For
the first time X-ray scientists have combined high-resolution imaging
with 3-D viewing of the surface layer of material using X-ray vision in a
way that does not damage the sample.
This
new technique expands the range of X-ray research possible for biology
and many aspects of nanotechnology, particularly nanofilms, photonics,
and micro- and nano-electronics. This new technique also reduces
“guesswork” by eliminating the need for modeling-dependent structural
simulation often used in X-ray analysis.
Scientists
from the Advanced Photon Source and Center for Nanoscale Materials at
the U.S. Department of Energy’s (DOE) Argonne National Laboratory have
blended the advantages of 3-D surface viewing from grazing-incident
geometry scattering with the high-resolution capabilities of lensless
X-ray coherent diffraction imaging (CDI). The new technique, an
adaptation of existing detector technology, is expected to work at all
X-ray light sources.
“This
is the future of how we will visualize structure of surfaces and
interface structures in materials science with X-rays,” said Argonne
scientist Jin Wang, the lead author of “Three-Dimensional Coherent X-ray
Surface Scattering Imaging near Total External Reflection” published
online August 12, 2012, in the journal Nature Photonics.
By
adjusting the angle with which the X-rays scatter off the sample, Wang
and fellow Argonne scientists brought the 3-D power of the new imaging
technique to the surface layers of the sample. In nanotechnology, most
of the atomic interactions that control the functionality and efficiency
of a product, such as a semiconductor or self-assembled nanostructure,
occur at or just below the surface. Without a direct 3-D viewing
capability, scientists have to rely on models rather than direct
measurement to estimate a surface structure’s thickness and form, which
weakens confidence in the estimate’s accuracy.
Using
grazing-incidence geometry, rather than traditional CDI transmission
geometry, scientists eliminated the need for modeling by using the
scattering pattern to directly reconstruct the image in three
dimensions.
Conventional
X-ray imaging techniques allow for 3-D structural rendering, but they
have lower image resolution and, therefore, greater uncertainty. Plus,
in some cases, the X-rays’ intensity destroys the sample. This new
APS-designed technique potentially can image a sample with a single
X-ray shot, making it non-destructive, a desirable quality for research
on biological cells and features formed by organic materials.
Another
benefit is the ability to expand CDI viewing from the nanometer to the
millimeter scale when the X-ray beamline impinges on the sample at a
glancing angle. This innovation allows scientists to relate the behavior
of a bundle of atoms or molecules to that of an entire device. This
area—the mesoscale, between nanoresearch and applied technology—has been
a particularly difficult area for scientists to access. In
nanotechnology, this area is thought to hold promise for making
stronger, more flexible and more efficient materials. In biology, it
connects intercellular behavior with the activity of individual cells
and the larger organism.
“Hopefully
this technique will be applied to research in biology, microelectronics
and photonics” said Tao Sun, a postdoctoral research fellow working at
the APS and the first author on the research. “This technique holds
great promise because the resolution we can reach is only limited by
wavelength, a fraction of a nanometer. So the APS upgrade and other
advances in light source and detector technology will easily provide
even higher-resolution images than we have achieved in this work.”
Three-Dimensional Coherent X-ray Surface Scattering Imaging near Total External Reflection
Source: DOE/Argonne National Laboratory
