Characterization of Silicon Nanocrystal Surfaces by Multidimensional Solid-State NMR Spectroscopy

Nathan Neale, Lance Wheeler, Michael Hanrahan, Ellie Fought, Theresa Windus, Aaron Rossini, Nicholas Anderson

Research output: Contribution to journalArticlepeer-review

34 Scopus Citations

Abstract

The chemical and photophysical properties of silicon nanocrystals (Si NCs) are strongly dependent on the chemical composition and structure of their surfaces. Here we use fast magic angle spinning (MAS) and proton detection to enable the rapid acquisition of dipolar and scalar 2D 1H-29Si heteronuclear correlation (HETCOR) solid-state NMR spectra and reveal a molecular picture of hydride-terminated and alkyl-functionalized surfaces of Si NCs produced in a nonthermal plasma. 2D 1H-29Si HETCOR and dipolar 2D 1H-1H multiple-quantum correlation spectra illustrate that resonances from surface mono-, di-, and trihydride groups cannot be resolved, contrary to previous literature assignments. Instead the 2D NMR spectra illustrate that there is large distribution of 1H and 29Si chemical shifts for the surface hydride species in both the as-synthesized and functionalized Si NCs. However, proton-detected 1H-29Si refocused INEPT experiments can be used to unambiguously differentiate NMR signals from the different surface hydrides. Varying the 29Si evolution time in refocused INEPT experiments and fitting the oscillation of the NMR signals allows for the relative populations of the different surface hydrides to be estimated. This analysis confirms that monohydride species are the predominant surface species on the as-synthesized Si NCs. A reduction in the populations of the di- and trihydrides is observed upon functionalization with alkyl groups, consistent with our previous hypothesis that the trihydride, or silyl (∗SiH3), group is primarily responsible for initiating surface functionalization reactions. Density functional theory (DFT) calculations were used to obtain quantum chemical structural models of the Si NC surface and reproduce the observed 1H and 29Si chemical shifts. The approaches outlined here will be useful to obtain a more detailed picture of surface structures for Si NCs and other hydride-passivated nanomaterials.

Original languageAmerican English
Pages (from-to)10339-10351
Number of pages13
JournalChemistry of Materials
Volume29
Issue number24
DOIs
StatePublished - 26 Dec 2017

Bibliographical note

Publisher Copyright:
© 2017 American Chemical Society.

NREL Publication Number

  • NREL/JA-5900-69045

Keywords

  • 29Si NMR
  • DFT
  • HETCOR
  • INEPT
  • silicon nanoparticles
  • silicon surface functionalization, solid-state NMR
  • solar-photochemistry
  • surface silicon hydride

Fingerprint

Dive into the research topics of 'Characterization of Silicon Nanocrystal Surfaces by Multidimensional Solid-State NMR Spectroscopy'. Together they form a unique fingerprint.

Cite this