Spherical Silicon Research Articles

Multipole couplings and resonance shifts in an array of dielectric particles at oblique incidence

In the present paper, we propose a coupled multipole model to treat the mutual interactions between nanoparticles aligned in a periodic array, which may be frequently encountered in designing metasurfaces and other functional electromagnetic structures. Our model is comprehensive in that it takes into account the electric and magnetic multipoles both up to the quadrupole order. Working under Cartesian coordinates, this model can readily give the multipole responses of the particles in an infinite array at both normal and oblique incidence. In particular, we work out the analytical expressions of the cross-multipole coupling tensors, which are much more complicated for oblique incidence than normal incidence. We invoke the Ewald method to efficiently and accurately calculate the involved lattice sum whose convergence is otherwise very slow. By quantifying the contributions from the various couplings, we are able to analyze the mechanisms of new resonances that emerge only at oblique incidence. As a prototypical example, we use this method to give physically clear explanations of and show flexible control on the resonance shifts of the multipoles of an array of silicon spheres. The power of this model makes it very promising for dealing with metasurfaces with extended areas or working at large numerical apertures.

Effect of Nanoparticle and Carbon Nanotube Additives on Thermal Stability of Hydrocarbon-Based Drilling Fluids

The article presents the results of experimental study on the effect of additives of silicon oxide nanoparticles, as well as single-walled and multi-walled carbon nanotubes on the colloidal stability and thermal degradation process of hydrocarbon-based drilling fluids. Such a comprehensive study of hydrocarbon-based drilling fluids was carried out for the first time. The effect of the concentration and size of silicon oxide nanoparticles, as well as the type and concentration of nanotubes on the colloidal stability of drilling fluids during thermal aging tests at different temperatures, was investigated. The nanoparticle size varied from 18 to 70 nm, and the concentration ranged from 0.25 to 2 wt.%. Single-walled and multi-walled nanotubes were studied, whose concentration varied from 0.01 to 0.5 wt.%. The thermal aging temperature varied from 30 to 150 °C. According to the results of the investigation, it was shown that the temperature stability of hydrocarbon-based drilling fluids can be significantly improved by adding the above substances. At the same time, it was shown that the use of single-walled nanotubes for thermal stabilization of drilling fluids was several times more effective than the use of multi-walled nanotubes, and tens of times more effective than the use of spherical silicon oxide nanoparticles.

Graphene interleaved SiOx/C spheres Via molecular polymerization as high-stability lithium-ion battery anodes

SiOx/carbon composite materials are a promising candidate for lithium-ion battery anodes because of their high capacity. However, their widespread application is hindered by poor electrical conductivity, and stability due to the volume expansion during cycling. Herein, electrodes comprised of spherical carbon-coated silicon oxide particles, interleaved between electrochemically exfoliated graphene, were prepared via molecular polymerization followed by physical mixing. The spherical silicon oxide was obtained by the carbonization of the reaction product between dialdehyde and (3-aminopropyl) trimethoxysilane. The interleaved graphene flakes both provided electrically conductive pathways between particles and formed a porous supporting structure between the silicon oxide particles and the graphene flakes, enabling a buffering for the volume expansion. A range of SiOx/C-G anodes are obtained by adjusting the content of graphene. The assembled batteries with an optimal graphene ratio (SiOx/C: G = 2:1 (w/w)) exhibit superior Li-ion storage behavior, including high cycle stability, with capacity retention of 88.6 % and high coulombic efficiency of 99 % after 250 cycles under 0.1 A·g−1. Promisingly, it was verified that with the support from the outer robust graphene layer and the porous support structure, the volume expansion of silicon oxide particles during lithiation/delithiation processes was suppressed, leading to a more stable solid electrolyte interface (SEI) layer.

