Si Chemical Bonds Research Articles

Silicon-doped cobal–aluminum layered double hydroxide electrocatalyst with high catalytic activity for oxygen evolution reactions

Electrochemical water splitting is a zero-carbon-emission and environmentally friendly method for hydrogen production. However, the process requires electrocatalysts to lower its energy requirements. In this study, Si-doped cobalt–aluminum layered double hydroxide (Si-CoAl-LDH) had been successfully synthesized by SiCl4 chemical etching at room temperature. The Co-O-Si chemical bonds promoted the formation of γ-CoOOHx during the process of water oxidation, thereby increasing the number of active sites. Moreover, Theoretical calculations revealed the overlap of atomic orbitals on the Si-CoAl-LDH catalyst surface and the improved electronic structure due to Co–O–Si chemical bonds. The Si-CoAl-LDH exhibited overpotentials of 295, 336, and 363 mV for oxygen evolution reactions (OERs) at current densities 10, 50, and 100 mA cm−2, respectively. The Tafel slope of the sample was 74.16 mV·dec−1. Physical characterization and in situ Raman analysis revealed the formation of intermediate hydroxylated cobalt species, which act as active centers during OER. This study serves as a basis for the surface reconstruction and activity enhancement of other electrocatalysts through Si doping.

Hydrophilic Surface Modification of Amorphous Hydrogenated Carbon Nanocomposite Films via Atmospheric Oxygen Plasma Treatment

Herein we investigated hydrophilic surface modification of SiOx containing amorphous hydrogenated carbon nanocomposite films (DLC:SiOx) via the use of atmospheric oxygen plasma treatment. The modified films exhibited effective hydrophilic properties with complete surface wetting. More detailed water droplet contact angle (CA) measurements revealed that oxygen plasma treated DLC:SiOx films maintained good wetting properties with CA of up to 28 ± 1° after 20 days of aging in ambient air at room temperature. This treatment process also increased surface root mean square roughness from 0.27 nm to 1.26 nm. Analysis of the surface chemical states suggested that the hydrophilic behavior of DLC:SiOx treated with oxygen plasma is attributed to surface enrichment with C-O-C, SiO2, and Si-Si chemical bonds as well as significant removal of hydrophobic Si-CHx functional groups. The latter functional groups are prone to restoration and are mainly responsible for the increase in CA with aging. Possible applications of the modified DLC:SiOx nanocomposite films could include biocompatible coatings for biomedical applications, antifogging coatings for optical components, and protective coatings to prevent against corrosion and wear.

Improvement of oxide chemical mechanical polishing performance by increasing Ce3+/Ce4+ ratio in ceria slurry via hydrogen reduction

Ceria-based abrasive is widely used in the oxide chemical mechanical polishing (CMP) process due to its high polishing performance. Ce3+ ions on the surface of ceria form a Ce–O–Si chemical bond with surface of the SiO2 wafer, significantly affecting the material removal rate (MRR). In this study, the ceria surface was reduced by contact with hydrogen gas in a high temperature isothermal environment. Hydrogen gas forms surface hydroxyls on the ceria. Then, the generated hydroxyls form H2O and oxygen vacancies occur through the desorption of the H2O. The color of ceria changed to blue due to a change of the crystal structure by the reduction reaction. The reducing ability of hydrogen gas increased as the reduction temperature increased and the Ce3+ ion concentration increased by 12.7% under isothermal conditions at 1000 °C. The MRR of reduced ceria was improved by up to 37.7% compared to the original ceria.

Mechanical properties and mechanisms of alkali-activated slag paste reinforced by graphene oxide-SiO2 composite

Alkali-activated slag (AAS) binders-based composites are considered potential alternatives to conventional cement-based composites. However, the quasi-brittle mechanical behavior of AAS binders-based composites limits their widespread application. In this study, a graphene oxide-SiO2 (GO-SiO2) composite was produced to address this issue. The experimental results showed that the flexural strength of an AAS paste increased by 133.2% with 1.5 wt% GO-SiO2 composite, and its corresponding flexural-to-compressive strength ratio increased 95% i.e. from 0.063 to 0.123. To explore the strengthening mechanism, the stability of the GO-SiO2 composite in alkaline solutions and the dispersion effect of GO-SiO2 composite on the mechanical properties of AAS paste were investigated. The experimental results showed that the prepared GO-SiO2 composite had stable C–O–Si chemical bonds connected GO with hydration products, thereby improving the strength of the AAS paste. The molecular dynamics study revealed the mechanism that the high-dispersed GO-SiO2 composite could improve the mechanical properties of the AAS paste dramatically.

