Interaction of nanoparticle properties and X-ray analytical techniques

Abstract

In this work, Pt-Ti core-shell nanoparticles (NP) of 2 nm to 3 nm in size and 30000 u ± 1500 u as specified single particle mass, deposited on flat silicon substrates by means of a massselected cluster beam source, were used for the investigation of the modification of the X-Ray Standing Wave (XSW) field intensity with increasing NP surface coverage. The focus of the investigation is on the determination of the range of validity of the undisturbed flat surface approach of the XSW intensity in dependence of the actual coverage rate of the surface. Therefore, the nanoparticles were characterized using reference-free grazing incidence X-ray fluorescence analysis (GIXRF) employing radiometrically calibrated instrumentation. In addition, near-edge X-ray absorption fine structure (NEXAFS) measurements were performed to investigate the binding state of titanium in the core-shell nanoparticles which was found to be amorphous TiO2. The combination of GIXRF measurements and of the calculated XSW field intensities allow for a quantification of the core-shell nanoparticle surface coverage. For six different samples, the peak surface coverage could be determined to vary from 7 % to 130 % of a complete monolayer-equivalent coverage. A result of the current investigation is that coreshell nanoparticles modify the intensity distribution of the XSW field with increasing surface coverage. This experimental result is in line with calculated XSW field intensity distributions at different surface coverages using an effective density approach.

Quantification of Element Mass Concentrations in Ambient Aerosols by Combination of Cascade Impactor Sampling and Mobile Total Reflection X-ray Fluorescence Spectroscopy

“…An upper limit for quantitative TXRF analysis is given by self-adsorption in the sampled material, which may impair the absolute quantification of elements [35][36][37]. Therefore, the maximum collection time on a set of carriers was several hours at the prevailing moderate average air pollution level of PM 10 below 20 µg/m 3 in Cassino.…”

“…This simple approach is, however, not applicable for samples from cascade impactors like the Dekati for the above-mentioned individual and complex deposition patterns with varying lateral extensions and coverage. These differ from stage to stage, and this has a crucial impact on the quantification of elements in the deposit [36]. There are no robust field-suited techniques that prepare carriers with element standards in patterns mimicking the deposition patterns.…”

“…The accuracy of elements quantification with mobile TXRF spectrometers depends on the carrier load factor, i.e., TXRF is limited by the absolute mass of deposit on the carrier, and non-linear XRF response effects will occur above a certain level. The reference-free XRS methodology of PTB detects these limits using of Grazing Incidence XRF measurements (GIXRF, [33,36,41]). This additional information can be used to assess the reliability of the quantification performed on existing samples and to establish thresholds on the mass of the collected PM.…”

Peculiarities in quantification of airborne particulate matter by means of Total Reflection X-ray Fluorescence

“…However, even if the incident photon energy dependent optical properties are measured beforehand from a blank Si substrate to not rely on tabulated data, the presence of the PM on the top of the Si wafer will impact the reflectivity to a certain extent as the contrast in electronic density at the interface separating the bulk Si from the vacuum or PM is changing. 41 Therefore, the reflectivity R(θ) for each wafer was measured by means of a photodiode positioned in a θ -2θ configuration during the GIXRF measurement. This approach allows for a direct calculation of the incident angle dependent XSW for each sample.…”

Grazing Emission X‐Ray Fluorescence: Novel Concepts and Applications for Nano‐Analytics

“…The attenuation of the X‐rays propagating at a grazing angle is, indeed, discussed in GIXRF for more regularly distributed nanoparticles. [ 139,140 ] Moreover, it has been shown for GIXRF [ 141 ] that the surface coverage can impact the angular intensity profiles, although the impact depends on the energy of interest for the grazing XRF experiment and the elemental composition of the nanoparticles. This aspect has to be kept in mind if accurate information on the nanoparticle morphology is to be extracted from the angular intensity profiles.…”