J.H. Craig

ESD and IID study of CO on nickel

Abstract Electron and ion induced desorption has been used to study release of ionic species from CO on nickel. O + , CO + , and O − are found to be released by electron impact. Thermal desorption spectra indicate the presence of two binding states. The O + species is observed to be released from state 1, the state of higher binding energy, while state 2, a more loosely bound state is the source of CO + . O − species appear to be released from both states. The cluster ions NiCO + and Ni 2 CO + released by argon ion impact were observed to originate from state 2.

Low coverage study of oxygen on platinum

Abstract TDS and ESD measurements have been carried out on the O 2 /Pt system using a recrystallized ribbon sample. TDS spectra demonstrate the presence of two adsorption states for oxygen exposures less than 1 L. ESD data suggest the existence of a large cross section state, interpreted as a precursor, during the very early stages of adsorption. The two states identified in the TDS spectra show very different ESD behavior. The lower temperature state is inactive to ESD. The high temperature state is found to yield significant electron desorption, but only in the absence of significant population in the lower temperature state.

Comparison of H+ and H− ESD from hydrogen on platinum

Abstract Electron desorption of H − from H 2 adsorbed on platinum is observed and compared with the corresponding H + emission. The H − signal is observed to track closely with the thermal desorption signal indicating a possible correlation between production of molecular hydrogen prior to desorption and formation of H − from polar dissociation. The energy distribution and thresholds for H + and H − are observed to be significantly different. The H − threshold is shown to be 7–8 eV higher than for H + .

Surface science lettersEvidence for multiple states of hydrogen on palladium

Abstract Adsorption of hydrogen on polycrystalline palladium has been investigated using ESD techniques. Although a single thermal desorption peak is observed for H 2 and Pd, total ESD cross section measurements suggest the existence of four distinct sources for desorbing H + and H - species. The very large cross section associated with the H - signal along with its behavior during sample heating suggests the possible existence of a molecular precursor state.

TDS and ESD study of CO on palladium

Abstract The adsorption of CO on polycrystalline Pd surface has been studied using the techniques of thermal desorption spectroscopy (TDS) and electron stimulated desorption (ESD). Thermal desorption spectra of CO at room temperature reveal the existence of a main single binding state (β 2 ) with an additional shoulder at higher exposure (β 1 ). O + , CO + , and O - are observed to desorb upon electron impact. CO + is found to be released from the β 1 state, the state of lower binding energy. On the other hand, O + is released exclusively from the β 2 state, a more tightly bound state. The O - species is shown to originate from both states with an estimated 75% of the O - signal coming from the CO + producing β 1 state.

Ion induced desorption of oxygen from platinum

Abstract Ion induced desorption has been used to study the initial uptake of oxygen on polycrystalline platinum. Rapid increase is observed in the O − secondary ion signal with oxygen exposure. The dependence of the O − signal on sample temperature is observed to exhibit a peak near the temperature corresponding to the main thermal desorption state.