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VALVE METAL-OXIDE SYSTEMS PROPERTIES 735 of precisely the expected magnitude. Even the apparently discrepant behavior of Zr, mentioned earlier, can be reconciled with the present model. In this regard, the most obvious assumption to make is that the metal-oxide interface plays a major role in the conduction process.Much additional data are required to properly test this theory. At present, however, it is the only quantitative theory which accounts for most of the observed conduction properties for these systems. ABSTRACTA potentiostatic method to permit determination of double layer capacity of electrodes under dynamic conditions has been developed. Small potential pulses are superimposed on a d-c sweep and the capacity is determined from the magnitude of current changes observed at the initiation and cessation of the pulse. Further, a method utilizing a transistor is described which permits rapid switching of a potentiostat from galvanostatic to potentiostatic operation.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.111.121.42 Downloaded on 2015-07-02 to IP

The reading speed of subjects was studied under conditions of simulated and real visual impairment. For subjects with normal visual field and average reading speeds, two types of visual impairment were simulated: cataracts and deteriorated retinas. Three groups of partially sighted persons also were studied: those with normal visual fields, those with defects in peripheral fields, and those with defects in the central field. The results for these three groups were similar to those obtained under conditions of simulated visual impairment. The authors conclude that reading speed depends on visual acuity.

Rapid potentiostatic capacity-potential measurements were carried out at Ge electrodes in solutions of pH 1, 7, and 12. Two distinct capacity curves were observed. If cathodic current flow was excluded, capacity-potential curves were measured which are in agreement with results reported in literature. The measuring parameters could be varied within a wide range without affecting the results. These capacity curves occur on an oxidized OH covered surface. Another capacity curve was measured by utilizing a galvanostatic pulse method in order to prepolarize the electrode cathodically prior to the measurement. The capacity curve measured with sufficient prepolarization is shifted 300 to 500 mv cathodic with respect to the curve measured in the absence of prepolarization. These curves correspond to the reduced surface.The electrochemical behavior of germanium electrodes differs from that of metal electrodes because Ge is a semiconductor. As a consequence of the Iow electron and (or) hole concentrations there exists a space charge layer on the semiconductor side of the interface. The capacity of this space charge layer is up to three orders of magnitude smaller than the capacity of the Helmholtz double layer in concentrated electrolytes. Both capacitors are considered to be in series (1). The smaller capacitor of the semiconductor determines the measured capacitance of the interface.The capacity of the space charge layer as a function of potential was calculated by Bohnenkamp and Engell (2) using the Poisson equation and a Boltzmann distribution of the carriers. A semilogarithmic plot of the capacity-potential curves gives V-shaped curves with a rounded minimum which occurs for intrinsic germanium at zero space charge potential difference or "flat band potential" (1). The capacity curves that were measured with a standard a-c bridge technique (2) were in poor agreement with the calculated curves. They were too broad and the minima were at higher capacity values than calculated. With the introduction of a fast pulse technique Brattain and Boddy (3) were able to measure capacity curves in agreement with theory.It was found experimentally that the potential of the capacity minimum depends on the pH of the solution (2) as well as on the "history" of the electrode (3). Obviously the position of the flat band potential depends on the chemical properties of the surface. Detailed studies of the pH effect (4, 5) yielded the result that the capacity minimum shifts by --58 mv per pH unit at 25~This observation and other experimental evidence led to the assumption that the germanium surface is covered with a homopolar bound layer of OH groups (1). The dissociation of the OH groups was made responsible for the observed shift of the curves with pH. Hofmann-Perez and Gerischer (4) called it a "dissociation double layer." Th.e second effect, the dependence of the capacity curves on the "history" of the electrode is reported by Brattain and Boddy in two papers (3, 5). The authors find that the higher the anodic current density prior to ...

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