Effect of surface diffusion on morphology and scaling properties during glancing angle deposition

The objective of this research work is to study the effect of surface diffusion on the morphology of porous thin films grown by Glancing Angle Deposition (GLAD) wherein atomic shadowing is the dominant physical phenomenon responsible for growth of isolated nano-rod structures. The morphology has been analyzed in terms of change in the width of the nanorods w at a given height h as well as changes in scaling relations as a function of diffusion length scale.;Atomic shadowing during kinetically limited physical vapor deposition causes a chaotic instability in the layer morphology that leads to nanorod growth. GLAD experiments indicate that the rod morphology, in turn, exhibits a chaotic instability with increasing surface diffusion. The measured rod width versus growth temperature converges onto a single curve for metallic systems when normalized by the melting point Tm. A model based on mean field nucleation theory reveals a transition from a two- to three-dimensional growth regime at (0.20 +/- 0.03) x Tm and an activation energy for diffusion on curved surfaces of (2.46 +/- 0.02) x kTm. The consistency in the GLAD data suggests that the effective mass transport on a curved surface is described by a single normalized activation energy that is applicable to all elemental metals.;Metallic nanorods grown by GLAD at Ts = 300--1123 K exhibit self-affine scaling, where the average rod width w increases with height h according to w ∝ h p. The growth exponent p for the investigated metals (Ta, Nb, Cr and Al) varies with temperature and material but collapses onto a single curve when plotted against the homologous temperature theta = Ts/Tm. It decreases from p = 0.5 at theta = 0 to 0.39 at theta = 0.22, consistent with reported theoretical predictions, but exhibits a transition to an anomalous value of p = 0.7 at theta = 0.26, followed by a decrease to 0.33 at theta = 0.41.;The change in the scaling relations has been related to changes in the surface roughness of the growth front of the nanorods as a function of diffusion length scale which effects the atomic shadowing. Analysis of shadowing by diffusion mediated surface roughness at the growth front of nanorods grown by GLAD indicates that self-shadowing plays an important role in determining the morphology of the layer. The growth exponent p is dependent on the nature of geometric shadowing interactions between the rods as well as due to self-inflicted shadowing by the islands at the growth fronts on the rods themselves. I propose an analytical model based on mean-field nucleation theory and non-linear chaos theory which predicts a linear dependence of p on the average island separation or the diffusion length scale <s> of the adatoms on the growth front. The model explains the occurrence of anomalous scaling at 0.24 ≤ theta ≤ 0.34 with of a transition from 2D to a 3D island growth mechanism. A fit based on the model predicts a critical homologous deposition temperature thetac of 0.24 +/- 0.02 for all metallic systems (Al, Cr, Nb and Ta) under consideration.