Spherical Si Research Articles

Effect of EMS Process on the Primary Si Refinement, Tensile and Fatigue Properties of Hyper-eutectic Al-15wt.%Si Alloy

This study investigated the effect of the electromagnetic stirring (EMS) process on the microstructure and mechanical properties of hyper-eutectic Al-15 wt.%Si alloy. The tensile and high-cycle fatigue properties of the EMS Al-15wt.%Si alloy were examined and compared with conventional direct chill (DC) cast alloy. The initial microstructure of the as-cast DC alloy showed a coarse primary Si of 70 µm, in contrast to the size (40 µm) of the as-cast EMS alloy. The DC extruded alloy exhibited a massive primary Si size of 40~55 µm. In contrast, the EMS extruded alloy had a spherical primary Si with 30~40 µm sizes. The average grain sizes were measured to be 8.8 µm (EMS extruded alloy) and 11.4 µm (DC extruded alloy), respectively. The EMS process was confirmed to contribute to the refinement of the grain size and the primary Si size of the hyper-eutectic Al-Si alloy. The yield strengths at room temperature were measured to be 388.0 MPa (EMS extruded alloy) and 375.0 MPa (DC extruded alloy), and the tensile strengths were 426.0 MPa (EMS extruded alloy) and 412.4MPa (DC extruded alloy), respectively. The elongations of both alloys were similar at room temperature. The fatigue limit of the EMS extruded alloy (130 MPa) was higher than that of the DC extruded alloy (120 MPa). The EMS extruded alloy exhibited superior fatigue resistance compared to the DC extruded alloy, regardless of the cyclic stress condition. This study also discussed the potential value of the EMS process as a method for improving the properties of hyper-eutectic Al-Si alloy, as well as the deformation and fracture mechanisms of the EMS Al-15wt.%Si alloy.

Evaluation of microstructure and mechanical properties of M-SIMA processed Al–7Si alloy

In this research article, the effect of the strain-induced melt activation (SIMA) process on the microstructure and mechanical properties of the Al–7Si alloy has been investigated. The morphology of α-Al grains is changed from dendritic to fine spherical and flaky type eutectic Si to a fine fibrous eutectic Si after the modified strain-induced melt activation (M-SIMA) process. The intermetallic compounds are refined and distributed uniformly throughout the matrix after the M-SIMA process. The mechanical properties have been improved due to fine spherical grain formation with refined eutectic Si. A high tensile strength (UTS: 204 MPa) with a remarkable improvement in ductility (El: 30%) is achieved after the M-SIMA process at 585°C for 30 min in comparison to the as-cast Al–7Si alloy (UTS: 117 MPa, El: 16%).

Enhanced Light Emission from Monolayer MoS2 by Doubly Resonant Spherical Si Nanoantennas

Enhanced Light Emission from Monolayer MoS₂ by Doubly Resonant Spherical Si Nanoantennas

Effects of Microstructure Modification by Friction Surfacing on Wear Behavior of Al Alloys with Different Si Contents.

In this work, Al alloys with 6.6%, 10.4%, and 14.6% Si were deposited as thick coatings by Friction Surfacing (FS), resulting in grain refinement and spheroidization of needle-shaped eutectic Si phase. Lubricated sliding wear tests were performed on a pin-on-disc tribometer using Al-Si alloys in as-cast and FS processed states as pins and 42CrMo4 steel discs. The chemical composition of the worn surfaces was analyzed by X-ray photoelectron spectroscopy (XPS). The wear mechanisms were studied by scanning electron microscopy (SEM) and focused ion beam (FIB), and the wear was evaluated by measuring the weight loss of the samples. For the hypoeutectic alloys, spheroidization of the Si phase particles in particular leads to a significant improvement in wear resistance. The needle-shaped Si phase in as-cast state fractures during the wear test and small fragments easily detach from the surface. The spherical Si phase particles in the FS state also break away from the surface, but to a smaller extent. No reduction in wear due to FS was observed for the hypereutectic alloy. Here, large bulky primary Si phase particles are already present in the as-cast state and do not change significantly during FS, providing high wear resistance in both material states. This study highlights the mechanisms and limitations of improved wear resistance of Si-rich Al alloys deposited as thick coatings by Friction Surfacing.

