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Silicon anodes have attracted considerable attention for their use in lithium-ion batteries because of their extremely high theoretical capacity; however, they are prone to extensive volume expansion during lithiation, which causes disintegration and poor cycling stability. In this article, we use two approaches to address this issue, by reducing the size of the Si particles to nanoscale and incorporating them into a carbon composite to help modulate the volume expansion problems. We improve our previous work on the solution-plasma-mediated synthesis of Si nanoparticles (NPs) by adjusting the electrolyte medium to mild buffer solutions rather than strong acids, successfully generating Si-NPs with <10 nm diameters. We then combined these Si-NPs with carbon using MgO-template-assisted sol-gel combustion synthesis, which afforded porous carbon composite materials. Among the preparations, the composite material obtained from the LiCl 0.2 M + H3BO3 0.15 M solution-based Si-NPs exhibited a high reversible capacity of 537 mAh/g after 30 discharge/charge cycles at a current rate of 0.5 A/g. We attribute this increased reversible capacity to the decreased particle size of the Si-NPs. These results clearly show the applicability of this facile and environmentally friendly solution-plasma technique for producing Si-NPs as an anode material for lithium-ion batteries.

Silicon anodes have attracted considerable attention for their use in lithium-ion batteries because of their extremely high theoretical capacity; however, they are prone to extensive volume expansion during lithiation, which causes disintegration and poor cycling stability. In this article, we use two approaches to address this issue, by reducing the size of the Si particles to nanoscale and incorporating them into a carbon composite to help modulate the volume expansion problems. We improve our previous work on the solution-plasma-mediated synthesis of Si nanoparticles (NPs) by adjusting the electrolyte medium to mild buffer solutions rather than strong acids, successfully generating Si-NPs with <10 nm diameters. We then combined these Si-NPs with carbon using MgO-template-assisted sol-gel combustion synthesis, which afforded porous carbon composite materials. Among the preparations, the composite material obtained from the LiCl 0.2 M + H3BO3 0.15 M solution-based Si-NPs exhibited a high reversible capacity of 537 mAh/g after 30 discharge/charge cycles at a current rate of 0.5 A/g. We attribute this increased reversible capacity to the decreased particle size of the Si-NPs. These results clearly show the applicability of this facile and environmentally friendly solution-plasma technique for producing Si-NPs as an anode material for lithium-ion batteries.

The microstructures of oxide scales formed on MoSi2 at medium-high temperatures in air were observed by TEM. Based on the observation, relationships between oxidation temperature and formation of MoO3 and crystallization of amorphous SiO2 scales were investigated. At 1273 K and 1373 K, the oxide scales had a structure consisting of amorphous SiO2 with small amounts of fine MoO3 particles. The oxide scales at 1573 K and 1773 K had a structure consisting of amorphous and crystalline SiO2. Growth rate of the oxide scale formed at 1773 K appreciably increased due to crystallization of amorphous SiO2. It was thought that the increase in the oxidation rate at 1773 K was caused by a change in the diffusion mechanism from O2 diffusion to lattice diffusion of O2- through SiO2. In addition, the diffusion coefficient of oxygen was estimated from the growth rate of SiO2 scale.

The microstructures of oxide scales formed on MoSi2 at medium-high temperatures in air were observed by TEM. Based on the observation, relationships between oxidation temperature and formation of MoO3 and crystallization of amorphous SiO2 scales were investigated. At 1273 K and 1373 K, the oxide scales had a structure consisting of amorphous SiO2 with small amounts of fine MoO3 particles. The oxide scales at 1573 K and 1773 K had a structure consisting of amorphous and crystalline SiO2. Growth rate of the oxide scale formed at 1773 K appreciably increased due to crystallization of amorphous SiO2. It was thought that the increase in the oxidation rate at 1773 K was caused by a change in the diffusion mechanism from O2 diffusion to lattice diffusion of O2- through SiO2. In addition, the diffusion coefficient of oxygen was estimated from the growth rate of SiO2 scale.

Treatment of surface silanol groups with hydrophilic compounds enabled silica-coated cadmium sulfide (SiO2/CdS) nanoparticles of core−shell morphologies to be dissolved in a water/methanol mixture. Size-selective photoetching of the particles was performed by irradiation with monochromatic light at 458 nm, resulting in a blue shift of its absorption onset because of the decreasing size of the CdS. TEM analyses revealed that the SiO2 shell structure was not shrunken by photoetching and that a void space (ca. 2.3 nm) was formed between the CdS core and the SiO2 shell to give a jingle-bell structure. The emission spectra of photoetched particles showed the development of band-gap emission when cadmium ion (Cd2+) was added and the pH was adjusted to 10, whereas the same treatment of original particles gave no peaks assigned to band-gap emission, indicating that the SiO2 shell was sufficiently porous for small ionic species such as Cd2+ to penetrate through the shell and that the photoetched CdS core incorporated in the SiO2 shell had a bare surface to be covered with a cadmium hydroxide layer. With increasing shell thickness, the rate of CdS photoetching was reduced as a result of decrease in the rate of scavenging of the photogenerated electrons in CdS by electron acceptors such as O2 and methyl viologen (MV2+) in solution. The structure of the SiO2 layer was varied by surface modification of the CdS with both 3-mercaptopropionic acid (MPA) and 3-mercaptopropyltrimethoxysilane (MPTS) followed by hydrolysis of its trimethoxysilyl group. FT-IR spectra showed that MPA molecules, but not MPTS molecules, attached to the CdS core surface were eliminated by photoetching of the particles, resulting in the formation of windows in the SiO2 shell. The behavior of CdS emission quenching suggested that MV2+ is transported through the windows to the void space inside the SiO2 shell to reach the CdS core.

Closely stacked multilayer structures of InAs islands with intermediate-layer thicknesses d of 3, 6, 10, and 20 nm were grown by the Stranski-Krastanow mode of molecular beam epitaxy and were observed using transmission electron microscopy (TEM) and atomic force microscopy (AFM). The multilayers consisted of five InAs layers each of a thickness of 1.8 monolayers and four GaAs layers each of a thickness d. Columns of coherent islands were observed by cross-sectional TEM. Changes in the size and density of the islands with d, determined by AFM, could be explained in terms of (i) change in the vertical pairing probability of islands, (ii) detachment of In from the top of the island, and (iii) surface segregation of In. The observed AFM images of the islands were elliptical. Their major axis was in the [110] direction, and the length of the minor axis was 80% of that of the major axis.