MATSE 81
Materials in Today's World

Energy Bands

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Now that you have finished the reading for this lesson, I would like to review the four possible electron band structures for solid materials, as well as p-n junction electrical behavior. In addition, we will define nanotechnology and explore one possible application of nanotechnology which might allow for the continuing improvement in microprocessor speed in coming decades.

So, what happens when you try to shove > 1023 atoms together to make a solid? When atoms are separated, electrons will tend to occupy the lowest available discrete energy states. When atoms are brought together, the electrons are forbidden by the Pauli exclusion principle of having identical energy and quantum numbers. As shown in the figure below, as the atoms are brought closer and closer together individual allowed energy states start to spread in energy.

1s Electron energy band and 2s Electron energy band (12 states), start to spread in energy as they are brough closer together.
As atoms are brought closer and closer together, individual allowed energy states start to spread in energy.
Credit: Fig. 12.2, Callister & Rethwisch 5e

When you bring ~1023 atoms together to make a solid, the separation between the allowed energy states becomes indistinguishable (too small for us to measure). We refer to them as bands as shown in the figure below.

Separation of energy states, depicts energy bands and gaps
Energy bands.
Credit: Fig. 12.3, Callister & Rethwisch 5e