Anomalous atomic transport in driven systems: Ion-sputtering induced enhanced intermixing and cratering in Pt/Ti

Probing the anomalous nanoscale intermixing using molecular dynamics (MD) simulations in the Pt/Ti bilayer we reveal the enhancement of the interfacial atomic transport. It is shown that the Pt atoms undergo anomalous atomic transport across the interface of Pt/Ti with surprisingly high rates. In particular, the low-energy (0.5 keV) ion-sputtering induced transient enhanced intermixing has been studied by MD simulations. Ab initio density functional calculations have been used to check and reparametrize the employed heteronuclear interatomic potential. The transient enhanced intermixing behavior explains the long diffusity tail in the concentration profile obtained by Auger electron spectroscopy depth profiling analysis in Pt/Ti bilayer (reported in Ref. P. Süle, M. Menyhárd, L. Kótis, J. Lábár, J.F. Egelhoff Jr., J. Appl. Phys. 101 (2007) 043502). Moreover, we point out that atomic mass-anisotropy has no effect on interdiffusion in the nanoscale hence other (unknown) factors are responsible for the anomalous interface broadening. The mean-square of atomic displacements scales superlinearly in Pt/Ti, while show sublinear scaling behavior in Ti/Pt. The exponent of a fitted power-law expression is 1.65 in Pt/Ti which suggests the anomalous character of intermixing. Anomalously long (ballistic) atomic jumps of Pt atoms across the interface are seen also only in Pt/Ti. Moreover, the robust Pt atomic injection into the Ti bulk takes place together with an enhanced surface cratering in Pt/Ti. No such behavior is seen for Ti/Pt. These surprising atomistic features could be the signature of an anomalous driven process not reported yet for bulk systems.