Silicon Bond Research Articles

Achieving Superior Durability of Environmental Barrier Coatings through the Use of a Modified Silicon Bond Coat

Achieving Superior Durability of Environmental Barrier Coatings through the Use of a Modified Silicon Bond Coat

Density of electronic states in silicon nanocrystals embedded in a SiO2 matrix and passivated by hydrogen

Subject of study. This study is devoted to the optical transitions and density of electron and hole states in silicon nanocrystals embedded in a SiO2 dielectric matrix and silicon nanocrystals passivated by hydrogen. Aim of study. The aim is to calculate the probability of optical transitions, density of electron and hole states, and absorption cross-section in silicon nanocrystals surrounded by different environments. Another goal is to adapt the tight-binding method for correct passivation of dangling bonds of silicon. Method. The calculations are performed using the variant of the tight-binding method that accounts for a large number of orbitals: s, p, d, and s∗. Main results. The local density of states of electrons and holes, probabilities of optical transitions, and absorption cross-sections of silicon nanocrystals passivated by hydrogen and nanocrystals embedded in a SiO2 matrix were calculated. It is shown that the electron and hole states in hydrogen-passivated silicon nanocrystals are localized within the crystal, and optical transitions occur at wavelengths in the range of 440–620 nm. The presence of the SiO2 matrix surrounding the nanocrystal increases the probability of optical transitions and leads to the appearance of the local density of states outside the nanocrystal, with radiative emission in the wavelength range of 410–620 nm. Practical significance. The results highlight the feasibility of utilizing silicon nanocrystals in photonics and photovoltaics. They are expected to contribute to the development of technology for creating silicon nanocrystals with specific optical properties.

Time-dependent design of hyperelastic bonded joints in structural glass

For glass constructions with a high degree of transparency, facade systems with structural sealant glazing are increasingly being used. However, the use of bonded joints is also suitable for many other applications in glass construction. Even today, the design of bonded joints is still based on the outdated global safety concept according to ETAG 002. Although the safety and predictability of hyperelastic silicone bonds have been continuously shown by research activities during recent years, high levels of safety are still required in the design, which is mainly due to the expected degradation of the adhesive. From a design perspective, it is necessary to consider the time dependency. On the one hand, the bonded joint must be able to withstand variable loads of different strain rates at any time during its service life, taking degradation into account. On the other hand, if the bonded joint is also under a permanent load due to dead load of the glazing, it must also be ensured that the failure time would only be attained at the end of the component's service life. This article presents a fully probabilistic method that considers the degradation of the adhesive as well as various statistical influencing quantities (such as wind effects, manufacturing tolerances or material scattering) and determines a modification coefficient kmod\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${k}_{mod}$$\\end{document} for silicone adhesives under variable loads by calibrating to specified reliability indices. In addition, partial safety factors are determined in accordance with Eurocode 0, which are investigated as part of a sensitivity analysis.

Environmental barrier coatings on SiC without a silicon bond coating: oxidation resistance, failure modes, and future improvements

Environmental barrier coatings on SiC without a silicon bond coating: oxidation resistance, failure modes, and future improvements

Layer-by-layer structured nanocomposite deposits from plasma-synthesized organosilicon nanoparticles and organosilicon nanoparticles decorated with Ag nanoparticles by taking advantage of cyclic nanoparticle formation in Ar/HMDSO reactive plasmas

Rational engineering of thin nanocomposite layers, deposited in reactive plasmas, requires knowledge on the plasma behavior in order to produce multifunctional deposits with tailored properties (structural, optical, electrical, etc.) This work presents an experimental study of nanoparticles synthesized in the plasma gas-phase and their subsequent use as building-blocks to form layer-by-layer nanostructures. The experiment is performed in a plasma process that successfully combines plasma polymerization of an organosilicon molecular precursor (hexamethyldisiloxane, HMDSO) and sputtering of a metallic (silver) target. Pulsed injection of the precursor is found to promote cyclic nanoparticle formation in Ar/HMDSO reactive plasmas. The plasma electron temperature is found to vary in the range 1.6—2.2 eV as derived from time-resolved optical emission spectroscopy of the plasma energetic conditions. This diagnostic method is also shown to provide a reliable tool for online monitoring of the nanoparticle synthesis process. Two types of layer-by-layer structured nanocomposites can be obtained depending on the type of nanoparticles synthesized: (i) organosilicon nanoparticles of size less than 100 nm in all studied plasma conditions for a large quantity of injected HMDSO and (ii) raspberry-like nanoparticles of size less than 150 nm when the quantity of injected HMDSO is reduced. The organosilicon nanoparticle growth follows a polydimethylsiloxane (PDMS)-like oligomerization scheme in which the R2-Si(-O)2 silicon bond tends towards the formation of polymeric structure in a R3-Si(-O)1 silicon chemical environment, containing Si-(CH2)-Si type bridges that are involved in cross-linking. The elemental composition of the raspberry-like nanoparticles is similar to that of the organosilicon nanoparticles, supplemented by the Ag component. The decorating silver nanoparticles are ∼15 nm of size, round in shape and polycrystalline. There is no evidence for silver oxides in the nanostructures. The Si-O-Ag bridges, revealed by infrared spectroscopy, suggest the presence of junction sites between the metallic and the organosilicon parts of the raspberry-like nanoparticles. The silver nanoparticles are found to decorate the organosilicon nanoparticles to form the raspberry-like nanoparticles in the plasma gas-phase, before being deposited. This reveals a very interesting phenomenon of simultaneous growth of the silver- and organosilicon-parts in the plasma without mixing during the nucleation phase.

