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Electronic stopping powers for 0.05–10 MeV protons in a group of organic materials are systematically calculated. The calculations are based on Ashley's dielectric model, and an evaluation approach of optical energy loss function is incorporated into Ashley's model because no experimental optical data are available for most of the organic materials under consideration. The Barkas-effect correction and Bloch correction are included. The proton stopping powers for the considered organic materials except for mylar in the energy range from 0.05 to 10MeV are presented for the first time. The results may be useful for studies of various radiation effects in these materials and for space research.

We perform the calculations on geometric and electronic structures of Si-doped heterofullerene C50Si10 and its derivatives, a C40Si20-C40Si20 dimer and a C40Si20-based nanowire by using density-functional theory. The optimized configuration of the C40Si20-based nanowire exhibits a regular dumbbell-shaped chain nanostructure. The electronic structure calculations indicate that the HOMO-LUMO gaps of the heterofullerene-based materials can be greatly modified by substitutionally doping with Si atoms and show a decreasing trend with increase cluster size. Unlike the band structures of the conventional wide band gap silicon carbide nanomaterials, the C40Si20-based nanowire has a very narrow direct band gap of 0.087eV.

The hydrogen storage capacity of (5, 5) single-walled carbon nanotubes (SWNTs) decorated chemically with benzene moieties is studied by using molecular dynamics simulations (MDSs) and density functional theory (DFT) calculations. It is found that benzene molecules colliding on (5, 5) SWNTs at incident energy of 50 eV form very stable configurations of benzene moiety adsorption on the wall of SWNTs. The MDSs indicate that when the benzene moiety decorated (5, 5) SWNTs and a pristine (5, 5) SWNT are put in a box in which hydrogen molecules are filled to a pressure of ~26 atm, the hydrogen storage capacity of the benzene moiety decorated (5, 5) SWNT is about 4.7 wt.% and that of the pristine (5, 5) SWNT is nearly 3.9 wt.%.

A Monte Carlo approach to simulate the transport and energy deposition of low energy electrons (E0≤10 keV) in liquid water is presented. The elastic scattering of electrons is described by Mott cross section, which is derived from the relativistic wave equation of Dirac. The inelastic scattering model of electrons is based on the dielectric response theory with exchange effect included. A new method of sampling various inelastic scattering events is proposed in the simulation. Using the approach stated, the spatial distribution of inelastic scattering events and energy deposition of electrons in liquid water are computed and the results are compared with other theoretical studies.

The motion and equilibrium distribution of water molecules adsorbed inside neutral and negatively charged single-walled carbon nanotubes (SWNTs) have been studied using molecular dynamics simulations (MDSs) at room temperature based on CHARMM (Chemistry at HARvard Molecular Mechanics) potential parameters. We find that water molecules have a conspicuous electropism phenomenon and regular tubule patterns inside and outside the charged tube wall. The analyses of the motion behaviour of water molecules in the radial and axial directions show that by charging the SWNT, the adsorption efficiency is greatly enhanced, and the electric field produced by the charged SWNTs prevents water molecules from flowing out of the nanotube. However, water molecules can travel through the neutral SWNT in a fluctuating manner. This indicates that by electrically charging and uncharging the SWNTs, one can control the adsorption and transport behaviour of polar molecules in SWNTs for using as a stable storage medium or long transport channels. The transport velocity can be tailored by changing the charge on the SWNTs, which may have a further application as modulatable transport channels.

We study the collisions of energetic methane molecules with single-walled carbon nanotubes in the incident energy range from 5 to 100 eV using classical molecular dynamics simulations combined with ab initio calculations. The methane molecules can be decomposed into different hydrocarbon radicals, e.g. CHn (n = 1–3), in the collisions depending on the incident energy. Chemical functionalization of the single-walled carbon nanotubes resulting from the chemical adsorption of these hydrocarbon radicals on the outside wall of single-walled carbon nanotubes can be achieved simultaneously. Some stable adsorption configurations of hydrocarbon-functionalized single-walled carbon nanotubes are also presented based on ab initio calculations.

