Power spectral density analysis and photoconducting behavior in copper(ii) phthalocyanine nanostructured thin films

Abstract

Surface morphology of copper(II) phthalocyanine (CuPc) nanostructured thin films deposited on polished silicon surface was characterized by using atomic force microscopy (AFM). Characteristic topographic parameters like fractals contribute substantially to the thin film morphology, which directly or indirectly influences the physical and optical properties. Fractal geometry and scaling concepts can concisely as well as more effectively describe the complex rough surface morphology. The power values of power spectral density (PSD) for the AFM digital data were determined by the fast Fourier transform (FFT) algorithms instead of the root-mean-square (rms) and peak-to-valley value. The PSD provides a more reliable description to the topography than the rms roughness and imparts some useful information of the surface, including fractal contributions. Fractal analyses, including area-perimeter and PSD methods, have been used to evaluate surface morphology of a vacuum deposited CuPc thin film surface formed under various film deposition temperatures. Film deposition temperature has affected the microstructural and related morphological evolutions very differently. The PSD plots are successfully approximated by the k-correlation model. The film growth is interpreted by the bulk and surface diffusion using parameter C of the k-correlation model. The dark and photoconductivity of CuPc nanostructures in Si/CuPc/Ag configuration at different temperatures have been studied and their changes with roughness and temperature have been discussed. A significantly higher value of the rectification ratio (RR) and photoswitching behavior in such configuration have been noticed.