title: Atomic-Scale Picture of the Composition, Decay, and Oxidation of Two-Dimensional Radioactive Films.
abstract: Two-dimensional radioactive (125)I monolayers are a recent development that combines the fields of radiochemistry and nanoscience. These Au-supported monolayers show great promise for understanding the local interaction of radiation with 2D molecular layers, offer different directions for surface patterning, and enhance the emission of chemically and biologically relevant low-energy electrons. However, the elemental composition of these monolayers is in constant flux due to the nuclear transmutation of (125)I to (125)Te, and their precise composition and stability under ambient conditions has yet to be elucidated. Unlike I, which is stable and unreactive when bound to Au, the newly formed Te atoms would be expected to be more reactive. We have used electron emission and X-ray photoelectron spectroscopy (XPS) to quantify the emitted electron energies and to track the film composition in vacuum and the effect of exposure to ambient conditions. Our results reveal that the Auger electrons emitted during the ultrafast radioactive decay process have a kinetic energy corresponding to neutral Te. By combining XPS and scanning tunneling microscopy experiments with density functional theory, we are able to identify the reaction of newly formed Te to TeO2 and its subsequent dimerization. The fact that the Te2O4 units stay intact during major lateral rearrangement of the monolayer illustrates their stability. These results provide an atomic-scale picture of the composition and mobility of surface species in a radioactive monolayer as well as an understanding of the stability of the films under ambient conditions, which is a critical aspect in their future applications.
authors.affiliation: Department of Chemistry, Tufts University , 62 Talbot Avenue, Medford, Massachusetts 02155, United States.
authors.forename: Alex
authors.initials: A
authors.lastname: Pronschinske
authors.affiliation: Thomas Young Centre, London Centre for Nanotechnology and Department of Chemistry, University College London , London WC1E 6BT, United Kingdom.
authors.forename: Philipp
authors.initials: P
authors.lastname: Pedevilla
authors.affiliation: Department of Chemistry, Tufts University , 62 Talbot Avenue, Medford, Massachusetts 02155, United States.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Coughlin
authors.affiliation: Department of Chemistry, Tufts University , 62 Talbot Avenue, Medford, Massachusetts 02155, United States.
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Murphy
authors.affiliation: Department of Chemistry, Tufts University , 62 Talbot Avenue, Medford, Massachusetts 02155, United States.
authors.forename: Felicia R
authors.initials: FR
authors.lastname: Lucci
authors.affiliation: Department of Chemical Engineering, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Payne
authors.affiliation: Department of Chemical Engineering, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Gellman
authors.affiliation: Thomas Young Centre, London Centre for Nanotechnology and Department of Chemistry, University College London , London WC1E 6BT, United Kingdom.
authors.forename: Angelos
authors.initials: A
authors.lastname: Michaelides
authors.affiliation: Department of Chemistry, Tufts University , 62 Talbot Avenue, Medford, Massachusetts 02155, United States.
authors.forename: E Charles H
authors.initials: EC
authors.lastname: Sykes
keywords: 2D material; STM; electron emission; iodine-125; radioactive; self-sustaining electron source