Multilayer Stack Research Articles

Cross-sectional high-resolution transmission electron microscopy at Mo/Si multilayer stacks

Abstract Using a Mo/Si multilayer stack, capabilities and limits of high-resolution transmission electron microscopy with respect to thin film analysis are pointed out. Image processing is shown to provide non-subjective criteria for the determination of layer thicknesses. In comparison to measurements by X-ray reflectometry, an integrating method capable of determining multilayer periodicities, preparation and observation artefacts in transmission electron microscopy is discussed. Special emphasis is placed on cleavage as a powerful method for TEM sample preparation, its advantages and disadvantages.

Effect of interfacial atomic mixing on the thermal conductivity of multi-layered stacking structure

Multi-layered stacking structures and atomic mixing interfaces were constructed. The effects of various factors on the thermal conductivity of different lattice structures were studied by non-equilibrium molecular dynamics simulations, including the number of atomic mixing layers, temperature, total length of the system, and period length. The results showed that the mixing of two and four layers of atoms can improve the thermal conductivities of the multi-layer structure with a small total length due to a phonon “bridge” mechanism. When the total length of the system is large, the thermal conductivity of the multi-layer structure with atomic mixing interfaces decreases significantly compared with that of the perfect interfaces. The interfacial atom mixing destroys the phonon coherent transport in the multi-layer structure and decreases the thermal conductivity to some extent. The thermal conductivity of the multi-layer structure with perfect interfaces is significantly affected by temperature, whereas the thermal conductivity of the multi-layer structures with atomic mixing is less sensitive to temperature.

Multilayer stacks of polycyclic aromatic hydrocarbons.

Polycyclic aromatic hydrocarbons (PAHs) show promise for applications in functional devices such as organic photovoltaics and field-effect transistors, but, although nanometre-sized PAHs-often referred to as nanographenes-have been well investigated as single-layer molecules, their multilayer counterparts remain rather unexplored. Here we show the assembly of a C64 nanographene derivative (comprising a planar core decorated with four meta-terphenyl-imide moieties at its periphery) into multilayer stacks with smaller PAHs ranging from naphthalene to ovalene and hexabenzocoronene. The functionalized C64 nanographene serves as a ditopic host that can accommodate a smaller PAH on either side of its planar core, in cavities delimited by its bulky imide substituents. Bilayers and trilayers (that is, complexes with 1:1 and 1:2 host:guest ratios, respectively) were observed in solution, and dimers of these complexes as well as multilayer compounds were isolated in the solid state. Quantum-chemical calculations indicate that dispersion forces are the main stabilizing factor for these complexes.

FLOCK -flare clock: Passive sweat-based eczematous flare detection system

FLOCK (flare clock) system is a novel platform that comprises of a nanoporous membrane based multilayer stack that works with passively secreted sweat. It is designed to capture eczema severity and circadian disruption caused due to its symptoms. This is aimed to be a wearable designed for efficient management of the flaring associated with Atopic Dermatitis (AD). The work presents the development of an eczematous flare tracker that detects Interleukin-31 and cortisol levels to create an AD management platform. The platform uses electrochemical detection for tracking these biomarkers in sweat. It is sensitive to IL-31 levels in various flare-based formulations tested through simulated sweating with a detection limit of 50 pg/mL and range 50–1000 pg/mL. On-body study highlights the ability of the wearable platform to track the rise and fall in the biomarkers’ levels. These levels are well correlated to salivary levels and commercial gold standard techniques (r > 0.8, R2 > 0.95).

