Embedded Si Nanoparticles Research Articles

High-efficiency silicon metasurface mirror on a sapphire substrate

For a possible implementation of high-efficiency Si-nanosphere metasurface mirrors functioning at telecom wavelengths in future gravitational wave detectors, exact dimensional and configuration parameters of the total system, including substrate and protective coating, have to be determined a priori. The reflectivity of such multi-layer metasurfaces with embedded Si nanoparticles and their potential limitations need to be investigated. Here we present the results on how the substrate and protective layer influence optical properties and demonstrate how dimensional and material characteristics of the structure alter light reflectivity. Additionally, we consider the impact of manufacturing imperfections, such as fluctuations of Si nanoparticle sizes and their exact placement, on the metasurface reflectivity. Finally, we demonstrate how high reflectivity of the system can be preserved under variations of the protective layer thickness, incident angle of light, and its polarization.

Graphene oxide microrolls as high- content Si carriers boosting Li-ion storage

As attractive anode materials of lithium-ion batteries, both microsized and nanosized silicon particles have been investigated widely, but each has lots of insurmountable problems to restrict their practical applications. In this work, combining the advantages of microsized and nanosized Si particles, we reported a new thought for constructing micrometer-sized Si/C particles by embedding Si nanoparticles into graphene oxide (GO)-based mirorolls. Differing to the traditional spherical shape, the resulted Si/C microrolls exhibit a unique elastic coil structure with opening ends, facilitating the stress buffer and fast charge diffusion. Besides, in order to maintain the stability of Si nanoparticles in microrolls, we chose the elastic and deformable liquid metal (LM) as the “cloth”, and sodium alginate (SA) as the “thread”, successfully tailor a novel “tight suit” for each Si nanoparticle by a facile self-assembly process. Thanks to the double protection of the conductive-elastic LM-SA coating and the microroll architecture, the resulted Si@LM-SA@GO microroll anode not only has a high Si content of 69 %, a high tap density of 0.62 g cm−3 and a high initial coulombic efficiency of 85.1 %, but also exhibits a superior volumetric capacity of 2506 mAh cm−3, and a superior cycling performance of 660 mAh cm−3 after 500 cycles at 2 A g−1. The full cell constructed using a LiNiCoMnO2 cathode can achieve a high reversible capacity of 150 mAh g−1 at 1C after 250 cycles, delivering a high-energy density of 510 Wh kg−1.

“Sticky” carbon coating enables high-area-capacity lithium storage of silicon-graphitic carbon hybrid

Pulverization and surface instability have been identified as the main impediments to the application of Si anodes in high-energy lithium-ion batteries (LIBs). In this study, a Si-graphitic carbon hybrid (SiG) is created via embedding Si nanoparticles in between expanding graphite interlayers, thus to be adopted as a model system to unravel structure-properties relations for LIBs applications. We explore the impact of artificial surface coating layers on the lithium cycling performance of SiG particles. In comparison with native SiG and carbon-coated SiG (CC-SiG), we find that the “sticky-carbon” coating, i.e., an epoxy-rich layer on top of the carbon coating, gave rise to superior cycle performance. In the “sticky carbon” coated SiG (SCC-SiG), the surface chemistry appears to have a pivotal role in both alleviating electrode disintegration and forming a favorable SEI rich in fluorine-polymers. These positive findings are examined in electrodes with mass loading ranging from 1.0 to 5.0 mg/cm2, achieving area capacities up to ∼5.0 mAh/cm2. A full cell adopting >6 mg/cm2 LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode and SCC-SiG delivers stable cycling performances. It is hence unraveled that the carbon coating layer with reactive surface groups on the top is an unrecognized key for wide range of Si-based anodes.

