Thin Materials Research Articles

Development of an empirical model for the prediction of the sound absorption coefficient for thin and low-density fibrous materials

Currently, FEA software such as ABAQUS uses empirical models to predict the sound absorption coefficient of poroelastic materials. However, based on a recent review of the literature it was found that the current sound absorption empirical models are inadequate for accurate prediction of thin (t < 20 mm), low-density materials (ρB < 50 kg/m3). Therefore, the predictions of the sound pressure levels in vehicle cabins, using such software, will be inaccurate since the trim materials are thin and have a low density. Thus, this research aimed to develop an empirical model that can accurately predict the sound absorption coefficient of these materials. Hence, polypropylene fibres consisting of four different diameters were manufactured and converted into nonwovens. Thereafter, airflow resistivity and impedance tube experimental testing were performed on the specimens. Subsequently, statistical analysis of the data was performed using SAS software. SAS was used to identify which independent variables should be included in the models to be developed. The empirical models were developed using the regression analysis toolbox in Microsoft Excel. Once the models were developed, various checks were performed to validate the assumptions of linear regression. The software NumXL was used to perform Cook’s distance tests. Thereafter, the models were validated against the validation dataset, where it was found that the developed exponential model performed best. Finally, the exponential model was compared to existing models using two data sets i.e. an internal dataset, and an external dataset derived from the literature. The developed model outperformed all the historic models on both datasets.

An investigation of glass, ITO, and quartz transparent substrates on Pd/SnO2 hydrogen sensor structure and sensitivity

Hydrogen energy has great potential as a fuel for the future, but its leakage poses a major threat. Thus, our main concern is to detect it very quickly. In this work, we investigate the effect of transparent glass, ITO, and quartz substrates on hydrogen gas sensing properties of magnetron sputter- deposited Pd-capped SnO2 (Pd/SnO2) thin film sensor material. The XRD study reveals that all Pd-capped SnO2 thin films deposited on different substrates has polycrystalline tetragonal structure. Sensors fabricated on quartz substrates exhibit homogeneous grain distributions at the interface, whereas sensors deposited on ITO and glass substrates have randomly size grains distribution at the interface. Sensors deposited on glass and ITO show lower sensitivity compare to sensors fabricated on quartz substrate at a working temperature of 250°C. The Pd/SnO2 sensor @ quartz shown a maximum response of ∼ 9.3 and better stability toward 500 ppm hydrogen gas, and a fast response/recovery time of 30/26 s for 5 ppm hydrogen gas. The sensor @ quartz substrate shows a small reduction in response and baseline at 60% RH. The sensor fabricated on quartz substrate exhibits better selectivity toward hydrogen gas and significant stability for long duration of three months in high humid conditions. The performance of the Pd/SnO2 thin sensor fabricated on quartz proves that the sensor based on average grains have a wide potential for real hydrogen gas monitoring.

2D Vanadium Sulfides: Synthesis, Atomic Structure Engineering, and Charge Density Waves.

Two ultimately thin vanadium-rich 2D materials based on VS2 are created via molecular beam epitaxy and investigated using scanning tunneling microscopy, X-ray photoemission spectroscopy, and density functional theory (DFT) calculations. The controlled synthesis of stoichiometric single-layer VS2 or either of the two vanadium-rich materials is achieved by varying the sample coverage and sulfur pressure during annealing. Through annealing of small stoichiometric single-layer VS2 islands without S pressure, S-vacancies spontaneously order in 1D arrays, giving rise to patterned adsorption. Via the comparison of DFT calculations with scanning tunneling microscopy data, the atomic structure of the S-depleted phase, with a stoichiometry of V4S7, is determined. By depositing larger amounts of vanadium and sulfur, which are subsequently annealed in a S-rich atmosphere, self-intercalated ultimately thin V5S8-derived layers are obtained, which host 2 × 2 V-layers between sheets of VS2. We provide atomic models for the thinnest V5S8-derived structures. Finally, we use scanning tunneling spectroscopy to investigate the charge density wave observed in the 2D V5S8-derived islands.

