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In October 2011 the European Commission (EC) published a "Recommendation on the definition of na-nomaterial" (2011/696/EU), to promote consistency in the interpretation of the term "nanomaterial" for legislative and policy purposes in the EU. The EC NM Definition includes a commitment to its review in the light of experience and of scientific and technological developments. This review is ongoing in 2017 and as a contribution to the review the Joint Research Centre of the European Commission (JRC) has already developed a series of three scientific-technical reports with the title: “Towards a review of the EC Recommendation for a definition of the term nanomaterial” which provides to the EC policy services sci-ence-based options on how the definition could be revised or supported with additional guidance.
The overarching nature and wide scope of the EC NM Definition, as it does not exclude a priori any particulate material regardless the state, form and size, creates many analytical challenges in its imple-mentation for all stakeholders, including enterprises and regulators.
The NanoDefine project has as core objective to support the implementation of the EC NM Definition. In an earlier report1 key aspects of the EC NM Definition were addressed, with the goal to improve the implementability of the EC NM Definition. Based on further developments and results obtained in NanoDefine project that first report was updated and is presented here. The key aspects are discussed based on the results of four years of research performed within the framework of the project. As a result this report assesses how well the requirements of the EC NM Definition can be fulfilled with currently available analytical possibilities. It presents recommendations and options on a revision of the EC NM Definition to improve the implementability of the definition based on currently available analytical possi-bilities, according to the state of the art in 2017. Of the technical issues considered in this report, the following seem to deserve the most attention in terms of clarification of the definition and/or provision of additional implementation guidance: 'external dimension', ‘number based particle size distribution‘, ‘polydispersity‘ and ‘upper size limit‘, the term ‘particle’, the ‘means to prove that a material is not a nanomaterial‘ and ‘the role of the volume specific sur-face area (VSSA)‘, and "particulate materials'.
The overall objective of project Improved traceability chain of nanoparticle size measurements is to improve the traceability chain for nanoparticle size measurements. The main impact will be achieved by manifold contributions to standard documents for CEN/TC 352 “Nanotechnologies”, which directly addresses the research needs of CEN, CENELEC and ETSI mandated by EC to develop standards for methods and reference materials to accurately measure the size and size distribution of nanoparticles. This will take place in collaboration with ISO/TC229 ‘Nanotechnologies’, ISO/TC24/SC4 ‘Particle characterization’ and ISO/TC201 ‘Surface analysis’/ SC9 ‘Scanning probe microscopy’.
The synthesis of TiO2 was studied in an original
hydrothermal process that uses triethanolamine titanium complex Ti(TeoaH)2 as a Ti precursor and triethanolamine (TeoaH3) as a shape controller to obtain bipyramidal anatase nanoparticles.
Backed-up by experimental evidence, i.e., time profiles for Ti(IV) species concentrations together with crystal shape and particle size distributions measured by dynamic light scattering and electron microscopy, a mathematical model was built. The model includes chemical reactions responsible for TiO2 generation in solution and the subsequent anatase nucleation and crystal growth. The oriented attachment mechanism was adopted to explain the build-up of crystals with equilibrium anatase structure (Wulff structure) and time-varying shape factor. This complex mathematical model was solved writing and validating an in-house
software using the Matlab (Natick, MA, USA) environment. The process was simulated for a batch time of 50 h, and the results, in terms of main species concentration and crystal size distributions, are in rather good agreement with the experimental measurements.
Self-assembly of TiO2 nanoparticles in multiple layers by layer-by-layer deposition has been selected of different deposition procedures usually applied for fabrication of TiO2 thin films with defined and homogeneous thickness on supports of interest for the large-scale applications. The substrates tested were: conductive (FTO) glass, silica glass and titanium alloy. The selected film fabrication technique consists of the deposition of alternating layers of oppositely charged, i.e. functionalized, TiO2 nanoparticle layers with wash steps in between. The controlled assembly of TiO2 nanoparticles on the supports surface requires both a proper functionalization of the supports to promote the adhesion of the TiO2 film to the substrates and proper functionalization of TiO2 nanoparticles to allow attachment to substrate and subsequent reaction between different NP layers. The current study focusses on the analytical control of the functionalization of the substrates with 3-Aminopropyltriethoxysilane (APTS) and glutaraldehyde (GA) by means of surface sensitive methods, XPS, Auger Electron Spectroscopy (AES) and ToF-SIMS. Chemical composition of surface of functionalized substrates shows differences in the degree and type of modification in dependence on substrate.
Manufacturing of new perovskite layered solar cells with constant high light conversion efficiency over time may be hampered by the loss of efficiency caused by structural and/or chemical alterations of the complex layered system. SEM/EDX combined with XPS were chosen as an appropriate methodical approach to characterize perovskite laboratory cells in depth and at surface, before and after light exposure. The layered perovskite system investigated here is based on glass covered with fluorine doped tin oxide (FTO), followed by thin films of TiO2, ZrO2 and a thick monolithic carbon. TiO2 film is subdivided into a dense layer covered by porous one constituted of nanoparticles (NPs) of truncated bipyramidal shape. This layered system serves as the matrix for the perovskite. EDX spectral maps on cross-sections of specimen have shown that Pb and I are distributed homogeneously throughout the porous layers C, ZrO2 and TiO2. SEM/EDX data show that 20 weeks of ambient daylight did not change significantly the indepth distribution of the elemental composition of Pb and I throughout the entire solar cell system. It was confirmed with EDX that NPs identified in high-resolution SEM micrographs contain mainly Pb and I, indicating these to be the perovskite crystals. However, a compositional and chemical altering began in the near-surface region of the outermost ~10 nm after 2 months of illumination which was observed with XPS.
