Introduction to Band Structure
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Many of the electrical and optical properties of NLO materials are related to the electronic band structure of the compounds. When many molecules are brought together to form a solid they can be considered to occupy continous broad bands as opposed to the discrete energy levels of isolated atoms. Semiconductors and insulators have a distinct zone or band gap that contain no orbitals. The bandgap determines how much energy must be added to the system to take a compound into the excited state. Modifying organic molecules so as to decrease the bandgap improves the performance of organic semiconductors polymers for certain applications.
Semiconducting polymers combine the electrical and optical properties of metals and semiconductors with the mechanical properties of plastics. Highly electrically conductive polymers were first discovered in the 1970s. Now these organic materials will be used just as silicon is used today. The goal is not to replace silicon but rather to do new things that silicon is not well suited for. Silicon has to be extremely pure, it is rigid and brittle, it is difficult to process. Organic materials can be simply printed on surfaces and may remain flexible. Finally organic materials can be synthesized to have specific characteristics.
See Wikipedia Band Structure
Alan J. Heeger, Alan G. MacDiarmid and Hideki Shirakawa won the Noble prize for chemistry in 2000 for their work with conductive polymers.
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