Multilayer Stack Research Articles

Strongly coupled piezoelectric energy harvesters: Optimised design with over 100 mW power, high durability and robustness for self-powered condition monitoring

Harvesting ambient vibration energy is a promising method to realise self-powered wireless sensors. However, most of the energy harvesters developed to date are not suitable for real-world applications because of low power output and/or poor durability and robustness. To overcome these challenges, this work develops a strongly coupled piezoelectric stack energy harvester (PSEH) with design considerations not just on the power output but also on the durability and robustness. The PSEH took advantages of the force amplification capability of an optimised mechanical transformer and the high coupling coefficient of a 33-mode multilayer piezoelectric stack to achieve strong coupling and therefore high-power generation. To increase the durability, the piezoelectric stack was pre-compressed to prevent the development of tensile stress, to exploit the high compressive strength of piezoelectric ceramics; the maximum dynamic stress in the mechanical transformer was kept below half of the material’s fatigue limit. Plate springs were used to guide the motion of the PSEH and prevent undesired vibration to enhance robustness. A finite element model was developed for design optimisation, which links the design parameters directly to the full performance matrix including maximum power generation. When actuated at 0.5 g, 157 Hz in the lab tests, the PSEH produced a maximum average power of 140 mW with a 1-mW-bandwidth of 72 Hz and 10-mW-bandwidth of 24 Hz. The PSEH showed no performance degradation after continuously actuated at 0.3 g, 157 Hz for 7.9 h. In addition to the lab tests, on-site tests were performed by installing the PSEH in two locations of a screw air compressor. On-site tests showed that the PSEH was able to produce average power of 15.95 ± 2.3 mW and 43.19 ± 1.52 mW when the acceleration produced by the air compressor was 0.125 ± 0.012 g and 0.259 ± 0.004 g, respectively.

Design, Simulation, Fabrication, and Characterization of an Electrothermal Tip-Tilt-Piston Large Angle Micromirror for High Fill Factor Segmented Optical Arrays.

Micro-electromechanical system (MEMS) micromirrors have been in development for many years, but the ability to steer beams to angles larger than 20° remains a challenging endeavor. This paper details a MEMS micromirror device capable of achieving large motion for both tip/tilt angles and piston motion. The device consists of an electrothermal actuation assembly fabricated from a carefully patterned multilayer thin-film stack (SiO2/Al/SiO2) that is epoxy bonded to a 1 mm2 Au coated micromirror fabricated from an SOI wafer. The actuation assembly consists of four identical actuators, each comprised of a series of beams that use the inherent residual stresses and coefficient of thermal expansion (CTE) mismatches of the selected thin films to enable the large, upward, out-of-plane deflections necessary for large-angle beamsteering. Finite element simulations were performed (COMSOL v5.5) to capture initial elevations and tip/tilt motion displacements and achieved <10% variance in comparison to the experiment. The measured performance metrics of the micromirror include tip/tilt angles of ±23°, piston motion of 127 µm at sub-resonance, and dynamics characterization with observed resonant frequencies at ~145 Hz and ~226 Hz, for tip/tilt and piston motion, respectively. This unique single element design can readily be scaled into a full segmented micromirror array exhibiting an optical fill-factor >85%, making it suitable for optical phased array beam control applications.

Emission wavelength control of InAs/GaAs quantum dots using an As2 source for near-infrared broadband light source applications

Herein, we report an emission wavelength control technique for self-assembled InAs quantum dots (QDs) grown via molecular beam epitaxy using an As2 source (As2-QDs). The As2-QDs exhibited photoluminescence with a shorter center wavelength and larger bandwidth than those of the QDs grown using an As4 source. In addition, the emission center wavelength could be controlled by adjusting the time between the growth and capping of the As2-QDs. We utilized the multilayer stack of emission-wavelength-controlled As2-QDs to fabricate an electrically-driven light source and demonstrated its broadband (approximately 130 nm) emission in the 1–1.3 μm wavelength range.

