Electrons band gap

However, to make these photonic devices some method of controlling light is required so that it can be manipnlated for a particular application. In other words there is a need to be able to trap a photon of a particular wavelength, and then release it only as reqnired. This is the photonic equivalent of the semi-conductor which controls the flow of electrical cnrrent in electronic devices such as transistors. These light manipnlating materials wonld have a photonic band gap that performs an equivalent role for photons as do electronic band gap semi-conductors for electrons. This new class of materials, known as photonic band gap crystals, was first proposed in 1987, and the constrnction of these artihcial crystals has been an area for intensive research since the mid-1990s. ... 

A consequence of the existence of an electronic band gap is that at sufficiently low temperature, intrinsic semiconductors or insulators show no absorption of photon related to electronic processes for energies below Eg. Inversely, the photons with energies above Eg are strongly absorbed by optical transitions between the valence and conduction bands, and this absorption is called fundamental or intrinsic. 

The electronic band gaps are correlated with the cohesive energies of the materials and, for covalent crystals, with the atomic binding energies. Hence, for group IV elements, the band gap decreases as the atomic number of the element increases. This rule is also followed by binary compounds with one element fixed, and it allows for a very few exceptions like PbSe and PbTe with band gaps of 0.26 and 0.29 eV, respectively, at RT. 

For an ionic solid whose electronic band gap is so great that no mobile electrons and holes are available, the corrosion occurs through the transfer of cations and anions from the ionic bonding state into the state of hydrated ions in aqueous solution. Let us suppose an ionic solid, MO, consisting of cation M2+ and anion O2. The ionic transfer occurs across the solid-aqua-solution interface ... 

Nanometer sized semiconductor dusters, expected to have properties different from those of molecular and bulk semiconductors of the same composition, represent a new class of materials. Interest in their preparation and potential applications as photocatalysts and device components used in quantum electronics and nonlinear optics is growing rapidly. Isolated, so-called nanophase semiconductors can be considered as zero and one dimensional quantum dots and quantum wires. Their electronic, optical, and photochemical properties change with cluster size. Wider electronic band gaps and new absorption maxima in the electronic spectra have been observed as the size of these materials decreases and have been interpreted as quantum size effects. For example, as the dimensions of the semiconductor particle are reduced, a shift to higher energy in the absorption spectrum relative to that of the bulk is generally observed. 

Hall coefficient R Thermoelectric coefficient Electronic band gap AE Temperature dependence Electronic work function Thermal work function... 

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