Ion-assisted phase separation during the growth of carbon-transition metal nanocomposite thin films

Nanostructures determine material properties at the macroscale, and are therefore a key issue in materials science of thin films. This is of particular importance for nanoscale multiphase films due to their multifunctionality and the combination of properties which cannot be predicted from the constituents alone. Control over the morphology and spatial correlations at the nanoscale becomes one of the major challenges. In this context, the tools allowing the structure control at the nanoscale are of utmost importance. The ion-solid interactions in the hyperthermal ion energy range (~10 -100 eV) are confined in the nanometer scale, and are therefore of key relevance. In this talk I will summarize recent research activities of our group on the phase separation during the growth of carbon-transition metal thin films. These materials are relevant in the context of sensing, fusion, electrochemistry, tribology, information storage as well as spintronics. Different processes can be 'switched off/on' by external control of the experimental parameters such as temperature, substrate type, matrix/dispersed phase chemical affinity or incoming particle energy. This results in a large variety of lateral or vertical composition modulations, such as encapsulated nanoparticles, high aspect ratio nanocolumns or self-organized layered 3D nanoparticle arrays. The latter deserve a special interest. They occur during ionized-PVD conditions if the metal amount surpasses a critical value. In addition, 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. Such self-organization process is versatile as different carbon-transition metal systems show this effect. The observed tendencies will be discussed on the basis of the interplay of thermal and energetic ion induced phenomena. 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 and can be used to sculpt (multi)functional nanomaterials.