Skip to main content
Article
Fabricating Fe nanocrystals via encapsulation at the graphite surface
Journal of Vacuum Science & Technology A
  • Ana Lii-Rosales, Iowa State University and Ames Laboratory
  • Yong Han, Iowa State University
  • King C. Lai, Iowa State University and Ames Laboratory
  • Dapeng Jing, Iowa State University
  • Michael C. Tringides, Iowa State University and Ames Laboratory
  • James W. Evans, Iowa State University and Ames Laboratory
  • Patricia A. Thiel, Iowa State University and Ames Laboratory
Document Type
Article
Publication Version
Published Version
Publication Date
11-13-2019
DOI
10.1116/1.5124927
Abstract

In this paper, the authors describe the conditions under which Fe forms encapsulated nanocrystals beneath the surface of graphite, and they characterize these islands (graphite + Fe) thoroughly. The authors use the experimental techniques of scanning tunneling microscopy (STM) plus x-ray photoelectron spectroscopy (XPS) and the computational technique of density functional theory (DFT). Necessary conditions for encapsulation are preexisting ion-induced defects in the graphite substrate and elevated deposition temperature of 875–900 K. Evidence of encapsulation consists of atomically resolved STM images of a carbon lattice, both on top of the islands and on the sloping sides. The nature of the images indicates that this carbon lattice corresponds to a graphene blanket consisting of more than one graphene sheet that drapes continuously from the top of the island to the graphite substrate. The formation of iron carbide is not observed based on XPS. Shapes of the island footprints are consistent with metallic Fe, predominantly in the hcp or fcc form, though larger islands tend toward bcc. Island structures with hexagonally close-packed lateral hcp or fcc planes are stabilized by their excellent lattice match with the graphite substrate. Evolution of island density with prolonged deposition time provides evidence of coarsening, perhaps via Smoluchowski ripening. The encapsulated Fe clusters are stable in air at room temperature, protected by smaller Fe clusters that decorate defect sites and block permeation of gases. DFT shows that two configurations of Fe are more stable within the gallery than adsorbed on top of the surface: a single atom of Fe and a film (slab) of metallic Fe. Comparison with other metals shows that encapsulated Fe is similar to Cu but dissimilar to Ru or Dy, leading the authors to conclude that carbon dissolution in the metal does not play a role in encapsulation.

Comments

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Lii-Rosales, Ann, Yong Han, King C. Lai, Dapeng Jing, Michael C. Tringides, James W. Evans, and Patricia A. Thiel. "Fabricating Fe nanocrystals via encapsulation at the graphite surface." Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 37, no. 6 (2019): 061403 and may be found at DOI: 10.1116/1.5124927. Posted with permission.

Copyright Owner
American Vacuum Society
Language
en
File Format
application/pdf
Citation Information
Ana Lii-Rosales, Yong Han, King C. Lai, Dapeng Jing, et al.. "Fabricating Fe nanocrystals via encapsulation at the graphite surface" Journal of Vacuum Science & Technology A Vol. 37 Iss. 6 (2019) p. 061403
Available at: http://works.bepress.com/patricia_thiel/170/