Ion induced compositionally modulated ripples during composite film growth: 3D sculpting at the nanoscale

Ion irradiation of multielement surfaces can induce regular compositionally modulated surface roughness nanopattern formation such as ripples or nanodots. This kind of bottom-up nanopatterning can provide means to not only structure the solid surfaces but also to create ordered heterogeneous structures in three dimensions (3D) when performed in growth mode: the compositional surface nanopattern is continuously buried by incoming species while the surface is again restructured due to ion irradiation. The present work is an experimental demonstration of this concept: 3D ordered nanocomposites are grown via ion induced two dimensional (2D, surface) nanopattern formation during bi-component film growth. The influence of low energy (50-140 eV) assisting Ar+ ion irradiation on the morphology of C:Ni (~ 5 at.% Ni to ~ 30 at.% Ni) thin films will be reported. It will be shown that for certain growth conditions surface ripples form during oblique incidence low energy ion beam assisted deposition of C:Ni films. These surface ripples are compositionally modulated: Ni is located on the crests and carbon in the valleys. The film cross sections show periodic distribution of metal nanoparticles in a carbon matrix with the same periodicity as the surface ripples. As this 3D patterning effect has a physical origin, it can be expected to occur in many material systems. Such an approach holds high potential for the growth of functional nanocomposite films for a wide range of applications.