Scanning Probe Microscopy of Carbon Nanotube Electronic Devices

Electron transport and dissipation mechanisms in single-walled carbon nanotube electronic devices are intriguing. In the past, electrostatic force microscopy and scanning thermal microscopy methods have been employed to obtain respectively the voltage and temperature profiles in carbon nanotube electronic devices. The measurement results have suggested weak electron-acoustic phonon scattering at low bias and intense optical phonon emission at high bias. However, because the thermal probe was in direct contact with the nanotubes during thermal imaging, the probe could disturb charge transport. Further, it was difficult to quantify the thermal contact between the probe and the nanotube, making it difficult to quantify the actual temperature rise in the device. We have recently overcome these problems by coating the nanotube device with a 5–10 nm thick polystyrene film. The ultra-thin uniform coating can effectively protect the nanotube device during thermal imaging without reducing the signal level. It can potentially allow us to quantify the temperature rise of the nanotube devices by calibrating the thermal probe using a nanometer scale resistance thermometer covered by the same coating. Our recent results reveal diffusive and dissipative charge transport in a possibly double wall carbon nanotube with a semiconducting outer wall. We have also observed uniform heat dissipation in a metallic single-walled carbon nanotube at an applied bias above 0.2 V. Measurements on metallic and semiconducting single wall carbon nanotubes of different lengths are currently underway in order to improve our understanding of the transport and dissipation mechanisms in carbon nanotube electronics at low biases.