Ill. - Developing novel ways to control the motion
of atoms on surfaces is essential for the future of
nanotechnology. Now, researchers at the University
of Illinois at Urbana-Champaign have found a phenomenon
of dislocation-driven nucleation and growth that creates
holes that spiral into a surface and pull atoms into
newly discovered mechanism - identified as a series
of spiral steps around dislocations terminating at
the surface of titanium nitride, a technologically
important material used in microelectronics and hard
coatings - could potentially be put to use in controlling
surface morphology and in preparing nanoscale structures
spiral step dynamics strongly suggests that the cores
of surface-terminated dislocations behave like 'whirlpools'
sucking surface atoms into the crystal structure,"
said Suneel Kodambaka, a postdoctoral research associate
and lead author of a paper that announced the team's
findings in the May 6 issue of the journal Nature.
are imperfections in a crystal structure where there
is a missing or an extra half plane of atoms in the
Dislocations can strongly influence nanostructural
and interfacial stability, mechanical properties and
found that the presence of a dislocation could reverse
the behavior and evolution of the nearby surface substructure,"
said Ivan Petrov, a research professor and director
of the Center for Microanalysis of Materials at the
Frederick Seitz Materials Research Laboratory on the
U. of I. campus.
study the dynamics of dislocation motion and morphological
evolution in single crystals at high temperature (1,300
to 1,400 degrees Celsius), the researchers used low-energy
- a technique that can visualize the surface at the
saw steps form at the dislocation site and expand
into spiral structures," Kodambaka said. "This
type of spiral growth had been seen previously under
applied stress, and when depositing or evaporating
material; but never during annealing, when the crystal
is neither gaining nor losing material."
steps on a spiral staircase, each step was one layer
of atoms thick and rotated around the dislocation
core. The spiral slowly spun while growing inward,
like a bathtub drain sucking water.
dislocation provides a path for atoms to move from
the surface to inside the crystal," Petrov said.
"The spiral structure is a manifestation of the
moving material. It is a vortex that consumes surface
atoms and drives the nearby surface kinetics."
researchers' results "provide fundamental insights
into mechanisms that control both the stability of
nanostructures and the formation of nanoscale patterns
on surfaces," Kodambaka said. "We think
this spiral growth process is quite general and will
be observed in many other materials."
addition to Kodambaka and Petrov, the research team
included materials science and engineering professor
Joseph Greene, electron microscopist Waclaw Swiech
and postdoctoral research associates Sanjay Khare
and Kenji Ohmori. The U.S. Department of Energy funded
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