We perform ab initio calculations on the self-assembled base-functionalized single-walled carbon nanotubes (SWNTs) which exhibit the quasi-1D `ladder' structure. The optimized configuration in the ab initio calculation is very similar to that obtained from molecular dynamics simulation. We also calculate the electronic structures of the self-assembled base-functionalized SWNTs that exhibit distinct difference from the single-branch base-functionalized SWNT with a localized state lying just below the Fermi level, which may result from the coupling interaction between the bases accompanied by the self-assembly behaviour.

The reaction channels and the reaction products in the collisional reactions between two C60 molecules are found to be sensitively dependent on the relative orientation between the colliding partners. The detailed collision processes and the stable structures of the products are studied by using a molecular dynamics simulation method combined with a Langevin molecular dynamics scheme. The defects of the reaction products are also analyzed.

The stopping power of an electron gas for hydrogen ions is calculated based on the full self-consistent nonlinear density-functional frame. Three different configurations of hydrogen ions are considered and a criterion to test the validity of the self-consistent calculation is proposed. Comparison of calculation with available experimental data shows good agreement.

Depth profiles of fluorine in 19F+ implanted Ni0.8Fe0.2 alloy have been accurately measured by using 19F(p, ??)16O resonance 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 range parameters, Rp and ?Rp, were thereby obtained and compared with those simulated with TRIM'90 code. It shows that the experimental Rp values agree with the Monte Carlo simulation values very well, while the experimental ?Rp values are systematically larger than the calculation values.

The sputtering of Hg0.8Cd0.2Te target by low energy Ar+ ions has been simulated using Monte Carlo method. The simulation results show that the concentration of Hg in the surface region of the target after ion bombardment is lower than the one before ion bombardment, but in a deeper region an excess concentration of Hg is produced due to recoil implantation. The excess concentration of Hg there may act as a donor dopant diffusion source for over doping the acceptor levels in the adjacent region and turn the p-type Hg0.8Cd0.2Te into an n-type material.

A shell-wise calculation method and a quantal harmonic-oscillator model have been used to calculate the electronic stopping cross sections for heavy ions colliding with atoms or penetrating matter. The electronic energy loss is given in an impact parameter formalism. In order to generalize the theoretical models, which pertain to the case of point charge interacting with matter, to the case for heavy ions, an effective stopping charge based on the modified BK theory is used by way of simple scaling in the calculations. The comparisons between the calculated results and the experimental data demonstrate a favourable evidence to justify the theoretical models.

Chemical adsorption and desorption of hydrogen atoms on single-walled carbon nanotubes (SWNTs) are investigated by using molecular dynamics simulations. It is found that the adsorption and desorption energy of hydrogen atoms depend on the hydrogen coverage and the diameter of the SWNTs. Hydrogen-adsorption geometry at the coverage of 1.0 is more energetically stable. The adsorption energy decreases with the increasing diameter of the armchair tubes. The adsorption and desorption energy of hydrogen atoms can be modified reversibly by externally radial deformation. The averaged C-H bond energy on the high curvature sites of the deformed tube increases with increasing radial deformation, while that on the low curvature sites decreases.

Si+ ions of 350 keV have been implanted into AlGaAs/AlGaInAs quantum well samples in the dose range from 5×1013cm-2to 5×1014cm-2. The Raman spectra and high resolution x-ray diffraction (HRXRD) were measured from these implanted samples as well as the non-implanted sample. In the implanted layers the average strain which was evaluated by HRXRD increases with the implantation doses and varies from 0.0011 to 0.0029. The quantum well interface intermixing effect and compositional modification are also observed from HRXRD. At the higher doses, an abnormal annealing procedure takes place and it partly removes damage, but the strain remains almost unchanged in the epilayers.

Experimental evidence of abnormally deep penetration in some botanical targets by low-energy ion beams is presented. The energy spectra of 818 keV He+ ions penetrating a 70 µm thick seed coat of maize, fruit peel of grape and of tomato all have a common feature. The leading edges of these broad spectra indicate that some of the penetrating ions pass through the thick targets easily and only lose a small fraction of their initial incident energy. Rutherford backscattering spectrometry and electron microprobe measurements are used to determine the argon concentration in multilayer samples of the seed coat of maize implanted by 200 keV Ar+ ions. The results show that about 10% of the Ar+ ions can penetrate deeper than ~100 µm in these samples.