Fabrication of pbs films for air mass filter of solar simulator

The production of solar panels is continuously increasing due to increasing demands at industrial and residential levels. This also leads to an increasing demand for solar simulator testing tools. A solar simulator is a tool to assess a solar panel's performance in lab and industry scales. One of the main components of the solar simulator is the Air Mass Filter (AMF). The primary function of AMF is to remove unwanted wave bands from the solar simulator light source (e.g., Xe arc lamp) so that the filtered spectrum is commensurate to that of solar irradiation. An AMF can be produced by fabricating a thin material layer on a transparent substrate like glass. The film would absorb certain wave bands in different ways. This paper reports the fabrication of the chalcogenide PbS thin films for applying AMF. The thermal evaporation technique is used for the film fabrication. PbS is known for its versatility for applications in different optical devices due to its tailorable optical properties. Different amounts (in grams) of PbS source powders are used to deposit the PbS thin films. The optical properties of the films are then examined using UV-Vis spectroscopy. The distributions of the transmittance intensity of the Xe-arc-lamp light with and without the use of the films as an optical filter are then examined using a solar simulator. From the experiments, the film deposited using a 0.012 g PbS powder source is regarded as the optimum one regarding the transmittance intensity distribution.

Self-Aligned Hybrid Nanocavities Using Atomically Thin Materials

Self-Aligned Hybrid Nanocavities Using Atomically Thin Materials

The Effect of Applying UV LED-Cured Varnish to Metalized Printing Elements during Cold Foil Lamination

The coating process involves applying a thin material layer to a surface to engender it with specific desirable properties or enhance its performance. In the production of print media (labels, packaging, printed textiles, and promotional materials), the standard functions of the coating process include visual decoration, which involves the addition of appealing colors, textures, and patterns. A pertinent issue in the printing industry is that at present, the predominant coating process uses printing and coating technologies (gravure, flexo, letterset, letterpress, screen printing, inkjet, and electrophotography) and lamination (i.e., attaching decorative layers of materials, such as films or fabrics). In this paper, we present a new method for testing the efficiency with which different-sized metalized printing elements (using gold foil) may be applied to paper substrates; to do so, we gradually vary the amount UV-cured inkjet varnish (or adhesive) that is applied. To test the effectiveness of this method in producing metallic visual effects, we utilize seven different thicknesses of UV-cured varnish with the aid of modular piezo inkjet heads (KM1024 iLHE-30) and three different printing speeds. Our research shows that to achieve optimal production of cold metalized foil, a 21 µm layer should be deposited, and the substrate should move at a speed of 0.30 m/s.

Use of Particle Induced X-Ray Emission (PIXE), Particle Induced Gamma–Ray Emission (PIGE), Energy Dispersive X-Ray Analysis (EDXRF) for Detecting Trace Elements in Soil Sample

This review paper provides a comprehensive overview of trace element analysis utilizing ion-atom interaction techniques, focusing on the principles, applications, and recent advancements in the field. Ion- atom interaction techniques, including Particle Induced X- Ray Emission (PIXE), Particle Induced Gamma–Ray Emission (PIGE), Energy Dispersive X-Ray Analysis (EDXRF), Rutherford backscattering spectroscopy (RBS), and ion beam analysis (IBA), offer unique capabilities for trace element analysis with high sensitivity and minimal sample preparation requirements. The paper begins by discussing the fundamental principles underlying ion-atom interaction techniques, such as the interaction of energetic ions with matter and the subsequent detection of emitted X-rays or backscattered particles. It explores the various analytical parameters that influence the sensitivity, resolution, and depth profiling capabilities of these techniques. Furthermore, the review highlights the diverse applications of ion-atom interaction techniques in fields such as environmental monitoring, forensic science, biomedical research, and materials science. It showcases how these techniques have been utilized to address specific analytical challenges, such as the detection of trace contaminants in environmental samples or the characterization of thin films and semiconductor materials.

