LOCAL WORK FUNCTION FOR CU(111)-AU SURFACE STUDIED BY SCANNING-TUNNELING-MICROSCOPY

We report results of the measurement of local work function, or appare nt barrier height, on the Au/Cu(111) surface using scanning tunneling microscopy (STM). By measuring a response of tunneling current to a ch ange of the tunneling gap distance during scanning, we can obtain a wo rk function image simultaneously with a topographic STM image. In this way, we could successfully observe the difference in local work funct ion due to different elements and atomic structures. Our results show that the mean work function value of the Au overlayer is 7 +/- 3 % lar ger than that of the Cu(lll) substrate and the value of the work funct ion of the second Au layer is the same as that of the first Au layers within the measurement uncertainty. At the step edges, the work functi on values are lower than that on the terrace. The width and depth of t he low work function trough at Au-Au, and Cu-Au single height steps we re also obtained. The measured values are consistent with those measur ed on vicinal surfaces. This work also suggests that the local work fu nction measurement can be used to identify the element on a surface an d that the STM is quite useful to get information on how the work func tion is related with surface structures and how the work function spat ially changes on nanometer scales. (C) 1997 American Vacuum Society.