Atomic-Scale Time-Resolved Imaging of Krypton Dimers, Chains and Transition to a One-Dimensional Gas

Ian Cardillo-Zallo; Johannes Biskupek; Sally Bloodworth; Elizabeth S Marsden; Michael W Fay; Quentin M Ramasse; Graham A Rance; Craig T Stoppiello; William J Cull; Benjamin L Weare; Richard J Whitby; Ute Kaiser; Paul D Brown; Andrei N Khlobystov

doi:10.1021/acsnano.3c07853

Atomic-Scale Time-Resolved Imaging of Krypton Dimers, Chains and Transition to a One-Dimensional Gas

ACS Nano. 2024 Jan 30;18(4):2958-2971. doi: 10.1021/acsnano.3c07853. Epub 2024 Jan 22.

Authors

Affiliations

¹ School of Chemistry, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
² Electron Microscopy Group of Materials Science, Central Facility for Electron Microscopy, Ulm University, Ulm 89081, Germany.
³ School of Chemistry, University of Southampton, Southampton SO17 1BJ, United Kingdom.
⁴ Nanoscale and Microscale Research Centre, University of Nottingham, Nottingham NG7 2QL, United Kingdom.
⁵ SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury WA4 4AD, United Kingdom.
⁶ School of Chemical and Process Engineering and School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, United Kingdom.
⁷ Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, Queensland 4072, Australia.
⁸ Department of Mechanical, Materials & Manufacturing Engineering, University of Nottingham, Nottingham NG7 2RD, United Kingdom.

Abstract

Single-atom dynamics of noble-gas elements have been investigated using time-resolved transmission electron microscopy (TEM), with direct observation providing for a deeper understanding of chemical bonding, reactivity, and states of matter at the nanoscale. We report on a nanoscale system consisting of endohedral fullerenes encapsulated within single-walled carbon nanotubes ((Kr@C₆₀)@SWCNT), capable of the delivery and release of krypton atoms on-demand, via coalescence of host fullerene cages under the action of the electron beam (in situ) or heat (ex situ). The state and dynamics of Kr atoms were investigated by energy dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS). Kr atom positions were measured precisely using aberration-corrected high-resolution TEM (AC-HRTEM), aberration-corrected scanning TEM (AC-STEM), and single-atom spectroscopic imaging (STEM-EELS). The electron beam drove the formation of 2Kr@C₁₂₀ capsules, in which van der Waals Kr₂ and transient covalent [Kr₂]⁺ bonding states were identified. Thermal coalescence led to the formation of longer coalesced nested nanotubes containing more loosely bound Kr_n chains (n = 3-6). In some instances, delocalization of Kr atomic positions was confirmed by STEM analysis as the transition to a one-dimensional (1D) gas, as Kr atoms were constrained to only one degree of translational freedom within long, well-annealed, nested nanotubes. Such nested nanotube structures were investigated by Raman spectroscopy. This material represents a highly compressed and dimensionally constrained 1D gas stable under ambient conditions. Direct atomic-scale imaging has revealed elusive bonding states and a previously unseen 1D gaseous state of matter of this noble gas element, demonstrating TEM to be a powerful tool in the discovery of chemistry at the single-atom level.

Keywords: carbon nanotubes; endohedral fullerenes; noble gases; one-dimensional gas; single-atom dynamics; time-resolved imaging; transmission electron microscopy.