Amorphous SiO2 Research Articles

Structural Transitions of Anionic, Cationic, and Nonionic Surfactant Solutions Confined between Amorphous SiO2 Slabs: Molecular Dynamics Simulations

Adsorption of surfactants of a different nature on solid surfaces has found remarkable enthusiasm in many industrial processes such as enhanced oil recovery, detergency, solubilization, and flocculation/dispersion. Surfactants can interact with solid slabs and alter their surface charge and hydrophobicity, which are essential in interfacial phenomena. Interestingly, the surface charges of amorphous materials are thoroughly different from crystalline materials due to the disordered distribution of surface atoms. Therefore, we performed molecular dynamics simulations to examine the interactions of surfactant solutions with SiO2 surface in detail. To this aim, aqueous solutions of various surfactants were confined between two amorphous SiO2 walls, which were 10 nm apart. The results indicate that the structure of the amorphous solid surfaces is changed substantially due to their interactions with surfactant solutions. The simulation results indicate the presence of the nonionic surfactant aggregates in the bulk solvent, while ionic surfactants without branching, such as SDS, form aggregates that adsorb on the SiO2 surface. The interactions of the confined surfactants with glassy SiO2 slabs change the structure of the surface layer and consequently alter the surface charge density during the simulation, which leads to the separation of cationic and anionic parts of the confined surfactants in the vicinity of amorphous SiO2 slabs.

Silicon Cutting Waste Derived Silicon Nanosheets with Adjustable Native SiO2 Shell for Highly‐Stable Lithiation/Delithiation

Silicon is an excellent candidate for the next generation of ultra-high performance anode materials, with the rapid iteration of the lithium-ion battery industry. High-quality silicon sources are the cornerstone of the development of silicon anodes, and silicon cutting waste (SCW) is one of them while still faces the problems of poor performance and unclear structure-activity relationship. Herein, a simple, efficient, and inexpensive purification method is implemented to reduce impurities in SCW and expose the morphology of nanosheets therein. Furthermore, HF is used to modulate the abundant native O in SCW after thermodynamic and kinetic considerations, realizing the mechanical support for the internal Si in the form of an amorphous SiO2 shell. Afterward, SCNS@SiO2 -2.5 with a 1.0nm thick SiO2 shell exhibits a reversible capacity of 1583.3 mAhg-1 after 200 cycles at 0.8 Ag-1 . Ultimately, the molecular dynamics simulations profoundly reveal that the amorphous SiO2 shell is transformed into the extremely ductile Lix SiOy shell to ditch stress and relieve strain during the lithiation/delithiation process.

Cold sintering of SiC ceramics with the assistance of amorphous SiO2 surface layer

The cold sintering process (CSP) densifies ceramics powder at lower temperatures (<300 °C) than conventional sintering by applying a small amount of solvent such as water and a uniaxial pressure of several hundred megapascals. However, this method can only be applied to materials with high solubility in solvents, and direct hardening of low solubility materials such as SiC is difficult. In this study, hardened SiC/SiO 2 bodies were fabricated by CSP from SiC particles whose surface was oxidized by preheating, using NaOH solution as a solvent. The compressive strength and relative density of the hardened SiC/SiO 2 bodies fabricated from a mixture of SiC particles with 15.3 mass% SiO 2 and 5 mol/L NaOH solution were 520 MPa and 80%, respectively. These values were considerably higher than those of hardened SiC/SiO 2 bodies fabricated by CSP from a mixed powder consisting of untreated SiC particles and amorphous SiO 2 particles. When the surface-oxidized SiC particles were used as a starting material, the mismatch in chemical bonding between SiC and SiO 2 and uneven distribution of the binder were reduced, resulting in high mechanical strength for the hardened SiC/SiO 2 bodies.

