Study of Interactions Between Coadsorbed Species on NICKEL(111) Using Infrared Reflection Absorption Spectroscopy

This dissertation presents studies of the physical chemical properties of CO chemisorbed on Ni(111) using infrared reflection absorption spectroscopy (IRAS) and other surface analysis instruments. Chapter 1 discusses mainly the theoretical basis of IRAS and the special spectral phenomena observed in reflection infrared measurements. Chapter 2 describes how to build up a state-of-the-art reflection infrared spectrometer. Chapter 3 explains the ultra-high-vacuum (UHV) system and the main surface instruments used in this dissertation work. On Ni(111), CO is found to occupy both bridged and terminal sites. Also, CO is adsorbed on the Ni(111) surface via a precursor adsorption process. This is discussed in Chapter 4. It is a natural question to ask which binding structure is more stable than the other for CO on Ni(111). This is answered in Chapter 5 with results from both reflection infrared and work function measurements. It is found that the bridged-CO species is more stable than the terminal -CO species on Ni(111), and the binding energy difference is about 1 kcal/mole. When a 270 eV electron beam is used to bombard a Ni(111) surface covered with both terminal-CO and bridged -CO species, should terminal-CO behave differently from the bridged-CO? The results presented in Chapter 6 say YES, although the binding difference of the two CO species (0.05 eV) is negligible in comparison with the energy of the incident electron beam. Chapter 7 is concerned with the study of interaction of CO with a physisorbed species, Xe. The interaction between the two is physical in nature. A frequency redshift and attenuation of CO band absorbance is observed when Xe is added into the CO layer. In Chapter 8, chemisorbed CO is used as a probe to test the effect of chemisorbed oxygen on a metal surface. It is found that the chemisorbed oxygen exhibits both long and short range interactions with Ni atom adsorption sites. A polarized overlayer physisorbed on top of a saturated CO layer on Ni(111) is found to cause a CO site interconversion from terminally-bound-CO species to bridged -bound-CO species in the CO underlayer. The site interconversion is independent of the molecular identity of the physisorbed layer, but is closely related to the work function decrease induced by the polarized overlayer. This phenomenon is discussed in Chapter 9 and Chapter 10.