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Enhancement of low-energy electron emission in 2D radioactive films


High-energy radiation has been used for decades; however, the role of low-energy electrons created during irradiation has only recently begun to be appreciated1,2. Low-energy electrons are the most important component of radiation damage in biological environments because they have subcellular ranges, interact destructively with chemical bonds, and are the most abundant product of ionizing particles in tissue. However, methods for generating them locally without external stimulation do not exist. Here, we synthesize one-atom-thick films of the radioactive isotope 125I on gold that are stable under ambient conditions. Scanning tunnelling microscopy, supported by electronic structure simulations, allows us to directly observe nuclear transmutation of individual 125I atoms into 125Te, and explain the surprising stability of the 2D film as it underwent radioactive decay. The metal interface geometry induces a 600% amplification of low-energy electron emission (<10 eV; ref. 3) compared with atomic 125I. This enhancement of biologically active low-energy electrons might offer a new direction for highly targeted nanoparticle therapies4,5,6.

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Figure 1: Overview of radioactive 125I monolayer film preparation and characterization.
Figure 2: Atomic-scale characterization of radioactive 125I monolayer and nuclear transmutation.
Figure 3: Electron emission from radioactive 125I monolayer.

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We thank M. McVey, A. Gellman, E. Rybak-Akimova, A. Utz and S. Thomas for advice and useful discussions. We thank M. Blecher for his assistance with materials preparation. We are grateful to G. Sirr, C. Rock and H. Bernheim for their oversight of safety protocols during the experiments. The work at Tufts was supported by the National Science Foundation under grants CHE-0844343/CHE-1412402 (A.P., C.J.M. and E.C.H.S.). E.A.L. thanks the Division of Chemical Sciences, Office of Basic Energy Sciences, Condensed Phase and Interfacial Molecular Science Program, US Department of Energy (Grant No. FG02-10ER16170) for support. Some of the research at UCL leading to these results has received financial support from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement No. 616121 (HeteroIce project) and the Royal Society through a Wolfson Research merit Award (A.M.). P.P. and A.M. are grateful for computational resources to the London Centre for Nanotechnology and the UK’s national high performance computing service HECToR (from which access was obtained through the UK’s Material Chemistry Consortium, EP/F067496).

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Authors and Affiliations



E.C.H.S. and A.P. conceived and designed the experiments. A.P., C.J.M. and G.B. fabricated the samples. A.P., C.J.M., E.A.L. and F.R.L. carried out STM, XPS and electron emission experiments. A.P. analysed the experimental data and wrote the paper. A.M. and P.P. conceived, designed and analysed the theoretical computations. P.P. performed the theoretical computations. G.P. and G.B. provided materials, radiation-safe laboratory space and safety oversight. All the authors discussed the results and edited the manuscript.

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Correspondence to E. Charles H. Sykes.

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The authors declare no competing financial interests.

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Pronschinske, A., Pedevilla, P., Murphy, C. et al. Enhancement of low-energy electron emission in 2D radioactive films. Nature Mater 14, 904–907 (2015).

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