Study on Friction Behaviors of Soft Materials Considering Sliding-Caused Deformation

Accurate and quantitative characterization of friction behavior is of critical importance for material design and manufacture, especially for soft materials. It is mainly because the sliding-caused deformation of soft materials has always been neglected during characterization. Here, a modified model considering sliding-caused deformation was proposed to characterize the friction behavior between a spherical glass indenter and silicon rubber. A novel friction apparatus consisting of a transparent spherical indenter connected with a camera was used in real-time to measure the friction contact status. The contact shape and area during friction were then extracted by a proposed shape function. Experimental results show that shrinking and expanding of the contact area occur simultaneously when a spherical-rigid indenter slides on a soft substrate due to sliding-caused deformation of soft materials. Based on these results, this study built a modified model considering the shape change and the accompanying deformation component of friction, which is an effective method for evaluating the friction behavior of soft materials.

Validation of the silicon nanoparticle production on the pilot plant scale via long-term gas-phase synthesis using a microwave plasma reactor

The formation of crystalline silicon nanoparticles by homogeneous gas-phase reactions as a direct way to produce high-purity raw material is applied. For this purpose, a microwave-assisted plasma reactor is used. Goal of this paper is to show the scalability of our process technology from laboratory scale to pilot plant scale while maintaining the particle characteristics. This is demonstrated by producing and analyzing silicon nanoparticles during long-term synthesis in a pilot-scale microwave plasma reactor over a period of six hours. The focus is on a high production rate in conjunction with consistent particle characteristics. A continuous production of the mostly spherical crystalline silicon particles with a count median diameter (CMD) of 23.4 nm and a geometric standard deviation of 1.5 is shown using TEM analysis. The stability of the synthesis process is monitored by means of regular sampling and analyzing batch samples extracted from the process every 30 min. Here it is shown that the CMD varies statistically between 21 and 26 nm. Moreover, the decomposition rate of the precursor was determined to be 99%, while the energy supply remained constant. A constant production rate of about 200 g∙h−1 is shown.

The gradient fabrication and optimization of metal-acid bifunctional catalysts for the hydrogenation of n-C16 to produce bio-jet fuel component

In the two-step hydrogenation of oil to produce bio-jet fuel, the yield of bio-jet fuel is determined by the hydrotreatment of long-chain alkanes over a metal–acid bifunctional catalyst. A strategy that the catalyst with better isomerization is conductive to the hydrotreatment of long-chain alkanes to produce jet fuel component is proposed. Based on the hollow silicon sphere (HSS), catalysts with different acid strength, diffusion performance, and intimacy between Pt and acid bifunctional sites were designed to gradually optimize the isomerization performance. After the gradient optimization of weak acid, strong diffusion performance, and minor-nanoscale intimacy between Pt and acid sites, the gradient catalysts exhibited a constantly improving yield of isomer product and jet fuel component. The yolk-shell WHSS@Pt catalyst with three levels of simultaneous optimization performed the favorable yield of jet fuel component (37 wt.%), which can be attributed to the combination of weak acid, strong diffusion performance, and minor-nanoscale intimacy between bifunctional sites that are beneficial to the isomerization of long-chain alkanes.

Real-space solution to the electronic structure problem for nearly a million electrons.

We report a Kohn-Sham density functional theory calculation of a system with more than 200 000 atoms and 800 000 electrons using a real-space high-order finite-difference method to investigate the electronic structure of large spherical silicon nanoclusters. Our system of choice was a 20nm large spherical nanocluster with 202 617 silicon atoms and 13 836 hydrogen atoms used to passivate the dangling surface bonds. To speed up the convergence of the eigenspace, we utilized Chebyshev-filtered subspace iteration, and for sparse matrix-vector multiplications, we used blockwise Hilbert space-filling curves, implemented in the PARSEC code. For this calculation, we also replaced our orthonormalization + Rayleigh-Ritz step with a generalized eigenvalue problem step. We utilized all of the 8192 nodes (458 752 processors) on the Frontera machine at the Texas Advanced Computing Center. We achieved two Chebyshev-filtered subspace iterations, yielding a good approximation of the electronic density of states. Our work pushes the limits on the capabilities of the current electronic structure solvers to nearly 106 electrons and demonstrates the potential of the real-space approach to efficiently parallelize large calculations on modern high-performance computing platforms.

