Ab Initio Study of Porous Graphene–CNT Silicon Composite for Li-Ion and Na-Ion Batteries

In this work, we investigated composite materials based on graphene and carbon nanotubes with a silicon cluster from the standpoint of using them as Li-ion battery (LIB) and Na-ion battery (NIB) anodes. For our study, we used the density functional theory method, taking into account the van der Waals interaction. The cavities of the composite were filled with lithium and sodium, and the energy characteristics of the structure were calculated through SIESTA molecular dynamics. The calculations showed the negative energy of adsorption for lithium and sodium and the negative value of the heat of formation of the composites. The introduction of a silicon cluster led to an increase in the specific capacity by 22.2% for the sodium and 37% for the lithium in comparison with the pure composite. The calculation of the transmission function showed a decrease in the resistance of the composite when a silicon cluster was added to the composite. We predict that the application of the considered composite will increase the efficiency of existing lithium-ion and sodium-ion batteries.

A highly unsaturated six-vertex amido-substituted silicon cluster

Thermal treatment of the bicyclo[1.1.0]tetrasilatetraamide [Si4{N(SiMe3)Dipp}4] 1 resulted in the formation of a highly unsaturated six-vertex silicon cluster [Si6{N(SiMe3)Dipp}4] 2 with only four amine-substituents and two ligand-free silicon atoms.

Endogenous Three-Dimensional Surface Structures and Tamm Surface State Characteristic of Silicon Cluster Superlattice

A silicon cluster superlattice was theoretically investigated with OpenMX code. Silicon (Si) clusters were quarried from monocrystalline Si to construct the initial crystallographic structures to faithfully reproduce the experimental results: Si clusters retained the sp3 structure to coalesce into a body-centered cubic (bcc) superlattice with lattice constant 2.134 nm. The Si211 and Si235 cluster superlattices can construct crystallographically stable bcc superlattice structures in good agreement with the experimental results. The stable Si211 cluster superlattice formed characteristic gap states to create a high-density-of-states peak near the Fermi level. The gap states, which are characterized as Tamm states, were induced by the endogenous surface network three-dimensionally formed in the Si211 cluster superlattice. The Tamm states clearly appearing in the Si L2,3 core-loss spectrum was reproduced by calculations of the oxidation of surface Si atoms in the Si211 cluster superlattice. The endogenous surfaces enclose a narrow region in the stable Si235 cluster superlattice to form an indigenous huge multivacancy. The gap states exhibited a p-type semiconductor quality. Retaining the sp3 structure, the Si cluster superlattice exhibited a high-symmetry structure, while their variation with the cluster size is very large. The symmetry causes the scale of the electronic properties of silicon to extend so widely from metallic quality to dielectrics.

Effect of SiH4 Flow Rates on the Structures and Properties of Si-Rich Silicon Nitride Films Prepared by Hot Wire Chemical Vapor Deposition

Silicon-rich silicon nitride thin films were deposited on the P type (100) of silicon and Corning7059 glass by hot-wire chemical vapor deposition method using SiH4 and NH3 as reaction gas source. The effects of SiH4 flow rate on the structures and optical properties of the thin films were studied under optimizing other deposition parameters. The structures, band gap width and surface morphology of the thin films were characterized by Fourier transform infrared absorption spectroscopy (FTIR), ultraviolet-visible (UV-VIS) light transmittance spectra and scanning electron microscope (SEM), respectively. The experiment results show that, with increasing of the SiH4 flow rate, the content of N and Si atoms in the thin films increases, and the Si-N bond density increases gradually, and the optical band gap of the films shows a trend of increasing. When the silane flow rate is less than 0.9sccm, there is no Si-H bond stretching vibration absorption peak, and silicon atoms mainly bond with nitrogen atoms. As the SiH4 flow rate decreases, silicon clusters embedded in silicon nitride matrix gradually become smaller. When SiH4 flow rate is 0.4sccm, we prepared the silicon cluster nanoparticles with an average diameter of about 50nm embedded in silicon nitride thin films matrix. Therefore, properly reduction of the SiH4 flow rate is favorable for preparing the smaller silicon cluster nanoparticles in silicon rich silicon nitride thin films. The results lay the foundation for the preparation of silicon quantum dots thin film materials.

Experimental and theoretical 2p core-level spectra of size-selected gas-phase aluminum and silicon cluster cations: chemical shifts, geometric structure, and coordination-dependent screening

2p binding energies of size-selected clusters reveal bonding motifs and help to assign new ground state geometries.