TRICYCLOHEXYLPHOSPHINE ADSORBED ON GOLD

Tricyclohexylphosphine adsorbates on gold, as well as multilayer films of tricyclohexylphosphine, are investigated by X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IRAS). Molecular orientation and molecular surface interaction for adsorbates prepared from solution are studied, using the multilayer films as references. Since phosphines are easily oxidized in contact with air, the reference, made from a pressed pellet of the starting material, consists of a considerable amount of oxidized tricyclohexylphosphine. Therefore an oxygen-free reference would also be desirable. Such a reference of a tricyclohexylphosphine multilayer was obtained by fractionating tricyclohexylphosphine from tricyclohexylphosphine oxide by a sublimation process under ultrahigh vacuum. The results from both a pressed pellet of the starting material and an evaporated tricyclohexylphosphine multilayer are compared with the results from the adsorbate. When tricyclohexylphosphine is adsorbed from solution onto gold, there is a preferential adsorption of the unoxidized tricyclohexylphosphine. The molecular structure is intact during adsorption and the molecules are oriented with the phosphine atoms close to the surface. The chemical shift of the P(2p(3/2)) binding energy during adsorption indicates an electron donation from the adsorbate to the metal.