Electron-Beam-Assisted Oxygen Purification at Low Temperatures for Electron-Beam-Induced Pt Deposits: Towards Pure and High- Fidelity Nanostructures Harald Plank, †,‡ Joo Hyon Noh, §,∥ Jason D. Fowlkes, § Kevin Lester, § Brett B. Lewis, ∥ and Philip D. Rack* ,§,∥ † Institute for Electron Microscopy and Nanoanalsis, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria ‡ Center for Electron Microscopy, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria § Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States ∥ Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States * S Supporting Information ABSTRACT: Nanoscale metal deposits written directly by electron-beam-induced deposition, or EBID, are typically contaminated because of the incomplete removal of the original organometallic precursor. This has greatly limited the applicability of EBID materials synthesis, constraining the otherwise powerful direct-write synthesis paradigm. We demonstrate a low-temperature purification method in which platinum−carbon nanostructures deposited from MeCpP- tIVMe 3 are purified by the presence of oxygen gas during a post-electron exposure treatment. Deposit thickness, oxygen pressure, and oxygen temperature studies suggest that the dominant mechanism is the electron-stimulated reaction of oxygen molecules adsorbed at the defective deposit surface. Notably, pure platinum deposits with low resistivity and retain the original deposit fidelity were accomplished at an oxygen temperature of only 50 °C. KEYWORDS: focused electron-beam-induced deposition, platinum, nanofabrication, electron-stimulated reactions ■ INTRODUCTION Electron-beam-induced deposition (EBID) is a nanoscale synthesis method in which a scanning focused electron beam induces the local dissociation of adsorbed precursor molecules. 1 Part of the dissociated precursor typically desorbs, and the rest of the original precursor locally condenses. Because this synthesis method is a direct-write technique, EBID has been used for many applications including lithography mask repair 2−4 and nanolithography; 5,6 nanoscale welding (partic- ularly for TEM specimen preparation); 7−10 advanced scanning probe microscopy probes; 11−13 magnetic storage, sensing, and logic applications; 14,15 nanoscale stress−strain sensors, 16−18 electron sources, 19 nano optics, 20 nanoscale gripping devices (nanotweezers), 21 and nanobio applications; 22 diodes; 23 seeds for nanofiber growth 24 and atomic layer deposition; 25 and nanoscale gas sensors. 26 Typically, EBID is performed at room temperature, so besides the metal atoms, nonvolatile byproducts remain on the surface and incorporate in the deposited material. Because most precursors are organometallics, carbonaceous contamination is common with a usually higher atomic content than the intended metal. One important application for EBID is depositing electrodes to contact various nanoscale elements; however, because the deposits have low metal fractions, they exhibit resistivities several orders of magnitude greater than pure metals. 27−29 A few exceptions have been demonstrated, for example, Fernandez-Pacheco et al. showed near-bulk cobalt resistivity without postprocessing 30 and Klein et al. showed single-crystal tungsten nanowires from WF 6 without additional processing. 31 Although a few precursors exhibit pure as-deposited material via EBID, most do not. Thus, much attention has been given towards both in situ and ex situ purification methods. For example, strategies include synchronized laser-assisted EBID, 32,33 annealing of the structures after deposition, 34−37 deposition onto heated substrates, 38,39 varying the deposition parameters (beam current, precursor flux, and scanning method), 36,40,41 introducing reactive gases into the chamber during deposition, 42 the use of carbon-free precursors, 40,43−45 and various other in situ and ex situ processes. 17,18,36,46 For more information on purification methods, see Botman et al. 47 In this study, we investigate the postgrowth purification of platinum−carbon deposits via electron-beam-induced exposure in a low-temperature oxygen ambient. The original Pt−C x Received: October 15, 2013 Accepted: December 30, 2013 Published: December 30, 2013 Research Article www.acsami.org © 2013 American Chemical Society 1018 dx.doi.org/10.1021/am4045458 | ACS Appl. Mater. Interfaces 2014, 6, 1018−1024