Metal Layer Thickness Research Articles

Control of coherent phonon dynamics in CoFeB/heavy metal heterojunction structures for future hybrid phononic and spintronic devices

Abstract The heterojunction structure of CoFeB/heavy metal has shown significant potential for spintronics, where both electrons and magnons potentially can serve as information carriers. However, another promising information carrier, coherent phonons, has not been fully explored for hybrid phononic and spintronic devices. In this study, we used time-resolved pump-probe spectroscopy to investigate the dynamic behavior of coherent phonons. We observed variations in reflectivity spectra, corresponding to changes in phonon frequency and relaxation times, with different thicknesses of the heavy metal and CoFeB layers. The experimental results demonstrated a decrease in coherent phonon oscillation frequency as the thickness of the CoFeB and heavy metal layers increased. These findings were further supported by first-principles calculations, which showed that the frequency of the optical modes is suppressed due to interface relaxation between the magnetic and heavy metal layers.

Monte Carlo Simulation of Electron Beam Induced Current in Au/Si Schottky Diodes: effects of metal layer thickness and minority carrier diffusion length

The Electron Beam Induced Current (EBIC) technique, when combined with scanning electron microscopy (SEM), offers valuable insights into the electronic properties of semiconductor materials at the nanoscale. This study leverages EBIC and Monte Carlo simulations to investigate the behavior of Schottky diodes, particularly focusing on the influence of gold layer thickness on current gain and backscatter electron (BSE) yield. The simulation results reveal the significant effects of depletion depth and minority carrier diffusion length on the diode’s performance. A key finding is that the EBIC current decreases with increased gold layer thickness, due to a higher BSE fraction. Additionally, at low beam energies, the current is negligible when the interaction volume is confined within the metal layer, while at higher energies, some penetration into the semiconductor occurs, generating a measurable EBIC current. These findings provide a better understanding of the interplay between metal layer thickness and semiconductor performance, which is crucial for optimizing semiconductor devices.

Fabrication of thick Cr masks for reactive ion substrate etching by electron beam lithography and lift-off techniques

Fabrication of tall Cr nanostructures of different shapes by lithography and lift-off processes is demonstrated. By varying resist thickness, metal layer thickness, and diameter of holes in the resist mask, it is demonstrated that metal structures with shapes ranging from sharp-tipped conical over flat-top cones to nearly cylindrical can be fabricated. A comparison of resist layer dissolution in acetone, covered by Ag and Cr films, reveals that Cr films grow with an open structure of particles that allow rapid solvent diffusion through Cr layers that are several hundred nanometers thick. On the other hand, the 2D growth of Ag on the resist forms a barrier against acetone diffusion. The open structure of Cr enables the lift-off process to fabricate several-μm-high nanostructures using a single resist layer. As an example, high-aspect-ratio Si structures are demonstrated by reactive ion etching using thick Cr layers as a mask, fabricating nanopillars with 3 μm height at room temperature.

Enhanced Photocatalytic Paracetamol Degradation by NiCu-Modified TiO2 Nanotubes: Mechanistic Insights and Performance Evaluation.

Anodic TiO2 nanotube arrays decorated with Ni, Cu, and NiCu alloy thin films were investigated for the first time for the photocatalytic degradation of paracetamol in water solution under UV irradiation. Metallic co-catalysts were deposited on TiO2 nanotubes using magnetron sputtering. The influence of the metal layer composition and thickness on the photocatalytic activity was systematically studied. Photocatalytic experiments showed that only Cu-rich co-catalysts provide enhanced paracetamol degradation rates, whereas Ni-modified photocatalysts exhibit no improvement compared with unmodified TiO2. The best-performing material was obtained by sputtering a 20 nm thick film of 1:1 atomic ratio NiCu alloy: this material exhibits a reaction rate more than doubled compared with pristine TiO2, enabling the complete degradation of 10 mg L-1 of paracetamol in 8 h. The superior performance of NiCu-modified systems over pure Cu-based ones is ascribed to a Ni and Cu synergistic effect. Kinetic tests using selective holes and radical scavengers unveiled, unlike prior findings in the literature, that paracetamol undergoes direct oxidation at the photocatalyst surface via valence band holes. Finally, Chemical Oxygen Demand (COD) tests and High-Resolution Mass Spectrometry (HR-MS) analysis were conducted to assess the degree of mineralization and identify intermediates. In contrast with the existing literature, we demonstrated that the mechanistic pathway involves direct oxidation by valence band holes.

