Article pubs.acs.org/cm
Cite This: Chem. Mater. 2018, 30, 5961−5967
Selective Removal of Ligands from Colloidal Nanocrystal Assemblies with Non-Oxidizing He Plasmas Santosh Shaw,† Xinchun Tian,† Tiago F. Silva,‡ Jonathan M. Bobbitt,§,# Fabian Naab,∥ Cleber L. Rodrigues,‡ Emily A. Smith,§,⊥ and Ludovico Cademartiri*,†,#,⊥
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Department of Materials Science & Engineering, Iowa State University of Science and Technology, 2220 Hoover Hall, Ames, Iowa 50011, United States ‡ Instituto de Física da Universidade de São Paulo, Rua do Matão, trav. R 187, 05508-090 São Paulo, Brazil § Department of Chemistry, Iowa State University of Science and Technology, Gilman Hall, Ames, Iowa 50011, United States ∥ Michigan Ion Beam Laboratory, University of Michigan, 2600 Draper Road, Ann Arbor, Michigan 48109, United States ⊥ Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011, United States # Department of Chemical & Biological Engineering, Iowa State University of Science and Technology, Sweeney Hall, Ames, Iowa 50011, United States S Supporting Information *
ABSTRACT: Helium plasmas are attractive reagents for the removal of organics from hybrid materials because of their minimal ablative power and relative inertness, compared to oxidizing feed gases such as O2 and highly ablative inert gases such as Ar. This work describes the use of dilute helium plasmas to selectively remove the organic ligands from films of colloidal nanoparticles (i.e., colloidal nanoparticle assemblies). We determine the relative contribution to etching of different plasma species in a model system consisting of films of ZrO2 nanoparticles capped with trioctylphosphine oxide. Unexpectedly, we find that the strong ultraviolet radiation of He plasma is only a minor contributor to etching (25% of the etched carbon). Excited He species are responsible for most of the etching (75% of the etched carbon). Carbon concentrations as low as 3.5 atom % can be achieved under non-optimized plasma processing conditions.
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ineffective5). Recently, we reported that oxidizing plasmas (O2 and air) can remove ligands from colloidal nanocrystal assemblies (CNAs). The removal of ligands is essentially complete (