Studies on Ni–SnO2 Nanocomposites for Humidity Sensing Application

AbstractWe report a hydrothermal method for synthesis of nickel‐doped tin oxide (Ni–SnO2) nanoparticles. The samples are characterized by different analysis techniques to understand their structural, morphological, and optical properties. The synthesized nanomaterials are characterized by X‐ray diffraction, it is crystallized in a tetragonal rutile crystal structure and the crystallite size increases from ∼5 to ∼23 nm with the increasing nickel (Ni) doping concentration. The field emission electron microscopy demonstrates that in case of doping the addition of polyethylene glycol is responsible for the development of densely packed flower like bunches. Further, the synthesized n‐type SnO2 materials are systematically investigated for humidity sensing toward atmospheric moisture. The results indicate that nickel doping improves the performance of SnO2 sensor and is highly sensitive over a wide relative humidity (%RH) range from 10% to 100% at room temperature than pure SnO2. It is found that the resistance of the films decreases with increasing RH as the multilayer stacking of water molecules occurred on the surface of synthesized nanomaterials. Also, the fast response time of 15 s and recovery time of 4 s are observed for the 5% nickel‐doped SnO2 sensor. This improved sensing performance is attributed to nickel doping as doping developed the proportions of oxygen vacancy and improves the large surface to volume ratio as well as exhibited high conductivity. Thus, the doping of SnO2 nanoparticles with Ni should be a promising approach for designing and fabricating the high‐performance humidity sensor.

Ferromagnetic resonance and spin-wave exchange stiffness of FeGaB/Al2O3 multilayer thin film stack for microwave applications

In this article, we have illustrated the deposition of multilayer film stack of Ta (5 nm)/[FeGaB (15 nm)/Al2O3 (3 nm)] n/Ta (3 nm)/Al2O3 (2 nm); n = 1,5, and 10, onto Si substrates, and studied magnetodynamic properties with multilayer thickness and temperature dependence. The results of surface morphology of thin film stacks suggest dipolar coupling generates for n = 5 and 10 thin film stack, which influence the ferromagnetic absorption results. From results of ferromagnetic resonance spectroscopy (FMR), the resonance peak for each excitation frequency provides the effective magnetization, the gyromagnetic ratio and damping factor. The damping factor for multilayer stack n = 1 shows a lower value compared to the other two samples. The multilayer stack provides perpendicular surface magnetic anisotropy (ks) from thickness dependence of effective magnetization. The analysis of spin-wave resonance spectra at multiple frequencies allows manipulate the exchange stiffness (D) of multilayer film stack n = 5 and n = 10 and temperature dependence the exchange stiffness follows the itinerant-electron model (T2 law) and suggests electron - magnon scattering exists in the thin film stack.

Gate-induced half metals in Bernal-stacked graphene multilayers

Recent experiments indicate that the Bernal stacked graphene multilayer (BGM) have an interaction induced gapped (or pseudo gapped) ground state. Here, we propose that, due to the electron correlation, the BGM can be induced into a half metallic phase by applying a vertical electric field and doping. The half metallic states in even-layer and odd-layer BGMs have totally different behaviors, due to their different band structures. We systematically calculate the graphene tetralayer (4L-BGM) and trilayer (3L-BGM) as the typical examples of the even-layer and odd-layer BGMs, respectively. In 4L-BGM, we find an interesting phenomenon of electric field induced inversion of the spin-polarized bands. Namely, in the half metallic phase, the spin polarization of the conducting channel and the net magnetic moment are inversed when the applied electric field exceeds a critical value. In 3L-BGM, a remarkable feature is that the inequivalence of the the two sublattices will intrinsically break the degeneracy of the the spin-up and spin-down bands even in the zero electric field case. Our results suggest that 4L-BGM should be an ideal platform to detect the proposed half metallic phase in BGM systems.

Composition-dependent ultrafast THz emission of spintronic CoFe/Pt thin films

We measure the transient THz emission of ultrathin spintronic bilayers composed of a cobalt–iron alloy (CoxFe1−x) and platinum (Pt), depending on the Co content 0 ≤ x ≤ 1. We find that the THz emission amplitude changes only slightly over the entire concentration range, indicating that Fe and Co contribute similarly to the THz generation process. Additionally, we fabricate multilayer stacks and find that the THz amplitude is increased by up to 36% compared to a single bilayer CoFe/Pt spintronic emitter.