Grain boundary diffusion of Si in polycrystalline copper film

Grain boundary (GB) diffusion of Si in polycrystalline Cu film was studied in the temperature range of 403–453 K, in the C-type kinetic regime. The amorphous Si layer (80 nm) and polycrystalline Cu layer (40 nm) were successively deposited by magnetron sputtering at room temperature onto a Si (111) wafer. Appearance of Si atoms on the copper surface due to GB diffusion through the copper layer was detected by low energy ion scattering spectroscopy with high sensitivity. The depth distribution of Si in Cu grain boundaries was revealed by secondary neutral mass spectrometry. Surface morphology of Cu films was investigated by scanning tunneling microscopy. Identification of Si chemical bonds on the surface layer was made by X-ray photoelectron spectroscopy. GB diffusion coefficients were estimated by the relation used for calculation of diffusant distribution from a constant source in assumption that the diffusion path equals to the film thickness at the moment of appearing Si atoms on the Cu surface. At 453 K we estimated the surface segregation factor and detected formation of Cu–O–Si atomic bonds on the Cu film surface.

Development of a novel wet cleaning solution for Post-CMP SiO2 and Si3N4 films

After CMP, the removal of ceria nanoparticle residues is difficult due to the formation of Ce–O–Si chemical bonds on the SiO2 film surface. After STI CMP, several post-CMP cleaning processes are performed, including the application of PVA brushing and megasonic technologies using conventional cleaning solutions such as SC1, SC2, and SPM. However, more effective post-CMP cleaning technologies are still needed for the fabrication of advanced integrated circuit devices. In this study, we developed a novel post-CMP cleaning solution consisting of tetramethylammonium hydroxide (TMAH), ethylenediaminetetraacetic acid (EDTA), and Disponil to replace existing cleaning solutions. In its non-diluted form, this cleaning solution removed 99.5% of residual particles and 98.3% of ceria residue on an SiO2 film surface, as well as 98.5% of residual particles and 98.1% of ceria residue on an Si3N4 film surface, respectively. At 5 × dilution, it removed 97.8% of residual particles and 97.0% of ceria residue on the SiO2 film surface, as well as 97.8% of residual particles and 96.3% of ceria residue on the Si3N4 film surface, respectively. The effectiveness of this cleaning solution for residual ceria nanoparticles is highly comparable to SC1 and SPM conventional cleaning solutions, even though it is used at a relatively low temperature with less etching. Additionally, AFM of the surface topography showed fewer particles and better surface roughness compared with SC1 and SPM cleaning. Thus, this approach can be used to remove ceria nanoparticles from polished SiO2 and Si3N4 films through increased wettability, slight dissolving of the film, and extremely enhanced repulsive force.

Preparation of Ceria-Coated Silica Nanoparticles and Their Chemical Mechanical Planarization Performance on Si-Face 6H-SiC Substrates

Ceria-coated silica (SiO2/CeO2) composite abrasives were prepared through a novel homogeneous precipitation method using commercial silica (SiO2) sol as the silicon resource and cerium nitrate (Ce(NO3)3) and hexamethylenetetramine (HMT) aqueous mixtures as coating precursors. The phase composition, nano-topography, size distribution, and chemical structure of as-prepared particles were characterized by X-ray diffraction, transmission electron microscopy, Zetasizer Nano ZS90 and Fourier infrared spectra. In addition, the possible coating mechanism was discussed. Then, chemical mechanical planarization behaviors of SiO2 sol, ceria (CeO2) sol, and the novel abrasives and on Si-face (0001) 6H-SiC were investigated by atomic force microscopy. The results indicated that the composite particles were mono-dispersed nano-spheres composed of amorphous SiO2 core and cubic fluorite CeO2 shell, possessing complete core–shell structure and particle size of about 110 nm. CeO2 shell (10 nm) grew on the surface of SiO2 core by formation of Ce–O–Si chemical bonds, forming stable core–shell structure. SiO2/CeO2 composite abrasives provided an exponentially high material remove rate (MRR) of 1207 nm h−1 and an impressive surface finish with roughness average (Ra) 0.216 nm due to its active chemical property and unique structure.

