Pulling Electrons Out of Metals by Intense Electrical Fields

Citation

Eyring, Carl Ferdinand (1924) Pulling Electrons Out of Metals by Intense Electrical Fields. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/JV7K-YR82. https://resolver.caltech.edu/CaltechETD:etd-10262004-145617

Abstract

Two types of electrodes, placed in a vacuum better than 10^-6 mm Hg., were used; viz., points and plane with electrode distances from .005 cm to .03 cm, and a fine tungsten wire of .00125 cm diameter and a copper cylinder of 1.625 cm diameter. Making measurements on a micro-photograph of a point--sharp tungsten, dull tungsten, sharp platinum, or dull nickel--and determining the distance between point and plane, the relation between the potential gradient at the end of the point and the potential applied was determined; this relation for the wire surface was determined from the diameters of the wire and cylinder. The maximum available d. c. potential was 12,000 volts which produced a gradient of several million volts per centimeter at the metal surfaces under investigation. The results of the experiments show that electrons are pulled from metals by intense electrical fields, the "field-current" thus produced depending upon the gradient at the surface and not upon the difference of potential between the electrodes. The "field current" sets in at a "critical" gradient and increases in some cases (untreated tungsten wire and cylinder) over ten million-fold with only a threefold increase in gradient. The metal points give different "critical" gradients, but these gradients are not thought to be characteristic of the metals but of the surfaces. It is found that the gradient needed to pull electrons out of a metal is controlled by the surface irregularities and especially by surface impurities. The metal surface may be conditioned by heat treatment and by drawing large currents from the surface. The "critical" potential gradient may be increased fourfold by heat treatment, and twofold by the "field current" conditioning process. The rate of increase of the "field-current" with potential gradient is large when the "critical" gradient is small and vice versa, and large currents drawn from surfaces which have been subjected to intense heat treatment show a fatiguing effect which recovers with time. The "field-current" in general has its origin in a few minute surface spots which presumably locate surface impurities, or surface protrusions, or both. This current is completely independent of temperature between 300°K and 1000° K, but it is slightly greater at 1100° K than at room temperature. The assumption that the "field-current" is made up of conduction electrons, which core out of the surface by virtue of their kinetic energy when the external field has partly annuled the surface attraction, is not tenable in light of the results of this investigation. A new postulate is proposed, viz., that the loosely-bound electrons of the outermost atoms--atoms of impurity of lower electron affinity, or atoms on the tips of protrusions--are pulled away from their atoms by the strong field and then replaced by near electrons, presumably conduction electrons from the interior of the metal. Because of the control which surface conditions have upon "critical" gradients it seems unlikely that any of the results so far given by investigators can be taken as the true characteristic "critical" gradients of the metals, if perchance such characteristic gradients exist. All experimenters obtain gradients of the order of million volts per centimeter; this investigation agrees with others in this particular. A correct surface conditioning technique must be found and agreed upon, then concordant results, which agree not only in order of magnitude but in exact value, may be expected. It is felt that this investigation has added something toward this accomplishment.

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