Core-level shift at a jelliumlike surface: Al(001)

The shift of $2p$ core-level binding energies associated with surface atoms relative to bulk atoms for an Al(001) surface has been determined using photoemission partial-yield techniques. The observed shift is -57 meV. A possible mechanism for the core-level shift is discussed using a simple jellium model; i.e., the shift is related to the variation in the electrostatic potential associated with the conduction-electron response to the jelliumlike surface potential step.