Showing papers on "Silicon published in 2013"
TL;DR: Infiltration of a conducting polymer hydrogel into Si-based anodes results in a well-connected three-dimensional network structure consisting of Si nanoparticles conformally coated by the conducting polymer, demonstrating a cycle life of 5,000 cycles with over 90% capacity retention at current density.
Abstract: Silicon has a high-specific capacity as an anode material for Li-ion batteries, and much research has been focused on overcoming the poor cycling stability issue associated with its large volume changes during charging and discharging processes, mostly through nanostructured material design. Here we report incorporation of a conducting polymer hydrogel into Si-based anodes: the hydrogel is polymerized in-situ, resulting in a well-connected three-dimensional network structure consisting of Si nanoparticles conformally coated by the conducting polymer. Such a hierarchical hydrogel framework combines multiple advantageous features, including a continuous electrically conductive polyaniline network, binding with the Si surface through either the crosslinker hydrogen bonding with phytic acid or electrostatic interaction with the positively charged polymer, and porous space for volume expansion of Si particles. With this anode, we demonstrate a cycle life of 5,000 cycles with over 90% capacity retention at current density of 6.0 A g(-1).
1,181 citations
TL;DR: Various fundamental studies that have been conducted to understand structural and volumetric changes, stress evolution, mechanical properties, and fracture behavior of nanostructured Si anodes for lithium-ion batteries are reviewed and the reaction process of Si is compared to other novel anode materials.
Abstract: Alloying anodes such as silicon are promising electrode materials for next-generation high energy density lithium-ion batteries because of their ability to reversibly incorporate a high concentration of Li atoms. However, alloying anodes usually exhibit a short cycle life due to the extreme volumetric and structural changes that occur during lithium insertion/extraction; these transformations cause mechanical fracture and exacerbate side reactions. To solve these problems, there has recently been significant attention devoted to creating silicon nanostructures that can accommodate the lithiation-induced strain and thus exhibit high Coulombic efficiency and long cycle life. In parallel, many experiments and simulations have been conducted in an effort to understand the details of volumetric expansion, fracture, mechanical stress evolution, and structural changes in silicon nanostructures. The fundamental materials knowledge gained from these studies has provided guidance for designing optimized Si electrode structures and has also shed light on the factors that control large-volume change solid-state reactions. In this paper, we review various fundamental studies that have been conducted to understand structural and volumetric changes, stress evolution, mechanical properties, and fracture behavior of nanostructured Si anodes for lithium-ion batteries and compare the reaction process of Si to other novel anode materials.
1,134 citations
TL;DR: By combining this state-of-the-art photoanode with an earth-abundant cobalt phosphate water-oxidation catalyst and a double- or single-junction amorphous Si solar cell in a tandem configuration, stable short-circuit water-splitting photocurrents of ~4 and 3 mA cm(-2) are achieved under 1 sun illumination.
Abstract: The photoactivity of metal oxide electrodes for water splitting is often limited by poor charge separation. Abdi et al. improve the solar-to-hydrogen efficiency in a hybrid device that comprises a gradient-doped bismuth vanadate photoanode and a double-junction amorphous silicon tandem solar cell.
1,126 citations
TL;DR: It is shown that directivity of the far-field radiation pattern of single silicon spheres can be strongly dependent on the light wavelength and the nanoparticle size.
Abstract: Directional light scattering by spherical silicon nanoparticles in the visible spectral range is experimentally demonstrated for the first time. These unique optical properties arise because of simultaneous excitation and mutual interference of magnetic and electric dipole resonances inside a single nanosphere. Such behaviour is similar to Kerker's-type scattering by hypothetic magneto-dielectric particles predicted theoretically three decades ago. Here we show that directivity of the far-field radiation pattern of single silicon spheres can be strongly dependent on the light wavelength and the nanoparticle size. For nanoparticles with sizes ranging from 100 to 200 nm, forward-to-backward scattering ratio above six can be experimentally obtained, making them similar to 'Huygens' sources. Unique optical properties of silicon nanoparticles make them promising for design of novel low-loss visible- and telecom-range metamaterials and nanoantenna devices.