Solving the electronic structure problem for over 100 000 atoms in real space

Using a real-space high-order finite-difference approach, we investigate the electronic structure of large spherical silicon nanoclusters. Within Kohn-Sham density functional theory and using pseudopotentials, we report the self-consistent field convergence of a system with over 100 000 atoms: a ${\mathrm{Si}}_{107,641}{\mathrm{H}}_{9,084}$ nanocluster with a diameter of 16 nm. Our approach uses Chebyshev-filtered subspace iteration to speed up the convergence of the eigenspace, and blockwise Hilbert space-filling curves to speed up sparse matrix-vector multiplications, all of which are implemented in the parsec code. For the largest system, we utilized 2048 nodes (114 688 cores) on the Frontera machine in the Texas Advanced Computing Center. Our quantitative analysis of the electronic structure shows how it gradually approaches its bulk counterpart as a function of nanocluster size. The band gap is enlarged due to quantum confinement in nanoclusters, but decreases as the system size increases, as expected. Our work serves as a proof of concept for the capacity of the real-space approach in efficiently parallelizing very large calculations using high-performance computer platforms, which can straightforwardly be replicated in other systems with more than ${10}^{5}$ atoms.

Preparation of highly dispersed silicon spheres supported cobalt-based catalysts and their catalytic performance for Fischer-Tropsch synthesis

A series of silicon spheres supported cobalt catalysts were prepared by incipient wetness impregnation followed by decomposition under treatment of glow discharge plasma with different intensities. The catalysts were characterized by X-ray powder diffraction, N2 physical adsorption-desorption, H2 temperature-programmed reduction, transmission electron microscope and Fourier-Transform Infrared spectroscopy. The Fischer-Tropsch synthesis performance were tested on a fixed bed reactor. The influence of plasma treatment on cobalt dispersion, reducibility and cobalt-support interaction were analyzed and discussed. The results showed that the plasma-treated catalysts had better catalytic performance than the calcined sample. The Co/SP-P650W catalyst showed the highest reaction activity due to the proper cobalt dispersion and higher cobalt reducibility.

Molecular‐level fabrication strategies for the POSS cross‐linked polybenzoxazines

AbstractIn order to study the dispersion and compatibility of polysilsesquioxane (POSS) with different functional groups in benzoxazine resin, four different polysilsesquioxane/polybenzoxazine (POSS/PBZ) composites are prepared based on 3‐phenyl‐3,4‐dihydro‐2H‐benzoxazine (PHa), unreactive Octaphenylsilsesquioxane (OPS), Mercaptopropyl‐isobutyl silsesquioxane (SPOSS) containing one reactive sulfhydryl group, Aminopropyl‐isobutylsilsesquioxane (NPOSS) containing one reactive amino group and Octa (aminophenyl) silsesquioxane (OAPS) containing eight reactive amino groups, respectively. Scanning electron microscope (SEM), transmission electron microscope (TEM), and transmission electron microscope with probe corrector (AC‐TEM) are used to investigate compatibility. The results indicate that OAPS have very good compatibility and interaction with benzoxazine in the molecular level based on the microstructure. Besides, molecular and mesoscopic dynamic simulations (MesoDyn) also confirms OAPS and PHa have the best compatibility based on the micro and mesoscopic aspects. Then their properties of thermal stability and glass transition temperature (Tg) are identified by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. While OAPS is beneficial to increase the initial decomposition temperature (T5%) of PBZ by 26 °C and the Tg by 16 °C, comparing with pure PHa. However, NPOSS and SPOSS aggregate into micron‐sized silicon spheres, and OPS precipitates and deposits on the bottom of the resin, which could weaken the property of their thermal stability.

