Periodic Ta nanopillar arrays were grown onto patterned substrates by Glancing Angle sputter Deposition (GLAD). Both the effects of surface patterning and surface diffusion on morphological evolution were studied by varying the pattern length-scale created by Nanosphere lithography (NSL) and by growing at temperatures T_s ranging form 200 to 900 °C, respectively.

Statistical size analyses from nanopillars grown on NSL patterns show that the distribution in width (w) broadens with decreasing interspacing (D) and increasing height (h), but remains constant with a fixed h/D-ratio. This is attributed to an intercolumnar growth competition that exacerbates nanopillar size fluctuations but scales with pillar height, indicating that the overall pillar morphologies are determined by geometric shadowing and are independent of material parameters such as the characteristic length-scale for surface diffusion at room temperature.

The pillar tops branch into subcolumns that form on surface mounds caused by kinetic roughening under limited adatom mobility conditions. The fraction of branched pillars decreases with increasing T_s, as described with a simple nucleation model that provides an effective activation energy for Ta surface diffusion of 2.0 eV. At high T_s ≥ 500 °C, sub-pillars nucleate at the pillar bottom. This is attributed to a competitive growth mode that is caused by an increased adatom diffusion length and results in an increase in the average pillar width, a decrease in the pillar separation and pillar number density, the accelerated growth of some pillars at the cost of others which die out, and an increased probability for the merging of neighboring pillars.

Different approaches have been developed concerning growth description of the compact nitride layers, especially those produced by ammonia. The atomic nitrogen flux from the surface to the solid is produced by ammonia dissociation. Microwave post-discharge nitriding is carried out in iron and steel samples. Nitriding by this process involves molecular nitrogen dissociation in the post-discharge and on the sample surface. The thermo-chemical simulation of the concomitant evolution nitride layers relates the representation of reference states of neutral and excited nitrogen in a gas mixture, surface nitrogen concentration produced by molecular dissociation on the surface and nitrogen flux from the surface into the solid.

This work presents a mathematical model of the kinetics of compound layer formation during a post-discharge nitriding process. The model is related to a moving boundary value problem which takes into account the observed qualitative behavior in a laboratory. The model assumes several steps: diffusion process, formation of the layers, layer growth and quasi-stabilization of the layer growth. An analytical approximate solution of the Goodman's type is proposed, which allows us to obtain a representation of the motion of the interfaces and the nitrogen concentration profiles. Through this approach the thermodynamics of the irreversible diffusion process is applied in order to describe the evolution towards equilibrium between the growing layers.