Liquid conduction band energies

Allen, A.O.(1976), Drift Mobilities and Conduction Band Energies of Excess Electrons in Dielectric Liquids, NSRDS-NBS 58, National Bureau of Standards, Washington, D.C. 

Figure 9. A schematic representation of the energetics of an excess electron interacting with bulk liquid helium, where it can reside either in a surface state with a binding energy El = —0.7 meV or in an interior bubble state with a radius Rj = 17 A and a total binding energy of 0.36 eV (i.e., 0.70 eV below the conduction band energy Vo)- A sufficiently large (He) cluster can attach an excess electron in an external surface state or in an internal bubble state.

Holroyd, R. A., Nishikawa, M., Nakagawa, K., and Kato, N., Pressure dependence of the conduction band energy of nonpolar liquids, Phys. Rev., B45, 3215, 1992. 

Plenkiewicz, B. and Jay-Gerrin, J. R, Plenkiewicz R, Conduction band energy of excess electrons in liquid argon, Europhys. Lett., 1, 455, 1986. 

Holroyd, R.A., Tames, S., and Kennedy, A., 1975b, Effect of temperature on conduction band energies of electrons in nonpolar liquids, J. 

Conduction band energy of excess electrons in liquid argon, Eurohpysics Letters, 1 455. 

Fig. 10. Energy states for an insulating micro-region on a metal cathode under an applied field (after Latham, 1982). Electrons tunnel from cathode to conduction band of insulator through Schottky barrier, A. Electron traps become filled, B. Electrons accumulate at electron-affinity barrier at insulation-vacuum interface, C. Holes produced by collision ionization drift to A and enhance electron tunnelling. Electrons with enhanced kinetic energy emitted over barrier C into liquid conduction band, D. Positive hole states of liquid E, ...

TABLE III. Examples of Conduction Band Energies " for Various Liquids versus the Vacuum Level... 

For instance, the more efficiently the photoholes are trapped from the valence band of an n-type semiconductor, the higher is the probability that the photoelectrons in the conduction band reach the surface and can reduce a thermodynamically suitable electron acceptor at the solid-liquid interface. This is illustrated with an example taken from a paper by Frei et al, 1990. In this example methylviologen, MV2+, acts as the electron acceptor and TiC>2 as the photocatalyst. Upon absorption of light with energy equal or higher than the band-gap energy of Ti02, a photoelectron is formed in the conduction band and a photohole in the valence band ... 

Electrons in nonpolar liquids are either in the conduction band, trapped in a cavity in the liquid, or in special cases form solvent anions. The energy of the bottom of the conduction band is termed Vq. Vq has been measured for many liquids and its dependence on temperature and pressure has also been measured. New techniques have provided quite accurate values of Vq for the liquid rare gases. The energies of the trapped state have also been derived for several liquids from studies of equilibrium electron reactions. A characteristic of the trapped electron is its broad absorption spectrum in the infrared. 

Fig. 4. Energy below the conduction band of levels reported in the literature for GaP. States are arranged from top to bottom chronologically, then by author. At the left is an indication of the method of sample growth or preparation liquid phase epitaxy (LPE), liquid encapsulated Czochralski (LEC), irradiated with 1-MeV electrons (1-MeV e), and vapor phase epitaxy (VPE). Next to this the experimental method is listed photoluminescence (PL), photoluminescence decay time (PLD), junction photocurrent (PCUR), photocapacitance (PCAP), transient capacitance (TCAP), thermally stimulated current (TSC), transient junction dark current (TC), deep level transient spectroscopy (DLTS), photoconductivity (PC), and optical absorption (OA).

An electron in the conductivity band is quasi-free, since for it to escape from the solid or the liquid we must supply the electron with the so-called work function, which equals the energy an electron has at the bottom of the conductivity band taken with an opposite sign. (This energy is measured from the energy of an electron in vacuum.) Denoting it as V0, we can write the relation between the ionization potential 7C and the external emission threshold as... 

Figure 1. Band Structure in a n-type Semiconductor A. Solid State. B. In contact with a liquid phase redox couple (0/R). IL=energy of the conduction band. Vertical line indicates solid-liquid interface. CB= conduction band VB = valence band.

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