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Research

Facility Highlight: 
Electron Probe Instrumentation Center (EPIC)

NUANCE provides core analytical characterization instrumentation resources in a collaborative environment, with 24/7 open-access for research and education, for the NU community and beyond. Within NUANCE, the Electron Probe Instrumentation Center (EPIC) is a shared user facility that supports a broad range of nanoscale science and technology projects, specializing in nanoscale analysis and characterization. EPIC is a multi-user, multi-departmental facility offering continually updated state-of-the-art equipment to qualified researchers from any field and institution. Managed by expert technical staff, EPIC instrument users have access to advanced electron microscopes and related sample preparation instruments. Highlighted amongst transmission electron microscope instruments are:

  • Probe corrected JEOL JEM-ARM200CF (S)TEM―equipped with dual JEOL silicon drift detectors (SDD, collection angle of 1.7sr) for EDS acquisition, a Gatan K2 IS direct detector to capture dynamic phenomena and high-speed spectroscopic data, and a Gatan Quantum Dual-EELS system, amongst others

  • JEOL JEM-ARM300F (S)TEM―equipped with BF/ABF/ADF/HAADF detectors for simultaneous imaging, a wide gap pole-piece accommodating numerous in situ holders, and a recently installed K3 IS direct detector to capture dynamic images and diffraction at low electron dose using counting mode.


Research Highlight

Nanostructural features of new generation low-cost ultrahigh strength steels strengthened by dual phases of β-NiAl and M2C carbide

Due to the high total detector area and large solid angle, the EDS capability of ARM 200CF is very effective in performing chemical analysis at high spatial resolution and with a high signal-to-noise ratio (SNR). The figure below illustrates the nanostructural analysis of a recently developed novel low cost ultrahigh strength steel, which is hardened through a dual phase strengthened mechanism. By conventional image analysis, we cannot observe the structural features of the precipitated phases. However, by means of high spatial resolution EDS analysis, we can clearly visualize the morphological features and the distribution of nanoscale precipitates.(1)


EPIC
(a) Low and (b) high magnification bright field scanning TEM (BF-STEM) image showing the general microstructural features of aged AIR0509 steel. (c) [001]M electron diffraction pattern (EDPs) obtained from the circled region indicated in (a). (d) High resolution TEM (HRTEM) image along [001]M direction. (e) and (f) Fast fourier transform (FFT) patterns corresponding to region A and B indicated in (d). (g–l) Elemental maps corresponding to Al–K, Cr–K, Mo-L, Ni–K, Fe–K and Co–K respectively.
Xiaobing
"Knowledge of the structural and chemical information of materials with higher spatial resolution ranging from the nano to the atomic scale is very critical for revealing structure-property relationships. Benefiting from the combination of the probe corrector, advanced dual SDDs and the fast EELS detection systems, we are able to perform microstructural and chemical analysis on most of the materials at the sub-nanometer and atomic scale. ”

- Dr. Xiaobing Hu, TEM Facility Manager / Research Assistant Professor at NUANCE/MSE
 


Research Highlight

Electron counting 4D STEM studies of electron beam-sensitive human tooth enamel

The Gatan K3 IS coupled with a STEMx system on our JEOL ARM300F were used to capture low-dose 4D STEM diffraction datasets (300 frames per second; dose ~200 e/Å) of human dental enamel, the outer layer component of human teeth. Understanding enamel structural details are of high importance in multiple human health contexts, from understanding enamel formation to development of its defects. Enamel crystallites, the nanoscale building blocks of human enamel, can be investigated from the micro- to the atomic scale using (S)TEM, however, sensitivity of this mineral to the electron beam is one of the limiting factors for performing such studies. Although recently atomic resolution STEM imaging at cryogenic temperatures successfully revealed the apparent coherent atomic structure of crystallites in detail, (2) the field-of-view (FoV) was limited. While the 4D STEM dataset has a ~12x larger FoV, qualitative analysis of the difference in intensity between two opposing virtual segmented detectors reveals that certain individual crystallites display a tilt within the mineral lattice. This suggests that enamel crystallites may not be as coherent as previously thought, which in turn could have important implications on mechanical properties and provide unique insights in crystallite growth during enamel formation.

Paul Smeets"We were very fortunate to be the first site in the world to have a K3 IS camera installed at the end of 2018, with support from Gatan. Thanks to electron counting, we can now routinely acquire high speed and low-dose images, with at least a 3-fold increase in speed (full frame) compared to our conventional Oneview CMOS camera ― with as a bonus an even larger field-of-view! This allows us to expand our research to include characterization of various material classes (such as soft and hybrid) which are sensitive to electron radiation, albeit in a dynamic environment. Additionally, we are exploring using this camera for advanced material analysis using 4D-STEM approaches.”

