Biomedical subjects

Dawn A Bonnell

Publications and source records attributed to Dawn A Bonnell.

4 recordsLinked to original sources

PubMed2006

Clean electromigrated nanogaps imaged by transmission electron microscopy.

Electromigrated nanogaps have shown great promise for use in molecular scale electronics. We have fabricated nanogaps on free-standing transparent SiN(x) membranes which permit the use of transmission electron microscopy (TEM) to image the gaps. The electrodes are formed by extending a recently developed controlled electromigration procedure and yield a nanogap with approximately 5 nm separation clear of any apparent debris. The gaps are stable, on the order of hours as measured by TEM, but over time (months) relax to about 20 nm separation determined by the surface energy of the Au electrodes. A major benefit of electromigrated nanogaps on SiN(x) membranes is that the junction pinches in away from residual metal left from the Au deposition which could act as a parasitic conductance path. This work has implications to the design of clean metallic electrodes for use in nanoscale devices where the precise geometry of the electrode is important.

Journal Article↗

PubMed2005

Low-temperature resistance anomaly at SrTiO3 grain boundaries: evidence for an interface-induced phase transition.

Variable temperature transport between 1.4 and 300 K, structural imaging, and theoretical calculations were used to characterize the properties of electrically active 24 degrees and 36.8 degrees [001] tilt SrTiO3 grain boundaries with 0.1 at. % niobium doping. An anomaly in boundary resistance and capacitance characteristics typical of a positive temperature coefficient effect is observed. This behavior is indicative of interface-induced dipole ordering. The detailed atomic structures of these grain boundaries were determined from a comparison of ab initio calculations and Z-contrast TEM images. The number of excess electrons at the boundaries determined experimentally and theoretically agrees and is associated with the boundary structural units.

Journal Article↗

PubMed2005

High frequency scanning gate microscopy and local memory effect of carbon nanotube transistors.

We use impedance spectroscopy to measure the high-frequency properties of single-walled carbon nanotube field effect transistors (swCN-FETs). Furthermore, we extend scanning gate microscopy (SGM) to frequencies up to 15 MHz and use it to image changes in the impedance of swCN-FET circuits induced by the SGM tip gate. In contrast to earlier reports, the results of both experiments are consistent with a simple RC parallel circuit model of the swCN-FET, with a time constant of 0.3 micros. We also use the SGM tip to show the local nature of the memory effect normally observed in swCN-FETs, implying that nanotube-based memory cells can be miniaturized to dimensions of the order of tens of nm.

Electric Impedance↗

PubMed2002

Role of single defects in electronic transport through carbon nanotube field-effect transistors.

The influence of defects on electron transport in single-wall carbon nanotube field-effect transistors (CNFETs) is probed by combined scanning gate microscopy (SGM) and scanning impedance microscopy (SIM). SGM images are used to quantify the depletion surface potential, and from this the Fermi level, at individual defects along the CNFET length. SIM is used to measure the voltage distribution along the CNFET. When the CNFET is in the conducting state, SIM reveals a uniform potential drop along its length, consistent with diffusive transport. In contrast, when the CNFET is "off," potential steps develop at the position of depleted defects. High-resolution imaging of a second set of weak defects is achieved in a new "tip-gated" SIM mode.

Journal Article↗