Formation of the amorphous multicomponent iron-based alloy during carbothermal reduction of Fe2O3 by waste activated sludge

The process related to the formation of a multicomponent amorphous material during the reduction of α-Fe2O3 with the products of thermodestruction of WAS is studied using x-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Because WAS contains sand and clay along with its bio-components, the thermal treatment of WAS is accompanied by the formation of amorphous carbon, SiO2, Al2O3, and multicomponent alloys. At T = 1000 °C, under oxygen-deficient conditions, iron oxide was reduced according to the scheme: α-Fe2O3 → (amorphous phase)main part + (Fe + Fe0.94O)(crystalline)little part. The main product of the Fe2O3 reduction is amorphous iron with a lamellar structure. Newly formed amorphous alloys form interlayers between the iron plates and 3D inclusions. Inclusions of C, SiO2, and Al2O3 agglomerates are observed between the lamellar packs. This macrostructure of the material allows slow cooling of the 3D-samples while preserving the amorphous state of iron.

Preparation and Characterization of SiO2/α‐Al2O3 Tritium Permeation Barriers at Low Temperature

A tritium permeation barrier on the surface of structural materials can effectively solve the problem of tritium fuel penetration and leakage. Herein, SiO2/α‐Al2O3 ceramic coatings are prepared on 316L stainless steel through slurry spin coating method. Different particle sizes of α‐Al2O3 powder are used to prepare three kinds of coatings. The particle sizes of α‐Al2O3 used are 30 nm (sample 1), 200 nm (sample 2), and equal mass ratio of 30 nm and 200 nm mixed (sample 3), respectively. The results show that the ceramic coating is composed of α‐Al2O3 and amorphous SiO2. The coating surface of sample 3 is uniform and compact and exhibits the best microstructure. Compared with samples 1 and 2, sample 3 has better thermal shock resistance. The binding strength of sample 3 is up to 69 N. Electrochemical hydrogen penetration tests indicate that SiO2/α‐Al2O3 ceramic coating can effectively improve the electrochemical hydrogen resistance of 316 L stainless steel substrate. Sample 3 has the lowest stable hydrogen penetration current density and current density difference value. Although the hydrogen resistance of sample 3 is reduced after 50 thermal shocks, it is still better than that of the substrate.

Reorientation of pentacene molecules from flat-lying to standing manners on a surface-modified amorphous SiO2 substrate investigated by molecular dynamics simulations

Reorientation of pentacene molecules from the flat-lying manner to the standing one which occurs at the early stage of thin film growth by physical vapor deposition was investigated by molecular dynamics simulations with a surface-modified amorphous SiO2 substrate. A molecular cluster comprising 50 standing pentacene molecules was placed on the substrate together with lying molecules and clusters, and the standing cluster acted as a trigger for the reorientation of lying molecules and clusters. Some lying molecules and clusters adjacent to the standing cluster stood up probably by the short-range van der Waals interaction. Some lying clusters apart from the standing cluster also stood up, and this phenomenon was possibly caused by the effect of the long-range Coulomb interaction between clusters. The number of standing molecules on the substrate increased with increasing temperature, and the temperature dependence of the orientational transition rate was discussed in view of thermal fluctuation.

A yolk-shell eGaSn@Void@SiO2 nanodroplet design for high-performance cathodes in room temperature liquid metal batteries

Gallium-based liquid alloys that exhibit high capacity and self-healing properties have been demonstrated to be promising cathodes for room temperature liquid metal batteries (RTLMBs). However, the electrochemical performances of these alloys are poor due to severe volume expansion and an unstable solid electrolyte interface layer during the lithiation process. Here, a sol-gel strategy was performed to construct yolk-shell structure nanodroplets (eGaSn@Void@SiO2) that contain sufficient void space by amorphous silicon oxide, which generated a liquid metal electrode with a high performance. The amorphous SiO2 shells not only play an important role in building stable SEI films, providing efficient electron/ion conduction channels and preventing agglomeration of active substances, but exhibit good elastic behavior during charging/discharging. Due to the appropriate voids in the yolk-shell structure, the eGaSn nanodroplets can expand freely without breaking or disrupting the electrode structure; thus, the resulting eGaSn@Void@SiO2 NDs exhibited high capacities of 538, 454, and 338 mA h g−1 at current rates of 0.2, 1 and 5 C, respectively. No obvious decay was observed with more than 500 cycles and a capacity of 377 mA h g−1 at 2 C. Interestingly, the density functional theory (DFT) calculations revealed that the effective chemisorption between the discharge products and SiO2 provides sufficient electrical contact sites with a significant drop in electrochemical impedance during cycling. The causes of the superior electrodes performance were investigated in depth using in situ X-ray diffraction and theoretical calculations. Our rational design may shed unprecedented light on the development of liquid alloy-based cathodes for high-performance RTLMBs.

