Growth by surface diffusion during vapor deposition polymerization

We investigate the growth mechanism of polymer films using dynamic scaling analysis of atomic force microscopy (AFM) images of parylene-AF4 films at various film thicknesses in the steady growth regime. Unlike conventional methods that rely on the scaling ansatz based on the power spectral density function, we introduce a simplified approach based solely on the height-difference correlation function to extract the scaling parameters of film surface. Notably, nonlocal effect associated with anomalous surface fluctuations−commonly observed in parylene-C and parylene-N films−are nearly absent in parylene-AF4 film. The extracted scaling exponents are consistent with a linear continuum growth equation for molecular beam epitaxy (MBE), indicating that fourth-order surface diffusion (−K∇⁴h) governs the growth process. These findings establish the intrinsic growth mechanism of vapor-deposited linear chain polymer films in the absence of nonlocal effects. Parylene-AF4 thus represents the first experimental realization of the linear MBE equation proposed over three decades ago.