MRI: Acquisition of a Monochromated, Magnetic-Field-Free, Atomic-Resolution Scanning Transmission Electron Microscope Enabling Multidisciplinary Research and Education

Non-technical Description:

Nanometer scale materials represent a class of substances with at least one dimension that approaches the size of individual atoms. These materials exhibit properties that are dramatically different from substances at larger length scales and are essential to advance a wide array of technologies, ranging from magnetic data-storage systems to superconducting quantum computers to biomaterials applications.

To study and improve upon these materials, tools are required to examine them at the atomic level while minimizing any disturbance to their structure. Electron microscopy, which uses electrons to "see" atoms, is one of the fundamental means by which the structures of such nanoscale materials can be studied. Current designs of high-resolution transmission electron microscopes require a lens to focus the electron beam on the sample surface.

A side effect of this design is that the sample material is inadvertently exposed to a high magnetic field. Yet, turning the lens off to eliminate the magnetic field when studying magnetic or superconducting materials makes atomic-resolution analysis impossible. The instrument acquired through this major research instrumentation grant has a new lens design, providing a magnetic-field-free sample region and, when combined with a nearly mono-energetic electron source, allows for atomic-resolution imaging as well as chemical analysis of these critical materials.

In addition, atomic resolution, magnetic-field-free analysis can now also be achieved during heating or cooling experiments or when a controlled magnetic field is applied. To reach a broader user community and for communicating the capabilities of the instrument, the principal investigators hold annual workshops, organize sessions at national and international conferences, and engage with local microscopy societies.

The instrument, moreover, provides the diverse undergraduate and graduate student body at University of Illinois - Chicago (UIC), a Research-1 Hispanic-serving institution with opportunities for hands-on research and learning experiences in cutting-edge quantum, superconducting or biomaterials science. New in-class course modules and online teaching resources are developed and freely distributed online using data from the field-free transmission electron microscope.

Technical Description:

While the development of aberration-correctors, monochromated electron sources, and advanced detectors has fueled the current revolution in resolution, nearly all high-resolution transmission electron microscopy (TEM) experiments are still performed with the sample being exposed to a high magnetic field, since the objective lens (OL) pole-pieces require a magnetic field of about 3 tesla. Such a magnetic field limits the samples that can be studied, preventing magnetic, magneto-optical, magneto-electric, superconductive or topological materials from being characterized under relevant conditions.

Traditional magnetic imaging methods, where the OL is turned off, limit the spatial resolution to nanometer length-scales and do not allow for atomic-resolution chemical analysis. This instrument has a novel lens design that allows for better than 100 pm spatial resolution at 200 kV with a residual magnetic field of less than 0.3 mT and 40 meV energy resolution with a probe size of 110 nm.

Atomic-resolution chemical analysis, as well as novel image modes, such as 4D-STEM and differential phase contrast imaging, can be combined with in-situ heating or cooling experiments to study magnetic, superconducting or other electronic phase transitions. Research projects at UIC enabled by the new instrument include the study of novel magnetic phases in Ni-based perovskite oxides, excitons in 2-dimensional materials, conventional and near-room temperature superconductors, nanoparticles/quantum dots as topological insulators, and anti-cavity biofilms and the mechanical manipulation of cells.

External users, ranging from universities, national laboratories and companies across the United States to international partner institutions, can take advantage of the capabilities provided by the instrument to study novel quantum materials, new magnetic structures, photovoltaic materials, energy-storage devices, and biological systems under controlled magnetic-field conditions and with atomic resolution.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.