Traps, for electrons

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]. 

The formation of an electron-deficient bond (as in reaction 35) can also be instigated by photogenerated holes. It has been shown that the resultant intermediates (especially for Group III-V materials) can act as effective electron traps for CB... 

The CTRW methodology described in Sect. 2.1 was used to compare the tracer diffusion coefficient Dtracer in the presence of electron trapping for different porosities and nanoparticle sizes and for trap locations on the surface or extended throughout the nanoparticles, as illustrated in Fig. 8 [37]. >tracer describes the diffusion of a single electron and is obtained from the mean-squared electron displacement using... 

At the beginning, the first electron trap for free electrons and the upper valence band for free holes in the lower valence band have similar effects on the carrier transport, because their reexcitation energies are the same. Accordingly, the shoulders in the dispersion spectra are similar. The delay of the electrons at long times is due to multitrapping in deep traps and to... 

Joo JB, Dillon R, Lee I, Yin Y, Bardeen CJ, Zaera F (2014) Promotion of atranic hydrogen recombination as an alternative to electron trapping for the role of metals in the photocatalytic production of H2. Proc Natl Acad Sci lll(22) 7942-7947... 

The electron can be trapped, for example by an interstitial which is converted to an H atom. The AlO is the hole color center which absorbs light and gives the color to smoky quart2. Bleaching is the result of thermal energy releasing the trapped electron, which then produces the reverse of reaction 1. The amethyst color center in quart2 is exactly like the smoky, except that Fe " replaces. ... 

A typical absorption curve obtained for a metal-free vitreous sihca after a large dose of y-rays is shown in Eigure 13. The main band is at 215 nm three smaller bands occur at 230, 260, and 280 nm. The 230-nm band may result from an electron trapped at a sihcon atom having an incomplete oxygen bond (205). 

One-electron cleavage of the oxaziridine ring is especially useful in the case of the oxaziridine (114), easily obtained from cyclohexanone, methylamine and hypochlorite. The radical formed from (114) by uptake of one electron from the iron(II) ion can be trapped, for example, by acrylonitrile to form products derived from radical (297) (68TL5609). 

Further evidence for the unique nature of the shock-formed point defects is the dispersion in ESR lineshape characteristic of conductivity at temperatures above 30 K. In shock-modified powder the conductivity is constant down to 2 K, indicating that the electrons responsible for the conductivity are not trapped. These observations indicate that shock-modified rutile is in a physical defect state that has not been obtained in more conventional vacuum-reduction defect studies. 

Highly reactive dipolar bis(tnfluoromethyl)-subsmtuted heterodienes are excellent traps for one-skeleton-atom species , even when these are short lived The hetero-1,3-dienes add electron nch and electron poorcarbenes[/2,, 125,126,127,128 129,130], carbene complexes [131], carbene analogues [SnClj, Sn(C< H, )2, GeCl2, Gey [132, 133], isonitriles [128], etc, to give [4-t-l] cycloadducts (equation 29)... 

Figure 12-11. Thickness dependence of the electron only j(V) characteristics at L=0.22, 0.31, and 0.37 pm. Solid lines have been calculated for an exponential distribution of electron traps of the total density 101 cnTJ and a characteristic temperature T,.= 1500 K (Ref. [41[).

Using a stable dopant as the emissive dye has been shown to greatly enhance the lifetime of small molecule LEDs. Rubrene doped into the Alq, electron transport layer ] 184] or into the TPD hole transport layer 1185] can extend the lifetime by an order of magnitude. Similarly, dimclhylquinacridone in Alq has a beneficial effect ]45 ]. The likely mechanism responsible for this phenomenon is that the dopant acts as a trap for the excilon and/or the charge. Thus, molecules of the host maLrix are in their excited (cationic, anionic or cxcitonic) states for a smaller fraction of the time, and therefore have lower probability to undergo chemistry. 

Trilayer structures offer the additional possibility of selecting the emissive material, independent of its transport properties. In the case of small molecules, the emitter is typically added as a dopant in either the HTL or the ETL, near the interface between them, and preferably on the side where recombination occurs (see Fig. 13-1 c). The dopant is selected to have an cxciton energy less than that of its host, and a high luminescent yield. Its concentration is optimized to ensure exciton capture, while minimizing concentration quenching. As before, the details of recombination and emission depend on the energetics of all the materials. The dopant may act as an electron or hole trap, or both, in its host. Titus, for example, an electron trap in the ETL will capture and hold an election until a hole is injected nearby from the HTL. In this case, the dopant is the recombination mmo.-... 

The catalytic activity of doped nickel oxide on the solid state decomposition of CsN3 decreased [714] in the sequence NiO(l% Li) > NiO > NiO(l% Cr) > uncatalyzed reaction. While these results are in qualitative accordance with the assumption that the additive provided electron traps, further observations, showing that ZnO (an rc-type semi-conductor) inhibited the reaction and that CdO (also an rc-type semi-conductor) catalyzed the reaction, were not consistent with this explanation. It was noted, however, that both NiO and CdO could be reduced by the product caesium metal, whereas ZnO is not, and that the reaction with NiO yielded caesium oxide, which is identified as the active catalyst. Detailed kinetic data for these rate processes are not available but the pattern of behaviour described clearly demonstrates that the interface reactions were more complicated than had been anticipated. 

Species such as 5 and 6 are called benzynes (sometimes dehydrobenzenes), or more generally, arynes, and the mechanism is known as the benzyne mechanism. Benzynes are very reactive. Neither benzyne nor any other aryne has yet been isolated under ordinary conditions, but benzyne has been isolated in an argon matrix at 8 where its IR spectrum could be observed. In addition, benzynes can be trapped for example, they undergo the Diels-Alder reaction (see 15-58). It should be noted that the extra pair of electrons does not affect the aromaticity. The... 

Nanocrystals are receiving significant attention for nano-electronics application for the development of future nonvolatile, high density and low power memory devices [1-3]. In nanocrystal complementary metal oxide semiconductor (CMOS) memories, an isolated semiconductor island of nanometer size is coupled to the channel of a MOS field effect transistor (MOSFET) so that the charge trapped in the island modulates the threshold voltage of the transistor (Fig. 1). 

Let us now return to MMCT effects in semiconductors. In this class of compounds MMCT may be followed by charge separation, i.e. the excited MMCT state may be stabilized. This is the case if the M species involved act as traps. A beautiful example is the color change of SrTiOj Fe,Mo upon irradiation [111]. In the dark, iron and molybdenum are present as Fe(III) and Mo(VI). The material is eolorless. After irradiation with 400 nm radiation Fe(IV) and Mo(V) are created. These ions have optical absorption in the visible. The Mo(VI) species plays the role of a deep electron trap. The thermal decay time of the color at room temperature is several minutes. Note that the MMCT transition Fe(III) + Mo(VI) -> Fe(IV) -I- Mo(V) belongs to the type which was treated above. In the semiconductor the iron and molybdenum species are far apart and the conduction band takes the role of electron transporter. A similar phenomenon has been reported for ZnS Eu, Cr [112]. There is a photoinduced charge separation Eu(II) -I- Cr(II) -> Eu(III) - - Cr(I) via the conduction band (see Fig. 18). 

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