Investigating Stability of Si Sphere Surface Layer in Ambient–Vacuum Cyclic Measurements Using Ellipsometry

This paper reports an investigation conducted to evaluate the stability of surface layers on a Si sphere in ambient–vacuum cyclic measurements. An ellipsometer equipped with a vacuum chamber and a vapor-controlling system was developed to characterize the surface layers on the Si spheres. To investigate the stability and reproducibility of the surface layer, particularly for realizing and disseminating the kilogram, surface layer thickness measurements by ellipsometry were repeatedly conducted in air and vacuum for 1.5 months on a Si sphere with natural isotopic abundance. The surface layers of the Si sphere were relatively stable throughout the cyclic measurements, and no significant contamination was observed. We also conducted ellipsometry on the Si sphere after introducing water vapor into the vacuum chamber. The adsorbed water layer thickness in the air–vacuum and water vapor–vacuum measurements were almost identical, showing that gas components other than water vapor, such as carbonaceous materials stemming from the environment, had little effect on surface layer thickness in the air-vacuum cyclic measurements.

Physical and chemical characterization of fugitive particulate matter emissions of the iron and steel industry

The iron and steel industry is a notable particulate matter emitter. In source apportionment of particulate matter, it is important to identify the characteristics of particulate matter originating from steel sites. However, previous studies mostly focus on stack emission sources, while few reports on fugitive emission sources are available. Aiming to fill this gap, the physical and chemical characteristics of fugitive emission sources in the whole iron and steel production process were explored. The emission factor, particle size distribution (PSD), and morphological and chemical profiles of fugitive particulate matter (FPM) originating from fugitive emission sources at the observed site were analyzed through on-site sampling and in-lab testing. The emission factors in descending sequence are those of steelmaking plants, sinter plants, ironmaking plants and coking plants. The particle size of FPM mainly ranges from 0.1 to 716 μm, while distribution forms with both unimodal and bimodal peaks occur. The microscopic morphology of FPM is mainly divided into: irregular Fe-, Si-, Ca- and Mg-rich mineral particles formed by physical means, layered carbonaceous particles formed by mechanical crushing and combustion cracking, spherical Si-, Al- and Fe-rich particles in a high-temperature molten state, and chain and agglomerate particles formed by the polymerization of high-temperature flue gas and volatile minerals. The mass fraction of Fe ranks first in the sintering, ironmaking, and steelmaking processes, with values ranging from 1.40% to 57.79%. C attains the highest mass fraction, 69.80%, in the PFM originating from crushing mills.

Matryoshka-type carbon-stabilized hollow Si spheres as an advanced anode material for lithium-ion batteries

Silicon (Si) is regarded as the potential anode for lithium-ion batteries (LIBs), due to the remarkable theoretical specific capacity and low voltage plateau. However, the rapid capacity decay resulting from volume variation and slow electron/ion transportation of Si limit its practical application. Here, matryoshka-type carbon-stabilized hollow silicon spheres (Si/C/Si/C) are synthesized by an aluminothermic reduction and calcination process. The Si/C/Si/C anode materials prepared at 500 °C (Si/C/Si/C-500) exhibit unique structures, in which amorphous region and porous structure are preserved in the Si layers. The anode based on Si/C/Si/C-500 displays an initial specific capacity of 2792 mAh/g at a current density of 100 mA/g. At 1000 mA/g, this anode retains a reversible capacity of 1673 mAh/g, 86.9% of the initial capacity after 200 cycles. Such synthetic strategy can be employed to fabricate other high-capacity anode materials with large volume variation during charge/discharge process

