demonstrated the fabrication error tolerance of the proposed absorber is demonstrated. Also analyzed is the influence of the thickness of the metallic top layer and tolerance to fabrication error of the proposed absorber is demonstrated. Finally, the physical mechanisms for the coupling of the electromagnetic field and the absorbed optical power in the structure proposed are presented and discussed. This study allows the beginning of the development of hybrid devices to control the absorption of light in the region of the electromagnetic spectrum used in optical communications.

Influence of metal roadway supports on transient electromagnetic detection in mines

To study the influence of metal supports in roadways on the detection of mines using the transient electromagnetic method, authors treated metal supports including anchor nets as a thin metal layer. According to the finite differences principle, the characteristics of the full-space transient electromagnetic response under the thin metal layer’s influence were calculated using a non-uniform grid. The thin metal layer’s presence slowed the electromagnetic field’s diffusion rate and hindered the overall diffusion. The transient electromagnetic response curve observed under the thin metal layer’s influence was higher than that without the supports. Thicker metal layers resulted in higher early response values and slower decay rates. The decay rate increased as a function of time, gradually approaching that of the curve without metal supports. The simulation of the transient electromagnetic response to the model of water-containing low-resistance structures showed that the metal roadway support reduced the sensitivity of the transient electromagnetic method and weakened its response to low-resistance anomalies.

Three-dimensional numerical simulation of droplet formation by Rayleigh–Taylor instability in multiphase corium

During a severe accident in a nuclear reactor, the melting of the core may lead to the formation of a multiphase liquid pool (corium) in the vessel lower head. The heat transfer at the boundary with the vessel is affected by diffusive and convective mass fluxes. In particular, the development of Rayleigh–Taylor instabilities influence the thickness of the top metallic layer and therefore the “focusing effect” of the heat flux, which is the main risk for the vessel integrity. We use a Cahn–Hilliard pseudo-binary model to describe the uranium/oxygen/zirconium/iron mixture. The diffusion and the convection are governed by the Cahn–Hilliard equation and the Navier–Stokes equations under the Boussinesq approximation. In this work, the model is isothermal and the buoyancy force is only due to the gradient of chemical composition. The model is solved in three dimensions with a pseudo-spectral code. The initial configuration consists of a light layer of iron-rich fluid above a heavy layer of uranium/oxygen/zirconium mixture. A thin layer of heavier metallic phase lays at the interface and eventually triggers a Rayleigh–Taylor instability. The metallic phase forms a plume which falls downward and then breaks up into droplets due to the Rayleigh-Plateau instability. The phenomenon is alimented by diffusion which generates the heavy metallic phase at the interface. The droplet formation observed in an experiment of corium stratification transient from the literature is qualitatively captured. The mobility, the viscosity and the surface tension are shown to have an influence on the mass transfer.

Research from ultraviolet to near-infrared band covering materials based on graphene photonic crystals

This paper proposes and designs a (Graphene/TiO2/Metal/TiO2/Graphene)N structure based on the symmetrical periodic arrangement of graphene photonic crystals, metals and titanium dioxide. In a single layer of this structure, nano-scale metal materials are used as the center. Graphene and titanium dioxide materials are arranged symmetrically to form a period. The transfer matrix method is used for the numerical simulation study of the GPC (Graphene Photonic Crystals) structure in the ultraviolet, visible light and near-infrared ranges. The optical response of the GPC structure under different parameters (periods, TiO2 thickness and metal layer thickness) is analyzed. The results are displayed in the ultraviolet, visible light and near-infrared band, this structure can accurately shield and reflect ultraviolet and near-infrared, while maintaining a high transmittance in the visible band, which is conducive to improving the growth quality and yield of plants. Greenhouse covering materials have high potential application prospects in the field of agriculture.