Design aspects of a CMC coating-like system for hot surfaces of aero engine components

Ceramic Matrix Composite (CMC) is an emerging material system that can be a game changer in the aerospace industry, both civil and military. CMCs components are, in fact, lighter and less prone to fatigue failure in a high temperature environment. However, at high temperatures, the diffusion of oxygen and water vapour inside the CMC can have detrimental effects. Therefore, the presence of protective coating is necessary to extend the life of CMC components. In the present work, a three-layers coating, consisting of a silicon bond (BND), adhesively bonded to the CMC, an Environment Barrier Coating (EBC) and a softer layer 3 (LAY3), is investigated for a CMC component. An aero-engine high pressure turbine seal segment was considered. Two design aspects are covered: (i) creep law is determined and calibrated in environment Abaqus from the experimental data of each coating layer available in the open literature, to provide a suitable instrument for the creep relaxation analyses of hot components; (ii) thickness sensitivity study of each layer of the coating is conducted to minimise the interface stresses of coating with substrate in order to mitigate cracking and removal/spalling phenomena when exposed to temperature gradients and to increase their service life. These two different aspects are combined together to predict the coating stress field as a function of service time.

Surface roughness of pigmented and non-pigmented maxillofacial silicone elastomer before and after artificial aging

Maxillofacial prostheses are frequently made from silicone elastomer. The silicone material’s rough surface can lead to the accumulation of microorganisms, irritation of the surrounding soft tissue, and the progression of some microsites into mechanical failure and color deterioration. This in vitro study aimed to compare the surface roughness of M511 heat-vulcanized maxillofacial silicone before and after artificial aging. Eighty disk-shaped specimens were prepared and divided equally among five experimental groups based on pigmentation, with 16 samples in each group. The colorless specimens were prepared without adding any pigment. The four study groups were prepared using distinct pigments (red, blue, yellow, and their mixture). Half of the specimens in each group were tested before aging, while the other half was tested after 750 h of artificial aging. Surface roughness was measured using atomic force microscopy (AFM), and the silicone bonds and pigments were observed using Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR). Data were compared between groups using a two-way analysis of variance, independent sample t-test, and Tukey’s post hoc test, considering a p < 0.05 statistically significant. FTIR-ATR showed no differences between the pre-and post-aging groups, with similar peaks observed. The surface roughness significantly increased in the colorless, blue, and mixed pigment groups (p < 0.001), surface roughness increased by 155.66%, 14.83%, and 96.12% respectively for colorless, blue pigment, and the mixture of pigments after 750 h of artificial aging. In contrast, the surface roughness significantly decreased in the yellow pigment (90.98%) and red pigment (5.7%) (p ≤ 0.001) after aging. The yellow pigment showed the smoothest surface after aging, while colorless specimens showed the roughest surface. Two-way ANOVA showed that pigment type and aging time significantly affected surface roughness. Therefore, induced aging considerably impacted the surface topography of maxillofacial silicone. The pigment type and distribution in the silicone matrix affected its surface roughness. The AFM analysis is a simple and straightforward method for assessing surface roughness at the nanometer level.

