Electron-defect interaction

The linear and nonlinear optical properties of the conjugated polymeric crystals are reviewed. It is shown that the dimensionality of the rr-electron distribution and electron-phonon interaction drastically influence the order of magnitude and time response of these properties. The one-dimensional conjugated crystals show the strongest nonlinearities their response time is determined by the diffusion time of the intrinsic conjugation defects whose dynamics are described within the soliton picture. 

Electronic Defect States in Alkali Halides Effects of Interaction widi Molecular Ions By V. Dierolf 2003. 80 figs., XII, 196 pages... 

As an example of adatom-lattice defect interactions on a surface, we will describe here a study of the interaction between an adatom and an impurity atom in a surface layer. An impurity atom, like any other lattice defect, in the surface layer can perturb the periodicity of the surface both electronically and elastically. Such a perturbation will change the potential energy of a diffusing adatom on the surface. A study of adatom-... 

Defect clustering is the result of defect interactions. Pair formation is the most common mode of clustering. Let us distinguish the following situations a) two point defects of the same sort form a defect pair (B + B = B2 = [B, B] V+V = V2 = [V, V]) and b) two different point defects form a defect pair (electronic defects can be included here). The main question concerns the (relative) concentration of pairs as a function of the independent thermodynamic variables (P, T, pk). Under isothermal, isobaric conditions and given a dilute solution of B impurities, the equilibrium condition for the pair formation reaction B + B = B2 is 2-pB = The mass balance reads NB + 2-NBi = NB, where NB denotes the overall B content in the matrix crystal. It follows, considering Eqns. (2.39) and (2.40), that... 

Compared with the momentum of impinging atoms or ions, we may safely neglect the momentum transferred by the absorbed photons and thus we can neglect direct knock-on effects in photochemistry. The strong interaction between photons and the electronic system of the crystal leads to an excitation of the electrons by photon absorption as the primary effect. This excitation causes either the formation of a localized exciton or an (e +h ) defect pair. Non-localized electron defects can be described by planar waves which may be scattered, trapped, etc. Their behavior has been explained with the electron theory of solids [A.H. Wilson (1953)]. Electrons which are trapped by their interaction with impurities or which are self-trapped by interaction with phonons may be localized for a long time (in terms of the reciprocal Debye frequency) before they leave their potential minimum in a hopping type of process activated by thermal fluctuations. 

The solution of the equation (4.2.26) cannot be found in an analytical form and thus some approximations have to be used, e.g., variational principle. Its formalism is described in detail [33, 57, 58] for both lower bound estimates and upper bound estimates. Note here only that there are two extreme cases when a(r)/D term is small compared to the drift term, reaction is controlled by defect interaction, in the opposite case it is controlled by tunnelling recombination. The first case takes place, e.g., at high temperatures (or small solution viscosities if solvated electron is considered). 

There are three reasons why the temperature change can affect the tunnelling luminescence of radiation defects in wide-gap insulators characterized by a strong electron-phonon interaction ... 

Analysis of mechanisms of the defect formation, thermodynamics, interaction, association and - diffusion in solid materials, validated by deep experimental studies centered on numerous particular cases, including - solid electrolytes such as -> stabilized zirconia (see also - defects in solids, -> vacancies, -> electrolytic domain, -> electronic defects, -> doping). 

When the defect interaction energy is much larger than the thermal energy, it can lead to an ordering of defects into superlattice structures and to the appearance of phases having ordered arrays of defects. Other interactions may also become important as the spin-dependent interactions between the d electrons in the Fj gS system (24). We shall not consider these order-disorder phenomena, since they are discussed by Wadsley (30). Some of the structural-consequences of ordering are considered below. 

The thermal conductivity of a pure metal is lowered by alloying, whether the alloy formed is a single phase (solid solution) or multiphase mixture. There are several reasons for this. First, electrons are scattered by crystal imperfections and solute atoms (electron-defect scattering). Second, a substantial portion of the thermal conductivity in alloys, in contrast to that of pure metals, is by phonons, Kph (phonons are the sole contribution in electrically insulating solids) and phonons are also scattered by defects. Finally, electron-phonon interactions limit both Kei and Kp. ... 

The factor / indicates that F(r) is 90° out of phase with the local displacements. Such an electron potential, arising from phonons in crystals, is called an electron-phonon interaction. We saw that electrons may be freed in the crystal when impurities are present and may also be freed by thermal excitation even in the pure crystal. Any such free electrons contribute to the electrical conductivity, but that conductivity will in turn be limited by the scattering of the electrons by lattice vibrations or by defects. We will not go into the theories of such transport properties as electrical conductivity these arc discussed in most solid state physics texts- but will examine the origin of certain aspects of solids such as the electron-phonon interaction, which enter those theories. 

These satellite points will give rise to electron scattering, just as did the structure factors that arose from defects in the crystal. The satellite matrix elements -i q uw, and -iq u w, arc sometimes called the electron-phonon interaction we shall return to them. It may be desirable first to discuss the vibration spectrum itself. 

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