Strategy for accurately measuring the conductivity of a very thin film along the vertical direction

What is it about?

When people make extremely thin materials, usually their properties are different depending on the direction we look at. This is called anisotropy. For example, electrical conductivity along the surface can be higher than that in the perpendicular flow. When the thickness is rather thin, for instance, thinner than human hair, then measuring resistance along that perpendicular direction by, say a conventional voltmeter becomes difficult because the reading becomes out-of-range. Another undesired effect which can be made irrelevant along the surface turns out to be of high impact now - contact resistance. This is because in this vertical configuration the contact resistance is connected in parallel to the resistance we are measuring. To overcome these limitations, we propose to use another well-known technique called impedance measurement, and suggest a model to fit the result so that we can extract the vertical conductivity. This fitting model takes into account the contact resistance rendering the measurement more accurate. Impedance itself is nothing but so called 'complex' resistance which accounts for reactive elements in a system including capacitance and/or inductance. In our case, it turns out that inductance is playing a huge role because the material is in air. This is in contrast to the situation where the material is in a liquid electrolyte, in a battery, in which case the capacitance would have been important.

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Photo by Clint Patterson on Unsplash

Photo by Clint Patterson on Unsplash

Why is it important?

Conductivity of a material is important because in many devices high conductivity is required. As the new-generation devices shrink each year in size, we are approaching a situation where artificially made thin materials may replace the conventional technique of metal deposition atom by atom. While this is just a suggestion by scientists in the academy, many companies are already looking at this option. One obstacle on this way of advancement is the anisotropy of such man-made materials. To deal with it, first we have to measure it reliably. Then, we need to understand what does it depend on, and how it can be controlled. Such a fundamental study will be crucial for putting us in the right direction for controlling the anisotropy better, allowing for thinner devices made easier in the future.

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