A multiplicative finite strain deformation for diffusion-induced stress: An incremental approach

Understanding the evolution of lithium concentration and stresses in electrode materials during electrochemical cycling is of paramount importance in studying the fundamental mechanisms contributing to the structural degradation of lithiated electrode materials. In this work, we use the change rate of the volume of a host material in analyzing diffusion-induced volume expansion and obtain the volume expansion as an exponential function of the concentration of solute atoms and the coefficient of linear expansion in contrast to the widely used linear relation between the diffusion-induced volume expansion and the coefficient of linear expansion. Using the principle of multiplicative decomposition in the framework of elastic deformation and thermodynamic free energies, we derive the constitutive relation for diffusion-induced finite deformation of elastic materials. The symmetric Piola-Kirchhoff stress is an exponential function of the coefficient of linear expansion and the concentration of solute atoms. Incorporating the change of strain field with the change in the number of solute atoms in Helmholtz free energy, we derive the chemical potential of the solute atoms in the host material the same as the one given by Li et al. (Zeitschrift für PhysikalischeChemie, 49 (1966) 271–290). Numerical results for the lithiation of a spherical silicon electrode reveal that the spatial distributions of lithium concentration and stresses for small dimensionless time (dilute solution) exhibit similar trends to the corresponding ones calculated from the theory of linear elasticity and nonlinear characteristics for large dimensionless time (concentrated solution).

A simple and green self-conversion method to construct silicon hollow spheres for high-performance Li-ion battery anodes

Silicon (Si) anode has garnered attention as a potential replacement for high energy density lithium-ion battery anodes. Its commercial application, however, is still hindered by the issues of rapid capacity attenuation due to large volume change during (de)lithiation process, complex preparation process, and high cost. In this work, a simple and green strategy was proposed to fabricate carbon-coated hollow porous silicon spheres (Hp-Si@C) by a self-conversion method and subsequent magnesiothermic reduction. The synthesis of Hp-Si@C by this method used inexpensive tetraethyl orthosilicate precursors and did not involve the use of additional sacrificial template, complicated CVD and toxic hydrofluoric acid, which was simple, inexpensive, green and scalable. NaCl was introduced as a heat scavenger to avoid the formation of SiC and maintain the hollow morphology of the precursor. The electrochemical behaviors of Hp-Si@C were investigated by in situ electrochemical characterization. The structure of Hp-Si@C defined fast ion transport routes and provided expansion space during lithiation process, endowing it with stable cycling performance and fast electrochemical reaction kinetics. Hp-Si@C had a delithiation capacity of 1228 mAh g−1 with a capacity retention of 69% at 2 A g−1, and a rate capacity of 865 mAh g−1 at 10 A g−1.

Eco-friendly Approach for Creation of Resonant Silicon Nanoparticle Colloids

The commercial application of Mie-resonant nanophotonic technologies currently used in various laboratory studies, from biosensing to quantum optics, appears to be challenging. Development of colloidal-based fabrication approaches is a solution to face the issue. In our research, we studied the fabrication of resonant Si nanoparticle (NP) arrays on a surface with controlled wettability. First, we use nanosecond (ns) laser ablation in water and subsequent density gradient separation to obtain colloids of resonant spherical crystalline silicon NPs with a low polydispersity index. Then, the same industrial ns laser is applied to create a wetting gradient on the steel substrate to initiate a self-assembly of the NPs deposited by drop casting. Thus, we use a single commercial ns laser for producing both the NPs and the hydrophilic wetting gradient. We apply an easily operating size separation technique and only non-toxic media. This research contributes to the large-scale fabrication of various optical devices based on resonant high-refractive index nanostructures by ecologically friendly self-assembly techniques.

Tungsten doped diamond shells for record neutron yield inertial confinement fusion experiments at the National Ignition Facility

We report on fabrication and characterization of layered, tungsten doped, spherical about 2 mm diameter microcrystalline diamond ablator shells for inertial confinement fusion (ICF) experiments at the National Ignition Facility. As previously reported, diamond ICF ablator shells can be fabricated by chemical vapor deposition (CVD) on solid spherical silicon mandrels using an ellipsoidal microwave plasma reactor. In the present work, we further developed these ablator shells by embedding a W-doped diamond layer sandwiched between two undoped diamond regions. W incorporation in diamond was achieved by adding tungsten hexacarbonyl to the CH4/H2 CVD feed gas. We observe that the W doping concentration decreases with increasing deposition rate which, in turn, is controlled by adjusting the total gas pressure. Cross sectional microstructural analysis reveals sharp interfaces between doped and undoped regions of the diamond shell and uniform W distribution with concentrations up to about 0.3 at.%. At higher W concentrations (>0.3 at.%) formation of tungsten carbide precipitates is observed. Using a 3‐shock 1.6 MJ laser pulse, the targets described in this work produced the first laser driven implosion to break the 1 × 1016 neutron yield barrier, followed by experiments (described in future publications) with similar targets and slightly more laser energy producing yields as high as 4 × 1017.

