How Adsorbate Alignment Leads to Selective Reaction

There has been much interest in the effect of adsorbate alignment in a surface reaction. Here we show its significance for an electron-induced reaction occurring along preferred axes of the asymmetric Cu(110) surface, characterized by directional copper rows. By scanning tunneling microscopy (STM), we found that the heterocyclic aromatic reagent, physisorbed <i>meta</i>-iodopyridine, lay with its carbon–iodine either <i>along</i> the rows of Cu(110), “A”, or <i>perpendicular</i>, “P”. Electron-induced dissociative attachment with the C–I bond initially along “A” gave a chemisorbed I atom and chemisorbed <i>vertical</i> pyridyl, singly surface-bound, whereas that with C–I along “P” gave a chemisorbed I atom and a <i>horizontal</i> pyridyl, doubly bound. An impulsive two-state model, involving a short-lived antibonding state of C–I, accounted for the different product surface binding in terms of closer Cu···Cu atomic spacing along “A” accommodating only one binding site of the pyridyl ring recoiling from I and wider spacing along “P” accommodating simultaneously both binding sites, N–Cu and C–Cu, in the meta-position on the recoiling pyridyl ring. STM studies combined with dynamical modeling can be seen as a way to improve understanding of the role of surface alignment in determining reactive outcomes in induced reaction at asymmetric crystalline surfaces

Retention of Bond Direction in Surface Reaction: A Comparative Study of Variously Aligned <i>p</i>‑Dihalobenzenes on Cu(110)

Previous studies indicated that the reagent bond direction of a bond being broken in surface reaction dominated the subsequent product recoil direction. Here we test this in an STM study of the electron-induced bond breaking for three clearly different alignments of each of two dihalobenzene reactions on Cu(110). A strong correlation was observed between the physisorbed adsorbate bond direction and the subsequent recoil direction of the chemisorbed halogen-atom product. The correlation was also evident in the theoretical modeling for the case of variously aligned diiodobenzene. The theory employed the impulsive two-state (I2S) approach to compute the reaction dynamics following electron attachment. This showed that the correlation between the prior bond direction and the subsequent product angular distribution was due to the directionality of the antibonding repulsion responsible for extending the molecule’s carbon–halogen bond, en route to reaction. Retention of bond direction in reaction dominated the effect of differing roughness of the surface along markedly different crystal axes

Crystallization at Multiple Sites inside Particles of Amorphous Calcium Phosphate

Calcium phosphates are the main minerals in human bone, enamel, atherosclerosis, and dental calculus. Amorphous precursors may play a key role in biomineralization. We studied the formation and transformation of calcium phosphate particles of amorphous phase by stopped-flow spectrophotometry, simultaneous measurements of particle size and solution pH, and high-resolution transmission electron microscopy. Ion pairs and clusters formed in the first few seconds. They then constituted initial amorphous phase containing protonated phosphates and hydrated calcium ions, which was different from that containing Ca9(PO4)6. Crystalline domains developed at multiple sites inside the primary particles of the amorphous phase. With the consuming of interdomain constituents, these particles partially collapsed, liberating crystallites and inducing rapid precipitation. This study sheds new light on the understanding of crystallization in amorphous phase, as well as the induction period in precipitation kinetics

Designing Optoelectronic Properties by On-Surface Synthesis: Formation and Electronic Structure of an Iron–Terpyridine Macromolecular Complex

