Jens Ebbecke

Carbon nanotube alignment by surface acoustic waves

We present a realization of carbon nanotube alignment. Surface acoustic waves are applied to a multiwalled carbon nanotube suspension and the lateral piezoelectric field of the standing wave aligns the carbon nanotubes with an angle of 25° to 45° on LiNbO3 with respect to the direction of wave propagation. This angle results from a superposition of the aligning electric field and a perpendicular fluidic flux in the carbon nanotube suspension caused by the energy transfer from the surface acoustic wave into the liquid. On LiTaO3, the multiwalled carbon nanotubes align parallel to the wave vector due to negligible fluidic processes.

Alignment of carbon nanotubes on pre-structured silicon by surface acoustic waves

Carbon nanotubes have been deposited and aligned onto the pre-structured metal contacts of a silicon chip. Crucial for the deposition and alignment process are micro-fluidic flow fields combined with electric dipole fields generated by surface acoustic waves within a gap filled with an aqueous carbon nanotube suspension. This gap is formed when the pre-structured silicon chip is flipped onto the piezoelectric lithium niobate substrate, allowing for the generation of surface acoustic waves. The contacting probability of carbon nanotubes on the prestructured metal contacts has been found to be 37%. In combination with back-gates, these structures define three-terminal devices and the first current–voltage characteristics.

Acoustoelectric current transport through single-walled carbon nanotubes

We have contacted single-walled carbon nanotubes after aligning the tubes by the use of surface acoustic waves. The acoustoelectric current has been measured at 4.2 K and a probing of the low-dimensional electronic states by the surface acoustic wave has been detected. By decreasing the acoustic wavelength resulting in an adjustment to the length of the defined carbon nanotube constriction a quantization of the acoustoelectric current has been observed.

Intra- and intertube tunneling transport in ropes of single-walled carbon nanotubes

The authors report on intra- and intertube tunneling induced current oscillations in an individual rope of single-walled carbon nanotubes. Defects within single tubes and tube-tube contacts provide tunneling barriers of different transparencies and heights, respectively, and the formation of quantum dots in between. As a function of the bias voltage, the authors observe a transition from an intratube to an intertube tunneling dominated transport. The samples were fabricated on prepatterned silicon substrates employing surface acoustic wave induced streaming leading to an alignment of the ropes with respect to the contacts.