Significantly improved optoelectronic performances of two-dimensional WS2(Er3+)/WSe2(Er3+) van der waals heterojunctions

Two-dimensional heterostructures with excellent properties are potential for high performance optoelectronic applications, since the ultimate thickness limit is possible to be broken with the advent of atomically thin materials. Yet the studies have also been largely constrained by the low physical doping space and absorption rates due to the atomic-thickness layers, and the efforts for high carrier concentrations and gain remain a significant challenge. Herein, high concentration of Er3+ ions are in-situ doped in WS2 and WSe2 atomic layers by chemical vapor deposition (CVD) method. The prepared layers are characterized by atomic force microscopy, transmission electron microscopy, photoluminescence (PL) spectroscopy, and Raman spectroscopy, respectively. 13–14 at% of Er3+ doping concentration in WSe2 and WS2 are examined by energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) with high consistency. A microregion fixed-point transfer technique is used to transfer the WS2(Er3+) monolayers onto the WSe2(Er3+) monolayers to form vertical van der Waals heterojunctions. Excellent performances are measured from the WS2(Er3+)/WSe2(Er3+) photodetector with the photoresponsivity of up to 67.4 A/W, external quantum efficiency of 13,202 %, and detectivity of 7.07 × 1011 Jones. Our results prove the effectiveness of Er3+ in-situ doping in WS2(Er3+)/WSe2(Er3+) heterojunctions for high-performance photodetectors.

Application of material point method in modeling soil-geosynthetics interactions-a literature survey

The material point method (MPM) has garnered significant attention in recent years owing to its advantages in solving soil–water-structure interaction problems involving large deformations in geotechnical engineering. The MPM combines the benefits of point-based and mesh-based approaches (finite element method) with both Eulerian computational mesh and continuum descriptions of materials. The successful integration of MPM in simulated landslides, internal erosion, and excavation has been frequently reported. However, solving the soil–geosynthetic interaction problem with the MPM has not been explored, although such problems often entail large deformations. The goal of this study is to collate studies on the simulation of geosynthetics and their interactions with soil using MPM. This paper first discusses the basics of MPM and the formation of thin membrane materials using MPM. It also includes limited applications of MPM in simulating soil–geosynthetic interactions. The applications demonstrate that the MPM is particularly effective in resolving large deformation problems associated with geosynthetics, including problems of landfill settlement, reinforced-slope stability, and geocontainer dropping.

First-principles study of the thickness-dependent shift current in γ-GeSe thin layers

We investigate the stable structure and optoelectronic properties of thin γ-GeSe layers through first-principles calculations. We examine three stacking configurations (A-A, A-B, and A-C) of adjacent quadruple layers (QLs), revealing the structural stability of A-C stacking. Due to broken inversion symmetry in atomically thin γ-GeSe layers, shift currents are generated, which are very sensitive to their stacking order and thickness. Despite similar optical absorption trends in A-B and A-C stackings, their shift current responses differ significantly. The shift current is notably decreased at odd-number stackings for all cases, attributed to opposite generated flows between the top and bottom surfaces. The analysis of orbital contributions reveals the charge shift's origin in γ-GeSe. We also explore mechanical modifications, such as sliding and strain, demonstrating the tunability of the shift current spectrum in γ-GeSe. This research enhances our understanding of the optoelectronic response in atomically thin materials, providing valuable insights for future applications.

Ultrathin and Deformable Graphene Etch Mask for Fabrication of 3D Microstructures.

Three-dimensional (3D) microfabrication techniques play a crucial role across various research fields. These techniques enable the creation of functional 3D structures on the microscale, unlocking possibilities for diverse applications. However, conventional fabrication methods have limits in producing complex 3D structures, which require numerous fabrication steps that increase the costs. Graphene is an atomically thin material known for its deformability and impermeability to small gases and molecules, including reactive gases like XeF2. These features make graphene a potential candidate as an etch mask for 3D microfabrication. Here, we report the fabrication of various 3D microstructures using graphene etch masks directly grown and patterned on a Si substrate. The patterned graphene deforms and wraps the etched structures, allowing for the fabrication of complicated 3D microstructures, such as mushroom-like and step-like microstructures. As a practical demonstration of the graphene etch mask, we fabricate an omniphobic surface of reentrant 3D structures on a Si substrate. Our work provides a method for fabricating complex 3D microstructures using a graphene etch mask, contributing to advancements in etching and fabrication processes.

