Random fractal surface analysis of disordered organic thin films

Study of surface morphologies reveals useful information about interfacial contacts and materials properties such as charge carrier mobility, optical absorption and adhesion that directly affect system performance. The total effective interface area and root mean square (rms) of surface height fluctuations are among the common parameters often used to corroborate device performance upon surface modification. In this paper, random fractal surface analysis is used to characterize geometrical features of microstructure morphologies in disordered organic nickel tetrasulfonated phthalocyanine (NiTsPc) films under different solvent treatment. The different but complementary approaches are used, namely the power spectral density analysis, variogram method based on generalized Cauchy process (GCP) and grayscale fractal box counting approach. It is shown that each of these approaches offers certain perspective about the complex morphologies often found in disordered thin films and thus joint interpretation of these approaches offer better characterization of the surface properties, filling the gap left by others. The morphologies are also interpreted in the context of percolation network supported by the photocurrent density measurements.