Imaging Surface Atomic Structure by Means of Auger Electrons

Abstract

Measurements of the complete angular distribution of Auger electrons emitted from well-defined platinum[111] single-crystal surfaces have led to the discovery that the distributions are composed of "silhouettes" of surface atoms "back lit" by emission from atoms deeper in the solid. Theoretical simulations of Auger electron angular distributions based upon atomic point emitters and spherical atomic scatterers of uniform cross section are in close agreement with these experimental results, but opposite to previous theoretical predictions. In view of the definitive results obtained and the straightforward agreement between theory and experiment, angular distribution Auger microscopy (ADAM) is useful for direct imaging of interfacial structure and investigation of electron-solid interactions in the physical and biological sciences and engineering. Applicability of ADAM is illustrated by images obtained for monolayers of silver and iodine on platinum[111].

Photoelectron Diffraction and Synchrotron Radiation

“…Most low-index directions are present in the data as local intensity maxima, and the projections of high atomic density crystal planes appear as bright, narrow bands. This simple interpretation was found valid on many other crystal surfaces [4][5][6][7], and can also be used to analyze similar data from ultrathin films [24].…”

“…First, it has been recognized in the past few years that the measurement of data sets over a large part of the solid angle above the surface, i.e. of twodimensional intensity maps, strongly increases the power of this surface stuctural technique [4][5][6][7]. A high photon flux is therefore needed in order to keep (237) measuring times within reasonable bounds.…”

Unequal-sphere packing model for the structural arrangement of the well-ordered adsorbate-substrate system

“…It is the so-called ͑3 ϫ 3͒-asym structure. [24][25][26][27][28][29][30][31][32][33][34][35][36][37]41,42 We believe that our model based on geometrical principles can also explain the appearance of this particular structure. Note that the arrangement of ͑3 ϫ 3͒-asym iodine adlayer on Pt(111) has been described in many papers, so far.…”

“…In case of ͑3 ϫ 3͒-asym, each threefold iodine atoms is surrounded by six neighboring adatoms positioned at a higher level. [24][25][26][27][28][29][30][31][32][33][34][35][36][37] In order to understand the conditions for appearance and differences between ͑3 ϫ 3͒-sym and ͑3 ϫ 3͒-asym structures we employ our model, looking for a full range of possible FIG. 4.…”

“…Using our model of the unequal spheres we have been able to identify and determine as the most probable, all structural arrangements of the iodine atoms adsorbed at the Pt(111) surface, previously found in experiments by STM, 18,23-30 low-energy electron diffraction (LEED), 5,[31][32][33][34][35][36] and some other techniques. 9,[37][38][39][40][41][42][43][44] In other words, our question, "Up to which level (how far) a system like chemisorbed iodine on the Pt (111) surface can be described in terms of the possible atomic arrangements, by our model based on geometrical principles?" has a simple answer, "completely."…”