We investigate electronic transport through two types of conjugated molecules. Mechanically controlled break junctions are used to couple thiol end groups of single molecules to two gold electrodes. Current-voltage characteristics ( IVs) of the metal-molecule-metal system are observed. These IVs reproduce the spatial symmetry of the molecules with respect to the direction of current flow. We hereby unambiguously detect an intrinsic property of the molecule and are able to distinguish the influence of both the molecule and the contact to the metal electrodes on the transport properties of the compound system.

We have designed and synthesized a molecular rod that consists of two weakly coupled electronic -systems with mutually shifted energy levels. The asymmetry thus implied manifests itself in a current-voltage characteristic with pronounced dependence on the sign of the bias voltage, which makes the molecule a prototype for a molecular diode. The individual molecules were immobilized by sulfur-gold bonds between both electrodes of a mechanically controlled break junction, and their electronic transport properties have been investigated. The results indeed show diode-like current-voltage characteristics. In contrast to that, control experiments with symmetric molecular rods consisting of two identical -systems did not show significant asymmetries in the transport properties. To investigate the underlying transport mechanism, phenomenological arguments are combined with calculations based on density functional theory. The theoretical analysis suggests that the bias dependence of the polarizability of the molecule feeds back into the current leading to an asymmetric shape of the current-voltage characteristics, similar to the phenomena in a semiconductor diode. molecular electronics ͉ rectification ͉ single-molecule studies

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The noise within the electrical current through single-molecule junctions is studied cryogenic temperature. The organic sample molecules were contacted with the mechanically controlled break-junction technique. The noise spectra refer to a where only few Lorentzian fluctuators occur in the conductance. The frequency dependence shows qualitative variations from sample to sample.

To improve the performance of the central element of the Karlsruhe Micronose—a gas‐sensor microarray—the gas sensitive layer is modified toward a highly porous nanogranular layer. To synthesize those layers, the Karlsruhe Microwave Plasma Process which is in its native form a precursor‐based process to produce nanoparticles with diameters below 10 nm, was modified for in situ tin‐dioxide layer deposition. The produced layers have due to their structure a very large active surface area. The process parameters were optimized to generate thin layers with high surface homogeneity. This was mostly established by significantly reducing the precursor feed and therefore reducing the primary particle size to below 2 nm. The layers were analyzed for their mechanical stability, structural, and chemical properties. It is shown that the precursor residue can be completely removed by applying a default annealing step. The structure of the layers reminds of little clubs starting on top of the substrate growing wider toward the surface. Prototype sensors were fabricated and tested for their gas sensory properties in comparison to a standard gas‐sensor microarray with a sputtered tin‐dioxide layer. The gas‐sensor microarrays with nanogranular layer show an increased signal response of up to one order of magnitude to isopropanol. The time of response is equal in both sensor systems while the time of recovery is nearly doubled for the sensors with nanogranular layer due to increased surface area and gas absorption.