X-ray photoelectron spectroscopy: From origins to future directions

In this overview, I will briefly explore some of the earliest seeds of modern X-ray photoelectron spectroscopy, as pioneered by Siegbahn and collaborators, and then turn to some examples of how these seeds have sprouted in several present and promising future applications of this technique. Some of the future areas explored will be the use chemical shifts and multiplet splittings in the study of strongly correlated materials, photoelectron diffraction and holography for atomic structure determinations, standing-wave and hard X-ray excited photoemission for probing buried interfaces and bulk properties, valence-band mapping with soft and hard X-ray excitation, and time-resolved measurements with the sample at high ambient pressures in the multi-torr regime.