An Ultra-Wideband Antenna with Triple Band-Notched Characteristics for Wearable Application

This work presents a compact UWB antenna with triple band-notched at WiMAX (3.2 GHz to 3.7 GHz), C-band (3.7 GHz to 4.2 GHz) and WLAN (5.15 GHz to 5.35 GHz) for wearable applications. The UWB antenna is fabricated on a semi-flexible thin FR-4 substrate. In order to reduce the complexity, only two slots are introduced on the radiating patch instead of three slots to reject each narrow band frequency. In this case, one slot rejects a combination of WiMAX and C-band and the other slot rejects the WLAN frequency band. The UWB antenna on the thin FR-4 material has an overall size of 21×16 mm2, which is very compact and thus, suitable for wearable applications without causing discomfort when worn on-body. Although the antenna is small in size, the performance is not compromised. The UWB antenna has the frequency range from 2.51 GHz to 12.09 GHz, maximum radiation efficiency of 100% and maximum gain of 4 dBi. Nevertheless, the antenna is able to reject the WiMAX and C-band as well as the WLAN band. The simulated specific absorption rate (SAR) results show that the antenna complies with the SAR limit Federal Communication Commission (FCC) and International Commission of Non-Ionizing Radiation Protections (ICNIRP) standards for 1 mW input power. Bending investigations performed on different diameters of Styrofoam cylinders shows that the frequency range and the notch bands are not very much affected.

Structural, morphological, and EMI shielding evaluations of Sm-Mn co-doped Sr-based M-type hexaferrite for Ku band applications

High-performance, thin, and lightweight EMI (Electromagnetic interference) materials with outstanding shielding effectiveness were explored over the last years to solve the problems in electronic devices. Magnetic absorbing materials have extensive bandwidth, good impedance matching, and excellent absorption features. In the present study, Sm-Mn Sr-doped M hexaferrites with Sr1-xSmxFe12-yMnyO19 whereas (x= 0.00, 0.025, 0.05, 0.075, y = 0.00, 0.25, 0.5, 0.75) were prepared by the chemical route. XRD, FESEM, HRTEM, FTIR, VSM, and VNA are used to evaluate the properties of the Sm-Mn doped Sr-based M-type hexagonal ferrite. The XRD (X-ray diffraction) results revealed the presence of a hexagonal phase in the prepared samples. Rietveld refinement also confirmed the phase purity for the Sm-Mn doped Sr-based M-type hexagonal ferrites. The FESEM (Field emission scanning electron microscopy) and HRTEM (High-resolution transmission electron microscopy) images revealed the hexagon-type shapes of the particles in the Sm-Mn doped Sr-based M-type hexagonal ferrites. The FTIR (Fourier transform infrared spectroscopy) spectra showed the 446–620 cm-1 lines, confirming the presence of the tetrahedral and octahedral phases of hexagonal ferrites. Dielectric and electromagnetic shielding effectiveness (SE) parameters are evaluated for Sm-Mn doped Sr-based M-type hexagonal ferrite. The electromagnetic parameters, such as complex refractive index, absorption and impedance, are also investigated for the Sm-Mn doped Sr-based hexagonal ferrite powder with x=0.075, y=0.75 having epoxy resin with 20 wt%, 30 wt% and 50 wt% samples, respectively. SE parameters are higher at more extensive filler loading. The green shielding index was found higher for Sm-Mn doped Sr-based hexagonal ferrite powder with x=0.075, y=0.75 having 20 wt% epoxy resin and decreased with filler loading. It is found the epoxy/Sm-Mn doped Sr-based M-type hexagonal ferrites-based composites are excellent absorbers in the Ku band. The investigated absorbers could be the best candidates for next-generation EMI green shielding absorbing devices and applications.

Effects of Polarizer-Analyzer Configurations for FTIR Spectroscopy: Implications for Multiple Polarization Algorithms.