1,006 citations
TL;DR: In this paper, a CMOS compatible graphene/silicon-heterostructure photodetector formed by integrating graphene onto a silicon optical waveguide on silicon-on-insulator and operating in the near and mid-infrared regions is demonstrated.
Abstract: A CMOS-compatible graphene/silicon-heterostructure photodetector formed by integrating graphene onto a silicon optical waveguide on silicon-on-insulator and operating in the near- and mid-infrared regions is demonstrated. A responsivity as high as 0.13 A W−1 is obtained at a bias of 1.5 V for 2.75-μm light at room temperature.
739 citations
TL;DR: In this article, a metal-insulator-semiconductor photo-anode for photoelectrochemical (PEC) water oxidation in both aqueous potassium hydroxide (KOH, pH = 14) and aaqueous borate buffer (pH = 9.5) solutions is presented.
Abstract: Silicon’s sensitivity to corrosion has hindered its use in photoanode applications. We found that deposition of a ~2-nanometer nickel film on n-type silicon (n-Si) with its native oxide affords a high-performance metal-insulator-semiconductor photoanode for photoelectrochemical (PEC) water oxidation in both aqueous potassium hydroxide (KOH, pH = 14) and aqueous borate buffer (pH = 9.5) solutions. The Ni film acted as a surface protection layer against corrosion and as a nonprecious metal electrocatalyst for oxygen evolution. In 1 M aqueous KOH, the Ni/n-Si photoanodes exhibited high PEC activity with a low onset potential (~1.07 volts versus reversible hydrogen electrode), high photocurrent density, and durability. The electrode showed no sign of decay after ~80 hours of continuous PEC water oxidation in a mixed lithium borate–potassium borate electrolyte. The high photovoltage was attributed to a high built-in potential in a metal-insulator-semiconductor–like device with an ultrathin, incomplete screening Ni/NiO x layer from the electrolyte.
601 citations
TL;DR: The field of plasma etching is reviewed in this paper, where basic principles related to plasma etch such as evaporation rates and Langmuir-Hinshelwood adsorption are introduced.
Abstract: The field of plasma etching is reviewed. Plasma etching, a revolutionary extension of the technique of physical sputtering, was introduced to integrated circuit manufacturing as early as the mid 1960s and more widely in the early 1970s, in an effort to reduce liquid waste disposal in manufacturing and achieve selectivities that were difficult to obtain with wet chemistry. Quickly, the ability to anisotropically etch silicon, aluminum, and silicon dioxide in plasmas became the breakthrough that allowed the features in integrated circuits to continue to shrink over the next 40 years. Some of this early history is reviewed, and a discussion of the evolution in plasma reactor design is included. Some basic principles related to plasma etching such as evaporation rates and Langmuir–Hinshelwood adsorption are introduced. Etching mechanisms of selected materials, silicon, silicon dioxide, and low dielectric-constant materials are discussed in detail. A detailed treatment is presented of applications in current silicon integrated circuit fabrication. Finally, some predictions are offered for future needs and advances in plasma etching for silicon and nonsilicon-based devices.
539 citations
TL;DR: The unique wetness-resistant adhesion provided by the catechol groups allows the silicon nanoparticle electrodes to maintain their structure throughout the repeated volume expansion and shrinkage during lithiation cycling, thus facilitating substantially improved specific capacities and cycle lives of lithium-ion batteries.
Abstract: Conjugation of mussel-inspired catechol groups to various polymer backbones results in materials suitable as silicon anode binders. The unique wetness-resistant adhesion provided by the catechol groups allows the silicon nanoparticle electrodes to maintain their structure throughout the repeated volume expansion and shrinkage during lithiation cycling, thus facilitating substantially improved specific capacities and cycle lives of lithium-ion batteries.
529 citations
TL;DR: In this article, a detailed study of the doping-less tunnel field effect transistor (TFET) on a thin intrinsic silicon film using charge plasma concept was performed using calibrated simulations.
