Direct evidence of electron tunneling in the ionization of sputtered atoms

Direct evidence has been obtained for electron tunneling between sputtered Cs+ ions and the solid surfaces from which they originate. Strong neutralization of the Cs+ ions is observed whenever the tunneling channel is opened by changing the surface work function so that a crossing of the Fermi level by the Cs 6s level occurs. A tunneling model which takes the spatial dependences of the position and the width of the atomic level into account explains the data successfully. © 1983 The American Physical Society.