SECOND LAYER MIGRATION WITH TRAPPING ON FIRST LAYER SITES - HYDROGEN NITROGEN AND CARBON MONOXIDE ON TUNGSTEN

Second layer migration of hydrogen, nitrogen and carbon monoxide with trapping on first layer sites of tungsten is observed with a field emission microscope. The initial deposition on the tungsten surface at 4.2 °K is made with molecular beams with the tungsten emitter axis perpendicular to the beam direction. The migration of the deposit is effected at temperatures far below those for which the chemisorbed layer is mobile. The shapes of the sharp line boundaries as the second layer migrates over the chemisorbed layer and onto the clean tungsten substrate are quite different for the three gases observed. It is proposed that, in addition to the barrier effects of certain planes of the tungsten, the density of trap sites on the clean surface determines the boundary configuration. © 1968.