Automated 3D scoring of fluorescence in situ hybridization (FISH) using a confocal whole slide imaging scanner

Fluorescence in situ hybridization (FISH) is a technique to visualize specific DNA/RNA sequences within the cell nuclei and provide the presence, location and structural integrity of genes on chromosomes. A confocal Whole Slide Imaging (WSI) scanner technology has superior depth resolution compared to wide-field fluorescence imaging. Confocal WSI has the ability to perform serial optical sections with specimen imaging, which is critical for 3D tissue reconstruction for volumetric spatial analysis. The standard clinical manual scoring for FISH is labor-intensive, time-consuming and subjective. Application of multi-gene FISH analysis alongside 3D imaging, significantly increase the level of complexity required for an accurate 3D analysis. Therefore, the purpose of this study is to establish automated 3D FISH scoring for z-stack images from confocal WSI scanner. The algorithm and the application we developed, SHIMARIS PAFQ, successfully employs 3D calculations for clear individual cell nuclei segmentation, gene signals detection and distribution of break-apart probes signal patterns, including standard break-apart, and variant patterns due to truncation, and deletion, etc. The analysis was accurate and precise when compared with ground truth clinical manual counting and scoring reported in ten lymphoma and solid tumors cases. The algorithm and the application we developed, SHIMARIS PAFQ, is objective and more efficient than the conventional procedure. It enables the automated counting of more nuclei, precisely detecting additional abnormal signal variations in nuclei patterns and analyzes gigabyte multi-layer stacking imaging data of tissue samples from patients. Currently, we are developing a deep learning algorithm for automated tumor area detection to be integrated with SHIMARIS PAFQ.

Highly efficient SERS substrates with different Ag interparticle nanogaps based on hyperbolic metamaterials

Surface-enhanced Raman scattering (SERS) substrates based on Hyperbolic metamaterials (HMM) have received tremendous attention due to the presence of confined optical modes, i.e., the surface plasmon polaritons (SPP) and bulk plasmon polaritons (BPP). In the present study, a multilayer HMM SERS substrate was fabricated, comprising a monolayer of silver nanoparticles (Ag NPs) and Au-Al2O3 films. Our study demonstrates that the Ag NPs layer excited SPP and BPP, and the localized surface plasmon (LSP) resonance of the Ag NPs layer coupled with BPP, creating a strong electromagnetic field at the interparticle gaps of the Ag NPs. Interestingly, increasing the multilayer stacking of HMM will strengthen the SERS activity until a certain threshold. On the top of HMM, the interparticle gaps of the Ag NPs were adjusted to enhance the SERS characteristics and the maximum EF appeared at the gap of 10 nm. Performing theoretical simulations as well as experiments, the ultra-sensitivity, good reproducibility, reusability, and high enhancement factor of the proposed SERS substrate were assessed. Lastly, the ultralow limits of detection for melamine in milk were 10−7 M, satisfying the needs for successful implementation in the food safety field.

Research on the Prediction of A-Share "High Stock Dividend" Phenomenon-A Feature Adaptive Improved Multi-Layers Ensemble Model.

Since the “high stock dividend” of A-share companies in China often leads to the short-term stock price increase, this phenomenon’s prediction has been widely concerned by academia and industry. In this study, a new multi-layer stacking ensemble algorithm is proposed. Unlike the classic stacking ensemble algorithm that focused on the differentiation of base models, this paper used the equal weight comprehensive feature evaluation method to select features before predicting the base model and used a genetic algorithm to match the optimal feature subset for each base model. After the base model’s output prediction, the LightGBM (LGB) model was added to the algorithm as a secondary information extraction layer. Finally, the algorithm inputs the extracted information into the Logistic Regression (LR) model to complete the prediction of the “high stock dividend” phenomenon. Using the A-share market data from 2010 to 2019 for simulation and evaluation, the proposed model improves the AUC (Area Under Curve) and F1 score by 0.173 and 0.303, respectively, compared to the baseline model. The prediction results shed light on event-driven investment strategies.

Band-Gap Landscape Engineering in Large-Scale 2D Semiconductor van der Waals Heterostructures.

We present a growth process relying on pulsed laser deposition for the elaboration of complex van der Waals heterostructures on large scales, at a 400 °C CMOS-compatible temperature. Illustratively, we define a multilayer quantum well geometry through successive in situ growths, leading to WSe2 being encapsulated into WS2 layers. The structural constitution of the quantum well geometry is confirmed by Raman spectroscopy combined with transmission electron microscopy. The large-scale high homogeneity of the resulting 2D van der Waals heterostructure is also validated by macro- and microscale Raman mappings. We illustrate the benefit of this integrative in situ approach by showing the structural preservation of even the most fragile 2D layers once encapsulated in a van der Waals heterostructure. Finally, we fabricate a vertical tunneling device based on these large-scale layers and discuss the clear signature of electronic transport controlled by the quantum well configuration with ab initio calculations in support. The flexibility of this direct growth approach, with multilayer stacks being built in a single run, allows for the definition of complex 2D heterostructures barely accessible with usual exfoliation or transfer techniques of 2D materials. Reminiscent of the III-V semiconductors' successful exploitation, our approach unlocks virtually infinite combinations of large 2D material families in any complex van der Waals heterostructure design.

