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Title: Tuning Confinement in Colloidal Silicon Nanocrystals with Saturated Surface Ligands

The optical properties of silicon nanocrystals (Si NCs) are a subject of intense study and continued debate. In particular, Si NC photoluminescence (PL) properties are known to depend strongly on the surface chemistry, resulting in electron-hole recombination pathways derived from the Si NC band-edge, surface-state defects, or combined NC-conjugated ligand hybrid states. In this Letter, we perform a comparison of three different saturated surface functional groups - alkyls, amides, and alkoxides - on nonthermal plasma-synthesized Si NCs. We find a systematic and size-dependent high-energy (blue) shift in the PL spectrum of Si NCs with amide and alkoxy functionalization relative to alkyl. Time-resolved photoluminescence and transient absorption spectroscopies reveal no change in the excited-state dynamics between Si NCs functionalized with alkyl, amide, or alkoxide ligands, showing for the first time that saturated ligands - not only surface-derived charge-transfer states or hybridization between NC and low-lying ligand orbitals - are responsible for tuning the Si NC optical properties. To explain these PL shifts we propose that the atom bound to the Si NC surface strongly interacts with the Si NC electronic wave function and modulates the Si NC quantum confinement. Furthermore, these results reveal a potentially broadly applicable correlation between the optoelectronicmore » properties of Si NCs and related quantum-confined structures based on the interaction between NC surfaces and the ligand binding group.« less
Authors:
ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Report Number(s):
NREL/JA-5900-71481
Journal ID: ISSN 1530-6984
Grant/Contract Number:
AC36-08GO28308
Type:
Accepted Manuscript
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 18; Journal Issue: 5; Journal ID: ISSN 1530-6984
Publisher:
American Chemical Society
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 77 NANOSCIENCE AND NANOTECHNOLOGY; lifetime; photoluminescence; quantum confinement; recombination; silicon nanocrystals; surface chemistry
OSTI Identifier:
1436402

Carroll, Gerard M., Limpens, Rens, and Neale, Nathan R.. Tuning Confinement in Colloidal Silicon Nanocrystals with Saturated Surface Ligands. United States: N. p., Web. doi:10.1021/acs.nanolett.8b00680.
Carroll, Gerard M., Limpens, Rens, & Neale, Nathan R.. Tuning Confinement in Colloidal Silicon Nanocrystals with Saturated Surface Ligands. United States. doi:10.1021/acs.nanolett.8b00680.
Carroll, Gerard M., Limpens, Rens, and Neale, Nathan R.. 2018. "Tuning Confinement in Colloidal Silicon Nanocrystals with Saturated Surface Ligands". United States. doi:10.1021/acs.nanolett.8b00680. https://www.osti.gov/servlets/purl/1436402.
@article{osti_1436402,
title = {Tuning Confinement in Colloidal Silicon Nanocrystals with Saturated Surface Ligands},
author = {Carroll, Gerard M. and Limpens, Rens and Neale, Nathan R.},
abstractNote = {The optical properties of silicon nanocrystals (Si NCs) are a subject of intense study and continued debate. In particular, Si NC photoluminescence (PL) properties are known to depend strongly on the surface chemistry, resulting in electron-hole recombination pathways derived from the Si NC band-edge, surface-state defects, or combined NC-conjugated ligand hybrid states. In this Letter, we perform a comparison of three different saturated surface functional groups - alkyls, amides, and alkoxides - on nonthermal plasma-synthesized Si NCs. We find a systematic and size-dependent high-energy (blue) shift in the PL spectrum of Si NCs with amide and alkoxy functionalization relative to alkyl. Time-resolved photoluminescence and transient absorption spectroscopies reveal no change in the excited-state dynamics between Si NCs functionalized with alkyl, amide, or alkoxide ligands, showing for the first time that saturated ligands - not only surface-derived charge-transfer states or hybridization between NC and low-lying ligand orbitals - are responsible for tuning the Si NC optical properties. To explain these PL shifts we propose that the atom bound to the Si NC surface strongly interacts with the Si NC electronic wave function and modulates the Si NC quantum confinement. Furthermore, these results reveal a potentially broadly applicable correlation between the optoelectronic properties of Si NCs and related quantum-confined structures based on the interaction between NC surfaces and the ligand binding group.},
doi = {10.1021/acs.nanolett.8b00680},
journal = {Nano Letters},
number = 5,
volume = 18,
place = {United States},
year = {2018},
month = {4}
}