Silicon quantum dots

Figure 10.9. (a) Schematic structure of a silicon quantum dot crystal and (b) its calculated electronic structure as a function of interparticle distance H. The size of the nanoparticles is L = 6.5 nm. At small H, a splitting of the quantized energy levels of single dots results in the formation of three-dimensional minibands. Reproduced from Ref. 64, Copyright 2001, with permission from the American Institute of Physics. 

Jiang, C.-W. Green, M. A. 2006. Silicon quantum dot superlattices Modeling of energy bands, densities of states, and mobilities for silicon tandem solar cell applications. J. Appl. Phys. 99 114902-114909. 

Warner JH, Hoshino A (2005) Water-soluble photoluminescent silicon quantum dots. Angew Chem Int Ed 44 4550 1554... 

Another way that nanotechnology may impact solar cells is the use of quantum dots instead of silicon. Quantum dots, which are nanoscale semiconductor crystals, could significantly lower the cost of photovoltaic cells. In 2006, Victor Klimov of Los Alamos National Laboratory in New Mexico demonstrated that quantum dots have the capability to react to light and store energy more efficiently than silicon. Although scientists are years away from actually manufacturing usable quantum dot solar cells on a commercial scale, the technology has been established. 

Brus et al. prepared isolated silicon particles by high temperature pyrolysis of disilane with a subsequent passivation of the surface by oxidation [33]. The particles of various size are then processed by high-pressure, liquid-phase, size exclusion chromatography to separate sizes and obtain various fractions of monosize particles. Such particles represent an almost ideal model of silicon quantum dots. 

Warner JH, Tilley RD. Synthesis of water-soluble photolumines-cent germanium nanocrystals. Nanotechnol. 2006 17 3745-3749. Warner J, Hoshino A, Yamamoto K, Tilley R. Water-soluble photoluminescent silicon quantum dots. Angewandte Chemie-Internat. Ed. 2005 44 2-6. 

Carrier relaxation due to both optical and nonradiative intraband transitions in silicon quantum dots (QDs) in SiOa matrix is considered. Interaction of confined holes with optical phonons is studied. The Huang-Rhys factor governing intraband multiphonon transitions induced by this interaction is calculated. The new mechanism of nonradiative relaxation based on the interaction with local vibrations in polar glass is studied for electrons confined in Si QDs. 

Propionic-Acid-Terminated Silicon Quantum Dots... 

Fig. 3.2 (a) —HOMO energy (ionization potential) and (b) —LUMO energy (electron affinity) for SiQDs in ground-state (SO) or excited-state (SI) configuration (see text) as a function of the adsorbed PA number [22]. Reprinted with permission from (Li QS, Zhang RQ, Niehaus TA, Frauenheim T, Lee ST (2007) Theoretical studies on optical and electronic properties of propionic-acid-terminated silicon quantum dots, J Chem Theory Comput 3 1518-1526). Copyright (2007), American Chemical Society... 

Fig. 3.8 Schematic diagram for the orbitals of silicon quantum dots with different passivations. For absorption spectra, the electrons transit from the orbitals in the middle column to the orbitals in the right column [24]. Reprinted with permission from (Wang X, Zhang RQ, Niehaus TA, Frauen-heim T (2007) Excited state properties of allylamine-capped sihcon quantum dots, J Phys Chem C 111 2394-2400). Copyright (2007), American Chemici Society...

Table 3.1 The energies of HOMO and LUMO, and energy gaps (AE) between HOMO and LUMO, the absorption (Eabs) and emission (Eemi) energies of SiQDs with different diameters (denoted by do in nanometers) in their ground and first singlet excited states [25]. Reprinted with permission from (Li QS, Zhang RQ, Lee ST, Niehaus TA, Frauenheim T (2008) Amine-capped silicon quantum dots, Appl Phys Lett 92 053107). Copyright (2008), American Institute of Physics...

Li QS, Zhang RQ, Niehaus TA, Frauenheim T, Lee ST (2007) Theoretical studies on optical and electronic properties of propionic-acid-terminated silicon quantum dots. 1 Chem Theory Comput 3 1518-1526... 

Reboredo FA, Galli G (2004) Theory of alkyl-terminated silicon quantum dots. 1 Phys Chem B 109 1072-1078... 

APPLICATION TO SILICON QUANTUM DOTS, WIRES AND SLABS... 

Other Processes of Plasma Production of Nanoparticles Synthesis of Aluminum Nanopowder and Luminescent Silicon Quantum Dots... 

Keywords silicon quantum dots, quantum confinement, photoluminescence... 

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