Using intense coherent X-ray pulses from the Linac Coherent Light Source free-electron laser at Stanford, an international team of researchers has demonstrated a new in situ fractal method for imaging individual sub-micron particles to nanometer resolution in their native environment. The research appears in the 28 June issue of the journal Nature.
Complex airborne particulate matter (PM) with a diameter less than 2.5 microns can efficiently transport into the human lungs and constitutes the second most important contribution to global warming. The structure of this micron-size particulate matter is thus important in a wide range of fields from toxicology to climate science.
However, properties of the particles are surprisingly difficult to measure in their native environment: electron microscopy requires the collection of particles on a substrate, visible light scattering provides insufficient resolution, and X-ray studies have, to date, been limited to a collection of particles.
Pulsed X-ray beams were shot into a jet of aerosolized particles. Since the beam is so small and the particulate matter density is so large, only single particles were hit. The beams were so intense that diffraction from individual particles could be measured for structural analysis. Mass spectrometry on the ejected ion fragments was used to simultaneously probe the composition of single aerosol particles.
Our results show the extent of internal symmetry of individual soot particles and the surprisingly large variations in their fractal dimensions. More broadly, our methods can be extended to resolve both static and dynamic structures of general ensembles of disordered particles.—Stefan Hau-Riege, Lawrence Livermore National Laboratory
Other Livermore researchers include Matthias Frank, Mark Hunter, George Farquar and W. Henry Benner. Other collaborators include: SLAC National Accelerator Laboratory; Center for Free-Electron Laser Science, DESY; Max-Planck-Institut fur medizinische Forschung; Max Planck Advanced Study Group, Center for Free Electron Laser Science (CFEL); Max-Planck-Institut fur Kernphysik, Saupfercheckweg; PNSensor GmbH, Otto-Hahn-Ring; Max-Planck-Institut Halbleiterlabor, Otto-Hahn-Ring; Max-Planck-Institut fur extraterrestrische Physik, Giessenbachstrasse; Sincrotrone Trieste, Microscopy Section; Advanced Light Source, Lawrence Berkeley National Laboratory; Laboratory of Molecular Biophysics, Department of Cell and Molecular Biology, Uppsala University; Cornell University, Division of Nutritional Sciences; Photon Science, DESY; National Energy Research Scientific Computing Center (NERSC); University of Hamburg; and European XFEL GmbH, Albert-Einstein-Ring.
N. D. Loh, C. Y. Hampton, A. V. Martin, D. Starodub, R. G. Sierra, et al. (2012) Fractal morphology, imaging and mass spectrometry of single aerosol particles in flight. Nature 486, 513-517 doi: 10.1038/nature11222