First-Principles Methods for Simulating Inelastic Scattering of High Energy Electron Beams by Materials*

 

Recent work relying on the convergent electron beams found in aberration-corrected scanning transmission electron microscopes (STEMs) has demonstrated that highly localized chemical reactions can be controllably induced in materials via electron irradiation.  In certain cases, electron beam-induced reactions can be promoted with true atomic precision.  Such reactions are understood to be driven largely by elastic electron-nucleus scattering processes, through which beam electrons can transfer significant linear momentum to individual nuclei.  However, inelastic scattering —which results in coupled electronic and vibrational excitations in the material — can also occur simultaneously with the elastic scattering by the nuclei.  Whether changes in the potential energy landscape of materials due to such excitations nontrivially influence the reaction kinetics remains an open question.  Our group has recently developed a suite of first-principles tools capable of simulating the electronic and vibrational response of materials to electron beams, both in real- and momentum-space.  The methods are first overviewed, and their application to some simple systems of experimental interest is then presented.  Finally, we provide some perspective on the use of these simulations to guide experimental efforts in the area of beam-induced materials chemistries, and how machine learning approaches can provide a bridge between the disparate timescales of these STEM experiments and ab initio simulations.