The ion-sputtering induced intermixing is studied by Monte-Carlo TRIM, molecular dynamics (MD) simulations, and Auger electron spectroscopy depth profiling (AES-DP) analysis in Pt/Ti/Si substrate (Pt/Ti) and Ta/Ti/Pt/Si substrate (Ti/Pt) multilayers. Experimental evidence is found for the asymmetry of intermixing in Pt/Ti, and in Ti/Pt. In Ti/Pt we get a much weaker interdiffusion than in Pt/Ti. The unexpected enhancement of the interdiffusion of the Pt atoms into the Ti substrate has also been demonstrated by simulations. We are able to capture the essential features of intermixing using TRIM and MD simulations for ion-beam sputtering and get reasonable values for interface broadening which can be compared with the experimental measurements. However, the origin of the asymmetry remains poorly understood yet.

Molecular dynamics simulations have been used to study the mechanism of ion beam mixing in metal bilayers. We are able to explain the ion induced low-temperature phase stability, atomic mixing and melting behavior of bilayers using only a simple ballistic picture up to 10 keV ion energies. The atomic mass ratio of the overlayer and the substrate constituents seems to be a key quantity in understanding atomic mixing. This picture explains in a simple way ion beam mixing in a overwhelming number of miscible and immiscible bilayer systems up to high ion energies. Remarkably the existing experimental data follow the same trend as the simulated values. The critical bilayer mass ratio of ␦ Ͻ 0.33 is required for the occurrence of a thermal spike ͑local melting͒ with a lifetime of Ͼ 0.3 ps at low-energy ion irradiation ͑1 keV͒ due to a ballistic mechanism. These findings might be important in understanding the mechanism of ion induced phase evolution in solids and could improve the controlled fabrication of metal nanostructures.

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Please cite this article as: Süle, P., Szendrő, M., Hwang, C., Tapasztó, L., Rotation misorientated graphene moiré superlattices on Cu(111): Classical molecular dynamics simulations and scanning tunneling microscopy studies, Carbon (2014), doi: http://dx. AbstractGraphene on copper is a system of high technological relevance, as Cu is one of the most widely used substrates for the CVD growth of graphene. However, very little is known about the details of their interaction. One approach to gain such information is studying the superlattices emerging due to the mismatch of the two crystal lattices. However, graphene on copper is a low-corrugated system making both their experimental and theoretical study highly challenging. Here, we report the observation of a new rotational moiré superlattice of CVD graphene on Cu(111), characterized by a periodicity of (1.5 ± 0.05) nm and corrugation of (0.15 ± 0.05)Å , as measured by Scanning Tunneling Microscopy (STM). To understand the observed superlattice we have developed a newly parameterized Abell-Tersoff potential for the graphene/Cu(111) interface fitted to nonlocal van der Waals density functional theory (DFT) calculations. The interfacial force field with time-lapsed classical molecular dynamics (CMD) provides superlattices in good quantitative agreement with the experimental results, for a misorientation angle of (10.4 ± 0.5 • ), without any further parameter adjustment. Furthermore, the CMD simulations predict the existence of two nonequivalent high-symmetry directions of the moiré pattern that could also be identified in the experimental STM images.