A Fluid Dynamics Calculation of Sputtering from a Cylindrical Thermal Spike

The sputtering yield, Y, from a cylindrical thermal spike is calculated using a two dimensional fluid dynamics model which includes the transport of energy, momentum and mass. The results show that the high pressure built-up within the spike causes the hot core to perform a rapid expansion both laterally and upwards. This expansion appears to play a significant role in the sputtering process. It is responsible for the ejection of mass from the surface and causes fast cooling of the cascade. The competition between these effects accounts for the nearly linear dependence of $Y$ with the deposited energy per unit depth that was observed in recent Molecular Dynamics simulations. Based on this we describe the conditions for attaining a linear yield at high excitation densities and give a simple model for this yield.Comment: 10 pages, 9 pages (including 9 figures), submitted to PR

Modeling of Martensitic Transformations in Pure Iron by a Phase Field Approach Using Information from Atomistic Simulation

A phase field approach for martensitic transformations is introduced. The parameters are determined due to results from molecular dynamic simulations for pure iron. The continuum model is provided with the atomistic input data to examine the evolution of microstructure in 2D, both under the influence of external load and for interface motion through the transformation induced eigenstrain. Therefore, different configurations of the two phases are used. In addition, the energy evolution of the system is studied in detail during the transformation process. The numerical implementation of the model is performed with finite elements while an implicit time integration scheme is applied for the transient terms

Melting of Al Induced by Laser Excitation of 2p Holes

Novel photon sources—such as XUV- or X-ray lasers—allow to selectively excite core excitations in materials. We study the response of a simple metal, Al, to the excitation of 2p holes using molecular dynamics simulations. During the lifetime of the holes, the interatomic interactions in the slab are changed; we calculate these using WIEN2k. We find that the melting dynamics after core-hole excitation is dominated by classical electron–phonon dynamics. The effects of the changed potential surface for excited Al atoms occur on the time scale of 100 fs, corresponding to the Debye time of the lattice

Origin of atomic clusters during ion sputtering

Previous studies have shown that the size distributions of small clusters ( n<=40 n = number of atoms/cluster) generated by sputtering obey an inverse power law with an exponent between -8 and -4. Here we report electron microscopy studies of the size distributions of larger clusters ( n>=500) sputtered by high-energy ion impacts. These new measurements also yield an inverse power law, but one with an exponent of -2 and one independent of sputtering yield, indicating that the large clusters are produced when shock waves, generated by subsurface displacement cascades, ablate the surface

Molecular dynamics simulations of non-equilibrium systems

Peer reviewe

Superior regularity in erosion patterns by planar subsurface channeling

The onset of pattern formation through exposure of Pt(111) with 5 keV Ar+ ions at grazing incidence has been studied at 550 K by scanning tunneling microscopy and is supplemented by molecular-dynamics simulations of single ion impacts. A consistent description of pattern formation in terms of atomic scale mechanisms is given. Most surprisingly, pattern formation depends crucially on the angle of incidence of the ions. As soon as this angle allows subsurface channeling of the ions, pattern regularity and alignment with respect to the ion beam greatly improves. These effects are traced back to the positionally aligned formation of vacancy islands through the damage created by the ions at dechanneling locations

Desolvation of macromolecules by ultrafast heating: A molecular-dynamics study

Using molecular-dynamics simulation, we investigate the consequences of ultrafast laser-induced heating of a water droplet containing a solvated polymer, using the example of a 1 ps laser irradiation. We study the isolation process and the properties of the isolated polymer as a function of the polymer size, the droplet size, and the temperature to which the droplet is heated. We find that the isolation process occurs on a time scale of a few ten ps. The final polymer temperature increases linearly with the heating. Polymers embedded in larger droplets acquire higher temperatures, while larger polymers are less heated. In spite of the ultrafast heating, the isolated polymer remains in its coiled conformation