Substrate temperature dependence of the structure of polythiophene thin films obtained by Matrix Assisted Pulsed Laser Evaporation (MAPLE)

Abstract

Thin films of head-tail (H-T) regio-regular poly[3-(4-octyloxyphenyl) thiophene] (POOPT) were grown using the MAPLE (Matrix Assisted Pulsed Laser Evapn.) technique in which the target is a frozen soln. of the polymer in chloroform. Target evapn. was obtained by laser irradn. at 1064 nm and substrates were kept at different temps. Information concerning the preservation of the polymer local chem. structure following laser irradn. was obtained by FTIR (Fourier Transform IR) spectroscopy. Based on FTIR data, the chem. structure of the deposited polymer seemed to undergo little or no damage. From UV-Visible spectroscopic anal., it turned out that the degree of order of the film is strongly affected by the substrate temp.: the polymer was deposited in a disordered form on the substrate at room temp. whereas on the hot surface we locally obtained the .pi.-stacked structure characteristic of polythiophenes. Atomic force microscopy (AFM) images showed that the polymer formed aggregates of different dimensions (<1 .mu.m to 5 .mu.m) with a columnar shape and showed micrometric domains with sharp and apparently regular edges for the film grown on a hot substrate. Elec. measurements performed by a std. two-probe technique confirm that the structural order degree strongly affects the film charge transport properties.