Effect of thermo-mechanical treatment and strontium addition on workability and mechanical properties of Al Si Cu casting alloy

In this study, the potential application of Al-Si-Cu aluminum alloy (ALDC12), which is widely used in the high-pressure die-casting (HPDC) process, for fabricating a wrought product was evaluated. The effects of thermo-mechanical treatment and Sr addition on the microstructure, workability, and mechanical properties of the ALDC12 alloy were investigated in detail. The introduction of thermo-mechanical treatment significantly reduced the interconnectivity of the brittle eutectic Si phase formed during solidification and average grain size. Therefore, the uniformly distributed spherical Si particles and fine grain size considerably improved both the strength and ductility of the ALDC12 alloy. Furthermore, the addition of Sr effectively modified the eutectic Si phase in the casting process, which significantly reduced the occurrence of edge cracks in the subsequent rolling step and further improved the mechanical properties of the final sheets. Consequently, through microstructural control of the ALDC12 aluminum alloy by the thermo-mechanical treatment and Sr addition, it was possible to obtain suitable workability and significantly improved mechanical properties compared with those of cast products.

Hollow Si nanospheres with amorphous TiO2 layer used as anode for high-performance Li-ion battery

This work introduces a novel, nanostructured Si-based material comprised of hollow Si spheres encapsulated in an amorphous TiO2 layer (HN-Si@aTiO2). The HN-Si@aTiO2 is prepared by magnesiothermic reduction and sol-gel methods. As an anode material, the composite exhibits high capacity performance and enhanced cycling stability. When tested at a current density of 1 A g−1, the nanocomposite achieves a high initial specific capacity of 2804.6 mA h g−1 with a high initial coulombic efficiency of 78.47% and its discharge capacity is 1196.3 mA h g−1 after 100 cycles. Meanwhile, the HN-Si@aTiO2 electrode exhibits high capacity performance with 524.6 mA h g−1 even after 500 cycles at 5 A g−1. The outstanding cycling stability of HN-Si@aTiO2 is attributed to its hollow core-shell nanostructure. The hollow structure of the anode material provides space for volumetric change of the silicon core, while the amorphous TiO2 coating layer maintains the integrity of the electrode material. Therefore, HN-Si@aTiO2 nanocomposites have great prospects as next-generation lithium-ion anode materials owing to their outstanding electrochemical performance and scalable synthesis methods.

Development of a combined XRF/XPS surface-analysis system for the surface-layer quantification of 28Si spheres

<p class="Abstract">To achieve a new kilogram definition using the X-ray crystal density method, the Center for Measurement Standards, Industrial Technology Research Institute in Taiwan has established the combined XRF (X-ray fluorescence)/XPS (X-ray photoelectron spectroscopy) surface analysis system for the quantitative surface-layer analysis of Si spheres. The surface layer of a Si sphere is composed primarily of an oxide layer, carbonaceous contamination and physisorbed/chemisorbed water. This newly combined instrument has been implemented to measure the XRF for the direct determination of the mass deposition of oxygen (ng/cm<sup>2</sup>) with a calibrated silicon drift detector and the XPS for the ratio between the elements (O, Si, C) and composition identification. These two complementary methods of X-ray metrology allow an accurate determination of the surface-layer mass of the Si sphere. In this paper, the construction of a combined XRF/XPS surface-analysis system is reported, including the surface characterisation method, the assembly of parts of the load-lock chamber and ultra-high-vacuum analysis chamber, the vacuum-system design, hardware integration and the intended research on surface-layer measurement. It is anticipated that the measured surface-layer mass will be combined with the core mass of the Si sphere.</p>

Introducing High School Students to the Avogadro Number and the Mole Concept Using Discovery with Calculations Based on Physical Properties of Elements, Crystal Structures, and 28Si Spheres

An instructional approach is presented for teaching the mole concept to high school introductory-level chemistry classes. Extensions to the strategy are presented for more advanced classes. The strength of the approach is based upon discovery. Students discover the Avogadro number and the mole concept. The discovery is based upon calculations that are similar to that used by the International Avogadro Coordination (IAC) in determining the Avogadro constant. Students in advanced classes use data from the IAC to calculate the most precise and accurate values for the Avogadro constant.