Dual-mode near-infrared light tunable absorber based on graphene by optical Tamm state and microcavity

A metal dual distributed Bragg reflector (DBR)-based cavity structure embedded with graphene and spacer layer is proposed to tune the dual-mode absorption in the near-infrared wavelength induced by the Optical Tamm state (OTS) and Fabry–Perot (FP) cavity. The effects of optical spacer thickness, fermi level of graphene, DBR pair number and Bragg wavelength on tuning dual-mode absorption of graphene are explored using the transfer matrix method (TMM). The proposed configuration shows the capability of multilayer stack to achieve tunable dual-mode absorption. It is expected that the planar structure can be compatible with large-scale manufacturing and can have potential applications in color displays, multi-wavelength detection, and dual-mode absorbers.

Spectrally Selective Solar Absorber Coating of W/WAlSiN/SiON/SiO2 with Enhanced Absorption through Gradation of Optical Constants: Validation by Simulation

The properties of spectrally selective solar absorber coatings can be fine-tuned by varying the thickness and composition of the individual layers. We have deposited individual layers of WAlSiN, SiON, and SiO2 of thicknesses ~940, 445, and 400 nm, respectively, for measuring the refractive indices and extinction coefficients using spectroscopic ellipsometer measurements. Appropriate dispersion models were used for curve fitting of Ψ and Δ for individual and multilayer stacks in obtaining the optical constants. The W/WAlSiN/SiON/SiO2 solar absorber exhibits a high solar absorptance of 0.955 and low thermal emissivity of 0.10. The refractive indices and extinction coefficients of different layers in the multilayer stack decrease from the substrate to the top anti-reflection layer. The graded refractive index of the individual layers in the multilayer stack enhances the solar absorption. In the tandem absorber, WAlSiN is the main absorbing layer, whereas SiON and SiO2 act as anti-reflection layers. A commercial simulation tool was used to generate the theoretical reflectance spectra using the optical constants are in well accordance with the experimental data. We have attempted to understand the gradation in refractive indices of the multilayer stack and the physics behind it by computational simulation method in explaining the achieved optical properties. In brief, the novelty of the present work is in designing the solar absorber coating based on computational simulation and ellipsometry measurements of individual layers and multilayer stack in achieving a high solar selectivity. The superior optical properties of W/WAlSiN/SiON/SiO2 makes it a potential candidate for spectrally selective solar absorber coatings.

Color Glass by Layered Nitride Films for Building Integrated Photovoltaic (BIPV) System

We investigated layered titanium nitride (TiN) and aluminum nitride (AlN) for color glasses in building integrated photovoltaic (BIPV) systems. AlN and TiN are among suitable and cost-effective optical materials to be used as thin multilayer films, owing to the significant difference in their refractive index. To fabricate the structure, we used radio frequency magnetron deposition method to achieve the target thickness uniformly. A simple, fast, and cheap fabrication method is achieved by depositing the multilayer films in a single sputtering chamber. It is demonstrated that a multilayer stack that allows light to be transmitted from a low refractive index layer to a high refractive index layer or vice-versa can effectively create various distinct color reflections for different film thicknesses and multilayer structures. It is investigated from simulation based on wave optics that TiN/AlN multilayer offers better color design freedom and a cheaper fabrication process as compared to AlN/TiN multilayer films. Blue, green, and yellow color glasses with optical transmittance of more than 80% was achieved by indium tin oxide (ITO)-coated glass/TiN/AlN multilayer films. This technology exhibits good potential in commercial BIPV system applications.

The interplay of stratal and vertical migration pathways in shallow hydrocarbon plumbing systems

AbstractHydrocarbon plumbing systems have been extensively documented in the past two decades using high‐resolution 3D seismic data, exploiting the ability of seismic imaging techniques to reveal the subsurface geometry of gas charged sediments. In this paper, we present a detailed study of a hydrocarbon plumbing system from the South China Sea, that involves both vertical and lateral (stratal) hydrocarbon migration in Miocene to Recent clastic sediments that comprise multilayer stacking of thinly layered clays, silts and sands. We show that a transtensive fault system that provides lateral seal for fault‐dip traps of deep Miocene reservoirs, and offers a vertical pathway for migration to shallower silty units. These silty units in turn form a ‘spillway’ in a regional, northward migration path. This path involves filling each shallow fault‐dip trap to spill point towards the fault tips, with stratal migration forced around the outer flanks of the fault‐related folds. Successive fill‐to‐spill leads to a continuous trail of amplitude anomalies that merge into a continuous, larger, gas‐charged anomaly pattern. The migrating gas finally accumulates within a zone bounded by a large boundary fault with full juxtaposition seal. The pattern of anomaly distribution suggests that the hydrocarbon migration has been active in the Late Pleistocene and is probably continuing at the present day. Hence this plumbing system may be one of very few examples described to date in which dynamic hydrocarbon migration pathways have been directly imaged by seismic data.

