Advanced electron energy loss spectroscopy inside Electron Microscopes

Electron energy loss spectroscopy (EELS) measures the probability of energy loss of an electron beam after it has transversed through a sample. The fine structure in EELS contains a wealth of information about the sample and can be data-mined to know not only the chemical composition, but also chemical bonding as well as local electronic structure of materials. The information deduced is similar to that available in photo-absorption spectroscopy, but EELS has the advantage of a broad energy range, covering from optical to UV and further to X-ray wavelength, and atomic scale resolution because the ability of focusing electron beams using electromagnetic lenses. Our aim is to develop the EELS inside Electron Microscope to study the spatially resolved chemical, bonding and electronic information of materials in nanoscales. We have a broad range of research activities, from novel instrumental development, to new methodology and ab-initio simulation of fine structures.

XL HU, YK SUN AND J YUAN

Multivariate statistical analysis of electron energy-loss spectroscopy in anisotropic materials

Ultramicroscopy, 108, 465 (2008)

YK SUN AND J YUAN

Electron Energy Loss Spectroscopy of Core-electron Excitation in Anisotropic Systems: Magic angle, Magic Orientation and Dichroism
Phys. Rev. B 71, 125109-125119 (2005).

J ZHU, SP GAO, AH ZHANG, AND J YUAN

Theoretical Electron Energy Loss Spectroscopy and its Application in Materials Research
J. Electron Microscopy, 54(3), 293-298 (2005).

YK SUN AND J YUAN

Spatially Resolved Core Level Spectroscopy of Nanotube
Materials Science Forum, 475-479, 4085-4088 (2005).

SP GAO, J ZHU, AND J YUAN

Identification of Polymorphs of sp³ Bonded Carbon and Boron Nitride Using Core-level Absorption Spectroscopy
Chem. Phys. Lett. 400(4-6), 413-418 (2004).

SP GAO, J JIANG, MH CAO, J ZHU, J YUAN

Unoccupied Electronic States in CaB6 Studied by Density Functional Theory and EELS Measurements
Phys. Rev. B 69, 214419 (2004).

SP GAO, A ZHANG, J ZHU, J YUAN

Anisotropic Spectroscopy of Nitrogen K-Edge in Group III Nitrides
Appl. Phys. Lett., 84, 2784 (2004).

An illustration of strong dependence of the EELS fine structure as a function of specimen orientation and collection condition used inside an electron microscope. The example is taken from Carbon 1s absorption from graphite. To overcome this uncertainty in relative intensity of the spectral fine structure, we have developed methods in which either the spectra fine structure are invariant against specimen orientation (magic angle electron energy loss spectroscopy, or MAEELS) or against collection conditions (magic orientation electron energy loss spectroscopy, MOEELS). MAEELS is particularly suitable for nanoscale analysis.

A comparison of experimental EELS spectrum (Nitrogen K-edge absorption, background and Nitrogen 1s level binding energy subtracted) and the theoretical spectrum generated using a modified DECAPO electronic structure simulation code (Yuan 2008).