Abstract: Using calibrated simulations, we report a detailed study of the doping-less tunnel field effect transistor (TFET) on a thin intrinsic silicon film using charge plasma concept. Without the need for any doping, the source and drain regions are formed using the charge plasma concept by choosing appropriate work functions for the source and drain metal electrodes. Our results show that the performance of the doping-less TFET is similar to that of a corresponding doped TFET. The doping-less TFET is expected to be free from problems associated with random dopant fluctuations. Furthermore, fabrication of doping-less TFET does not require a high-temperature doping/annealing processes and therefore cuts down the thermal budget, opening up possibilities for fabricating TFETs on single crystal silicon-on-glass substrates formed by wafer scale epitaxial transfer.
433 citations
TL;DR: In this paper, high-strained germanium on silicon samples with up to 3.1% uniaxial strain is fabricated and then investigated by Raman spectroscopy.
Abstract: Highly strained germanium on silicon samples with up to 3.1% uniaxial strain are fabricated and then investigated by Raman spectroscopy. During optical pumping, changes in both the emission wavelength and output power are observed, indicating that bandgap modification and optical gain are occurring.
401 citations
TL;DR: A novel kind of self-supporting binder-free silicon-based anodes via the encapsulation of silicon nanowires with dual adaptable apparels (overlapped graphene (G) sheaths and reduced graphene oxide (RGO) overcoats) are developed.
Abstract: Silicon has been touted as one of the most promising anode materials for next generation lithium ion batteries. Yet, how to build energetic silicon-based electrode architectures by addressing the structural and interfacial stability issues facing silicon anodes still remains a big challenge. Here, we develop a novel kind of self-supporting binder-free silicon-based anodes via the encapsulation of silicon nanowires (SiNWs) with dual adaptable apparels (overlapped graphene (G) sheaths and reduced graphene oxide (RGO) overcoats). In the resulted architecture (namely, SiNW@G@RGO), the overlapped graphene sheets, as adaptable but sealed sheaths, prevent the direct exposure of encapsulated silicon to the electrolyte and enable the structural and interfacial stabilization of silicon nanowires. Meanwhile, the flexible and conductive RGO overcoats accommodate the volume change of embedded SiNW@G nanocables and thus maintain the structural and electrical integrity of the SiNW@G@RGO. As a result, the SiNW@G@RGO elec...
TL;DR: This work employs first-principles calculations to investigate the interaction of Li with Si in model electrodes of free-standing single-layer and double-layer silicene, and identifies strong binding sites for Li, calculates the energy barriers accompanying Li diffusion, and presents the findings in the context of previous theoretical work related to Li-ion storage in other structural forms of silicon.
Abstract: The energy density of Li-ion batteries depends critically on the specific charge capacity of the constituent electrodes. Silicene, the silicon analogue to graphene, being of atomic thickness could serve as high-capacity host of Li in Li-ion secondary batteries. In this work, we employ first-principles calculations to investigate the interaction of Li with Si in model electrodes of free-standing single-layer and double-layer silicene. More specifically, we identify strong binding sites for Li, calculate the energy barriers accompanying Li diffusion, and present our findings in the context of previous theoretical work related to Li-ion storage in other structural forms of silicon: the bulk and nanowires. The binding energy of Li is ∼2.2 eV per Li atom and shows small variation with respect to Li content and silicene thickness (one or two layers) while the barriers for Li diffusion are relatively low, typically less than 0.6 eV. We use our theoretical findings to assess the suitability of two-dimensional sil...
TL;DR: A simple experiment demonstrates that room-temperature thermal transport in Si significantly deviates from the diffusion model already at micron distances, indicating a transition from the diffusive to the ballistic transport regime for the low-frequency part of the phonon spectrum.
