Paper SE+TF+NC-ThM4
Scaling of Nanorods during Glancing Angle Deposition: Effect of Surface Diffusion

Thursday, October 23, 2008, 9:00 am, Room 204

Ta, Al, and Cr nanorods, 65–430 nm wide and 440 nm tall, were grown by glancing angle sputter deposition onto continuously rotated Si(001) substrates from a deposition angle of 84º at substrate temperatures T_s = 300–1125 K. Surface diffusion is negligible at low homologous temperatures T_s/T_m < 0.08 (T_m: melting point) and for systems with a high activation energy for surface diffusion E_m. This leads to a chaotic growth process where the surface morphological evolution is controlled by long-range shadowing interactions and the rod width w (= 58 nm) at a constant height h (= 400 nm) is material independent. However, at higher growth temperatures, w increases with T_s and scales with T_s/T_m for all investigated metals as well as for data from the literature. This is attributed to an increase in the average island size on the growth surface which results in additional shadowing interactions and a chaotic divergence in the microstructure. Applying mean-field nucleation theory and non-linear dynamics within the kinetically limited growth regime yields a Lyapunov exponent λ of 0.033 for the divergence from the zero-temperature morphology and an effective E_m that scales with the melting point according to E_m = 2.46kT_m. The data also suggests a transition from a 2D to a 3D island growth mechanism as T_s increases from below to above a critical temperature T_c = 0.24T_m. The growth exponent p decreases monotonously from 0.5 to 0.31 as T_s increases from 300 K to T_c, in agreement with Meakin and Krug’s model and Mullins-Herring model for 2+1 dimensional moving interfaces. However, p exhibits a discontinuity at Tc and becomes anomalous (p > 0.5) for T_s > T_c.