Epitaxial growth of the first two members of the Ban+1InnO2.5n+1 Ruddlesden–Popper homologous series

We demonstrate the epitaxial growth of the first two members, and the n=∞ member of the homologous Ruddlesden–Popper series of Ban+1InnO2.5n+1 of which the n=1 member was previously unknown. The films were grown by suboxide molecular-beam epitaxy where the indium is provided by a molecular beam of indium-suboxide [In2O (g)]. To facilitate ex situ characterization of the highly hygroscopic barium indate films, a capping layer of amorphous SiO2 was deposited prior to air exposure. The structural quality of the films was assessed by x-ray diffraction, reflective high-energy electron diffraction, and scanning transmission electron microscopy.

Optimal Microstructure of Silicon Monoxide as the Anode for Lithium-Ion Batteries.

Because of its metastable nature, silicon monoxide (SiO) consists of Si nanodomains in an amorphous matrix of SiO2. The microstructure of SiO, including SiO2, Si domains, and interphase (SiOx) between domains, was modified via an annealing treatment in argon gas and thoroughly characterized by in-situ and ex-situ X-ray diffraction, pair distribution function, and electron energy loss spectroscopy. Two microstructure transformation routes were observed during the annealing process: (1) at a temperature of <800 °C, the annealing treatment was found to affect mainly the structural conformation of the amorphous SiO2 matrix and the interphase, while (2) an annealing temperature of >800 °C led to significant Si nanodomain growth. We found that the microstructure has a great impact on the electrochemical performance of SiO. The optimized microstructure of SiO appears to be achieved through annealing treatment at 800 °C or less, which results in interphase (SiOx) reduction without causing significant Si domain growth. This work provides a deep insight into the domain and interphase transformation of SiO upon heat treatment. The improved understanding of the relationship between SiO microstructure and its electrochemical behavior will enable proper design and development of high-energy SiO for lithium-ion batteries.

Fabrication of ceramic sealing coatings for shell bionic structures and their failure mechanism during thermal cycling

The porous ceramic coating as a "brick" layer sprayed by air plasma spraying(APS) and MK resin as a "mud" layer prepared by a high viscosity spray gun were characterized and tested. Three specifications of the "brick-mud" layered ceramic sealing coating were fabricated through the cyclic and orderly deposition of the "brick" layer and "mud" layer, and the thermal cycling performance and failure mechanism of the three new coatings were studied. The results showed that the agglomerated Y2O3 partially stabilized ZrO2 (YSZ) particles had porous spherical structures and good sprayability, and the content of the YSZ phase in the prepared "brick" layer was 54.2%. The "mud" layer had good phase stability and was amorphous SiO2 at and below 1100 °C. The fracture toughness of the pure YSZ coating was 2.295 ± 0.135 MPa‧m0.5, and which of the “mud” layer was reduced by 72.3%. The thermal cycling life of the conventional coating was only 67.3 times, which of A1, A2 and A3 coatings with 2, 3 and 6 "mud" layers were increased by 32.4%, 124.8% and 88.3%, respectively. In the thermal cycling process, the "weak" layer in the "brick-mud" layered coating led to the redistribution of internal stress and reduced the stress concentration in the top coating (TC)/TGO interface. Moreover, the initiation of microcracks in the "weak" layer, along with the "crack branching" effect and the "crack deflection" effect during the crack propagation process, could consume partial internal stress. Thus, the crack growth rates in the TC coating/TGO interface of the A1, A2 and A3coatings were lower than that of the conventional coating due to the above stress release mechanisms. In addition, the thermal cycling lives of the three new coatings with 2, 3 and 6 "mud" layers were improved to different degrees because of different stress effects.

