Depositions of Si,Ge and C atoms onto a preliminary Si(001) substrate at difierent 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 pattes of adatoms at difierent 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 aiong the perpendicular[110]dixection.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 tus 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.