INTRINSIC LINEWIDTHS OF IMAGE-POTENTIAL STATES ON NI(111)

With high-resolution two-photon photoemission we fully resolved the lowest three image-potential states on Ni(111) and measured the intrinsic linewidths of the two lowest states. The values 84"10 and 12"10 meV are substantially larger than experimental results and theoretical predictions for other surfaces. A decrease in linewidth of the lowest state after adsorption is observed and indicates that surface states are involved in the decay mechanism. Further possible reasons for this large intrinsic linewidth or Ni(111) are discussed. © 1990 The American Physical Society.