My
research currently focuses on two areas of nanoscale science.
New methods are developed to grow and efficiently process high quality
nanomaterials into useful forms. This research currently focuses on
carbon nanotubes,
and on ordered arrays of vertically aligned carbon nanofibers (VACNFs)
that are grown using plasma-enhanced chemical vapor deposition. Recent
studies
have emphasized understanding the connections between growth conditions
and the morphology, structure, and electron field-emitting properties
of
the latter nanoscale materials. Extensions to nanotubes, rods and wires
of other materials also are of interest. See also Dave
Geohegan, Alex
Puretzky, Mike
Simpson, Anatoli
Melechko, and Tim
McKnight.
Engineered nanostructures, and effects of reduced and experimentally
variable dimensionality (3D and 2D), are used to study the emergence
of cooperative
phenomena on the nanoscale. Epitaxial thin films and coupled films
(in superlattices) are grown by pulsed laser deposition, which enables
controlling
the layers’
structure and composition with sub-unit cell precision. Artificial multilayered
structures permit placing phases with different long-range orderings
(magnetic,
electric, or superconducting) in close proximity in order to study
their interactions, and to explore the idea that the complex properties
of TMOs
result from a competition between alternate ground states with nearly
equal energies. Four experimental variables can be used to “tune” this
competition: heteroepitaxial strain, layer composition, layer thickness,
and interlayer coupling. These (in effect) can help to locate the boundaries
of the electronic phase diagram. The goals are to better understand
the emergence of collective phenomena (and electronic phase separation)
on
the
nanoscale; the effects of reduced (and variable) dimensionality; and
to discover useful control mechanisms. See also Hans
Christen and Ho
Nyung Lee.
A key enabling tool for these studies is the development of experimental
methods to search more rapidly and efficiently than was previously
possible for interesting phenomena among the complex TMO materials. To
accomplish
this, a new method for combinatorial synthesis of metastable TMO phases
at elevated temperatures has been developed by Hans
Christen for search-and-discovery of novel TMO properties.
Both research areas involve interactions with theorists and modelers
and the use of well-developed shared synthesis, characterization and
nanofabrication
facilities, throughout ORNL. See also Thomas
Schulthess and Zhenyu
Zhang.
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