Depositions of Si, Ge and C atoms onto a preliminary Si （001） substrate at different temperatures are investigated by using the molecular dynamics method. The mechanism of atomic self-assembling occurring locally on...Depositions of Si, Ge and C atoms onto a preliminary Si （001） substrate at different temperatures are investigated by using the molecular dynamics method. The mechanism of atomic self-assembling occurring locally on the flat terraces between steps is suggested. Diffusion and arrangement patterns of adatoms at different temperatures are observed. At 900 K, the deposited atoms are more likely to form dimers in the perpendicular [110] direction due to the more favourable movement along the perpendicular [110] direction. C adatoms are more likely to break or reconstruct the dimers on the substrate surface and have larger diffusion distances than Ge and Si adatoms. Exchange between C adatoms and substrate atoms are obvious and the epitaxial thickness is small. Total potential energies of adatoms and substrate atoms involved in the simulation cell are computed. When a newly arrived adatom reaches the stable position, the potential energy of the system will decrease and the curves turns into a ladder-like shape. It is found that C adatoms can lead to more reduction of the system energy and the potential energy of the system will increase as temperature increases.展开更多
Certain stress and strain form a thermodynamic conjugate pair such that their strain energy equals to a scalar-valued potential energy.Different atomistic stresses and strains are analytically derived based on the wor...Certain stress and strain form a thermodynamic conjugate pair such that their strain energy equals to a scalar-valued potential energy.Different atomistic stresses and strains are analytically derived based on the work conjugate relation.It is numerically verified with both two-body and three-body potentials that the atomistic Kirchhoff stress,first-order Piola–Kirchhoff stress and second-order Piola–Kirchhoff stress are conjugates to atomistic logarithmic strain,deformation gradient and Lagrangian strain,respectively.Virial stress at 0 K based on original volume is the special form of atomistic Kirchhoff stress for pair potential.It is numerically verified that Hencky strain is not conjugate to any stress.展开更多
The phenomena of buckyball-graphene collisions were investigated by classical molecular dynamics(MD)simulation using the empirical Tersoff potential.Three cases were investigated:collisions between a buckyball and a s...The phenomena of buckyball-graphene collisions were investigated by classical molecular dynamics(MD)simulation using the empirical Tersoff potential.Three cases were investigated:collisions between a buckyball and a single-layer graphene;collisions between a nano-onion(a double-layer concentric spherical nanostructure:a C_(60) in a C_(320))and a single-layer graphene;collisions between a nano-onion and a double-layer graphene.The impact velocity of the buckyball or nano-onion ranged from 4.37 km/s to 15.31 km/s.Simulation results for the buckyball-graphene collisions show that the buckyball bounces back when the impact velocity is less than 8.75 km/s,sticks to the graphene when the impact velocity is between 8.75 km/s and 12.03 km/s,and breaks when the impact velocity is greater than 12.03 km/s.Similar phenomena are observed for the other two cases.A single buckyball can never go through a single-layer graphene intact;however,the inner structure(C_(60))of a nano-onion can penetrate through a single-layer graphene without any damage.The energy evolution during the whole simulation process was also studied.展开更多
基金Project supported by the National High Technology Research and Development Program of China (Grant No 2009AA03Z405)the National Natural Science Foundation of China (Grant No 60644004)
文摘Depositions of Si, Ge and C atoms onto a preliminary Si （001） substrate at different temperatures are investigated by using the molecular dynamics method. The mechanism of atomic self-assembling occurring locally on the flat terraces between steps is suggested. Diffusion and arrangement patterns of adatoms at different temperatures are observed. At 900 K, the deposited atoms are more likely to form dimers in the perpendicular [110] direction due to the more favourable movement along the perpendicular [110] direction. C adatoms are more likely to break or reconstruct the dimers on the substrate surface and have larger diffusion distances than Ge and Si adatoms. Exchange between C adatoms and substrate atoms are obvious and the epitaxial thickness is small. Total potential energies of adatoms and substrate atoms involved in the simulation cell are computed. When a newly arrived adatom reaches the stable position, the potential energy of the system will decrease and the curves turns into a ladder-like shape. It is found that C adatoms can lead to more reduction of the system energy and the potential energy of the system will increase as temperature increases.
文摘Certain stress and strain form a thermodynamic conjugate pair such that their strain energy equals to a scalar-valued potential energy.Different atomistic stresses and strains are analytically derived based on the work conjugate relation.It is numerically verified with both two-body and three-body potentials that the atomistic Kirchhoff stress,first-order Piola–Kirchhoff stress and second-order Piola–Kirchhoff stress are conjugates to atomistic logarithmic strain,deformation gradient and Lagrangian strain,respectively.Virial stress at 0 K based on original volume is the special form of atomistic Kirchhoff stress for pair potential.It is numerically verified that Hencky strain is not conjugate to any stress.
文摘The phenomena of buckyball-graphene collisions were investigated by classical molecular dynamics(MD)simulation using the empirical Tersoff potential.Three cases were investigated:collisions between a buckyball and a single-layer graphene;collisions between a nano-onion(a double-layer concentric spherical nanostructure:a C_(60) in a C_(320))and a single-layer graphene;collisions between a nano-onion and a double-layer graphene.The impact velocity of the buckyball or nano-onion ranged from 4.37 km/s to 15.31 km/s.Simulation results for the buckyball-graphene collisions show that the buckyball bounces back when the impact velocity is less than 8.75 km/s,sticks to the graphene when the impact velocity is between 8.75 km/s and 12.03 km/s,and breaks when the impact velocity is greater than 12.03 km/s.Similar phenomena are observed for the other two cases.A single buckyball can never go through a single-layer graphene intact;however,the inner structure(C_(60))of a nano-onion can penetrate through a single-layer graphene without any damage.The energy evolution during the whole simulation process was also studied.