Thermal stability of synthetic high basicity calcium silicate hydrates substituted with Cr3+ ions

In this work, the formation mechanism, the thermal stability (280–1000 °C) and the surface area properties of calcium silicate hydrates substituted with Cr3+ ions under hydrothermal conditions were investigated. In this experiment, CaO, amorphous SiO2·nH2O raw materials and Cr(NO3)3·9H2O (5 or 15 g Cr3+/dm3 (accordingly, Cr:Ca:Si:H2O ratios were equal to 0.002:1.5:1:1.098 and 0.006:1.5:1:1.094)) solutions were used. Hydrothermal synthesis was performed in unstirred suspensions, in an autoclave, under saturated steam pressure (∼ 10 bar) at a temperature of 200 °C for 1 h. The thermal stability of the synthesized samples was investigated at 280, 500 and 1000 °C with a temperature increase rate of 8.33 °C/h. It was determined that Cr3+ ions changed the formation mechanism of high basicity calcium silicate hydrates and yielded different synthesized compounds: a lower amount of Cr3+ ions accelerated the reaction of the raw material and promoted the crystallization of α-C2SH and xonotlite, while a higher concentration of Cr3+ ions effected only the formation of semicrystalline type compounds (C-S-H (I) and C-S-H (II)). Calcium silicate hydrates substituted with Cr3+ ions remained stable up to 250 °C temperature because, at a higher temperature, calcium chromate started to form. Also, when the calcination temperature was equal to 1000 °C, the Cr3+ ions additive accelerated the crystallinity of calcium silicates (wollastonite and belite). The results of the SBET measurements showed that the Cr3+ ions additive positively influenced the values of the specific surface area (total of 76.17 m2/g). However, these values decreased after the samples were calcinated at a temperature of 500 °C (the value dropped to 48.02 m2/g).

Visible-light-activated TiO2 photocatalysis regionally modified by SiO2 for lignin depolymerization

In the high-value utilization of lignin, the photocatalytic technology to break β-O-4 linkages is a green strategy to obtain small molecular oxygenated polycyclic aromatic hydrocarbons. TiO2 is regarded as a promising photocatalyst for breaking β-O-4 linkages, whose band gap width is up to 3.2 eV, unfortunately inhibiting the activity in the visible region. Surface engineering is an effective strategy that can shorten the bandgap width of TiO2 and modulate its photocatalytic performance via impurity-free introduction of oxygen defect sites. Herein, we report a TiO2 micrometer spheres with surface oxygen-deficient structures obtained directly by hydrogenated TiO2, whose regionalized surface is modified by amorphous SiO2. The oxygen vacancies prolong the carrier separation time on the TiO2 surface and transfer electrons through Ti–O–Si bonds to the lignin models bound to Si–OH thereby generating radicals. The surface modification of SiO2 not only enhances the adsorption capacity to the lignin models but also achieves the effective utilization of PV illumination per unit area by refracting the incident light. Simultaneously, the catalyst performance is reasonably optimized by the regional distribution of SiO2 when combined with lignin models in a point-to-point manner. The TiO2 photocatalysis regionally modified by SiO2 is designed as an ingenious model for the direct photocatalytic oxidation of target through a directional integrated avenue.

Enhanced luminescence and Judd-Ofelt analysis in SiO2 encapsulated CaWO4@CaWO4:Eu:Bi for visualization of latent fingerprints and anti-counterfeiting

Core nanoparticles (NPs) and core–shell particles have been synthesized using the low temperature reflux method. The structural and photo-physical properties of the developed phosphors have been investigated through various analytical techniques. The transmission electron microscopy (TEM) analysis evidences the formation of the shell on the core NPs. The optical band gap is estimated using the diffuse reflectance spectra. An 8-fold enhancement of emission intensity is observed in the core–shell particles as compared to that of core, due to the reduced surface quenchers after silica coating. In addition, the Judd-Ofelt (J-O) parameters have been calculated to reveal the site symmetry and coordination environment around Eu3+ ions. The tunable red emission on formation of core–shell structures is confirmed from the CIE diagram. These results are ascribed to the formation of the chemical bonds between CaWO4@ CaWO4:3%Eu3+:5%Bi3+ (core) and amorphous SiO2 shell via W – O – Si bridges. Better hydrophilicity developing from active functional groups in solutions and intense luminescence behavior with a quantum efficiency of 91% allow the developed phosphors for various potential applications such as solid state lighting, bio-labelling agent for the visualization of latent fingerprints (LFPs) and anti-counterfeiting, etc.

