Direct evidence for low-energy electron emission following O LVV Auger transitions at oxide surfaces

Alexander J Fairchild,Philip A Sterne,Randall W Gladen,Varghese A Chirayath,Ali R Koymen,Alex H Weiss

doi:10.1038/s41598-020-74953-6

Alexander J Fairchild, Philip A Sterne + Show 4 more

Open Access

https://doi.org/10.1038/s41598-020-74953-6

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Abstract

Oxygen, the third most abundant element in the universe, plays a key role in the chemistry of condensed matter and biological systems. Here, we report evidence for a hitherto unexplored Auger transition in oxides, where a valence band electron fills a vacancy in the 2s state of oxygen, transferring sufficient energy to allow electron emission. We used a beam of positrons with kinetic energies of sim 1 eV to create O 2s holes via matter-antimatter annihilation. This made possible the elimination of the large secondary electron background that has precluded definitive measurements of the low-energy electrons emitted through this process. Our experiments indicate that low-energy electron emission following the Auger decay of O 2s holes from adsorbed oxygen and oxide surfaces are very efficient. Specifically, our results indicate that the low energy electron emission following the Auger decay of O 2s hole is nearly as efficient as electron emission following the relaxation of O 1s holes in hbox {TiO}_2. This has important implications for the understanding of Auger-stimulated ion desorption, Coulombic decay, photodynamic cancer therapies, and may yield important insights into the radiation-induced reactive sites for corrosion and catalysis.

Highlights

Low-energy electrons are involved in most of the chemical and biological phenomena underlying radiation chemistry playing a central role, for example, in the radiation-induced damage of D NA1 and possibly the origins of life itself[2]
We have measured the kinetic energies of electrons emitted following O LVV Auger transitions for three surfaces: Cu, Si, and TiO2
A fraction of these trapped positrons will annihilate with core electrons creating core holes which may relax via Auger processes

Summary

Introduction

Low-energy electrons are involved in most of the chemical and biological phenomena underlying radiation chemistry playing a central role, for example, in the radiation-induced damage of D NA1 and possibly the origins of life itself[2]. Low-energy electrons are most commonly produced as a result of the ionization of core or valence levels by X-ray photons or energetic charged particles These already ionized atoms or molecules may become further ionized via Auger processes: where correlation effects associated with the filling of vacant electron states (holes) by less tightly bound electrons results in the emission of an electron, the Auger electron. The kinetic energies of these outgoing Auger electrons are characteristic of the electronic levels involved and form the basis of the Auger electron spectroscopies, which have found widespread application in the analysis of s urfaces[3] These low-energy electrons emitted as a result of Auger processes have prompted considerable recent interest in radiobiology due, in part, to their association with enhanced cell lethality[4]. The majority of the annihilation-induced holes and the resulting Auger electrons originate almost entirely from the top-most atomic layer

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