ORNL researchers
used a new scanning transmission electron microscopy technique
to sculpt 3-D
nanoscale features in a complex oxide material.
(November 10, 2015) Electron
microscopy researchers at the Department of Energy’s Oak Ridge National
Laboratory have developed a unique way to build 3-D structures with finely
controlled shapes as small as one to two billionths of a meter.
The ORNL study published in the journal Small demonstrates
how scanning transmission electron microscopes, normally used as imaging tools,
are also capable of precision sculpting of nanometer-sized 3-D features in
complex oxide materials.
By offering single atomic plane precision, the technique
could find uses in fabricating structures for functional nanoscale devices such
as microchips. The structures grow
epitaxially, or in perfect crystalline alignment, which ensures that the same
electrical and mechanical properties extend throughout the whole material.
“We can make smaller things with more precise shapes,” said
ORNL’s Albina Borisevich, who led the study. “The process is also epitaxial,
which gives us much more pronounced control over properties than we could
accomplish with other approaches.”
ORNL scientists happened upon the method as they were
imaging an imperfectly prepared strontium titanate thin film. The sample,
consisting of a crystalline substrate covered by an amorphous layer of the same
material, transformed as the electron beam passed through it. A team from
ORNL’s Institute for Functional Imaging of Materials, which unites scientists
from different disciplines, worked together to understand and exploit the
discovery.
“When we exposed the amorphous layer to an electron beam, we
seemed to nudge it toward adopting its preferred crystalline state,” Borisevich
said. “It does that exactly where the electron beam is.”
The use of a scanning transmission electron microscope,
which passes an electron beam through a bulk material, sets the approach apart
from lithography techniques that only pattern or manipulate a material’s
surface.
“We’re using fine control of the beam to build something
inside the solid itself,” said ORNL’s Stephen Jesse. “We’re making
transformations that are buried deep within the structure. It would be like
tunneling inside a mountain to build a house.”