Depth profiles of fluorine in F-doped tin oxide (FTO) films prepared by atmospherical pressure chemical vapour deposition method have been studied by use of 19F(p, αγ) 16O resonance nuclear reactions near 872.1 keV. A proper convolution method was used to get the real depth profiles of fluorine from the measured γ-ray excitation curves. Secondary ion mass spectrometry in conjunction with Rutherford backscattering spectrometry analysis was used to determine the density of the FTO films. It was found that the density of the films is markedly different from an earlier reported value.

A molecular dynamics simulation method is used to study the growth of narrow single-wall carbon nanotubes. It is found that the growth temperature and the species of small carbon clusters in the feedstock are important for the quality of the nanotubes grown. There is a temperature range of 1000-1500 K in which the narrow armchair single-wall carbon nanotubes can grow rapidly via adduction of C2 dimers, even without the existence of catalysts. The narrow zigzag tubes cannot keep open-ended growth. If the feedstock consists of various species of carbon clusters, the tubes cannot keep open-ended growth. At higher temperatures, the narrow nanotubes close rapidly in the noncatalytic environment, and the products grown are fullerene-like capsules. PACS: 61. 46. +w, 36. 40. -c

We theoretically investigate high-order harmonic generation in a two-color multi-cycle inhomogeneous field combined with a 27th harmonic pulse. By considering a bowtie-shaped gold nanostructure, the spatiotemporal profiles of enhanced plasmonic fields are obtained by solving the Maxwell equation using finite-domain time-difference method. Based on quantum-mechanical and classical models, the effect of 27th harmonic pulse, temporal profile of enhanced plasmonic field and inhomogeneity on supercontinuum generation are analyzed and discussed. As a result, broadband supercontinuum can be generated from our approach with optimized gap size of nanostructure. Moreover, these results are not sensitively dependent on the relative phase in the two-color field.

In this paper, the stable structure and the electronic and optical properties of nitric oxide (NO) adsorption on the anatase TiO2 (101) surface are studied using the plane-wave ultrasoft pseudopotential method, which is based on the density functional theory. NO adsorption on the surface is weak when the outermost layer terminates on twofold coordinated oxygen atoms, but it is remarkably enhanced on the surface containing O vacancy defects. The higher the concentration of oxygen vacancy defects, the stronger the adsorption is. The adsorption energies are 3.4528 eV (N end adsorption), 2.6770 eV (O end adsorption), and 4.1437 eV (horizontal adsorption). The adsorption process is exothermic, resulting in a more stable adsorption structure. Furthermore, O vacancy defects on the TiO2 (101) surface significantly contribute to the absorption of visible light in a relatively low-energy region. A new absorption peak in the low-energy region, corresponding to an energy of 0.9 eV, is observed. However, the TiO2 (101) surface structure exhibits weak absorption in the low-energy region of visible light after NO adsorption.

Inelastic mean free paths (MFPs) of 0.05–10 MeV protons in a group of 10 organic compounds are systematically calculated. The calculations are based on the method newly derived from the Ashley optical-data model and from the higher-order correction terms in stopping power calculations. Especially, in this method the new and empirical Bloch correction for the inelastic MFP is given. An evaluation for the optical energy loss function is incorporated into the present calculations because of the lack of available experimental optical data for the considered organic compounds expect for kapton. The proton inelastic MFPs for these 10 organic compounds in the energy range from 0.05 to 10 MeV are presented here for the first time, and the combination of these inelastic MFP data and our previous data of stopping power calculation for these bioorganic compounds may form a useful database for Monte Carlo track-structure studies of various radiation effects on these materials.

We theoretically show that H atoms can be chemically adsorbed onto the surface of the Si-C heterofullerene-based nanotubes. The adsorbing energy of the H atom on Si-C heterofullerene-based nanotubes is in the range of 4.28–5.66eV without any barrier for the H atom to approach to the Si-C heterofullerene-based nanotubes. The band-gap of Si-C heterofullerene-based nanotubes can be dramatically modified by introducing dopant states, i.e., there is a transition from semiconductor to conductor of the Si-C heterofullerene-based nanotubes induced by the adsorption of the H atom. These results actually open a way to tune electronic properties of heterofullerene-based nanotubes and thus may propose an efficient pathway for band structure engineering.