AVS 56th International Symposium & Exhibition
    Advanced Surface Engineering Tuesday Sessions
       Session SE+TF-TuA

Paper SE+TF-TuA8
Temperature Driven Anomalous Scaling during Glancing Angle Deposition

Tuesday, November 10, 2009, 4:20 pm, Room C4

Session: Glancing Angle Deposition II
Presenter: S. Mukherjee, Rensselaer Polytechnic Institute
Authors: S. Mukherjee, Rensselaer Polytechnic Institute
D. Gall, Rensselaer Polytechnic Institute
Correspondent: Click to Email

Ta, Nb, Cr and Al nanorod structures were grown by glancing angle physical vapor deposition on a continuously rotated Si(001) substrate at an incidence angle of 84° and at substrate temperatures Ts = 300-1125 K. The width w of the self-affine nanorods increases with the height h according to wαhp. The growth exponent p is a function of the homologous substrate temperature θ, which is the ratio of Ts to the melting point Tm. All studied metallic systems exhibit the same p(θ) curve: p approaches a value of 0.5 for negligible surface diffusion (θ < 0.1) and monotonously decreases to p = 0.39 for θ = 0.2, as predicted by Meakin and Krug’s model of nanorod growth with limited surface diffusion and by Mullins-Herring’s model of 2+1 dimensional interface growth, respectively. However, p increases dramatically for θ = 0.22-0.26, to reach an anomalous value of 0.71. Above the transition temperature θc = 0.24±0.02, the growth exponent decreases to reach p = 0.3 at θ = 0.42.

We present a semi-analytical model using mean-field nucleation and non-linear chaos theory that relates p with the exponential divergence λ from a surface diffusion limited material independent morphology that is controlled by atomic shadowing. p is a function of the average island separation distance <s>, which is a measure of the diffusion length scale and varies with θ, the activation energy Em for surface diffusion, the critical island size i, and the dimensionality of adatom surface diffusion. The model predicts a transition from a 2-d to a 3-d island growth mode at θc. This transition, in turn, exacerbates the chaotic bifurcation associated with the atomic shadowing by the islands on the nanorod growth fronts, resulting in the higher growth exponents above θc. The model also provides a single homologous activation energy Em/kTm = 2.46 for surface diffusion on curved nanorod growth fronts, applicable to all studied metallic systems at all temperatures. p follows a linear function with <s>, in both high and low temperature regimes and the slope correlates with the slope of λ vs ln(h), indicating that the growth exponent and hence the morphology is intricately related to both shadowing and surface diffusion.