With a scanning tunneling microscope we have taken local work function images of the Au/Cu(111) surface. The local work function measured from large Au-covered terraces is in good agreement with the result obtained by non-local techniques, and the local work function around step edges is significantly lower than that on terraces. The experimental details of the local work function lowering around a step can be reproduced nicely with a simple simulation if a dipole moment row with a proper linear density is put at the center of the step and if the influence of the topographic change of the step due to formation of the dipole moment is taken into account. It is demonstrated that STM has the ability to reveal the details of how local work function varies around steps and other defects on metal surfaces