Near-infrared emission in Er:ZnO thin films with embedded Si nanoparticles synthesized by ion implantation

Er-doped ZnO thin films on a SiO2/Si substrate were fabricated by radio frequency magnetron sputtering, in which embedded Si nanoparticles (NPs) were formed by ion implantation and subsequent thermal annealing. The effects of Si NPs on the Er photoluminescence (PL) at 1.54 μm were investigated. In addition to the typical emission at 1.54 μm from Er3+, a new 1.16-μm emission peak was also observed after a thermal treatment. Further annealing resulted in shift of emission intensity between the 1.16- and 1.54-μm luminescence features. The observed Si nanoparticles (NPs) were ∼4 nm in diameter. The formation of new components Zn2SiO4 and Er2Si2O7 was also presented in this study. The 1.16-μm luminescence is attributed to the Si NPs, and the suppression of Si NPs related emission is caused by consumption of Si in the formation of Er silicate and zinc silicide and the energy transfer between Si NPs and Er3+. The intensity of Er3+ related 1.54-μm PL can be modulated by the Si NPs fabricated by implantation and optimizing the annealing condition.

A simple spray assisted method to fabricate high performance layered graphene/silicon hybrid anodes for lithium-ion batteries

Incorporating silicon (Si) in anodes has shown great promise for the development of high capacity Li-ion batteries (LIBs). Moreover, it is a safe and environmentally benign material, and hence suitable for large-scale manufacturing. However, volumetric expansion of Si particles upon lithiation causes irreversible damage to the anode structure and promotes an unstable solid electrolyte interface (SEI), that cause a rapid capacity drop. The architecture of successful Si-based anodes, therefore, needs to cater to the large volumetric expansion such that the high specific capacity of Si can be taken advantage of without having to worry about the detrimental effects of expansion. In this study, we introduce a simple and cost-effective spray-drying method to fabricate a layered (sandwich-like) anode structure using synthesized Si nanoparticles (NPs) and thermally reduced graphene oxide (rGO). The Si NPs are obtained by the magnesiothermic reduction of SiO2 nanoparticles. Using an original, scalable, and simplistic spraying/drying method, we embedded Si NPs between two coats of strong yet flexible rGO sheets. The sandwich-like structure, which successfully contains the expansion of Si particles, protects the anode from detrimental conditions. With this new and uncomplicated production technique, the rGO-Si-rGO anode after 50 cycles, shows a high specific capacity of 1089 mAhg−1 at 1C with 97% coulombic efficiency and a stable cycling performance at current densities up to 5C.

Excavated carbon with embedded Si nanoparticles for ultrafast lithium storage

Due to their excellent mechanical durability and high electrical conductivity, carbon and silicon composites are potentially suitable anode materials for Li-ion batteries with high capacity and long lifespan. Nevertheless, the limitations of the composites include their poor ionic diffusion at high current densities during cycling, which leads to low ultrafast performance. In the present study, seeking to improve the ionic diffusion using hydrothermal method, electrospinning, and carbonization, we demonstrate the unique design of excavated carbon and silicon composites (EC/Si). The outstanding energy storage performance of EC/Si electrode provides a discharge specific capacity, impressive rate performance, and ultrafast cycling stability.

Uniform Si nanoparticle-embedded nitrogen-doped carbon nanofiber electrodes for lithium ion batteries

Preparing the homogeneous spinnable solutions with highly dispersed Li-electroactive nanoparticles has been of the crucial issues for electrospinning technique to develop nanocomposite with carbon nanofibers, because the particle aggregation can lead to a poor cyclic stability and formation of unstable solid electrolyte interface layers. Herein, we present that the commercial Si nanoparticles (≤50 nm in diameter), with using polyethylene glycol (PEG), are embedded uniformly into nitrogen-doped carbon nanofibers (w-Si@N-CNFs) through a facile electrospinning route, followed by carbonization at 800 °C. The PEG played a critical role as dispersion agent to prevent the aggregation of Si nanoparticles during electrospinning, which successfully leads to the high dispersion and incorporation of Si nanoparticles without any agglomeration on N-CNFs. As anode materials for Li-ion batteries, the electrochemical properties of w-Si@N-CNFs was evaluated and compared to the non-uniform Si@N-CNFs (wo-Si@N-CNFs) that is prepared without PEG. The w-Si@N-CNFs anodes exhibit not only the enhanced Li-storage performances with a high capacity-retention of 66.0% without any drastic capacity fading after 150 cycles at a current density of 200 mA g−1, but also the notable rate performances with a reversible capacity of 1076.8 and 640.8 mA h g−1 at current densities of 100 and 2000 mA g−1, respectively. These results demonstrate that the uniformly embedded Si nanoparticles enhance the electrochemical performances of the Si@carbon nanofibers, which is attributed to the well-dispersed Si nanoparticles surrounded by carbon layers without aggregation, resulted in leading to the formation of stable solid electrolyte interface layers and the alleviation of volume expansion of Si nanoparticles. This simple and cost-effective process is expected as a platform for development of anode materials based on nanoparticles-embedded CNFs nanocomposite along with electrospinning technique.

