Determining shell thicknesses in stabilised CdSe@ZnS core-shell nanoparticles by quantitative XPS analysis using an Infinitesimal Columns model

Häusler

et al. 2020

Sci Rep

Controlling thickness and tightness of surface passivation shells is crucial for many applications of core–shell nanoparticles (NP). Usually, to determine shell thickness, core and core/shell particle are measured individually requiring the availability of both nanoobjects. This is often not fulfilled for functional nanomaterials such as many photoluminescent semiconductor quantum dots (QD) used for bioimaging, solid state lighting, and display technologies as the core does not show the application-relevant functionality like a high photoluminescence (PL) quantum yield, calling for a whole nanoobject approach. By combining high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS), a novel whole nanoobject approach is developed representatively for an ultrabright oleic acid-stabilized, thick shell CdSe/CdS QD with a PL quantum yield close to unity. The size of this spectroscopically assessed QD, is in the range of the information depth of usual laboratory XPS. Information on particle size and monodispersity were validated with dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) and compared to data derived from optical measurements. In addition to demonstrating the potential of this novel whole nanoobject approach for determining architectures of small nanoparticles, the presented results also highlight challenges faced by different sizing and structural analysis methods and method-inherent uncertainties.

mentioning

confidence: 99%

Combining HR-TEM and XPS to elucidate the core–shell structure of ultrabright CdSe/CdS semiconductor quantum dots

Weigert

Häusler

et al. 2020

Sci Rep

“…With prior knowledge of the structure, and an understanding of the attenuation of electrons within the material, this surface sensitivity can also be utilised to provide measurements of the thickness of coating layers for both flat 12,13 and topographic samples such as nanoparticles. [14][15][16][17][18][19][20] This paper summarises ISO Technical Report ISO/TR 23173 Measurement of the thickness and composition of nanoparticle coatings, recently published under ISO Technical Committee (ISO/TC) 201, Surface Chemical Analysis, Subcommittee (SC) 7, Electron Spectroscopies. 21 This ISO Technical Report is intended to address the capabilities of electron spectroscopies for measurement of nanoparticle coatings and to aid the reader in understanding the available analysis methods, their advantages, disadvantages and potential pitfalls for users performing such measurements.…”

Section: Introductionmentioning

confidence: 99%

Summary of ISO/TC 201 Technical Report 23173—Surface chemical analysis—Electron spectroscopies—Measurement of the thickness and composition of nanoparticle coatings

Cant

Surface & Interface Analysis

Clifford

et al. 2021

including X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and synchrotron techniques, can be employed to calculate the coating thicknesses and compositions of nanoparticles. The document has been developed to review and outline the current state-of-the-art for such measurements. Such analyses of core-shell nanoparticles are common within the literature, however the methods employed are varied; the relative advantages and disadvantages of these methods, and the optimal usage of each may not be clear to the general analyst. ISO Technical Report 23173 aims to clarify the methods that are available, describe them in clear terms, exhibit examples of their use, and highlight potential issues users may face. The information provided should allow analysts of electron spectroscopy data to make clear choices regarding the appropriate analysis of electron spectroscopy data from coated nanoparticle systems and provide a basis for understanding and comparing results from different methods and systems.

“…Efficient synthesis and optimization of such complex systems depend critically on sophisticated analytical techniques for nanoparticle characterization. Because the technical performance and toxicological properties of CSNPs are determined by chemical composition and thickness of their shell, the quantitative analysis of these two parameters by surface analytical techniques, such as X‐ray photoelectron spectroscopy (XPS), has been extensively developed in recent years 1–6 . Not only the high surface sensitivity but also an element specific sensitivity down to 0.1 at% make XPS a very powerful tool for the investigation of nanoparticle coatings.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper, we demonstrate that analysis of inelastically scattered electrons in XPS can provide critical information about the completeness, uniformity, and thickness of nanoparticle coatings. So far, the majority of quantitative analyses of CSNPs by XPS are by default based on the model of a spherical core fully encapsulated by a shell of homogeneous thickness (ideal core‐shell model) 2–5 . However, many real CSNP samples are poorly described by this model and instead show one or several deviations from ideality, including an incomplete encapsulation of the cores by the shell material, a nonuniform shell thickness, nonspherical cores, and intermixing of core and shell material.…”

Section: Introductionmentioning

confidence: 99%

Determining nonuniformities of core‐shell nanoparticle coatings by analysis of the inelastic background of X‐ray photoelectron spectroscopy survey spectra

Surface & Interface Analysis

Sparnacci

Unger

et al. 2020

Most real core-shell nanoparticle (CSNP) samples deviate from an ideal core-shell structure potentially having significant impact on the particle properties. An ideal structure displays a spherical core fully encapsulated by a shell of homogeneous thickness, and all particles in the sample exhibit the same shell thickness. Therefore, analytical techniques are required that can identify and characterize such deviations. This study demonstrates that by analysis of the inelastic background in X-ray photoelectron spectroscopy (XPS) survey spectra, the following types of deviations can be identified and quantified: the nonuniformity of the shell thickness within a nanoparticle sample and the incomplete encapsulation of the cores by the shell material. Furthermore, CSNP shell thicknesses and relative coverages can be obtained. These results allow for a quick and straightforward comparison between several batches of a specific CSNP, different coating approaches, and so forth. The presented XPS methodology requires a submonolayer distribution of CSNPs on a substrate. Poly(tetrafluoroethylene)-poly(methyl methacrylate) and poly(tetrafluoroethylene)polystyrene polymer CSNPs serve as model systems to demonstrate the applicability of the approach.