Manipulation of Carbon Nanotubes

In an Electron Microscope


Fig.1: Adhesion of a Carbon Nanotube at the end of the tip

Fig.2: Positioning the CNT on electrodes and pressing the CNT by the counter CNT bundle

Fig.3: Fabricated carbon-nanotube transistor

Fig.4: Attachment of a CNT at the AFM tip

Fig.5: Intentional bending of the CNT by squeezing with two Nanomanipulators

Fig.6: The I-V curve measured from Fig. 3b

Two Nanomanipulators were installed inside of an field-emission scanning electron microscope (FE-SEM, JEOL JSM-6700F) for moving, bending, cutting, and biasing of nanostructured materials. In situ characterizations of electron beam-induced junctions between the tip and carbon nanotubes were carried out and a carbon-nanotube transistor on pre-patterned metal electrodes was produced.
The Nanomanipulators allow positioning on several millimeters, transporting and the assembly of nanomaterials into a desired device, which generally requires a tremendous effort because of the small dimension. For the manipulation etched tungsten tips were used. The FE-SEM can monitor the movement of the two Nanomanipulators, including in situ characterization.

The diameter of the produced Carbon Nanotubes (CNT) ranges from 30 to 50 nm and the tube is metal-particle free. A fragment of soot was brought into a specimen chamber. Fragments usually revealed nanotubes sticking out in all directions, as shown in Fig. 1.

Adhering by hydrocarbon deposit:
It is possible to fix a single carbon nanotube strand at the tip of one manipulator in the following way:
The Nanomanipulator was moved until the tungsten tip touches a CNT. The electron beam was focused on this contact area and intensively irradiated for around 10 minutes in order to solidify the adhesion. The adhesion is achieved by depositing an extra material in the contact, where the inset demonstrates one end of nanotube exposed to the electron beam to be swollen. This electron beam-induced deposit (EBID) is reportedly attributed to the hydrocarbons. A measurable size of the deposit is required for the secure adhesion. It is observed that the hydrocarbon deposit is very simple and convenient means for welding nanostructured materials. A strong adhesion between the nanotube and the tip was established through this method. It is physically strong enough to endure the tensile stress necessary to break apart the CNT wall.

After attaching the single nanotube to the tip, the manipulator was moved away from the fragment of nanotubes to pull this single tube out of its bundle.

A carbon-nanotube transistor:
A carbon-nanotube transistor is constructed on patterned electrodes, where four electrodes are aligned in parallel within a mm. In order to place an individual CNT on those electrodes, first a single strand of nanotube was moved onto the electrodes. A new CNT bundle on the tip of the second Nanomanipulator was prepared by similar EBID method to form a second sharp tip. This allows to press a single strand of nanotube placed already on the electrode without damage, as shown in Fig. 2. The other manipulator was then pulled out carefully, which left a single strand of the nanotube successfully on the metal electrodes, as shown in Fig. 3. It turned out that this approach with two maneuverable manipulators can save labor time and reduce the trial and error during the manipulation and could be applied for any type of interconnections between nanostructured materials and macroworld characterization systems and even in cautious MEMS fabrications.

Assembly at an AFM tip:
A CNT was attached at an AFM tip, as shown in Fig. 4. An electrostatic force exerted between the nanotube and AFM tip attracted the nanotube towards the AFM tip and the nanotube abruptly stuck to the tip. When the nanotube was misaligned to the tip axis, it was carefully dragged to align along the tip axis by the counter manipulator. After locally spot-welding with the EBID a single nanotube was well adhered at the AFM tip, see Figure 4.

Current measurements:
The conductivity trough a CNT and its junctions is measured by connecting two manipulators through a single strand of the CNT, as shown in Fig. 5. The I-V curve is demonstrated in Fig. 6 and the characteristics of the I-V curve is under study.

Contact to the authors:
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This described application was developed at the Center for Nanotubes and Nanostructured Composites at Sungkyunkwan University in Korea
Products in this application:
  • The paper about this CNT manipulation is available on request
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