Soft abrasive facilitating materials removal of SiO2/Si bilayer materials: A molecular dynamics study

In this work, three different tips are considered to study the influences on the friction and wear behaviors of monocrystalline silicon covered with an amorphous SiO2 film using molecular dynamics simulation. The results show that the friction force for the SiO2 tips, especially for the non-rigid tip is much higher than that of the diamond tip because of the adhesion effect between the SiO2 tips and SiO2/Si bilayer sample. The film beneath the diamond tip undergoes densification and phase transformation occurs to silicon substrate during sliding. However, materials removal takes place in SiO2/Si samples against the non-rigid SiO2 tip because of compressed and sheared soft tip during sliding, causing enhanced true contact area and generation of more Si–O bridge bonds between the sliding interfaces. Meanwhile, the resultant contact area results in declined contact stress and a damage-free silicon substrate. It is found that the indentation-plowing model of material removal is no longer valid during sliding against the diamond tip, and that the indentation-adhesion mechanism contributes to the materials removal of sample slid by a soft SiO2 tip and results in a damage-free surface under the normal force of 40 nN.

Monte-Carlo simulation and experimental study of the effect of internal charging on the electron emission yield of amorphous SiO2 thin films

A Monte-Carlo code has been developed for the transport of low energy electrons and the simulation of the internal charge buildup induced by the electron irradiation in thin films of amorphous SiO2. The code is validated with time resolved experimental Electron Emission Yield (EEY) data on 20 nm SiO2 thin films for incident electrons of 300 eV and 1 keV. As the EEY is greater than 1, this corresponds to the case of positive charging. In order to assess the impact of the charge buildup on the electron emission yield, the samples have been negatively polarized to suppress the positive external charging effects, and irradiated with a defocused beam (mm²). A direct correlation is found between the value of the EEY and the density of holes created in the material. This clearly shows that the recombination of the secondary electrons with trapped holes significantly affects the EEY of insulators.

Ab initio investigations in amorphous silicon dioxide: Proposing a multi-state defect model for electron and hole capture

Experiments as well as theoretical calculations indicate that point defects in the amorphous SiO2 layer of electronic devices as well as in optical fibers are responsible for numerous stability and reliability phenomena, including noise, hysteresis, bias temperature instabilities and decreasing transmission efficiency. In addition to the well-known oxygen vacancy, hydrogen related defects such as the hydrogen bridge and the hydroxyl-E′ center have gained a considerable amount of attention in the recent past, as they are suspected to negatively influence the device performance by capturing charge carriers from e.g. both Si and SiC substrates in field effect transistors. Here, we present a thorough ab initio study of these oxide defects and develop a unified description of electron and hole capture processes in a single multi-state model, supported by a comprehensive analysis of various defect parameters like relaxation energies, charge transition levels, (meta-)stability and transition barriers. We show that a single oxide defect can have two different trap levels for both electron and hole capturing processes, which might be the cause of anomalous device degradation phenomena. Based on its low formation energy compared to other defect types, we find that the hydroxyl-E′ center is the most promising defect candidate to explain charge capture processes in Si/SiO2 systems. Furthermore, we argue that the reduced effect of positive bias temperature instability (PBTI) observed in MOS devices compared to its negative counterpart (NBTI) can be explained by the locations of the hydroxyl-E′ centers charge transition levels.

Formation of subsurface Cu-O-Si system through laser-induced plasma-assisted copper penetration for fabricating robust adhesive copper wire on glass substrate

This study reports an approach, laser-induced plasma-assisted penetration (LIPAP), to facilitate copper diffusion to the glass interior using a femtosecond laser. TEM images and EDS analysis showed copper particles could diffuse into the glass up to 300 nm from the surface. The diffusion was driven by the local high temperatures generated by consecutively incident highly repetitive laser pulses. Furthermore, the HR-TEM images showed that, between the surface copper layer and the internal amorphous SiO2, there were crystalline regions of copper nanoparticles and copper oxides and an amorphous zone, belonging to the Cu-O-Si system, through which, the surface copper layer was firmly connected with the glass substrate. The LIPAPed copper layer then served as a patterning seed for electroless-plating of highly conductive copper wires. Consequently, copper wires with a resistivity of 9.9×10-8Ωm were obtained. Finally, a scratch adhesion test was performed to quantify the adhesion of the resulting copper films. Results showed that copper remained adhered to the surface before reaching the ultimate glass crush load of 30 N, corresponding to normal scratch stress of 240 MPa. Accordingly, based on the LIPAP-formed special subsurface nanostructures serving as the mechanical anchoring basis, highly conductive and adhesive electroless-plated copper wires were achieved.

