ZnO is a material of interest in fundamental studies of the semiconductor/electrolyte (SC/EL) interface. ZnO also has practical applications in transparent conducting electrodes, sensors, and topical medical pastes that take advantage of its UV-induced generation of peroxide species, which act as sterilizing agents. ZnO nanorods can act as charge collecting electrodes in dye-sensitized www.selleckchem.com/products/CHIR-258.html Inhibitors,Modulators,Libraries photo-electrochemical cells. Many of these applications are based on electrochemical reactions at the ZnO surface, which involve free carriers.Semiconductor problems have also stimulated many physicists to probe electrochemical questions. In this paper, we discuss several areas in which ZnO semiconductors have offered new perspectives on electrochemistry. For this discussion, we have chosen the principal areas listed below.
Energy levels in semiconductors and electrolytesThe electrical double layerMapping of the semiconductor band edge positions relative to solution redox levels (pH-sensing).The role of surface states.We will, in the present paper, look at the distributions of charge, potential, and capacitance Inhibitors,Modulators,Libraries at the zinc oxide-electrolyte interface. The distinction between metal and semiconductor electrodes is important when we consider the electrostatics across the corresponding solid-liquid interfaces.2.?Energy Levels in Semiconductors and Liquids2.1. Electron Energy Levels in Semiconductors and the Energy Band ModelThe quantum theory of solids presents a complete description of the energy levels in a semiconductor, the nature of charge carriers, and laws governing their motion [1,2].
The filled energy states correspond to the valence band (its upper edge is denoted as Ev) and the empty states to the conduction band (its lower edge is denoted Ec). The energy bands are separated by the band gap, Eg, as illustrated in Figure 1a. In solid state physics, Inhibitors,Modulators,Libraries the vacuum level is taken as the zero energy reference.Figure 1.Energy levels in (a) a semiconductor and (b) a redox electrolyte, shown with a common vacuum reference scale, where �� and are the semiconductor electron affinity and work function, respectively.The density of energy states within the energy bands increases with the square root of energy above the conduction band or below the valence band edge and is given Inhibitors,Modulators,Libraries by:NC=82��h3(me*)32(E?Ec)12(1)for the conduction band and:NC=82��h3(mh*)32(E?EV)12(2)for the valence band, in which h is Planck��s constant and me* and mh* are the effective masses of electrons and holes, respectively.
The electron and hole densities in the conduction and valence bands, respectively, are related to the corresponding Fermi levels, EF,n and EF,p, by:n=Nc exp(?Ec?EF,nkT)(3)p=NV exp(?EV?EF,pkT)(4)in which Nc and Nv are given by Equations (1) and (2). At equilibrium, the Entinostat Fermi levels of electrons and holes are identical, i.e., EF,n = EF,p = EF, n = normally n0, and p = p0.