Determination of Single- and Multi-Component Nanoparticle Sizes by X-ray Absorption Spectroscopy (original) (raw)
Related papers
The Journal of Physical Chemistry C, 2014
Nanoparticles research represents one of the most active fields in science due to the importance of nanosized materials in a wide variety of applications. Their characterization needs the comparison of data coming from different experimental techniques, but the peculiar properties of the nanosystem that each technique points out are not always properly taken into account and misleading results have been often reported. In this work, we generated transmission electron microscopy like (TEM-like) data to predict the extended X-ray absorption fine structure (EXAFS) and chemisorption-like typical outputs as the average coordination numbers up to fourth shell of the particles distribution and the surface area. The aim of the simulations is to explore the dependence of the calculated average coordination number (ACN) and average dispersion (AD) values from each parameter characterizing a particle size distribution (PSD), as the mean diameter, the width, the shape, and the profile, and shows that a range of distributions is compatible with given values of ACN and AD. In this way, we have established a general method to properly take into account the above-mentioned parameters and to allow for an accurate analysis and comparison of results. Furthermore, it will be shown that unfavorable distribution shape makes the comparison among techniques critical and potentially misleading if performed with an oversimplified model of the PSD such as those using the average diameter only.
International Journal of Nanoscience, 2004
Powder X-ray diffraction has become a cornerstone technique for deriving crystallite size in nanoscience due to speed and 'simplicity'. Unfortunately, this apparently simple technique commonly has unexpected problems. Anisotropic peak broadening related to crystallite shape, defects, and microstrain occur frequently in nanomaterials and can significantly complicate analyses. In some instances usage of the conventional single peak approach would give erroneous results, and in others this type of analysis is not even possible. A number of different nanocrystalline oxides have been examined to determine their crystallite sizes by different techniques. They differ in terms of crystal symmetry, crystallinity, density, and present different challenges with regard to size analysis.
Journal of Applied Crystallography, 1999
According to Bertaut's theorem [Acta Cryst.(1950),3, 14–18], the size distribution of a powder sample constituted by perfect single-crystal particles can be easily determined from the peak shape analysis. The comparison between particle size distributions determined by a Monte Carlo fitting algorithm and those determined by direct observation using transmission electron microscopy shows that, as expected, the X-ray diffraction determination cannot be confidently used for particles with maximum dimensions above about 60 nm.
Determination of size distributions in nanosized powders by TEM, XRD, and SAXS
Journal of Experimental Nanoscience, 2006
Crystallite size distributions and particle size distributions were determined by transmissions electron microscopy (TEM), X-ray powder diffraction (XRD), and small-angle X-ray scattering (SAXS) for three commercially available TiO 2 powders (P25, UV100, and TiO2_5 nm) and one SSEC produced powder (SSEC78). The theoretical Guinier model was fitted to the experimental obtained XRD data and compared to analytical expressions. Modeling of the XRD spectra showed a difference between the analytical size dependent expressions and the theoretical Guinier model. Primary particle size distributions were extracted from SAXS measurements by the hard sphere model including an interparticle interference factor. The sizes obtained from SAXS were smaller than the sizes obtained from the XRD experiments; however, a good agreement was obtained between the two techniques. Electron microscopy confirmed the primary particle sizes and the shapes obtained by XRD and SAXS. The SSEC78 powder and the commercially available powders showed different morphologies, but SSEC78, UV100, and TiO2_5 nm all consisted of both primary particles as well as a secondary structure comprised of nanosized primary particles agglomeration into larger clusters. P25 showed the largest primary particle size, but did not show a secondary structure.
Crystallography and Shape of Nanoparticles and Clusters
Introduction: Nanotechnology is a leading interdisciplinary science that is emerging as a distinctive field of research. Its advances and applications will result in technical capabilities that will allow the development of novel nanomaterials with applications that will revolutionize the industry in many areas. It is now well established that dimensionality plays a critical role in determining the properties of materials, and its study has produced important results in chemistry and physics. Nanoparticles are one of the cornerstones of nanotechnology. Indeed, even though the research in this field has been underway for a long time, many present and future applications are based on nanoparticles. For instance, the electron tunneling through quantum dots has led to the possibility of fabricating single-electron transistors [4–9]. One concept particularly appealing is a new three-dimensional periodic table based on the possibility of generating artificial atoms from clusters of all of the elements [10]. This idea is based on the fact that several properties of nanoparticles show large fluctuations, which can be interpreted as electronic or shell-closing properties with the appearance of magic numbers. Therefore, it is conceivable to tailor artificial superatoms with given properties by controlling the number of shells on a nanoparticle. ... intro continues....