Electrochemically converting micro-sized industrial Si/FeSi2 to nano Si/FeSi for the high-performance lithium-ion battery anode

Low-cost silicon (Si) feedstocks and a facile method to downsize the particle size are two determinants for the application of Si for the lithium-ion battery anode. Among various Si feedstocks, the industrial bulk ferrosilicon (b-Si/FeSi2) alloy is a promising Si resource, but decreasing the particle size and increasing the utilization of Si remain challenging. Herein, we report a self-driven alloying-electrochemical dealloying approach to converting the b-Si/FeSi2 to nano-sized Si/FeSi (n-Si/FeSi) in molten salts using Mg to extract one Si atom from one FeSi2 molecule by breaking down the FeSi–Si chemical bond and simultaneously forming Mg2Si. Subsequently, the obtained FeSi and Mg2Si are converted to nano Si and FeSi by electrochemically removing Mg from the Mg2Si anode to the cathode, making a circular use of Mg and increasing the electroactive Si content. Moreover, the polydopamine-coated n-Si/FeSi (n-Si/FeSi@C) anode exhibits a high capacity of 1449.7 mAh g−1 after 500 cycles at 0.4 A g−1, and an extremely stable reversible capacity of 846.8 mAh g−1 is retained even after 1500 cycles at 2 A g−1. Overall, this work provides an efficient method to convert industrial bulk Si/FeSi2 to nano-sized Si/FeSi by leveraging the chemical bonds of Fe–Si and Mg–Si.

Self-cleaned zirconia coatings prepared using a co-precursor sol–gel method

ABSTRACT The experimental work on the self-cleaned zirconia coatings prepared using a co-precursor sol–gel method is presented here. The zirconia coatings were synthesised using zirconium n-propoxide (ZrPro) precursor and different organosilanes such as trimethyl cholorosilane (TMCS), hexamethyl disilzane (HMDZ) and perfluorodecyl triethoxy silane (FDTES) as co-precursors. The organosilanes have a profound impact in modifying the surfaces making them water repellent. Therefore, the influences of various organosilane co-precursors on the chemical structure, thermal stability, hydrophobicity and roughness of the zirconia coatings were studied by varying the ZrPro:Co-precursor molar ratios. FTIR spectra of zirconia coatings revealed the high intensity of peaks related to C–H, Si–C and Zr–O–Si chemical bonds manifesting their hydrophobic characteristics. The TMCS and HMDZ co-precursors-based hydrophobic zirconia coatings retained their hydrophobicity up to a temperature of 300 °C as confirmed from TG-DSC analyses. The maximum contact angle of 154° and roughness of nearly 0.316 μm were measured for zirconia coatings prepared using the ZrPro:TMCS molar ratio of 0.3. These superhydrophobic zirconia coatings can be applied for the self-cleaning purpose.

Contamination Mechanism of Ceria Particles on the Oxide Surface after the CMP Process

The contamination behavior of ceria particles (50 and 100 nm) with oxide surfaces at pH 4 and 8 was studied using dipping and polishing conditions. Higher contamination at pH 4 than pH 8 was observed for dipping cases. In contrast, pH 8 conditions produced higher contamination than pH 4 for polishing cases. The difference in the contamination between dipping and polishing could be attributed to electrostatic attraction and chemical bonding. During polishing, weak or no chemical bonding may occur at pH 4, whereas the Ce–O–Si bond may form due to the surface charges of ceria and silica at pH 8. XPS analysis revealed that strong additional peaks related to Ce–O–Si bonding were detected for O 1s spectra at a binding energy of around 532 eV for surfaces polished at pH 8. Similar results were observed for 50 nm as well as 100 nm ceria particles. Based on the results, we concluded that ceria particles would have different adhesion behaviors for dipping and polishing at the same pH value. Also, higher ceria adhesion was observed at higher pH compared to lower pH during the CMP process, which was correlated to strong Ce–O–Si chemical bond formation due to the CMP conditions.

