Adsorbate-induced Work Function Research Articles

The influence of work function changes on the charge exchange in low-energy ion scattering

The influence of adsorbate-induced work function changes on the neutralization of noble gas and Li + ions scattered from a Ni(100) surface was studied. The resonance neutralization of Li + ions is unaffected by a work function increase due to CO adsorption, however neutralization becomes more effective as the work function decreases with Cs adsorption. He + and Ne + ions are neutralized by Auger type processes which also holds in the case of CO adsorption. Lowering the work function opens an additional neutralization channel by resonant charge transfer: while the scattering from Ni surface atoms shows the usual increase of the ion yield with increasing energy, scattering from Cs at the same surface is dramatically different, showing a decrease of the ion yield with increasing energy. This different neutralization behaviour shows the strong localisation of the charge exchange processes involved. In all cases where resonant charge exhange is dominant, the data can be consistently described by a model in which the distance of closest approach during the collision is explicitly taken into account, thus demonstrating that the resonant charge exchange itself is a local effect.

Semi-empirical mathematical relationships for electropositive adsorbate induced work function changes

Semi-empirical mathematical relationships for electropositive adsorbate induced work function changes

The growth of Fe overlayers on Ag(100)

Using LEED and Auger spectroscopy the growth of Fe overlayers on Ag(100) was observed to follow an epitaxial layer-by-layer mode for three monolayers, after which islanding occurred. The large (0.9 eV) work function change seen on deposition is not consistent with the prediction of either the uniform positive background model or the virtual level model of adsorbate-induced work function change.

The growth of Fe overlayers on Ag(100)

Using LEED and Auger spectroscopy the growth of Fe overlayers on Ag(100) was observed to follow an epitaxial layer-by-layer mode for three monolayers, after which islanding occured. The large (0.9 eV) work function change seen on deposition is not consistent with the prediction of either the uniform positive background model or the virtual level model of adsorbate-induced work function change.

Adsorption and surface diffusion of titanium on tungsten in a field emission microscope

The adsorption, thermal desorption and surface diffusion of titanium on tungsten in ultra-high vacuum have been studied by field emission microscopy. The work function versus coverage curve has a minimum of 3.95 eV. The theory of metallic adsorbate-induced work function changes given by Gyftopoulos and Levine gives results which are in good agreement with our experimental values. In some experiments the work function minimum occurs at 3.65 eV. This value corresponds to the value of the work function of β-titanium. It is believed that α-titanium to β-titanium phase transformation occurs when the emitter tip is annelaed at 1100 °K to sperad the titanium uniformly over its surface. Surface diffusion of titanium on tungsten occurs with a sharp boundary at 800 °K and the activation energies for the (211)→(411) directions are 43.0 and 42.3 kcal mole respectively. The activation energy of thermal desorption was dependent on the coverage and ranges from 115.3 to 160.4 kcal mole . A satisfactory qualitative correlation between the theory and experiment is established.

Adsorbate-induced work function changes

The model for adsorbate-induced work function changes developed by Gyftopoulos and Levine 1) is shown to quantitatively predict increased work function changes for adsorption of silicon and boron on tungsten substrates. Qualitative correlations with the resonance-tunneling 2,3) model of adsorbate-induced work function changes are given.