Composition Of Thin Layers Research Articles

Recent improvements in quantification of energy‐dispersive X‐ray spectra and maps in electron microscopy of semiconductors

AbstractThis tutorial‐style article describes recent improvements in the quantitative application of energy‐dispersive X‐ray spectroscopy and mapping in electron microscopes to semiconductors, with a focus on spatial resolution, sensitivity and accuracy obtainable in characterising the chemical composition of thin layers, quantum wells and quantum dots. Various approaches applicable in scanning electron microscopy of bulk and (scanning) transmission electron microscopy of thin film samples are outlined. Applications to semiconductor quantum well systems, mainly based on indium gallium arsenide and silicon germanium studied in the author's laboratory, are provided as examples.

Optimal design of thin-layered composites for type IV vessels: Finite element analysis enhanced by ANN

For a type IV hydrogen storage vessel, the complexity of the mechanical system is a result of the increased number of thin-layered composites and geometrical details at dome parts, which significantly prolongs the computation time for traditional numerical analysis and optimal design. In this work, a framework couples machine learning (ML) and finite element (FE) analysis is proposed for a 70 MPa type IV vessel. Providing an approach that allows the winding parameters optimization process to include the corresponded feasible dome geometry. High-fidelity FE models are established and different failure modes are included. The artificial neural network (ANN) is developed and coupled with the FE models, where the irregularity of directional material distribution on both cylindrical and dome regions is adequately considered during the optimization process. Winding parameters extended by practical production modifications such as transition areas and layer ending adjustments are introduced to the modified input layer of ANN, to ensure the integrality of the complex geometrical details. The computational cost is greatly reduced with satisfying accuracy compared to FE analysis, where the optimized lay-up scheme could be obtained with a prediction error of less than 2% on the damage state function. The associated simulation results show an obvious improvement in mechanical response under designed burst pressure. Particularly, the prototypical vessels are further produced to carry out comparative experiments, which indicate that the burst pressure of the type IV vessel has been improved from 145 MPa to 157.74 MPa. This is also consistent with the numerical prediction of burst pressure using Hashin failure criteria and progressive damage analysis.

Automation of a Thin-Layer Load-Bearing Structure Design on the Example of High Altitude Long Endurance Unmanned Aerial Vehicle (HALE UAV)

In the aerospace industry, thin-layer composites are increasingly used for load-bearing structures. When designing such composite structures, particular attention must be paid to the development of an appropriate geometric form of the structure to increase the structure’s load capacity and reduce the possibility of a loss of stability and harmful aeroelastic phenomena. For this reason, the use of knowledge-based engineering support methods is complicated. Software was developed to propose and quickly evaluate a thin-layer load-bearing structure using generative modeling methods to facilitate development of the initial concept of an aerospace load-bearing structure. Finite Element Method (FEM) analysis verifies and improves such structures. The most important contributions of the paper are a methodology for automating the design of ultralight and highly flexible aircraft structures with the use of generative modelling, proposing and verifying the form of generative models for selected fragments of the structure, especially wings, and integration of the use of generative models for iterative improvement of structures using low- and middle-fidelity methods of numerical verification.

Modeling and Simulation of Thin Layered Composites Under Non-mechanical Stimuli

This study presents a nonlinear deformation analysis of a thin composite plate undergoing shape reconfigurations triggered by electric field inputs. The composite plate consists of electro-active and inactive (substrate) layers. Prescribing electric field inputs to the electro-active layer induces large curvatures in the composites, while the in-plane stretch is relatively small. This has a consequence that only shapes with zero (or nearly zero) Gaussian curvature can be attained by prescribing the electric field, which leads to snap-through shape reconfigurations in order to achieve developable surfaces. When the substrate is made of an elastic layer, the shape returns to its original planar configuration upon removal of the electric field. In order to fully or partially retain the reconfigured shape upon removing the electric field input, a substrate layer made of a shape memory polymer is considered. Shape reconfigurations and retentions of the composites having elastic substrate and shape memory substrate are simulated.

