Electron trap Coulomb

Figure 7. A configuration coordinate diagram for electron trapping at a positively charged defect. The Coulombic trap depth for the hydrogenlike Is ground state of the shallowly-trapped electron is . (Here Ec is equivalent to Eb in Eq. (3).) a, the energy barrier to deep trapping, is less than Ec for the potential surface with a minimum at q. This condition facilitates relaxation to the deeply trapped state. For the surface with a mimimum at q", a is greater than c so that the shallow trap will thermally ionize rather than relax to the deeper trapped state. , is the thermal trap depth of the relaxed deep state and opI is its optical trap depth.

We shall now address ourselves to the fate of the secondary electrons trapped in phases A and B following their release from these traps on warm-up of the sample to T > Tg and Tg . The electrons trapped in phase A should more or less all combine with ions present in the same phase. Very likely they will combine with the parent ion IjJ from which the electron originated or with an ion /a belonging to a cluster of ions formed along with the parent ion by a 8 electron of higher energy. Those electrons which transferred and were trapped in phase B could in principle recombine with ion Ib of the B phase. Again, however, it is probable that most of these electrons, attracted by the Coulomb field of their parent ions or of ions of the parent spur, will return to phase A and recombine there. The reason for this is that once an electron is released from one... 

A simple model for the Verwey transition has been proposed (Honig, Spalek Gopalan, 1990) octahedral sites in magnetite were represented by a site pair, with a ground energy state (an electron trapped), a first excited state (the electron resonating between the two components of the site pair) and a second excited state (two electrons in the site pair). An important characteristic of this model was that the Verwey transition was driven by the coulomb repulsive interaction between electrons in the site pair. 

Figure 5.23 Idealized periodic rhomb pattern showing the Coulomb blockade region on the plane of voltages U and Uq. A transistor conducts only outside the rhombic-shaped regions. The value ofthe number n is the number of extra electrons trapped in the island in the blocked state.

The energ E2 shown in Fig. 1, results of the same case when a charge pair is formed. In that case, instead of the energies of the polarisation P of the polymer by a single trapped hole and the depth q of an electron trap, the Coulomb energ>" Q(r) of the charge pair (distance r) and the depth of the electron-hole-trap q j have to be taken into account. 

Intense research efforts have been devoted to characterize the electronic trap states in single crystal and colloidal Ti02 [173-176], although it is still unclear whether these states originate from defects in the bulk and surface regions, from the grain boundaries of the particles, from Coulomb trapping due to interactions of electrons with the cations of the electrolyte, or from a combination of all these factors. 

Coulomb blockades in metallic quantum dots inform on the ability to trap and to store single electrons in a distinct voltage region. Practically this means nothing but to have a single electron switch If this is the case at room... 

In fact, with small particles or clusters, a range of excited state lifetimes could be observed by spectroscopic methods . The observed non-Arrhenius dependence indicated the importance of multiphonon electron tunnelling, probably to preexistent traps. The shorter lifetimes observed at shorter emission wavelenths indicated significant coulombic interaction between traps. 

It should be stressed that means the effective radius at which mobile defect is trapped by the Coulomb field of its partner but the electron tun-... 

Fig. 4.6. Schematic pattern of the tunnelling recombination of positively changed Vk centre with neutral electron centre (e.g., F centre) (a) and with oppositely charged activator atom (e.g., Tl°) (b). In the second case the Coulomb field traps Vk at long distance R n, but electron transfer itself occurs at much shorter distance.

Two suggestions have been advanced as to why the rate constant does not vanish at low n. First, Beterov et al.91 have suggested that before the electron is captured by the SF6 n increasing collisions with SF6 lower the binding energy to the point that coulomb trapping does not eliminate SF6 production. In their... 

Because of its lower electron affinity, Te sites trap holes which can then coulombically bind an electron in or near the conduction band to form an exciton. Subsequent radiative collapse of this exciton leads to emission (10,11,12,13). In the context of the PEC, emission thus serves as a probe of electron-hole (e -h" ) pair recombination which competes with e - h+ pair separation leading to photocurrent. Except for intensity, the emitted spectral distribution is found to be independent of the presence and/or composition of polychalcogenide electrolyte, excitation wavelength (Ar ion laser lines, 457.9-514.5 nm) and intensity (<30 mW/cnZ), and applied potential (-0.3V vs. SCE to open circuit) (6,1,8,9). 

The last three involve the capture of a charged carrier at an oppositely charged center. In all of these events except the free-hole trapped-electron recombination, the free carrier is the electron and the trapping center has a charge of +e/2. The key assumption is that the cross section for electron capture is determined by the coulombic attraction. On this basis, Hamilton derived an equation that includes one term to cover low-intensity reciprocity failure and another which is a first-order approximation of high-intensity reciprocity failure. Its predictions were in good accord with experimental data on the effects of sulfur sensitization. 

In the Gurney-Mott mechanism, the trapped electron exerts a coulombic attraction for the interstitial silver ion. This attraction would be limited to a short distance by the high dielectric constant of the silver bromide. Slifkin (1) estimated that the electrostatic potential of a unit point charge in silver bromide falls to within the thermal noise level at a distance of "some 15 interatomic spacings." The maximum charge on the sulfide nucleus would be 1 e. The charge on a positive kink or jog site after capture of an electron would not exceed e/2. An AgJ would have to diffuse to within the attraction range before coulombic forces could become a factor. 

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