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Differential photoelectron holography

Atoms near a selected surface atomic site can be imaged in three dimensions by photoelectron holography. The experiment involves acquiring hundreds or thousands of angle-resolved photoemission spectra from a core level of the selected atomic site over a wide range of photon energy and for a large number of emission directions. For good image quality, the precision of the intensity measurement must be better than ∼1% over the entire data set, but this is difficult to achieve. Two methods based on differential measurements that allow intensity self-normalization are presented here as a solution. One method is based on measurements of intensity branching ratios between spin–orbit-split core level peaks, and the other is based on measurements of logarithmic derivatives of the intensity function. These methods are illustrated by two examples, As-terminated Si(1 1 1) and Bi-terminated Si(1 1 1). The As/Si(1 1 1) results are in excellent agreement with the accepted structure of the system, thus verifying the efficacy of the methods. The Bi/Si(1 1 1) results resolve a long-standing controversy regarding the correct structure of this system.