Preparations of Silver/Montmorillonite Biocomposite Multilayers and Their Antifungal Activity

In this study, the results about the influence of the surface morphology of layers based on montmorillonite (MMT) and silver (Ag) on antimicrobial properties are reported. The coating depositions were performed in the plasma of a radio frequency (RF) magnetron sputtering discharge. The studied layers were single montmorillonite layers (MMT) and silver/montmorillonite multilayers (MMT-Ag) obtained by magnetron sputtering technique with a different surface thickness. The resultant MMT-Ag biocomposite multilayers exhibited a uniform distribution of constituent elements and enhanced antimicrobial properties against fungal biofilm development. Glow-discharge optical emission spectroscopy (GDOES) analysis revealed the formation of MMT-Ag biocomposite multilayers following the deposit of a silver layer for an MMT layer that was initially deposited on a Si substrate. The surface morphology and thickness evaluation of deposited biocomposite layers were performed by scanning electron microscopy (SEM). A qualitative analysis of the chemical composition of thin layers was performed and the elements O, Ag, Mg, Fe, Al, and Si were identified in the MMT-Ag biocomposite multilayers. The in vitro antifungal assay proved that the inhibitory effect against the growth of Candida albicans ATCC 101231 CFU was more emphasized in the case of MMT-Ag biocomposite multilayers that in the case of the MMT layer. Cytotoxicity studies performed on HeLa cells showed that the tested layers did not show significant toxicity at the time intervals during which the assay was performed. On the other hand, it was observed that the MMT layers exhibited slightly higher biocompatible properties than the MMT-Ag composite layers.

Composite films of single-walled carbon nanotubes with strong oxidized graphene: Characterization with spectroscopy, microscopy, conductivity measurements (5–291 K) and computer modeling

The hybridization of 1D carbon nanotubes and 2D graphene family is able to form 3D nanostructures with significantly improved electrical, mechanical and thermal properties, which make them very useful for huge potential applications. In this work the graphene oxide-single walled carbon nanotube (GO-SWNT) hybrids prepared in aqueous suspension and films obtained by vacuum filtration are studied with UV–IR absorption spectroscopy, scanning electron microscopy (SEM) and computer simulation. Low-temperature measurements of conductivity of these films in the temperature range 5–291 K were also performed. For hybrid preparation SWNTs with prevailing content of semiconducting nanotubes (up to 95%) and graphene oxide with small C:O ratio (about 1.3) were selected. SEM analysis of a cutoff of the composite GO-SWNT film showed that the film is formed by composition of thin layers which are preferably located along the surface of the film with laminar, rather dense package. We have found spectroscopic manifestation of the interaction between GO and SWNT in the hybrid, estimated the interaction energy between components, revealed the conductivity in the composite film although in the GO film we have not observed a noticeable conductivity. It was also demonstrated that the behavior of the temperature dependence of the conductivity in the film of pure SWNTs and in the composite one is different. The decrease in the conductivity with lowering of temperature indicates that this dependence is similar with the conductivity observed in semiconducting systems.

Thin-layer nanocrystalline composite coatings: Production, structure, and properties

To obtain a nanocrystalline structural state of materials based on aluminum and titanium, high degrees of deformation are employed: rolling with considerable reduction; and shear under high pressure (5 GPa). The nanocrystalline materials obtained are used to create thin-layer composites, with nanocrystalline silicon between the uniform layers. Measurements show that the microhardness of the composites after the application of high pressure is 2.5 (for Al–Si) and 6 (for Ti–Si) times that of the initial material, while optimal practical properties are retained. The nanocrystalline composites obtained may be recommended for ultrahard thin-layer coatings on narrow or stressed local sections of components and for local corrosion protection.

NANOCRYSTALLINE THIN-LAYER COMPOSITE COATINGS: PRODUCTION, STRUCTURE AND PROPERTIES

The authors have used high degree of deformation (rolling on the great degree of deformation and the shift under high (5 GPa) pressure) to receive nanocrystalline structural state of the materials based on aluminum and titanium. The received materials in the nanocrystalline state have been used to create thin-layer composites with the introduction of nanocrystalline silicon among homogeneous layers. The measure of microhardness has shown that the microhardness of the composites after pressing under high pressure is in 2.5 times (Al – Si) and in 6 times (Ti – Si) more than the microhardness of the materials in the initial state. The study of the composite structure has showed (according to the received fracture pictures) that the composites are plastic. The increase of composites microhardness is observed at the preservation of an optimal level of the practical properties. The obtained nanocrystalline composites can be recommended as thin-layer very hard coatings on narrow or tensed areas of billets, as well as for the corrosion protection of local sites of the items.

