MSE Colloquium - Dr. Renu Sharma, NIST
Date: March 25, 2011 from 2:00 pm to 3:00 pm EDT
Location: Room 214 in S.W. Mudd
Contact: For further information regarding this event, please contact Wesley Hattan by sending email to wjh2121@columbia.edu or by calling 2128547860.
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Combining Synthesis and Characterization of nanomaterials using Transmission Electron Microscope

Renu Sharma
Center for Nanoscale Science and Technology, National Institute of Science and Technology
& Center for Solid State Science, Arizona State University

Scanning-Transmission electron microscope (STEM) is ideally suited to obtain atomic scale structural and chemical information using electron diffraction, imaging and spectroscopy. Recent modifications to samples holders, or TEM column, such as environmental STEM (ESTEM), have made it possible to obtain such information during the chemical process, i.e. synthesis and characterization are performed simultaneously. ESTEM has been employed to understand a number catalytic processes including but not limited to synthesis of 1-D nanostructures such as nanotubes and nanowires. These structures are fundamental building blocks for nanotechnology. Most of these structures are synthesized using chemical vapor deposition (CVD) processes where a catalyst activates the decomposition of the precursor molecule and/or acts as a nucleation site for the growth of nanotubes or nanowires. Using the ESTEM, we make dynamic observations under the reaction conditions to elucidate the exact function and nature of the catalyst during nucleation and growth. Presentation will cover the design and function of an ESTEM, planning in situ experiments, and select applications such as the growth of carbon nanotubes (CNTs) and Nanowires (e.g. Si, Ge and GaN). The small probe size (~0.2 nm) of a Tecnai F-20 FEG is also used to selectively synthesize model catalysts, by electron beam induced decomposition of a metal-organic precursor, for CNT growth. These experiments have provided invaluable insights into the nucleation and growth processes as well into reaction conditions suitable for selective synthesis.