― Dr. Paul Smeets, Facility Manager FIB&TEM / Research Associate at NUANCE/EPIC

Research 

 a) Cryo-STEM image displaying part of an enamel crystallite (see ref. (2)) b) Average diffraction pattern of the 4D STEM data set (high SNR). Inset: single diffraction pattern of the 4D STEM data set (low SNR). c) Average diffraction pattern with 12 segmented virtual detectors (indicated by white lines). d) Virtual image created from the average diffraction pattern, combining intensities from all segmented virtual detectors. e,f) Maps displaying the differences in intensity between two selected opposite partial virtual detectors (indicated in inset). This difference in intensity is indicated in the red to blue color bar on the right. The black arrows indicate places within single grains that show variations in intensity between the opposed virtual detectors, which signify a tilt in the crystallographic directions of the apatite lattice with respect to one other. 
A special thanks to Dr. Roberto dos Reis & Stephanie M. Ribet for helping with data analysis using Python scripting.


User Research Highlight

Unconventional defects within quasi-one-dimensional KMn6Bi5 nanowires

Quasi-1D KMn6Bi5, which comprises ideal 1D nanowire (NW) motifs as an intrinsic part of the crystal structures and its defect mechanism is unusual in that the 1D nanowires slide linearly as a whole rather than conventional atomic displacements. Unconventional motific defects, which lead to two domains of inter-NW spacing larger or smaller than the pristine NW array, are unraveled by aberration-corrected scanning transmission electron microscopy (AC-STEM) images and corresponding multislice image simulation, which can image each atomic column using a sub-Å electron probe.(3) Inter-NW spacings without compositional or structural modulation can shift bulk plasmon energy at two different domains using electron energy loss spectroscopy (EELS) at the low energy range of 0-50 eV, which can measure optical and electronic properties such as the bandgap, local density of states (LDOS) and bulk/surface plasmon excitation.

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Microstructure and atomic scale structure of quasi one-dimensional KMn6Bi5 (upper left and right). Spectrum imaging analysis of the plasmon peak variations among different domains (bottom left and right).
 


User Research Highlight

Visualization of structure dynamics upon external forces

The K3 IS installed on the JEOL ARM300F enabled a new method to view the dynamic motion of atoms in atomically thin 2D materials.(4) This method helps to reveal the underlying cause behind the performance failure of a widely used 2D material, and it could help researchers develop more stable and reliable materials for future wearables and flexible electronic devices. With this new way to study 2D materials at the atomic level, the team believes researchers could use this imaging approach to synthesize materials that are less susceptible to failure in electronic devices. In memory devices, for example, researchers could observe how regions where information is stored evolve as electric current is applied and adapt how those materials are designed for better performance.

Schematic of sample fabrication process for in situ measurements (top), Electric field induced structural changes across grain boundaries in monolayer MoS2 (bottom). The electric field induces migration of sulfur atoms from grain boundaries in the material and leaves behind voids at the grain boundary.
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1) Gao, Y. H., Liu, S. Z., Hu, X. B., Ren, Q. Q., Li, Y., Dravid, V. P., and Wang. C. X. (2019) A novel low cost 2000 MPa grade ultra-high strength steel with balanced strength and toughness. Materials Science and Engineering A, 759, 298-302. https://doi.org/10.1016/j.msea.2019.05.039

2) DeRocher, K. A. #, Smeets, P. J. M.#, Goodge B. H., Zachman M. J., Balachandran P. V., Stegbauer, L., Cohen, M. J., Gordon, L. M., Rondinelli, J. M., Kourkoutis, L. F., and Joester, D. (2020) Chemical gradients in human enamel crystallites. Nature (accepted)

3) Jung, H. J., Bao, J. -K., Chung, D. Y., Kanatzidis, M. G., and Dravid, V. P. (2019) Unconventional Defects in a Quasi-One-Dimensional KMN6Bi5. Nano Letters 19(10), 7476-7486. https://doi.org/10.1021/acs.nanolett.9b03237

4) Murthy, A. A., Stanev, T. K., Dos Reis, R., Hao, S., Wolverton, C., Stern, N. P., and Dravid, V. P. (2020). Direct Visualization of Electric-Field-Induced Structural Dynamics in Monolayer Transition Metal Dichalcogenides. ACS Nano, 14(2), 1569-1576. https://doi.org/10.1021/acsnano.9b06581