Semiconductors crystallites

Brus L E 1984 Electron-electron and electron-hole Interactions In small semiconductor crystallites the size dependence of the lowest excited electronic state J. Chem. Phys. 80 4403-9... 

Brus, L. E. (1983). A simple model for ionization potential, electron affinity and aqueous redox potentials of small semiconductor crystallites. /. Chem. Phys., 79, 5566-5571. 

As the radius of a semiconductor crystallite approaches the exciton-Bohr-radius its electronic properties begin to change, whereupon quantum size effects can be expected. The Bohr radius ub of an exciton is given by... 

Brus LE (1984) Electron-Electron and Electron-Hole Interactions in Small Semiconductor Crystallites - the Size Dependence of the Lowest Excited Electronic State. J Chem Phys 80 4403-4409... 

Electron microscopy has been performed using a sample synthesised at w = 10, [Cd2+]/[S2 ] = 2, and characterized by 430-nm absorption onset, which corresponds to a CdS diameter equal to 25 A. The microanalysis study shows the characteristic lines of sulfide and cadmium ions, indicating that the observed particles are CdS semiconductor crystallites. The electron diffractogram shows concentric circles, which are compared to a simulated diffractogram of bulk CdS. A good agreement between the two spectra is obtained, indicating the particles keep zinc-blend crystalline structure (fee) with a lattice constant equal to 5.83 A. 

Brus, L., Size-dependent development of band structure in semiconductor crystallites, New. Chem., 11, 123,1990. 

An interesting development in this field is the recent report by Dameron et al. (88) of the biosynthesis of quantum-sized CdS crystals in the yeast cells Candida glabrata and Schizo saccharomyces pombe. Exposed to Cd ions these cells synthesize certain peptides with an enhanced sulfide production. Small CdS crystals are formed inside the cells. These crystallize in the rock salt structure (and not in the thermodynamically stable hexagonal configuration). The organism controls particle nucleation and growth, so that uniformly sized CdS particles of about 20 A are formed. They show pronounced quantum-size effects. This is the first example of the biosynthesis of quantum-sized semiconductor crystallites. It constitutes a metabolic route for the detoxification of Cd " -infected living cells (see also 89). 

Schmidt H. M. and Weller H. (1986), Photochemistry of colloidal semiconductors. 15. Quantum size effects in semiconductor crystallites—calculation of the energy spectrum for the confined exciton , Chem. Phys. Lett. 129, 615-618. 

Louis E. Brus (NAS) is a professor of chemistry at Columbia University. He has been a pioneer in the synthesis, size control, and spectroscopy of nanometer-scale semiconductor crystallites. His elucidation of quantum-size effects in these materials is central to our understanding of the transition between molecular and bulk behavior. He received a B.S. in chemical physics from Rice University and his Ph.D. in chemical physics from Columbia University. 

L, E, Brus, A simple-model for the ionization-potential, electron-affinity, and aqueous redox potentials of small semiconductor crystallites, J. Chem. Phys., 79 5566-5571, 1983 L, E, Brus, Electron electron and electron-hole interactions in small semiconductor crystal-htes - the size dependence of the lowest excited electronic state, J. Chem. Phys., 80 4403-4409,1984... 

Quantum confinement is defined as the space where the motions of electrons and holes in a semiconductor are restricted in one or more dimensions. This quantum confinement occurs when the size of semiconductor crystallites is smaller than the bulk exciton Bohr radius. Quantum wells, quantum wires, and quantum dots are confined in one, two, and three dimensions, respectively [1, 2]. The confinement can be created due to electrostatic potentials, the presence of an interface between different semiconductor materials, and the presence of a semiconductor surface. A valence band and a conduction band are separated by an energy range known as the band gap ( g). These amounts of energy will be absorbed in order to promote an electron from the valence band to the conduction band and emitted when the electron relaxes directly fi om the conduction band back to the valence band. By changing the size of the semiconductor nanoparticles, the energy width of the band gap can be altered and the optical and electrical responses of these particles are changed (Fig. 1). 

L. E. Brus Electron-electron and electron-hole interactions in small semiconductor crystallites The 3.40... 

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