Real-time observation of coadsorption layers on Ru(001) using a temperature-programmed ESDIAD/TOF system

For the purpose of utilizing ESDIAD as a real-time probe for surface processes, we have developed an instrument which can measure ESDIAD images and time of flight (TOF) spectra of desorbing ions in temperature-programmed surface processes. TOF measurements are carried out to identify the mass and to determine the kinetic energy distribution of the desorbed ions. This temperature-programmed (TP-) ESDIAD/TOF system was used to observe coadsorption layers of methylamine and CO on Ru(001) which have been previously studied by our group using LEED, TPD and HREELS, also drawing upon a comparison of findings with the coadsorption system of CO and ammonia. ESDIAD images acquired for temperature-programmed surface processes in real time were found to provide new insight into the dynamic behaviour of the coadsorption layers. As to the pure adsorption of ammonia and methylamine, the second and the first (chemisorbed) layers can be easily discriminated in their different ESD detection efficiency due to the difference in neutralization rate. The intensity change of H⁺ ions with temperature shows the process of the decomposition of methylamine to be dependent on CO coverage. The intensity of O⁺ originating from CO changes due to the change of CO adsorption site in the reaction process. The angular distribution of H⁺ ions which correspond to CH2=NH…Ru species appears at 250–300 K in the presence of high CO pre-coverage.