| Popis: |
The vast majority of organic solids are electrical insulators with electrical conductivity values on the order of 10-20-10-15 Ω-1’cm -1. This property is of course exploited in many everyday applications. Two principal reasons are responsible for this fact: (1) The highest occupied molecular orbital (HOMO) of most organic molecules is completely filled, and there is a significant energy difference to the lowest unoccupied molecular orbital (LUMO). (2) Organic solids are usually molecular, i.e., they do not possess a system of covalent bonds extending over macroscopic distances. Therefore the quantum mechanical interactions between the HOMOs of adjacent molecules are small. The valence band formed by these interactions remains therefore very narrow. Similarly, the conduction band arising from the interactions between the LUMOs is also small, and the band gap is essentially that of the free molecule. This holds even in the case of conventional polymers, e.g. polyethylene, that are a-bonded. |
