Research Abstracts Online
January - December 2011
University of Minnesota Twin Cities
College of Science and Engineering
of Chemical Engineering and Materials Science
PI: K. Andre Mkhoyan
Simulations in Analytical Transmission Electron Microscopy
The work in this group is based on examining the atomic and electronic structure of hard materials. Transmission electron microscopy (TEM) is used to study materials at atomic-level resolution. TEM images, diffraction patterns (DPs), and spectroscopic data are often difficult, even impossible, to understand intuitively. Hence, the researchers simulate images and DPs of possible structures and compare them with experimental results to make conclusions about the properties of materials of interest. C programs written by E.J. Kirkland are used to simulate TEM results; these programs require use of the supercomputers.
In the past year, the group has used MSI resources to examine several interesting samples. Sparsely doped materials were studied to examine the ability to detect a single dopant atom. Parameters characterizing the specimen and incident electron beam were varied systematically to understand the trends in visibility of dopant atoms and interested trends were discovered and published. A different type of material was also examined, namely nanotubes composed of molybdenum disulfide (MoS2). The group is also studying materials that are composed of single atomic layers, such as boron nitride and graphene.
In the upcoming year, the researchers plan to continue studying doped materials and single atomic layer materials. They also model the behavior of the electron beam as it scatters through a TEM sample. They intend to combine the expected intensity of the electron beam at a particular point inside the sample with electron energy loss spectrum (EELS) to quantify the number of atoms contributing to the EELS signal in hopes to quantify the number of atoms in the sample. This will benefit in understanding the concentration and distribution of a particular atom in new compound materials in which this information is unknown, such as many types of doped materials and graphene oxide. Understanding the atomic structure of a material is essential as it leads to being able to understand and tune its properties, necessary for implementing it in devices.
Alex Chov, Undergraduate Student
Aloysius Gunawan, Graduate Student
Anudha Mittal, Graduate Student
Michael Odlyzko, Graduate Student