Electron injection voltage

As Figure 10 shows, the n—p—n bipolar junction transistor (BJT) may be regarded as two back-to-back p—n junctions separated by a thin base region (26,32,33). If external voltages are applied so that the base-emitter (BE) junction is forward biased and the base-coUector (BC) junction is reverse biased, electrons injected into the base from the emitter can travel to the base-coUector junction within their lifetime. If the time for minority carrier electrons to... 

In bilayer LEDs the field distribution within the device can be modified and the transport of the carriers can be controlled so that, in principle, higher efficiencies can be achieved. On considering the influence of the field modification, one has to bear in mind that the overall field drop over the whole device is given by the effective voltage divided by the device thickness. If therefore a hole-blocking layer (electron transporting layer) is introduced to a hole-dominated device, then the electron injection and hence the efficiency of the device can be improved due to the electric field enhancement at the interface to the electron-injection contact, but only at expense of the field drop at the interface to the hole injection contact This disadvantage can be partly overcome, if three layer- instead of two layer devices are used, so that ohmic contacts are formed at the interfaces [112]. 

Figure 11-8. Linear-linear (upper panel) and log-linear (lower panel) plots of calculated current density as a (unction of bias voltage for 100 nm MliH-PPV devices with a 2.2 eV barrier to electron injection and 0.1, 0.2, 0.3, 0.4. 0.5. and 0.6 eV barriers to hole injection.

Figure 11-9. Measured (solid lines) and calculated (dashed lines) current density us a (unction o( voltage bias for MBH-PPV devices o( about 110 nut in thickness with Au us the electron injecting contact and Pt, Au, Cu. and Al us the hole injecting contact. The upper panel shows a schematic energy level diagram for the structures.

Conditions apparatus, Hewlett-Packard HP5890 equipped with an HP5972 mass-selective ion detector (quadruple) column, PTE-5 (30 m x 0.25-mm i.d.) with 0.25- am film thickness column temperature, 50 °C (1 min), increased at 20 °C min to 150 °C(5 min) and then at 4 °Cmin to 280 °C (30 min) inlet and detector (GC/MS transfer line) temperature, 250 and 280 °C, respectively gas flow rate, He carrier gas ImLmin" injection method, splitless mode solvent delay, 3 min electron ionization voltage, 70eV scan rate, 1.5 scanss scanned-mass range, m/z 50-550. The retention times of benfluralin, pendimethalin and trifluralin are 15.2, 25.1 and... 

Chlornitrofen and nitrofen conditions for GC/MS column, cross-linked methyl silicone capillary (12 m x 0.22-mm i.d., 0.33- am film thickness) column temperature, 60 °C (1 min), 18 °C min to 265 °C inlet, transfer line and ion source temperature, 260, 200 and 200 °C, respectively He gas column head pressure, 7.5 psi injection method, splitless mode solvent delay, 3 min electron ionization voltage, 70 eV scan rate, 0.62 s per scan cycle scanned mass range, m/z 100-400. The retention times for chlornitrofen and nitrofen were 11.8 and 11.3 min, respectively. The main ions of the mass spectrum of chlornitrofen were at m/z 317, 319 and 236. Nitrofen presented a fragmentation pattern with the main ions at m/z 283, 202 and 285. ... 

Several groups introduced an oxadiazole moiety as a part of the PPV backbone (polymers 139a [169,170], 139b [171], 140 [172], 141 [169], and 142 [170]). Not unexpected, the oxadiazole moieties lowered the LUMO energy of these polymers (as demonstrated by CV measurements). The decreased electron injection barrier is manifested by lowered turn-on voltage (6 V for ITO/139b/Al) [171]. However, relatively low efficiency (0.15% for 139b [171]) was reported for these copolymers (Chart 2.28). 

HBT Device Characteristics. The HBT consists of two back-to-back n—p diodes. In the most typical configuration the emitter—base diode is forward biased, with the collector—base diode reverse biased. Because the current in a forward-biased n—p diode is exponentially dependent on the bias, small changes in the emitter—base voltage result in large changes in the emitter current. The current across the emitter—base junction is a combination of the electrons injected into the base and the holes injected into the emitter. If the diode was semi-infinite to each side, the electron current density, Jn> could be expressed as follows (44), where q is the electron charge, Vis the bias across the diode, kT... 

Under normal operation, the emitter-base junction is forward biased, whereas the collector-base junction is reverse biased (Figure 11). The voltage across the emitter-base junction is varied by an input signal. Because the donor concentration in the emitter is higher than the acceptor concentration in the emitter, the current through the junction is primarily due to electrons injected into the base. The base width is smaller than the mean... 

In very pure nonpolar dielectric liquids, electron injection currents at very sharp tips follow the Fowler-Nordheim voltage dependence (Halpem and Gomer, 1969), just as is the case in solid insulators, and in a gas, as described before. In a study of the electrochemical behavior of CNT cathodes (Krivenko et al., 2007) direct experimental proof was found of electron emission into the liquid hexamethylphosphortriamide, which was chosen because it is a convenient solvent for the visualization of solvated electrons at room temperature the solution will show an intense blue coloration upon the presence of solvated electrons. Electron spin resonance showed prove of a free electron. Electrogenerated (as opposed to photogenerated) solvated electrons have been used in the synthesis of L-histidinol (Beltra et al., 2005), albeit that in that work the electrons were generated electrochemically from a solution of LiCl in EtNH2, which is a solvent that is easier to handle than liquid ammonia (boiling points at atmospheric pressure are 17 °C and -33.34 °C, respectively). 

Fig. 7.2. Schematic representation of the forward reactions (steps 1-4, indicated by plain arrows) and recombination routes (steps 5-7, indicated by dotted arrows) taking place in the nc-DSC. (1) Optical excitation of the sensitizer. (2) Electron injection from the excited sensitizer (S ) to the conduction band of Ti02. (3) Electron percolation through the network of Ti02 particles. (4) regeneration of the oxidized sensitizer (S+) by iodide (I ). (5) Deactivation of the excited state of the sensitizer (S ). (6) Recombination of injected electrons with oxidised sensitizer (S+). (7) Recombination of conduction band electrons with triiodide (Ig ) in the electrolyte. Al/max is the maximum voltage that can be generated under illumination and corresponds to the difference between the Fermi level of the conduction band of TiC>2 under illumination and the electrochemical potential of the electrolyte...

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