The revolutionary new Band Excitation (BE) technique, co-developed by Oak
Ridge National Laboratory (ORNL) and Asylum
Research, has provided clues to the origins of unique properties of materials
including spin and cluster glasses, phase-separated oxides, polycrystalline
ferroelectrics, and ferromagnets, that are rooted in their highly disordered
structures.
Spatial maps of non-linearity for different film thicknesses (thicknesses shown across top). The onset of nonlinearity with thickness proceeds through formation and merger of clearly visible micron-scale clusters with bulk nonlinearity value, as opposed to gradual increase of average nonlinearity.
These behaviors influence the scaling properties of the materials, including
the thickness of thin films at which improved properties manifest. So-called
"Rayleigh behaviors" have a direct bearing on the properties of nanoscale
materials and, eventually, the uniformity of nanoscale devices. The new observations,
which were made possible by advances in scanning probe microscopy (SPM) at ORNL's
Center for Nanophase Materials Sciences and Asylum Research, may result in the
rethinking of 100-year-old theories behind the "quanta of nonlinearity"
and properties of heterogeneous materials.
This work is funded by the Department of Energy’s Basic Energy Sciences
CNMS user program. The principal investigators for this ground-breaking work
are Stephen Jesse and Sergei Kalinin of ORNL, and Susan Trolier-McKinstry from
Penn State. The findings were recently published in Proceedings of the National
Academy of Sciences (PNAS), April 20, 2010 entitled “Collective dynamics
underpins Rayleigh behavior in disordered polycrystalline ferroelectrics.”
Sergei Kalinin of ORNL commented, “The nonlinear responses are a ubiquitous
aspect of disordered materials that is directly linked to their unique functional
properties. Our studies illustrate that the emergence of the nonlinear behavior
is associated with large-scale collective responses, providing new clues to
century-old problems.”
Added Roger Proksch, President of Asylum Research, "The amazing aspect
of BE measurements is that the local nonlinearity is measured quantitatively
with less than 10% absolute error in volumes millions of times smaller than
those addressable by macroscopic measurements. This is highly unusual for SPM."