The expression “beauty’s only skin-deep” has often been applied to the chemistry of materials because so much action takes place at the surface. However, for many of the materials in today’s high technologies, such as semiconductors and superconductors, once a device is fabricated, it is the electronic structures below the surface, in the bulk of the material or in buried layers, that determine its effectiveness.

For the past 30 years, one of the most valuable and widely used techniques for studying electronic structures has been ARPES—Angle-Resolved PhotoEmission Spectroscopy. However, this technique primarily looks at surfaces. Now, for the first time, bulk electronic structures have been opened to comparable scrutiny through a new variation of this standard called HARPES—Hard X-ray Angle-Resolved PhotoEmission Spectroscopy—whose development was led by researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).

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