Biomedical subjects

Theresa S Mayer

Publications and source records attributed to Theresa S Mayer.

6 recordsLinked to original sources

PubMed2006

Synchronous electrorotation of nanowires in fluid.

We demonstrate electrorotation of metal nanowires phase-locked to a driving alternating current electric field. Field rotation was accomplished by a low-frequency signal that modulates the amplitude of the high-frequency field. Steady, synchronous rotation of the nanowires was observed for frequencies up to a maximum rotational frequency, which depends on the magnitude of the applied electric field. A locally two-dimensional nanowire fluid flow model was developed to calculate the viscous fluid drag torque, including drag contributions due to the proximity of the floor. Synchronicity and phase-lock angle predicted by equating the calculated fluid drag and electrical driving torques is in good agreement with experimentally determined values, which provides support for the model. Synchronous electrorotation allows for precise control of nanowire rotational speed and orientation for frequencies as low as a fraction of 1 Hz. Potential applications include reconfigurable polarization filters, microfluidic valves, and stirring devices.

Computer Simulation↗

PubMed2005

Effect of local environment on molecular conduction: isolated molecule versus self-assembled monolayer.

Developing a fundamental understanding of molecular conduction in different device environments is essential to the advance of molecular electronics. We show through a quantitative comparison of two types of junctions with the same molecule - one based on an isolated individual molecule and the other on a self-assembled monolayer - that intrinsic differences in the conduction per molecule as large as several orders of magnitude can exist simply as a function of the presence or absence of neighboring molecules. This behavior can be understood on the basis of thermal and electrostatic effects that depend critically on the local molecular environment. These results will help to unify data obtained from disparate device structures and to provide an improved basis for designing future molecular electronic devices.

Journal Article↗

PubMed2005

Reversible bistable switching in nanoscale thiol-substituted oligoaniline molecular junctions.

Single molecular monolayers of oligoaniline dimers were integrated into sub-40-nm-diameter metal nanowires to form in-wire molecular junctions. These junctions exhibited reproducible room temperature bistable switching with zero-bias high- to low-current state conductance ratios of up to 50, switching threshold voltages of approximately +/-1.5 V, and no measurable decay in the high-state current over 22 h. Such switching was not observed in similarly fabricated saturated dodecane (C12) or conjugated oligo(phenylene ethynylene) (OPE) molecular junctions. The low- and high-state current versus voltage was independent of temperature (10-300 K), suggesting that the dominant transport mechanism in these junctions is coherent tunneling. Inelastic electron tunneling spectra collected at 10 K show a change in the vibrational modes of the oligoaniline dimers when the junctions are switched from the low- to the high-current state. The results of these measurements suggest that the switching behavior is an inherent molecular feature that can be attributed to the oligoaniline dimer molecules that form the junction.

Aniline Compounds↗

PubMed2005

Use of phosphine as an n-type dopant source for vapor-liquid-solid growth of silicon nanowires.

Phosphine (PH3) was investigated as an n-type dopant source for Au-catalyzed vapor-liquid-solid (VLS) growth of phosphorus-doped silicon nanowires (SiNWs). Transmission electron microscopy characterization revealed that the as-grown SiNWs were predominately single crystal even at high phosphorus concentrations. Four-point resistance and gate-dependent conductance measurements confirmed that electrically active phosphorus was incorporated into the SiNWs during VLS growth. A transition was observed from p-type conduction for nominally undoped SiNWs to n-type conduction upon the introduction of PH3 to the inlet gas. The resistivity of the n-type SiNWs decreased by approximately 3 orders of magnitude as the inlet PH3 to silane (SiH4) gas ratio was increased from 2 x 10(-5) to 2 x 10(-3). These results demonstrate that PH3 can be used to produce n-type SiNWs with properties that are suitable for electronic and optoelectronic device applications.

Journal Article↗

PubMed2004

Thermally activated conduction in molecular junctions.

We report temperature dependence measurements on the conductance of individual molecular wires. The results show for the first time in a molecular junction the theoretically predicted transition from coherent superexchange tunneling conductance to an activated hopping mechanism as temperature is increased.

Journal Article↗

PubMed2002

Template synthesis of metal nanowires containing monolayer molecular junctions.

Metal nanowires containing in-wire monolayer junctions of 16-mercaptohexanoic acid were made by replication of the pores of 70 nm diameter polycarbonate track etch membranes. Au was electrochemically deposited halfway through the 6 microm long pores and a self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid was adsorbed on top. A thin layer of Au was then electrolessly grown to form a metal cap separated from the bottom part of the wire by the SAM. Electron micrographs showed that the bottom and top metal segments were separated by an approximately 2 nm thick organic monolayer. Current-voltage measurements of individual nanowires confirmed that the organic monolayer could be contacted electrically on the top and bottom by the metal nanowire segments without introducing electrical short circuits that penetrate the monolayer. The values of the electrical properties for zero-bias resistance, current density, and breakdown field strength were within the ranges expected for a well-ordered alkanethiol SAM of this thickness.

Journal Article↗