Carbon and oxygen – difficult to analyze if they are embedded inside other materials. A new synchrotron X-ray technique can detect them and even distinguish between their chemical bonds. Credit: Tuomas Pylkkänen (University of Helsinki). |
Scientists
from Finland and France have developed a new synchrotron X-ray
technique that may revolutionise the chemical analysis of rare materials
like meteoric rock samples or fossils. The results have been published
on 29 May 2011 in Nature Materials as an advance online publication.
Life,
as we know it, is based on the chemistry of carbon and oxygen. The
three-dimensional distribution of their abundance and chemical bonds has
been difficult to study up to now in samples where these elements were
embedded deep inside other materials. Examples are tiny inclusions of
possible water or other chemicals inside Martian rock samples, fossils
buried inside a lava rock, or minerals and chemical compounds within
meteorites.
X-ray
tomography, which is widely used in medicine and material science, is
sensitive to the shape and texture of a given sample but cannot reveal
chemical states at the macroscopic scale. For instance graphite and
diamond both consist of pure carbon, but they differ in the chemical
bond between the carbon atoms. This is why their properties are so
radically different. Imaging the variations in atomic bonding has been
surprisingly difficult, and techniques for imaging of chemical bonds are
highly desirable in many fields like engineering and research in
physics, chemistry, biology, and geology.
Now
an international team of scientists from the University of Helsinki,
Finland, and the European Synchrotron Radiation Facility (ESRF),
Grenoble, France, has developed a novel technique that is suitable
exactly for this purpose. The researchers use extremely bright X-rays
from a synchrotron light source to form images of the chemical bond
distribution of different carbon forms embedded deep in an opaque
material; an achievement previously thought to be impossible without
destroying the sample.
Currently
the required radiation doses are too large for an immediate application
on biological tissue, but perhaps future dedicated instruments may be
optimised for such applications as well. The most promising applications
can thus be found from physics, materials science, geology, chemistry,
and industry.
Application of direct tomography to a layered C/SiC sample. The left part of the image shows a photograph of the sample, measuring approximately 7 x 10 x 5 mm3. The part studied with X-rays was the indicated subvolume of 7 x 2 x 1 mm3. The result, a detailed 3D map of chemical bonds, is visualised here as a set of isosurfaces within the subvolume, shown on the right, where the different colours represent the different carbon bonds present in the sample. Credit: Simo Huotari (University of Helsinki), with permission from Nature Materials. |
“Now
I would love to try this on Martian or moon rocks. Our new technique
can see not only which elements are present in any inclusions but also
what kind of molecule or crystal they belong to. If the inclusion
contains oxygen, we can tell whether the oxygen belongs to a water
molecule. If it contains carbon, we can tell whether it is graphite,
diamond-like, or some other carbon form. Just imagine finding tiny
inclusions of water or diamond inside Martian rock samples hidden deep
inside the rock”, says Simo Huotari from the University of Helsinki.
The
newly developed method will give insights into the molecular level
structure of many other interesting materials ranging, for example, from
novel functional nanomaterials to fuel cells and new types of
batteries.
This work was carried out at beamline ID16.
Study abstract: Direct tomography with chemical-bond contrast
