Band-gap control

Roncali J (1997) Synthetic principles for band gap control in linear n-conjugated systems. Chem Rev 97 173... 

These and other derivatives have different band gaps, and as the band gap controls the wavelength of the emitted hght, they can cover a wide range of the visible electromagnetic spectrum and even into the infrared region. 

The denominator and the numerator of the above equation are delineated in Fig. IV.20. One sees that the energy of the band gap controls the available conversion efficiency critically. For very small... 

R. M. Walczak, J. S. Cowart, Jr., K. A. Abboud, and J. R. Reynolds. 2006. Conformational locking for band gap control in 3,4-propylenedioxythiophene based electrochromic polymers. Chem Commun (15) 1604-1606. 

Several factors detennine how efficient impurity atoms will be in altering the electronic properties of a semiconductor. For example, the size of the band gap, the shape of the energy bands near the gap and the ability of the valence electrons to screen the impurity atom are all important. The process of adding controlled impurity atoms to semiconductors is called doping. The ability to produce well defined doping levels in semiconductors is one reason for the revolutionary developments in the construction of solid-state electronic devices. 

The careful control of electronic properties is, of course, a key motivation of such structural changes the so-called band-gap tuning being a particularly important concern. Efficiency of synthesis and structural homogeneity of the products are essential ingredients of such an approach since failure to achieve e.g. quantitative transformation of precursor polymers or to couple benzene units exclusively in a para-fashion interrupts the extensive -conjugation and hampers a reliable structure-propcrty-relalion. 

Molecular-dynamics simulations also showed that spherical gold clusters is stable in the form of FCC crystal structure in a size range of = 13-555 [191]. This is more likely a key factor in developing extremely high catalytic activity on reducible Ti02 as a support material. Thus, it controls the electronic structure of Au nanoparticles (e.g. band gap and BE shift of Au 4f7/2 band) and thereby the catalytic activity. 

The emission properties of QDs can be adjusted based upon core diameter and nanoparticle composition. Nanoparticle diameters typically are carefully controlled during manufacture to be between 2 and 10 nm. In addition, the band gap energy or energy of fluorescence emission is inversely proportional to the diameter of the QD particle. Thus, the smaller the particle, the... 

The band gap Eg of semiconductors is typically of the order of 0.5 - 2 eV (e.g., 1.12 eV for Si, and 0.67 eV for Ge at room temperature), and consequently the conductivity of intrinsic semiconductors is low. It can be greatly enhanced by doping, which is the controlled introduction of suitable impurities. There are two types of dopants Donors have localized electronic states with energies immediately below the conduction band, and can donate their electrons to the conduction band in... 

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