Quantifying the Impact of Nanoparticle Coatings and Nonuniformities on XPS Analysis: Gold/Silver Core-Shell Nanoparticles

Citation

Wang, Y. C.; Engelhard, M. H.; Baer, D. R.; & Castner, D. G. (2016). Quantifying the Impact of Nanoparticle Coatings and Nonuniformities on XPS Analysis: Gold/Silver Core-Shell Nanoparticles. Anal Chem, 88(7), 3917-3925. PMCID: 4821750

Abstract

Spectral modeling of photoelectrons can serve as a valuable tool when combined with X-ray photoelectron spectroscopy (XPS) analysis. Herein, a new version of the NIST Simulation of Electron Spectra for Surface Analysis (SESSA 2.0) software, capable of directly simulating spherical multilayer NPs, was applied to model citrate stabilized Au/Ag-core/shell nanoparticles (NPs). The NPs were characterized using XPS and scanning transmission electron microscopy (STEM) to determine the composition and morphology of the NPs. The Au/Ag-core/shell NPs were observed to be polydispersed in size, nonspherical, and contain off-centered Au-cores. Using the average NP dimensions determined from STEM analysis, SESSA spectral modeling indicated that washed Au/Ag-core-shell NPs were stabilized with a 0.8 nm layer of sodium citrate and a 0.05 nm (one wash) or 0.025 nm (two wash) layer of adventitious hydrocarbon, but did not fully account for the observed XPS signal from the Au-core. This was addressed by a series of simulations and normalizations to account for contributions of NP nonsphericity and off-centered Au-cores. Both of these nonuniformities reduce the effective Ag-shell thickness, which effect the Au-core photoelectron intensity. The off-centered cores had the greatest impact for the particles in this study. When the contributions from the geometrical nonuniformities are included in the simulations, the SESSA generated elemental compositions that matched the XPS elemental compositions. This work demonstrates how spectral modeling software such as SESSA, when combined with experimental XPS and STEM measurements, advances the ability to quantitatively assess overlayer thicknesses for multilayer core-shell NPs and deal with complex, nonideal geometrical properties.

Keyword(s)

Gold/*analysis
Metal Nanoparticles/*analysis
Microscopy, Electron, Scanning Transmission
Particle Size
Photoelectron Spectroscopy
Silver/*analysis
Software
Surface Properties

Notes

Wang, Yung-Chen
Engelhard, Mark H
Baer, Donald R
Castner, David G
P41 EB002027/EB/NIBIB NIH HHS/
U19 ES019544/ES/NIEHS NIH HHS/
EB-002027/EB/NIBIB NIH HHS/
Anal Chem. 2016 Apr 5;88(7):3917-25. doi: 10.1021/acs.analchem.6b00100. Epub 2016 Mar 17.

Reference Type

Journal Article

Secondary Title

Anal Chem

Author(s)

Wang, Y. C.
Engelhard, M. H.
Baer, D. R.
Castner, D. G.

Year Published

2016

Date Published

1743811200

Volume Number

88

Issue Number

7

Pages

3917-3925

ISSN/ISBN

1520-6882 (Electronic)
0003-2700 (Linking)

DOI

10.1021/acs.analchem.6b00100

PMCID

4821750