Oxide films positive holes

Any electrons which reach the oxide—oxygen interface will be quickly utilized in the formation of 0" ions, and similarly, any positive holes which manage to reach the metal—oxide interface will be quickly annihilated by electrons from the parent metal. The asymmetrical surface reactions thus lead us to expect widely different electron concentrations in the oxide at the two interfaces of the oxide. This difference in electron concentration is equivalent to a difference in the chemical potential for the electronic species at the two interfaces. As in the case of the ionic defect species, such differences in concentration (and chemical potential) can be expected to produce particle currents of the defect species in question. If the primary electronic defects are excess electrons, then we can expect an electron particle current from metal to oxygen if the primary electron defects are the positive holes, then we can expect a positive-hole particle current from oxygen to metal. Of course, an intermediate situation is also possible in which electrons flow from the metal towards the oxygen while simultaneously a positive-hole current flows from the oxygen towards the metal, with recombination [8] (partial or total) occurring within the oxide film. 

Another variant calls for a metal or alloy to be melted in an unwetted and chemically inert closed ceramic tube positioned and to be dispensed on to the substrate surface through a small hole in the tube end by applying a back pressure of inert gas, Figure 3.7.c, (Nicholas et al. 1984), or using a piston (Naidich et al. 1983, Rado et al. 1998). One advantage of this technique is that oxide films on... 

Figures 6 and 7 IS) summarize several important results obtained with cuprous oxide films at 200° and 20° respectively. Exposure to oxygen at a few microns pressure is seen to be accompanied by an abrupt fall in resistance (i.e., rise in conductivity) showing that the concentration of current carriers—positive holes in the case of CU2O—has increased. Oxygen is therefore being adsorbed as negative ions. The fact that recovery of the original conductivity is possible on evacuation at 200°, but not at 20°,...

In the light of the present study it is possible to draw up the following interpretation of the interaction of oxygen with cuprous oxide. During the adsorption of the monolayer, the electron transfer imparts a negative potential to the adsorbed film (which probably exists as 0 ) and positive holes are formed in the surface layers. This process has an activation energy of 7 kcal./mole and proceeds with a heat of adsorption (I) of 60-55 kcal./ mole. 

The question about the physical origin of the template effect of the alumina film is not easy to answer, moreover since not only a unique site seems to function as template but rather two different sites are active depending on the deposited metal. Indeed the strong preference of Pd for nucleation on the so-called dot structure of the alumina film was attributed to the presence of a localized electronic state in the band gap of the oxide at this particular position [68,186]. This view was lately however challenged by high-resolution STM investigations, which suggest the presence of a hole in the oxide film at that very position. It was claimed that Pd - as opposed to other metals -... 

An organic light-emitting diode consists of polymer film in between two electrodes. One electrode, such as gold or indium tin oxide (ITO), should have a high work funchon, to achieve the injection of positive hole charges. The other electrode consists of a metal with low work funchon in order to inject electrons. Suitable metals with low work functions are aluminum, calcium, or magnesium. 

Since the transfer of Ni " " from the metal surface to the outside controls the oxidation of nickel, the addition of Cr " " (a high-valence cation) requires a positive hole. This triggers the transfer of Ni " ", resulting in an increased oxidation rate. On the contrary, when a low-valence cation such as Li" " is added to NiO, Li" " occupies the positive holes, and this results in a decreased oxidation rate. This is a description of valency control. Thus, the addition of Cr accelerates the oxidation of steel, but the Cr-enriched layers near the outside surface forms a tight oxide film, resulting in improved corrosion resistance. 

The pair of electron and hole imdergoes another process in which the electrons in the conduction band are recombined with the positive holes in the valence band to radiate the energy. A part of the energy is emitted as a luminescence hght. Since the recombination process preferentially occurs rmder the reverse bias, the potential is applied of the negative or zero bias for the n-type semiconductor and of the positive or zero-bias condition for the p-lype. Since spectra of the photo-excited luminescence inclnde the information on the band gap eneigy and mid gap levels, the energy levels of the oxide film can be discussed. ... 

A positive Hamaker constant corresponds to an attractive force between the silicon oxide-polystyrene and the polystyrene-air interfaces. This implies that the film is not stable. If it is thin enough and has a chance, for instance when annealing, the film ruptures and holes are formed. 

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