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joel.martens
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This seems like almost too much of an elementary question, but what properties of metals / insulators cause their bandgaps to differ?
the gap between the two bands of allowed states
fatra2 said:Hi there,
For me, it has been a long time that I have reviewed solid state physics, but I believe you are talking about two different things.
The gap between the valence band and the conduction band has (to my knowledge) nothing to do with the wavefunctions of electrons. The energy gap simply explains the energy necessary to extract an electron from the valence band. The electron wavefunction explains behaviour of electrons as a wave-like particle.
Cheers
joel.martens said:Im not sure what hafsa is saying exactly, but in response to ZzapperZs reply the bloch theorem just shows us that a periodic potential causes the separation of energy levels into bands. But a metal is a crystal structure with a periodic potential so why does band theory say that there is not energy gap in a metal?
according to the periodic chart atoms with larger nuclei or with fewer valence electrons tend to be metals. also metals tend to be much denser.joel.martens said:This seems like almost too much of an elementary question, but what properties of metals / insulators cause their bandgaps to differ?
A band gap is an energy range in a solid material where no electron states can exist. It is the energy difference between the highest occupied energy state (valence band) and the lowest unoccupied energy state (conduction band).
The band gap determines whether a material is a conductor, semiconductor, or insulator. Metals have very small or no band gaps, allowing electrons to move freely and conduct electricity. Insulators have large band gaps, making it difficult for electrons to move and thus have low conductivity. Semiconductors have intermediate band gaps and can be manipulated to conduct or block electricity.
The size of a band gap is influenced by the arrangement of atoms in a material, known as its crystal structure. Materials with a more tightly packed crystal structure tend to have larger band gaps. The type of bonding between atoms also plays a role, with stronger bonds leading to larger band gaps. Additionally, temperature and pressure can affect the size of a band gap.
The band gap is related to the color of a material through the absorption and reflection of light. Materials with smaller band gaps absorb and reflect lower energy (longer wavelength) light, appearing red or orange. Materials with larger band gaps absorb higher energy (shorter wavelength) light and appear blue or purple. Insulators, with their large band gaps, tend to appear colorless as they absorb almost no visible light.
Yes, the band gap of a material can be altered through various methods, such as doping or applying an external electric field. Doping involves adding impurities to a material to create new energy states within the band gap, effectively changing its conductivity. An electric field can also manipulate the band gap by shifting the energy levels of the valence and conduction bands. This is the principle behind devices such as transistors and solar cells.