Yueyuan Xia

First-principles calculations for nitrogen-containing single-walled carbon nanotubes

We present calculations for possible configurations of nitrogen-containing single-walled carbon nanotubes and their electronic properties obtained with the ab initio tight-binding FIREBALL method. It is found that nitrogen atoms can be energetically incorporated into the carbon network in three forms: Substitution, substitution with formation of a vacancy structure, and chemical adsorption. The different forms exhibit different local densities of states near the Fermi levels, which might suggest a potential method to control the electronic properties of nitrogen-doped carbon nanotubes.

Graphdiyne: A promising anode material for lithium ion batteries with high capacity and rate capability

We have carried out first-principles calculations to explore the energetics and dynamics of Li in graphdiyne monolayers. The porous structure of graphdiyne enables both in-plane and out-plane diffusion of Li ions with moderate barriers, 0.35–0.52 eV. A unique Li occupation pattern named as a triangular pattern is identified, with Li atoms occupying three symmetric sites in the triangular-like pores. Based on this occupation pattern, the Li storage capacity of single-layer graphdiyne can be as high as LiC3, which is twice the capacity of commonly used graphite (LiC6). With high Li mobility and high storage capacity, this experimentally available porous carbon material is expected to find applications in efficient lithium storage.

Fluorination-induced magnetism in boron nitride nanotubes from ab initio calculations

Ab initio calculations were conducted to investigate the electronic structures and magnetic properties of fluorinated boron nitride nanotube (F-BNNT). It was found that the chemisorption of F atoms on the B atoms of BNNT can induce spontaneous magnetization, whereas no magnetism can be produced when the B and N atoms are equally fluorinated. This provides a different approach to tune the magnetic properties of BNNTs as well as a synthetic route toward metal-free magnetic materials.

Covalent-adsorption induced magnetism in graphene

Magnetism and the mechanism of magnetic coupling in graphene decorated with monovalent and divalent adsorbates were investigated using first-principles calculations based on spin polarized density functional theory. The effects of adsorption concentration and the electronegativity of the adsorbate species on the magnetic and electronic properties were analyzed. For monovalent chemisorptions, the magnetic order originates from the instability of π electrons induced by the adsorption, opening a narrow energy gap and resulting in antiparallel spin directions on adjacent carbon atoms on the graphene sheet. The magnetic order is only possible for the separation between the adsorbing sites less than 10 A. On the contrary, divalent chemisorptions cause long-range magnetic coupling, which is originated from the exchange interactions between localized nonbonding π electrons (spin-polarized) mediated by the conduction π electrons around the Fermi energy, similar to the s–d interaction in transition metals. We demonstrate that our results are well consistent with recent experimental findings.

Distribution patterns and controllable transport of water inside and outside charged single-walled carbon nanotubes

The density distribution patterns of water inside and outside neutral and charged single-walled carbon nanotubes (SWNTs) soaked in water have been studied using molecular dynamics simulations based on TIP3P potential and Lennard-Jones parameters of CHARMM force field, in conjunction with ab initio calculations to provide the electron density distributions of the systems. Water molecules show different electropism near positively and negatively charged SWNTs. Different density distribution patterns of water, depending on the diameter and chirality of the SWNTs, are observed inside and outside the tube wall. These special distribution patterns formed can be explained in terms of the van der Waals and electrostatic interactions between the water molecules and the carbon atoms on the hexagonal network of carbon nanotubes. The electric field produced by the highly charged SWNTs leads to high filling speed of water molecules, while it prevents them from flowing out of the nanotube. Water molecules enter the neutral SWNTs slowly and can flow out of the nanotube in a fluctuating manner. It indicates that by adjusting the electric charge on the SWNTs, one can control the adsorption and transport behavior of polar molecules in SWNTs to be used as stable storage medium with template effect or transport channels. The transport rate can be tailored by changing the charge on the SWNTs.