Ballistic resistance of ceramic and metal target plates impacted against different projectile’s nose shape: A numerical investigation

Layered ceramic/metal plates are investigated for ballistic impact against projectiles with different nose shapes. Explicit finite element method is used to model the target and projectile. This study examines the effect of nose shapes on the ballistic performance of target. This includes replacing the metallic layer with a ceramic plate of the same thickness to identify the best ceramic-to-target plate ratio for maximum BLV. Ballistic performance is compared between two different configurations having equal total thickness of ceramic and metallic layer. Increased ceramic layer thickness upto certain thickness-ratio may significantly improve the target plate’s ballistic resistance for all bullet types.

Nickel release from 316L stainless steel following a Ni-free electroplating cycle

Electroplating can induce nickel release even from 316L stainless steel, typically considered safe. In this work, the influence of different electroplating processes and surface treatments on nickel release was evaluated. The nickel release was tested according to the EN 1811 standard. The impact of surface roughness on nickel release was assessed by comparing polished and unpolished samples. Results indicate that internal stresses can worsen nickel release, while increasing the thickness of the precious metal layer is beneficial. To corroborate our hypothesis, it was verified that coatings obtained through physical vapor deposition (PVD), without removing the passivation layer of the steel, did not release nickel. For these reasons, we identified the main cause of nickel release as the combined effect of the removal of the passivation layer of stainless steel and the microporosity of the electroplating process.

Analysis of current and heat transfer in locations with reduced critical current in coated conductor tape

Abstract Variation of the critical current along the conductor length is a feature commonly encountered in industrially produced REBCO tapes called coated conductors (CCs). A reduction of the critical current exceeding several percent in portions a few millimetres long can be observed in the data obtained by reel-to-reel characterization provided by manufacturers. Metallic layers in the CC architecture can take over some current in such a ‘weak spot’, and help to keep the local temperature stable, preventing its thermal runaway and conversion to a ‘hot spot’. Understanding this phenomenon is particularly crucial when space and weight limitations do not allow for the addition of a metallic layer with a thickness that would be sufficient to match the lost transport capability of superconductors. For this purpose, we studied a set of samples, representing both standard as well as infrequent profiles of weak spots identified in direct transport experiments. Analytical theory is then utilized as a basic tool for recovering the properties serving as input for numerical modelling. Temperature profiles and current redistribution at weak-spot locations were found, and the effect of cooling conditions and metallic layer thickness on the weak-spot resistance against thermal runaway was analyzed. Quantitative assessment of the possibility to improve the performance of CC tape by adding a Cu stabilizing layer or improving cooling settings could help to optimize the architecture of CCs intended for use in electrical transport.

Kretschmann configuration as a method to enhance optical absorption in two-dimensional graphene-like semiconductors

