Electrostatic models interface

Westall, J. C. and H. Hohl, 1980, A comparison of electrostatic models for the oxide/solution interface. Advances in Colloid Interface Science 12, 265-294. 

Based on the discussion above, it seems evident that a detailed understanding of kinetic processes occurring at semiconductor electrodes requires the determination of the interfacial energetics. Electrostatic models are available that allow calculation of the spatial distributions of potential and charged species from interfacial capacitance vs. applied potential data (23.24). Like metal electrodes, these models can only be applied at ideal polarizable semiconductor-solution interfaces (25)- In accordance with the behavior of the mercury-solution interface, a set of criteria for ideal interfaces is f. The electrode surface is clean or can be readily renewed within the timescale of... 

Reactions at the Oxide-Solution Interface Chemical and Electrostatic Models... 

The structure of the interface according to the Stern model and several limiting-case approximations is presented in Figure 4. The electrostatic models of the interface will be introduced in terms of the most complete one, the triple layer model (Figure 4a). Then the relationship of the triple layer model to the simplified models in Figures 4b-d will be discussed. 

Figure 4. Electrostatic models for the surface-electrolyte solution interface. These models were conceived for metal surfaces but have been used for oxide surfaces as well.

Furthermore, although other electrostatic models for the oxide/ water interface may yield different relationships among postulated system components, it appears unlikely that either Xp nor x alone will adequately represent the postulated true adsorbate/proton exchange ratio. 

Nevertheless, an important application of electrostatic models is to the interface between two immiscible electrolyte solutions. This can be viewed as two electrolyte double layers arranged back to back. In reality, however, total immiscibility never occurs and the degree of miscibility increases with the presence of electrolyte, so that corrections to the models need to be introduced. 

Tel. 714-955-2120, fax 714-955-2118, e-mail support wavefun.com Model building, molecular mechanics, and ab initio (Hartree-Fock, Moller-Plesset, direct HF) and semiempirical (MNDO, AMI, PM3) molecular orbital calculations. Graphical front-end and postprocessor of the output. Electron density and electrostatic plots. Interface to Gaussian 92. Cray, Convex, DEC, HP, IBM, and Silicon Graphics versions. 

The above techniques have been used in numerous calculations of solute free energy profiles. Wilson and Pohorille [52] and Benjamin[53] have determined the free energy profiles for small ions at the water liquid/vapor interface and compared the results to predictions of continuum electrostatic models. The transfer of small ions to the interface involves a monotonic increase in the free energy which is in qualitative agreement with the continuum model. This behavior is consistent with the increase in the surface tension of water with the increase in the concentration of a very dilute salt solution, and it represents the fact that small ions are repelled from the liquid/vapor interface. On the other hand, calculations of the free energy profile at the water liquid/vapor interface of hydrophobic molecules, such as phenol[54] and pentyl phenol[57] and even molecules such as ethanol [58], show that these molecules are attracted to the surface region and lower the surface tension of water. In addition, the adsorption free energy of solutes at liquid/liquid interfaces[59,60] and at water/metal interfaces[61-64] have been reported. 

Studies[71-73] of the free energy curves for electron transfer at liquid/liquid interfaces have been concerned with several issues. First, to what degree is the linear response assumption which leads to parabolic free energy curves accurate Second, what qualitatively new features does the interface region introduce into the solvent free energy curves Finaly, how do continuum electrostatic models for the free energy curves compare with the molecular dynamics results Here we consider the first two points. For a recent study of continuum models see reference [73]. 

Westall, J. C., and Hohl, H. (1980) A Comparison of Electrostatic Models for the Oxide Solution Interface, Adv. Colloid Interface Sci. 12, 265-294. 

Figure 10,18 Schematic plot of surface species and charge (a) and potential ) relationships versus distance from the surface (at the zero plane) used in the constant capacitance (CC) and the diffuse-layer (DL) models. The capacitance, C is held constant in the CC model. The potential is the same at the zero and d planes in the diffuse-layer model i/fj). Reprinted from Adv. Colloid Interface Sci. 12, J. C. Westall and H. Hohl, A comparison of electrostatic models for the oxide/solution interface, pp. 265-294, Copyright 1980 with kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.

Westall, j. C. 1986. Reactions at the oxide-solution interface Chemical and electrostatic models. In Geochemical processes and mineral surfaces, ed J. A. Davis and K. F. Hayes. Am. Chem. Soc. Symp. Ser. 323, pp. 54-78. Washington DC Am. Chem. Soc. 

Another extreme is to neglect the exponential term in Eq. (5.24) at all. This leads to overestimated effect of the pH on tjo (assuming a fixed value). A model neglecting the surface potential is physically unrealistic, but non-electrostatic models of adsorption at solid-aqueous solution interface can be found even in very recent literature. According to the prevailing opinion the actual surface potential is between the above two extremes (Nemst potential and 0 = 0). The electrostatic models of oxide - inert electrolyte solution interface were discussed in detail by Westall and Hohl [25]. In this section the most common electrostatic models are combined with the 1-pK model in order to illustrate their ability to simulate the actual surface charging data. 

Pivovarov, S., Acid-base properties and heavy and alkaline earth metal adsorption on the oxide-solution interface Non-electrostatic model, J. Colloid Interf. Sci., 206, 122, 1998. 

Westall, J. C. (1986). Reactions at the oxide-solution interface chemical and electrostatic models. In Geochemical Processes at Mineral Surfaces, ed. 

As shown in Fig. 7.26, when the sensor is exposed to vapor, individual molecules can diffuse into the semiconductor thin film and be adsorbed mostly at the grain boundaries [13], If the adsorbed analytes have large dipole moment, such as H2O ( 2 debye) and DMMP ( 3 debye), the adsorption of those analyte molecules at the grain boundaries close to or at the semiconductor-dielectric interface can locally perturb the electrical profile around the conduction channel, and hence change the trap density in the active layer. We can interpret the trapping effects by a simple electrostatic model discussed briefly in Sect. 7.2. The electric field induced by a dipole with dipole moment of p (magnitude qL in Fig. 7.4) is ... 

Fig.l a Schematic view of the ferroelectric capacitor considered in [87], The epitaxy on SrTiOs is effectively taken into account by choosing the appropriate lattice parameter in the direction parallel to the interfaces, b Evolution of the energy as a function of the soft-mode I for different thickness of the ferroelectric film m. Symbols stand for the first principles results and lines present the results of a simpUfied electrostatic model. Reproduced with permission from [87]... 

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