Jacques Lefebvre

Fabrication of nanometer size gaps in a metallic wire

We present a simple shadow mask method to fabricate electrodes with nanometer scale separation. Metal wires with gaps are made by incorporating multiwall carbon nanotubes or single-wall carbon nanotube (SWNT) bundles into a trilayer electron beam lithography process. The simple, highly controllable, and scaleable method has been used to make gaps with widths between 20 and 100 nm and may be extended to gap sizes of 1 nm. We report electron transport measurements of individual SWNTs bridging nanogaps with electrode spacings of approximately 20 nm. Metallic SWNTs exhibit quantum dot behavior with an 80 meV charging energy and a 20 meV energy level splitting. We observe a strong field effect behavior in short semiconducting SWNT segments, evidence for diffusive electron transport in these samples.

Single-wall carbon nanotube circuits assembled with an atomic force microscope

We have developed a method to assemble single-wall carbon nanotube (SWNT) circuits using a tapping mode atomic force microscope. Nanotubes can be controllably translated, rotated, cut, and placed on top of one another by varying the tip–sample force, and the tip speed. These operations let us construct complex nanotube circuits, which are contacted using electron beam lithography. We present data from a circuit of two crossed SWNT bundles. The lower bundle behaves as two quantum dots in series, separated by a tunnel barrier created at the junction. Gate voltages can tune the number of charges on each dot and the tunnel barrier transmission.

Single-wall carbon nanotube based devices

Abstract We have developed a variety of fabrication techniques for single-wall nanotube (SWNT) circuits. Our methods range from variants of electron beam lithography to AFM nanomanipulations. In this talk, we present our most recent data on three different types of SWNT based devices: the SWNT with a local impurity, the tube–tube junction and the SWNT contacted with electrodes whose separation is less than 30 nm. Each has a specific behavior ranging from a rectifying diode to a double quantum dot in series to an ultra short quantum wire. The functionality of each device can be ascribed to specific molecular adsorbates or controlled mechanical deformation.

Single carbon nanotube electronic devices

We review recent progress towards the fabrication of engineered single nanotube circuits. Single wall carbon nanotubes are manipulated into circuits on a silicon dioxide surface using an AFM. Nanotubes can also be incorporated into an electron beam lithography resist system and used as “shadow masks” to create electrode pairs with sub-20 nm separation. Measurements of very short channel nanotube FETs indicate that the molecules may be highly doped due to exposure to the atmosphere, a fact not taken into account in earlier models of nanotube FETs.

Temperature dependent resistivity of large ropes of single walled carbon nanotubes

The electrical resistance of ropes of single walled carbon nanotubes is presented as a function of temperature, magnetic field and electrostatic doping. The entire set of data obtained on many samples can be understood on the basis of data already published for individual nanotubes. The main conclusion is that a rope is well described on the basis of two independent parallel channels, one of semiconducting and one of metallic nanotubes.