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Electron conduction through bare metal oxide nanocrystal (NC) films is hindered by surface depletion regions resulting from the presence of surface states. We control the radial dopant distribution in tin-doped indium oxide (ITO) NCs as a means to manipulate the NC depletion width. We find in films of ITO NCs of equal overall dopant concentration that those with dopant-enriched surfaces show decreased depletion width and increased conductivity. Variable temperature conductivity data show electron localization length increases and associated depletion width decreases monotonically with increased density of dopants near the NC surface. We calculate band profiles for NCs of differing radial dopant distributions and in agreement with variable temperature conductivity fits find NCs with dopant-enriched surfaces have narrower depletion widths and longer localization lengths than those with dopant-enriched cores. Following amelioration of NC surface depletion by atomic layer deposition of alumina, all films of equal overall dopant concentration have similar conductivity. Variable temperature conductivity measurements on alumina-capped films indicate all films behave as granular metals. Herein, we conclude that dopant-enriched surfaces decrease the near-surface depletion region, which directly increases the electron localization length and conductivity of NC films.
Bibliographical noteFunding Information:
This research was supported by the National Science Foundation (NSF), including NASCENT, an NSF ERC (EEC-1160494, C.M.S.), CHE-1609656 (A.A.), the University of Texas at Austin MRSEC (DMR-1720595), the University of Minnesota MRSEC (DMR-1420013; Z.L.R., B.L.G., U.R.K.), a Graduate Research Fellowship under Award Number (DGE-1610403, S.L.G.), and the Welch Foundation (F-1848). This work was performed in part at the Molecular Foundry, Lawrence Berkeley National Laboratory, which is supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231. S.D.L. was supported by a DOE Early Career Research Program grant to D.J.M.
© 2018 American Chemical Society.
- band profile
- dopant distribution
- tin-doped indium oxide
How much support was provided by MRSEC?
Reporting period for MRSEC
- Period 5
PubMed: MeSH publication types
- Journal Article
- Research Support, U.S. Gov't, Non-P.H.S.
- Research Support, Non-U.S. Gov't