Electron Microscope Facility
Electron microscopy provides atomic-resolution images of the structure, composition and bonding of our fuel cells and their components. Three-dimensional images of catalyst particles and their support materials are constructed using electron tomography - a similar approach to medical CAT scans or MRI images, except here the image resolution is a few atoms. Using ultra-thin and electron-transparent membrane structures we hope to construct electrochemical liquid cells that will allow us to image fuel cells and batteries during their operation.
The Cornell electron microscopy facility is located in dedicated low-field, low-vibration space using acoustic designs developed for anechoic chambers coupled with radiant cooling for high thermal stability and low, quiet airflow. The facility and its technical staff are supported through the Cornell Center for Materials Research. The two main microscopes used in this study for atomic resolution structure and defects characterization will be the Nion UltraSTEM and a monochromated Tecnai TEM/STEM.
The Cornell UltraSTEM is the first of a new generation of electron microscopes designed for chemical analysis and imaging at the atomic scale. With almost a nano-Amp of current focused into a subatomic electron beam, it can form atomic-resolution images of composition and bonding in under a minute. The microscope was designed by Nion Co. to correct all geometric aberrations out to fifth order, reducing chromatic aberrations and energy spread and producing a smaller spot size and larger beam current than third-order correctors. Combined with a cold field emission gun and an efficiently-coupled spectrometer, this machine is optimized for high spatial and spectral resolution electron energy loss spectroscopy.
Other microscopes include a Monochromated Tecnai TEM/STEM used for electron tomography and ultra-high energy resolution spectroscopy, a Dual Beam/Low Voltage Focused-Ion Beam for sample preparation and patterning, two 120 kV T12 TEM general workhorse tools and 3 field-emission SEMs. Specimen preparation equipment Allied Multiprep diamond lapping tripod polishing systems, wire saw, high quality water filtration, ultrasonic disc cutter, dimpler, stereo and transmission/reflection light low energy Ar-ion mill for final thinning of bulk specimens and a plasma cleaner and UHV baking oven to ensure samples are contamination-free before microscopy. For air-sensitive samples where mechanical polishing (even water-free) can fail, we have had good success with low-voltage focused ion beam (FIB) lift-out and immediate transfer to the microscope. Prof. David Muller is the faculty advisor for the Cornell electron microscopy facility.