Abstract: The "textbook" phonon mean free path of heat carrying phonons in silicon at room temperature is ∼40 nm. However, a large contribution to the thermal conductivity comes from low-frequency phonons with much longer mean free paths. We present a simple experiment demonstrating that room-temperature thermal transport in Si significantly deviates from the diffusion model already at micron distances. Absorption of crossed laser pulses in a freestanding silicon membrane sets up a sinusoidal temperature profile that is monitored via diffraction of a probe laser beam. By changing the period of the thermal grating we vary the heat transport distance within the range ∼1-10 μm. At small distances, we observe a reduction in the effective thermal conductivity indicating a transition from the diffusive to the ballistic transport regime for the low-frequency part of the phonon spectrum.
TL;DR: Hollow porous SiO2 nanocubes have been prepared via a two-step hard-template process and evaluated as electrode materials for lithium-ion batteries and found that the formation of irreversible or reversible lithium silicates in the anodes determines the capacity of a deep-cycle battery.
Abstract: The high theoretical capacity and low discharge potential of silicon have attracted much attention on Si-based anodes. Herein, hollow porous SiO2 nanocubes have been prepared via a two-step hard-template process and evaluated as electrode materials for lithium-ion batteries. The hollow porous SiO2 nanocubes exhibited a reversible capacity of 919 mAhg−1 over 30 cycles. The reasonable property could be attributed to the unique hollow nanostructure with large volume interior and numerous crevices in the shell, which could accommodate the volume change and alleviate the structural strain during Li ions' insertion and extraction, as well as allow rapid access of Li ions during charge/discharge cycling. It is found that the formation of irreversible or reversible lithium silicates in the anodes determines the capacity of a deep-cycle battery, fast transportation of Li ions in hollow porous SiO2 nanocubes is beneficial to the formation of Li2O and Si, contributing to the high reversible capacity.
TL;DR: The antireflection treatment was realized by a simple spin-coating process, which significantly increased the short-circuit current density and the incident photon-to-electron conversion efficiency to about 90% across the visible range.
Abstract: Carbon nanotube-Si and graphene-Si solar cells have attracted much interest recently owing to their potential in simplifying manufacturing process and lowering cost compared to Si cells. Until now, the power conversion efficiency of graphene-Si cells remains under 10% and well below that of the nanotube-Si counterpart. Here, we involved a colloidal antireflection coating onto a monolayer graphene-Si solar cell and enhanced the cell efficiency to 14.5% under standard illumination (air mass 1.5, 100 mW/cm2) with a stable antireflection effect over long time. The antireflection treatment was realized by a simple spin-coating process, which significantly increased the short-circuit current density and the incident photon-to-electron conversion efficiency to about 90% across the visible range. Our results demonstrate a great promise in developing high-efficiency graphene-Si solar cells in parallel to the more extensively studied carbon nanotube-Si structures.
TL;DR: Eliminating isotopic impurities from the host material improves coherence times, as observed for qubits, based on the nuclear spin of neutral P donors in Si, and shows that a coherent spin superposition can be cycled from 4.2 kelvin to room temperature and back, and a cryogenic coherence time of 3 hours is reported.
Abstract: Quantum memories capable of storing and retrieving coherent information for extended times at room temperature would enable a host of new technologies. Electron and nuclear spin qubits using shallow neutral donors in semiconductors have been studied extensively but are limited to low temperatures (≲10 kelvin); however, the nuclear spins of ionized donors have the potential for high-temperature operation. We used optical methods and dynamical decoupling to realize this potential for an ensemble of phosphorous-31 donors in isotopically purified silicon-28 and observed a room-temperature coherence time of over 39 minutes. We further showed that a coherent spin superposition can be cycled from 4.2 kelvin to room temperature and back, and we report a cryogenic coherence time of 3 hours in the same system.
TL;DR: The device design principles presented here balance the photonic and electronic effects together and are an important step to realizing highly efficient, thin Si and other types of thin solar cells.