Stability of Mn2RuxGa-based multilayer stacks

Perpendicular heterostructures based on a ferrimagnetic Mn2RuxGa (MRG) layer and a ferromagnetic Co/Pt multilayer were examined to understand the effects of different spacer layers (V, Mo, Hf, HfOx and TiN) on the interfaces with the magnetic electrodes, after annealing at 350∘C. Loss of perpendicular anisotropy in MRG is strongly correlated with a reduction in the substrate-induced tetragonality due to relaxation of the crystal structure. In the absence of diffusion, strain and chemical ordering within MRG are correlated. The limited solubility of both Hf and Mo in MRG is a source of additional valence electrons, which results in an increase in compensation temperature Tcomp. This also stabilises perpendicular anisotropy, compensating for changes in strain and defect density. The reduction in squareness of the MRG hysteresis loop measured by anomalous Hall effect is <10%, making it useful in active devices. Furthermore, a CoPt3 phase with (220) texture in the perpendicular Co/Pt free layer promoted by a Mo spacer layer is the only one that retains its perpendicular anisotropy on annealing.

Research on Processing Technology of Multi-Layer Heterogeneous Material Composite Micron Cantilever Beam Structure.

In order to overcome the simplicity and instability of micron cantilever membrane structure, sacrificial layer technology and multi-layer heterogeneous material composite stacking technology were designated. Based on the research with respect to a multi-layer heterogeneous cantilever beam structure, multi-layer heterogeneous material composite, and sacrificial layer release craft, different characteristics of sacrificial layer material and film preparation craft were analyzed. According to these results, the suitable film preparation craft was generated to reduce the stress between materials and to improve the reliability and percentage of finished products. Our work put multi-layer material composite micro-cantilever beam structure into practice, and accelerated the manufacturing of a micro-acceleration sensor and vibration sensor in the future.

Capillary zone electrophoresis of lipoarabinomannan by multi-layered concentration.

The present article describes a capillary zone electrophoresis method which relies on a multilayered water-alkali solvent stacking with online ionization to enhance detection of mannose, arabinose, and their oligosaccharides, which are used as the migration profile standards but are also the distinctive structural components of lipoarabinomannan. Lipoarabinomannan is detected in patients having tuberculosis. The capillary electrophoresis method with ionization of the whole saccharides without degradation in alkaline solution inside the capillary is based on the structural deprotonation of the molecules under ultrahigh pH conditions. The validation of the capillary electrophoresis parameters revealed that the 15-fold electrolyte-water-injection plug allowed detection of one-third lower concentrations than detected without online concentration. For the first time, the better detectability was seen especially for highly polymerized, but otherwise poorly ionized, arabinooctaose. The applicability of the method for detecting whole large biological saccharide complexes was confirmed by the glycolipid lipoarabinomannan. For the first time also, the migration of the indestructible lipoarabinomannan was detected together with oligosaccharides used representing the capping units, namely mannose, mannobiose, and mannotriose. The myo-inositol-phosphate-lipid unit was seen to migrate separately from the arabinomannan, since it was hydrolyzed from one lipoarabinomannan product under alkaline conditions in capillary electrophoresis.

Design of QoS on data collection in wireless sensor network for automation process

WSNs facilitate the analysis of the universe with an unprecedented resolution. WSN is a network that connects many low-cost, low-powered sensor nodes capable of sensing/actuating and can interact with one another over short distances through a low-power radio. The article aims to provide strategies for enhancing and maintaining QoS in WSN communication in particular. As a result, we implemented a classification-based multi-layer WSN stack prototype that takes CDC applications into account. This method decreases the increasing point load by control messages, resulting in higher application throughput. In the presence of reasonably large unicast data traffic, the CDC multi-layer stack achieves 85.16% throughput while running at less than 12.14% delay. While WSN is the transmission technique and automation are the implementation scenario, the existing methods can be extended to certain other WSN and scenarios with related communication patterns and QoS issues.

Hard coatings for cutting applications: Physical vs. chemical vapor deposition and future challenges for the coatings community

Since decades, protective hard coatings with thicknesses of a few micrometers are grown by physical or chemical vapor deposition (PVD, CVD) on cutting tools to improve their application performance. For the huge variety of cutting applications, different coating materials are used, which typically belong to the material classes of nitrides, carbides, carbonitrides, borides, boronitrides or oxides, frequently in bi- or multilayer stacks. The present work surveys typical hard coatings belonging to the respective material classes, deposited by PVD as well as CVD. Pioneering studies in this field as well as recent findings contributing to the establishment of comprehensive “synthesis – structure – property – application performance” relationships of the respective coatings are discussed and the current state-of-research is reviewed. Condensed summaries and comparisons between PVD and CVD coatings are given at the end of each subsection. In addition, current and future challenges for the hard coatings community are surveyed. • Review of the current state-of-research of hard coatings for cutting applications • Advanced characterization methods enable an in-depth insight in coating structure. • Comparison and condensed summaries of properties of coatings grown by PVD and CVD • Different characteristics of PVD and CVD hard coatings highlighted • Survey of current and future challenges for the hard coatings community