TGO Growth Behavior in Environmental Barrier Coatings with Modified Silicon Bond Coat

TGO Growth Behavior in Environmental Barrier Coatings with Modified Silicon Bond Coat

Steam oxidation performance of Yb2Si2O7 environmental barrier coatings exposed to CMAS

Environmental barrier coatings (EBCs) are necessary for use of SiC/SiC ceramic matrix composites (CMCs) in gas turbine engines. Due to the complex operational environments, it is increasingly important to understand the interplay of damage modes to project the durability of the EBC/CMC system. Two life-limiting failure mechanisms of EBCs are steam oxidation and molten calcium-magnesium-aluminosilicate (CMAS) attack. Steam oxidation results in the formation of a thermally grown oxide (TGO) that acts as a weak interface and CMAS/EBC interactions cause thermomechanical and thermochemical changes that compromise coating integrity. EBCs consisting of a Yb2Si2O7 topcoat and a silicon bond coat were subjected to low (2 mg/cm2) loadings of two CMAS compositions prior to steam oxidation at 1316 °C for up to 300 h. Exposure to CMAS reduced the TGO thickness and the low CaO content glass resulted in the thinnest oxide scales. However, glass exposure had mechanical consequences that caused premature coating delamination.

Si-containing interlayer using tetramethylsilene for diamondlike carbon film adhesion on low-alloy steel: The role of the interlayer deposition time

Diamondlike carbon (DLC) coatings provide interesting properties for industrial applications. However, the low adhesion of DLC coatings on any type of ferrous alloy compromises technological applications. One possible solution to this issue is the application of adhesion interlayers. The aim of this study is to investigate the adhesion of DLC films on low-alloy steel through the use of silicon-containing interlayers at different deposition times using tetramethylsilane. The role of time on the physical-chemical, microstructural, and tribological properties of the material system was evaluated. The interlayer thickness linearly increased and greater contributions of silicon bonds were measured as a function of the interlayer deposition time. Nevertheless, longer deposition times increased the roughness and defect ratio in DLC coatings. Although good enough adhesion for decorative applications was acquired, no drastic variation in the average critical load (∼4.2 N) for delamination was observed at different deposition times for the samples that achieved adhesion.

Investigations of the formation of nanosized objects in manganese implanted silicon single crystals by the methods of Raman scattering of light and atomic force microscopy

This article presents the results of experimental studies on the formation of nanosized objects in single crystals of silicon ion-implanted with manganese ions with an energy of 40 keV at various doses. The formation of nanosized objects was determined by atomic force microscopy (AFM) and Raman spectroscopy (RS). It was found that in the Raman spectrum of non-implanted samples there are peaks with a wave number of 520 cm-1 characteristic of pure silicon associated with the crystalline phase and satellites with frequencies 301 cm-1, and 971 cm-1. The band with a wave number of 971 cm-1 corresponds to the main band of the tetrahedral bond in silicon. The intensity of this peak depends on the sample thickness. When the sample thickness changes from 200 μm to 3 mm, the intensity of this peak decreases by almost two times. And in the Raman spectra of ion-implanted samples, several bands with different intensities are observed, and their number and intensity strongly depend on the implantation dose. It has been suggested that the observed peaks are possibly associated with radiation defects and nanosized formations. This assumption was verified using AFM investigation. The AFM images show various nanosized objects, apparently associated with manganese ions.

A Cyclic Phosphonium Ion with an Asymmetrically Substituted Selenide‐Stabilized Silicon Center: Synthesis, Structure, and Substituent Effects

AbstractA new heterocyclic four‐membered CPSeSi cation was synthesized in its racemic form by B(C6F5)3‐mediated ring‐closing reaction starting from the hydrosilane precursor. The cation has an asymmetrically substituted silicon center, which is stabilized by a selenium–silicon bond. The phosphonium hydroborate and its precursor were characterized by single‐crystal X‐ray diffraction analysis and NMR spectroscopy. 77Se, 31P, and 29Si NMR spectroscopic parameters proved to be sensitive probes for determining small electronic changes around the silylium‐type center. Density functional theory (DFT) calculations of the ring‐opening energy of the selenium‐based cation gave insight into the stability of the Se–Si bond and revealed a stronger intramolecular stabilization of the silicon atom compared to a coordinating phosphane sulfide function. For the first time, the influence of a C6F5 group at the silicon atom of these type of cations was also investigated, showing a slightly increased stabilization of the Se–Si linkage in the cyclic selenium‐based cation.

