Field ionization behavior of cyclohexane on Au tips

Abstract Ion formation by field ionization (FI) of molecules also depends on the chemical reactivity of the field anode surface and of the molecules in the neutral and ionized state. Since cyclohexane is known not to chemically interact with Au surfaces and in addition does not form fragment ions by field dissociation its FI behavior on Au tip surfaces was investigated by field ion microscopy (FIM) and FI MS. It is shown that cyclohexane does not react with Au tip surfaces at lower field strengths up to the onset of FI of molecules remote from the surface. However, at higher field strengths the Au tip surface becomes chemically reactive and the electron bombardment of the surface by FI of molecules remote from the surface leads to the dissociation of C–H bonds of adsorbed molecules with a preferential binding of the H atoms to the surface. The cyclohexyl radicals are either field desorbed or chemisorb on the Au surface. The subsequent FI of chemisorbed cyclohexyl molecules forms surface ions at which the FI probability for molecules supplied from the gas phase is enhanced. This is indicated by the appearance of bright spots in the field ion microscope.