Development of traceable and reliable x-ray analytical techniques for chemical analysis of airborne particle

The aim of this work package is to develop and establish traceable and reliable x-ray methods to measure the elemental mass deposition per unit area, elemental composition, and the chemical binding state (species) of airborne particles deposited on flat substrates (such as Quartz glass or Si wafers) as used in cascade impactors for size discriminating coarse and ultrafine fractions.

For the further qualification of x-ray analytical techniques under grazing incidence such as TXRF and GIXRF to analyse fine and ultrafine particles reliably, methodological studies with systematic parameter variations are needed. Therefore, artificial nano- and micro-structures will be designed and produced by different techniques, with scalable dimensions and well-known elemental composition (Task 5.1). This includes the preparation of nano and microparticles with various chemical compositions and architectures, including core-shell particles consisting of a silica core and a polymer shell, a metal core and a polymer shell or a metal core and a silica shell. In addition, a three component particle sample consisting of a metal core, a silica layer and a polymer shell will be prepared. These particles will be deposited on the flat surface of the substrate leading to mainly disordered assemblies, or on pre-patterned structures thus providing long range ordered structures.

In a parallel and complementary approach, nanostructures with smaller characteristic size will be prepared in Task 5.2 using the asymmetric diblock copolymer-based technology leading to the formation of nanospheres, consisting of the minor component of the block copolymer, embedded into the matrix of the major component of the diblock copolymer, followed by a metal infiltration to obtain metal particles included into a polymer matrix. In this case, the use of pre-patterned substrates will provided samples featuring long range order. Complementary structures produced by e-beam lithography are to be used for XSW / TXRF studies under well controlled conditions of areal deposition density. All these samples will be used as test materials for TXRF/GIXRF analysis.

The synchrotron radiation based TXRF / GIXRF approaches will be used to qualify laboratory based TXRF/GIXRF, as e.g. available by industrial stakeholders, and to enhance SOPs which commonly rely on calibration samples or reference materials. However for most nanomaterials and many micro materials, there are only few existing reference materials available for ultra-fine aerosols and particulate matter, so the development of traceable reference micro and nanostructures is crucial for the application of x-ray techniques to aerosols metrology.

An aspect of special interest in the qualification of TXRF and GIXRF is that the XSW field occurring in the TXRF and GIXRF regime influences the quantification significantly. Thus in WP5 different approaches for the calculation of the field intensity will be used and compared, as when the rate of coverage is sufficiently high, there is an impact on the XSW field distribution.

Based on the outcome of Task 5.1 and Task 5.2, application related samples from A4.1.4 will be characterised in Task 5.3 to demonstrate the feasibility of a non-destructive and contact-less chemical analysis of deposited aerosol samples. The comparison of synchrotron-based TXRF/GIXRF and bench top instrumentation will also be used to validate the developed SOPs. In addition, for a complete chemical analysis NEXAFS spectrometry will be carried out, which allows for the determination of the chemical binding state including the related mass deposition.


Task 5.1: Identification and production of artificial micro- and nanostructured model systems

The aim of this task is to design and produce artificial micro- and nanostructured samples that are suited for the qualification of calibration standards for aerosols and PM. These samples will be used to adapt TXRF and GIXRF for quantitative and a size dependent analysis of particles. These artificial micro- and nanostructures will be developed with different lithographic and fabrication approaches, ranging from optical and electron beam lithography to self-assembly of single nanospheres and diblock copolymers. Other than traceable dimensions, these structures will be composed of different species, (metals and oxides) with controlled mass quantities, obtained by using different methods of synthesis.


Task 5.2: Traceable and reliable analysis of elemental composition and dimension of reference micro- and nanostructures by X-rays techniques supported by theoretical modelling.

The aim of this task is to qualify the methods TXRF and GIXRF for quantitative and a size sensitive analysis of particles by using the structures provided in A5.1.2 and A5.1.4 using both directed self-assembly of single nano-objects onto pre-patterned substrates and diblock copolymers metal infiltration. Under grazing incidence conditions (i.e. GIXRF) interference effects of incident and reflected beam (also known as XSW) influence the quantitative analysis. Due to that, theoretical modelling will be included to estimate the influence on the TXRF / GIXRF results. Moreover, different approaches, such as classical Fresnel theory (e.g. analytical calculations, raytracing and the usage of a Maxwell solver including 2D structures equations numerical solution) for modelling of the XSW will be compared to identify XSW influencing parameters such as the particle dimensions and the particle deposition density. Furthermore, SOPs will be developed to qualify the TXRF / GIXRF approach for use as table-top instrumentation.


Task 5.3: Application of the improved TXRF / GIXRF method on aerosols and chemical analysis

The aim of this task is to demonstrate the feasibility of non-destructive and contact-less chemical analysis of deposited aerosol samples. The comparison of synchrotron-based TXRF/GIXRF and bench top instrumentation will be used to validate the SOPs developed in Task 5.2. A complete chemical analysis with TXRF/GIXRF and NEXAFS spectrometry will also be applied to determine the chemical binding state of coarse aerosols and ultrafine particles.