Physics
Surface Charge
Surface charge refers to the distribution of electric charge on the surface of a material. It can result from the accumulation or depletion of electrons, leading to an imbalance of positive or negative charge. Surface charge plays a crucial role in phenomena such as electrostatic interactions, surface tension, and the behavior of materials in electric fields.
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5 Key excerpts on "Surface Charge"
eBook - PDF- E Ilisca, Kenji Makoshi(Authors)
- 1996(Publication Date)
- World Scientific(Publisher)
Charge transfer is a key concept in surface science. This is reflected by the central role it plays in the history of surface science. For instance, workfunction changes occurring upon, e.g., alkali-atom adsorption have been driving forces behind essential conceptual developments. 1.2. Aim The modest aim of this article is to indicate some major trends, concepts, and results in the subfield of surface physics concerned with electron transfer and to give some introduction. By necessity this introductory contribution to the volume has to be broad, sketchy, and somewhat superficial. At best it might serve to indicate the basic physics issues addressed and the primary achieve-ments to the interested non-specialist reader. The perspective is a personal one, and the reference list is far from complete (See also Refs. 39 and 41). The emphasis will be on documenting the multitude of electron-transfer phenom-ena and on extracting key observations and concepts. There are many other contributions to this volume that dress such a skeleton with facts and details. It should also be stressed that the area is viewed with a theorist's eyes. This means that particular attention is paid to the concepts that have emerged and 4 B. I. Lundqvist to stress the important interplay between various experimental techniques and theoretical studies. The many manifestations of charge transfer are given an initial classification as static and dynamic ones. Among the former, workfunction changes upon adsorption are central. The historical development of the understanding of these phenomena illustrates how delicate the mechanisms can be, and yet with important consequences. The dynamic manifestations are here first grouped with respect to their external agents. For instance, an atom falling towards a surface can result in many things: heating of the surface, light emission, electron emission, ion emis-sion, atom desorption, surface reaction, etc.
eBook - PDFIntroduction to the Properties of Crystal Surfaces
International Series on Materials Science and Technology
- J. M. Blakely, W. S. Owen(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
C H A P T E R 5 S O M E T H E O R E T I C A L ASPECTS OF SURFACE STUDIES 5.1. I N T R O D U C T I O N A detailed understanding of surface phenomena will require a knowledge of the equilibrium structure and properties of the pure surface itself. By this we mean the time average coordinates of the atoms or ions in the surface region, the electronic states associated with surface atoms, and their dynamical behavior. In the present chapter we describe some of the theoretical work in this direction. Because the inert gas crystals and ionic crystals can be adequately represented, for many purposes, by pair potentials, the most detailed calculations of structure have been carried out for these cases. We will consider the method of calculating lattice relaxation near simple surfaces of these materials and the corresponding effects on surface tension. With metals the distribution of conduction electrons is expected to be perturbed appreciably at the surface unit cells. We will consider some aspects of the electronic charge distribution and sur-face tension of metals, and investigate the origin of the electronic work function and inner potential. Finally, we mention the existence of surface electronic states and surface phonons. Surface electronic states strongly influence the electrical properties of semiconductor surfaces where they lead to the formation of regions of electronic space charge extending into the crystal. 107 108 P R O P E R T I E S O F C R Y S T A L S U R F A C E S 5.2. S U R F A C E S T R U C T U R E A N D S U R F A C E T E N S I O N O F I O N I C C R Y S T A L S A N D I N E R T G A S C R Y S T A L S The calculation of the surface tension of a crystal is, of course, intimately connected with that of determining the equilibrium struc-ture in the surface region.
eBook - PDF- Pierluigi Zotto, Sergio Lo Russo, Paolo Sartori(Authors)
- 2022(Publication Date)
- Società Editrice Esculapio(Publisher)
Non-uniformity is a com- bined consequence of electrostatic equilibrium and repulsive forces ex- erted between charges of the same sign. Initially, suppose that some excess charge must distribute on a flat conduc- tor. Excess charges must gather on the surface in order to ensure electrostatic equilibrium, but they have the same sign, so they repel trying at the same time to find a static equilibrium on the surface. The coulomb interaction be- tween any two charges lies along the line connecting them, thus in this case it is parallel to the surface (figure (a)). Neglecting edge effects, i.e. for charges sufficiently far from the plane edges, the charge distribution must be uniform because they must keep a constant dis- tance in order to cancel the effect of repulsive forces, as result of a symmet- rical charge disposal around any of them. If the surface is convex, the compo- nent along the surface of the repulsive force reduces its magnitude for sym- metrically disposed charges, becoming less intense as the curvature radius reduces, as it is clear by looking at figures (b) and (c). Obviously, if the surface is spherical, symmetry suggests again that the resulting charge distribution is uniform, but, for irregular surfaces, the charges come closer in the places where the net repulsive force is weaker. Hence, Surface Charge density is greater for a smaller radius and, accordingly, in those zones the electric field magnitude will be higher. – – F ij j i F ji – – F ij j i F || F ⊥ F ji F || F ⊥ F ⊥ – – F ij j i F || F ⊥ F ji F || – – j i F || F ⊥ F ij F ji F || F ⊥ (a) (b) (c) (d) Conductors in Equilibrium Chapter 5 60 † The introduced arguments are simple indications of the processes involved in establishing the electrostatic equilibrium in a conductor featuring a generic shape.