Objectives. The optical properties of two-dimensional semiconductor materials, specifically monolayered transition metal dichalcogenides, present new horizons in the field of nano- and optoelectronics. However, their practical application is hindered by the issue of low light absorption. When working with such thin structures, it is essential to consider numerous complex factors, such as resonance and plasmonic effects which can influence absorption efficiency. The aim of this study is the optimization of light absorption in a two-dimensional semiconductor in the Kretschmann configuration for future use in optoelectronic devices, considering the aforementioned phenomena. Methods. A numerical modeling method was applied using the finite element method for solving Maxwell’s equations. A parametric analysis was conducted focusing on three parameters: angle of light incidence, metallic layer thickness, and semiconductor layer thickness.Results. Parameters were identified at which the maximum area of absorption peak was observed, including the metallic layer thickness and angle of light incidence. Based on the resulting graphs, optimal parameters were determined, in order to achieve the highest absorption percentages in the two-dimensional semiconductor film.Conclusions. Based on numerical studies, it can be asserted that the optimal parameters for maximum absorption in the monolayer film are: Ag thickness <20 nm and angle of light incidence between 55° and 85°. The maximum absorption in the two-dimensional film was found only to account for a portion of the total absorption of the entire structure. Thus, a customized approach to parameter selection is necessary, in order to achieve maximum efficiency in certain optoelectronic applications.

The Tunable Parameters of Graphene-Based Biosensors.

Graphene-based surface plasmon resonance (SPR) biosensors have emerged as a promising technology for the highly sensitive and accurate detection of biomolecules. This study presents a comprehensive theoretical analysis of graphene-based SPR biosensors, focusing on configurations with single and bimetallic metallic layers. In this study, we investigated the impact of various metallic substrates, including gold and silver, and the number of graphene layers on key performance metrics: sensitivity of detection, detection accuracy, and quality factor. Our findings reveal that configurations with graphene first supported on gold exhibit superior performance, with sensitivity of detection enhancements up to 30% for ten graphene layers. In contrast, silver-supported configurations, while demonstrating high sensitivity, face challenges in maintaining detection accuracy. Additionally, reducing the thickness of metallic layers by 30% optimizes light coupling and enhances sensor performance. These insights highlight the significant potential of graphene-based SPR biosensors in achieving high sensitivity of detection and reliability, paving the way for their application in diverse biosensing technologies. Our findings pretend to motivate future research focusing on optimizing metallic layer thickness, improving the stability of silver-supported configurations, and experimentally validating the theoretical findings to further advance the development of high-performance SPR biosensors.

High-performance semi-transparent organic solar cells for window applications using MoO3/Ag/MoO3 transparent anodes

The optimization of semi-transparent organic solar cells involves balancing average visible transparency (AVT) and power conversion efficiency (PCE). We propose enhancing ST-OSC performance by replacing the conventional opaque Ag electrode with a MoO3/Ag/MoO3 as a dielectric/metal/dielectric (DMD) layer structure, explored theoretically and experimentally. A prototype ST-OSC configuration, comprising ITO/ZnO/P3HT: PCBM/MoO3/Ag/MoO3, was fabricated with varying thicknesses of the MoO3/Ag/MoO3 layer, determined through theoretical calculations utilizing MATLAB software. This study investigates the impact of metal layer thickness on two active layer densities (10 and 18 mg/mL) and evaluates AVT, color rendering index, Correlated Color Temperature, and CIELAB color coordinates (a*, b*). Both theoretical calculations and experimental results confirm that the optimized configuration of the DMD structure with specific layer thicknesses for each component (MoO3 = 10nm/Ag = 6nm/MoO3 = 30 nm) achieves an AVT of over 59.60 %. This high level of transparency makes this configuration suitable for applications requiring both high transparency and efficient light transmission. The optimized device delivered high-quality light transmission, approaching white perception to the human eye. This combined approach validates empirical results and provides a deeper understanding of transparent OSC mechanisms.

Measurements of Sensitivity and Figure of Merit for Noble Metals (Au, Ag, Cu) Thin Film Biosensor Based on SPR Simulation Characterizations

