Xi-Jing Ning

Mechanisms for adatoms diffusing on metal fcc(111) surfaces

Abstract On a series of fcc(111) surfaces modeled by the embedded atom method, adatom diffusion mechanisms are studied systematically by molecular dynamics. On most surfaces, as expected, the diffusion mechanism is only hopping. For some other surfaces, however, we find that the exchange mechanism is possible besides the well-known hopping mechanism. More interesting is that the hcp and fcc sites are now different for adatom diffusion: the exchange diffusion process only occurs between the hcp sites.

Reversible atomic modification of nanostructures on surfaces using direction-depended tip-surface interaction with a trimer-apex tip

Using first-principles simulations, we propose a simple mechanism and an easy-controlled method for reversible modification of supported nanoclusters on surfaces with atomic precision. As illustrated, individual atoms at edges of a Al nanocluster on a Al(111) surface can be extracted vertically and repositioned with a Al trimer-apex tip, which allows to rearrange a ten-atom hexagonal nanocluster to a triangular one in a reversible way. The governing mechanism is the atomic tip-surface interaction whose distinct dependence on directions plays a key role in manipulations.

Electronic rectification devices from carbon nanocones

The electronic rectification effects of single wall carbon nanocones (SWCNCs) with cone angles 113°, 60°, and 39° are shown by density functional theory calculation and non-equilibrium Green’s functional method, and the 113° cone owns the best rectification. Based on this result, the experiment on the rectification effects of cone-like structures is explained. To realize the rectification device, a scheme for fabricating single wall carbon nanocones standing on substrates with the controlled cone shapes is suggested and was verified via molecular dynamics simulations.

Predicting the melting temperatures of bulk materials

Design of crystal materials requires predicting melting temperatures, challenging current theories of material design. By introducing the concept of condensing potential (CP), it is shown that melting temperatures are proportional to CP 1/2 for a series of fcc metals (Ni, Cu, Al, Ir, Rh, Ag, Pd, Pt). In order to understand the dependence of melting upon different surfaces of the same crystal, a new concept of surface melting potential (SMP) is introduced, showing that the surface melting points increase monotonically with increasing SMP. Due to the calculation simplicity of CP and SMP, this evaluating system might prove a convenient way to predict melting temperatures of newly designed materials.