Field-emission barrier height of an alloy tip: Possible effect of surface segregation

We have investigated the influence of surface segregation on the field-emission characteristics of alloy emitters. Our tip material is a Ni-0.8 at. % Au alloy where gold segregates to the surface. Emission barrier height was obtained from the slope of the Fowler-Nordheim plot assuming the field proportionality constant estimated from the best image voltage in the field-ion imaging. Upon annealing the alloy tip at 700 K, the barrier height is found to decrease by similar to 0.5 eV. As no lowering of the barrier height was observed in an annealed Ni tip, the observed reduction of the barrier height is attributable to the surface enrichment of gold due to its partial segregation. Our findings thus support the claim by Yoshihara and Yoshitake [J. Vac. Sci. Technol. A 13, 2407 (1995)] that the surface segregation can be used as a method for improving the emission characteristics of field emitters. (C) 1997 American Vacuum Society.