Prerequisites and Specifications for Sub Ångström Low-Voltage Transmission Electron Microscopy (SALVE) operation for investigating nano-scale properties of beam-sensitive objects

• Applicant: Professorin Dr. Ute Kaiser
• Subject Area: Synthesis and Properties of Functional Materials ; Experimental Condensed Matter Physics
• Term: from 2014 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 270370833

• Final Report Year: 2021

Final Report Abstract

The project has successfully reached the aims of the SALVE-proposal. The SALVE project explored thin electron beam-sensitive matter at the atomic scale by employing high-resolution imaging and spectroscopy at voltages in the range between 20kV and 80kV. A new unique electron microscope with CC/CS correction operating at-voltages of 80kV, 60kV, 40kV, 30kV, and 20kV was developed. As during the runtime of the project, a new physical limit for contrast and resolution especially at low voltages - the so-called image spread originating from Johnson noise -, has been discovered, the otherwise strong contrast-increase with lowering the electron accelerating voltage is lost. This limited the application for imaging only one of the challenging objects of the SALVE project, the single molecules at atomic resolution. Fortunately, and unforeseeable at the project start, a completely new class of materials developed fast, just in parallel to the running time of our project, the new class of 2-dimensional objects, demanding characterisation at the atomic level in particular with low electron accelerating voltages! Results from the SALVE project benchmarked what is possible to achieve in highresolution imaging and property determination. These results required as prerequisite precise understanding of the performance of the microscope as well as calculating the image contrast fitting the experiments quantitatively with the calculations, considering the contribution of the of elastic and inelastic scattering and determining material’s properties based on quantum mechanical calculations. Moreover, our results required development of new methods of specimen preparation for beam-sensitive materials, which were strongly advanced within the current phase of the project. Thus, the SALVE project contributed strongly to the development of application of the low-voltage method with respect to imaging the pristine material at the highest-possible resolution as compromise of image contrast, image resolution and damaging processes. It is well known that imaging beam-sensitive objects in the transmission electron microscope is a very challenging experiment, because the same electrons that form the image in the TEMs simultaneously modify the specimen causing irreversible modifications. Nowadays one starts to achieve on-requestmodification of the two-dimensional material by the microscope’s electron probe on the atomic scale, resulting in a new section in low-voltage electron microscopy: “In-situ functionalizing of two-dimensional materials”, where we contributed strongly in pioneering this field within the frame of the SALVE project. Such functionalization on the atomic level results in completely new material properties, which can be determined accurately by means of quantum mechanical calculations, as atomic coordinates can be given with picometer accuracy as input data for the calculations. Moreover, the electron beam can also be used for stimulating chemical reactions inside carbon nanotubes, thus allows one to discover basic new physics and chemistry. Within the voltage range of the SALVE instrument, a large fraction of scattered electrons over a wide field of view are used for imaging and spectroscopy on in-situ nanostructures and observing their dynamics also under the influence of the electron beam, heat, current-biasing, and other external sources. Almost all scattered electrons could be used if it were possible in future to eliminate the Johnson noise, for example by operating the objective lens and the corrector at temperatures of about four Kelvin using helium cooling. The high public interest in the SALVE project and its results is reflected in numerous press releases and other public news about SALVE.

Publications

• “Atomic mechanism of metal crystal nucleus formation in a single-walled carbon nanotube” Nature Chemistry 12(10) (2020) 921-928
  K. Cao, J. Biskupek, C.T. Stoppiello, R.L. McSweeney, T.W. Chamberlain, Z. Liu, K. Suenaga, S.T. Skowron, E. Besley, A.N. Khlobystov, U. Kaiser
  
• “Carbon Nanotubes as Electrically Active Nanoreactors for Multi-Step Inorganic Synthesis: Sequential Transformations of Molecules to Nanoclusters, and Nanoclusters to Nanoribbons” JACS 138 (2016) 8175
  A. Botos, J. Biskupek, T. W. Chamberlain, G. A. Rance, C. Stoppiello, J. Sloan, Z. Liu, K. Suenaga, U. Kaiser, A. N. Khlobystov
  
• “Chromatic Aberration Correction for Atomic Resolution TEM Imaging from 20 to 80 kV “Phys. Rev. Lett. 117 (2016) 07610
  M. Linck, P. Hartel, S. Uhlemann, F. Kahl, H. Müller, J. Zach, M. Haider, M. Niestadt, M. Bischoff, J. Biskupek, Z. Lee, T. Lehnert, F. Börrnert, H. Rose, U. Kaiser
  
• “Significance of matrix diagonalization in modelling inelastic electron scattering”, Ultramicroscopy 175 (2017) 58-66
  Z. Lee, R. Hambach, U. Kaiser and H. Rose
  
• “Chromatic- and geometric-aberration-corrected TEM imaging at 80 kV and 20 kV” Physical Review A 98 (2) (2018) 023861-1–10
  F. Börrnert and U. Kaiser
  
• “Comparison of atomic scale dynamics for the middle and late transition metal nanocatalysts” Nature Communications 9 (2018) 3382
  K. Cao, T. Zoberbier, J. Biskupek, A. Botos, R. L. McSweeney, A. Kurtoglu, C. T. Stoppiello, A. V. Markevich, E. Besley, T. W. Chamberlain, U. Kaiser, A. N. Khlobystov
  
• “Reversible superdense ordering of lithium between two graphene sheets” Nature 564 (2018) 234-239
  M. Kühne, F. Börrnert, S. Fecher, M. Ghorbani-Asl, J. Biskupek, D. Samuelis, A. V. Krasheninnikov, U. Kaiser, J. H. Smet
  
• „Electron Source Brightness and Illumination Semi-Angle Distribution Measurement in a Transmission Electron Microscope” Microscopy and Microanalysis 24 (2018) 249
  F. Börrnert, J. Renner, U. Kaiser
  
• “Comparison of atomic scale dynamics for the middle and late transition metal nanocatalysts” Nature Com. 9 (2019) 3382
  K. Cao, T. Zoberbier, J. Biskupek, A.Botos, R.L. McSweeney, A. Kurtoglu, C.T. Stoppiello, A. V. Markevich, E. Besley, T.W. Chamberlain, U. Kaiser, A.N. Khlobystov
  
• “Imaging an unsupported metal–metal bond in dirhenium molecules at the atomic scale” Sci. Adv. 6 (2020), eaay5849
  K. Cao, S. T. Skowron, J. Biskupek, C. T. Stoppiello, C. Leist, E. Besley, A. N. Khlobystov, and U. Kaiser