PIXE (particle induced X-ray emission): A non-destructive analysis method adapted to the thin decorative coatings of antique ceramics

Recent trends in study of Greek and Roman potteries have been to develop non-abrasive methods to determine the elemental composition of their thin coatings. This paper investigates the potential of PIXE (particle induced X-ray emission) in this field. This technique has been currently used to determine the bulk elemental composition of several types of artifacts because of its fast and simultaneous ability to measure a large number of elements with good accuracy and without any damage to the sample. However, until now it has never been applied to the measurement of the composition of thin layers owing to the difficulty in limiting the depth of analysis to the layer thickness. In this paper, we show, through a comparative study of reference clay pellets and thin coatings of Terra Sigillata ceramics that reducing the energy of the particle beam the problem can be solved. The decrease of proton energy from 3MeV (standard condition) to 1.5MeV allowed us to limit the analyzed depth to the coating thickness without significant alteration of the results. Quantitative elemental analysis remains possible and the quality of results is similar to the one obtained from electron microprobe.

Thin layer composition profiling with angular resolved x-ray photoemission spectroscopy: Factors affecting quantitative results

Composition profiling of thin films in the nanometer range is critical to the development of future electronic devices. However, the number of techniques with such depth resolution is limited. Among them, angle-resolved x-ray photoelectron spectroscopy (ARXPS) can be used for thin layers up to a few nanometers, but it is not yet a fully established method. In order to evaluate its capabilities for use as a routine and general method, the authors evaluate both its intrinsic capabilities in comparison with other methods and the factors affecting quantification by analyzing its variability when applied at various laboratory locations with different tools and data treatments. For this purpose, dedicated samples based on multilayers of HfO2 and SiON were produced with a well-determined layer structure. The results show that ARXPS, including depth profiling reconstruction, is very efficient and compares favorably with nuclear analysis techniques. It allows the separation of the surface contamination signal from the interfacial layer signal and allows determination of the coverage quantitatively. An accuracy of ±10% is achieved for most elements except for nitrogen, where strong peak interference with hafnium and a low intensity increase the inaccuracy up to 20%. This study also highlights several technique limitations. First, the quality of the retrieved profile is strongly dependent upon the exact determination of each photoemission peak intensity. Also it demonstrates that, while favorable for chemical identification, very high resolution spectra may lead to larger errors in profile reconstruction due to larger statistical errors in the intensities, though this is true mainly for deeper layers. Finally, it points out the importance of the physical parameters used in the final obtained results.

Study on the axial compression buckling behaviors of concentric multi-walled cylindrical shells filled with soft materials

Via the energy-based analytical and numerical methods, this paper studies the pre- and post-buckling compression behaviors of concentric multi-walled cylindrical shells filled with low-shear-modulus (or fluid like) materials, which are widely observed in biological composites. It is found that if the bulk modulus of the filled materials is on the same order of (or larger than) the Young's modulus of the shell, the axial compression resistance in the post-buckling stage can be significantly improved. In specific, the tangent stiffness increases quickly with the increase of the compression strain, and finally may become compatible with that for a non-buckled hollow shell. Moreover, it is interesting to note that the compression resistance after buckling is approximately in proportion to the net shell-wall area, and independent of the thickness or the number of shell-walls. These investigations may quantitatively reveal a mechanism adopted by the nature: rolling the flat thin-layered composites into a filled concentric multi-walled cylindrical shell to achieve better compression resistance. The biological concentric shell can also be viewed as a double-leveled hierarchical structure, which is capable to sustain more complex loadings than the bottom leveled structure.

Cathodic doping of thin-layered composites. Formed by electroactive polymers and rubbed single-walled carbon nanotubes

A simple method of electrostatic rubbing is developed for the application of single-walled carbon nanotubes (SWNT) to solid substrates. The method is applicable both to conducting materials (for example, glassy carbon) and insulators (for example, Teflon). The surface development of the obtained coatings is comparable to the bodies of multi-walled carbon nanotubes, which are grown on the TiN substrates. The possibility of cathodic doping of electron-conducting polybithiophene polymer and poly-o-phenylenediamine redox polymer on the substrates with SWNT is shown. The presence of nanotubes accelerates anodic synthesis of test polymers and improves the reversibility of their cathodic doping, the electrode surface development being the main factor.

