Dipole surface electric

The surface potential, x, is defined as the differential work done for a unit positive charge to transfer from the position of the outer potential into the condensed phase. This potential arises from surface electric dipoles, such as the dipole of water molecules at the surface of liquid water and the dipole due to the spread-out of electrons at the metal surface. The magnitude of x appears to remain constant whether the condensed phase is charged or uncharged. 

In the second step the charge arrives at the internal phase passing through the interface. The associated potential is known as the surface potential jump (also called surface potential, surface electrical potential, etc.). It is determined by dipoles aligned at the interface and by surface charges. It is not identical with the Volta potential difference (also sometimes called the surface potential) that has so far been used for the description of the electrical double layer. For the treatment of the electrical double layer, dipoles did not play a role. In particular in water, however, the aligned water molecules contribute substantially to the surface potential jump x- The Galvani potential, Volta potential, and surface potential jump are related by... 

In this model, the structural symmetry of the boundary region is reflected in the form and magnitude of the tensor elements of the surface nonlinear susceptibility, xf and the bulk anisotropic susceptibility, . For 1.06/tm excitation, the penetration depth of E(co) is about 100 A. The surface electric dipole contribution is thought to arise from the first 10 A. The electric quadrupole allowed contribution to E(2to) from the decaying incident field is attenuated by e-2 relative to the surface dipole contribution. Consequently, the symmetry of the SH response should reflect the symmetry of at least the first two topmost layers. For a perfectly terminated (111) surface, the observed symmetry should be reduced from the 6 m symmetry of the topmost layer to 3 m symmetry as additional layers are included. This is consistent with the observations for the centrosymmetric Si(lll) surface response shown in Fig. 3.2 [67, 68]. 

Induction forces brought about by the operation of a surface electric field on induced or permanent dipoles of resident molecules... 

The adsorption potential contains contributions from two sources dispersion interactions, and a potential that is due to the electrostatic interaction of the induced dipole of the adsorbate molecules with the surface electric field—i.e.,... 

Note that the surface electric field, induced by the incident IR radiation characterizing the thin-film model catalysts, is mainly determined by the NiAl substrate. Consequently, because only the components of the dynamic dipole moment that are perpendicular to the metallic substrate contribute to the SFG signal, the effective dipole moment of tilted molecules is reduced. As a result, the intensity of the signal characterizing tilted molecules is smaller than that of CO molecules oriented perpendicular to the substrate (such as those on the particle top facet). 

Tlie experimental values are in fact in agreement with such a pure surface electric dipole origin, see Figure 6. This fact was not Immediately recognized at that time although Are incompatibility with tlie model of perfect spheres was noticed. 

Another useful method, especially when only a single wavelength is available, is the different dependence of Y and surface electric field on the polarisation and angle of incidence.72 From the Fresnel equations and the known optical constants of metals the electric field experienced by the adsorbate and the absorbance of the substrate can be calculated. 72.73 por substrate excitation Y should follow (1-R). For adsorbate excitation some knowledge (or model) of the symmetry of the adsorbate layer (orientation of transition dipole) is required to relate the electric field to the excitation probability. The angle of incidence dependence of Y for different input polarisations have been calculated for some typical cases.72.74 Cavanagh s group have... 

For sorbate, field-dipole interactions occur that exhibit a permanent dipole moment (e.g., H2O), which interacts with the surface electric field to give an attractive energy. An example is hydrogen... 

The interaction of a Pd4 (C4v) cluster with the oxide surface was analyzed in more detail with the help of electron density difference plots and other theoretical tools, such as population analysis, core level shifts as well as induced and dynamic dipole moments [175]. Three interaction mechanisms were found to contribute to different extent metal polarization with the subsequent electrostatic attraction, Pauli repulsion, and covalent orbital interactions. Electrostatic interactions make up a sizeable fraction of the adhesion energy the polarization of the metal adsorbate by the surface electric field provides an important bonding mechanism. For the adsorption of Pd on-top or in the vicinity of the surface Mg " cations this electrostatic interaction accounts for almost the entire adsorption energy, albeit counteracted by Pauli repulsion. For adsorption on-top 0 , on the other hand, mixing of adsorbate and substrate orbitals becomes noticeable. This hybridization or covalent bonding at the interface with the oxide anions is complemented by electrostatic polarization. Further work is required to establish in a more quantitative way the relative importance of electrostatic and chemical bonding contributions. However, in line with our other studies of... 