In this paper, we investigate the influence of varying the thickness of noble metals, namely gold (Au), silver (Ag) and copper (Cu), and the incident light wavelength on the surface plasmon resonance (SPR) properties for biosensor applications. Our analysis employs the Fresnel equations to examine the absorption characteristics of these metals when the refractive index shifts by (0.03,0.06). We explore metal layer thicknesses ranging from [Formula: see text][Formula: see text]nm and incident light wavelengths of [Formula: see text] and 600[Formula: see text]nm, with incident angles ([Formula: see text]) ranging from 0∘ to 90∘. Utilizing simulation analysis in MATLAB, we simulate the SPR responses of these metals when deposited on BK-7 glass prisms, with air as the surrounding medium. Our calculations reveal the absorption properties of Au, Ag and Cu, as indicated by the angle of incidence ([Formula: see text]SPR). Our findings demonstrate that the highest absorption occurs with copper (Cu) at [Formula: see text] (a.u.) for [Formula: see text][Formula: see text]nm and [Formula: see text][Formula: see text]nm. When [Formula: see text] is adjusted to 600[Formula: see text]nm, gold (Au) exhibits the highest absorption (A) at 0.997 (a.u.) with a thickness of [Formula: see text][Formula: see text]nm. Additionally, we calculate sensitivity values for all three metals, with copper (Cu) yielding the highest sensitivity of 101.6 Reflected Index Units (RIU-1) for both [Formula: see text] and 600[Formula: see text]nm. Furthermore, we compute the Figure Of Merit (FOM), with silver (Ag) achieving the highest FOM of 443 at [Formula: see text][Formula: see text]nm and 451 at [Formula: see text][Formula: see text]nm. These results provide important signs about noble metals’ SPR properties in biosensing, and serve as guides for optimizing the biosensors.

Low insertion loss interposer approach for RF applications based on commercial LTCC tape, alkaline-free glass and printed metallization

Materials with high RF performance are in increasing demand due to the needs of modern telecommunications. Glass and low-temperature co-fired ceramics (LTCCs) are both interesting candidates for the design of complex signal transmission systems. Glass can be processed in large panels, and has suitable structure dimensions for silicon processing, but its multilayer capability is limited. LTCC is a mature technology for complex multilayer assemblies, but the structure dimensions and conductor line resolution are restricted by the need to use screen printing technology. The approach presented here combines the advantages of both technological domains: a thin glass sheet is bonded with no additional material to a LTCC multilayer ceramic and sintered to form a tight joint. Metallization of the glass is created using printable pastes and electroplating. Two fabrication routes are compared: etching of printed thick film metal layers, and semi-additive structuring. The results of RF measurements show a low attenuation per unit length for both types of metallization, indicating that our approach is a promising one for the integration of heterogeneous systems of RF transmission modules.

Selective Cu electroplating enabled by surface patterning and enhanced conductivity of carbon fiber reinforced polymers upon air plasma etching

We demonstrate a sustainable post-processing of carbon fiber reinforced epoxy polymer (CFRP) composites by air plasma etching that permits regular electroconductive surface patterning through direct Cu galvanic metallization, in contrast to the untreated composite. Our study reveals a significant property dependence of the composite with respect to the position to the fiber/matrix composite surface and treatment. The enhancement in electrical conductivity was not compromised by the lower structural integrity of the composite, as the embedded carbon fibers remained unaffected by the air plasma etching process. The metallized Cu domains on the composite exhibit good hardness and excellent solderability potential. Thus, the electroconductive surface patterning of the composite, preceding galvanic metallization, facilitates the selective deposition of Cu layer domains. This step by step process, relying on the creation of selective electroconductive areas on the composite by plasma etching, enables galvanic metallization. Consequently, it enhances the potential for multifunctional composite applications. The feasibility of galvanic metallization brings new perspectives in selective metallization of composites by allowing the tailoring of the metal layer thickness, microstructure and selection of the metal.

Reliable formulas for accurately determining the resonance and antiresonance frequencies of thin film bulk acoustic resonators

Expanding upon Lakin’s theory by considering the phase shift of the acoustic waves in the metallic layers, we have developed an impedance formula for a piezoelectric layer covered by a finite thickness of metal layers, enabling the precise determination of its resonant and anti-resonant frequencies. Compared to experimental data and 3D finite element simulations, our formula can accurately and quickly predict resonant, anti-resonant frequencies, and bandwidth across a wide range of piezoelectric and metallic layer thickness combinations.

