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Home > Nanotechnology Columns > Practical Nano-Tech > Use a Multimeter to Measure the Resistance of Carbon Nanotubes

Judith Petterhof

Abstract:
A very interesting look at the use of carbon nanotubes as resistors, and how their resistance can be measured. It provides a practical guide with the basic requirements for the exercise.

June 14th, 2012

Use a Multimeter to Measure the Resistance of Carbon Nanotubes

On the planet earth, all living organisms are carbon-based. New technologies are being developed that rely on allotropes of carbon, a different form of the element. Carbon nanotubes, which are single- or double-layer sheets of graphite (a form of carbon) rolled up into cylindrical structures, have technological features that scientists have started appreciating only since 1991.

You can measure the electrical resistance between two points on carbon nanotubes. You will only need to make a simple lithography pattern to find the value of the resistors using a multimeter.

The things that you will need for this investigation are:

• 1cm gold wire.
• multimeter.
• Acetone.
• Evaporator.
• Photo mask aligner.
• Hot plate.
• Electrode photo pattern.
• Photoresist S1813.
• Developer.
• Carbon nanotube sample grown on a silicon substrate.

To make the lithography pattern, the surface of the nanotube sample is coated in resist. Do do this, the carbon nanotube sample is placed on the chuck of a spin-coater. A few drops of resist are placed on the sample. If you are using the resist S1813, you will need to rotate the spin-coater at 4,000 revolutions per second. For a 1,000nm thickness of resist, the spin-coater should rotate for 60 seconds or 1 minute.

After the spinning stops, remove the sample from the spin-coater and place it on a hot plate. Since resist type S1813 is being used, the sample has to be baked at 100ēC for three minutes. The optimum baking time and temperature will differ for other types of resist, and this must be determined by consulting the documentation. This bonds the resist onto the surface of the sample.

The sample is then placed into a mask aligner, and a simple two-electrode mask exposed onto the resist. The parts of the resist thus exposed will undergo a chemical reaction. These parts can now be removed using a chemical known as a developer.

Place the sample in the resist developer. Depending on the individual resist, the time the sample is exposed to the developer will vary. To make sure of accurate times, the documentation of the resists and developers must be consulted. The parts of the resist that were exposed to the developer will be removed leaving behind a pattern. Metal now has to be deposited into this pattern to generate the electrodes. For this, the sample has to be placed in the evaporator. Place the 1cm gold wire in the crucible for evaporation - deposit about 100nm of gold.

The sample has now to be placed in acetone, and all the resist on the nanotube sample that was unexposed will be removed. This will leave only the gold pattern on the carbon nanotube. The carbon nanotube between the gold patterns forms a resistor that can be measured with the multimeter.

Switch on the multimeter and set it to the resistance mode. Place one probe of the multimeter on each electrode, and read the resistance displayed. This is the resistance of the carbon nanotube.

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