Observation of transient photocurrents on suspended nanotubes

Transient photocurrents are measured on a suspension of single walled carbon nanotubes in an applied electric field. A rapid electronic response time of 150 ps is achieved in these measurements. Attaining such a rapid response has required the development of an advanced technique to reduce impedance mismatch between the measuring equipment and sample. This technique, which incorporates the sample into a global 50 Omega architecture, is described here. The technique allows the problem of contacting nanotubes to be avoided in the study of basic electronic transport properties. Some early results on transient photocurrents induced by a 25 ps mode locked laser pulse are shown along with the electric field dependence of the peak photocurrent and integrated photocharge. Problems associated with the long term evolution in the conductivity of suspended samples are also addressed. (C) 2004 American Institute of Physics.