Abstract: Thinner Si solar cells with higher efficiency can make a Si photovoltaic system a cost-effective energy solution, and nanostructuring has been suggested as a promising method to make thin Si an effective absorber. However, thin Si solar cells with nanostructures are not efficient because of severe Auger recombination and increased surface area, normally yielding 80% EQEs at wavelengths from 400 to 800 nm in a sub-10-μm-thick Si solar cell, resulting in 13.7% power conversion efficiency. This significant improvement was achieved with an all-back-contact design preventing Auger recombination and with a nanocone structure having less surface area than any other nanostructures for solar cells. The device design principles presented here balance the photonic and electronic effects together and are an important step to realizing highly efficient, thin Si and other types of thin solar cells.
TL;DR: By 3D wrapping of silicon nanoparticles/single-wall carbon nanotubes with conducting polymer nanostructures, a greatly improved cycling performance is achieved with reversible discharge capacity over 1600 mAh/g and 86% capacity retention over 1000 cycles at the current rate of 3.3 A/g.
Abstract: Silicon is considered one of the most promising anode materials for high-performance Li-ion batteries due to its 4200 mAh/g theoretical specific capacity, relative abundance, low cost, and environmental benignity. However, silicon experiences a dramatic volume change (∼300%) during full charge/discharge cycling, leading to severe capacity decay and poor cycling stability. Here, we report a three-dimensional (3D) ternary silicon nanoparticles/conducting polymer/carbon nanotubes hybrid anode material for Li-ion batteries. The hierarchical conductive hydrogel framework with carbon nanotubes as the electronic fortifier offers a continuous electron transport network and high porosity to accommodate the volume expansion of Si particles. By 3D wrapping of silicon nanoparticles/single-wall carbon nanotubes with conducting polymer nanostructures, a greatly improved cycling performance is achieved with reversible discharge capacity over 1600 mAh/g and 86% capacity retention over 1000 cycles at the current rate of 3...
TL;DR: In this article, the switching stability of a Si-doped HfO2 film under bipolar pulsed-field operation was investigated and a de-pinning of domains due to reduction of the defect concentration at bottom electrode interface was suggested as the origin of the wake-up.
Abstract: Hafnium oxide based ferroelectric thin films have shown potential as a promising alternative material for non-volatile memory applications This work reports the switching stability of a Si-doped HfO2 film under bipolar pulsed-field operation High field cycling causes a “wake-up” in virgin “pinched” polarization hysteresis loops, demonstrated by an enhancement in remanent polarization and a shift of negative coercive voltage The rate of wake-up is accelerated by either reducing the frequency or increasing the amplitude of the cycling field We suggest de-pinning of domains due to reduction of the defect concentration at bottom electrode interface as origin of the wake-up
TL;DR: In this paper, the pore structure and interfacial transition zone (ITZ) of concrete incorporating slag, silica fume and metakaolin were analyzed in 28 and 180 days.
TL;DR: In this article, an optical model that combines a ray-tracing algorithm and a thin-film simulator reveals why parallel-polarized light arriving at the rear surface at oblique incidence excites surface plasmons in the metal reflector can exceed the absorption in the TCO layer itself.
Abstract: Silicon heterojunction solar cells have record-high open-circuit voltages but suffer from reduced short-circuit currents due in large part to parasitic absorption in the amorphous silicon, transparent conductive oxide (TCO), and metal layers. We previously identified and quantified visible and ultraviolet parasitic absorption in heterojunctions; here, we extend the analysis to infrared light in heterojunction solar cells with efficiencies exceeding 20%. An extensive experimental investigation of the TCO layers indicates that the rear layer serves as a crucial electrical contact between amorphous silicon and the metal reflector. If very transparent and at least 150 nm thick, the rear TCO layer also maximizes infrared response. An optical model that combines a ray-tracing algorithm and a thin-film simulator reveals why: parallel-polarized light arriving at the rear surface at oblique incidence excites surface plasmons in the metal reflector, and this parasitic absorption in the metal can exceed the absorption in the TCO layer itself. Thick TCO layers—or dielectric layers, in rear-passivated diffused-junction silicon solar cells—reduce the penetration of the evanescent waves to the metal, thereby increasing internal reflectance at the rear surface. With an optimized rear TCO layer, the front TCO dominates the infrared losses in heterojunction solar cells. As its thickness and carrier density are constrained by anti-reflection and lateral conduction requirements, the front TCO can be improved only by increasing its electron mobility. Cell results attest to the power of TCO optimization: With a high-mobility front TCO and a 150-nm-thick, highly transparent rear ITO layer, we recently reported a 4-cm2 silicon heterojunction solar cell with an active-area short-circuit current density of nearly 39 mA/cm2 and a certified efficiency of over 22%.