eBook - PDFNanostructures And Nanomaterials: Synthesis, Properties And Applications
Synthesis, Properties and Applications
- Guozhong Cao(Author)
- 2004(Publication Date)
- ICP(Publisher)
At pH < P.z.c., H+ is the charge deter- mining ions and the surface is positively charged. The Surface Charge density or surface potential, E in volt, can then be simply related to the pH and the Nernst equation [Eq. (2.1 S)] can be written as45: 2.303 R,T [(P.z.c.) - pH] F E = (2.19) At room temperature, the above equation can be further simplified: E z 0.06 [@.z.c.)-PH] (2.20) 2.4.2. Nectric potential at the proximity of solid surface When a Surface Charge density of a solid surface is established, there will be an electrostatic force between the solid surface and the charged species in the proximity to segregate positive and negatively charged species. However, there also exist Brownian motion and entropic force, which homogenize the distribution of various species in the solution. In the solution, there always exist both Surface Charge determining ions and counter ions, which have charge opposite to that of the determining ions. Although charge neutrality is maintained in a system, distributions of 34 Nanostructures and Nanomaterials charge determining ions and counter ions in the proximity of the solid sur- face are inhomogeneous and very different. The distributions of both ions are mainly controlled by a combination of the following forces: (1) Coulombic force or electrostatic force, (2) Entropic force or dispersion, (3) Brownian motion. The combined result is that the concentration of counter ions is the high- est near the solid surface and decreases as the distance from the surface increases, whereas the concentration of determining ions changes in the opposite manner. Such inhomogeneous distributions of ions in the prox- imity of the solid surface lead to the formation of so-called double layer structure, which is schematically illustrated in Fig.
eBook - PDFSoil Colloids
Properties and Ion Binding
- Fernando V. Molina(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
111 © 2010 Taylor & Francis Group, LLC 5 Surface Charge of Colloidal Particles 5.1 CONTRIBUTIONS TO Surface Charge As it was already stated in Chapter 3, particles suspended in a polar liquid medium such as water show an electrical charge. This charge can be verified and determined by methods such as electrophoretic mobility measurement, discussed in Section 5.4.1. In the following, we discuss how the charge arises from a number of sources, some due to the particle itself and some due to the interaction between the particle and the medium (Hiemenz and Rajagopalan 1997; Sparks 2002; Sposito 2008). 5.1.1 P ERMANENT C HARGE Consider a (hypothetical) simple neutral molecule of silicon dioxide, SiO 2 ; the Si atom is in its normal + 4 oxidation state, whereas the two oxygen atoms are in the –2 state. Now if we replace the Si atom by an Al atom, the species can no longer be neu-tral, because aluminum has an oxidation state of + 3, and we would end up with the aluminate anion AlO 2 −1 . Now if we consider a (crystalline) solid with the stoichiom-etry SiO 2 and a few Si atoms are replaced with Al, we will get a particle with a fixed negative charge, which must be compensated by cations on the outer side. Likewise, if in a solid with the stoichiometry Al(OH) 3 (such as gibbsite or bayerite), some Al 3 + species are substituted with a + 2 cation (such as Mg 2 + or Fe 2 + ); the solid will have a fixed negative charge. If the number of substituting species is small, the crystalline structure of the unsubstituted solid will remain unchanged, the foreign atoms being forced to adopt the host structure. This situation is termed “isomorphic substitu-tion,” and the resulting negative charge of the particle is a fixed, permanent one. It has been termed the “fixed” (Zachara and Westall 1998) or “structural” (Sposito 1999) or “permanent” (Sparks 2002) particle charge q f .
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