Low-energy neon-ion scattering and neutralization on first and second layers of a Ni(001) surface

The scattering and neutralization of 2.4 and 5 keV Ne⁺ ions on the Ni(001) surface have been studied by time-of-flight (TOF) and electrostatic analyzer (ESA) techniques. The scattering yield of neutrals plus ions (by TOF) is strongly dependent on crystal orientation, in one direction being reduced by the shadowing of 2nd layer atoms by 1st layer atoms, or in another being increased by focussing of ions onto the 2nd layer by 1st layer atoms. Ion yields (by ESA) show little of this variation since the ions are largely neutralized on scattering from the second layer. The results thus demonstrate and explain the first layer selectivity of low-energy ion scattering by ESA for a case in which there is no shadowing of second layer atoms by the first layer. On the other hand, the ability to measure and distinguish first and second layer scattering of neutrals and ions by TOF suggests the possibility of composition analysis of individual layers of single crystal alloys and compound semiconductors.