Trap states

Concerning the nature of electronic traps for this class of ladder polymers, we would like to recall the experimental facts. On comparing the results of LPPP to those of poly(para-phenylene vinylene) (PPV) [38] it must be noted that the appearance of the maximum current at 167 K, for heating rates between 0.06 K/s and 0.25 K/s, can be attributed to monomolecular kinetics with non-retrapping traps [26]. In PPV the density of trap states is evaluated on the basis of a multiple trapping model [38], leading to a trap density which is comparable to the density of monomer units and very low mobilities of 10-8 cm2 V-1 s l. These values for PPV have to be compared to trap densities of 0.0002 and 0.00003 traps per monomer unit in the LPPP. As a consequence of the low trap densities, high mobility values of 0.1 cm2 V-1 s-1 for the LPPPs are obtained [39]. 

Issac, A., Borczyskowski, C. V. and Cichos, F. (2005) Correlation between photoluminescence intermittency of CdSe quantum dots and self-trapped states in dielectric media. Phys. Rev. B, 71, 161302 (R)-l-161302(R)-4. 

Figure 7.5 Schematic presentation of photoactivation and relaxation processes in a CdSe quantum dot aggregate (a) surface-passivation of photoexcited quantum dots by solvent molecules or dissolved oxygen, (b) thermal activation followed by the formation ofa stabilized state, (c) the formation of deep-trap states, (d) non-radiative relaxation of deep-...

The SQ method extracts resonance states for the J = 25 dynamics by using the centrifugally-shifted Hamiltonian. In Fig. 20, the SQ wavefunc-tion for a trapped state at Ec = 1.2 eV is shown. The wavefunction has been sliced perpendicular to the minimum energy path and is plotted in the symmetric stretch and bend normal mode coordinates. As anticipated, the wavefunction shows a combination of one quanta of symmetric stretch excitation and two quanta of bend excitation. The extracted state is barrier state (or quantum bottleneck state) and not a Feshbach resonance. 

The authors assume different and statistically independent mechanisms of electron-ion recombination in the quasi-free and trapped states. Thus P = w, where and wt are respectively the probabilities of escaping recombination in the quasi-free and trapped states. Based on some heuristic and not entirely plausible arguments, wq( is approximately equated to 1/2. The probability of finding a trapped electron at a distance between r and r + dr from the positive ion is given by (crtP dr/v) exp(-crPr/v), where P, is again the probability of finding an... 

The new model is called quasi-ballistic because the electron motion in the quasi-free state is partly ballistic—that is, not fully diffusive, due to fast trapping. It is intended to be applied to low- and intermediate-mobility liquids, where the mobility in the trapped state is negligible. According to this, the mean... 

Baird and Rehfeld (1987) have analyzed the thermodynamics of electron transport in the two-state trapping model. According to these authors, the effective mobility, ignoring the mobility in the trapped state, is given by... 

Baird and Rehfeld express A ° in terms of the trap concentration and the chemical potentials of the empty trap and of the electron in the quasi-free and trapped states. Further, they indicate a statistical-mechanical procedure to calculate these chemical potentials. Although straightforward in principle, their actual evaluation is hampered by the paucity of experimental data. Nevertheless, Eq. (10.13) is of great importance in determining the relative stability of the quasi-free versus the trapped states of the electron if data on time-of-flight and Hall mobilities are available. 

Mozumder (1996) has discussed the thermodynamics of electron trapping and solvation, as well as that of reversible attachment-detachment reactions, within the context of the quasi-ballistic model of electron transport. In this model, as in the usual trapping model, the electron reacts with the solute mostly in the quasi-free state, in which it has an overwhelmingly high rate of reaction, even though it resides mostly in the trapped state (Allen and Holroyd, 1974 Allen et ah, 1975 Mozumder, 1995b). Overall equilibrium for the reversible reaction with a solute A is then represented as... 

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