Polarized Fourier transform infrared (p-FTIR) spectroscopy is a widely used technique for determining orientational information in thin organic materials. Conventionally, a single polarizer is placed in the path of the incident light (termed the polarizer). Occasionally, a second polarizer is also placed after the sample (referred to as the analyzer). However, this polarizer-analyzer configuration has the potential to induce polarization-dependent variances in the final spectra beyond those that are expected, i.e., the squared-cosine relationship of absorptance with respect to polarization angle is no longer accurate. These variances are due to changes in the polarization state of the transmitted light induced by the sample and have yet to be explored in the context of p-FTIR. Consequently, this study employs both theoretical and experimental approaches to identify the effects of including a second polarizer in p-FTIR analyses of anisotropic organic samples. For thin samples, the most significant spectral variance arising from only birefringence is observed on the shoulders of the dichroic peaks. By adopting a crossed polarizer configuration, it is shown that there is potential to identify anisotropy of samples that are generally considered too thick for p-FTIR analysis by exploiting this feature. Furthermore, the squared-cosine relationship of absorptance with respect to the polarization angle is also shown to be inapplicable when a second parallel-oriented polarizer is included. Accordingly, a function that accounts for the second polarizer is proposed for multiple polarization techniques.

Optimizing Ultrathin 2D Transistors for Monolithic 3D Integration: A Study on Directly Grown Nanocrystalline Interconnects and Buried Contacts.

The potential of monolithic 3D integration technology is largely dependent on the enhancement of interconnect characteristics which can lead to thinner stacks, better heat dissipation, and reduced signal delays. Carbon materials such as graphene, characterized by sp2 hybridized carbons, are promising candidates for future interconnects due to their exceptional electrical, thermal conductivity and resistance to electromigration. However, a significant challenge lies in achieving low contact resistance between extremely thin semiconductor channels and graphitic materials. To address this issue, an innovative wafer-scale synthesis approach is proposed that enables low contact resistance between dry-transferred 2D semiconductors and the as-grown nanocrystalline graphitic interconnects. A hybrid graphitic interconnect with metal doping reduces the sheet resistance by 84% compared to an equivalent thickness metal film. Furthermore, the introduction of a buried graphitic contact results in a contact resistance that is 17 times lower than that of bulk metal contacts (>40nm). Transistors with this optimal structure are used to successfully demonstrate a simple logic function. The thickness of active layer is maintained within sub-7nm range, encompassing both channels and contacts. The ultrathin transistor and interconnect stack developed here, characterized by a readily etchable interlayer and low parasitic resistance, leads to heterogeneous integration of future 3D integrated circuits (ICs).

Validation of the lead-in method in a practical shooting scenario.

The ability to determine bullet trajectories after a shooting incident can allow investigators to reconstruct the locations of individuals and the sequence of events that took place. By using trajectory rods, investigators can be provided with an immediate visual estimate as to what the path of the projectile may have been. In certain instances, the use of the probing method with trajectory rods is not appropriate due to their being a single, thin target material, or no secondary bullet impact site. In these cases, other methods such as the lead-in or the ellipse method may be useful. Overall, the lead-in method has not been well studied in the application to practical scenarios, such as those including bullet impacts on vehicle metal surfaces. This study has explored the accuracy of the lead-in method when a bullet impacts a typical vehicle metal surface using three firearm calibers, three blind participants, and two non-blind participants. The results of this study have shown that each caliber has its own characteristic error curve. In general, it was found that the lower the impact angle, the less errors were made by the participants. As the impact angle increases, the measurement errors increased, due to the smaller lead-in area present. The errors were found to have a wide range, with some being as low as 1° and some being as high as 13.9°. Further, it was found there was no significant effect on the errors of blind versus non-blind participants.

