Morphology and stability of Au nanoclusters in HOPG nanopits of well-defined depth

Gold nanoparticles with a diameter comprised between 4 and 6 nm are stabilized in nanosized pits of well defined depth in highly oriented pyrolytic graphite (HOPG). These pits are produced by creation of artificial defects, followed by etching under a controlled oxygen atmosphere. At low Au coverage, clusters are found on the edges of the hexagonal pits maximizing the contact to dangling bonds on graphite multisteps. Larger coverage results in Au beads of surprisingly well defined shape and with a constant bead density per unit length. Most remarkable is the stability of these nanostructures under ambient conditions. Temperatures as high as 650K do not alter the morphology of the gold clusters. Higher temperatures do not lead to a change of the cluster morphology but to catalytically driven etching of the HOPG substrat

An experimental setup combining a highly sensitive detector forreaction products with a mass-selected cluster source andalow-temperature STM for advanced nanocatalysis measurements

We report on a home-built detector for catalytic reaction measurements offering good gas isolation from the surrounding ultrahigh vacuum components, high sensitivity for reaction products and a fast response time of 10ms enabling dynamic studies correlated to reactant gas pulses. The device is mounted in ultrahigh vacuum and combined with a low-temperature scanning tunneling microscope and a source for the deposition of mass-selected clusters. This combination allows for a direct correlation between surface morphology and catalytic properties of model catalysts. The performances of the new detector are illustrated by measurements on two model systems. Thermal desorption spectroscopy of CO carried out on morphologically well characterized Pt on TiO2(110)-(1×1) reveals several desorption features, which can be attributed to different surface sites. Catalytic CO oxidation performed by alternatingly pulsing isotopic CO and O2 on a Pt film on yttria stabilized zirconia reveals the CO or O rich temperature regimes. The CO2 production rate correlated with either one of the reactants can perfectly be reproduced by a kinetic reaction model giving access to the respective adsorption energie

Morphology and stability of Au nanoclusters in HOPG nanopits of well-defined depth

Gold nanoparticles with a diameter comprised between 4 and 6 nm are stabilized in nanosized pits of well defined depth in highly oriented pyrolytic graphite (HOPG). These pits are produced by creation of artificial defects, followed by etching under a controlled oxygen atmosphere. At low Au coverage, clusters are found on the edges of the hexagonal pits maximizing the contact to dangling bonds on graphite multisteps. Larger coverage results in Au beads of surprisingly well defined shape and with a constant bead density per unit length. Most remarkable is the stability of these nanostructures under ambient conditions. Temperatures as high as 650 K do not alter the morphology of the gold clusters. Higher temperatures do not lead to a change of the cluster morphology but to catalytically driven etching of the HOPG substrate

An experimental setup combining a highly sensitive detector for reaction products with a mass-selected cluster source and a low-temperature STM for advanced nanocatalysis measurements

We report on a home-built detector for catalytic reaction measurements offering good gas isolation from the surrounding ultrahigh vacuum components, high sensitivity for reaction products and a fast response time of 10 ms enabling dynamic studies correlated to reactant gas pulses. The device is mounted in ultrahigh vacuum and combined with a low-temperature scanning tunneling microscope and a source for the deposition of mass-selected clusters. This combination allows for a direct correlation between surface morphology and catalytic properties of model catalysts. The performances of the new detector are illustrated by measurements on two model systems. Thermal desorption spectroscopy of CO carried out on morphologically well characterized Pt on TiO2(110)-(1×1) reveals several desorption features, which can be attributed to different surface sites. Catalytic CO oxidation performed by alternatingly pulsing isotopic CO and O2 on a Pt film on yttria stabilized zirconia reveals the CO or O rich temperature regimes. The CO2 production rate correlated with either one of the reactants can perfectly be reproduced by a kinetic reaction model giving access to the respective adsorption energies

Palladium nano-clusters grown on prestructured HOPG substrates

The growth of Palladium nano-clusters prepared by atomic beam deposition on prestructured highly oriented pyrolytic graphite (HOPG) surfaces has been investigated by means of scanning tunnelling microscopy (STM). Preformed nanosized pits created on the HOPG surfaces are used as localized pinning sites for Pd cluster nucleation and growth at room temperature. We succeeded in obtaining Pd clusters of nanometric size and with rather sharp size distributions. A systematic morphological study conducted by STM reveals a linear dependence between the height and the diameter of the Pd nanostructures. Finally, Pd nano-clusters stabilized on prestructured HOPG surfaces were found to be active catalysts in the Heck cross-coupling reaction

Influence of different digital terrain models (DTMs)on alpine permafrost modeling

The thawing of alpine permafrost due to changes in atmospheric conditions can have a severe impact, e.g., on the stability of rock walls. The energy balance model, PERMEBAL, was developed in order to simulate the changes and distribution of ground surface temperature (GST) in complex high-mountain topography. In such environments, the occurrence of permafrost depends greatly on the topography, and thus, the digital terrain model (DTM) is an important input of PERMEBAL. This study investigates the influence of the DTM on the modeling of the GST. For this purpose, PERMEBAL was run with six different DTMs. Five of the six DTMs are based on the same base data, but were generated using different interpolators. To ensure that only the topographic effect on the GST is calculated, the snow module was turned off and uniform conditions were assumed for the whole test area. The analyses showed that the majority of the deviations between the different model outputs related to a reference DTM had only small differences of up to 1 K, and only a few pixels deviated more than 1 K. However, we also observed that the use of different interpolators for the generation of a DTM can result in large deviations of the model output. These deviations were mainly found at topographically complex locations such as ridges and foot of slopes