Field desorption of caesium and barium from graphen nanoclueters on the iridium surfaces

The features of the field desorption of caesium and barium from the surface of an iridium tip with two-dimensional graphene nanoclusters on the surface are investigated. Both adsorbates are located both on the surface of iridium and carbon clusters, and in the intercalated state under the graphene film in the close packed planes of the iridium crystal. Field desorption proceeds in different ways. With an increase in the intensity of the applied electric field, the pulse removal of the adsorbate from the surface occurs. With further strengthening of the field in the case of caesium, desorption of adsorbate atoms from the intercalated state occurs. Caesium atoms come out from under the film, diffuse onto the surface of the cluster and are desorbed in the ion form. Barium atoms remain under the graphene film until the cluster is destroyed. The difference in the mechanisms of field desorption from graphene clusters is explained by the presence of a second electron on the valence shell of alkali metal atoms, which provides a chemical bond between the adsorbed atoms and the substrate. The only valence electron of alkali metal atoms during adsorption goes into the metal, and provides an electrostatic bond of the adsorbate with the substrate and electrostatic repulsion of the adatoms among themselves

The effect of the interaction of barium atoms on the surface of the rhenium field emitter on the work function

Modification of the emission surface on a nanometer scale during adsorption of barium atoms on the surface of a rhenium field emitter was investigated using field electron and desorption microscopy. Field electronic images of the emitter surface reflecting the localization of barium atoms on the emitter surface, representing the quasi-spherical surface of a rhenium single crystal, were obtained. The influence of the temperature of the emitter with adsorbed barium on the change in the emitter work function is shown. Deposition at room temperature leads to the appearance of a dependence of the work function on the concentration of adsorbate with a minimum in the area of optimal coating. Annealing of the emitter at T = 600 K after deposition of each portion of barium causes the minimum to disappear. After reaching the minimum value (optimal coverage with adsorbed atoms), the work function remains constant with an increase in the number of adsorbed barium atoms on the surface of the emitter. A sharp change in the localization of barium atoms due to a phase transition with the formation of islands in the region of the rhenium face was detected on the field electronic image. The change in the nature of the dependence of the work function is associated with a phase transition in the barium film with the formation of barium islands. The concentration of barium in the islet is constant and corresponds to the optimal coating