Anisotropic Hyperfine Interaction of Surface-Adsorbed Single Atoms

Abstract

Hyperfine interactions have been widely used in material science, organic chemistry, and structural biology as a sensitive probe to local chemical environments. However, traditional ensemble measurements of hyperfine interactions average over a macroscopic number of spins with different geometrical locations and nuclear isotopes. Here, we use a scanning tunneling microscope (STM) combined with electron spin resonance (ESR) to measure hyperfine spectra of hydrogenated-Ti on MgO/Ag(100) at low-symmetry binding sites and thereby determine the isotropic and anisotropic hyperfine interactions at the single-atom level. Combining vector-field ESR spectroscopy with STM-based atom manipulation, we characterize the full hyperfine tensors of 47Ti and 49Ti and identify significant spatial anisotropy of the hyperfine interactions for both isotopes. Density functional theory calculations reveal that the large hyperfine anisotropy arises from highly anisotropic distributions of the ground-state electron spin density. Our work highlights the power of ESR-STM-enabled single-atom hyperfine spectroscopy in revealing electronic ground states and atomic-scale chemical environments.

Experimental Determination of a Single Atom Ground State Orbital through Hyperfine Anisotropy

“…While writing this manuscript, we became aware of a similar experiment performed in another group. 17 Overall, their results agree very well with those presented here: A strong anisotropy of the hyperfine splitting along the oxygen direction is also found in their experiment. In contrast to our work, they determine the shape of the ground state orbital via DFT, which allows to shed light onto the origin of anisotropic and isotropic contributions to the hyperfine interaction from a first-principles perspective.…”

“…While writing this manuscript, we became aware of a similar experiment performed in another group . Overall, their results agree very well with those presented here: A strong anisotropy of the hyperfine splitting along the oxygen direction is also found in their experiment.…”

MOF-derived single-atom catalysts for oxygen electrocatalysis in metal–air batteries

“…have rarely been used as the metal node during the MOF synthesis, which thus limits the construction of noble metal SACs. [60][61][62][63] In recent years, some functional organic ligands have been reported to possess great advantages in coordination with noble metal ions and enable a strong anchoring effect to stabilize the noble metal single atoms. 64,65 Therefore, designing and tuning the ligand coordination of MOFs affords a promising strategy for the synthesis of noble metal SACs.…”

Coupling Transition Metal Compound with Single‐Atom Site for Water Splitting Electrocatalysis

“…The atomic properties of different types of TMC‐based SACs could be characterized by different techniques. Bae et al [60] . a scanning tunneling microscope (STM) combined with electron spin resonance (ESR) to measure hyperfine spectra of hydrogenated‐Ti on MgO/Ag (100) at low‐symmetry binding sites and thereby determine the isotropic and anisotropic hyperfine interactions at the single‐atom level.…”

“…[59] The atomic properties of different types of TMC-based SACs could be characterized by different techniques. Bae et al [60] a scanning tunneling microscope (STM) combined with electron spin resonance (ESR) to measure hyperfine spectra of hydrogenated-Ti on MgO/Ag (100) at low-symmetry binding sites and thereby determine the isotropic and anisotropic hyperfine interactions at the single-atom level. Li and coworkers [61] have obtained the HAADF-STEM images and atomically resolved elemental mapping to investigate the structure of Ni(OH) x catalyst with atomically dispersed Pt sites, which revealed the formation of nanoboard structure.…”