High Power Density Thermoelectric Generators with Skutterudites

AbstractThermoelectric generators (TEGs) offer a versatile solution to convert low‐grade heat into useful electrical power. While reducing the length of the active thermoelectric legs provides an efficient strategy to increase the maximum output power density pmax, both the high electrical contact resistances and thermomechanical stresses are two central issues that have so far prevented a strong reduction in the volume of thermoelectric materials integrated. Here, it is demonstrated that these barriers can be lifted by using a nonconventional architecture of the legs which involves inserting thick metallic layers. Using skutterudites as a proof‐of‐principle, several single‐couple and multi‐couple TEGs with skutterudite layers of only 1 mm are fabricated, yielding record pmax ranging from 3.4 up to 7.6 W cm−2 under temperature differences varying between 450 and 630 K. The highest pmax achieved corresponds to a 60‐fold increase per unit volume of skutterudites compared to 1 cm long legs. This work establishes thick metallic layers as a robust strategy through which high power density TEGs may be developed.

On the Transmittance of Metallic Superlattices in the Optical Regime and the True Refraction Angle

Transmission of electromagnetic fields through (dielectric/metallic)n superlattices, for frequencies below the plasma frequency ωp, is a subtle and important topic that is reviewed and further developed here. Recently, an approach for metallic superlattices based on the theory of finite periodic systems was published. Unlike most, if not all, of the published approaches that are valid in the n→∞ limit, the finite periodic systems approach is valid for any value of n, allows one to determine analytical expressions for scattering amplitudes and dispersion relations. It was shown that, for frequencies below ωp, large metallic-layer thickness, and electromagnetic fields moving along the so-called “true” angle, anomalous results with an apparent parity effect appear. We show here that these results are related to the lack of unitarity and the underlying phenomena of absorption and loss of energy. To solve this problem we present two compatible approaches, both based on the theory of finite periodic systems, which is not only more accurate, but has also the ability to reveal and predict the intra-subband resonances. In the first approach we show that by keeping complex angles, above and below ωp, the principle of flux conservation is fully satisfied. The results above ωp remain the same as in Pereyra (2020). This approach, free of assumptions, where all the information of the scattering process is preserved, gives us insight to improve the formalism where the assumption of electromagnetic fields moving along the real angles is made. In fact, we show that by taking into account the induced currents and the requirement of flux conservation, we end up with an improved approach, with new Fresnel and transmission coefficients, fully compatible with those of the complex-angle approach. The improved approach also allows one to evaluate the magnitude of the induced currents and the absorbed energy, as functions of the frequency and the superlattice parameters. We show that the resonant frequencies of intra-subband plasmons, which may be of interest for applications, in particular for biosensors, can be accurately determined. We also apply the approach for the transmission of electromagnetic wave packets, defined in the optical domain, and show that the predicted space-time positions agree extremely well with the actual positions of the wave packet centroids.

Tuning the Sensitivity of a Fiber-Optic Plasmonic Sensor: An Interplay Among Gold Thickness, Tapering Ratio and Surface Roughness

The performance of a multimode fiber optic surface plasmon resonance (FO-SPR) sensor has been studied, both theoretically and experimentally, as a function of three crucial parameters - metal layer thickness, tapering ratio (TR) and fiber surface roughness. A combined approach is adopted to investigate the effect of these three parameters on FO-SPR sensor performance instead of considering them individually. Intriguingly, the three parameters are found to be highly correlated and their combined effect significantly influences the FO-SPR sensitivity. It is observed that optimum gold thickness to attain maximal sensitivity varies for different tapering ratios. Moreover, increasing the tapering ratio does not always increase the sensitivity as claimed in previous studies, but instead depends on the fiber surface roughness generated during chemical etching. The optimized FO-SPR sensor exhibits a high sensitivity of 4714 nm RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with standard glycerol solution in the refractive index (RI) range of 1.372-1.388. Furthermore, the optimized FO-SPR sensor has been employed for label-free detection of bovine serum albumin (BSA) and parathion pesticide. The system is able to detect BSA concentration as low as 1.5 pM and the parathion pesticide is detected at 0.1 ppb levels.

