1 Dec
2011
1 Dec
'11
7:58 a.m.
Center for Excitonics Seminar Series
Thursday, December 1, 2011
3:00 PM - 4:00 PM
Haus Conference Room - 36-428
"Real time observations of the nucleation and growth of nanowires and
nanotubes"
Eric Stach, Center for Functional Nanomaterials, Brookhaven National
Laboratory
abstract Crucial to the application of nanostructured materials is
control over their nucleation and growth, as these aspects determine their
structure and thus properties. We will review our work concerning these
issues in both semiconductor nanowires and carbon nanotubes. These studies
exploit a combination of environmental and ultra-high vacuum transmission
electron microscopy approaches to observe these processes in real time and
at high resolutions. Interestingly, nanowire and nanotube growth share many
similarities. In each case small metal nanoparticles are used to catalyze
the decomposition of relatively simple source gas. This ecomposition leads
to incorporation of the growth element (Si, Ge, C, ./) into the particle
until supersaturation is reached and the new nanostructure nucleates and
grows. We will present measurements of the nucleation and growth process in
Si nanowires, quantifying the process as it proceeds from the initial solid
Au nanoparticle, through the creation of the AuSi eutectic liquid and
finally towards Si nanowire nucleation and growth. The observations will
demonstrate the reproducibility of the process, and allow determination of
the rate limiting steps for nanowire growth. In the case of carbon nanotube
growth, we will demonstrate that both Ostwald ripening and atomistic
diffusion of the Fe catalytic nanoparticles lead to growth termination and
we will present early results that suggest a pathway towards the creation of
an 'immortal' catalyst to support continuous nanotube growth. Recent
observations suggesting a route towards chirality control will also be
outlined. Specific parallels and differences between our nanowire and
nanotube observations will be made.
bio Eric Stach leads the Electron Microscopy Group in the Center for
Functional Nanomaterials (CFN) at Brookhaven National Laboratory. He
received his Ph.D. in Materials Science and Engineering from the University
of Virginia. He has held positions as Staff Scientist and Principal
Investigator at the National Center for Electron Microscopy at the Lawrence
Berkeley National Laboratory and as Associate then Full Professor at Purdue
University, where he retains an Adjunct appointment. His research interests
focus on the development and application of electron microscopy techniques
to solve materials problems in nanostructure growth, catalysis, thin film
growth and materials deformation.
The Center for Excitonics is an Energy Frontier Research Center funded by
the U.S. Department of Energy, Office of Science and Office of Basic Energy
Sciences
Light refreshments will be served