Characterization of an Unexpected μ Adsorption of Molecular Oxygen on Ag(100) with Low-Temperature STM.

Precise description of the interaction between molecular oxygen and metal surfaces is one of the most challenging topics in quantum chemistry. In this work, we use low-temperature scanning tunneling microscopy (STM) to identify and characterize an adsorption state of molecular oxygen that coordinates to three Ag atoms (μ) on Ag(100). Surprisingly, μ-O cannot be identified as a stable configuration with generalized gradient approximation (GGA)-level density functional theory (DFT) calculations.

Thermal Rates and High-Temperature Tunneling from Surface Reaction Dynamics and First-Principles.

Studying dynamics of the dissociative adsorption and recombinative desorption of hydrogen on copper surfaces has shaped our atomic-scale understanding of surface chemistry, yet experimentally determining the thermal rates for these processes, which dictate the outcome of catalytic reactions, has been impossible so far. In this work, we determine the thermal rate constants for dissociative adsorption and recombinative desorption of hydrogen on Cu(111) between 200 and 1000 K using data from reaction dynamics experiments. Contrary to current understanding, our findings demonstrate the predominant role of quantum tunneling, even at temperatures as high as 400 K.

Cooperative adsorbate binding catalyzes high-temperature hydrogen oxidation on palladium.

Atomic-scale structures that account for the acceleration of reactivity by heterogeneous catalysts often form only under reaction conditions of high temperatures and pressures, making them impossible to observe with low-temperature, ultra-high-vacuum methods. We present velocity-resolved kinetics measurements for catalytic hydrogen oxidation on palladium over a wide range of surface concentrations and at high temperatures. The rates exhibit a complex dependence on oxygen coverage and step density, which can be quantitatively explained by a density functional and transition-state theory-based kinetic model involving a cooperatively stabilized configuration of at least three oxygen atoms at steps.

Long-Lived Magnetization in an Atomic Spin Chain Tuned to a Diabolic Point.

Scaling magnets down to where quantum size effects become prominent triggers quantum tunneling of magnetization (QTM), profoundly influencing magnetization dynamics. Measuring magnetization switching in an Fe atomic chain under a carefully tuned transverse magnetic field, we observe a nonmonotonic variation of magnetization lifetimes around a level crossing, known as the diabolic point (DP). Near DPs, local environment effects causing QTM are efficiently suppressed, enhancing lifetimes by three orders of magnitude.

A quantum sensor for atomic-scale electric and magnetic fields.

The detection of faint magnetic fields from single-electron and nuclear spins at the atomic scale is a long-standing challenge in physics. While current mobile quantum sensors achieve single-electron spin sensitivity, atomic spatial resolution remains elusive for existing techniques. Here we fabricate a single-molecule quantum sensor at the apex of the metallic tip of a scanning tunnelling microscope by attaching Fe atoms and a PTCDA (3,4,9,10-perylenetetracarboxylic-dianhydride) molecule to the tip apex.