Thiocyanate-capped nanocrystal colloids: Vibrational reporter of surface chemistry and solution-based route to enhanced coupling in nanocrystal solids

Aaron T. Fafarman, Weon Kyu Koh, Benjamin T. Diroll, David K. Kim, Dong Kyun Ko, Soong Ju Oh, Xingchen Ye, Vicky Doan-Nguyen, Michael R. Crump, Danielle C. Reifsnyder, Christopher B. Murray, Cherie R. Kagan

Research output: Contribution to journalArticle

241 Citations (Scopus)

Abstract

Ammonium thiocyanate (NH4SCN) is introduced to exchange the long, insulating ligands used in colloidal nanocrystal (NC) synthesis. The short, air-stable, environmentally benign thiocyanate ligand electrostatically stabilizes a variety of semiconductor and metallic NCs in polar solvents, allowing solution-based deposition of NCs into thin-film NC solids. NH 4SCN is also effective in replacing ligands on NCs after their assembly into the solid state. The spectroscopic properties of this ligand provide unprecedented insight into the chemical and electronic nature of the surface of the NCs. Spectra indicate that the thiocyanate binds to metal sites on the NC surface and is sensitive to atom type and NC surface charge. The short, thiocyanate ligand gives rise to significantly enhanced electronic coupling between NCs as evidenced by large bathochromic shifts in the absorption spectra of CdSe and CdTe NC thin films and by conductivities as high as (2 ± 0.7) × 103 ω-1 cm-1 for Au NC thin films deposited from solution. NH4SCN treatment of PbTe NC films increases the conductivity by 1013, allowing the first Hall measurements of nonsintered NC solids, with Hall effect mobilities of 2.8 ± 0.7 cm2/(V·s). Thiocyanate-capped CdSe NC thin films form photodetectors exhibiting sensitive photoconductivity of 10-5 ω-1 cm-1 under 30 mW/cm2 of 488 nm illumination with Iphoto/Idark > 103 and form n-channel thin-film transistors with electron mobilities of 1.5 ± 0.7 cm2/(V·s), a current modulation of >106, and a subthreshold swing of 0.73 V/decade.

Original languageEnglish
Pages (from-to)15753-15761
Number of pages9
JournalJournal of the American Chemical Society
Volume133
Issue number39
DOIs
Publication statusPublished - 2011 Oct 5
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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    Fafarman, A. T., Koh, W. K., Diroll, B. T., Kim, D. K., Ko, D. K., Oh, S. J., Ye, X., Doan-Nguyen, V., Crump, M. R., Reifsnyder, D. C., Murray, C. B., & Kagan, C. R. (2011). Thiocyanate-capped nanocrystal colloids: Vibrational reporter of surface chemistry and solution-based route to enhanced coupling in nanocrystal solids. Journal of the American Chemical Society, 133(39), 15753-15761. https://doi.org/10.1021/ja206303g