(Invited) Miniaturized Infrared Lenses Realized By Wafer Bonding Technologies

All surfaces in our surrounding radiate heat as an electromagnetic wave - similar to light, but invisible to our eyes. The ability to sense and quantify thermal radiation opens up a vast field of application scenarios such as person detection, thermal analysis of buildings or equipment, and health monitoring.Especially the latter has become a matter of utmost importance with the sudden outbreak of the SARS-CoV-2 pandemic in the beginning of 2020. In such an event, the most important task is to closely observe the spreading of the infection and to initiate adequate measures for social distancing.In many cultures, monitoring the health of citizens is a legally delicate issue, and prescribing confinement to an individual would raise difficult questions when it comes to compensate for lost wages. However, having precise instruments at hand to monitor and control the pandemic would allow governments to provide individual support rather than bringing the whole economy to a shutdown.The widespread availability of medical grade temperature sensors could contribute valuable information to a multi-parametric pandemic monitoring. Many infections are accompanied by an elevated body temperature, and often fever is not only one of the most obvious symptoms but also an early stage indicator. Hence, there is a renewed interest in ultra-small medical grade IR sensors which can be integrated into mobile consumer products such as wearables and smart phones.In order to produce IR sensors for a global mass market, a thorough consideration of all aspects on the system level is necessary to optimize cost, size and performance for the targeted application. Infrared detectors for temperature measurement have not yet reached high-volume applications for two main reasons: (1) The optical design necessitates far-infrared transparent materials like ZnSe, CaF or Ge, which are expensive and not always robust for the target application. (2) The state-of-the-art assembly and packaging mostly uses large metal housings (“TO cans”) for their vacuum capability. The size and price of such housings definitely prevents their integration into extremely compact, mobile devices.We are presenting a technological approach that allows effective scaling of production volumes into high quantities by using a fully wafer-based optical assembly and integration using spherical silicon lens preforms. The complete vacuum packaging and optical alignment are performed as a CMOS post-process in our MEMS cleanroom, using industrial state-of-the-art equipment for 200 mm wafers.Considering a spot thermometer where light just needs to be concentrated, convex lenses can either be manufactured as Fresnel lens or as a spherical lens. Both types can be produced only laboriously with standard Silicon technology using dry etching processes and generally multiple lithography cycles when it comes to larger apertures. For a small F number, the Fresnel lens would rather generate stray light than concentrate incoming radiation on the detector element. Additionally, it is not sufficient to just produce a lens - obtaining a precise spherical shape with defined radius of curvature with good uniformity across the wafer is challenging with etching processes. Expensive equipment would be needed for 100% optical test coverage and any lens failure or parametric deviation would equally bring down the CMOS yield when using wafer-to-wafer bonding.In our paper, a detailed review of the IR packaging solutions, lens materials and their fabrication process will be given. A novel technology platform being developed at Fraunhofer ISIT together with the end user will be presented. At the core of the fabrication process, preformed Si spheres with a defined curvature are used that are subsequently grinded to form multiple plano-convex lenses on the wafer level. The process is a new element in our glass forming process portfolio that already enabled many technological innovations in wafer-level optics. Using spherical preforms results in excellent optical properties for IR spot detectors and eliminates the need for expensive 100% optical testing. Although certain limitations with respect to the pitch and the availability of intermediate sphere sizes exist, a clever design (e.g. focal length adjustment, placement of IR pixels etc.) allows covering a commercially very relevant spot on the IR detector market. Figure 1

Ultrafast Carrier Relaxation Dynamics in Quantum Confined Non-Isotropic Silicon Nanostructures Synthesized by an Inductively Coupled Plasma Process.

