Study the Order of Morphology Self-Assembled Triblock Copolymer Thin Films by FFT of the AFM Images

A variety of block copolymer thin films with well-ordered nanostructures, which can be employed as templates for nanotechnologies including nanostructure membranes, nanoparticle synthesis, photonic crystal, and high-density information storage media, can be realized simply and at low cost by self-assembly. Long range ordering of morphology is paramount to realize applications of self-assembled block copolymer thin films in nanotechnologies. A better understanding of what parameters affect the ordering process can lead to the production of highly ordered arrays of nanostructures. In this paper, in order to effectively analyze the improvement in ordering, the Fast Fourier transform (FFT) analysis of the AFM images is used. Fast Fourier transform provide a mathematical analysis of the image that is similar to producing a diffraction pattern. From this “diffraction pattern” information on the order in the system can be obtained. Moreover, calculating an ordering parameter from the FFT provides a quantitative measure of the order present in the polymer template. The order parameter is calculated using equations which were tested against a manufactured perfect system and imperfect system to ensure that a perfect system would provide an order parameter of 1 and an imperfect system would create an order parameter of 0. The results show that the method is reasonable and effective to analyze the improvement in ordering that is achieved by using solvent annealing. Furthermore, the method can be used to understand the parameters in triblock copolymer thin film self-assembly process that create the most well ordered system.