Ion-assisted growth of carbon-transition metal nanocomposite thin films: from self-organization to spin-dependent transport

Morphology control, especially at the nanoscale, is of primary importance in the field of thin film materials. Our results on energetic-ion-assisted growth of carbon-transition metal nanocomposite thin films are reported here. The films were grown by ion beam assisted deposition (IBAD) and ionized physical vapour deposition (iPVD) using a pulsed filtered cathodic vacuum arc (PFCVA). The two methods differ in the way the ion energy is transferred into the near surface layers: for IBAD the bombarding Ar+ ions transfer the energy via collisions to the near-surface layers of nanocomposite films while for PFCVA the energetic species are themselves the film forming material. The influence of the metal type, metal-to-carbon ratio, ion energy and ion incidence angle on the morphology has been studied.

During growth under energetic bombardment at low temperatures, atomic displacements are caused solely by impacting energetic ions, resulting in phase separation in an advancing surface layer. If the metal amount surpasses a critical value, this layer switches to an oscillatory mode, and a nanoscale precipitation pattern emerges. For iPVD, the ion induced atomic mobility is not isotropic, as it would be in the case of thermally excited migration, but conserves to a large extent the initial direction of the incoming ions, resulting in a tilting of the periodic precipitation structures for oblique ion incidences. The metal nanopatterns no longer align with the advancing surface, but with the incoming ions. The experimental observations are consistent with metal (recoil) ion sub-plantation into light carbon as the key atomistic mechanism. As the dominating driving force for the pattern formation is of neither thermal nor chemical origin, we believe that the presented results are applicable to other immiscible or partially miscible systems as well. Applications of these nanopatterns for sensing and spin manipulation are discussed.