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

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@C 60 )@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@C 120 capsules, in which van der Waals Kr 2 and transient covalent [Kr 2 ] + 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. continued...

Scattering of ultrashort electron wave packets: optical theorem, differential phase contrast and angular asymmetries

“…The location of the target (i.e., the impact parameter) is shifted with respect to the beam, which is equivalent to the situation of a fixed target and a scanned electron beam. Examples of a spatially fixed target are a defect in a two-dimensional material [40] or an atom enclosed in a nanomaterial [41]. An optically trapped ultracold atom [42] will become available for this purpose by future research.…”