Emission field dependence

Fig. 13. Electric-field dependence of the emission current obtained for a carefully aligned MWCNT film [38], Inset Fowler-Nordheim plot, where y is the field-enhancement factor.

The analytic theory outlined above provides valuable insight into the factors that determine the efficiency of OI.EDs. However, there is no completely analytical solution that includes diffusive transport of carriers, field-dependent mobilities, and specific injection mechanisms. Therefore, numerical simulations have been undertaken in order to provide quantitative solutions to the general case of the bipolar current problem for typical parameters of OLED materials [144—1481. Emphasis was given to the influence of charge injection and transport on OLED performance. 1. Campbell et at. [I47 found that, for Richardson-Dushman thermionic emission from a barrier height lower than 0.4 eV, the contact is able to supply... 

In this chapter, we have chosen from the scientific literature accounts of symposia published at intervals during the period 1920 1990. They are personal choices illustrating what we believe reflect significant developments in experimental techniques and concepts during this time. Initially there was a dependence on gas-phase pressure measurements and the construction of adsorption isotherms, followed by the development of mass spectrometry for gas analysis, surface spectroscopies with infrared spectroscopy dominant, but soon to be followed by Auger and photoelectron spectroscopy, field emission, field ionisation and diffraction methods. 

As in Section III.B, the question of causality immediately arises. If there is no source, why are there nontrivial solutions for the fields E,B Again, the alternatives discussed in Section III.B may provide an answer. Another standpoint is to assume that Eqs. (28) and (29) describe an independent reality. Then, after being produced, fields E,B exist on their own, quite independently of the continued existence of the source. Of course, the properties of the fields depend of the source at the moment of emission. 

This induced emission has a classical analog in classical mechanics, an oscillator of frequency v can either absorb energy from, or add energy to, a radiation field, depending on the phase of the vibration with respect to the phase of the oscillating radiation field. 

Fig. 46. Magnetic field dependent increase of the Elc deactivation rate of Ba[Pt(CN)4] 4 H20 at T = 1.9 K. th and x0 are the emission lifetimes at magnetic field strengths H and H = 0, respectively94 ...

For the same vector orientations Hie, HIO, Ole the low energetic E c emission (at 18,000 cm-1, cf. Fig. 19) shows a similar field dependence of its deactivation rate but exhibits a relatively weak magnetically induced intensity growth. 

CIDNP of the enol product showed a net emissive spectrum. Despite the complex mechanism, a field-dependent CIDNP study resolved that QH2 and the enol were the main in-cage products while the acetone was formed largely in the scavenged reaction. This conclusion was consistent with similar kinetic and mechanistic systems studied by Laroff and Fischer (87). 

Figure 2 shows results calculated from Eq. (28). The calculations assume g = 3.0, L = 20 im. VQ = 500 V. 7J0 = 1.0. and nQ = 10-6 cm2/ys at VQ. The results show the maximum intensities for which emission-limited discharge can be sustained for different values of Pe and Pm. The results show the importance of a field-dependent carrier supply and mobility on the discharge process. Only in the case where Pm = Pe is the discharge independent of the field dependencies of the photogeneration and transport processes. 

Other Applications. Despite the ability of TED spectroscopy to detect surface states, comparatively little work has been done with semi-conductors. In a careful study of germanium Shepherd identified emission from the valence band and also from a band of surface states. Conduction band emission is negligible in the [100] direction but has been detected in emission from Ge (111). TED spectra from both field-evaporated and annealed 200 ohm-cm p-type silicon tips show electrons to be emitted from occupied surface states within the band gap which lie close to, and overlap, the valence band edge. TED spectra from CdS, PbTe, and GaP have proved to be broad and to contain tittle information. Weak unidentified features appear in the TED from TiC crystals and much stronger field-dependent peaks... 

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