Tip-activated single-atom catalysis: CO oxidation on Au adatom on oxidized rutile TiO surface.

Single-atom catalysis of carbon monoxide oxidation on metal-oxide surfaces is crucial for greenhouse recycling, automotive catalysis, and beyond, but reports of the atomic-scale mechanism are still scarce. Here, using scanning probe microscopy, we show that charging single gold atoms on oxidized rutile titanium dioxide surface, both positively and negatively, considerably promotes adsorption of carbon monoxide. No carbon monoxide adsorption is observed on neutral gold atoms.

Raman Activity of Multilayer Phosphorene under Strain.

Using computational tools, we study the behavior of activities of lattice vibrational Raman modes in few-layered phosphorene of up to four layers subjected to a uniaxial strain of -2 to +6% applied in the armchair and zigzag directions. We study both high- and low-frequency modes and find very appreciable frequency shifts in response to the applied strain of up to ≈20 cm. The Raman activities are characterized by A /A activity ratios, which provide very meaningful characteristics of functionalization via layer- and strain-engineering.

Imaging the surface potential at the steps on the rutile TiO(110) surface by Kelvin probe force microscopy.

Although step structures have generally been considered to be active sites, their role on a TiO surface in catalytic reactions is poorly understood. In this study, we measured the contact potential difference around the steps on a rutile TiO(110)-(1 × 1) surface with O exposure using Kelvin probe force microscopy. A drop in contact potential difference was observed at the steps, indicating that the work function locally decreased.

Tip-Induced Control of Charge and Molecular Bonding of Oxygen Atoms on the Rutile TiO (110) Surface with Atomic Force Microscopy.

We study a low-temperature on-surface reversible chemical reaction of oxygen atoms to molecules in ultrahigh vacuum on the semiconducting rutile TiO(110)-(1 × 1) surface. The reaction is activated by charge transfer from two sources, natural surface/subsurface polarons and experimental Kelvin probe force spectroscopy as a tool for electronic charge manipulation with single electron precision. We demonstrate a complete control over the oxygen species not attainable previously, allowing us to deliberately discriminate in favor of charge or bond manipulation, using either direct charge injection/removal through the tip-oxygen adatom junction or indirectly via polarons.

Subatomic-scale resolution with SPM: Co adatom on p(2 × 1)Cu(110):O.

We study the limits of SPM subatomic resolution in imaging orbital magnetic features on a model system of a Co atom on a p(2 × 1)Cu(110):O surface. We show that scanning tunneling spectroscopies allow the determination of the occupation of the Co d shells and the value of the Hubbard U in the DFT + U modeling, and that standard near-contact AFM can in principle image the asymmetry due to partial filling of the d shells at close distances in the small-amplitude regime. Due to the partially ionic character of Co, a faint asymmetry is predicted to also arise in the electrostatic force.