ISO/TR 23173:2021 pdf download.Surface chemical analysis一Electron spectroscopies一Measurement of the thickness and composition of nanoparticle coatings.
6.3 Nanoparticle coating thickness Several methods for the determination of nanoparticle coating thicknesses from XPS data are available. These can broadly be categorised into three types: simple numerical modelling, empirically determined formulae and the use of more rigorous simulation software. When any analysis of XPS data from nanoparticles is considered however, there are several assumptions which are typically made. Hereafter, particles conforming to these assumptions are described as “ideal” core-shell particles.
— The analysis area is assumed to be representative of the whole sample, exhibiting no macroscopic variation. In situations where this is not the case, multiple non-overlapping analysis areas can be used to assess the effect of any variation.
— Unless specifically accounted for, the nanoparticles are assumed to be randomly deposited, with no large-scale ordering [22] . This assumption is not necessary if the analysis method requires, or is capable of modelling, particles in a specific distribution.
— All of the measured XPS peak intensities are assumed to arise from the nanoparticles, with no significant contribution from the substrate or contaminants [10] . — The core material and coating are each assumed to be uniform in density, i.e. possess no gaps, density gradients, or similar. It follows from this assumption that the boundary between the core and coating materials is abrupt, with no mixing layer. — The core and coating are assumed to form a pair of concentric spheres.
— All the particles in the analysed population are identical in both chemical and physical structure.
— There is no significant contribution to the signal from particles below the outermost layer, i.e. the electron path lengths do not exceed the particle size. Depending on the analysis method selected, some of these assumptions might not be necessary, or deviations can be accounted for. This is particularly true for more advanced simulation methods, as these can be capable of accounting for many possible structural variations. Because there are a large number of possible structural variations which are indistinguishable directly from XPS data, it is important that deviations from the typical assumed case are understood and characterised using relevant analytical techniques. In some cases, variation in the XPS measurements taken can be used to corroborate or disprove these assumptions; for example the use of multiple separate analysis areas to judge sample homogeneity.ISO/TR 23173 pdf download.