Building 3D porous, elastic and hydrophilic current collectors: Prolonging the cycling life of Si based anode for lithium ion batteries

Huge volume variation plagued silicon for large-scale application in high energy density lithium ion batteries serving as anodic materials, making active layers cracked or delaminated from current collectors after several cycles. To address this issue, a free-standing 3D porous carbon based current collector with recoverable mechanical robustness is dedicatedly designed and fabricated. Atmospheric pressure Ar plasma jet irradiation is applied to transit its surface wettability from hydrophobic to hydrophilic, making it compatible with the aqueous slurry casting process. Embedding Si nanoparticles without any architecture modification into such a state-of-the-art current collector delivers an excellent reversible capacity (1138mAhg−1), prolonged cycling performance (>400cycles) at the current density of 0.5Ag−1 and low capacity fading rate (<0.09% per cycle). This also provides considerable opportunities as a current collector of choice for the energy storage units in the ever-growing flexible and wearable electronic devices.

Conductive Additive for Si/Mesoporous C Anode in Li-Ion Batteries: Conductive Graphite Vs Carbon Black C65

Silicon exhibits the highest theoretical capacity of 4200 mAh g-1, which is 10 times more than the capacity of graphite. Therefore, Si is a promising candidate for anode in lithium-ion batteries. However, Si has low electrical conductivity (theoretical: 6.7 x 10-4 S cm-1). To reach the high performance anode, the proper conductive additives are still needed in order to improve the electrical conductivity of Si-based anode. Here we investigated the effects of conductive nano-graphite and Carbon Black (CB65) on electrochemical performance of silicon-mesoporous carbon composite anode (Si/MC). The material has been synthesized by pyrolysis of polymer aerogel with embedded Si nanoparticles. The electrode was made by 75% active material, 15% conductive additive, and 10% polyacrylic acid (PAA) binder. The electrochemical characterization using impedance spectroscopy, voltammetry, and galvanostatic charge/discharge tests were conducted for both samples. Impedance spectroscopy showed that Si/MC anode with conductive graphite exhibited lower charge-transfer resistance (Rct ≈ 150 Ω), compared to those with carbon black (Rct ≈ 380 Ω). The collected results showed that the graphite additive improved significantly the electrochemical performance of Si/MC anode. In addition, the thermal and long cycling tests will be demonstrated.

Enabling a high capacity and long cycle life for nano-Si anodes by building a stable solid interface with a Li+-conducting polymer

A new nano-Si/polymer composite with a stable electrochemical interface is synthesized by embedding Si nanoparticles into a Li+-conducting polymer matrix to prevent the direct contact of the Si surface with the electrolyte.

Silicon/carbon composite microspheres with hierarchical core–shell structure as anode for lithium ion batteries

Silicon/carbon composite microspheres with hierarchical core–shell structure were prepared by spray drying polyvinyl alcohol (PVA) solution containing silicon (Si) nanoparticles, followed by surface coating with polyacrylonitrile (PAN) and heat treatment. For the hierarchical structure, the core section (Si/po-C) was composed of PVA-based porous carbon framework and the embedded Si nanoparticles, and the desired Si/po-C@C microspheres were formed by encapsulating the Si/po-C core with PAN-based carbon shell. The Si/po-C@C anode gave rise to stable cycling performances with high capacity and excellent rate capability attributed to the hierarchical structure. The compact PAN-based carbon shell was able to block electrolyte to contact with Si effectively, promoting the formation of stable solid-electrolyte interphase. The porous carbon framework could accommodate the volume change of embedded Si nanoparticles and enhance the internal conductivity.

