Stephen T. Skowron

Indium selenides (In_xSe_y) have been shown to retain several desirable properties, such as ferroelectricity, tunable photoluminescence through temperature-controlled phase changes, and high electron mobility when confined to two dimensions (2D). In this work we synthesize single-layer, ultrathin, subnanometer-wide In_xSe_y by templated growth inside single-walled carbon nanotubes (SWCNTs). Despite the complex polymorphism of In_xSe_y we show that the phase of the encapsulated material can be identified through comparison of experimental aberration-corrected transmission electron microscopy (AC-TEM) images and AC-TEM simulations of known structures of In_xSe_y. We show that, by altering synthesis conditions, one of two different stoichiometries of sub-nm In_xSe_y, namely InSe or β-In₂Se₃, can be prepared. Additionally, in situ AC-TEM heating experiments reveal that encapsulated β-In₂Se₃ undergoes a phase change to γ-In₂Se₃ above 400 °C. Further analysis of the encapsulated species is performed using X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX), and Raman spectroscopy, corroborating the identities of the encapsulated species. These materials could provide a platform for ultrathin, subnanometer-wide phase-change nanoribbons with applications as nanoelectronic components.

We report experimental methodologies utilising transmission electron microscopy (TEM) as an imaging tool for reaction kinetics at the single molecule level, in direct space and with spatiotemporal continuity.

A methodology for measuring activation parameters of a thermally driven chemical reaction by direct imaging and counting reactant molecules has been developed. The method combines the use of single walled carbon nanotubes (SWNTs) as a nano test tube, transmission electron microscopy (TEM) as an imaging tool, and a heating protocol that decouples the effect of the electron beam from the thermal activation. Polycyclic aromatic perchlorocoronene molecules are stable within SWNTs at room temperature, allowing imaging of individual molecules before and after each heating cycle between 500–600 °C. Polymerisation reaction rates can be determined at different temperatures simply by counting the number of molecules, resulting in an enthalpy of activation of 104 kJ mol⁻¹ and very large entropic contributions to the Gibbs free energy of activation. This experimental methodology provides a link between reactions at the single-molecule level and macroscopic chemical kinetics parameters, through filming the chemical reaction in direct space.

We induce and study reactions of polyoxometalate (POM) molecules, [PW₁₂O₄₀]³⁻ (Keggin) and [P₂W₁₈O₆₂]⁶⁻ (Wells–Dawson), at the single-molecule level, utilising TEM as an analytical tool, and nanotubes as test tubes.

Porous graphene has shown promise as a new generation of selective membrane for sieving atoms, ions and molecules. However, the atomistic mechanisms of permeation through defects in the graphenic lattice are still unclear and remain unobserved in action, at the atomic level. Here, the direct observation of palladium atoms from a nanoparticle passing through a defect in a single‐walled carbon nanotube one‐by‐one has been achieved with atomic resolution in real time, revealing key stages of the atomic permeation. Bonding between the moving atom and dangling bonds around the orifice, immediately before and after passing through the subnano‐pore, plays an important role in the process. Curvature of the graphenic lattice crucially defines the direction of permeation from concave to convex side due to a difference in metal‐carbon bonding at the curved surfaces as confirmed by density functional theory calculations, demonstrating the potential of porous carbon nanotubes for atom sieving.

Porous graphene has shown promise as a new generation of selective membrane for sieving atoms, ions and molecules. However, the atomistic mechanisms of permeation through defects in the graphenic lattice are still unclear and remain unobserved in action, at the atomic level. Here, the direct observation of palladium atoms from a nanoparticle passing through a defect in a single‐walled carbon nanotube one‐by‐one has been achieved with atomic resolution in real time, revealing key stages of the atomic permeation. Bonding between the moving atom and dangling bonds around the orifice, immediately before and after passing through the subnano‐pore, plays an important role in the process. Curvature of the graphenic lattice crucially defines the direction of permeation from concave to convex side due to a difference in metal‐carbon bonding at the curved surfaces as confirmed by density functional theory calculations, demonstrating the potential of porous carbon nanotubes for atom sieving.