Image charge, induced

When an electron is located inside a tunneling barrier, positive charges are induced on both metal surfaces. The total force can be treated by a series of image charges induced by both metal surfaces. The force acting on the electron inside the barrier is the sum of forces from all the image charges, as shown in Fig. 2.3,... 

The determination of the image charges/induced charges makes it possible to obtain the induced potential... 

Fig. 5. ElecUostatic image charges induced in a grounded, conducting substrate due to the presence of 1 (a) and 2 (b) charged spherical particles.

We use the image charges method to account for the surface influence on the defects electric field [43, 47]. The geometry of the image charges induced by the surface defect with two electrons is shown in Fig. 4.1 Ic, d. 

Another important aspect of the electrical properties of liquid interfaces is the so-called image charge induced by a real charge near the surface of an insulating liquid or near the surface of an electronically conducting liquid (or solid) metal such as Hg. This problem is of importance in (a) adsorption of ions at Hg, (b) negative adsorption of... 

Let us have a look at the image charges induced by an atomic dipole in the polarizable substrate. According to classical electrodynamics (Stratton 1941), the electrostatic field of a charge q located at a distance z from a flat surface of a medium with real dielectric function e can be described by introducing a charge... 

One potentially powerfiil approach to chemical imaging of oxides is to capitalize on the tip-surface interactions caused by the surface charge induced under electrolyte solutions [189]. The sign and the amount of the charge induced on, for example, an oxide surface under an aqueous solution is detenuined by the pH and ionic strength of the solution, as well as by the isoelectric point (lEP) of the sample. At pH values above the lEP, the charge is negative below this value. 

Schematic diagram showing how placing a thin layer of highly dispersed carbon onto the surface of a metal filament leads to an induced dipolar field having positive and negative image charges. The positive side is always on the metal, which is much less electronegative than carbon. This positive charge makes it much more difficult to remove electrons from the metal surface. The higher the value of a work function, the more difficult it is to remove an electron. Effectively, the layer of carbon increases the work function of the filament metal. Very finely divided silicon dioxide can be used in place of carbon.

To a first approximation, the ions in both Helmholtz layers can be considered point charges. They induce an equal and opposite image charge inside the conductive electrode. When the electrode is negative to the point of zero charge, cations populate the inner Helmholtz layer. 

Consider a hydrogen atom with its nucleus at the origin located above the surface of a conducting metal at the position d = (0,0,d) and an electron at r = (x,y,z) (Fig. 6.1).The nucleus and the electron both induce image charges in the metal equal to... 

There is also the normal dipole selection rule in operation, as illustrated in Figure 5.48, due to Liith (1981). Any dipole at a surface induces an image charge within the surface. If the dipole orientation is normal to the surface, the effect is enhanced by the image dipole. If, however, the orientation is parallel to the surface, the effect is annihilated by the image dipole. This orientation selection rule thus strongly favours normally oriented dipoles. 

As soon as an electron should leave the surface an image charge is induced within the metal and the electron is pulled back across the edge. A characteristic amount of energy, known as the work function W, is required to remove an electron from a metal. Suppose now that the metal is placed in a strong electric field which is directed to pull electrons from the metal. The electric potential —eEx, where E is the electric field and x the distance from the edge, now modifies the potential at the surface to resemble the situation shown in figure 4. 

The plane of the center of mass of induced image charge, oJ,x), is called the effective image plane [Lang-Kohn, 1973], and its position, Xm, is given by Eqn. 5-28 ... 

FIG. 34. A sequence of STM images of a surface charge-induced transition from the disordered to the ordered phase of 2-2 bipyridine adsorbed on Au(lll). At positive charges the molecules stack into polymeric chains, which are initially disordered as shown in (A). As the potential is increased, small ordered domains begin to form and expand as the potential is increased from 0.14 to 0.25 V (B-E). The domains follow the symmetry of the Au(lll) substrate. (From Ref. 467.)... 

Fig. 2.2. The image potential of an electron near a metal surface. The electron induces positive charge at the metal surface, (a) The effect of the positive surface charge is equivalent to a fictitious image charge behind the metal surface, (b) fhe distance dependence of the image potential.

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