Annealing Effect on the Structural and Optical properties of SiOx films deposited by HFCVD: Features for its possible use as Optical Sensor

Abstract Non-stoichiometric silicon oxide (SiOx) with embedded Si nanoparticles (Si-nps) shows novel physical characteristic, which permits its use in optoelectronic devices as photodetectors and light emitters. In this work, a detailed analysis of the structural and optical properties of silicon rich oxide films deposited via hot filament chemical vapor deposition is done. SiOx films with different Si content were obtained at different hydrogen flow. FTIR spectra show vibrational bands related to the presence of hydrogen in as-deposited SiOx films. This band is more intense as the hydrogen flow is increased, but disappears after thermal annealing. SiOx films exhibit a broad photoluminiscence (PL) spectra with main peaks at 700 and 750 nm. The PL band at 700 nm is enhanced as the hydrogen content in the SiOx films is increased. XPS spectra show a high Si concentration and a low oxygen concentration in the SiOx films. Transmittance spectra have a shifted to high wavelength after thermal annealing, and optical band gap was from 2.34 to 3.95 eV.

Tunable and stable UV-NIR photoluminescence from annealed SiO_x with Si nanoparticles

We demonstrate stable and tunable light emission in ultraviolet to near infrared regime by using annealed SiOx sample. By adjusting the ratio of Si and O of SiOx, different wavelengths such as ultraviolet, visible and near infrared photoluminescence can be tuned. From the results of transmission electron microscope, various sizes (1~4 nm) of the embedded Si nanoparticles were formed. Nanoparticles with smaller sizes were indeed formed for UV-blue emitting samples and the origin of light emission may be misattributed to the quantum confinement effects. However, we found the efficient and stable light emission in UV-blue regime, with lifetime on the order of nanoseconds, is dominantly from the defects.

Floating substrate luminescence from silicon rich oxide metal-oxide-semiconductor devices

The electro-optical properties of metal-oxide-semiconductor devices with embedded Si nanoparticles in silicon-rich (4at.%) oxide films have been studied. Devices show intense visible continuous luminescence not only in the regular metal-oxide-semiconductor configuration, but when biased via surface electrodes (floating substrate) separated 10μm. Electroluminescence manifests as extremely bright randomly scattered discrete spots on the gate area or the periphery of the devices depending on the bias direction. The mechanism responsible for the surface-electroluminescence has been related to the recombination of electron–hole pairs injected through enhanced current paths within the silicon-rich oxide film.

Synthesis of embedded Si nano-particles using swift heavy ions and its optical properties

ABSTRACTEmbedded Si nano-particles of average size around 5nm were synthesized in an amorphous Si matrix by two stage ion implantation processes. It has been observed that amorphous Si (a-Si) layers were recrystallized using 50 MeV Au ions with enhanced regrowth rate with activation energy in the range of 0.29 eV. During the crystallization process Si nanocrystals were formed in the a-Si layers due to sudden quenching of the molten tracks created by MeV Au ions. The recrystalizations were confirmed by Rutherford backscattering spectrometry-Channeling (RBSC) technique. The structural modification and nanocluster creation that emerged during recrystallization process was observed in high-resolution transmission electron microscopy and photoluminescence (PL) spectroscopy. The PL emission was observed over a broad band of 2.8 – 3.4 eV and centered at 3.25 eV. The Si nano-crystal formation can be explain by a mechanism combining the melting within the ion tracks by thermal spike process and the subsequent recrystallization nucleated from the crystalline sides at the interface.

Role of light and heavy embedded nanoparticles on the thermal conductivity of SiGe alloys

We have used an atomistic {\it ab initio} approach with no adjustable parameters to compute the lattice thermal conductivity of Si$_{0.5}$Ge$_{0.5}$ with a low concentration of embedded Si or Ge nanoparticles of diameters up to 4.4 nm. Through exact Green's function calculation of the nanoparticle scattering rates, we find that embedding Ge nanoparticles in $\text{Si}_{0.5}\text{Ge}_{0.5}$ provides 20% lower thermal conductivities than embedding Si nanoparticles. This contrasts with the Born approximation which predicts an equal amount of reduction for the two cases, irrespective of the sign of the mass difference. Despite these differences, we find that the Born approximation still performs remarkably well, and it permits investigation of larger nanoparticle sizes, up to 60 nm in diameter, not feasible with the exact approach.

