Sample Preparation
In order to use the van der Pauw method, the sample thickness must be much less than the width and length of the sample. In order to reduce errors in the calculations, it is preferable that the sample is symmetrical. There must also be no isolated holes within the sample.
The measurements require that four ohmic contacts be placed on the sample. Certain conditions for their placement need to be met:
- They must be on the boundary of the sample (or as close to it as possible).
- They must be infinitely small. Practically, they must be as small as possible; any errors given by their non-zero size will be of the order D/L, where D is the average diameter of the contact and L is the distance between the contacts.
In addition to this, any leads from the contacts should be constructed from the same batch of wire to minimise thermoelectric effects. For the same reason, all four contacts should be of the same material.
Read more about this topic: Van Der Pauw Method
Famous quotes containing the words sample and/or preparation:
“All that a city will ever allow you is an angle on it—an oblique, indirect sample of what it contains, or what passes through it; a point of view.”
—Peter Conrad (b. 1948)
“Living each day as a preparation for the next is an exciting way to live. Looking forward to something is much more fun than looking back at something—and much more constructive. If we can prepare ourselves so that we never have to think, “Oh, if I had only known, if I had only been ready,” our lives can really be the great adventure we so passionately want them to be.”
—Hortense Odlum (1892–?)