Davisson-Germer Prize in Atomic or Surface PhysicsTwist and turn of electron diffraction

De Broglie hypothesized the bold concept of matter waves in 1924. Davisson and Germer validated the wave nature of electrons experimentally using low-energy electron diffraction (LEED) from a single crystal nickel in 1927. It was a milestone in the creation of quantum mechanics. In the 60s, with the availability of commercial vacuum technology and advanced electron detection plus the short mean free path of low energy electrons, LEED has opened a new field of surface science.

A conventional LEED has a broad instrument response function that limits the largest distance that the long-range order in real space can be resolved. In the 80s, our group used a high-resolution LEED or spot profile analysis LEED (SPALEED) developed by Henzler [1] where the Ewald sphere is twisting instead of fixing at normal incidence in conventional LEED. We studied surface roughening transition before surface melting, vacancy induced disordering, and kinetics of overlayer ordering.

For electrons with higher energy in the tens of keV used in reflection high-energy electron diffraction (RHEED), it has a longer mean free path. RHEED has been widely used to monitor epitaxial thin film growth in molecular beam epitaxy. In the early 2000s, our group demonstrated RHEED pole figure analysis for surface texture evolution of polycrystalline and nanostructured films [2]. In the last decade our group used the azimuthal RHEED by turning the sample azimuthally in-plane and map out the reciprocal space structure above the sample [3]. Selected examples of wafer scale TMDC (transition-metal dichalcogenide) monolayers, heterostructures, compound semiconductors, and ultrathin epitaxial oxide film will be presented. An outlook on electron diffraction is exciting with continued development by scientists that will further advance the understanding of nanoscale surfaces and their structural dynamics.