Optical spectroscopy of plasma produced by laser ablation of Ti alloy in air

Time‐resolved emission spectrum from the plasma produced by 1.06 μm, 10 ns pulsed‐laser irradiation of titanium alloy targets in air at a flux of 9.3×109 W cm−2 was analyzed in the wavelength range of 2000–8800 A. From the evolutions of the specific spectrum lines of N II, Ti I, and Fe I, the velocities of N+ ions and the excited neutral Ti and Fe atoms have been obtained using a time‐of‐flight diagnostic method. The electron temperatures were deduced using the relative emission intensities of N II and Fe I isolated spectrum lines, and an electron number density was determined from the Stark‐broadened line of the N II line at wavelength λ=3995 A.

First-principles study of ZnS nanostructures: nanotubes, nanowires and nanosheets.

We performed first-principles calculations to study the energetics, geometric and electronic properties of zinc sulfide (ZnS) nanostructures. ZnS nanowires (ZnSNWs), nanotubes (ZnSNTs) and nanosheets (ZnSNSs) were considered. Both ZnSNWs and ZnSNTs modeled using hexagonal prisms with the atomic arrangement displaying the characters of wurtzite crystal are more stable than the single-walled ZnS nanotubes presented in previous literature. The energy evolution of ZnSNWs and ZnSNTs as a function of tube diameter and wall thickness was calculated and explained using a simple model. The comparison between the energetics and electronic structures of these ZnS nanostructures was also addressed.

Density-functional theory calculations of XH3-decorated sic nanotubes (X ={C, Si}) : Structures, energetics, and electronic structures

We have investigated the structures, energetics, and electronic structures of XH3-radical-decorated silicon carbide nanotubes (SiCNTs), where X={C,Si}, using density-functional theory. Our results show that all the XH3 radicals can be chemically adsorbed on Si sites or C sites on the tube wall, with the adsorption energies ranging from −2.01 to −2.90eV for a (5,5) SiCNT. The modification in electronic structures of these decorated SiCNTs highly depends on the adsorption site rather than the XH3 species. The electronic structures of XH3-decorated SiCNTs demonstrate characteristics of n-type semiconductors for XH3 adsorbed on a C atom, whereas p-type semiconductors can be achieved by XH3 adsorption on a Si atom.

Collision of hydrogen atom with single-walled carbon nanotube: Adsorption, insertion, and healing

Interaction of hydrogen atom with (5, 5) single-walled carbon nanotube (SWNT) has been studied over the collision energy range from 1 to 30 eV using a molecular dynamics simulation method. In the energy interval of 1–3 eV, the hydrogen atom can be chemisorbed on the outer wall of the SWNT, provided the impact point is near a vertex carbon atom of a hexagon. The lowest incident energy needed for a hydrogen atom to pass through a hexagon ring on the SWNT is estimated to be 14 eV. Hydrogen atoms that enter into the SWNT would either be encapsulated in it to form endohedral H@tube complex, or escape out of it. The hole on the sidewall of the nanotube induced by the collision of hydrogen atom can be healed after relaxation for several picoseconds.

Range distributions of ion‐implanted fluorine in Hg1−xCdxTe, CdTe, and Pb1−xSnxTe

Depth profiles of ion‐implanted fluorine in Hg1−xCdxTe, CdTe, and Pb1−xSnxTe have been measured by use of the 19F(p,αγ)16O resonance nuclear reaction at 872.1 keV with width Γ=4.2 keV. In order to obtain the true range distribution of implanted fluorine from the experimental excitation yield curve, a convolution calculation method is presented, from which the range distribution parameters such as the average projected range RP, the projected range straggling ΔRP and the skewness of the projected range distribution SK were obtained. These experimental range parameters were compared with those obtained by a theoretical calculation and by use of the trim89 program, and shows that for all the materials studied here the experimental RP values agree with the theoretical and the trim values very well but the experimental range straggling ΔRP are larger than those obtained by the theoretical calculation and the trim89. This phenomenon may be attributed to the enhanced diffusion during the ion implantation.