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

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, non-spherical, 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 0.025nm (two wash) layer of adventitious hydrocarbon, but didn’t 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 non-sphericity and off-centered Au-cores. Both of these non-uniformities 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 non-uniformities 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.

Differential effects of silver nanoparticles on DNA damage and DNA repair gene expression in Ogg1-deficient and wild type mice

“…Nanoparticles were supplied by the National Institute of Environmental Health Sciences Centers for Nanotechnology Health Implications Research (NCNHIR) consortium and their physiochemical characteristics were described in other studies (Bergin et al 2016; Munusamy et al 2015; Wang et al 2014, 2016). Briefly, ~20 nm diameter particles had been grown on ~7–8 nm gold (Au) seed particles and had a thin layer (~1 nm) of sodium citrate (Munusamy et al 2015; Wang et al 2016). AgNPs were supplied as particles dispersed in 2 mM sodium citrate at Ag concentration of 1 mg/ml (Biopure™).…”

“…Physicochemical characterization of AgNPs was performed by the manufacturer (nanoComposix), the Nanotechnology Characterization Laboratory (NCL) at the National Cancer Institute, the NCNHIR consortium (Bergin et al 2016; Munusamy et al 2015; Wang et al 2014, 2016), and in-house prior to use. AgNP colloidal stability was monitored by UV-visible (UV-vis) spectroscopy with a NanoDrop1000 Spectrophotometer v3.8 (Thermo Fisher Scientific, Franklin, MA).…”

A surfactant‐free synthesis of the silica nanosphere‐supported ultrafine silver nanoparticles and their antibacterial effects

“…First, the wide scan spectra confirmed the existence of carbon, oxygen, silicon, sulfur, and silver elements on the surface of the product. Then, the high‐resolution XPS spectrum of silver, as shown in the inset, showed peaks of 374.1 and 368.1 eV, which could be assigned to the 3 d 3/2 and 3 d 5/2 of metallic silver, respectively, as another evident for silver in the metallic form …”

Use of XPS to Quantify Thickness of Coatings on Nanoparticles

“…Recent work has combined STEM/HAADF images of many particles with XPS data from a collection of particles to obtain insights regarding the impact of non-ideal structural features within a collection of particles, such as non-circularity and off-center cores, on XPS results [19]. …”