Ferroelectric Vertical Gate-All-Around Field-Effect-Transistors With High Speed, High Density, and Large Memory Window

Ferroelectric vertical gate-all-around field-effect-transistor (Fe-VGAAFET) suits a memory cell with a 5 nm technology node and beyond since it is less constrained by gate length, thereby providing sufficient space for the ferroelectric film compared with ferroelectric FinFET (Fe-FinFET) and ferroelectric lateral gate-all-around field-effect-transistors (Fe-LGAAFET). Also, Fe-VGAAFET achieves multilayer vertical stacking, which further increases the integrated density of devices. Here, we develop ferroelectric vertical sandwich gate-all-around field-effect-transistors (Fe-VSAFETs) with large memory windows (the maximum 2.3 V), high program/erase speeds (100 ns), and excellent retention properties using a self-aligned high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa $ </tex-math></inline-formula> metal gate process. Furthermore, vertical nanosheet devices with two channel thicknesses of approximately 16 and 42 nm and nanowire devices with a channel diameter of 30 nm were successfully fabricated, and excellent device characteristics were obtained.

Proof Mass Effects on a Flextensional Piezoelectric Energy Harvester

This paper presents a comprehensive study of proof mass effects on a piezoelectric multilayer stack-based flextensional piezoelectric energy harvester (PM-Flex-PEH). For a weighted 23.7-gram PM-Flex-PEH, the proof mass of 10 grams, 20 grams, 50 grams, and 100 grams was applied on its top, respectfully, at different levels of vibrations. Both finite element modeling and experimental studies were carried out. An equivalent multilayer stack model and a full PM-Flex-PEH finite element model were developed. The impedance and sweep sin vibration tests were carried out on the PM-Flex-PEH. The simulation results were in alignment with the experimental results. The four mass ratios, including the mass ratio of the proof mass over the PM-Flex-PEH mass, and the mass ratio of the proof mass over the total mass and their square roots, were compared with the corresponding resonant frequency and generated voltage. It is shown that the generated voltage is linearly increase with the weight ratio of the proof mass over the PM-Flex-PEH by a factor of 2. However, the resonance frequency ratio for with proof mass over without proof mass is linearly decrease with the square root of the weight ratio of proof mass over the PM-Flex-PEH by factor of 0.32.

Reduce Wafer Remnants Through Pre-Assembly Process Optimization

Wafer fabrication technology has been seeing exponential growth in recent years. This development is driven by the demand for better reliability, superior performance, and lower cost of electronic consumer products. Generally, the standard soft-soldering wafer backside metallization multilayer stack is AuAs/Ag/Ni/Ag. The present backside metallization being developed is Ti/NiV/Ag as the cost of Ti is almost neglectable compared to Au. However, this new wafer backside metallization leads to increased remnants remaining on the dicing tape after die pickup. The reduced effective area of the die backside surface may cause adhesion issues in the subsequent die attach process. In realizing this essential phase, in pre-assembly process optimization has been carried out using some assessment on the process flow and data analysis through statistical analyses image and measurement of wafer skeleton remnants was taken showing a reduction from 70μm to 40μm in width. This method shows that skipping the baking process in the pre-assembly process will undoubtedly lessen the adhesion with the back metal with mounting tape. Without compromising the saw quality will indeed give a reduced wafer remnant. Henceforth, skipping baking in the pre-assembly process will significantly reduce wafer remnants and further improve die attach process.