Isotope Effect in Electrical Characteristics of Polysilicon Based-Photodetector

The electrical conduction of polysilicon can be improved through the passivation of defects located at grain boundaries. Most passivation proceeds by hydrogen bonding to dangling bonds of silicon. However, more research is needed on the reliability of the Si-H bond. A process using deuterium instead of hydrogen can be expected to improve the performance of silicon devices because Si-D bonds have much higher stability than Si-H bonds. In this study, we have investigated how the isotope effect appears in polysilicon applications. For this purpose, a photodetector composed of a polysilicon film incorporated with hydrogen or deuterium was prepared, and then, current–voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}\text{)}$</tex-math> </inline-formula> characteristics, photo response, and degradation thereof were investigated. Hydrogen and deuterium incorporation was performed by both furnace annealing and ion implantation methods. It was found that in order for the isotope effect to occur in polysilicon grain structure, the density of grain boundary must be maintained properly, and there must be no additional damage during the hydrogen or deuterium process. Through this study, it was confirmed that the electrical characteristics and the reliability of the polysilicon based-photodetector were improved by forming a Si-D bond inside the polysilicon with the furnace annealing.

Preparation of a Cation Exchange Membrane by a Sol-Gel Method-Based Polyvinyl Alcohol to Improve Alkali Recovery via Diffusion Dialysis in the Textile Industry

In this work, a novel silane coupled cationic precursor (SAGS) was synthesized by 3-glycidyloxypropyltrimethoxysilane and sodium 2-((2-aminorthyl)amino) ethanesulfonate. A series of cation exchange membranes were prepared with poly(vinyl alcohol) (PVA) and SAGS by a sol-gel-based process. The structure of the prepared membranes were characterized by Fourier transform infrared spectrum (FTIR) and scanning electron microscopy (SEM), and its properties were studied by water uptake (WR), cation exchange capacity (CEC), linear expansion ratio (LER), alkali stability, thermogravimetric analysis (TGA), mechanical properties, and diffusion dialysis performance. FTIR and X-ray photoelectron spectroscopy (XPS) confirmed the successful preparation of SAGS membranes, and SEM images showed that the prepared membranes were dense and uniform. The WR values of the SAGS membranes were in the range of 91.49–122.39%, and the LER values were 17.65–28.21%. In addition, the SAGS membranes had suitable CEC value, good alkali resistance, and thermal stability which ensured the application of membranes in the field of diffusion dialysis (DD) for alkali recovery. In the DD test, the dialysis coefficients of NaOH (UOH) ranged from 0.012 mm/h to 0.023 mm/h, and the separation factors (S) was in the range of 30.77–16.43. In conclusion, the prepared CEM containing silicon oxygen bonds by PVA and SAGS reaction has the advantages of low price, friendly environment, good alkali resistance, simple preparation process, and great application potential in the textile manufacturing wastewater recovery.

Approach for the simulation of the load-deformation behaviour of hyperelastic bonded joints using strain and strain rate dependent tangent moduli

In structural glass, Structural Sealant Glazing (SSG) systems are often used to realise facades with maximum transparency. The used silicone adhesives are currently designed in accordance to the European Technical Approval Guideline 002 (ETAG 002) by a simplified two-dimensional stress calculation concept. For a more precise calculation of the adhesive stresses and deformations, finite element analyses are used. The quality of the results, however, strongly depends on the calculation concept and material model used. In this paper, a practice-oriented viscoelastic approach using strain and strain rate dependent tangent moduli within FEA is presented. Required material parameters can be determined with a simple uniaxial tension test only. The proposed model is validated with numerous FE calculations of reality-based adhesively bonded component tests with different geometric ratios that include complex multiaxial stress states. The proposed approach allows a precise prediction of the strain state- and time-dependent stress behaviour of hyperelastic silicone bonds. The prediction quality is significantly more accurate than often used linear-elastic material models or commonly available hyperelastic models.

Hybrid chemical-physical vapor deposition of highly durable environmental barrier coatings

Environmental barrier coatings (EBCs) are needed to protect SiC based ceramic matrix composites (CMCs) from steam attack in next generation aircraft engines. In this study, EBCs consisting of a dense Yb2Si2O7 top coat and a columnar structure silicon bond coat were deposited using a hybrid chemical-physical vapor deposition process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the coating phase composition and microstructure. The as-deposited Yb-Si-O coating is highly amorphous, and it transformed to crystalline Yb2Si2O7 and Yb2SiO5 phases after 1300 °C heat treatment in air. The durability of Yb2Si2O7/Si EBC was evaluated in a steam cycling test in flowing 90% H2O (g) + 10% air at 1316 °C, and the EBC survived 1000 1-h steam cycles without failure, which demonstrated the excellent durability of the hybrid vapor deposited Yb2Si2O7/Si EBC.

Compounds with Alternating Single and Double Bonds of Antimony and Silicon; Isoelectronic to Ethane-1,2-diimine.