To exploit the optoelectronic properties of silicon nanostructures (SiNS) in real devices, it is fundamental to study the ultrafast processes involving the photogenerated charges separation, migration and lifetime after the optical excitation. Ultrafast time-resolved optical measurements provide such information. In the present paper, we report on the relaxation dynamics of photogenerated charge-carriers in ultrafine SiNS synthesized by means of inductively-coupled-plasma process. The carriers’ transient regime was characterized in high fluence regime by using a tunable pump photon energy and a broadband probe pulse with a photon energy ranging from 1.2 eV to 2.8 eV while varying the energy of the pump photons and their polarization. The SiNS consist of Si nanospheres and nanowires (NW) with a crystalline core embedded in a SiOx outer-shell. The NW inner core presents different typologies: long silicon nanowires (SiNW) characterized by a continuous core (with diameters between 2 nm and 15 nm and up to a few microns long), NW with disconnected fragments of SiNW (each fragment with a length down to a few nanometers), NW with a “chaplet-like” core and NW with core consisting of disconnected spherical Si nanocrystals. Most of these SiNS are asymmetric in shape. Our results reveal a photoabsorption (PA) channel for pump and probe parallel polarizations with a maximum around 2.6 eV, which can be associated to non-isotropic ultra-small SiNS and ascribed either to (i) electron absorption driven by the probe from some intermediate mid-gap states toward some empty state above the bottom of the conduction band or (ii) the Drude-like free-carrier presence induced by the direct-gap transition in the their band structure. Moreover, we pointed up the existence of a broadband and long-living photobleaching (PB) in the 1.2–2.0 eV energy range with a maximum intensity around 1.35 eV which could be associated to some oxygen related defect states present at the Si/SiOx interface. On the other hand, this wide spectral energy PB can be also due to both silicon oxide band-tail recombination and small Si nanostructure excitonic transition.

One-Pot Synthesized Biomass C-Si Nanocomposites as an Anodic Material for High-Performance Sodium-Ion Battery.

Aiming at materializing an excellent anodic source material of the high-performance sodium-ion battery (SIB), we fabricated the biomass carbon-silicon (C-Si) nanocomposites by the one-pot synthesis of facile magnesiothermic reduction using brown rice husk ashes. The C-Si nanocomposites displayed an aggregated morphology, where the spherical Si nanoparticles (9 nm on average) and the C nanoflakes were encapsulated and decorated with each other. When utilizing the nanocomposites as an SIB anode, a high initial discharge capacity (i.e., 378 mAh/g at 100 mA/g) and a high reversible capacity (i.e., 122 mAh/g at 200 mA/g) were achieved owing to their enhanced electronic and ionic conductivities. Moreover, the SIB device exhibited a high cyclic stability in its Coulombic efficiency (i.e., 98% after 100 charge-discharge cycles at 200 mA/g). These outstanding results depict that the one-pot synthesized biomass C-Si nanocomposites are beneficial for future green energy-storage technology.

Curvature-Modulated Si Spherical Cap-Like Structure Fabricated by Multistep Ring Edge Etching.

To create approximately spherical structures with curved sidewalls, this paper presents a method for building a series of decreasing slopes along the sidewall of a circular truncated cone. The multistep ring-edge etching technology of first reducing the concentric mask and then cutting the top off to create a mesa shape can be used to form the slopes. This wet-etching method avoids the constraints of crystallographic properties with surfactant-added Tetramethylammonium hydroxide (TMAH), enabling the manufacture of successive given inclination angles, the precise modulation of the spherical curvature by reduction design of concentric masks, and the setting of etching time. The newly approximated spherical Si microstructure patterns can be used for microlenses, quartz crystal resonators, micropulleys, and other applications. The present research is an approach to fabricate advanced microelectromechanical systems (MEMS) curved-surface structures, extending the range of 3D structures fabricated by silicon wet etching.

