Quantum confinement

Ogut S, Chelikowsky J R and Louie S G 1997 Quantum confinement and optical gaps in Si nanocrystals Phys. Rev. Lett. 79 1770... 

Empedocles S A and Bawendi M G 1997 Quantum-confined Stark effect in single CdSe nanocrystalline quantum dots Science 278 2114-17... 

An explanation for these size-dependent optical properties, tenned quantum confinement , was first outlined by Bms and co-workers in the early 1980s, [156, 158, 159, 160 and 161] and has fonned the basis for nearly all subsequent discussions of these systems. Though recent work has modified and elaborated on this simple model, its basic predictions are surjDrisingly accurate. The energy of the lowest-lying exciton state is given by the following simple fonnula ... 

Figure C2.17.11. Exciton energy as a function of particle size. The Bms fonnula is used to calculate the energy shift of the exciton state as a function of nanocrystal radius, for several different direct-gap semiconductors. These estimates demonstrate the size below which quantum confinement effects become significant.

Banin U ef a/1997 Quantum confinement and ultrafast dephasing dynamics in InP nanocrystals Phys. Rev. B 55 7059... 

The unique electronic properties of CNTs are due to the quantum confinement of electrons normal to the CNT axis. In the radial direction, electrons are... 

In low-dimensional systems, such as quantum-confined. semiconductors and conjugated polymers, the first step of optical absorption is the creation of bound electron-hole pairs, known as excitons [34). Charge photogcncration (CPG) occurs when excitons break into positive and negative carriers. This process is of essential importance both for the understanding of the fundamental physics of these materials and for applications in photovoltaic devices and photodctcctors. Since exciton dissociation can be affected by an external electric field, field-induced spectroscopy is a powerful tool for studying CPG. 

We have reported a simple, green, bench top, economical and environmentally benign room temperature synthesis of MSe (M=Cd or Zn) nanoparticles using starch, PVA and PVP as passivating agents. The whole process is a redox reaction with selenium acting as the oxidant and MSe as the reduction product. An entire "green" chemistry was explored in this synthetic procedure and it is reproducible. The optical spectroscopy showed that all the particles are blue shifted from the bulk band gap clearly due to quantum confinement. Starch capped CdSe nanoparticles showed the presence of monodispersed spherical... 

Generation of nanoparticles under Langmuir monolayers and within LB films arose from earlier efforts to form nanoparticles within reverse micelles, microemulsions, and vesicles [89]. Semiconductor nanoparticles formed in surfactant media have been explored as photocatalytic systems [90]. One motivation for placing nanoparticles within the organic matrix of a LB film is to construct a superlattice of nanoparticles such that the optical properties of the nanoparticles associated with quantum confinement are preserved. If mono-layers of capped nanoparticles are transferred, a nanoparticle superlattice can be con-... 

The formation of semiconductor nanoparticles and related stmctures exhibiting quantum confinement within LB films has been pmsued vigorously. In 1986, the use of the metal ions in LB films as reactants for the synthesis of nanoscale phases of materials was described [167]. Silver particles, 1-2 mn in size, were produced by the treatment of silver be-henate LB films with hydrazine vapor. The reaction of LB films of metal salts (Cd, Ag, Cu, Zn, Ni, and Pb ) of behenic acid with H2S was mentioned. The use of HCl, HBr, or HI was noted as a route to metal halide particles. In 1988, nanoparticles of CdS in the Q-state size range (below 5 mn) were prepared inside LB films of cadmium arachi-... 

Well-defined CdS/CdSe superlattices have been formed by means of ECALE [74]. In these structures the CdS component - and not CdSe - suffered from substantial crystallographic strain as was evidenced by surface-enhanced Raman spectroscopy (SERS) - a valuable tool for characterizing the superlattice phonons in electrochemical or other ambient environments. Torimoto et al. reported quantum confinement in superlattices of ZnS/CdS grown by ECALE [75]. 

Lead sulfide, PbS, nanoparticulate thin films having pancake-like geometry and exhibiting ID quantum confinement, as controlled by the lowest dimension of the particles, have been synthesized by cathodic electrodeposition on TTO/glass and titanium electrodes from a pH 0.62 solution containing Pb(N03)2 and Na2S203 [162]. 

Vaidyanathan R, Stickney JL, Happek U (2004) Quantum confinement in PbSe thin films electrodeposited by electrochemical atomic layer epitaxy (EC-ALE). Electrochim Acta 49 1321-1326... 

Nanda KK, Sahu SN (2001) One-dimensional quantum confinement in electrodeposited PbS nanocrystaUine semiconductors. Adv Mater 13 280-283... 

Hyun et al. [345] prepared PbS Q-dots in a suspension and tethered them to Ti02 nanoparticles with a bifunctional thiol-carboxyl linker molecule. Strong size dependence due to quantum confinement was inferred from cyclic voltammetry measurements, for the electron affinity and ionization potential of the attached Q-dots. On the basis of the measured energy levels, the authors claimed that pho-toexcited electrons should transfer efficiently from PbS into T1O2 only for dot diameters below 4.3 nm. Continuous-wave fluorescence spectra and fluorescence transients of the PbS/Ti02 assembly were consistent with electron transfer from small Q-dots. The measured charge transfer time was surprisingly slow ( 100 ns). Implications of this fact for future photovoltaics were discussed, while initial results from as-fabricated sensitized solar cells were presented. 

Empedocles, S. A. and Bawendi, M. G. (1997) Quantum-confined stark effect in single CdSe nanocrystallite quantum dots. Science, 278, 2114-2117. 

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