FROM SMALL-AREA TO IMAGING PHOTOABSORPTION SPECTROSCOPY

We demonstrate a technique for recording atomic core-level photoabsorption spectra from areas as small as 20 μm in diameter using a magnetic-projection photoelectron microscope of the type originally conceived by the Turner group at Oxford University. This microscope relies on the imaging and magnifying properties of a diverging magnetic field and in its present configuration achieves a resolution on the order of microns. In addition to small-area analysis this instrument is capable of performing imaging photoabsorption spectroscopy. In this mode of operation many laterally resolved photoabsorption spectra are collected in parallel by recording sets of total-yield images at various photon energies. The number of spectra is equal to the number of pixels in an image, and taken together these spectra constitute such a complex data set that automated data analysis techniques are warranted. We offer an introduction to principal-component analysis as a tool for analyzing such data sets. This procedure linearly combines the original images so that spectrally similar pixels are more easily recognized. This technique is well established in the field of earth imaging and should be found applicable to surface-sensitive imaging spectroscopies independent of whether the images originate from photon-stimulated, electron-stimulated or ion-stimulated processes. © 1990.