X-ray absorption measurements on nanoparticle systems: self-assembled arrays and dispersions
Journal of Physics D: Applied Physics, 2010
X-ray absorption spectroscopy methods are presented as a useful tool to determine local structure, composition and magnetic moments as well as to estimate the effective anisotropy of substrate supported self-assembled arrays of wet-chemically synthesized FePt nanoparticles. A compositional inhomogeneity within the nanoparticles yields reduced magnetic moments with respect to the corresponding bulk material and may also hinder the formation of the chemically ordered L1 0 phase in FePt nanoparticles. The latter is indicated by a reduced effective anisotropy, which is one order of magnitude smaller than expected from the known value of the corresponding bulk material. As a new approach, measurements of the x-ray absorption near-edge structure of Fe-oxide nanoparticles in dispersion are presented and ageing effects are discussed on the basis of multiplet calculations.
Journal of Applied Crystallography, 2017
This paper presents the first worldwide inter-laboratory comparison of smallangle X-ray scattering (SAXS) for nanoparticle sizing. The measurands in this comparison are the mean particle radius, the width of the size distribution and the particle concentration. The investigated sample consists of dispersed silver nanoparticles, surrounded by a stabilizing polymeric shell of poly(acrylic acid). The silver cores dominate the X-ray scattering pattern, leading to the determination of their radius size distribution using (i) the generalized indirect Fourier transformation method, (ii) classical model fitting using SASfit and (iii) a Monte Carlo fitting approach using McSAS. The application of these three methods to the collected data sets from the various laboratories produces consistent mean number-and volume-weighted core radii of R n = 2.76 (6) nm and R v = 3.20 (4) nm, respectively. The corresponding widths of the lognormal radius distribution of the particles were n = 0.65 (1) nm and v = 0.71 (1) nm. The particle concentration determined using this method was 3.0 (4) g l À1 or 4.2 (7) Â 10 À6 mol l À1 . These results are affected slightly by the choice of data evaluation procedure, but not by the instruments: the participating laboratories at synchrotron SAXS beamlines, commercial and in-house-designed instruments were all able to provide highly consistent data. This demonstrates that SAXS is a suitable method for revealing particle size distributions in the sub-20 nm region (at minimum), out of reach for most other analytical methods.
Phase Transitions, 2003
The applicability of standard methods for the evaluation of powder diffraction data of nano-size crystallites is analyzed. Based on theoretical considerations, it is shown that deviations of the structure of small particles from the Bragg approximation on an infinite crystal lattice leads to significant differences in the diffraction patterns, which may lead to an erroneous interpretation of the experimental results. An alternative evaluation of the diffraction data of nano-particles, based on the so-called ''apparent lattice parameter'', alp, is proposed. Based on this method, it is shown that real nano-crystals constitute a complex, heterogeneous multi-phase structure.
Nanoparticle size evaluation of catalysts by EXAFS: Advantages and limitations
Zastita materijala, 2016
In this article we determine particle size of nanocatalysts using the first-shell fitting results of Extended X-ray Absorption Fine Structure (EXAFS) measurements. The EXAFS technique measures the average coordination number of nanoparticles in the path of X-ray beam. Since nanoparticles can be found in variety of cluster structures with varying coordination number of surface atoms, the discussion is limited to the structures of face centered cubic (fcc) lattice in which most metals of interest for catalysis crystalize. Two nanoparticle structures, namely cuboctahedron and icosahedron, were analyzed and their calculated average coordination numbers compared to those determined by EXAFS. It was found that the particle size determined using EXAFS corresponds best to the diameter of the sphere that has the same volume as the nanoparticle. This volume-corrected sphere was calculated for a number of platinum group metals. It is further shown that the model for particle size evaluation can be extended to bimetallic and trimetallic nanoparticles. Advantages and limitations of the technique in assessing the particle size are discussed.