Experimental measurement of the intensity profiles of a low-energy electron beam extracted from a scanning tunneling microscope tip by field emission

The intensity profile of a low-energy electron beam (e-beam) extracted from the tip apex of a scanning tunneling microscope (STM) in the field emissio n mode was measured in an ultrahigh-vacuum environment. The sizes of areas where the native Si oxide was removed by exposure to the low-energy e-beam were measured as a function of the e-beam exposure time, and it was found t hat the e-beam has a Gaussian-type lateral profile. The results show that t he e-beam profile can be controlled by adjusting the parameters of the e-be am emission and that the sizes of the Si oxide opening windows can he adjus ted by varying the e-beam exposure time.