A new composite consisting of Y zeolite and ZrO2 for fluid catalytic cracking reaction

In fluid catalytic cracking (FCC) unit, basic nitrogen species in heavy oil result in the poison of Y zeolite acid sites and the loss of heavy oil conversion. To solve this issue, Y/ZrO2 composites are prepared by a two-stage crystallization method. The composite bears a uniform particle size and micro-mesoporous hierarchical structure. The Zr–O–Si chemical bonds are observed between Y zeolite and ZrO2 in Y/ZrO2 composites, which result from the incorporation of Zr species into the framework of Y zeolite. Compared to the mechanical mixture of Y zeolite and ZrO2, composites have abundant Lewis acid sites, which capture basic nitrogen species to protect the acid sites over Y zeolite. It endows a higher heavy oil conversion (increased by 2 wt%) to the Y/ZrO2 composites in the catalytic cracking of heavy oil with high-basic nitrogen compounds. It is worth noting that the hierarchical pore structure of Y/ZrO2 composite inhibits coke deposition. These results are important to propose a new FCC catalyst to catalytic crack heavy oil with high amount of bulky basic nitrogen compounds.

Selective Decomposition Process and Mechanism of Si–O–Si Cross-Linking Bonds in Silane Cross-Linked Polyethylene by Solid-State Shear Milling

Material recycling of silane cross-linked polyethylene (Si-XLPE) by the solid-state shear milling (S3M) technology could produce thermoplastic polyethylene. To take advantage of thermoplastic polyethylene from Si-XLPE, the de-cross-linked mechanism of Si-XLPE in S3M must be evaluated. The products prepared by the S3M technology were characterized using gel content, molecular weight measurement (GPC), Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (29Si-NMR), and re-cross-linking test to obtain insight into the selective de-cross-linking effect of the S3M technology. The results had confirmed that a cross-linking element consisting of Si–O–Si chemical bonds was destroyed during S3M, which was responsible for the destruction of cross-linked structures of Si-XLPE materials, and the molecular structures of the resulting products were close to that of silane-grafted polyethylene. The mechanical properties of Si-XLPE materials prepared by the S3M technology before and after water-cross-linking treatment were compared. It was found that the products obtained by the S3M technology could still undergo the cross-linking reaction and form more silane-grafted polyethylene with the increase of milling cycles. Based on the results of this study, we expected that practical applications of de-cross-linking of Si-XLPE materials could be successfully achieved. In this study, favorable conditions were established for the direct recovery of thermoplastic polyethylene from Si-XLPE by the selective de-cross-linking reaction in S3M and an idea about the recycling of Si-XLPE materials was developed.

Multiscale modeling of nano-SiO2 deposited on jute fibers via macroscopic evaluations and the interfacial interaction by molecular dynamics simulation

To improve the interfacial combination of jute fiber reinforced polymer composites, sol-gel method was used to deposit nano-SiO2 layer on the surface of jute fibers. The macroscopic evaluations and molecular dynamics (MD) simulation were carried out to characterize the deposition effect of nano-SiO2 layer on jute fibers. In addition, the multiscale modeling of nano-SiO2 deposited on jute fibers was established. The results showed that the deposition effect could be affected by the morphologies of nano-SiO2 layer including gel, array and aggregated particles. Compared with nano-SiO2 gel and aggregated nano-SiO2 particles, nano-SiO2 array may fill up the surface flaws of jute fibers efficiently, which would eliminate the stress concentration and lotus leaf effect on the jute fibers. The surface energy and tensile strength of jute fibers coated with nano-SiO2 array were increased by 9.79% and 16.47%, respectively. Additionally, MD simulation confirmed that non-bonding and C–O–Si chemical bonding interactions guaranteed the interfacial combination between the jute fiber and nano-SiO2 layer. C–O–Si chemical bond could provide with the strong interfacial strength between the jute fiber and nano-SiO2 layer.

