Thermal reaction and desorption behaviors of 2,5-diiodothiophene on clean and passivated Au surfaces

Thermal reactions and desorption behaviors of 2,5-diiodothiophene on Au were studied with temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Diiodo-substituted hetero-cyclic molecules are an important precursor molecule for photochemical production of conjugated polymers. This paper describes the surface reactions and multilayer structure of 2,5-diiodothiophene in the absence of photon irradiation. 2,5-Diiodothiophene adsorbs molecularly on Au at 100 K. At 200–300 K, the C–I bond of the molecule dissociates producing atomic iodine. The C–I bond cleavage appears to induce further dissociation of the thiophene ring structure. The iodine species desorb at 600–750 K from the surface. The dissociated carbon and sulfur remain on the Au surface even at 800 K. The desorption of thin multilayers occurs at ∼220 K. During the desorption of these layers, a clustering process seems to occur. The desorption of thick multilayer occurs at ∼235 K.