01 Jan 2013
TL;DR: In this paper, a simple experiment demonstrating that room-temperature thermal transport in Si significantly deviates from the diffusion model already at micron distances is presented, indicating a transition from the diffusive to the ballistic transport regime for the low-frequency part of the phonon spectrum.
Abstract: The "textbook" phonon mean free path of heat carrying phonons in silicon at room temperature is ∼40 nm. However, a large contribution to the thermal conductivity comes from low-frequency phonons with much longer mean free paths. We present a simple experiment demonstrating that room-temperature thermal transport in Si significantly deviates from the diffusion model already at micron distances. Absorption of crossed laser pulses in a freestanding silicon membrane sets up a sinusoidal temperature profile that is monitored via diffraction of a probe laser beam. By changing the period of the thermal grating we vary the heat transport distance within the range ∼1-10 μm. At small distances, we observe a reduction in the effective thermal conductivity indicating a transition from the diffusive to the ballistic transport regime for the low-frequency part of the phonon spectrum.
TL;DR: In this article, a low-loss and wavelength insensitive Y-junction for submicron silicon waveguides was proposed using FDTD and particle swarm optimization (PSO).
Abstract: A compact, low-loss and wavelength insensitive Y-junction for submicron silicon waveguides. The design was performed using FDTD and particle swarm optimization (PSO). The device was fabricated in a 248 nm CMOS line. Measured average insertion loss is 0.28±0.02 dB across an 8-inch wafer. The device footprint is less than 1.2 μm×2 μm, orders of magnitude smaller than MMI and directional couplers.
TL;DR: In this paper, the authors present a direct preparation of porous silicon nanoparticles as a new kind of nanostructured silicon using a novel two-step approach combining controlled boron doping and facile electroless etching.
Abstract: Nanostructured silicon has generated significant excitement for use as the anode material for lithium-ion batteries; however, more effort is needed to produce nanostructured silicon in a scalable fashion and with good performance. Here, we present a direct preparation of porous silicon nanoparticles as a new kind of nanostructured silicon using a novel two-step approach combining controlled boron doping and facile electroless etching. The porous silicon nanoparticles have been successfully used as high performance lithium-ion battery anodes, with capacities around 1,400 mA·h/g achieved at a current rate of 1 A/g, and 1,000 mA·h/g achieved at 2 A/g, and stable operation when combined with reduced graphene oxide and tested over up to 200 cycles. We attribute the overall good performance to the combination of porous silicon that can accommodate large volume change during cycling and provide large surface area accessible to electrolyte, and reduced graphene oxide that can serve as an elastic and electrically conductive matrix for the porous silicon nanoparticles.
TL;DR: It is shown that LiFSI allows avoiding the fluorination process of the silicon particles surface upon long-term cycling, which is observed with the common salt LiPF6 and the favorable interactions between the binder and the active material surface are preserved.
Abstract: Silicon is a very good candidate for the next generation of negative electrodes for Li-ion batteries, due to its high rechargeable capacity. An important issue for the implementation of silicon is ...
TL;DR: It is demonstrated that size-separation of ncSi leads to drastically improved lifetimes of the devices and much less sensitivity of the emission wavelength to the applied drive voltage.
Abstract: We present highly efficient electroluminescent devices using size-separated silicon nanocrystals (ncSi) as light emitting material. The emission color can be tuned from the deep red down to the yellow-orange spectral region by using very monodisperse size-separated nanoparticles. High external quantum efficiencies up to 1.1% as well as low turn-on voltages are obtained for red emitters. In addition, we demonstrate that size-separation of ncSi leads to drastically improved lifetimes of the devices and much less sensitivity of the emission wavelength to the applied drive voltage.