Polar-embedded phenyl dendritic stationary phase for multi-mode chromatographic separation

In this study, 1,4-butanediol diglycidyl ether (BDDE) and aniline were grafted on the silicon sphere surface for preparing the polar-embedded phenyl dendritic multi-mode stationary phase (Sil-BD-AN). Results of Fourier transform infrared spectrometry (FT-IR), scanning electron microscope (SEM), elemental analysis (EA) and thermogravimetric analysis (TGA) confirmed the successful construction of the multi-mode stationary phase. The prepared column showed mixed separation mechanisms including hydrophilic interaction chromatography (HILIC) and reversed-phase liquid chromatography (RPLC) that realized the separation of different kinds of analytes including polycyclic aromatic hydrocarbons (PAHs), anilines, nucleic bases, nucleosides, alkylbenzenes and positional isomers. Moreover, effects of chromatographic conditions with retention time, such as injected volume, column temperature and acetonitrile content, were also examined. Furthermore, the application of the Sil- BD-AN column was proved by the accurate determination of p-phenylenediamine (PPD) content in the hair dye. The above results affirmed that the Sil-BD-AN column has the application potential for separating complicated samples under multiple modes.

Unsteady Water-Based Ternary Hybrid Nanofluids on Wedges by Bioconvection and Wall Stretching Velocity: Thermal Analysis and Scrutinization of Small and Larger Magnitudes of the Thermal Conductivity of Nanoparticles

The uniqueness of nanofluids in the field of thermal analysis and engineering is associated with their thermal conductivity and thermodynamics. The dynamics of water made up of (i) single-walled carbon nanotubes with larger magnitudes of thermal conductivity of different shapes (i.e., platelet, cylindrical, and spherical) and (ii) moderately small magnitudes of thermal conductivity (i.e., platelet magnesium oxide, cylindrical aluminum oxide, spherical silicon dioxide) were explored in order to address some scientific questions. In continuation of the exploration and usefulness of ternary hybrid nanofluid in hydrodynamics and geothermal systems, nothing is known on the comparative analysis between the two dynamics outlined above due to the bioconvection of static wedges and wedges with stretching at the wall. Reliable and valid numerical solutions of the governing equation that models the transport phenomena mentioned above are presented in this report. The heat transfer through the wall increased with the wall stretching velocity at a smaller rate of 0.52 and a higher rate of 0.59 when the larger and smaller thermal conductivity of nanoparticles were used, respectively. Larger or smaller magnitudes of the thermal conductivity of nanoparticles were used; the wall stretching velocity had no significant effects on the mass transfer rate but the distribution of the gyrotactic microorganism was strongly affected. Increasing the stretching at the wedge’s wall in the same direction as the transport phenomenon is suitable for decreasing the distribution of temperature owing to the higher velocity of ternary hybrid nanofluids either parallel or perpendicular to the wedge.

Improvement in Injection Molding Quality Performance with Innovative Cyclone Mixers Used in Polypropylene with Spherical Silicon Dioxide Composites.

