Biomedical subjects

Daniel C Ralph

Publications and source records attributed to Daniel C Ralph.

4 recordsLinked to original sources

PubMed2006

Electrochemical properties of self-assembled monolayers of polyaniline: effects of the thiol substituent and reduced dimensionality.

Self-assembled monolayers and bulk films of thioanilines, polymerized on gold and platinum surfaces, have been characterized and compared to bulk polyaniline (PANI) films. In a previous study [Kuwabata; et al. Langmuir 1999, 15, 6807-6812], only one redox couple was observed in the cyclic voltammetric profile of a polymerized monolayer of thioaniline on gold, in contrast to the known profiles of bulk PANI, which exhibit two couples. We observe two couples in both a polymerized thioaniline monolayer and a bulk polythioaniline (S-PANI) film, but the 200 mV window between the couples (the width of the region of high conductivity) in the S-PANI films is much smaller than the 600 mV window in bulk PANI. We ascribe this difference to the presence of the thiol substituent. The windows of high conductivity of the polymerized thioaniline monolayer and the bulk S-PANI film are the same within the limits of our experiment, implying that the difference in the dimensionality of the films (a 2D monolayer vs 3D bulk films) has a limited effect on the films' voltammetric profiles.

Journal Article↗

PubMed2005

Mechanically adjustable and electrically gated single-molecule transistors.

We demonstrate a device geometry for single-molecule electronics experiments that combines both the ability to adjust the spacing between the electrodes mechanically and the ability to shift the energy levels in the molecule using a gate electrode. With the independent in-situ variations of molecular properties provided by these two experimental "knobs", we are able to achieve a much more detailed characterization of electron transport through the molecule than is possible with either technique separately. We illustrate the performance of the device using C(60) molecules.

Elasticity↗

PubMed2004

The Kondo effect in the presence of ferromagnetism.

We measured Kondo-assisted tunneling via C60 molecules in contact with ferromagnetic nickel electrodes. Kondo correlations persisted despite the presence of ferromagnetism, but the Kondo peak in the differential conductance was split by an amount that decreased (even to zero) as the moments in the two electrodes were turned from parallel to antiparallel alignment. The splitting is too large to be explained by a local magnetic field. However, the voltage, temperature, and magnetic field dependence of the signals agree with predictions for an exchange splitting of the Kondo resonance. The Kondo effect leads to negative values of magnetoresistance, with magnitudes much larger than the Julliere estimate.

Journal Article↗

PubMed2002

Coulomb blockade and the Kondo effect in single-atom transistors.

Using molecules as electronic components is a powerful new direction in the science and technology of nanometre-scale systems. Experiments to date have examined a multitude of molecules conducting in parallel, or, in some cases, transport through single molecules. The latter includes molecules probed in a two-terminal geometry using mechanically controlled break junctions or scanning probes as well as three-terminal single-molecule transistors made from carbon nanotubes, C(60) molecules, and conjugated molecules diluted in a less-conducting molecular layer. The ultimate limit would be a device where electrons hop on to, and off from, a single atom between two contacts. Here we describe transistors incorporating a transition-metal complex designed so that electron transport occurs through well-defined charge states of a single atom. We examine two related molecules containing a Co ion bonded to polypyridyl ligands, attached to insulating tethers of different lengths. Changing the length of the insulating tether alters the coupling of the ion to the electrodes, enabling the fabrication of devices that exhibit either single-electron phenomena, such as Coulomb blockade, or the Kondo effect.

Journal Article↗