Supramolecular chemistry protocols applied on surfaces offer compelling avenues for atomic-scale control over organic–inorganic interface structures. In this approach, adsorbate–surface interactions and two-dimensional confinement can lead to morphologies and properties that differ dramatically from those achieved via conventional synthetic approaches. Here, we describe the bottom-up, on-surface synthesis of one-dimensional coordination nanostructures based on an iron (Fe)-terpyridine (tpy) interaction borrowed from functional metal–organic complexes used in photovoltaic and catalytic applications. Thermally activated diffusion of sequentially deposited ligands and metal atoms and intraligand conformational changes lead to Fe–tpy coordination and formation of these nanochains. We used low-temperature scanning tunneling microscopy and density functional theory to elucidate the atomic-scale morphology of the system, suggesting a linear tri-Fe linkage between facing, coplanar tpy groups. Scanning tunneling spectroscopy reveals the highest occupied orbitals, with dominant contributions from states located at the Fe node, and ligand states that mostly contribute to the lowest unoccupied orbitals. This electronic structure yields potential for hosting photoinduced metal-to-ligand charge transfer in the visible/near-infrared. The formation of this unusual tpy/tri-Fe/tpy coordination motif has not been observed for wet chemistry synthetic methods and is mediated by the bottom-up on-surface approach used here, offering pathways to engineer the optoelectronic properties and reactivity of metal–organic nanostructures

Unconventional Superconducting Diode Effects via Antisymmetry and Antisymmetry Breaking

Symmetry breaking plays a pivotal role in unlocking intriguing properties and functionalities in material systems. For example, the breaking of spatial and temporal symmetries leads to a fascinating phenomenon: the superconducting diode effect. However, generating and precisely controlling the superconducting diode effect pose significant challenges. Here, we take a novel route with the deliberate manipulation of magnetic charge potentials to realize unconventional superconducting flux-quantum diode effects. We achieve this through suitably tailored nanoengineered arrays of nanobar magnets on top of a superconducting thin film. We demonstrate the vital roles of inversion antisymmetry and its breaking in evoking unconventional superconducting effects, namely a magnetically symmetric diode effect and an odd-parity magnetotransport effect. These effects are nonvolatilely controllable through in situ magnetization switching of the nanobar magnets. Our findings promote the use of antisymmetry (breaking) for initiating unconventional superconducting properties, paving the way for exciting prospects and innovative functionalities in superconducting electronics

Unconventional Superconducting Diode Effects via Antisymmetry and Antisymmetry Breaking

Symmetry breaking plays a pivotal role in unlocking intriguing properties and functionalities in material systems. For example, the breaking of spatial and temporal symmetries leads to a fascinating phenomenon: the superconducting diode effect. However, generating and precisely controlling the superconducting diode effect pose significant challenges. Here, we take a novel route with the deliberate manipulation of magnetic charge potentials to realize unconventional superconducting flux-quantum diode effects. We achieve this through suitably tailored nanoengineered arrays of nanobar magnets on top of a superconducting thin film. We demonstrate the vital roles of inversion antisymmetry and its breaking in evoking unconventional superconducting effects, namely a magnetically symmetric diode effect and an odd-parity magnetotransport effect. These effects are nonvolatilely controllable through in situ magnetization switching of the nanobar magnets. Our findings promote the use of antisymmetry (breaking) for initiating unconventional superconducting properties, paving the way for exciting prospects and innovative functionalities in superconducting electronics

Unconventional Superconducting Diode Effects via Antisymmetry and Antisymmetry Breaking

Symmetry breaking plays a pivotal role in unlocking intriguing properties and functionalities in material systems. For example, the breaking of spatial and temporal symmetries leads to a fascinating phenomenon: the superconducting diode effect. However, generating and precisely controlling the superconducting diode effect pose significant challenges. Here, we take a novel route with the deliberate manipulation of magnetic charge potentials to realize unconventional superconducting flux-quantum diode effects. We achieve this through suitably tailored nanoengineered arrays of nanobar magnets on top of a superconducting thin film. We demonstrate the vital roles of inversion antisymmetry and its breaking in evoking unconventional superconducting effects, namely a magnetically symmetric diode effect and an odd-parity magnetotransport effect. These effects are nonvolatilely controllable through in situ magnetization switching of the nanobar magnets. Our findings promote the use of antisymmetry (breaking) for initiating unconventional superconducting properties, paving the way for exciting prospects and innovative functionalities in superconducting electronics