Energy and angular distribution of secondary electrons emitted from Si(111)-7x7,root 3x root 3-Ag and 5x2-Au surfaces

Energy and angular distribution of secondary electrons (SE) emitted from Si(111)-7 x 7, root 3 x root 3-Ag and 5 x 2-Au surfaces, excited by a 15 keV primary electron beam, has been measured in an ultrahigh-vacuum (UHV) chamber. SE from 7 x 7 and root 3 x root 3-Ag surfaces show angular dependence nearly proportional to cos (theta) with theta denoting the emission angle referred to surface normal; while those from 5 x 2-Au decrease more rapidly with theta. The latter can be explained by an additional field between the sample and the detector, resulting from the larger work function of 5 x 2-Au. The measurement of the spectra of SE emitted normally from the surface reveals that, compared with a 7 x 7 surface, a root 3 x root 3-Ag surface has much larger intensity in the whole energy range measured (0-10 eV), while a 5 x 2-Au surface shifts the whole spectrum by similar to 0.5 eV with slight reduction in intensity. These can be well accounted for by the effect of band-bending and the difference in work functions. On a surface where 5 x 2-Au and 7 x 7 domains are simultaneously present, it is experimentally verified that the lowest energy SE emitted from the smaller work function (7 x 7) domains cannot reach the detector. The measurements are in qualitative agreement with observations with UHV scanning electron microscope (SEM), reported by the present authors before, showing that root 3 x root 3-Ag and 5 x 2-Au domains appear brighter in SE images than simultaneously present 7 x 7 domains.