This research proposes an innovative design of a new cyclone mixer for the quality of polymer materials, and it presents a systematic optimization model of process parameters for plastic injection molding. Thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to determine the appropriate thermal properties of processing in order to select appropriate control factors and level values for a Taguchi orthogonal array. The injection molding machine was used to make sample test pieces for tensile strength, hardness and impact strength. Significant factors were found by the signal-to-noise (S/N) ratio with an analysis of variation (ANOVA), and the single-quality optimal parameter combination was obtained. The reproducibility of the experiment was evaluated, and various quality weights were evaluated by principal components analysis (PCA). The multi-quality optimal parameter combination was found, and the comprehensive scores were compared. Finally, the process capability indices were combined with a multi-process capability analysis chart (MPCAC) to compare the process yields of cyclone mixing and screw mixing. The mechanical properties of products were evaluated to verify the performance of cyclone mixing and to provide perfect information for the injection molding quality performance of cyclone mixing and screw mixing. It was concluded that the overall quality of the cyclone mixing products is 42.72, and the total quality of the screw mixing products is 41.85. The total number of defects for the cyclone mixing is 9659 ppm, and that of the screw mixing is 10688 ppm. It can be seen that, for the overall product quality performance, cyclone mixing can be applied in the plastic injection molding process instead of screw mixing.

Designing disordered multi-functional metamaterials using the discrete dipole approximation

The ability to design passive structures that perform different operations on different electromagnetic fields is key to many technologies, from beam-steering to optical computing. While many techniques have been developed to optimise structures to achieve specific functionality through inverse design, designing multi-function materials remains challenging. We present a semi-analytic method, based on the discrete dipole approximation, to design multi-functional metamaterials. To demonstrate the generality of our method, we present two key examples. Firstly, we work at optical wavelengths to design a disordered 2D arrangement of silicon spheres that beams light into different directions depending on the source polarisation. Secondly, we design a 3D device that works at microwave wavelengths and sorts plane waves by their angle of incidence. In this case, the scatterers are more complicated meta-atoms, with a strong dipole resonance at microwave frequencies.

Measuring liquid density in a system for ensuring uniformity of measurements

The article presents the results of a study aimed at creating the national standard for liquid density. The standard provides reproduction, storage and transmission of the liquid density unit in the range from 650 to 2000 kg/m3. Based on the method of hydrostatic weighing, the measurement of liquid density was implemented in accordance with the GOST OIML R 111-1-2009 «State system for ensuring the uniformity of measurements. Weights of classes Е1, Е2, F1, F2, M1, M1–2, M2, M2–3 and M3. Part 1. Metrological and technical requirements». It is shown that the use of a high-precision mass comparator can significantly reduce the systematic measurement error and the standard deviation when reproducing and transferring the unit of liquid density to reference measuring instruments of the 1st and 2nd category and working measuring instruments. A method for transferring a unit of liquid density by means of a standard density measure – a silicon sphere and a comparator liquid – has been implemented, which made it possible to exclude the transfer link in the form of a standard liquid density solution. In the range of reproduction, storage and transmission of the liquid density unit, a systematic error of 2.1 ⋅ 10–3 kg/m3 was obtained, the standard deviation in the reproduction of the liquid density unit was 4.0 ⋅ 10–4 kg/m3, the standard deviation of the total error in the transmission of the liquid density unit 3.14 ⋅ 10–3 kg/m3.

A Hollow Silicon Nanosphere/Carbon Nanotube Composite as an Anode Material for Lithium-Ion Batteries

Silicon possesses a high theoretical specific capacity and is a promising high-performance anode material for lithium-ion batteries (LIBs). However, it shows a poor cycling performance because of volume expansion. A hollow structure can improve Si cycling performance, and the template method is one of the most common methods for hollow micro/nanosphere preparation. A polystyrene (PS) microsphere has the advantages of having a uniform and controllable particle size, easy modification, and high stability, thus being an ideal template for preparing hollow structure material. Herein, PS microspheres are used as templates to obtain hollow silica spheres, and then obtain hollow silicon spheres with an inner pore diameter of ~50 nm by a magnesium thermal reduction method. Lithium-ion battery anode material is obtained using carbon nanotubes supporting hollow silicon spheres (Si-CNTs). Si-CNTs exhibit excellent cycling performance (1188 mAh g−1 after 200 cycles) and excellent rate capability (484 mAh g−1 at 1 A g−1). Hollow porous Si-CNTs show great potential, providing a promising idea for solving the volume expansion problem of Si.