TL;DR: Taking advantage of the interconnected nanoporous structure naturally existing in rice husk, the converted silicon exhibits excellent electrochemical performance as a lithium battery anode, suggesting that rice husks can be a massive resource for use in high-capacity lithium battery negative electrodes.
Abstract: The rice husk is the outer covering of a rice kernel and protects the inner ingredients from external attack by insects and bacteria. To perform this function while ventilating air and moisture, rice plants have developed unique nanoporous silica layers in their husks through years of natural evolution. Despite the massive amount of annual production near 108 tons worldwide, so far rice husks have been recycled only for low-value agricultural items. In an effort to recycle rice husks for high-value applications, we convert the silica to silicon and use it for high-capacity lithium battery anodes. Taking advantage of the interconnected nanoporous structure naturally existing in rice husks, the converted silicon exhibits excellent electrochemical performance as a lithium battery anode, suggesting that rice husks can be a massive resource for use in high-capacity lithium battery negative electrodes.
TL;DR: The electro-optical properties of thin barium titanate films epitaxially grown on silicon substrates are reported, and a large effective Pockels coefficient is extracted, five times larger than in the current standard material for electro- optical devices, lithium niobate.
Abstract: The development of silicon photonics could greatly benefit from the linear electro-optical properties, absent in bulk silicon, of ferroelectric oxides, as a novel way to seamlessly connect the electrical and optical domain. Of all oxides, barium titanate exhibits one of the largest linear electro-optical coefficients, which has however not yet been explored for thin films on silicon. Here we report on the electro-optical properties of thin barium titanate films epitaxially grown on silicon substrates. We extract a large effective Pockels coefficient of r(eff) = 148 pm V(-1), which is five times larger than in the current standard material for electro-optical devices, lithium niobate. We also reveal the tensor nature of the electro-optical properties, as necessary for properly designing future devices, and furthermore unambiguously demonstrate the presence of ferroelectricity. The integration of electro-optical active films on silicon could pave the way towards power-efficient, ultra-compact integrated devices, such as modulators, tuning elements and bistable switches.
TL;DR: In this review, the merits of using porous silicon for anodes through both theoretical and experimental study are discussed and recent progress in the preparation of porous silicon through the template-assisted approach and the non-template approach are highlighted.
Abstract: Silicon is of great interest for use as the anode material in lithium-ion batteries due to its high capacity. However, certain properties of silicon, such as a large volume expansion during the lithiation process and the low diffusion rate of lithium in silicon, result in fast capacity degradation in limited charge/discharge cycles, especially at high current rate. Therefore, the use of silicon in real battery applications is limited. The idea of using porous silicon, to a large extent, addresses the above-mentioned issues simultaneously. In this review, we discuss the merits of using porous silicon for anodes through both theoretical and experimental study. Recent progress in the preparation of porous silicon through the template-assisted approach and the non-template approach have been highlighted. The battery performance in terms of capacity and cyclability of each structure is evaluated.
TL;DR: This investigation suggests that established industrial processes could be adaptable to the production of battery active materials that require sophisticated nanostructures as well as large quantity syntheses.
Abstract: Nanostructured silicon electrodes have shown great potential as lithium ion battery anodes because they can address capacity fading mechanisms originating from large volume changes of silicon alloys while delivering extraordinarily large gravimetric capacities. Nonetheless, synthesis of well-defined silicon nanostructures in an industrially adaptable scale still remains as a challenge. Herein, we adopt an industrially established spray drying process to enable scalable synthesis of silicon–carbon composite particles in which silicon nanoparticles are embedded in porous carbon particles. The void space existing in the porous carbon accommodates the volume expansion of silicon and thus addresses the chronic fading mechanisms of silicon anodes. The composite electrodes exhibit excellent electrochemical performance, such as 1956 mAh/g at 0.05C rate and 91% capacity retention after 150 cycles. Moreover, the spray drying method requires only 2 s for the formation of each particle and allows a production capabil...