Electrical characterization of single-walled carbon nanotubes with Scanning Force Microscopy

Characterization of contact resistances in ceramic-coated vertically aligned carbon nanotube arrays

Despite the technological significance of carbon nanotube (CNT) arrays and metal-oxide coated CNTs for electronic and electrochemical devices such as supercapacitors, lithium-ion batteries, and solar-chemical cells, sub-optimal device performance often results due to large contact resistance between the CNTs and the metallic current collectors or between the CNTs and their ceramic coatings. While contact resistance measurements are regularly carried out on individually contacted CNTs, contact resistance measurements on vertically aligned (VA) CNT arrays are not routine. Here, we demonstrate that two-probe electrical current-voltage measurements and electrochemical impedance spectroscopy can be used to probe the end contact resistance and side contact resistances of coated and uncoated VACNT arrays in order to optimize material deposition and selection.

ELECTRON BEAM INDUCED CARBONACEOUS DEPOSITION AS A LOCAL DIELECTRIC FOR CNT CIRCUITS

Evaluating the electrical nature of carbon nanotubes (CNTs) from a collection requires establishing electrical contacts across individual CNTs lying on a dielectric layer. In this work, it is shown how a dielectric layer may be inserted underneath a chosen CNT. This has been accomplished by the electron beam induced carbonaceous deposition process in the presence of moisture and residual hydrocarbons present in the SEM chamber. When performed at a CNT location on a Si substrate, the CNT instead of getting buried underneath is found to be lifted on top of the carbonaceous platform, as if due to nonwetting nature of CNT surface. By fixing one end of the CNT on the Ag/Si substrate using a Pt deposit and lifting rest of the length to lie on a carbonaceous platform, the I–V data from nanotubes of varying resistances have been collected using conducting AFM. The chosen nanotubes have also been examined by Raman measurements. The method is particularly useful while working with a random collection of nanotubes resulting from a chemical process.

Self-assembled CNT circuits with ohmic contacts using Pd hexadecanethiolate as in situ solder

An easy and elegant method of CNT nanocircuit fabrication using a metal organic precursor of Pd, namely, Pd hexadecanethiolate, is presented. This precursor directs the self-assembly of individual CNTs spanning a gap between Au electrodes. This is achieved by first patterning the precursor along the edges of the gap electrodes, as it enables direct patterning by e beam. Further, thermal activation of the precursor at 250 degrees C leads to metallization and the ohmic electrical contact between the CNTs and the electrodes beneath. A resistive fuse action of the soldered CNTs is observed as well.

Molecular bioelectronics

Biological macromolecules have evolved over many millions of years into structures primed, in some cases, for both specific surface recognition and facile, directional electron tunnelling. The redox-active centres of metalloproteins play a central role in photosynthesis and respiration. The processes by which constructive man-made interfaces to these moieties can be generated have advanced greatly during the past two decades or so. Together with recent advances in molecular manipulation, analyses and lithographic fabrication, this knowledge has led to us to the point where bioelectronic devices can be designed and interrogated with good levels of reproducibility.