Uncooled Antenna-Coupled Microbolometer for Detection of Terahertz Radiation

In this contribution, we describe the design, technology, and physical parameters of antenna-coupled microbolometer, used for broadband detection of terahertz electromagnetic spectrum. This microbolometer features an application of La0.67Sr0.33MnO3 layer grown on multilayered material stack ensuring lattice matching of the sensing LSMO layer to silicon. By virtue of bulk micromachining of silicon-on-insulator substrates, the sensing structure is built on thin suspended membrane to provide weak thermal link, increasing thermal response, thus sensitivity. Additionally, it helps suppressing excitation of in-plane guided surface modes that will otherwise deteriorate the antenna radiation diagram and affect the spectral responsivity of the sensor. Finally, the operation of sensor is demonstrated using a molecular laser setup at 762 GHz (and also 1.4 THz) emission line. The parameters of the said microbolometers are analyzed in terms of response and time constant. Optimal working temperature of the detectors is about 65 °C.

Refined extreme ultraviolet mask stack model.

A refined model of an extreme ultraviolet (EUV) mask stack consisting of the Mo/Si multilayer coated by a Ru protective layer and a TaBN/TaBO absorber layer was developed to facilitate accurate simulations of EUV mask performance for high-NA EUV photo-lithography (EUVL) imaging. The model is derived by combined analysis of the measured EUV and x ray reflectivity of an industry-representative mask blank. These two sets of measurements were analyzed using a combined free-form analysis procedure that delivers high-resolution x ray and EUV optical constant depth profiles based on self-adapted sets of sublayers as thin as 0.25 nm providing a more accurate description of the reflectivity than obtained from only EUV reflectivity. "Free-form analysis" means that the shape of the layer interfaces in the model is determined experimentally and is not given a priori by the structure model. To reduce the numerical effort for EUV imaging simulations, a low-resolution model of the multilayer and absorber stack with sublayer thicknesses larger than 2 nm, that fits to only the EUV reflectance, was derived from the high-resolution model. Rigorous high-NA EUVL simulations were done to compare the performance of the new model to our previous work [Proc. SPIE8886, 88860B (2013)PSISDG0277-786X10.1117/12.2030663].

Compaction, nesting and image based permeability analysis of multi-layer dry preforms by computed tomography (CT)

Textile preforms have a multi-scale hierarchy of fibres, tows and plies; geometry at each scale influences the manufacturing processes, the permeability of the textile to resin as well as the mechanical properties of the finished laminate. High-fidelity structural models for textile composites require accurate non-idealised tow geometry as well as changes to this geometry during processing. This paper presents a CT-based experimental technique for capturing the realistic meso-scale geometry of individual tows in a 2D fabric layer and the nesting or ply shifting between fabric layers in a multi-layer stack during a simulated consolidation process. An in-situ compression loading mechanism has been implemented in order to capture multi-layer preform geometry. Inter-tow and inter-ply void geometry has been captured in 3D due to high x-ray contrast between the fibres and the air. The degree of ply nesting and the connectivity between adjacent voids have been assessed at each stage of the compaction process. An image-based flow analysis has been performed on the extracted 3D realistic void geometry and the effect of layer nesting on resin flow has been evaluated. Image-based prediction of permeability values have been in good agreement with experimental values found in the literature when normalised as a function of fibre volume fractions.

Ultra-wideband perfect reflection and tunneling by all-dielectric metamaterials.

All-dielectric metamaterials are a promising low-loss alternative to plasmonic metamaterials for near-infrared perfect reflection, but the working bandwidth is still limited. Here we propose an ultra-wideband all-dielectric metamaterial perfect reflector that has a compact structure consisting of the subwavelength high-index grating, connection layer, and multilayer stack. Such a perfect reflector combines the advantages of quarter-wave design and resonant leaky mode, and covers an extremely wide wavelength range from 966 to 2203 nm under the normal incidence of transverse magnetic wave. By engineering the connection layer, the reflection band can be split with an ultra-narrowband tunneling of light transmission. These achievements demonstrate the promising potential of all-dielectric metamaterials as ultra-wideband reflectors for extensive applications in optical devices and systems.

