Philip Moriarty

Core-level and tunnelling spectroscopies applied to noble gas endofullerenes offer complementary insights into electron transfer rates, addressing both intramolecular and extramolecular processes. Elastic and inelastic tunnelling spectroscopy of empty C₆₀ and Kr@C₆₀ on Pb/Cu(111) each show that the encapsulated atom is essentially invisible to scanning probes. We interpret the lineshape of the lowest unoccupied molecular orbital (LUMO) of Pb-adsorbed (endo)fullerenes in tunnelling spectra as a signature of the dynamic Jahn-Teller (DJ-T) effect. This effect persists in electronically decoupled second-layer molecules, which also display distinct vibronic progressions in on-resonance tunnelling. DFT calculations reproduce the LUMO alignment and low density of states at the Fermi level seen in experimental tunnelling spectra for (endo)fullerenes on Pb, and, in line with submolecular resolution STM images, also predict that an atom-down orientation of the fullerene cage is energetically most favourable (although other adsorption geometries differ only by tens of meV at most). In contrast to the tunnelling data, core-level-focussed techniques -namely, photoemission, X-ray absorption, and resonant Auger-Meitner electron spectroscopy -of Ar@C₆₀/Pb(111) indicate that the encapsulated atom is heavily coupled to the molecular environment, with both a clear influence of substrate screening on the core-level lineshape and the absence of spectator signal in decay spectra.

Charge transfer is fundamentally dependent on the overlap of the orbitals comprising the transport pathway. This has key implications for molecular, nanoscale, and quantum technologies, for which delocalization (and decoherence) rates are essential figures of merit. Here, we apply the core hole clock technique—an energy-domain variant of ultrafast spectroscopy—to probe the delocalization of a photoexcited electron inside a closed molecular cage, namely the Ar 2p ⁵4s ¹ state of Ar@C₆₀. Despite marginal frontier orbital mixing in the ground configuration, almost 80% of the excited state density is found outside the buckyball due to the formation of a markedly diffuse hybrid orbital. Far from isolating the intracage excitation, the surrounding fullerene is instead a remarkably efficient conduit for electron transfer: we measure characteristic delocalization times of 6.6 ± 0.3 fs and ≲ 500 attoseconds, respectively, for a 3D Ar@C₆₀ film and a 2D monolayer on Ag(111).

OpenAI’s ChatGPT, a formidable large language model (LLM) based on a generative pre-trained transformer architecture, has a remarkable, and rather unsettling, ability to solve conceptually challenging physics problems. One of the more impressive demonstrations of ChatGPT’s capabilities in this regard is its expert-physicist-level performance on the questions that make up the Force Concept Inventory [CG West, https://arxiv.org/abs/2303.01067]. Motivated by the deep implications of these advances in LLM technologies for student learning, attainment, and assessment, we asked a class of undergraduate physics students (N = 119) to use ChatGPT to solve problems, and write Python code, related to the eigenfunctions of the Hamiltonian of the 1D quantum harmonic oscillator—a staple of introductory quantum mechanics courses. We discuss the significant pitfalls we encountered when incorporating ChatGPT into coursework in this manner, and make recommendations as to how LLMs might be better embedded into the undergraduate physics curriculum.

Philip Moriarty reviews Quantum Bullsh*t: How to Ruin Your Life with Advice from Quantum Physics by Chris Ferrie.

Submolecular resolution scanning tunnelling microscopy and qPlus atomic force microscopy reveal that, close to thermal equilibrium, bi-isonicotinic acid (4,4'-COOH-2,2'-bpy) assembles into extended molecular rows on both Au(111) and Ag(100) surfaces, driven primarily by the formation of OH··· N hydrogen bonds. Both the intermolecular separation and inter-row spacing for Au(111) and Ag(100) are identical within experimental uncertainty, highlighting that the assembly of bi-isonicotinic acid networks on both metal surfaces is predominantly driven by intermolecular hydrogen-bonding and that the potential energy variation due to the substrate has relatively little influence. Nonetheless, the surface plays a key role in molecular organisation: symmetry-breaking induces prochiral behaviour, which drives the molecular enantiomers to form a racemic mixture of rows of different handedness. We adapt a tiling model previously introduced to model the formation of 2D networks of tetracarboxylic derivatives [Blunt et al. Science 322, 1077 (2008)] to the bi-isonicotinic acid system, providing key insights into the growth kinetics and attaining good agreement with the molecular morphologies observed in experiment. GRAPHICAL ABSTRACT

Motivated by the quest for experimental procedures capable of controlled manipulation of single atoms on surfaces, we set up a computational strategy that explores the cyclical vertical manipulation of a broad set of single atoms on the GaAs(110) surface. First-principles simulations of atomic force microscope tip–sample interactions were performed considering families of GaAs and Au-terminated tip apexes with varying crystalline termination. We identified a subset of tips capable of both picking up and depositing an adatom (Ga, As, Al, and Au) any number of times via a modify–restore cycle that “resets” the apex of the scanning probe to its original structure at the end of each cycle. Manipulation becomes successful within a certain window of lateral and vertical tip distances that are observed to be different for extracting and depositing each atom. A practical experimental protocol of special utility for potential cyclical manipulation of single atoms on a nonmetallic surface is proposed.

Molecular surgery provides the opportunity to study relatively large molecules encapsulated within a fullerene cage. Here we determine the location of an H₂O molecule isolated within an adsorbed buckminsterfullerene cage, and compare this to the intrafullerene position of HF. Using normal incidence X-ray standing wave (NIXSW) analysis, coupled with density functional theory and molecular dynamics simulations, we show that both H₂O and HF are located at an off-centre position within the fullerene cage, caused by substantial intra-cage electrostatic fields generated by surface adsorption of the fullerene. The atomistic and electronic structure simulations also reveal significant internal rotational motion consistent with the NIXSW data. Despite this substantial intra-cage interaction, we find that neither HF or H₂O contribute to the endofullerene frontier orbitals, confirming the chemical isolation of the encapsulated molecules. We also show that our experimental NIXSW measurements and theoretical data are best described by a mixed adsorption site model.