The Technology - Intermediate

When you heat a material, the material's electrons move around a bit. By heating, you give the material additional energy and, in certain materials like semiconductors, this could have a profound effect on the electron's "mobility". Often times we approximate the motion of electrons as a free gas in visualizing what happens in a semiconductor. As the electrons get bumped into the "conduction band" in a semiconductor, they are able to move relatively freely (like a gas) through the materials. Furthermore, they tend to drift from hot to cold, as you would expect from a free gas. As the electrons move from their initial location, they leave behind a "hole". Holes also "transport" from hot to cold and, though a bit more difficult to visualize, the same free gas treatment and mobility concepts hold for hole transport as well. A TE device is arranged in such a way to force holes to move one direction while electrons move another way, both driven by a temperature gradient. When this occurs, there is a charge separation, which can really be translated into useful electrical current produced from the applied temperature gradient. The cool thing is that this process is reversible. That is to say, if you apply a current, you can generate a temperature gradient! So, you can use TE as a heater or refrigerator simply by passing current through, thus avoiding the compressors and working fluids associated with traditional refrigeration systems. The markets and promise of this technology are enormous, but traditional materials are less than ideal for realistic applications because their efficiencies are so low.

At Evident Technologies, we make nano-sized semiconductors that have many advantages over traditional materials. Hence, we can get to the Promised Land (Mountain Top?) for TE applications by increasing the efficiency. We do this with the help of some quantum mechanical effects that allow for decoupling the heretofore intrinsic material properties. Things like thermal and electrical conductivity are inherently coupled and, in naturally offering (occurring?) semiconductors, they are fixed - God (nature?) -given. Using nano-sized semiconductors as the building blocks for TE elements can grant you additional freedom to tune the thermal, electrical, and inherent temperature-dependent mobility to an extent. If you use care, these new freedoms can make for a novel nanocomposite that has never-before-seen TE properties. As a crude example, imagine a nanocomposite where semiconductor nanocrystals are self-assembled on top of each other. The material may look like oranges stacked in the grocery store if you could see things on a nanoscale. If you do it correctly, you can design it such that electrons flow relatively freely through the composite while heat phonons have a torturous time transporting through the material. The electrical conductivity can be relatively high while the thermal conductivity is low, making for an ideal TE material. And there you have it!