Research on the effect of water-cooling steel pipe on preventing spontaneous combustion of coal pile and its thermal migration behavior

During the storage and transportation process after mining, coal piles are placed in open environments, making them prone to self-heating and spontaneous combustion due to the nature of coal and factors like natural wind flow. In recent years, there have been frequent spontaneous combustion incidents involving coal piles, posing significant safety risks. To effectively prevent and control spontaneous combustion disasters in open-air coal storage piles, we propose a method involving the arrangement of water-cooling steel pipes within the coal piles. This method applies theories of coal spontaneous combustion mechanisms, porous media heat transfer, and non-isothermal pipeline heat transfer. The multi-physics coupling model of COMSOL numerical simulation software is used to analyze the spontaneous ignition process and prevention effect of open pit coal pile. In the model, the thin material transfer of porous media is taken as the oxygen concentration field, the heat transfer of porous media is taken as the temperature field, and the free and porous media flow is taken as the air seepage velocity field. The simulation results of the spontaneous combustion process in the coal pile indicate that the high-temperature zone of spontaneous combustion is situated within the range of 0.5 ~ 1.5 m inside the wind-facing surface and extends 0.5 m above the ground level. These findings serve as a basis for determining the optimal placement of water-cooling steel pipes within the coal pile. The simulation results of a single water-cooling steel pipe demonstrate a positive correlation between the cooling effect on the coal pile and the water cool flow, and a negative correlation with the water cool temperature. Additionally, the cooling radius of the water-cooling steel pipe is determined by the circumference of the pipe and remains unaffected by the water cool flow. Finally, simulations were conducted to evaluate the cooling effect of multiple rows of steel pipes, and optimal arrangement parameters were determined: a center distance between steel pipes of 1 m and a water cool flow rate of 1500 L/min. As a result, the onset of the self-heating period in the coal pile was delayed by 11 days, and the spontaneous combustion period was extended by 56 days. The arrangement of water-cooling steel pipes in the coal pile has demonstrated significant efficacy in preventing and controlling spontaneous combustion.

Ultra-low friction of flexoelectric bubble on atomically thin suspended h-BN

Strain and interface engineering has made significant progress in modulating the friction properties of atomically thin two-dimensional materials, especially in ultra-low friction. Here, it is demonstrated that ultra-low friction of atomically thin suspended h-BN is feasible on the bubble magnitude by the biased tip using atomic force microscopy (AFM). The degree of ultra-low friction decreases with the diameter of the bubbles. A prominent upward shift of the contact potential difference (CPD) was observed using SKPM in the atomically thin suspended bubbleless h-BN due to strain gradients, while the reverse downward shift of CPD on the atomically thin suspended h-BN bubble was figured out. The strain gradient induces a reverse flexoelectric voltage on both sides of the atomically thin suspended h-BN bubble. The Coulomb attraction between the bubble and the tip, along with the interlayer repulsion, collectively contribute to interlayer friction, ultimately leading to the achievement of superlubricity. Our work combines flexoelectricity with interlayer engineering to achieve a novel two-dimensional material superlubric structure.

Free-standing ultra-thin carbon nanofiber films with controllable thickness for lithium ion batteries

Thin and porous anode materials enable short ion migration distances and high-rate performance. However, the current freestanding anode materials are too thick (typically around 100 μm) for high-rate lithium ion batteries (LIBs). Here, we have developed a facile and scalable process to synthesize ultra-thin (<400 nm) freestanding films. In comparison to other chemical and physical deposition methods that yield thin films (<500 nm), our freestanding films do not require the substrate material, achieving a 100 % loading of active material. Our ultra-thin carbon nanofiber films exhibit an exceptional specific capacity of 599 mAh/g even after 10,000 cycles at a current density of 10 A/g. Compared to thick carbon nanofiber films, the utilization of ultra-thin carbon nanofiber films as anode materials exhibits a remarkable enhancement of more than tenfold in cycling performance

Atomistic origins of compound semiconductor synthesis with computational neuromorphic engineering

We propose the usage of multi-element bulk materials to mimic neural dynamics instead of atomically thin materials via the modeling of group II–IV compound semiconductor growth using vacancy defects and dopants by creating and annihilating one another like a complex artificial neural network, where each atom itself is the device in analogy to crossbar memory arrays, where each node is a device. We quantify the effects of atomistic variations in the electronic structure of an alloy semiconductor using a hybrid method composed of a semiempirical tight-binding method, density functional theory, Boltzmann transport theory, and a transfer-matrix method. We find that the artificial neural network resembles the neural transmission dynamics and, by proposing resistive switching in small areas with low energy consumption, we can increase the integration density similar to the human brain.