Klaus Wandelt

Bio: Klaus Wandelt is an academic researcher from University of Bonn. The author has contributed to research in topics: Adsorption & Scanning tunneling microscope. The author has an hindex of 50, co-authored 376 publications receiving 9548 citations. Previous affiliations of Klaus Wandelt include University of Science and Technology of China & Fritz Haber Institute of the Max Planck Society.

The electro-oxidation of formic acid on Pt–Pd single crystal bimetallic surfaces

Abstract: The interrelationship between the macroscopic kinetic rate of HCOOH oxidation in 0.1 M HClO4 solution and the morphology/composition of the electrode is studied on Pt(111) modified by Pd (denoted hereafter as the Pt(111)–PdxML system, 0 < x < 1) and on Pt–Pd bulk single crystal alloy surfaces (denoted hereafter as the PtPdxat%(111) system, x = 6 and x = 25). The Pd surface composition of the Pt(111)–PdxML and PtPdxat%(111) electrodes was established previously ex-situ by low energy ion scattering (LEIS) measurements. The nature of adsorbed intermediates (COad) and the electrocatalytic properties (the onset of CO2 formation) at the Pt(111)–PdxML and the PtPdxat%(111) interface were studied by FTIR spectroscopy. The results show that Pd atoms either on the surface or in the surface have an unique catalytic activity for HCOOH oxidation, with Pd atoms being three (bulk alloys) or five times (Pd films) more active than Pt atoms at 0.4 V. FTIR spectra reveal that on Pt atoms adsorbed CO is produced from dehydration of HCOOH, whereas no CO adsorbed on Pd can be detected although a high production rate of CO2 is observed at low potentials, indicating that the reaction can proceed on Pd at low potentials without the Pt typical “poison” formation.

A new and sophisticated electrochemical scanning tunneling microscope design for the investigation of potentiodynamic processes

Abstract: One of the main topics in electrochemistry is the investigation of the potential controlled solid/liquid interface. As a local probe technique electrochemical scanning tunneling microscopy becomes more and more important for the analysis of atomic structures and local structuring effects. The described microscope is optimized for potentiodynamic imaging, i.e., the sample potential can be varied in a wide range during the scan of an image. In combination with cyclic voltammetry potential induced phase transitions on the surface can be imaged and directly correlated to distinctive profiles in the simultaneously recorded voltammogram. The new design grew out of the parallel development of the tunneling unit and the electrochemical periphery. This guarantees the best adaptation of tunneling microscopy to electrochemistry and vice versa. Low drift, high resolution, flexibility, reliability, and ease of handling are the characteristics of the new instrument.

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Surface-enhanced spectroscopy

Abstract: In 1978 it was discovered, largely through the work of Fleischmann, Van Duyne, Creighton, and their coworkers that molecules adsorbed on specially prepared silver surfaces produce a Raman spectrum that is at times a millionfold more intense than expected. This effect was dubbed surface-enhanced Raman scattering (SERS). Since then the effect has been demonstrated with many molecules and with a number of metals, including Cu, Ag, Au, Li, Na, K, In, Pt, and Rh. In addition, related phenomena such as surface-enhanced second-harmonic generation, four-wave mixing, absorption, and fluorescence have been observed. Although not all fine points of the enhancement mechanism have been clarified, the majority view is that the largest contributor to the intensity amplification results from the electric field enhancement that occurs in the vicinity of small, interacting metal particles that are illuminated with light resonant or near resonant with the localized surface-plasmon frequency of the metal structure. Small in this context is gauged in relation to the wavelength of light. The special preparations required to produce the effect, which include among other techniques electrochemical oxidation-reduction cycling, deposition of metal on very cold substrates, and the generation of metal-island films and colloids, is now understood to be necessary as a means of producing surfaces with appropriate electromagnetic resonances that may couple to electromagnetic fields either by generating rough films (as in the case of the former two examples) or by placing small metal particles in close proximity to one another (as in the case of the latter two). For molecules chemisorbed on SERS-active surface there exists a "chemical enhancement" in addition to the electromagnetic effect. Although difficult to measure accurately, the magnitude of this effect rarely exceeds a factor of 10 and is best thought to arise from the modification of the Raman polarizability tensor of the adsorbate resulting from the formation of a complex between the adsorbate and the metal. Rather than an enhancement mechanism, the chemical effect is more logically to be regarded as a change in the nature and identity of the adsorbate.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

Abstract: Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.