Field ion and field emission microscopy of gallium, indium, and tin on tungsten

Gallium, indium and tin were deposited on a tungsten tip by making a contact between the tip and these metals in the liquid state. The activation energies of diffusion of the adsorbates on tungsten were found to be 0.29 eV for Ga, 0.35 eV for In and 0.71 eV for Sn. The adsorbates were field-evaporated by gradually increasing a positive tip voltage by a small increment each time and the variation of the work function with the decreasing coverage was examined for each evaporation stage. The result indicates that the adatoms assume one of two different adsorption states. The adatoms bound as strongly as in a bulk crystal were field-evaporated at a low evaporation field. The remaining adatoms form a more strongly bound covering layer which maximizes the average work function of the substrate, 4.75 eV for Ga, 4.63 eV for In and 5.10 eV for Sn, and are field-evaporated at a significantly higher field. The covering layer of the strongly bound adatoms were hardly noticed on the (011) and (112) areas. The arrangement of the strongly bound adatoms, particularly on the (114) planes, is found to be a precise replica of the substrate