Electron collisions with atoms, ions, molecules, and surfaces: Fundamental science empowering advances in technology

Abstract

Electron collisions with atoms, ions, molecules, and surfaces are critically important to the understanding and modeling of low-temperature plasmas (LTPs), and so in the development of technologies based on LTPs. Recent progress in obtaining experimental benchmark data and the development of highly sophisticated computational methods is highlighted. With the cesium-based diode-pumped alkali laser and remote plasma etching of Si 3 N 4 as examples, we demonstrate how accurate and comprehensive datasets for electron collisions enable complex modeling of plasma-using technologies that empower our high-technology-based society.electron scattering | close coupling | ab initio | plasmas | kinetic modeling Electron collisions with atoms, ions, molecules, and surfaces are critically important to the understanding and the modeling of laboratory plasmas, astrophysical processes, lasers, and planetary atmospheres, to name just a few examples. In addition to the investigation of naturally occurring phenomena, electron collisions form the basis of a vast array of plasma-using technologies, which continue to empower our high-technology-based society (1). Atomic, molecular, and optical (AMO) physics, the field that encompasses electron-atom and electron-molecule collisions, has made tremendous contributions to our fundamental understanding of nature. Despite the field's longevity, breakthrough developments in atomic collisions continue to be made at the fundamental level of both experiment and theory. The Need for Atomic and Molecular DataIn low-temperature plasmas (LTPs), electron and ion collisions with otherwise unreactive gas and surfaces activate those atoms and molecules through forming excited states, ions, and radicals. Those activated species are then used in applications ranging from microelectronics fabrication (2) to human healthcare (3). The most basic, necessary, and first step in the development of those technologies is the electron or ion impact with the initially unreactive species to produce the activated species. As a result, fundamental AMO physics is closely and beneficially connected to technology development.Examples of experimental progress in advancing the knowledge base for LTPs include, but are certainly not limited to, the "magnetic angle changer" (MAC) (4) and the so-called "reaction microscope" (RM) (5). The MAC makes it possible to carry out measurements of electron impact cross sections in angular regimes that were previously inaccessible because of geometric limitations due to the position of the electron gun. Furthermore, taking advantage of dramatic improvements in detector technology and fast electronics, the RM has enabled unparalleled detailed studies of electron-atom and electron-molecule collision processes over a wide range of parameters (energies, angles), and so provided an extensive database to test theory.At the same time, theoretical and particularly computational advances have made the calculation of data for atomic/molecular structure as well as electron collision processes both r...

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