SiOx Nanoparticles Research Articles

Highly efficient and scalable synthesis of SiOx/C composite with core-shell nanostructure as high-performance anode material for lithium ion batteries

SiOx-based electrodes have shown great potential as lithium ion battery anodes because of their high specific capacity. Nonetheless, synthesis of SiOx-based anodes in an industrially adaptable scale still remains as a great challenge. Herein, we adopt a highly efficient colloidal route to enable scalable and high yield synthesis of core-shell SiOx/C composite. The prepared SiOx/C composite presents a well-distributed nanostructure composing of SiOx nanoparticles coated with a thinner carbon layer. The electrode delivers a stable reversible capacity of ca. 820 mAh g−1 over 100 cycles, and exhibits excellent rate capability. The nano-scale feature of SiOx and the coating carbon layer ensure the excellent electrochemical performance of SiOx/C. The approach is facile, mild and mass-productive, which can be adopted for tunable large-scale production of high-capacity SiOx/C composite anode.

High throughput production of nanocomposite SiOx powders by plasma spray physical vapor deposition for negative electrode of lithium ion batteries

Nanocomposite Si/SiOx powders were produced by plasma spray physical vapor deposition (PS-PVD) at a material throughput of 480 g h−1. The powders are fundamentally an aggregate of primary ∼20 nm particles, which are composed of a crystalline Si core and SiOx shell structure. This is made possible by complete evaporation of raw SiO powders and subsequent rapid condensation of high temperature SiOx vapors, followed by disproportionation reaction of nucleated SiOx nanoparticles. When CH4 was additionally introduced to the PS-PVD, the volume of the core Si increases while reducing potentially the SiOx shell thickness as a result of the enhanced SiO reduction, although an unfavorable SiC phase emerges when the C/Si molar ratio is greater than 1. As a result of the increased amount of Si active material and reduced source for irreversible capacity, half-cell batteries made of PS-PVD powders with C/Si = 0.25 have exhibited improved initial efficiency and maintenance of capacity as high as 1000 mAh g−1 after 100 cycles at the same time.

Electrochemical Behaviors of SiOx Nanoparticles as an Anode Material for Lithium-Ion Battery

not Available.

Facile Synthesis and High Anode Performance of Carbon Fiber-Interwoven Amorphous Nano-SiOx/Graphene for Rechargeable Lithium Batteries

We present the first report on carbon fiber-interwoven amorphous nano-SiOx/graphene prepared by a simple and facile room temperature synthesis of amorphous SiOx nanoparticles using silica, followed by their homogeneous dispersion with graphene nanosheets and carbon fibers in room temperature aqueous solution. Transmission and scanning electron microscopic imaging reveal that amorphous SiOx primary nanoparticles are 20-30 nm in diameter and carbon fibers are interwoven throughout the secondary particles of 200-300 nm, connecting SiOx nanoparticles and graphene nanosheets. Carbon fiber-interwoven nano-SiO0.37/graphene electrode exhibits impressive cycling performance and rate-capability up to 5C when evaluated as a rechargeable lithium battery anode, delivering discharge capacities of 1579-1263 mAhg(-1) at the C/5 rate with capacity retention of 80% and Coulombic efficiencies of 99% over 50 cycles, and nearly sustained microstructure. The cycling performance is attributed to synergetic effects of amorphous nano-SiOx, strain-tolerant robust microstructure with maintained particle connectivity and enhanced electrical conductivity.

Erratum to: Effects of Hydrogen Gas Injection on the Properties of SiO x Nanoparticles Synthesized by Using an Evaporation and Condensation Process

