Quantum tunneling enabled self-assembly of hydrogen atoms on Cu(111)

Atomic and molecular self-assembly are key phenomena that underpin many important technologies. Typically, thermally enabled diffusion allows a system to sample many areas of configurational space, and ordered assemblies evolve that optimize interactions between species. Herein we describe a system in which the diffusion is quantum tunneling in nature and report the self-assembly of H atoms on a Cu(111) surface into complex arrays based on local clustering followed by larger scale islanding of these clusters. By scanning tunneling microscope tip-induced scrambling of H atom assemblies, we are able to watch the atomic scale details of H atom self-assembly in real time. The ordered arrangements we observe are complex and very different from those formed by H on other metals that occur in much simpler geometries. We contrast the diffusion and assembly of H with D, which has a much slower tunneling rate and is not able to form the large islands observed with H over equivalent time scales. Using density functional theory, we examine the interaction of H atoms on Cu(111) by calculating the differential binding energy as a function of H coverage. At the temperature of the experiments (5 K), H(D) diffusion by quantum tunneling dominates. The quantum-tunneling-enabled H and D diffusion is studied using a semiclassically corrected transition state theory coupled with density functional theory. This system constitutes the first example of quantum-tunneling-enabled self-assembly, while simultaneously demonstrating the complex ordering of H on Cu(111), a catalytically relevant surface.

A Conversation with Haldor Topsøe

Haldor Topsøe was born in Copenhagen, Denmark, in 1913. He studied chemical engineering at the Technical University of Denmark (DTU). In 1940, he founded the company Haldor Topsøe, which has become one of the most successful companies in the field of heterogeneous catalysis. The company develops and markets catalysts and processes for petroleum refining, air-pollution control, synthesis gas production, ammonia and methanol production and solid oxide fuel cells. The company Haldor Topsøe is also a leader in the production and state-of-the-art scientific characterization of new catalysts. Dr. Topsøe is currently the sole owner of the company. He has written numerous articles on ammonia synthesis, catalysis, and energy questions. He is the author of several books on economics. Dr. Topsøe has received numerous awards, including honorary doctorates from Aarhus University, DTU, and the Chalmers University in Sweden; the Gold Medal from the Royal Academy of Sciences; the Hoover Medal for his technical abilities and entrepreneurship; and the Grove Memorial Medal for Advances in Fuel Cell Technology. Topsøe is a member of the Danish and the Swedish Academies of Technical Sciences and of the U.S. National Academy of Engineering.

The following interview was conducted on August 16, 2010.

–Manos Mavrikakis

Water-mediated proton hopping on an iron oxide surface

The diffusion of hydrogen atoms across solid oxide surfaces is often assumed to be accelerated by the presence of water molecules. Here we present a high-resolution, high-speed scanning tunneling microscopy (STM) study of the diffusion of H atoms on an FeO thin film. STM movies directly reveal a water-mediated hydrogen diffusion mechanism on the oxide surface at temperatures between 100 and 300 kelvin. Density functional theory calculations and isotope-exchange experiments confirm the STM observations, and a proton-transfer mechanism that proceeds via an H(3)O(+)-like transition state is revealed. This mechanism differs from that observed previously for rutile TiO(2)(110), where water dissociation is a key step in proton diffusion.

Abnormal spatial QRS-T angle, a marker of ventricular repolarisation, predicts serious ventricular arrhythmia in systemic sclerosis

OBJECTIVES

Cardiac involvement may be under-diagnosed in asymptomatic patients with systemic sclerosis (SSc). Standard electrocardiography-derived spatial QRS-T angle (spQRS-Ta) is an established marker of ventricular repolarisation heterogeneity, and a strong independent predictor of cardiac morbidity and mortality, including sudden death, in the general population. We examined whether spQRS-Ta is abnormal in asymptomatic SSc patients and assessed its predictive value for possibly concurrent, serious ventricular arrhythmia.

METHODS

SpQRS-Ta and 24-hour Holter recordings were obtained from 69 SSc patients (aged 51±13 years, 63 women) without clinically evident cardiac involvement and having left ventricular ejection fraction at least 50% by echocardiography. 'Healthy' subjects matched 1:1 with patients for age, gender and body mass index served as controls.

RESULTS

SpQRS-Ta was wider in SSc (median value 15.6°, interquartile range 10.6-24.3°) than controls (10.5°, 7.3-13.5°, p=0.0001) and not associated with skin fibrosis extent or specific clinical manifestations and autoantibodies. Twenty-four-hour Holter recordings revealed couplets of ventricular beats in six (Lown class IVa) and non-sustained ventricular tachycardia in five patients (Lown class IVb); spQRS-Ta was wider in those eleven patients with serious ventricular arrhythmia than the remaining patients (24.9°, 14.9-31.3° vs. 14.4°, 9.6-22.3°; p=0.02). A spQRS-Ta>19.3° demonstrated 80% sensitivity and 68% specificity (area under the curve 0.81, p=0.02) to predict the presence of non-sustained ventricular tachycardia in Holter monitoring.

CONCLUSIONS

Ventricular repolarisation heterogeneity, as reflected by wider spQRS-Ta, is common in SSc. Increased spQRS-Ta could serve as a simple screening test for further investigation to identify patients at risk or prone to develop life-threatening ventricular arrhythmia.

Low-temperature CO oxidation on Ni(111) and on a Au/Ni(111) surface alloy

From an interplay between scanning tunneling microscopy, temperature programmed desorption, X-ray photoelectron spectroscopy, and density functional theory calculations we have studied low-temperature CO oxidation on Au/Ni(111) surface alloys and on Ni(111). We show that an oxide is formed on both the Ni(111) and the Au/Ni(111) surfaces when oxygen is dosed at 100 K, and that CO can be oxidized at 100 K on both of these surfaces in the presence of weakly bound oxygen. We suggest that low-temperature CO oxidation can be rationalized by CO oxidation on O(2)-saturated NiO(111) surfaces, and show that the main effect of Au in the Au/Ni(111) surface alloy is to block the formation of carbonate and thereby increase the low-temperature CO(2) production.