Electronic fluctuations in nanotube circuits and their sensitivity to gases and liquids

The temperature-dependent noise of individual, single-walled carbon nanotubes is measured here in a variety of different gases and liquids. The ambient environment is found to have only a weak relationship with device noise, even in cases where adsorption significantly changes the dc resistance. Correspondingly, a 450 K degassing procedure typically reduces the device noise by only 1 order of magnitude. An important exception to this finding is a pronounced, 100-fold increase in noise observed near gas -liquid phase transitions of the ambient. Wide-range temperature scans clearly identify the condensation of N 2 ,H 2, and CH4 onto metallic nanotubes, but not the sublimation of CO2. The observations suggest that nanotube devices can directly transduce ambient density fluctuations, though without an inherent gas specificity. Even so, the method is a particularly sensitive characterization of nanotube chemical interactions, one which is successful even for the extreme case of inert gases adsorbed on metallic nanotubes. Field-effect transistors, chemical sensors, and field emission sources and displays 1 are three carbon nanotube (CNT) research areas seeing preliminary commercialization efforts. In all three applications, and particularly in the first two, high levels of electronic noise threaten commercial viability. The noise levels of CNT devices are substantially higher than those in macroscopic films or materials of comparable resistance, 2 so controlling noise may be critical to the success of these applications. Despite this potential hurdle, noise sources in CNTs have remained relatively poorly characterized, particularly in comparison to the low temperature, quantum properties of these circuits. While the exact mechanisms have not yet been identified, the observed noise magnitude of CNTs 2-6 is compatible with the empirical Hooge observation 7 that 1/f noise scales inversely to the number of carriers in a system. Large amplitude noise is common in nanoscale circuits, 8,9 and a typical single-walled nanotube (SWNT) conductor 100 nm long incorporates less than 10 000 atoms and even fewer free carriers. The Hooge law predicts a 1/f noise singularity in very small circuits which is of interest from both fundamental and applied points of view, and SWNT circuits represent an ideal model system to further examine this issue. 9