We present an approach for preparing chain-type unsaturated molecules with low oxidation state Si(I) and Sb(I) supported by amidinato ligands that exploit to generate heavy analogues of ethane 1,2-diimine. The reduction of antimony dihalide (R-SbCl2) with KC8 in the presence of silylene chloride afforded L─(Cl)Si═Sb─Tip (1) and L(Cl)Si═Sb─TerPh (2), respectively. Compounds 1 and 2 further undergo reduction with KC8 to produce Tip─Sb═LSi─LSi═Sb─Tip (3) and TerPh─Sb═LSi─LSi═Sb─TerPh (4). The solid-state structures and DFT studies show that all compounds have σ-type lone pairs at each Sb atom. It forms a strong pseudo-π-bond with Si. The pseudo-π-bond is formed by the hyperconjugative donation of the π-type lone pair at Sb to the Si-N σ* MO. The quantum mechanical studies indicate that compounds 3 and 4 has delocalized pseudo-π-MOs arising from hyperconjugative interactions. Hence, 1 and 2 can be considered as isoelectronic to imine, while 3 and 4 are isoelectronic to ethane-1,2-diimine. The proton affinity studies indicate that the pseudo-π-bond resulting from the hyperconjugative interaction is more reactive than the σ-type lone pair.

Effect of Surface Cleaning Process on the Wafer Bonding of Silicon and Pyrex Glass

Anodic bonding is a reliable packaging method for MEMS devices, and the surface properties of the wafer directly affect the bonding efficiency. Therefore, the surface treatment of the wafer to be bonded is necessary. Herein, the effects of three different surface cleaning processes (degreasing, piranha solution and RCA solution) on the wafer surface were investigated by atomic force microscopy, scanning electron microscopy, infrared spectroscopy, and anodic bonding experiments. The analysis showed that during the anodic bonding of the RCA solution-cleaned wafer and Pyrex glass, the bonding interface was more closely attached, and the best surface properties were obtained. The anodic bonding experiments of the wafer and Pyrex glass showed that the bonding current increased with the applied voltage, and the bonding time decreased accordingly. This was most evident in the case of RCA cleaning. The SEM images showed that as the bonding voltage increased, the bonding interface became more uniform without obvious voids. Due to the influence of the strong electric field and temperature field, an irreversible chemical reaction occurred at the bonding interface, which formed a bonding layer that was key to successful bonding.

Application of SCF-LTDP technology for a-Si:H film defective passivation in X-ray PIN-based photosensor

The quality and stability of X-ray flat panel detectors and fingerprint identifiers are crucial requirements for high-resolution applications and to ensure successful manufacture and commercially applicability. To achieve higher resolutions, the areas of the photodiodes must be reduced, which results in an increase in the leakage current owing to sidewall defects caused by the photodiodes. This study introduces a supercritical fluid low-temperature defect passivation (SCF-LTDP) treatment to repair the dangling bonds of amorphous silicon (a-Si) PIN-diode-based photo sensors. Unlike traditional atmospheric annealing processes, the hydrogen achieves a low-temperature and high-pressure fluid state in this technique, which offers the advantages of deeper penetration, higher surface tension, and greater viscous force. This technique helps suppress the leakage current generated in the reverse bias voltage by passivating the defects under illumination. The recombination current caused by the defects is, therefore, reduced, resulting in an overall increase of the photocurrent in the X-ray photodiode. The results obtained in this study are beneficial for the development of PIN diodes for panel detector applications.

Silicon–Hydrogen Bonding Configuration Modified by Layer Stacking Sequence in Silicon Heterojunction Solar Cells

Recent improvements in highly efficient crystalline silicon (c-Si) solar cells have relied on surface passivation. Hydrogen plays a crucial role in the surface passivation of silicon heterojunction (SHJ) solar cells because Si–H bonds passivate dangling bonds in amorphous silicon and on the c-Si surface. In this work, we demonstrate that the Si–H bonding configuration is modified by layer stacking sequence for SHJs. The quality of surface passivation strongly correlates with low-temperature hydrogen effusion from the SHJ structure. Our results show that the deposition of doped layers on intrinsic amorphous silicon supplies additional hydrogen to the amorphous/crystalline heterostructure. Moreover, the deposition of a p-layer modifies the microstructure of the intrinsic layer underneath, whereas depositing an n-layer does not induce structural changes. We suggest that the low-temperature hydrogen effusion characteristics can be used as a sensitive indicator for examining the passivation quality of SHJ solar cells.