Showing papers by "Gerhard Meyer published in 2012"

Bond-order discrimination by atomic force microscopy.

Abstract: We show that the different bond orders of individual carbon-carbon bonds in polycyclic aromatic hydrocarbons and fullerenes can be distinguished by noncontact atomic force microscopy (AFM) with a carbon monoxide (CO)–functionalized tip. We found two different contrast mechanisms, which were corroborated by density functional theory calculations: The greater electron density in bonds of higher bond order led to a stronger Pauli repulsion, which enhanced the brightness of these bonds in high-resolution AFM images. The apparent bond length in the AFM images decreased with increasing bond order because of tilting of the CO molecule at the tip apex.

Imaging the charge distribution within a single molecule

Abstract: Kelvin probe force microscopy can reveal the distribution of charge within a single naphthalocyanine molecule.

A Combined Atomic Force Microscopy and Computational Approach for the Structural Elucidation of Breitfussin A and B: Highly Modified Halogenated Dipeptides from Thuiaria breitfussi†

Abstract: The use of atomic-force microscopy (AFM) with atomic resolution shows great potential for the structural characterization of planar, proton-poor compounds, as these compounds are prone to structural corrections. [1,2] Currently, AFM has limited ability to identify element type and consequently functional groups. Additional computational techniques, such as computer-aided structure elucidation (CASE) and the calculation of 13 C NMR shifts using electronic structure calculations (DFT) may assist in this respect. Herein we show the combined use of spectroscopic methods, AFM, CASE, and DFT to solve the structures of breitfussins A and B, which could not be solved using either method alone. The subject of this study was the Arctic hydrozoan Thuiaria breitfussi (Family Sertulariidae). The few publications on the chemistry of this family show the presence of sterols, [3] polyhalogenated monoterpenes, [4] and anthracenone derivatives. [5] Arctic marine environments support highly diverse and dense populations of marine invertebrates. [6,7] A

A simple model of molecular imaging with noncontact atomic force microscopy

Abstract: Using functionalized tips, the atomic resolution of a single organic molecule can be achieved by noncontact atomic force microscopy (nc-AFM) operating in the regime of short-ranged repulsive Pauli forces. To theoretically describe the atomic contrast in such AFM images, we propose a simple model in which the Pauli repulsion is assumed to follow a power law as a function of the probed charge density. As the exponent in this power law is found to be largely independent of the sample molecule, our model provides a general method for simulating atomically resolved AFM images of organic molecules. For a single perylene-tetracarboxylic-dianhydride (PTCDA) molecule imaged with a CO-terminated tip, we find excellent agreement with the experimental data. Our model eliminates the need to take into account the full tip and sample system and therefore reduces computational cost by three orders of magnitude.

Force and conductance during contact formation to a C60 molecule

Abstract: Force and conductance were simultaneously measured during the formation of Cu-C60 and C60-C60 contacts using a combined cryogenic scanning tunneling and atomic force microscope. The contact geometry was controlled with submolecular resolution. The maximal attractive forces measured for the two types of junctions were found to differ significantly. We show that the previously reported values of the contact conductance correspond to the junction being under maximal tensile stress.

Force and conductance during contact formation to a C 60 molecule

Abstract: Force and conductance were simultaneously measured during the formation of Cu?C60 and C60?C60 contacts using a combined cryogenic scanning tunneling and atomic force microscope. The contact geometry was controlled with submolecular resolution. The maximal attractive forces measured for the two types of junctions were found to differ significantly. We show that the previously reported values of the contact conductance correspond to the junction being under maximal tensile stress.

Scanning probe microscopy of atoms and molecules on insulating films: from imaging to molecular manipulation.

Abstract: Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) of single atoms and molecules on ultrathin insulating films have led to a wealth of novel observations and insights. Based on the reduced electronic coupling to the metallic substrate, these techniques allow the charge state of individual atoms to be controlled, orbitals of individual molecules to be imaged and metal-molecule complexes to be built up. Near-contact AFM adds the unique capabilities of imaging and probing the chemical structure of single molecules with atomic resolution. With the help of atomic/molecular manipulation techniques, chemical binding processes and molecular switches can be studied in detail.

Atomic and Molecular Manipulation

Abstract: This outstanding textbook provides an introduction to electronic materials and device concepts for the major areas of current and future information technology. On about 1,000 pages, it collects the fundamental concepts and key technologies related to advanced electronic materials and devices. The obvious strength of the book is its encyclopedic character, providing adequate background material instead of just reviewing current trends. It focuses on the underlying principles which are illustrated by contemporary examples. The third edition now holds 47 chapters grouped into eight sections. The first two sections are devoted to principles, materials processing and characterization methods. Following sections hold contributions to relevant materials and various devices, computational concepts, storage systems, data transmission, imaging systems and displays. Each subject area is opened by a tutorial introduction, written by the editor and giving a rich list of references. The following chapters provide a concise yet in-depth description in a given topic. Primarily aimed at graduate students of physics, electrical engineering and information technology as well as material science, this book is equally of interest to professionals looking for a broader overview. Experts might appreciate the book for having quick access to principles as well as a source for getting insight into related fields.