Effective cross-plane thermal conductivity of metal-dielectric multilayers at low temperatures

Heat transfer in layered metal-dielectric structures is considered theoretically based on an analytical solution of the Boltzmann transfer equation for the phonon distribution function. Taking into account the size effect, the problem of effective cross-plane thermal conductivity of structures containing two metal layers is analyzed in detail. If the thickness of the metal layers is less than the phonon mean free path, interlayer heat transfer is carried out predominantly by phonons, and the effective cross-plane thermal conductivity is determined by the reflection of phonons from the metal/dielectric interfaces. In the opposite case of thick metal layers, the effective cross-plane thermal conductivity is determined both by the thermal conductivity of the metal layers and by the thermal resistance of the dielectric layers. The results obtained are generalized to multilayer structures and superlattices.

Structural, optical and electrochromic properties of WAW films for profound electrochromic applications deposited by DC & RF magnetron sputtering

One of the most frequently used transition conducting oxides (TCO) is indium tin oxide. Indium is very expensive because of the lack of availability. So Most of the researchers focused on cost-effective materials and they have developed Dielectric/Metal/Dielectric (DMD) structures for ITO-free applications. Examples of dielectric materials are AZO, MoO3, TiO2, and WO3. The dielectric material is sandwiched between metals such as Au, Ag, Pt, Cu, and Al. The efficacy of these DMD structures is purely based on the thickness of the dielectric and metal layers. Once the metal layer thickness is more than 15 nm, the transmittance is much less due to the thickness of the material and it will work as a reflector. Moreover, as WO3 is the most widely and frequently used material we focus on the fabrication of WO3/Ag/WO3 (WAW) for replacing TCO in the electrochromic device and making it indium-free. WAW structures are widely used in smart windows, gas sensors, solar cells, photodetectors, etc. For electrochromic applications, these WAW structures showed good transmittance, fast switching speed, best coloration efficiency, and best optical modulation in comparison to WO3/ITO structure and are also cost-effective.

Influence of the Schottky Junction on the Propagation Characteristics of Shear Horizontal Waves in a Piezoelectric Semiconductor Semi-Infinite Medium

In this paper, a theoretical model of the propagation of a shear horizontal wave in a piezoelectric semiconductor semi-infinite medium is established using the optimized spectral method. First, the basic equations of the piezoelectric semiconductor semi-infinite medium are derived with the consideration of biased electric fields. Then, considering the propagation of a shear horizontal wave in the piezoelectric semiconductor semi-infinite medium, two equivalent mathematical models are established. In the first mathematical model, the Schottky junction is theoretically treated as an electrically imperfect interface, and an interface characteristic length is utilized to describe the interface effect of the Schottky junction. To legitimately confirm the interface characteristic length, a second mathematical model is established, in which the Schottky junction is theoretically treated as an electrical gradient layer. Finally, the dispersion and attenuation curves of shear horizontal waves are numerically calculated using these two mathematical models to discuss the influence of the Schottky junction on the dispersion and attenuation characteristics of shear horizontal waves. Utilizing the equivalence of these two mathematical models and the above numerical results, the numerical value of the interface characteristic length is reliably legitimately confirmed; this value is independent of the thickness of the upper metal layer, the doping concentration of the lower n-type piezoelectric semiconductor substrate, and biasing electric fields. Only the biasing electric field parallel to the Schottky junction can provide an evident influence on the attenuation characteristics of shear horizontal waves and enhance the interface effect of the Schottky junction. Since the second mathematical model is also a validation of our previous mathematical model established through the state transfer equation method, some numerical results calculated using these two mathematical models are compared with those obtained using the previous method to verify the correctness and superiority of the research work presented in this paper. Since these two mathematical models can better calculate the dispersion and attenuation curves of high-frequency waves in micro- and nano-scale piezoelectric semiconductor materials, the establishment of mathematical models and the revelation of physical mechanisms are fundamental to the analysis and optimization of micro-scale resonators, energy harvesters, and amplifications.

