Francisco Lagunas Vargas1,Chenkun Zhou2,Dmitri Talapin2,Robert Klie1
University of Illinois at Chicago1,The University of Chicago2
Francisco Lagunas Vargas1,Chenkun Zhou2,Dmitri Talapin2,Robert Klie1
University of Illinois at Chicago1,The University of Chicago2
MXenes are an emerging family of two-dimensional materials. They are synthesized by etching the A element -typically from periodic groups 13 or 14- from a MAX phase crystal (M denoting an early transition metal and X either is carbon or nitrogen). In MAX crystals, the A element is located between MX layers and forms metallic bonds with the M element. Upon the removal of the A-element, functional surface groups, T<sub>x</sub>, can be introduced producing ordered MX stacked nanosheets where consecutive layers are held together by van der Waals (vdW) forces. MXenes (M<sub>n+1</sub>X<sub>n</sub>T<sub>x</sub> with n=1,2,3) owe their large design space, and consequently their broad variety of properties, to a wide range of chemical modifications possible in M and functional T<sub>x</sub> surface groups <sup>[1]</sup>.<br/>In this contribution, we will present a study of MXenes functionalized with organic surface groups. As part of our study, we will utilize atomic resolution scanning transmission electron microscopy (STEM) to determine the structure of the material as well as the nature of local defects. Additionally, we will use electron energy loss spectroscopy (EELS) and x-ray energy dispersive spectroscopy (XEDS) to gain insights into the local chemical composition and bonding environment with high spatial resolution.<br/>Organic-metallic hybrid MXenes pose a unique challenge to high-resolution STEM imaging since the organic material in the sample is highly electron-beam sensitive. At typical doses required for high resolution imaging, organic material will readily degrade. In this study, we borrow elements of transmission electron cryomicroscopy (Cryo-TEM), namely cooling our samples <i>in-situ</i> to liquid nitrogen temperatures. This will increase the robustness of the hybrid MXenes allowing us to conduct high-resolution imaging of the organic-to-metallic interface, as well as to gain insights into the arrangement of organics between MX layers.<br/>To cool the MXene sheets, we will use a Gatan cold stage capable of reaching liquid nitrogen temperatures. The primary instrument we will utilize is an aberration-corrected cold field emission JEOL ARM200CF operating at 200kV primary electron energy. With the emission current set to 12A, the electron probe will be operated at 24mrad convergence semi-angle. High angle annular dark field, low angle annular dark field and annular bright field detectors will be set to inner angles of 75 mrad, 30 mrad, 11mrad respectively. Atomic scale chemical identification will be conducted using a large solid-angle Oxford XMAX100TLE XEDS detector. The ARM200CF is equipped with a post-column Gatan Continuum GIF spectrometer which allows will allow us to probe unoccupied density of states (DOS) with high spatial resolution. Using this approach, we will demonstrate that metal-organic hybrid MXenes form highly ordered, flexible structures with well defined elemental layers.<sup>[2]</sup><br/><sup>[1]</sup> Gogotsi, Yury, and Babak Anasori. "The rise of MXenes." (2019): 8491-8494.<br/><sup>[2] </sup>This project is supported by a supported by the National Science Foundation (DMREF CBET-1729420) and made use of instruments in the Electron Microscopy Service at the UIC Research Resources Center. The acquisition of UIC JEOL JEM ARM200CF is supported by an MRI-R<sup>2</sup> grant from the National Science Foundation (Grant No. DMR-0959470) and the upgraded Gatan Continuum spectrometer was supported by a grant from the NSF (DMR-1626065).