Electrical Detection of DC Spin Current Propagation Through an Epitaxial Antiferromagnetic NiO Layer

A method for detecting dc spin current propagation through an epitaxial antiferromagnetic (AFM) NiO layer is presented. Spin current is generated by spin pumping from an adjoining ferromagnetic (FM) layer and detected in a non-magnetic metallic layer by the inverse spin Hall effect. Comparison is made with a YIG/Pt bilayer, where only the Pt layer is electrically conducting, but for which spin Hall magnetoresistance makes an additional contribution to the measured signal. The signal obtained from the multilayered stack containing the AFM NiO layer is found to contain additional contributions due to anisotropic magnetoresistance. By exciting the sample with out-of-plane rf magnetic field and making measurements with a static field applied at different orientations within the plane of the sample, a signal associated with the dc spin current may be identified.

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Anisotropic in-plane dielectric and ferroelectric properties of tensile-strained BaTiO3 films with three different crystallographic orientations

Ferroelectric properties of films can be tailored by strain engineering, but a wider space for property engineering can be opened by including crystal anisotropy. Here, we demonstrate a huge anisotropy in the dielectric and ferroelectric properties of BaTiO3 films. Epitaxial BaTiO3 films deposited on (100), (110), and (111) SrTiO3 substrates were fabricated by chemical solution deposition. The films were tensile-strained due to thermal strain confirmed by the enhanced Curie temperature. A massive anisotropy in the dielectric constant, dielectric tunability, and ferroelectric hysteresis loops was observed depending on the in-plane direction probed and the orientation of the films. The anisotropy was low for (111) BaTiO3, while the anisotropy was particularly strong for (110) BaTiO3, reflecting the low in-plane rotational symmetry. The anisotropy also manifested at the level of the ferroelectric domain patterns in the films, providing a microscopic explanation for the macroscopic response. This study demonstrates that the properties of ferroelectric films can be tailored not only by strain but also by crystal orientation. This is particularly interesting for multilayer stacks where the strain state is defined by the boundary conditions. We propose that other materials can be engineered in a similar manner by utilizing crystal anisotropy.

Ga-Doped ZnO Coating—A Suitable Tool for Tuning the Electrode Properties in the Solar Cells with CdS/ZnS Core-Shell Quantum Dots

Two layer system from sputtered indium tin oxide (ITO) and gallium doped zinc oxide (Ga:ZnO, GZO) were studied for transparency in the visible electromagnetic range, reflectivity in the near infrared range, conductivity and valent band for a solar cells with quantum dots. The bi-layer coatings produced at optimized oxygen partial pressure, films thickness and surface roughness exhibit improved optical properties without worsening the electrical parameters, even if additional oxygen introduction during the reactive sputtering of the GZO. With an average optical transmittance of 91.3% in the visible range, average reflection and resistivity lower than 0.4 × 10−2 Ω.cm, these coatings are suitable for top electrode in the solar cells. The obtained results reveal that multilayered stacks of transparent ITO/Ga-doped ZnO coatings possess relatively low surface roughness (7–9 nm) and appropriate refractive index. The additional oxidation of GZO films induces modification of the film thickness and respectively of their optical performances.

N-doped MWCNTs from catalyst-free, direct pyrolysis of commercial glue

We report a unique, catalyst-free, direct pyrolysis process to obtain nitrogen-doped multiwall carbon nanotubes (N-MWCNTs). The process includes the polymerization of ethyl cyanoacrylate (ECA) based commercial super glue with aqueous NaCl solution. The resultant poly-ethyl cyanoacrylate (PECA)-NaCl composite was washed to remove NaCl and subsequently calcined at 1000 °C in an inert atmosphere to obtain carbon nanotubes. The field emission scanning electron microscopy and high-resolution transmission electron microscopy studies confirm that these are nitrogen-doped multiwall carbon nanotubes (N-MWCNTs) with diameters in the range of 80–110 nm. Compared to conventional MWCNTs, these nanotubes exhibit distinct multilayer stacking of carbon with short-range ordering with interlayer spacing slightly larger than graphitic carbon. XPS studies reveal the presence of doped nitrogen substituting for carbon atoms, whereas Raman spectroscopy data shows that these nitrogen-doped nanotubes exhibit nanocrystalline, graphitic carbon. Washing of PECA-NaCl composite results in the removal of NaCl leading to the unique porous PECA intermediate structure. These unique morphological changes and structural transformations of PECA in DI water along with the peculiar degradation behavior of PECA during the heat treatment process may be responsible for the formation of N-MWCNTs.