Showing papers by "John Bechhoefer published in 2013"
TL;DR: A new method is introduced to reduce greatly backgrounds of conductance values for both platinum and gold contacts by dividing by a 1-octanethiol (OMT, C(8)H(17)SH) reference histogram, without data selection.
Abstract: The charge transport mechanism between 1,8-octanedithiol (ODT, C(8)H(16)S(2)H(2)) and platinum and gold electrodes is studied by breaking bonds between single ODT molecules and atomic metal junctions using conductive probe atomic force microscopy. Histograms of conductance values show peaks that are obscured by background processes that differ from the metal-molecule-metal conduction path of interest. We introduce a new method to reduce greatly such backgrounds by dividing by a 1-octanethiol (OMT, C(8)H(17)SH) reference histogram, without data selection. The method reveals three series of conductance values for both platinum and gold contacts, which we associate with geometrically different configurations between thiol and metal atoms. The ordering of conductance values, Pt-ODT-Pt > Pt-ODT-Au> Au-ODT-Au, is consistent with a relative dependence on both the number of electron channels and the density of states.
20 citations
TL;DR: In this article, the authors characterize the relevant experimental parameters and compare to theory the observed power spectra and variance for a particle in a virtual harmonic potential, and show that deviations from the dynamics expected of a continuous potential are measured by the ratio of these small time scales to the relaxation time scale of the virtual potential.
Abstract: Feedback traps can create arbitrary virtual potentials for exploring the dynamics of small Brownian particles. In a feedback trap, the particle position is measured periodically and, after each measurement, one applies the force that would be produced by the gradient of the “virtual potential,” at the particle location. Virtual potentials differ from real ones in that the feedback loop introduces dynamical effects not present in ordinary potentials. These dynamical effects are caused by small time scales associated with the feedback, including the delay between the measurement of a particle’s position and the feedback response, the feedback response that is applied for a finite update time, and the finite camera exposure from integrating motion. Here, we characterize the relevant experimental parameters and compare to theory the observed power spectra and variance for a particle in a virtual harmonic potential. We show that deviations from the dynamics expected of a continuous potential are measured by the ratio of these small time scales to the relaxation time scale of the virtual potential.
8 citations