Modulation of surface plasmon resonance by magnetization reversal in Au/Fe/Au trilayer and wedge structure for achieving higher refractive index sensitivity

We report enhancement of the transverse magneto-optic Kerr effect (TMOKE) in Au/Fe/Au trilayers for improving the refractive index (RI) sensitivity in surface plasmon resonance sensors by magnetic modulation. The thicknesses of the upper Au layer, the Fe layer and the lower Au layer with required thickness resolution were theoretically optimized to maximize the TMOKE intensity with perfect momentum matching, and 3% TMOKE intensity was obtained in a trilayer. Furthermore, a wedge-shaped Au thin film was fabricated on a glass substrate, and the incident angle showing minimum reflectivity was modulated, corresponding to a difference in momentum matching. Resolution of the metal layer thickness (0.26 nm) was demonstrated in a single sensor chip for maximizing the TMOKE intensity. Enhanced RI resolution is expected in sensor chips formed of a Au/Fe/wedge Au trilayer, which will contribute to improvements in the limit of detection when measuring the analytes by analyzing the resulting signals.

Influence of Rugate Filters on the Spectral Manifestation of Tamm Plasmon Polaritons.

This study theoretically investigated light reflection and transmission in a system composed of a thin metal layer (Ag) adjacent to a rugate filter (RF) having a harmonic refractive index profile. Narrow dips in reflectance and peaks in transmittance in the RF band gap were obtained due to the excitation of a Tamm plasmon polariton (TPP) at the Ag–RF interface. It is shown that the spectral position and magnitude of the TPP dips/peaks in the RF band gap depend on the harmonic profile parameters of the RF refractive index, the metal layer thickness, and the external medium refractive index. The obtained dependences for reflectance and transmittance allow selecting parameters of the system which can be optimized for various applications.

High-velocity impact response of titanium-based fiber metal laminates. Part I: experimental investigations

This two-part article examines the distribution of metallic layers through the thickness of fiber metal laminates (FMLs) on their response and damage when subjected to high-velocity projectile impact. Glass fiber/epoxy and Ti-6Al-4V titanium alloy sheets are used to obtain four different layups of FMLs fabricating by the hand layup process and exhibiting the same thickness of the total metal layer. Part I deals with experimental investigations of fully clamped square FMLs normally impacting at the center by hemispherical steel projectile using compressed air gun set up. Different parameters are considered to evaluate the FMLs’ performance, which includes damage degree, first cracking energy, crack length, deformation profile, and damage developed on the surface and inside the laminate. The results indicate that the highest permanent deformation and cracking are exhibited by FML 4/3-0.3, exhibiting separation of composite layers with different orientations by the metallic layer. The other FMLs exhibit lower and approximately similar permanent deformations. However, lower cracking and a relatively higher lateral delamination spread and opening of the interlayer are exhibited by FML 2/1-0.6 in which composite layers are arranged together than FML 4/3-0.3, signifying that the damage spreading laterally can be reduced by dispensing titanium layers. The ballistic resistance is found to be similar for FMLs. The levels of permanent deformation, cracking, and delamination with their opening and spreading are lesser for titanium-based FMLs than aluminium-based FMLs. The ballistic response of FMLs will be evaluated using analytical modeling in an accompanying study (Part II).

High-velocity impact response of titanium-based fiber metal laminates. Part II: Analytical modeling

This two-part article scrutinizes the influence of metal layer distribution through the thickness of titanium-based fiber metal laminates (FMLs) on their high-velocity projectile impact response and damage. The four different layups of FMLs consist of layers of glass fiber/epoxy and Ti-6Al-4V titanium alloy sheets, exhibiting the thickness of the total metal layer the same. Part I presents the experimental investigations of fully clamped FMLs demonstrating performance parameters, damage mechanisms, and ballistic resistance. Part II concerns the ballistic impact behavior of FMLs using analytical modeling, which is based on test results obtained in an accompanying study. An equivalent mass-spring system is used to obtain the transient deformation, ballistic limit, and absorbed energy of the laminate by various mechanisms. Good agreement is obtained between experimental and analytical ballistic limit velocity. The foremost part of the total energy absorption is by bending and membrane energy absorption (68 % - 72 %), with FML 4/3-0.3 absorbing a higher percentage of aforementioned energies followed by that of both FMLs 3/2 and FML 2/1-0.6. The predicted total energy absorption by several damage mechanisms of FMLs at the ballistic limit displays a reasonable matching with experiments.