Switchable multi-wavelength coherent polarization manipulation component based on single-layered hollowed S-shaped metasurface

High-performance metasurface polarization manipulation components have important applications in the fields of polarization imaging, polarization detection, and communication. Single-layered metasurface components have attracted a great deal of interest, but it is still a challenge to realize high-efficiency and dynamic polarization manipulation. Combined with coherent control techniques, we propose a single-layered hollowed S-shaped metasurface design that may accomplish multi-wavelength polarization switching in the optical to near-infrared band. The single-layered metasurface enables a real-time switchable effect between dual-wavelength and single-wavelength polarization properties by controlling the phase difference between two coherent counter-propagating lights. The physical mechanism of switchable multi-wavelength coherent polarization manipulation is elucidated based on the electric field distribution of the hollowed S-shaped structure. The effect of metal layer thickness on the switchable coherent polarization properties is investigated in detail. The proposed hollowed S-shaped metasurface significantly improves the polarization performance of the single-layered structure, which is expected to facilitate the development of switchable and compact polarization components.

Fast cycling of lithium metal in solid-state batteries by constriction-susceptible anode materials.

Interface reaction between lithium (Li) and materials at the anode is not well understood in an all-solid environment. This paper unveils a new phenomenon of constriction susceptibility for materials at such an interface, the utilization of which helps facilitate the design of an active three-dimensional scaffold to host rapid plating and stripping of a significant amount of a thick Li metal layer. Here we focus on the well-known anode material silicon (Si) to demonstrate that, rather than strong Li-Si alloying at the conventional solid-liquid interface, the lithiation reaction of micrometre-sized Si can be significantly constricted at the solid-solid interface so that it occurs only at thin surface sites of Si particles due to a reaction-induced, diffusion-limiting process. The dynamic interaction between surface lithiation and Li plating of a family of anode materials, as predicted by our constrained ensemble computational approach and represented by Si, silver (Ag) and alloys of magnesium (Mg), can thus more homogeneously distribute current densities for the rapid cycling of Li metal at high areal capacity, which is important in regard to solid-state battery application.

Optimizing skyrmionium movement and stability via stray magnetic fields in trilayer nanowire constructs.

Skyrmioniums, known for their unique transport and regulatory properties, are emerging as potential cornerstones for future data storage systems. However, the stability of skyrmionium movement faces considerable challenges due to the skyrmion Hall effect, which is induced by deformation. In response, our research introduces an innovative solution: we utilized micro-magnetic simulations to create a sandwiched trilayer nanowire structure augmented with a stray magnetic field. This combination effectively guides the skyrmionium within the ferromagnetic (FM) layer. Our empirical investigations reveal that the use of a stray magnetic field not only reduces the size of the skyrmionium but also amplifies its stability. This dual-effect proficiently mitigates the deformation of skyrmionium movement and boosts their thermal stability. We find these positive outcomes are most pronounced at a particular intensity of the stray magnetic field. Importantly, the required stray magnetic field can be generated using a heavy metal (HM1) layer of suitable thickness, rendering the practical application of this approach plausible in real-world experiments. Additionally, we analyze the functioning mechanism based on the Landau-Lifshitz-Gilbert (LLG) equation and energy variation. We also develop a deep spiking neural network (DSNN), which achieves a remarkable recognition accuracy of 97%. This achievement is realized through supervised learning via the spike timing dependent plasticity rule (STDP), considering the nanostructure as an artificial synapse device that corresponds to the electrical properties of the nanostructure. In conclusion, our study provides invaluable insights for the design of innovative information storage devices utilizing skyrmionium technology. By tackling the issues presented by the skyrmion Hall effect, we outline a feasible route for the practical application of this advanced technology. Our research, therefore, serves as a robust platform for continued investigations in this field.