Gravity and anisotropy effects in the volume determination of Si spheres for the kilogram realisation

The counting of 28Si atoms plays a fundamental role in the realisation of the unit of mass in terms of stipulated values of fundamental physical constants. In this realisation, the measurement of the volume of a 28Si sphere is a fundamental step. This paper reports a finite element analysis of the self-weight effect on the volume determination, taking the crystal anisotropy into account. The sphere volume might be overestimated from 0.3 × 10−9 to 5.1 × 10−9 (relative terms), depending on the crystal orientation and measurement procedure.

Comparative Study of Light Guiding by Freestanding Linear Chains of Spherical Au and Si Nanoparticles

Electromagnetic energy guiding by free‐standing straight finite chains of Au and Si spherical nanoparticles is comparatively studied on the basis of a system of integral equations for self‐consistent currents excited inside particles. Self‐consistent currents are given in terms of an electric field T‐scattering tensor (dyadic) operator of a single particle of any shape. Simplifying the T‐scattering operator, the equations system is resolved analytically in the nearest‐neighbor coupling approximation. Interactions beyond the nearest neighbors are accounted for by the perturbative theory. It is shown that electromagnetic excitation propagates along a chain of coupled particles without radiation losses in the form of a dark mode. The resonant conditions for the coupling parameter yield the frequency of the dark mode and the corresponding radius of the particles. As a result, unlike Au chains, no long‐range electromagnetic energy transfer was revealed along the Si chains. Physically, in both cases of Au and Si spheres, the resonant frequencies fall within the bands of the corresponding electric dipole Mie resonances. However, the positive value of the real part of the Si refraction index at the resonant frequency causes exponential excitation currents decreasing with the particle number.

Soft Magnetic Properties of Fe-6.5wt%Si/SrFe12O19 Composites

Fe-6.5wt%Si/SrFe12O19 composites with different SrFe12O19 contents are prepared and their soft magnetic properties are investigated. SEM morphology shows that Fe-6.5wt%Si spheres are separated by SrFe12O19 small powders. Magnetic hysteresis loop measurement indicates that the saturation magnetization of all composites is more than 200 emu/g. Magnetic loss analysis reveals that Fe-6.5wt%Si/SrFe12O19 composites have excellent loss characteristics and SrFe12O19 can be used as insulating agent in SMCs.

Magnetoelectric Plasma Preparation of Silicon-Carbon Nanocomposite as Anode Material for Lithium Ion Batteries

A high-performance silicon-carbon nanocomposite facilely prepared by one-step magnetoelectric plasma pyrolysis of the mixture of methane, silane, and hydrogen is proposed for lithium-ion batteries. The ratio of silane, methane, and hydrogen was studied to optimize the properties of the composite. When the ratio of hydrogen/silane/methane is 1:1:3, the composite is composed of spherical Si nanoparticles that uniformly attach to the surface of the tremelliform carbon nanosheets framework, in which the tremelliform carbon nanosheets can effectively resist the volumetric change of the Si nanoparticles during the cycles and serve as electronic channels. The silicon-carbon nanocomposite exhibits a high reversible capacity (1007 mAh g−1 after 50 cycles), a low charge transfer resistance, and an excellent rate performance. In addition, the proposed process for synthesizing silicon-carbon nanocomposite without expensive materials or toxic reagents is an environmentally friendly and cost-effective method for mass production.

Geometrical Constraints of Poly(diethylene glycol methyl ether methacrylate) Brushes on Spherical Nanoparticles and Cylindrical Nanowires: Implications for Thermoresponsive Brushes on Nanoobjects

We report on the polymerization kinetics of thermoresponsive poly(diethylene glycol methyl ether methacrylate) (PDEGMA) brushes, which are used in novel cell release coating, on curved spherical si...