60 GHz Broadband LTCC Antenna for 5G Mobile Communication Systems

This paper provides a numerical investigation in designing wideband circularly polarized 60 GHz antenna using Low-Temperature Co-fired Ceramic technology (LTCC). The LTCC provides high-density multilayer integration, low dielectric loss, and low costs. The use of LTCC technology is advantageous for easy and flexible 3D integration and freer vias distribution in the substrate. The designed antenna focuses on obtaining a better trade-off in terms of size, gain, circular polarization (CP), and large bandwidth. The circular polarization was chosen in order to minimize the transmission errors caused by polarization inconsistency between the transmitter and the receiver. The antenna geometry is developed taking into consideration the design rules of the LTCC with a layer thickness of 100 µm after firing and a metal layer thickness of 9 µm. A bandwidth of more than 33% centered at 60 GHz was obtained for this designed multilayer antenna. The results are obtained by using the High-Frequency Structure Simulator (HFSS). The proposed integrated antenna can be used in future 5G wireless communication systems and other 60 GHz spectrum applications.

Simulation on the nonuniform electrical pumping efficiency of THz quantum-cascade lasers

The efficiency of electric pumping of THz quantum-cascade lasers (QCLs) with strip geometry is studied depending on the number and position of contact pads. The numerical simulation of the electric potential distribution in the THz QCL active region is used to determine the required thicknesses of the upper metallisation layers of the THz QCLs to minimize the voltage drop along the laser structure in the case of nonuniform current supply. It is found that the efficiency of electric pumping in the case of a centrally located contact is significantly higher than when the contact pads are located near the laser structure edges. From the calculated dependence of the THz QCL integral power on the thickness of the upper metal layer, it is shown that for effective current injection, the contact pads must be located at a distance of less than 0.5 mm from each other.

Method for forming a titanium-germanium contact layer for thermostabilization of transistors

Objective. The objective of the study is to obtain high-quality and reproducible electrophysical parameters of thin-film metal layers, the formation technology of which determines the reliability and quality of microelectronic products – silicon transistors.Methods. A method for forming a two-layer titanium-germanium metallization to create a contact and remove heat from the collector junction of high-power semiconductor transistors on the reverse side of plates with formed structures is proposed. The proposed method ensures the quality of the soldered connection and thermal stabilization of semiconductor devices, increasing the reliability of the studied devices in radio electronic equipment systems.Results. This combination of sprayed metals provides a reliable contact to the collector area when the crystal is placed on the base of the case, which reduces the resistance of the ohmic transition and increases the output of suitable devices.Conclusion. Based on the results of experimental procedures, the optimal thicknesses of metal layers deposited on the reverse side of transistor crystals were obtained during the formation of metallization to fit crystals on the base of the case. The Ti-Ge system stability is studied. The technical result of the research is to improve the quality of planting by obtaining a uniform distribution of the Ti-Ge layer in a single technological cycle at a given temperature with a certain thickness for each metal separately.

Experimental Studies on the Influence of Electrochemical Dimensional Processing on the Surface Fatigue of Rolls in Rolling Machines

The state of surface layer in large part determines the performance characteristics of products, especially those operating at high contact loads, and in particular of rolls in rolling machines. As a rule, grinding is the final processing of rolls, but high specific work and high local heating in the cutting area lead to the appearance of a large variety of defects in the surface layer of the machined part. Subsequent electrochemical dimensional processing can significantly reduce their number. This article presents the results of comparative tests for surface fatigue of samples made of alloy steel 9Cr2MoV. The sequence of samples preparation for experimental studies is considered, they underwent a cycle of heat treatment according to a single standard mode, which made it possible to obtain a martensitic structure in the presence of inclusions of small carbides. Then the samples were ground to the height of irregularities Ra = 0.3-0.2 microns. Some of the ground samples were subjected to electrochemical dimensional processing at rational modes, when 0.2 mm thick metal layer was removed per side in the time equal to 0.5 min. The result was practically flaw-free surface with the microroughness height Ra = 0.25-0.18 microns. The sample tests for surface fatigue were carried out on a two-contact roller machine under rolling conditions with relative slip between the sample surface and pressure rollers at the peripheral speed of sample rotation 1.3 times lower than the circumferential speed of pressure roller rotation. The analysis on the contact stress diagram of the samples showed that higher resistance to fatigue fractures is observed in the samples after electrochemical dimensional processing. The number of cycles at which the limit of material contact endurance occurs for these samples is almost twice as large as for the samples after grinding.