The synthesis of TiO2 nanoplatelets with fluorine-containing reactants is carried out using Ti (IV) butoxide as precursor and concentrated HF as shape controller, the final product requires a working up in order to eliminate or at least to reduce the amount of residual fluorides, which is realized here by well-defined thermal treatment.
Qualitative investigation of the bulk elemental composition by means of EDX of TiO2 nanoparticles (NPs) has identified fluorine in case of the as-synthesized samples. EDX spectra of thermally treated products exhibit either a fluorine content close to the limit of detection. The latter holds also true for the reference sample, TiO2 NPs of bipyramidal shape and prepared by a different synthesis route. For differentiation whether fluorine is present in the bulk or at the surface of the TiO2 nanoplatelets, top-surface sensitive AES and ToF-SIMS has been applied. Secondary ions of fluorine are detected in ToF-SIMS spectra of all samples, but could be roughly quantified by measurement of same reference sample as for EDX, namely TiO2 nano-bipyramids. This revealed that the amount of fluorine within1 nm depth beneath the surface is reduced in the thermally treated specimen compared to the raw product down to a content about as low as in the reference sample. AES allows analyzing analysis of the first few nanometers from the top-surface of individual NPs by point analysis. An F KLL peak has been detected at the surface of samples of as-prepared TiO2 nanoplatelets under optimized measurement conditions, but was not detectable after their calcination, which is in agreement with ToF-SIMS results. Moreover, high resolution AES on single TiO2 nanoplatelets elucidated that the surface atomic layers surrounding the TiO2 nanopaltelet contain fluorides before thermal treatment of the NPs.
The practical performance of surface coatings in applications like catalysis, water splitting or batteries depends critically on the coating materials’ porosity. Determining the porosity in a fast and nondestructive way is still an unsolved problem for industrial thin-films technology. As a contribution to calibrated, non-destructive, optical layer characterisation, we present a multi-method comparison study on porous TiO2 films deposited by sol-gel synthesis on Si wafers. The ellipsometric data were collected on a range of samples with different TiO2 layer thickness and different porosity values. These samples were produced by templated sol-gel synthesis resulting in layers with a well-defined pore size and pore density. The ellipsometry measurement data were analysed by means of a Bruggeman effective medium approximation (BEMA), with the aim to determine the mixture ratio of void and matrix material by a multi-sample analysis strategy. This analysis yielded porosities and layer thicknesses for all samples as well as the dielectric function for the matrix material. Following the idea of multi-method techniques in metrology, the data was referenced to imaging by electron microscopy (SEM) and to a new EPMA (electron probe microanalysis) porosity approach for thin film analysis. This work might lead to a better metrological understanding of optical porosimetry and also to better-qualified characterisation methods for nano-porous layer systems.
1. IntroductionPorous materials, especially porous thin films play an importantrole in chemical and physical technology in every case where thecontact area between two media has to be maximised. From cataly-sis to photochemistry and photovoltaics, the applications of porouslayer materials are diverse and numerous [1–6].The accurate and non-destructive characterisation of porousfilms for layered systems poses a challenge. This applies especiallyfor the key parameter of porous films, their porosity, i.e. the mix-ing ratio between the Matrix of the film (host material) and thepore volume which is empty or filled with a fluid medium (inclu-sions). This parameter influences most of the physical and chemicalproperties of a porous thin film and is therefore essential for theunderstanding as well as the optimisation of this class of materials.
Evaluation of particle sizing techniques for implementation of the EC Definition of a nanomaterial
(2017)
Many techniques are available for measuring particle size distribution. For ideal materials (spherical particles, well dispersed) it is possible to evaluate the Performance of these methods. The performance of the analytical instrumentation for the purpose of classifying materials according to EC Definition is unknown. In this work the performance of commercially available particle sizing techniques on representative NanoDefine set of real-world testing materials (RTM) and quality control materials (QCM) for the implementation of the Definition is evaluated.
Electrospray ionization constitutes a promising deposition technique for high-resolution imaging. Particle distribution on TEM grids takes place homogeneously and no losses occur. Suspension must be appropriate (stabilizer may induce artefacts). ESI parameters need to be optimized for each material.
Volume specific surface area (VSSA) by BET: concept and demonstration on industrial materials
(2017)
Volume specific surface area (VSSA) as measured by BET constituites a simple and reliable solution to (most) powders. Porous, coated, polydisperse/multimodal materials are to be treated with care, i.e. doubled by analysis with electron microscopy or more advanced BET analysis (e.g. t-plot)for each material in part.