Nanophotonics-Enabled High-Efficiency Selective Solar Absorbers for Waste Heat Management

Selective solar absorbers (SSAs) harnessing solar energy as heat and converting it into thermal energy have gained much attention, specifically in solar thermoelectric generators and solar thermophotovoltaic systems. However, most of these SSAs suffer from low solar-to-heat conversion efficiency at moderately-high temperatures (100 – 400 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> C) and require complex nanofabrication techniques such as focused ion beam milling or electron beam lithography, hindering large-scale production. This article presents a large-area compatible and lithography-free design of SSA comprising a nanoscale multilayer stack of silica–titanium dioxide–silicon–germanium–chromium layers supported by a silicon substrate. We report 87% solar-to-thermal energy conversion efficiency with 889.4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{Wm}^{-2}$</tex-math></inline-formula> net absorbing power at 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> C. At this temperature, the absorption coefficient achieved is 0.90, and the emission coefficient is reported to be 0.04. A perfect match between theoretically and numerically obtained spectral responses validates our findings. The fabrication tolerance study unveils that the proposed SSA design is expected to be robust and would be less susceptible to fabrication imperfections. This angle-insensitive and polarization-independent design offers a high stagnation temperature of 378 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> C, thus indicating that the proposed SSA can efficiently operate at high temperatures.

Revealing of InP multi-layer stacks from KPFM measurements in the dark and under illumination

Solar cells are complex devices, being constituted of many layers and interfaces. The study and the comprehension of the mechanisms that take place at the interfaces is crucial for efficiency improvement. This paper applies Kelvin probe force microscopy (KPFM) to study materials and interfaces with nanometer scale imaging of the surface potential in the dark and under illumination. KPFM measurements are highly sensitive to surface states and to the experimental measurement environment influencing the atomic probe operating conditions. Therefore, in order to develop a quantitative understanding of KPFM measurements, we have prepared a dedicated structured sample with alternating layers of InP:S and InP:Fe whose doping densities were determined by secondary-ion mass spectroscopy. We have performed KPFM measurements and shown that we can spatially resolve 20 nm thick InP layers, notably when performed under illumination which is well-known to reduce the surface band-bending.

Selective ultrashort laser annealing of amorphous Ge/Si multilayer stacks

We report on single-short laser crystallization of Ge/Si multilayer stacks consisting of alternating amorphous nanosized films of silicon and germanium using near- and mid-infrared femtosecond and picosecond laser pulses. The phase composition of the irradiated stacks was investigated by the Raman scattering technique. Several non-ablative regimes of crystallization were found, from partial crystallization of germanium without intermixing the Ge/Si layers to complete intermixing of the layers with formation of GexSi1-x solid alloys. The roles of one- and two-photon absorption, thermal and non-thermal (ultrafast) melting processes, and laser-induced stresses in selective pico- and femtosecond laser annealing are analysed based on theoretical estimations and comparison with experimental data. It is concluded that, due to a mismatch of the thermal expansion coefficients between the adjacent stack layers, efficient explosive solid-phase crystallization of the Ge layers is possible at relatively low temperatures, well below the melting point. The possibility of ultrafast non-thermal phase transition in germanium in the studied regimes is also discussed.

Multilayer Stacked Ensemble Learning Model to Detect Phishing Websites

Phishing is a cyber attack that tricks the online users into revealing sensitive information with a fake website imitating a legitimate website. The attackers with stolen credentials not only use them for the targeted website but also can be used for accessing the other popular legitimate websites. There exists many anti-phishing techniques, toolbars, extensions to counter the phishing sites but still the phishing attacks are major concern in the current digital world. In this paper, we propose a multilayered stacked ensemble learning technique which consists of estimators at different layers where the predictions of estimators from current layer are fed as input to the next layer. From the experimental results, it is observed that the proposed model achieved a significant performance when evaluated with different datasets with an accuracy of ranging from 96.79%to 98.90%. The proposed model is evaluated with datasets from UCI(D1), Mendeley 2018(D2) and Mendeley 2020(D3,D4). The proposed model achieved detection rate of 97.76% with D1 dataset, achieved an accuracy of 98.9% with D2 dataset. Finally, the technique is tested with D3 and D4 which resulted in accuracy of 96.79% and 98.43% respectively. Also, the proposed model outperformed baseline models corresponding to datasets with a significant difference in accuracy and F score metrics.