Yuchen Ma

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.

Plasma properties of a laser-ablated aluminum target in air

The optical emission spectra of the plasma generated by a 1.06-μm Nd:YAG laser irradiation of Al target in air was recorded and analyzed in a spatially resolved manner. Electron temperatures and densities in the plasma were obtained using the relative emission intensities and the Stark-broadened linewidths of Al(I) emission lines, respectively. The dependence of the electron density and temperature on the distance from the target surface and on the laser irradiance were manifested. We also discussed how the air takes part in the plasma evolution process and confirmed that the ignition of the air plasma was by the collisions between the energetic electrons and the nitrogen atoms through a cascade avalanche process.

Structures of hydrogen molecules in single-walled carbon nanotubes

Abstract Molecular-dynamics simulations were used to investigate the structures of hydrogen molecules formed within (5,5), (9,0) and (10,10) single-walled carbon nanotubes (SWNT). In the (5,5) and (9,0) SWNTs, H 2 molecules preferably form linear lines and helical curves, showing the strong confinement of small-diameter SWNTs. The structure of H 2 molecules in the (5,5) and (9,0) SWNTs is different, showing the dependence on the helicities of the SWNTs. The accumulation process of H 2 molecules in the (10,10) SWNT is also presented, showing the formation of H 2 molecules cylindrical shells.

Collisions of deuterium and tritium atoms with single-wall carbon nanotube: adsorption, encapsulation, and healing

Abstract Molecular dynamics simulations (MDSs) are used to study the collisions of deuterium (D) and tritium (T) atoms with single-wall carbon nanotube (SWNT) in the incident energy range of 1–33xa0eV. The MDSs show the scattering, encapsulation of deuterium and tritium, and the formation of exohedral D-SWNT, T-SWNT complexes. The hole on the sidewall induced by energetic atoms can be healed in several picoseconds by annealing at room temperature.

Range distribution and electronic stopping powers for fluorine ions in -implanted potassium titanyl phosphate and LiNbO3

Abstract Range distributions and electronic stopping cross-sections for fluorine ions in 19 F + -implanted potassium titanyl phosphate (KTP) and LiNbO3 in an energy range of 50–330 keV were measured by using the 19 F(p,αγ)16O resonant nuclear reaction at ER=872.1 keV. A proper convolution calculation method was used to extract the true distribution of fluorine from the experimental excitation yield curves. The electronic stopping powers were derived by fitting the projected range distributions simulated by using TRIM/XLL code to the experimentally measured range distributions. The experimental range distribution parameters, Rp and ΔRp, and the electronic stopping cross-sections were compared with those obtained from different Monte Carlo simulation computer codes.

Low-energy interaction and adsorption of C60 on diamond surfaces

Abstract Molecular-dynamics simulations (MDSs) are used to investigate the microscopic processes of a low-energy ( 6∼30 eV ) C60 molecule colliding with clean (1 0 0)(1×1) diamond surface, dimer-reconstructed (1 0 0)(2×1) diamond surface and (1 1 1) diamond surface. While the C60 has high probability to rebound from the (1 1 1) surface, it usually has high probability to be adsorbed on the (1 0 0) surfaces upon the collision. The final structures of the adsorbed C60 and the diamond substrate depend on the collisional energy and the orientation of the incident C60 molecule. In this low-energy collisional regime, the adsorbed C60 keeps most of its structure.

Self-assembly growth of single-wall carbon nanotubes

Abstract The growth of single-wall carbon nanotubes through adduction of small carbon clusters is studied using a molecular-dynamics simulation method. The perfection of the tubes grown depends on the collisional direction, the growth temperature, and the cluster species involved. Narrow single-wall carbon nanotubes can grow without existence of catalysts under controlled conditions. C2, colliding with the side wall of the tubes, can be assembled into the network forming localized defects during annealing.

DFT calculation on the energy thresholds of DNA damages under irradiation conditions

Density functional theory (DFT) calculation of various segments of DNA have been performed to aid our understanding of DNA damages under the conditions of irradiation. These damages studied include strand breaks, base releasing from backbone, and amidogen/methyl removing from bases. In the calculation, the effect of the hydrogen bond interaction between bases in the base-pair, as well as, that of the stacking interaction between the base pairs in adjacent turns of the double helix are both considered. In addition, we also evaluated the effect of the biochemical environment, such as sodium counterions and water molecules, on the stabilization of DNA segment. Base release damage is found to have lowest energy threshold. The remove of an atom or a radical from sugar backbone, which may result in single-strand breaks or double-strand breaks, has the highest energy threshold. All the energy thresholds of these DNA damages are determined to be in the range from 4.5 to 8.7 eV.

Electronic structures of rutile (011)(2 * 1) surfaces: A many-body perturbation theory study

Using the GW method within many-body perturbation theory, we investigate the electronic properties of the rutile (011) surfaces with different reconstruction patterns. We find that keeping the Ti:O ratio on the reconstructedsurface to 1:2 enlarges the bandgap of the rutile (011) surface to ca. 4.0 eV. Increasing the content of O atoms in the surface can turn rutile into a semi-metal. For some surfaces, it is important to apply self-consistent GW calculation to get the correct charge distributions for the frontier orbitals, which are relevant to the photocatalytic behavior of TiO2.

Depth profiles and electronic stopping powers for fluorine ions in -implanted KTN

Abstract Range distributions for fluorine ions in 19 F + -implanted potassium tantalite niobate (KTN) in an energy range of 80–350 keV were measured by using the 19 F (p,αγ) 16 O resonant nuclear reaction at E R =872.1 keV, with width Γ =4.2 keV. Axa0proper convolution calculation method was used to extract the true distributions of fluorine from the experimental excitation yield curves. The experimental range distribution parameters, R p and ΔR p , were compared with those obtained from Monte Carlo simulation codes. The electronic stopping powers for F + ion in KTN were derived through fitting the projected range distributions simulated by using TRIM/XLL code to the experimentally measured range distributions. It is shown that the electronic stopping cross sections obtained in this work agree well with those calculated by using TRIM90 and can be well described by the four-parameter formulae. But they are systematically larger than the results obtained from TRIM98 code.