SiOx nanoparticles were synthesized by using an evaporation and condensation process involving induction melting of silicon (Si) chunks followed by the injection of a H2/Ar mixed gas into the melt. In particular, this research studied the effects of hydrogen gas on the nanoparticles’ microstructural and electrochemical properties, etc. During the microstructural analysis, regardless of H2 content, all the nanoparticles were observed to have random shapes; their average particle sizes were 30 ∼ 35 nm. However, a crystalline Si phase, even though it was a small amount, was formed when H2/Ar gas was injected. From the X-ray photoelectron spectroscopy (XPS) analysis, the amount of the SiO2 phase in SiOx decreased when the H2/Ar gas ratio was higher than 1.0 vol.%. Injected hydrogen produced a Si-H network in SiOx, and the Si-H concentration was independent of the amount of injected gas. Consequently, due to hydrogen incorporation, not only was a crystalline Si phase formed, but also the amount of the SiO2 phase decreased. In addition, Si-H bonds were formed in the nanoparticles. The crystalline Si phase and the relatively small amount of the SiO2 phase resulted in an enhancement of the Li-ion capacity when those nanoparticles were applied as an anode material for a Li-ion battery. Furthermore, cycle performance was improved even when hydrogen was incorporated. For the sample synthesized with 5.0-vol.% H2/Ar gas, the discharge capacity and the columbic efficiency at the 21st cycle were 889.1 mAhg−1 and 95.0%, respectively.

Effects of hydrogen gas injection on the properties of SiO x nanoparticles synthesized by using an evaporation and condensation process

SiOx nanoparticles were synthesized by using an evaporation and condensation process involving induction melting of silicon (Si) chunks followed by the injection of a H2/Ar mixed gas into the melt. In particular, this research studied the effects of hydrogen gas on the nanoparticles’ microstructural and electrochemical properties, etc. During the microstructural analysis, regardless of H2 content, all the nanoparticles were observed to have random shapes; their average particle sizes were 30 ∼ 35 nm. However, a crystalline Si phase, even though it was a small amount, was formed when H2/Ar gas was injected. From the X-ray photoelectron spectroscopy (XPS) analysis, the amount of the SiO2 phase in SiOx decreased when the H2/Ar gas ratio was higher than 1.0 vol.%. Injected hydrogen produced a Si-H network in SiOx, and the Si-H concentration was independent of the amount of injected gas. Consequently, due to hydrogen incorporation, not only was a crystalline Si phase formed, but also the amount of the SiO2 phase decreased. In addition, Si-H bonds were formed in the nanoparticles. The crystalline Si phase and the relatively small amount of the SiO2 phase resulted in an enhancement of the Li-ion capacity when those nanoparticles were applied as an anode material for a Li-ion battery. Furthermore, cycle performance was improved even when hydrogen was incorporated. For the sample synthesized with 5.0-vol.% H2/Ar gas, the discharge capacity and the columbic efficiency at the 21st cycle were 889.1 mAhg−1 and 95.0%, respectively.

SiOx Nanoparticles Preparation by an Evaporation and Condesation Process Using Induction Melting

not Available.

Developing UV-protective cotton fabric based on SiOx nanoparticles

Nano-SiOx suspension was prepared for its unique optical performance to improve the anti-ultraviolet property of cotton fabric in this paper. The experimental results showed that UV-resistance property of thus treated fabrics had been enhanced significantly. The spectrum of absorption, reflection, and transmittance of the treated fabric was analyzed during the optimized processing. The mechanical property of the treated fabric displayed a little increase compared with the original untreated fabric. The morphology of the treated fabric was studied by SEM. The UPF (Ultraviolet Protection Factor) of the fabric treated with nano-SiOx suspension reached 62, much higher than that of the original untreated fabric. Moreover, after 50 home launderings, the UV-blocking property of treated fabric changed little due to the strong affinity between the nano-SiOx particles and cotton fiber.

The measurement of internal strain in core–shellNi3Si(Al)–SiOx nanoparticles

Internal defects and strain in nanoparticles can influence their properties and thereforemeasuring these values is relevant. Powder diffraction techniques (neutron andsynchrotron) are successfully used to characterize internal strain in the core–shellNi3Si(Al)–SiOx nanoparticles havingmean diameters of ∼80 nm. The nanoparticles, which are strain-free after extraction from the bulkalloys, develop internal strain on heating. Both micro- and macro-strains can bemeasured from the analysis of Bragg peak shift and broadening. It is identifiedthat differences in thermal expansion coefficient of the metallic core and theamorphous shell of the nanoparticles, as well as partial disordering of theL12 ordered core phase, are the main causes of strain evolution. Synchrotron measurements alsodetected partial crystallization of the amorphous silica shell.

