Artifacts, Contrast mechanisms and Strategies for recording
EELS Spectroscopic Images for Different Energy Regimes with Applications for
Heterogeneous Catalysis
Huolin Xin
Materials Sciences Division, LBNL, Berkeley, CA 94720
When recording electron energy loss spectroscopic images,
there are many degrees of freedom. For instance, trade-offs must be made between
signal-to-noise, spatial resolution, and energy resolution: opening the EELS
collection angle increases signal collection efficiency and image
interpretability; however, it also reduces the jump ratio of core-loss edges. In
many spectrometers, there is also a reduction in energy resolution.
Optimizing spectral collection
requires forethought and consideration of the specimen, the microscope, and the
spectrometer. Different strategies are
required to extract the chemical and bonding information at different energy
losses. Nanoscale fingerprinting is possible from various statistical fits in
the low-loss region. At moderate energies, great care needs to be paid to
background subtraction. At high energies, the spatial resolution is better and
the interpretation is simple, however the signal-to-noise ratio is poor. In this
talk I will present practical details on recording and processing EELS
spectroscopic images for both chemical and electronic information. I will
discuss the underlying contrast mechanisms and artifacts in EELS spectroscopic
maps, various processing techniques for different energy regimes, and
applications for in-situ and ex-situ study of catalyst nanoparticles.