Robert Caldwell

Excitons and high-order optical transitions in individual carbon nanotubes: A Rayleigh scattering spectroscopy study

We examine the excitonic nature of high-lying optical transitions in single-walled carbon nanotubes by means of Rayleigh scattering spectroscopy. A careful analysis of the principal transitions of individual semiconducting and metallic nanotubes reveals that in both cases the line shape is consistent with an excitonic model, but not one of free carriers. For semiconducting species, sidebands are observed at

Hybrid carbon nanotube-silicon complementary metal oxide semiconductor circuits

\ensuremath{\sim}200\text{ }\text{meV}

Growth of Nanotubes and Chemical Sensor Applications

above the third and fourth optical transitions. These features are ascribed to exciton-phonon bound states. Such sidebands are not apparent for metallic nanotubes, as expected from the reduced strength of excitonic interactions in these systems.

Controlled Manipulation of Carbon Nanotubes for Nanodevices, Arrays, and Films

A hybrid technology is presented that combines carbon nanotube field-effect transistors (CNFET) with conventional, silicon-based complementary metal oxide semiconductor (CMOS) technology. The fabrication involves the chemical vapor deposition growth and optical characterization of carbon nanotubes, which are then transferred with lithographic precision onto a commercially fabricated CMOS substrate. In this manner, CNFET devices are fabricated on top of the interconnection network of the CMOS chip, providing a three-dimensional integration of active devices, “sandwiching” wiring, and passives. As a demonstration of this approach, a simple hybrid CNFET/CMOS inverter is fabricated and tested.

Covalently Bridging Gaps in Single-Walled Carbon Nanotubes with Conducting Molecules

We have used a number of methods to grow long aligned single-walled carbon nanotubes. Geometries include individual long tubes, dense parallel arrays, and long freely suspended nanotubes. We have fabricated a variety of devices for applications such as multiprobe resistance measurement and high-current field effect transistors. In addition, we have measured conductance of single-walled semiconducting carbon nanotubes in field-effect transistor geometry and investigated the device response to water and alcoholic vapors. We observe significant changes in FET drain current when the device is exposed to various kinds of different solvent. These responses are reversible and reproducible over many cycles of vapor exposure. Our experiments demonstrate that carbon nanotube FETs are sensitive to a wide range of solvent vapors at concentrations in the ppm range.

Mott Insulating State in Ultraclean Carbon Nanotubes

Carbon nanotubes hold great promise for a number of applications due to their outstanding electrical, thermal, and mechanical properties. However, nanomanufacturing issues constitute a major area of challenge for successful implementation of nanotubes. In particular, because subtle changes in physical structure (chirality) can cause the electronic structure to vary from metallic to semiconducting, the goal of fully controlled nanotube device fabrication has proven elusive. In addition, materials compatibility issues impose significant limitations toward integration of nanotubes with many substrates and systems. We have developed techniques for nanotube device manufacture that rely upon mechanical transfer of chemical vapor deposition (CVD)-grown nanotubes from one substrate to another. These techniques can be used on the level of individual nanotubes, for controlled fabrication of arrays, or for manufacture of thin films.Copyright