Electrons free mobility

Fio. 3. Dependence on hydrogenation temperature of the free-electron concentration (a) and the electron Hall mobility (b) in phosphorus-implanted n-type silicon (Johnson et al., 1987c). 

A representative example for the information extracted from a TRMC experiment is the work of Prins et al. [141] on the electron and hole dynamics on isolated chains of solution-processable poly(thienylenevinylene) (PTV) derivatives in dilute solution. The mobility of both electrons and holes as well as the kinetics of their bimolecular recombination have been monitored by a 34-GHz microwave field. It was found that at room temperature both electrons and holes have high intrachain mobilities of fi = 0.23 0.04 cm A s and = 0.38 0.02 cm / V s V The electrons become trapped at defects or impurities within 4 ps while no trapping was observed for holes. The essential results are (1) that the trap-free mobilities of electrons and holes are comparable and (2) that the intra-chain hole mobility in PTV is about three orders of magnitude larger than the macroscopic hole mobility measured in PTV devices [142]. This proves that the mobilities inferred from ToF and FET experiments are limited by inter-chain hopping, in addition to possible trapping events. It also confirms the notion that there is no reason why electron and hole mobilities should be principally different. The fact... 

Electrons have not been detected by optical absorption in alkanes in which the mobility is greater than 10 cm /Vs. For example, Gillis et al. [82] report seeing no infrared absorption in pulse-irradiated liquid methane at 93 K. This is not surprising since the electron mobility in methane is 500 cm /Vs [81] and trapping does not occur. Geminately recombining electrons have, however, been detected by IR absorption in 2,2,4-trimethyl-pentane in a subpicosecond laser pulse experiment [83]. The drift mobility in this alkane is 6.5 cm /Vs, and the quasi-free mobility, as measured by the Hall mobility, is 22 cm /Vs (see Sec. 6). Thus the electron is trapped two-thirds of the time. 

For many nonpolar liquids, the electron drift mobility is less than 10 cm /Vs, too low to be accounted for in terms of a scattering mechanism. In these liquids, electrons are trapped as discussed in Sec. 4. Considerable evidence now supports the idea of a two-state model in which equilibrium exists between the trapped and quasi-free states ... 

The magnitude of the mobility then depends on the value of the quasi-free mobility in such liquids multiplied by the fraction of time the electron is quasi-free since the trapped electron is relatively immobile. Thus ... 

The main experimental elfects are accounted for with this model. Some approximations have been made a higher-level calculation is needed which takes into account the fact that the charge distribution of the trapped electron may extend outside the cavity into the liquid. A significant unknown is the value of the quasi-free mobility in low mobility liquids. In principle, Hall mobility measurements (see Sec. 6.3) could provide an answer but so far have not. Berlin et al. [144] estimated a value of = 27 cm /Vs for hexane. Recently, terahertz (THz) time-domain spectroscopy has been utilized which is sensitive to the transport of quasi-free electrons [161]. For hexane, this technique gave a value of qf = 470 cm /Vs. Mozumder [162] introduced the modification that motion of the electron in the quasi-free state may be in part ballistic that is, there is very little scattering of the electron while in the quasi-free state. 

What are surface states In an ideal semiconductor, the electron distribution in the conduction band follows Fermi s distribution law and the assumptions behind the deduction is that the conduction electrons are mobile ( free ). In this model, electrons may come to the surface and overlap or underlap a bit, but there are no traps to spoil the sample distribution. 

Here t is the time elapsed from the moment the light is switched on, z 1 is the probability of the transition of an electron to a quasi-free (mobile) state per unit time under the action of light, Rz = (ae/2)lnver is the distance of electron tunneling from a trap to an acceptor within the time z. 

The electron-sea model affords a simple qualitative explanation for the electrical and thermal conductivity of metals. Because the electrons are mobile, they are free to move away from a negative electrode and toward a positive electrode when a metal is subjected to an electrical potential. The mobile electrons can also conduct heat by carrying kinetic energy from one part of the crystal to another. Metals are malleable and ductile because the delocalized bonding extends in all... 

Localized and Quasi-Free Electrons. The mobility of electrons in non-polar media ranges from 5 x 10 "3 cm2 v l s in liquid hydrogen to values as high as 2200 cm v s in liquid xenon( see reference 35). For common hydrocarbons the value range from 0.013 cm v s" for trans-decalin(53) to 100 cm v s for tetramethylsilane(54). These values are to be compared with that for e q of 2 x 10"3 cm v s (quoted in reference 37). 

Electron Diffraction in a Beam of Vapour (a) Determination of Atomic Radii (b) Cyclic Molecules (c) The Problem of Free Mobility... 

From the point of view of classical mechanics this free mobility of the electrons, which experiment clearly requires as a distinguishing feature of metals, perforce remained mysterious the actual order of magnitude of the forces exerted on an electron by the other electrons and the atomic residues would give the electron a Fig. i... 

On the other hand, it still remained a mystery how it is that the mutual action of the electrons does not completely destroy the free mobility of the electron. For this mutual action is not, as might be expected, a feeble one, but is of the same order as that between the atoms and the electrons, and certainly cannot be completely explained by a screening effect. If in the total potential acting on an electron. 

In order to prove that the method described here really reproduces metallic properties correctly, it Is essential that in this case also, lattice vibrations being neglected, we should have stationary states of the metal in which a current flows through it, i.e. free mobility of the electrons. 

Metals have high conductivity values because the number density of free, mobile electrons is quite high—at least one per atom in the solid is in the conduction band. The electron sea is delocalized throughout the solid, and the free electrons respond easily to applied electric fields. 

The description of electrostatic phenomena in condensed molecular environments rests on the observation that charges appear in two kinds. First, molecular electrons are confined to the molecular volume so that molecules move as neutral polarizable bodies. Second, free mobile charges (e.g. ions) may exist. In a continuum description the effect of the polarizable background is expressed by the dielectric response of such environments. 

When electrons are excited, thermally or optically to the bottom of the conduction band they behave essentially as free mobile charge carriers. Indeed, we may expand the conduction band energy E lk about the bottom, at k = kc, of the... 

The first successful theory of the metallic state may be said to have arisen from the work of Drude and Lorentz in the early years of the present century. On this theory a metal is to be regarded as an assemblage of positive ions immersed in a gas of free electrons. A potential gradient exists at the surface of the metal to imprison the electrons, but within the metal the potential is uniform.. Attraction between the positive ions and the electron ga gives, the structure its coherence, and the free mobility of this electron gas under the influence... 

Unlike ionic compounds, most covalent substances are poor electrical conductors, even when melted or when dissolved in water. An electric current is carried by either mobile electrons or mobile ions. In covalent substances the electrons are localized as either shared or unshared pairs, so they are not free to move, and no ions are present. 

In quasi-equilibrium plasma, Da = 2Dj in non-equilibrium plasma (Te T ), the ambipolar diffusion D = corresponds to the temperature of the fast electrons and mobility of the slow ions. To determine conditions of the ambipolar diffusion with respect to free diffusion, we should estimate the polarization field from equations (3-88) ... 

Each carbon atom in graphite has one free, mobile electron. There are no free electrons in diamond, they are all involved in covalent bonding. 

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