An example of such a 3D map is given in the figure, showing the arrangement of crystals in a 150nm thick nanometal aluminium film. The crystals have identical lattice structure (arrangement of atoms) but they are orientated in different ways in the 3D sample as illustrated by the labels 1 and 2. The colours represent the orientations of the crystals and each crystal is defined by volumes of the same colour. The individual crystals of various sizes (from a few nm to about 100 nm) and shapes (from elongated to spherical) are clearly seen and mapped with a resolution of 1 nanometer. Image: Science |
On May 13th 2011, the journal Science published
a paper where scientists from Risø DTU in collaboration with scientists
from China and USA, report a new method for revealing a 3D picture of
the structure inside a material.
Most
solid materials are composed of millions of small crystals, packed
together to form a fully dense solid. The orientations, shapes, sizes
and relative arrangement of these crystals are important in determining
many material properties.
Traditionally,
it has only been possible to see the crystal structure of a material by
looking at a cut surface, giving just 2D information. In recent years,
x-ray methods have been developed that can be used to look inside a
material and obtain a 3D map of the crystal structure. However, these
methods have a resolution limit of around 100nm (one nanometer is
100,000 times smaller than the width of a human hair).
In contrast, the newly developed technique now published in Science,
allows 3D mapping of the crystal structure inside a material down to
nanometer resolution, and can be carried out using a transmission
electron microscope, an instrument found in many research laboratories.
Samples
must be thinner than a few hundred nanometers. However, this limitation
is not a problem for investigations of crystal structures inside
nanomaterials, where the average crystal size is less than 100
nanometers, and such materials are investigated all over the world in a
search for materials with new and better properties than the materials
we use today.
For
example, nanomaterials have an extremely high strength and an excellent
wear resistance and applications therefore span from microelectronics
to gears for large windmills. The ability to collect a 3D picture of the
crystal structure in these materials is an important step in being able
to understand the origins of their special properties.
An
important advantage of such 3D methods is that they allow the changes
taking place inside a material to be observed directly. For example, the
mapping may be repeated before and after a heat treatment revealing how
the structure changes during heating.
This
new technique has a resolution 100 times better than existing
non-destructive 3D techniques and opens up new opportunities for more
precise analysis of the structural parameters in nanomaterials.