Magnetic Core/Shell Nanocomposites MgFe2O4/SiO2 for Biomedical Application: Synthesis and Properties

Magnetic core/shell (CS) nanocomposites (MNCs) are synthesized using a simple method, in which a magnesium ferrite nanoparticle (MgFe2O4) is a core, and an amorphous silicon dioxide (silica SiO2) layer is a shell. The composition, morphology, and structure of synthesized particles are studied using X-ray diffraction, field emission electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), scattering electrophoretic photometer, thermogravimetric analysis (TGA), and Mossbauer spectroscopy. It is found that the MgFe2O4/SiO2 MNC has the core/shell structure formed by the Fe‒O–Si chemical bond. After coating with silica, the MgFe2O4/SiO2 MNC saturation magnetization significantly decreases in comparison with MgFe2O4 particles without a SiO2 shell. Spherical particles agglomerated from MgFe2O4 nanocrystallites ∼9.6 and ∼11.5 nm in size function as cores coated with SiO2 shells ∼30 and ∼50 nm thick, respectively. The total size of obtained CS MNCs is ∼200 and 300 nm, respectively. Synthesized CS MgFe2O4/SiO2 MNCs are very promising for biomedical applications, due to the biological compatibility of silicon dioxide, its sizes, and the fact that the Curie temperature is in the region required for hyperthermal therapy, 320 K.

Магнитные нанокомпозиты MgFe-=SUB=-2-=/SUB=-O-=SUB=-4-=/SUB=-/SiO-=SUB=-2-=/SUB=- типа ядро/оболочка для биомедицинских применений: синтез и свойства

AbstractMagnetic core/shell (CS) nanocomposites (MNCs) are synthesized using a simple method, in which a magnesium ferrite nanoparticle (MgFe_2O_4) is a core, and an amorphous silicon dioxide (silica SiO_2) layer is a shell. The composition, morphology, and structure of synthesized particles are studied using X-ray diffraction, field emission electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), scattering electrophoretic photometer, thermogravimetric analysis (TGA), and Mössbauer spectroscopy. It is found that the MgFe_2O_4/SiO_2 MNC has the core/shell structure formed by the Fe‒O–Si chemical bond. After coating with silica, the MgFe_2O_4/SiO_2 MNC saturation magnetization significantly decreases in comparison with MgFe_2O_4 particles without a SiO_2 shell. Spherical particles agglomerated from MgFe_2O_4 nanocrystallites ∼9.6 and ∼11.5 nm in size function as cores coated with SiO_2 shells ∼30 and ∼50 nm thick, respectively. The total size of obtained CS MNCs is ∼200 and 300 nm, respectively. Synthesized CS MgFe_2O_4/SiO_2 MNCs are very promising for biomedical applications, due to the biological compatibility of silicon dioxide, its sizes, and the fact that the Curie temperature is in the region required for hyperthermal therapy, 320 K.

Surface modification of TiO2 nanotubes by grafting with APTS coupling agents

Titanium dioxide nanotubes (TNTs) have been considered the promising nanostructures employed for many practical applications such as biomedical, photonic and optoelectronic devices. Nevertheless, strong aggregation of TNTs within various aqueous media significantly hindered their practical utilizations and the capability of dispersing TNTs in the desired solvents are urgent to be improved. Therefore, in this study, the methodic investigations have been performed on the grafted modification of 3-aminopropyl triethoxysilane (APTS) on the surfaces of synthesized TNTs. A preliminary study was carried out to evaluate the influences of key parameters, including the concentrations of coupling agents, temperatures and the reaction durations, on the grafting efficiency of the aminosilane using Statistical design of experiments (DoE) methodology. TNTs with approximately 10–20 nm in diameter were prepared with the controlled hydrothermal treatment of commercialized P25 particles. The obtained products were revealed by the modern physicochemical systems including x-ray diffraction (XRD), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) analysis. The additions of silane agent, reaction temperature and time have been adjusted to reveal the influences of the grafting efficiency (from 2.5 to 7.8 wt %) by thermal gravimetric analysis (TGA). Analysis of Fourier transform infrared spectroscopy (FTIR) has confirmed the successful link of Ti–O–Si chemical bonds on the grafted TNTs.

