ION-BEAM ANALYSIS OF ELECTROPOLYMERIZED PORPHYRIN LAYERS

Homogeneous porphyrin layers (5-200 nm) obtained by electropolymerizat ion of zinc porphyrins on conducting glass, In2O3:Sn (ITO), were studi ed with Rutherford backscattering spectrometry (RBS)nd elastic recoil detection (ERD). These organic layers are sensitive to ion beam induce d damage. Therefore, in order to optimize the analysis conditions, the influence of MeV ion bombardment on the composition and thickness of the layers was systematically investigated over a wide range of projec tile and energy combinations. With RES, the porphyrin coverage is dete rmined from the yield of the heavy metal constituent of the porphyrin and from the substrate peak shifts. The metal and carbon constituents are not significantly subject to depletion under 2.0 MeV He bombardmen t. However, when ERD is employed to analyse the light element composit ion of the layers, degradation of the films is observed. The ion beam alters the layers into a thinner, mainly carbon and zinc containing, f ilm. A double exponential decay of hydrogen with ion dose is found, wh ile carbon degradation can be described with a single exponential. We report values for the degradation cross sections for several types of ion beams. The degradation cross sections of H and C depend almost qua dratically on the electronic stopping power of the primary projectile (sigma similar to(dE/dx)(1,8)) and seem not to be influenced by therma l or current density effects. Although the use of heavier particles re sults in an increased damage of the organic layers, ERD analysis emplo yed with heavy particles in combination with low energies is more accu rate, due to the increased recoil cross section of the particles. The results of the analyses indicate that the composition of the organic l ayers is equal to die composition of the zinc porphyrin molecule, with a slight excess of hydrogen.