User:Michaela Harper/Notebook/Biological Chemistry Lab/2011/10/11

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Objective

To make a 4 point probe in order to test the conductivity of the fibers we've made.

Description

  • Make four square or rectangular pieces of palladium foil from a sheet by cutting strips. Make them as small as is reasonable.
    • Need to know the area of each strip. The middle two pieces should be as close to the same as possible. The outer pieces are references.
  • Cut a small piece of teflon for the strips and wire to go on.
  • Put down conductive epoxy for the first lead.
  • Put down the first piece of wire on the epoxy, with about 0.5" of wire off the teflon.
  • Put down the first piece of foil on top of the wire, using epoxy to make them stick together.
  • Repeat for the remaining three leads.
  • Note: The pieces of foil should not be allowed to touch each other, and epoxy used for one lead cannot touch another.

Data

Measurements of palladium foil:

  1. 8.8 x 4.0 mm = 35.2 mm2
  2. 9.8 x 4.2 mm = 41.16 mm2
  3. 9.8 x 4.1 mm = 40.18 mm2
  4. 9.2 x 4.2 mm = 38.46 mm2

Here is a picture of the resulting 4-point probe:

Notes

The key advantage of four-terminal sensing is that the separation of current and voltage electrodes eliminates the impedance contribution of the wiring and contact resistances.



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