The hydrogen-storage behavior of single-wall carbon nanotubes was studied using molecular dynamics simulations and ab initio electronic calculations. Hydrogen atoms with kinetic energy of 16-25eV were observed to penetrate into and be trapped inside the tube. Consecutively injected H atoms form hydrogen molecules, and gradually condense to become liquid hydrogen in the tube. The density of injected hydrogen in the tube and the pressure on the wall of the nanotube induced by the stored hydrogen molecules were evaluated at room temperature.

Molecular-dynamics simulations were used to investigate the storage capacity of hydrogen in single-walled carbon nanotubes (SWNT's) and the strain of nanotube under the interactions between the stored hydrogen molecules and the SWNT. The storage capacities inside SWNT's increase with the increase of tube diameters. For a SWNT with diameter less than 20 ?, the storage capacity depends strongly on the helicity of a the SWNT. The maximal radial strain of SWNT is in the range of 11%-18%, and depends on the helicity of the SWNT. The maximal strain of armchair SWNT's is less than that of zigzag SWNT's. The tensile strengths of SWNT's decrease with increasing diameters, and approach that of graphite (20 GPa) for larger-diameter tubes.

Collisions between two C60 molecules are studied using molecular dynamics simulations. The results show that dumbbell-shaped (C60)2 dimers with almost intact cages can be formed at low collision energies, and when the collision energy is high enough to overcome the fusion barrier, the two colliding C60 molecules fuse to form one large C120 cluster. These coalescence reactions are found to have very clear threshold behavior. The threshold energy of dimerization is dependent on the classical impact parameter between the mass centers of the colliding partners, and on the collisional orientation. The coalescence reactions are shown to be deep inelastic. The total cross section for the coalescence reaction is estimated to be on the order of the area of a circle, that has a radius equal to the diameter of a C60 molecule.

The growth of narrow single-wall carbon nanotubes through adduction of small carbon clusters is studied using a molecular-dynamics simulation method. Statistical behavior of the growth and defect formation process is analyzed. For C2 dimer colliding onto the side-wall of narrow single-wall nanotubes, it is very easy to get the dimer to be incorporated into the network of the tube during annealing, forming localized topological defects. During long-time annealing at 2300K, thermal fluctuation can cause structural switching among different metastable states and thereby result in energy pulses in the energy vs time curve.

Defect structures of fullerenes and fullerenelike clusters produced by two C60 molecules colliding at different impact parameters and different collision directions in the energy range 50-600eV have been studied using a molecular-dynamics simulation method. The electronic structures around the defects are obtained using a self-consistent-field Hartree-Fock scheme. The results show that the numbers of coordination-number defects obey a magic rule, and the numbers of rings forming the closed cage structure of the fullerene or fullerenelike products can be well described by a modified formula deduced from Euler's theorem. The electronic structures around the defects are substantially changed in comparison with those of the carbon atoms on normal fullerene cages.

and Pb1-x Snx Te have been measured by use of the 19F(p, αγ) 16O resonance nuclear reaction at 872.1keV with width F=4.2keV. 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 △Rp 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 Re values agree with the theoretical and the TRIM values very well but the experimental range straggling △Re 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.

Different configurations of a single nitrogen atom adsorbed at different sites on the sidewall of single-walled carbon nanotubes (SWNT's) are studied through first-principles calculations. It is found that the outer surface of the tube wall is reactive to the nitrogen atom, and a nitrogen atom can be chemically adsorbed on it forming an exohedral complex with a binding energy of; 3.86eV for a (5,5) SWNT. Although the inner surface of the tube wall is less reactive than the outer surface, a nitrogen atom can still be adsorbed on the inner wall of the (5,5) tube forming an endohedral complex with the binding energy on the order of ～1.78eV. The local structure of the SWNT around the adsorption sites is substantially changed. From studying the binding energies of a nitrogen atom adsorbed on different armchair tubes (n, n) with n ranging from 5 to 16, it is found that the binding energy for exohedral adsorption decreases significantly with increasing radius (or increasing n) of the tube, while for endohedral adsorption the binding energy varies slightly. The influence of endohedral adsorption of a single nitrogen atom on the local density of states of a (5,5) SWNT is also discussed.

The growth process of higher fullerenes through adduction of small carbon clusters and carbon atoms is studied using a molecular-dynamics simulation method. Small clusters, such as C3 and C2, and carbon atoms easily adsorb on the surface of fullerene cages, which have coordination-number defects or topological defects, when they collide at thermal velocities with the fullerenes. Annealing the chemisorption complexes at 3000K, the attached clusters are soon incorporated into the network of the fullerene cages, via a self-assembly growth process. Although the fullerenes grown in this way usually have defects, their ring structures can be described by a formula deduced from Euler's theorem. The energies of the fullerenes remarkably decrease with their increasing size, when they are annealed to their low-lying energy structures.