Study of the effect of initial conditions on the scaling properties of CaF2 thin films

The growth of thermally deposited CaF₂ films was studied using three different substrates for deposition: glass, gold and silicon. Each substrate was chosen because of its different topography and used to determine the effect of substrate roughness on the growth of CaF₂ films. After thermally depositing a range of CaF₂ film thicknesses on the substrates, the CaF₂ surfaces were imaged using atomic force microscopy. The images were then used to determine the characteristic exponents which described the surface. In each case the Hurst exponent, H was found to rapidly increase from the initial substrate condition to a constant value (H ≈ 0.85) with increasing CaF₂ film thickness. This rapid crossover is quite remarkable and occurs in films with nominal thicknesses less than ≈20 nm. These data indicate that the roughness of the substrate, or in other words the initial conditions, have little effect on the growth properties of CaF₂ films beyond the crossover at very small values of the film thickness. The scaling of the dynamic exponent, β, is also presented as are measurements of the CaF₂ film porosity.