The second term hx includes function F(P,a), which depends on ratio of conductivities, more precisely, from parameter / . The appearance of this part of the field can be explained in the following way. Under action of the primary electric field of the dipole surface charges arise in a medium with density ... 

Recently, xenon has been used as a nonreactive probe of surface structure. As long as the surface can be cooled to a low enough temperature to adsorb this inert gas atom, its local interaction with surface sites of different structure yields large enough variations in its heat of adsorption to be used as a probe of the surface structure. As we shall see in the chapter on electrical properties of surfaces, the surface electric dipole varies from site to site, depending on the structure of the site. This electric dipole influences the polarizability and thus the bonding of adsorbed atoms or molecules at that site. 

In reality, the measured ( )m comprises two parts the bulk contribution to the work function or the internal work function, ( )n,b, and a surface electric dipole Aq associated with the tail of the electron wave function spilling out of metal surface into vacuum, as depicted in Figure 6.3. Thus, the work function of metal is in fact a parameter characterized by the metal/vacuum interface. When the metal comes in contact with an organic semiconductor, naturally the dipole... 

Since the intensity of IR light for s-polarization is very small at the metal surface, only vibrations with a transition dipole component along the surface normal are detected. This necessitates using p-polarized light for the IR beam. The transition dipole vector of the molecule and electric field vector of the IR light must have a non-zero projection on each other, the consequence is that molecules with their transition dipole parallel to the metal are not seen in the SFG spectrum. This effect is referred to as the IR dipole surface selection rule [45,46]. 

Electric Dipole Moments Electric dipole moments are prevalent in semiconductor NPs due to either the presence of an anisotropic crystal lattice or surface defects. However, strong electrostatic or steric repulsion from stabilizers overcompensates electric dipole attractions between NPs. Semiconductor NPs, silver NPs, and gold NPs were discovered to spontaneously form ID chains. However, the origin of the dipole interaction and the driving forces of chain formation in metallic colloids remain unknown. 

It is a general fact that at an interface or phase boundary between two dissimilar materials, there exists a surface electrical potential that reflects differences in the electronic makeup of the two phases. Because almost all surface-active materials (for aqueous systems, at least) have a polar head group, when the molecules adsorb at the surface, the dipole moments of those groups become at least partially oriented with respect to the interface. As a result of the orientation of the dipoles (or charges), the potential difference across the interface will be altered. The surface film potential due to the monolayer, AF, is the change in the interfacial potential due to the presence of the monolayer. 

Note that the polar vector reflects only polar symmetry of the interfacial layer and may be associated with the conical (not rod-like) form of the molecules. However, when the electric charges are involved in the game, the same polar order may results in appearance of the macroscopic surface electric polarization Psurf that is the dipole moment of a unit volume [units CGS(charge) cm/cm = CGSQ/cm = StatV/cm, or C/m in SI system]. When an electric field is applied to a liquid crystal the surface polarization contributes to the free energy of a surface layer... 

In another study of the same type of latex, Ottewill and Vincent have shown that even with a non-ionic adsorbate there may be interactions with the surface ionic groups. They studied ethanol, n-propanol and n-butanol and concluded that the initial adsorption, at low concentrations of alkanol, probably involved ion-dipole association of hydroxyl with surface carboxylate anions. This would result in the hydrophobic tails of the alkanols being oriented towards the aqueous phase and, more importantly, a desorption of counterions from the double layer, thus affecting the surface electrical potential, IPq [33]. 

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