Methods for producing of outer metal and central elastic layers three-layer seals

The limit values for the thicknesses of the outer metal layers for three-layer seals are established for conventional blanking and punching. New methods for manufacturing of these seals with increased thickness of the outer metal layers are developed.

Inverse Spin Hall Effect enhancement in Pt layer doped by Ge

We systematic studied the spin pumping (SP) and inverse spin Hall effects (ISHE) in yttrium iron garnet Y3Fe5O12 (YIG)/PtGe bilayer using a coplanar waveguide based broadband ferromagnetic resonance setup. More efficient spin injection occurs at the YIG/PtGe interface. The spin Hall angle of Pt (4.4%) and PtGe (9%) are obtained from the metal layer thickness dependent inverse spin Hall voltage measurement. PtGe films are promising materials with large spin Hall angles for future spintronics applications.

Surface Plasmon Resonance Sensor Based on Polymer Liquid-Core Fiber for Refractive Index Detection

In this work, a surface plasmon resonance (SPR) sensor based on a novel liquid-core polymer optical fiber (POF) is proposed and numerically analyzed for refractive index (RI) detection. The polytetrafluoroethylene (PTFE) fiber is selected as the platform for SPR sensing. We combine the PTFE-based POF with the liquid-core structure by introducing a hole filled with analyte into the fiber center. The hole also acts as the fiber core to guide the incident light. This design helps to realize the detection of solutions with low RI values (around 1.33), while keeping the distinguished sensing characteristics of the liquid-core structure. Two side air holes are introduced into the cladding and a thin silver film protected by a titanium dioxide layer is plated on the wall of one air hole, which helps to control the mode coupling. In order to optimize the design of this sensor, the impacts of parameters such as metal layer thicknesses and the central hole radius are investigated using the full-vector finite element method (FEM). After optimization, our design shows a wavelength interrogation sensitivity reaching up to 16,750 nm/RIU and an average full-width at half-maximum (FWHM) of 42.86 nm in the RI range of 1.325–1.35.

Effect of buffer layer index on short range surface plasmon polariton based TE pass polarizer

We investigate theoretically the dependence of the extinction ratio, metal layer thickness and buffer thickness of a short length plasmonic polarizer on the buffer layer index. The polarizer section consists of a thin metal layer above the single mode dielectric waveguide separated by a low index dielectric buffer layer. Strong coupling between the surface plasmon polariton (SPP) mode and the guided mode takes place when their phase constants are matched. The SPP mode being of TM type, interacts with the guided TM mode and is completely absorbed by metal film due to resonant coupling between the two modes. The TE guided mode does not couple to the SPP mode and is passed un-attenuated through the polarizer. The buffer layer thickness can be optimized to maximize the TM mode attenuation and reduce the TE losses, which provides a large extinction ratio. Since the polarizer is based on the interference of the SPP mode and the waveguide mode, a periodic coupling of the field takes place between these two modes. It is shown that for properly optimized layer thicknesses, an extinction ratio exceeding 200 dB can be achieved for various buffer layer indices. Effect of buffer layer index on the polarizer length is also presented.

High-resolution microscopy through optically opaque media using ultrafast photoacoustics.

We present a high-resolution microscope capable of imaging buried structures through optically opaque materials with micrometer transverse resolution and a nanometer-scale depth sensitivity. The ability to image through such materials is made possible by the use of laser ultrasonic techniques, where an ultrafast laser pulse launches acoustic waves inside an opaque layer and subsequent acoustic echoes from buried interfaces are detected optically by a time-delayed probe pulse. We show that the high frequency of the generated ultrasound waves enables imaging with a transverse resolution only limited by the optical detection system. We present the imaging system and signal analysis and demonstrate its imaging capability on complex microstructured objects through 200 nm thick metal layers and gratings through 500 nm thickness. Furthermore, we characterize the obtained imaging performance, achieving a diffraction-limited transverse resolution of 1.2 μm and a depth sensitivity better than 10 nm.