Fatigue behavior of basalt fiber-reinforced polymer tendons under a marine environment

Due to their advantageous mechanical behaviors and anti-salt properties, basalt fiber-reinforced polymer (BFRP) tendons are a promising prestressing component under a marine environment. However, the degradation law of fatigue behavior of BFRP tendons under a marine environment is still unclear. This paper studies the fatigue behavior of BFRP tendons after aging in a salt solution by temperature-accelerated experiments. The degradation mechanism of fatigue behavior is clarified based on previous studies and analysis of the failure mode. The effect of aging temperature on fatigue strength degradation is analyzed using both experimental data and scanning electron microscopy (SEM) images. Moreover, the fatigue strength degradation of BFRP tendons at different local temperatures was predicted according to the Arrhenius equation. The results show that the fatigue strength degradation of BFRP tendons is governed by the weakened fiber-matrix interface resulting from the hydrolyzation of Si–O–Si chemical bonds in salt solution. SEM showed that specimens aged at 55°C for 63days demonstrate increased corrosion than those in other groups. Through the Arrhenius equation, the fatigue strengths of BFRP tendons are predicted to be 0.41, 0.43 and 0.45fu, respectively, at three representative northern latitudes after 100years of aging in marine environments. The results provide guidance for fatigue design of BFRP tendons in a marine environment.

Electrochemical study on the corrosion behavior of Ti3SiC2 in 3.5% NaCl solution

The differences between the Ti–C and Ti–Si chemical bonds limit the passivation ability, resulting in a decreased passivation ability.

H2O incorporation in the phosphorene/a-SiO2 interface: a first-principles study

Based on first-principles calculations, we investigate (i) the energetic stability and electronic properties of single-layer phosphorene (SLP) adsorbed on an amorphous SiO2 surface (SLP/a-SiO2), and (ii) the further incorporation of water molecules at the phosphorene/a-SiO2 interface. In (i), we find that the phosphorene sheet binds to a-SiO2 through van der Waals interactions, even in the presence of oxygen vacancies on the surface. The SLP/a-SiO2 system presents a type-I band alignment, with the valence (conduction) band maximum (minimum) of the phosphorene lying within the energy gap of the a-SiO2 substrate. The structure and the surface-potential corrugations promote the formation of electron-rich and electron-poor regions on the phosphorene sheet and at the SLP/a-SiO2 interface. Such charge density puddles are strengthened by the presence of oxygen vacancies in a-SiO2. In (ii), because of the amorphous structure of the surface, we consider a number of plausible geometries for H2O embedded in the SLP/a-SiO2 interface. There is an energetic preference for the formation of hydroxyl (OH) groups on the a-SiO2 surface. Meanwhile, in the presence of oxygenated water or interstitial oxygen in the phosphorene sheet, we observe the formation of metastable OH bonded to the phosphorene, and the formation of energetically stable P–O–Si chemical bonds at the SLP/a-SiO2 interface. Further x-ray absorption spectra simulations are performed, which aim to provide additional structural/electronic information on the oxygen atoms forming hydroxyl groups or P–O–Si chemical bonds at the interface region.

Effects of Pb Intercalation on the Structural and Electronic Properties of Epitaxial Graphene on SiC.

The effects of Pb intercalation on the structural and electronic properties of epitaxial single-layer graphene grown on SiC(0001) substrate are investigated using scanning tunneling microscopy (STM), noncontact atomic force microscopy, Kelvin probe force microscopy (KPFM), X-ray photoelectron spectroscopy, and angle-resolved photoemission spectroscopy (ARPES) methods. The STM results show the formation of an ordered moiré superstructure pattern induced by Pb atom intercalation underneath the graphene layer. ARPES measurements reveal the presence of two additional linearly dispersing π-bands, providing evidence for the decoupling of the buffer layer from the underlying SiC substrate. Upon Pb intercalation, the Si 2p core level spectra show a signature for the existence of PbSi chemical bonds at the interface region, as manifested in a shift of 1.2 eV of the bulk SiC component toward lower binding energies. The Pb intercalation gives rise to hole-doping of graphene and results in a shift of the Dirac point energy by about 0.1 eV above the Fermi level, as revealed by the ARPES measurements. The KPFM experiments have shown that decoupling of the graphene layer by Pb intercalation is accompanied by a work function increase. The observed increase in the work function is attributed to the suppression of the electron transfer from the SiC substrate to the graphene layer. The Pb intercalated structure is found to be stable in ambient conditions and at high temperatures up to 1250 °C. These results demonstrate that the construction of a graphene-capped Pb/SiC system offers a possibility of tuning the graphene electronic properties and exploring intriguing physical properties such as superconductivity and spintronics.