Invited Paper IE-MoA3
Observation of Dynamic Nanoscale Processes Using Environmental Scanning Transmission Electron Microscope

Monday, October 15, 2007, 2:40 pm, Room 618

The world of nanomaterials has become the ‘real world’ for most of the applications in the area of nanotechnology. As post-synthesis handling of materials at a nanoscale is not practical, nanomaterials often need to be synthesized directly as part of a device or circuit. This demand posted by nanotechnology has led to the modifications in the design of transmission electron microscopes that permit us to perform in situ synthesis and characterization simultaneously. In situ observations of the synthesis process are used to understand and evaluate the effect of synthesis conditions (starting material (reactants), temperature and pressure) on the morphology, structure and chemistry of the product. Moreover, functioning (e.g. activity of a catalyst) of many nanosystems changes during operation. The effect of operating condition (time, temperature, and the ambient) can be elucidated by atomic scale in situ observation. Such in situ observations can be used to optimize the synthesis conditions for nanomaterials with desired structure and properties and improve the functioning of nano systems. Environmental scanning transmission electron microscope (ESTEM) permits us to observe gas-solid interactions at elevated temperatures in gaseous environment. A modern ESTEM, equipped with a field-emission gun (FEG), energy filter or electron energy loss spectrometer, scanning transmission electron microscopy (STEM) coils, and bright and dark field detectors, is a versatile tool for understanding chemical processes at nanometer level. Its applications range from in situ characterization of reaction steps such as oxidation-reduction or corrosion, to in situ synthesis of nanomaterials such as quantum dots, carbon nanotubes or Si nanowires. Examples including synthesis and characterization (e.g. CNT, Si nanowires) and structural modifications during functioning of nanomaterials (catalyst) will be used elucidate the applications of the ESTEM. Future applications and improvements in the instrument design will be discussed.