Analysis for the interlaminar stresses of thin layered composites subjected to thermal loads

Accurate stress analysis of layered material systems that are sometimes very thin is of great importance in the assessment of their structural integrity and performance. To give satisfactory results, the discretised meshes of the conventional domain solution techniques, such as the finite element method, must have reasonable aspect ratios in the same order of magnitude. Therefore, the domain modeling of ultra-thin structures, such as the facings of sandwich composites and adhesive layers, shall require an enormous amount of discretised meshes that may incur overloading computations. Using the boundary element method as an alternative, the present work proposes an effective approach to analyze the interlaminar stresses of thin layered composites subjected to general thermal loads. The transformed boundary integral equation for anisotropic thermoelasticity is fully regularized using the technique of integration by parts and analytical integration. At the end, the veracity and applicability of the proposed scheme are demonstrated by numerical examples.

Electrochemical properties of thin-layered composites formed by carbon nanotubes and polybithiophene

Redox behavior of thin films of polybithiophene deposited on substrates of conducting glass and single- or multi-walled carbon nanotubes is studied at positive potentials in a 0.1 M (C4H9)4NBF4 solution in acetonitrile. The polymer’s formal doping-undoping potentials are nearly the same for all substrates, which points to the absence of any marked donor-acceptor interaction between nanotubes and polybithiophene. Some polybithiophene electrochemical characteristics (reversibility, doping degree) are improved when deposited onto nanotubes, probably due to the developed surface of the electrode based on carbon nanotubes.

Mechanical and microstructural characterization of calcium aluminosilicate (CAS) and SiO 2/CAS composites deformed at high temperature and high pressure

We performed axial compression experiments on polycrystalline calcium aluminosilicate (CAS or anorthite) and on particulate and layered composites with equal volume fractions of CAS and SiO 2 (quartz) at a confining pressure of 300 MPa, temperatures of 1173–1473 K, and strain rates of 10 −5 to 10 −4 s −1. The dense samples were fabricated from quartz crystalline and CAS glass powders by hot isostatic pressing (HIP). Under the experimental conditions, triclinic CAS, regardless in monolithic aggregates or composites, deforms by dislocation creep as indicated by TEM microstructures, intensive grain boundary migration recrystallization and strong crystallographic preferred orientation (CPO). Dislocation creep of CAS is characterized by dominant glide on a single slip system (0 1 0)[1 0 0] while mechanical twinning, anisotropic growth and recrystallization play an role to relieve the strain incompatibilities which would otherwise result from such limited slip systems. Particulate and particularly layered composites are significantly stronger than monolithic CAS aggregates, indicating that quartz is an effective reinforcement to the CAS matrix even when the material is used at high temperature and high pressure. Under layer-normal compression, the flow strength of layered composites increases remarkably with decreasing the thickness of the layers, and the thin-layered composites are significantly stronger than particulate counterparts with the same composition. The observed layering-induced stiffening is due to constraint effects of rigid quartz on plastic flow of CAS.

Selective etching of chalcogenides and its application for fabrication of diffractive optical elements

Bulk samples of As and Ge based chalcogenides were synthesized from high purity elements, and thin layers (thickness d≈100–5000 nm) were deposited by vacuum thermal evaporation and/or spin coating. Photoinduced structural changes were studied by Raman and IR spectroscopy. The kinetics of dissolution of thin layers in aqueous and non-aqueous alkaline solvents were studied. Both, positive and negative selective etching behaviours were found and used for production of diffractive optical elements (DOEs). Exposure with a halogen lamp through a Cr mask, classical holographical exposure using an Ar+ laser, and direct writing laser lithography using a He–Cd laser were used to produce amplitude/phase DOEs with feature sizes of 0.37–4 μm. Prepared low efficiency and low lifetime amplitude/phase type DOEs were transformed into corrugated relief type phase DOEs by subsequent selective etching. Positive and/or negative copies of the pattern were obtained depending on the thin layer composition, its prehistory and the applied etching bath. The profiles of the structures produced by etching were subsequently investigated using AFM and REM techniques and basic performance parameters of formed DOE were measured and compared with theoretically calculated values.

