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The size of nanoparticles now traceably determined

Besonders interessant für:
  • Nanotechnologie
  • Verbraucherschutz

Dimensional nanometrology is a new field of work at PTB‘s laboratory at BESSY II by means of which – for nanolayers – the layer thickness and – for an ensemble of nanoparticles – the mean value and the distribution width of the diameter can be determined. Within the scope of an iMERA-plus project, the diameters in the range of 9 nm to 200 nm of various particles made of gold, silica, ferric oxide, latex and PMMA (acrylic glass) have – for the first time – been traceably measured via small angle X-ray scattering with synchrotron radiation. Thereby, relative uncertainties of 1 % could be achieved.

Distribution of the scattering intensity obtained from the scattering diagram as a function of the momentum transfer q (black) together with a fitted model curve (red) from which a mean diameter of the particles of (108.9 ± 0.7 ) nm and a distribution width of 12 nm result.

For some years now, PTB has been using monochromatised synchrotron radiation in the X-ray range to be able to determine the dimensions of nanoobjects. In contrast to X-ray tubes, the wavelength can thereby be optimally adapted to the nanosystem to be examined. To determine the thickness of oxide layers on silicon samples via X-ray reflectometry, radiation in the range of the oxygen absorption edge at 2.3 nm is used for contrast enhancement, for example, as is the case for the silicon spheres of the Avogadro project.

To determine the diameter of na-noparticles in suspension via small-angle X-ray scattering, wavelengths below 0.5 nm are selected. Such radiation can easily penetrate the thin-walled sample cavity containing the suspension. Thereby, the exact wavelength is measured by means of back reflection of the radiation from a silicon crystal. The scattering angle can be determined by means of length measurements carried out with incremental displacement indicators. The scatter diagram developing in forward direction under small angles – of just a few degrees – is recorded by means of a large-area
X-ray detector. For spherical nanoparticles with not too broad a distribution of the diameter, concentric rings result. The radial integration yields an oscillating curve for the scattering intensity as a function of the momentum transfer, to which modelled scattering curves are fitted. From this, not only the mean diameter of the particles is obtained, but also the distribution width, as – contrary to microscopic procedures – the mean is taken via a large number of particles.

If small-angle X-ray scattering is used for surfaces under grazing incidence – as is the case for a number of EMRP projects which are just being launched in the industry call – also nanoparticles or nanostructured surfaces can be characterised.

Scatter diagram for PMMA nanoparticles, measured at a radiation wavelength of 0.15 nm. The direct beam was blocked during the measurement.


Michael Krumrey
Department 7.1 X-ray Metrology with Synchrotron Radiation
Phone: +49 (0) 30 6392-5085
E-Mail: michael.krumrey(at)ptb.de

Scientific publication:

Krumrey, M.; Gleber, G.; Scholze, F; Wernecke, J.: Synchrotron radiation-based X-ray reflection and scattering techniques for dimensional nanometrology. Meas. Sci. Technol. (2011). In print.