Advanced Developments in Electron Microscopy: Novel Microscopy Techniques
Sponsored by: MS&T Organization
Program Organizers: Lawrence Allard, Oak Ridge National Laboratory; Velimir Radmilovic, Lawrence Berkeley national Laboratory; Paulo Ferreira, University of Texas at Austin; Daniel Ugarte, Universidade Estadual de Campinas - UNICAMP
Wednesday 8:00 AM
October 19, 2011
Room: E160A
Location: Greater Columbus Convention Center
Session Chair: Daniel Ugarte, Universidade Estadual de Campinas
8:00 AM Introductory Comments
8:20 AM Invited
Atomic Imaging of Surface and Bulk with an Aberration Corrected Scanning Electron Microscope: Yimei Zhu1; 1Brookhaven National Laboratory
We demonstrate using the newly developed Hitachi-HD2700C aberration corrected electron microscope, it is possible to achieve one angstrom resolution in secondary-electron imaging, which represents a fourfold improvement over the best-reported in literature. The accomplishment is attributed to better design of electro-optics and more efficient detectors. Furthermore, the instrument allows us to probe the same sample area using simultaneously secondary-electrons emerging from the surface and the transmitted-electrons passing through the bulk (Nature Materials, 8 808 (2009)). The capability of selective visualization of bulk as well as surface atoms is significant. It opens a door to a wide range of applications, such as observation of dopant atoms in electronic devices and study of the active sites and role of individual atoms and their bonding state during a catalytic chemical reaction.
9:00 AM Invited
Smart EFTEM-SI: A New Acquisition Procedure for Quantitative Elemental Imaging by Energy-Filtering TEM: Masashi Watanabe1; Frances Allen2; 1Lehigh University; 2Lawrence Berkeley National laboratory
Energy-filtering transmission electron microscopy (EFTEM) in combination with spectrum-imaging (SI) enables the determination of spatially resolved elemental distributions over a large field of view with a relatively high spatial resolution. However, the signal intensities in EFTEM images are generally lower, which may degrade following processing. Therefore, a new acquisition scheme for EFTEM SI, called SmartEFTEM-SI, has been developed by incorporating a number of improvements: (1) initialization of dark-current in a CCD camera prior to acquisition, (2) measurement of individual dark-currents prior to every filtered-image acquisition, (3) acquisition of the core-loss image-series from the higher energy-loss side, (4) multiple-frame acquisition of individual filtered images, (5) acquisition of a zero-loss image between successive filtered images for superior spatial drift-correction, and (6) acquisition of a low-loss image-series after the core-loss image-series acquisition for further advanced spectral-processing and quantification. In this talk, advantages and several applications of the SmartEFTEM-SI method will be presented.
9:40 AM Break
10:00 AM
Towards Even Higher Accuracy Electron Backscatter Diffraction: T Ben Britton1; Jun Jiang1; Angus Wilkinson1; 1Department of Materials, University of Oxford
Electron backscatter diffraction is routinely used worldwide to characterise materials. It is commonly utilised to examine macrotexture, phase transformations and material deformation in a variety of material systems. The use of cross correlation methods to track small shifts in electron backscatter patterns has opened up a new area of research and with this simple technique we can now routinely probe the full elastic strain tensor with a sensitivity of ~1E-4 and the lattice rotation tensor with a sensitivity of ~1E-4 rads. In this talk we will present some recent developments with this technique and illustrate their implementation on maps from samples of deformed copper.
10:20 AM Student
Diffraction Contrast STEM: Imaging and Simulations: Patrick Phillips1; Michael Mills1; Marc De Graef2; 1Ohio State University; 2Carnegie Mellon University
Conventional transmission electron microscopy (CTEM) has greatly benefited the field of crystalline defect analysis. Techniques such as bright field, dark field, and weak-beam dark field imaging are widely used and well documented. In the present work, the application of scanning transmission electron microscopy (STEM) has been extended to dislocations. STEM imaging has demonstrated the capability to penetrate thicker samples than CTEM and suppress bend contours and auxiliary contrast effects, while retaining defect contrast. Experimental and computational results will be presented for systematic row, 3g, and zone axis imaging conditions. It will also be demonstrated that CTEM diffraction contrast rules remain valid in STEM and that invisibility conditions can be attained.
10:40 AM Invited
Very Large Collection Angles Are Required to Limit Strain Contrast in Aberration-Corrected Z-Contrast STEM: Andrew Yankovich1; Paul Voyles1; 1University of Wisconsin, Madison
It is widely acknowledged that Z-contrast STEM images can contain some strain contrast. We have studied the effect of collection angle on the strain contrast in aberration-corrected Z-contrast STEM at a large probe convergence angle of 24.5 mrad at 200 kV. The sample was heavily Ga-doped ZnO on GaN. From pure Z-contrast, the GaN should be slightly brighter, but due to the doping, the ZnO has higher static disorder (non-uniform strain). For detector inner angles of 28 to 84 mrad, the ZnO layer was brighter than the GaN. Only for detector angles of 112 mrad and greater did we observe the proper Z-contrast. These data indicate that varying the collection angle can separate strain- and Z-contrast, but that interpreting aberration-corrected STEM as Z-contrast at collection angles <100 mrad should be treated with caution.
11:20 AM Invited
Dynamic TEM: Observing In Situ Reactions with Nanometer and Nanosecond Resolution: N. D. Browning1; M. A. Bonds2; G. H. Campbell3; J. E. Evans4; K. L. Jungjohann2; J. McKeown3; T. LaGrange3; B. W. Reed3; M. Santala3; 1Lawrence Livermore National Laboratory; and University of California-Davis, Department of Chemical Engineering and Materials Science, Department of Molecular and Cellular Biology; 2University of California-Davis, Department of Chemical Engineering and Materials Science; 3Lawrence Livermore National Laboratory; 4University of California-Davis, Department of Molecular and Cellular Biology
The dynamic TEM (DTEM) obtains both high spatial and high temporal resolution. Temporal resolution is achieved by using a laser to create a short electron pulse (~1µs or faster) through photo-emission. This electron pulse (containing ~109 electrons) is propagated down the microscope column as in a conventional TEM. To synchronize this pulse with a particular dynamic event, a second laser is used to “drive” the sample prior to its arrival. Most importantly, a single pulse of electrons is used to form the whole image, allowing both irreversible and cumulative phenomena to be studied directly. So far, the system has been used for in-situ processing, rapid phase transformations, and controlled thermal activation of materials. Here, a summary of the DTEM and in-situ stages for both the existing microscope at LLNL and a new aberration corrected DTEM at UC-Davis will be described.