Thermoacoustic Transduction in Individual Suspended Carbon Nanotubes

We report an experimental measurement of the acoustic signal emitted from an individual suspended carbon nanotube (CNT) approximate 2 μm in length, 1 nm in diameter, and 10^–21 kg in mass. This system represents the smallest thermoacoustic system studied to date. By applying an AC voltage of 1.4 V at 8 kHz to the suspended CNT, we are able to detect the acoustic signal using a commercial microphone. The acoustic power detected is found to span a range from 0.1 to 2.4 attoWatts or 0.2 to 1 μPa of sound pressure. This corresponds to thermoacoustic efficiencies ranging from 0.007 to 0.6 Pa/W for the seven devices that were measured in this study. Here, the small lateral dimensions of these devices cause large heat losses due to thermal conduction, which result in the relatively small observed thermoacoustic efficiencies

Electrical and Optical Characterization of Surface Passivation in GaAs Nanowires

We report a systematic study of carrier dynamics in Al_<i>x</i>Ga_1–<i>x</i>As-passivated GaAs nanowires. With passivation, the minority carrier diffusion length (<i>L</i>_diff) increases from 30 to 180 nm, as measured by electron beam induced current (EBIC) mapping, and the photoluminescence (PL) lifetime increases from sub-60 ps to 1.3 ns. A 48-fold enhancement in the continuous-wave PL intensity is observed on the same individual nanowire with and without the Al_<i>x</i>Ga_1–<i>x</i>As passivation layer, indicating a significant reduction in surface recombination. These results indicate that, in passivated nanowires, the minority carrier lifetime is not limited by twin stacking faults. From the PL lifetime and minority carrier diffusion length, we estimate the surface recombination velocity (SRV) to range from 1.7 × 10³ to 1.1 × 10⁴ cm·s^–1, and the minority carrier mobility μ is estimated to lie in the range from 10.3 to 67.5 cm² V^–1 s^–1 for the passivated nanowires