Characterization of advanced piezoelectric materials in the wide temperature range

We report about methods and results of our measurements of piezoelectric, dielectric and elastic properties of piezoelectric materials like crystals, ceramics, composites, polymers and thin layer composites. Among the methods, used in our laboratories are: the resonance method working in the temperature range 208–358 K, hydrostatic methods, both static and dynamic in the range 273–333 K, laser interferometric methods, using single and double-beam interferometer, working at room temperature, single and double-beam micro-interferometers, working inside of optical cryostat in the range 150–330 K, and pulse echo method for measurements of elastic coefficients, using ultrasonic set, working at room temperature. In our earlier papers we reported about some of our results of piezoelectric measurements of PZT ceramics using resonance method and laser interferometric method. The results of both methods were in good agreement. Now, the measurements are realized on 0–3 ceramic–polymer composites and thin layer composites. It is well known, that both intrinsic (material) and extrinsic (domain structure) contributions to properties of ferroelectric samples have characteristic, sometimes rather strong, temperature dependence. Therefore, any extension of temperature range of the above mentioned methods is welcomed.

ZrO2/ZrO2 Layered Composites for Crack Bifurcation

Laminates containing a thin layer (5 to 200 µm thick) sandwiched between two thick layers (2 mm thick) were fabricated by sequential slip casting in order to study crack bifurcation. The thin layer was formed with a mixture of a pure ZrO2 powder (MZ) and a Zr(Y)O2 powder containing 3 mol% Y2O3 (TZ). The thick layers were formed with TZ powder containing 0.05 volume fraction of Al2O3 powder to distinguish the interfaces between the different layers in the scanning electron microscope. Dilatometry data for monolithic specimens formed with the mixed MZ and TZ powders (0.30 to 1.00 volume fraction MZ) showed that the monoclinic‐to‐tetragonal transformation temperature and strain varied with the MZ content, suggesting the yttria in the TZ powder diffused into the MZ powder during processing at 1500°C/2 h. These data also showed that large compressive stresses developed in the thin layer due to the transformation. Conditions (thin layer composition and thickness) for observing edge cracks produced along the center line of the thin layer and for observing crack bifurcation during flexural failure were determined. Delamination occurred during cooling for layers fabricated with greaterthan equal to0.40 volume fraction of the MZ powder when the thin layers were 200 µm thick. Edge cracking, which occurred during cooling, and crack bifurcation, which occurred during flexural loading, occurred for thin layer compositions containing greaterthan equal to0.40 volume fraction MZ powder, when the thickness of the thin layer was between similar/congruent50 and 150 µm. Crack bifurcation was not observed in thinner layers. With decreasing layer thickness, thin layers fabricated with >0.60 volume fraction of the MZ powder contained multiple microcracks, parallel to the center line, on the surface, instead of a single edge crack. The flexural strength of all specimens depended on the strength of the thicker Zr(Y)O2 layers, regardless of whether bifurcation occurred.

Fatigue crack growth in a Ni–Sn multilayered composite

Fatigue crack growth behavior in a Ni–Sn metallic multilayer composite is investigated using the three-point bend fatigue test because of very limited literature on the fatigue behavior of thin layered composites. The multilayer composites are sandwiched between two thick layers of the monolithic nickel by electroplating in order to fabricate bar-shaped samples suitable for fatigue tests. The bar-shaped sample is notched on one side in the nickel phase, and the primary fatigue crack is propagated towards the multilayers in the normal direction. It is observed for the first time that the primary fatigue crack propagation is effectively arrested when the crack reached the first Sn layer of the Ni–Sn composite. Consequently, the composite exhibited a remarkable fatigue damage tolerance. This unusual phenomenon is caused by the extensive intergranular cracking within the Sn layers after fatigue while the Ni layers remained intact. Consequently, the primary crack is branched by these intergranular cracks in Sn layers which reduced the stress intensity factor at its tip. Thus, the Sn layers acted as a barrier to the primary fatigue crack growth. It is also shown that the intergranular fatigue cracking is an intrinsic behavior of the pure Sn phase.

Inelastic deformation of polyimide-copper thin films

Thin-layered composites of polyimide-copper are tested in tension. The specimens are prepared using standard thin film preparation techniques. The stress relaxation behaviour of the two phases is measured and modelled in terms of a single activated rate process. The internal stress in the polyimide is measured and increases with tensile strain. The deformed samples are examined with laser-scanning confocal microscopy and standard optical microscopy. Microcracks in copper and shear bands in polyimide are observed and correlated qualitatively with the stress relaxation model.