Influence of in situ applied ultrasound during Si+ implantation in SiO2 on paramagnetic defect generation

Electron spin resonance (ESR) results are presented on the influence of in situ ultrasound treatment (UST) during implantation at 300 K of Si+ ions into thermal SiO2 on (100)Si before and after subsequent high-temperature (T) annealing (1100 °C) intended to promote the formation of embedded Si nanoparticles. The as-implanted state exhibits high densities of three prominent types of point defects, including the SiO2-specific S and E′γ O-vacancy type centers, and an unknown broad (≈20 G) signal at g≈2.0026 denoted IS. The high-intensity S signal shows demagnetization shape effects, pointing to a distribution of high local density of defects over a thin layer. UST is observed to effectuate a drastic reduction in S and E′γ centers, and elimination of IS beyond detection. This reveals a strong healing influence of in situ transferred ultrasound (US) energy on implantation-induced damage, here quantified and identified on atomic level in terms of mainly intrinsic paramagnetic point defects elimination, viz., Frenkel pair elimination, while all three initial signals disappear. Other types of defects surface after annealing of the non-US treated sample, including the SiO2-specific EX defect signal and Pb-type Si/SiO2 interface centers, the appearance of the latter providing direct ESR evidence for crystallization of the excess Si nanoparticles. The influence of the UST healing effect is kept up after subsequent annealing, now resulting in the absence of virtually all ESR-active centers. The drop in Pb-type centers below the detection level in the UST annealed sample indicates improvement of the nanocrystalline-Si/SiO2 interface quality. The combination of UST with high-T annealing emerges as a highly efficient means to eradicate ion implantation damage in terms of intrinsic point defects.

Electrospun carbon nanofibers containing silicon particles as an energy-storage medium

A new energy-storage material has been developed by embedding Si nanoparticles as an alloying medium in electrospun carbon nanofibers. Anodes made from these carbon/Si composite nanofibers combine the advantages of both carbon (long cycle life) and Si (high lithium-storage capacity). They exhibit good electrochemical performance in terms of large reversible capacity, relatively good capacity retention and excellent rate capability upon insertion/extraction of lithium. As a result, they are promising anode candidates for storing energy in high performance batteries.

Ellipsometric characterization of SiO x films with embedded Si nanoparticles

In this work we present results on the ellipsometric study of SiO x films in the spectral range of 280–820 nm. The films were deposited by vacuum thermal evaporation of SiO onto Si substrates heated at 150 °C. To stimulate the formation of silicon clusters in the oxide matrix the films were annealed at temperatures 700, 1000 and 1100 °C in argon for 5, 15 and 30 min. By applying the Bruggeman effective-medium approximation theory and using multiple-layer optical models, from the ellipsometric data analysis the thickness, complex refractive index and composition of the films, as well as the size of the embedded Si nanocrystallites have been determined. Atomic-force microscopy imaging showed a very smooth surface, the roughness value of which correlated well with the top-layer thickness, determined from the ellipsometric data analysis.

The passive optical properties of a silicon nanoparticle-embedded benzocyclobutenepolymer waveguide

The passive optical properties of a silicon nanoparticle-embedded benzocyclobutene (BCB)waveguide were investigated. The silicon nanoparticles, of a size varying from 6 to 25 nm,were prepared by vapor condensation. The transmission modes and losses wereexamined by the prism coupler and cut-back methods. A He–Ne laser beam witha wavelength of 6328 Å was used to measure the effective index and thickness ofthe waveguide. Laser light could be efficiently coupled into the BCB waveguidewhen the embedded Si nanoparticles were smaller than 6 nm. The film thicknessand effective index of the Si-embedded BCB waveguide were measured to be1.825 µm and 1.565, respectively. The optical transmission losses of the pure BCB andSi-embedded ridge waveguides measured by the cut-back method were 0.85 and1.63 dB cm−1, respectively. Although the optical loss was increased by the embedded Si, thedisturbance of the output contour was quite small. This result demonstrates that thenanoparticle-embedded polymer waveguide may be used for optoelectronic integratedcircuits.