IMAGING MONOLAYER STRUCTURE BY MEANS OF AUGER ELECTRONS

We report the complete angular distribution of 507 and 518 eV Auger electrons emitted from a monolayer of iodine atoms on single-crystal platinum, Pt(111) (square-root 7 X square-root 7) R 19.1-degrees--I. This monolayer is of particular interest because: (i) it provides an opportunity to measure an angular distribution of relatively high kinetic energy Auger electrons emitted from a single monolayer of known structure; and (ii) the structure of the monolayer has been independently determined from scanning tunneling microscopy and low-energy electron diffraction, permitting one to unambiguously relate features in the angular distribution to the structure. The experimental angular distribution contains intensity minima along trajectories corresponding to the I-I internuclear directions and intensity maxima along trajectories corresponding to gaps between neighboring iodine atoms. A simulation of the angular distribution in which iodine atoms are treated as point-emitters and spherical blockers of Auger electrons predicts the features in the experimental angular distribution, and fits the data very closely (the correlation coefficient is > 0.98). This result indicates that iodine atoms act predominantly to block Auger electrons in this energy range, producing silhouettes in the angular distribution. The locations and shapes of the silhouettes are therefore a direct consequence of the relative positions of atoms, making angular distribution Auger microscopy a useful technique for real-space imaging of surface atomic and monolayer structure.