  Strongly differing static dipole moments of the trans and cis isomers of
photochromic azobenzene allow for optical switching the work function of
azobenzene-functionalized self-assembled monolayers (SAMs). We apply these
properties in a fundamental experiment to manipulate the area size of the
switched SAM. Azobenzene molecules were excited by ultraviolet laser
illumination and the transient isomerization profile of the SAM was spatially
resolved recording photoemission electron microscopy (PEEM) images. Thereby we
demonstrate the spatial tuning of the SAM work-function and discuss the role of
the laser spot-profile in generating sharp edges or gradual changes of the work
function.
