"The interface is the device," Nobel laureate
A new technique from an international team of researchers working at
"SWARPES allows us for the first time to selectively study buried interfaces with either soft or hard x-rays," Fadley says. "The technique can be applied to any multilayer prototype device structure in spintronics, strongly correlated/high-TC superconductors, or semiconductor electronics. The only limitations are that the sample has to have a high degree of crystalline order, and has to be grown on a nanoscale multilayer mirror suitable for generating an x-ray standing wave."
As the name indicates, SWARPES combines the use of standing waves of x-rays with ARPES, the technique of choice for studying electronic structure. A standing wave is a vibrational pattern created when two waves of identical wavelength interfere with one another: one is the incident x-ray and the other is the x-ray reflected by a mirror. Interactions between standing waves and core-level electrons reveal much about the properties of each atomic species in a sample. ARPES from the outer valence levels is the long-standing spectroscopic workhorse for the study of electronic structure. X-rays striking a material surface or interface cause the photoemission of electrons at angles and kinetic energies that can be measured to obtain detailed electronic energy levels of the sample. While an extremely powerful tool, ARPES, a soft x-ray technique, is primarily limited to the study of near-surface atoms. It's harder x-ray cousin, HARPES, makes use of more energetic x-rays to effectively probe subsurface interfaces, but the addition of the standing wave capability provides a much desired depth selectivity.
"The standing wave can be moved up and down in a sample simply by rocking the angle of incidence around the Bragg angle of the mirror," says
Fadley, Gray and their collaborators carried out their SWARPES tests at ALS Beamline 7.0.1. The Advanced Light Source is a
Results of this study have been published in Europhysics Letters (EPL). The paper is titled "
This research was supported primarily by the
For more about the research of
For more about
For more about NCEM go here (http://ncem.lbl.gov/)
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