Electrochemical Nucleation of SiO<SUB><I>x</I></SUB> Nanoparticles into the Pore Bottoms of an Anodic Aluminum Oxide

Utilizing the wafer-scale anodization of a thermally evaporated Ti layer onto a Si substrate, SiOx nanoparticles could be electrochemically nucleated into the pore bottoms of an anodic aluminum oxide. The formation of a Si-containing Ti layer (Ti(1-x)Six, x < 0.1) was identified between the Al and the silicon substrate by thermal diffusion of Si during the evaporation. Upon prolonged anodization of approximately 1 h after alumina barrier layer touched the Si-containing Ti layer, pyramid-shaped TiOx nanopillars formed underneath the pore bottoms as a result of a curvature inversion of the barrier oxide with Ti migration. These TiOx nanopillars were observed to act as a diffusion route of silicon from the Si-containing Ti layer. Only one SiOx nanoparticle (approximately 8 +/- 5 nm) for each pore was generally precipitated without Ti contamination. This finding suggests a new route which can make SiOx nanoparticles confined within an anodic aluminum oxide template.

Selective Formation of Size-Controlled Silicon Nanocrystals by Photosynthesis in SiO Nanoparticle Thin Film

The SiOx thin film with a thickness of about 1 mum was formed on a GaAs substrate by bar-coating with the organic solution of the SiOx nanoparticles (~40 nm). The as-formed SiOx thin film consists of the SiOx nanoparticles; thus the thin film is macroscopically discontinuous and is referred to as a nanoparticle thin film. Although there were no silicon (Si) nanocrystals in the as-formed SiOx nanoparticle thin film, Si nanocrystals were observed by Raman scattering measurement after the thin film was exposed to the laser beam. The growth of Si nanocrystals by laser irradiation is referred to as photosynthesis. The photosynthesis of Si nanocrystals is found to be a self-limiting process. After the average size reaches a certain value, further increase of irradiation time or laser power does not increase the average size. The photosynthesis is similar to the thermal synthesis of Si nanocrystals from SiOx but much faster and low-temperature growth of Si nanocrystals from SiO x. Furthermore, the laser irradiation makes nanoparticles larger by merging. This suggests a possibility of low-temperature formation of a Si-nanocrystal array embedded in a SiO2 thin film. Such a structure has many potential device applications

Preparation and characterization of core/shell SiOx/PAM nanospheres with ‘graft from’ method

The core/shell SiO2 encapsulated with polyacrylamide (SiOx/PAM) nanospheres were successfully prepared by the radical copolymerization of acrylamide (AM) and a macromonomer, methacryloxypropyl SiOx (MP-SiOx) nanoparticles, initiated with AIBN via a facile precipitation polymerization method in ethanol. The percentage of encapsulating (PE%) and the conversion of the AM (C%) of 327.5% and 93%, respectively, were achieved after a polymerizing time of 3 h. The formation mechanism of the core/shell SiOx/PAM nanospheres was explained. The nanospheres were characterized by elemental analysis (EA), Fourier transform infrared (FTIR), X-ray photoelectron spectrometer (XPS) and transmission electron microscope (TEM).

Optical emission from SiOx (x=1.2–1.6) nanoparticles irradiated by ultraviolet ozone

We have investigated the photoluminescence (PL) of SiOx (x=1.2–1.6) powder with nanoparticle sizes of 5–15 nm irradiated by ultraviolet ozone. A blue PL band was observed with a large intensity. The peak position of this band shows a redshift with increasing irradiation time and its intensity has a maximum in the sample with an irradiation time of 60 min. PL excitation spectral examinations reveal that this broad PL band arises from optical transition of the self-trapped excitons at the surfaces of SiOx nanoparticles, which are induced by ultraviolet ozone irradiation. Fourier transform infrared absorption result and energy-dispersive x-ray fluorescence analysis confirm the existence of oxygen interstitials and oxygen vacancies, which provides a basis for forming the self-trapped excitons. This work improves the understanding of the blue-emitting property in Si/oxygen-related nanomaterials.

