Substrate effect on the evolution of surface morphology of BaF2thin films: A study based on fractal concepts

Abstract

Fractal concepts are used to explore how different substrates affect the morphology of deposited barium fluoride (BaF2) thin films. BaF2 thin films of thickness 20 nm are prepared by electron beam evaporation technique at room temperature on glass, silicon and aluminum substrates. The structural properties and surface morphologies are investigated using glancing angle X-ray diffraction (GAXRD) and atomic force microscopy (AFM), respectively. Crystallite size, calculated from the XRD peaks, using the Debye Scherrer’s formula, is found to be significantly less for the case of Si substrate than for Al and glass substrates. Higuchi’s algorithm is applied to extract the fractal dimension of the horizontal and vertical sections of AFM images of the films. From the fractal dimension, the values of Hurst exponent (H) are inferred. For Al and glass substrates we find that H>0.5, which shows that the height fluctuations at neighboring pixels are positively correlated. However, for Si substrate, it is found that H<0.5 indicating that the height fluctuations at neighboring pixels are negatively correlated.