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THE DATA CENTER JOURNAL | 23 www.datacenterjournal.com where no electrons can exist) between atoms. Once they cross the bandgap, they will join other electrons in the conduction band and flow from one atom to another (see Figure 3). Inside a semiconductor, it takes energy to move an electron from the valence band to the conduction band. e bandgap that separates the valence band and the conduction band will deter- mine how a material's electrons behave as electric current. e material selected for the flow of electrons in the conduction band is the key to making electricity. Analysis of Materials Let's examine different types of materials and see how their bandgaps hinder or help the movement of electrons from the valence band to the conduction band (see Figure 4). Metals (on the le in the figure) have a valence band and conduction band that overlap. is structure makes them ideal for conducting electricity—there is no bandgap to cross! A good example of a metal is copper. Insulators (center) have a large bandgap that makes it extremely difficult for electrons to make the journey from the valence band to the conduction band. Ex- amples of insulators are sand, glass and plastic. A semiconductor (right) has a bandgap that is ideal for manipulation, meaning we can shrink the bandgap to facilitate the flow of electrons (current) or expand it and to stop the flow of electrons. Silicon has been the semiconductor material of choice for quite some time now. Note that it has four electrons in the valence band of each atom (see Figure 5). Figure 3: Electron bands and a bandgap. Figure 4: Band structure of different types of materials. Figure 5: Simple atomic model for silicon (Si).