Diamond-like carbon nanocomposite films

Diamond-like carbon (DLC) nanocomposite films were deposited at room temperature by inductively coupled plasma chemical vapor deposition using hexamethyldisilane (HMDS), hexamethyldisilazane (HMDSN), and hexamethyldisiloxane (HMDSO) precursors. High-resolution transmission electron microscopy showed that all the films contained nanoparticles. The DLC nanocomposite films deposited by HMDS contained hollow spherical nanocrystallites, called nanoballs, of hexagonal silicon carbide. The nanocomposite films deposited by HMDSN contained crystalline Si3N4 nanoparticles. The nanocomposite films deposited by HMDSO contained amorphous SiOx nanoparticles. Although both types of films had similar hardness, the DLC nanocomposite films exhibited much lower compressive stresses than the DLC films deposited by methane, i.e., 1.5 vs 11 GPa, respectively. Through the enhancement of gas phase reactions, the inductively coupled plasma should be responsible for the formation of nanoparticles in the nanocomposite films.

Growth of a Si nanocrystal in an oxygen atmosphere. Computer simulation

Growth of a Si nanocrystal in vacuum and in atomic-oxygen atmosphere was simulated on the basis of molecular dynamics. SiOx nanoparticles (x = 0–0.42) containing up to 302 atoms were obtained. The shape of the nanocrystals was primarily determined by the amount of oxygen contained in them. The growth of nanocrystals in an oxygen atmosphere was accompanied by the formation of oxygen clusters inside a nanoparticle, which gave rise to considerable internal stresses. In most cases, structural relaxation increases the volume of SiOx nanocrystals and decreases internal pressure. The angular and topological statistical characteristics of Voronoi polyhedra are indicative of a structural irregularity in oxygen clusters formed inside Si nanoparticles.

Photoluminescence from gas-suspended SiOx nanoparticles synthesized by laser ablation

Time-resolved photoluminescence (PL) spectra are reported for gas-suspended 1–10 nm diameter SiOx particles formed by laser ablation of Si into 1–10 Torr He and Ar. Three spectral bands (1.8, 2.5 and 3.2 eV) similar to PL from oxidized porous silicon were measured, but with a pronounced vibronic structure. Particle size and composition were determined with Z-contrast transmission electron microscopy imaging and high resolution electron energy loss spectroscopy linescans of individual nanoparticles. Maximized violet (3.2 eV) PL from the gas-suspended nanoparticles was correlated with an ex situ SiO1.4 overall particle stoichiometry. Cryogenically-collected gas-suspended nanoparticles produced web-like-aggregate films exhibiting very weak PL. Standard anneals restored strong PL bands without vibronic structure, but otherwise in agreement with the PL measured from the gas-suspended nanoparticles.

Time-Resolved Imaging and Photoluminescence of Gas-Suspended Nanoparticles Synthesized by Laser Ablation: Dynamics, Transport, Collection, and Ex Situ Analysis

AbstractThe dynamics of gas phase nanoparticle formation by pulsed laser ablation into background gases are revealed by imaging photoluminescence and Rayleigh-scattered light from gas-suspended SiOx nanoparticles following ablation of c-Si targets into 1-10 Torr He and Ar. Two sets of dynamic phenomena are presented for times up to 15 s after KrF-laser ablation. Ablation of Si into heavier Ar results in a uniform, stationary plume of nanoparticles while Si ablation into lighter He results in a turbulent ring of particles which propagates forward at 10 m/s. The effects of gas flow on nanoparticle formation, photoluminescence, and collection are described. The first in situ time-resolved photoluminescence spectra from 1-10 nm diameter silicon particles were measured as the nanoparticles were formed and transported. Three spectral bands (1.8, 2.5 and 3.2 eV) similar to photoluminescence from oxidized porous silicon were measured, but with a pronounced vibronic structure. The size and composition of individual gas-condensed nanoparticles were determined by scanning transmission electron microscopy and correlated with the gas-phase photoluminescence. Weblike-aggregate nanoparticle films were collected at room temperature and 77K on c-Si substrates. After standard passivation anneals, the films exhibited strong room temperature photo-luminescence consisting of 3 spectral bands in agreement with the gas-phase measurements, however lacking the vibronic structure. These techniques demonstrate new ways to study and optimize the luminescence of novel optoelectronic nanomaterials during synthesis in the gas phase, prior to deposition.