Strong uniaxial magnetic anisotropy in Fe3Si thin films

Thin Fe3Si films grown on Si/SiO2 substrates by ion-beam and pulsed laser deposition possess soft ferromagnetic behavior and strong in-plane uniaxial magnetic anisotropy. The material of the capping layer and deposition of the buffer layer do not affect the presence and character of obtained anisotropy. The structural studies showed that Fe3Si film deposited on amorphous SiO2 layer is polycrystalline while the same layer grown on polycrystalline Ta buffer layer is amorphous. It has also been found that uniaxial anisotropy is similar for amorphous and crystalline DO3 Fe3Si films. Magnetic properties yield a magnetization saturation of both amorphous and crystalline films as 1050 emu/cm3 at room temperature and coercive field not exceeding 5 Oe. The origin of such an anomalous behavior were discussed in terms of deposition technique features and parameters, substrate and capping layer type and resulting film parameters.

Formation of agglomerates with core–shell structure in a large-scale CFB boiler

Cylindrical agglomerates with cross-sectional diameters over 200 mm are found in the bottom ash discharging chute of a 550 MWe large-scale circulating fluidized bed (CFB) boiler, which results in disfunction of the bottom ash discharging system due to the blockage of the bottom ash discharging chute. The agglomerates with core–shell structure are found to be significant to understand the mechanisms of the agglomeration, and agglomerates with similar structure are also found inside the furnace. The X-ray diffraction analysis on the core–shell structured agglomerate particle shows both the core and the shell comprise a significant amount of mullite; meanwhile, cristobalite is found in the shell, which is supposed to be formed at temperature higher than the bed temperature. The results of the transmission electron microscopy analysis show that mullite crystal in the shell is distributed inside the amorphous SiO2. Sintering experiments show that the formation temperature for mullite and cristobalite is ca. 1050 ℃, while the transformation temperature of quartz to amorphous silica is ca. 1150 ℃, which is much higher than the bed temperature. Thus, the agglomeration is supposed to be resulted from the high-temperature condition caused by the burning char inside the furnace, and the core–shell structure of the agglomerates is supposed to be formed due to the temperature gradient along the particle diameter of the burning char.

Membrane fouling behaviors in a full-scale zero liquid discharge system for cold-rolling wastewater brine treatment: A comprehensive analysis on multiple membrane processes

The challenge of water scarcity drives zero liquid discharge (ZLD) treatment to maximize reuse of industrial wastewater. Deciphering the characteristics and mechanisms of membrane fouling in the membrane-based ZLD system is crucial for the development of effective fouling control strategies. However, current studies only focused on the membrane fouling of single step, lacking in-depth understanding on the ZLD systems using multiple membrane processes. Herein, membrane fouling characteristics and mechanisms in a full-scale ZLD system for cold-rolling wastewater brine treatment were investigated via a comprehensive analysis on multiple nanofiltration (NF) and reverse osmosis (RO) membrane processes. The membrane fouling behaviors showed distinct characteristics along the wastewater flow direction in the ZLD system. Increasing amounts of foulants were deposited on the membrane surfaces with the sequence of the 1st pass RO, 1st stage NF, and 2nd stage NF processes. The organic fouling and silica scaling were more intensive in the 1st stage NF and 2nd stage NF for treating the brine of the 1st pass RO, as the foulants were rejected and concentrated by previous membrane processes. Severe inorganic fouling, containing amorphous SiO2, Al2O3, and Al2SiO5, occurred on the membrane surface of the 2nd pass RO membrane, due to the recirculated high-concentration silica, high water recovery, and concentration polarization. For the 3rd pass RO process, both the amounts of organic and inorganic foulants decreased dramatically, due to the low foulant concentration in its influent. This work provides a comprehensive understanding of membrane fouling in a membrane-based ZLD system, facilitating the development of membrane fouling control strategies for multiple membrane processes.