Julius Cohen

Bio: Julius Cohen is an academic researcher. The author has contributed to research in topics: Work function & Contact resistance. The author has an hindex of 3, co-authored 5 publications receiving 62 citations.

Tunnel Emission into Vacuum

Abstract: Tunnel emission into vacuum is obtained from thin‐film sandwiches of (a) aluminum‐alumina‐aluminum and (b) aluminum‐alumina‐platinum. The alumina layer is made by oxidizing an evaporated film of aluminum in air. Cesium processing, to lower the work function, results in an increase of emission of five orders of magnitude.

Electrical Conductivity of Fused Quartz

Abstract: The electrical conductivities of two specimens of clear fused quartz were measured in vacuo in the temperature range of 600 to 1400°C. The method of potential probes was used to evaluate the platinum contacts and eliminate effects of high contact resistance. One specimen obeyed Ohm's law as evidenced by the linear dependence of the current on the potential between probes and the uniform potential distribution. This behavior established the specimen as an electronic conductor. The value of specific conductivity was ∼10−4 mho/cm over the interval from 1000 to 1400°C. Ohm's law was not found applicable for the other specimen, which displayed many dielectric anomalies and polarization effects such as polarization voltages, anomalous potential distributions, reverse currents, and current decays immediately after application of a voltage. The phenomena indicated the presence of space‐charge polarization and here the conductivity appeared to be substantially ionic. Heat treatment of this specimen stabilized the electrical behavior and caused increased or decreased resistance, depending on voltage, polarity, and temperature of measurement. The heating was also found to produce partial crystallization. It is suspected that the marked contrasts in the behavior of the two specimens are due to differences in the impurity contents.

Semiconducting Films of Antimony

Abstract: Thin films of antimony were condensed onto substrates at various temperatures. Films deposited at liquid oxygen temperatures showed large negative temperature coefficients of resistance. In general, reversible resistance changes occurred if the films were cooled below a temperature previously reached; irreversible changes took place if the films were heated above that at which they were prepared. Activation energies were calculated from logR vs 1/T curves and gave values of ∼0.07 ev for low temperatures and ∼0.13 ev for high temperatures. There appeared to be little or no influence of evaporation rate or thickness on the activation energies. A theory based on lattice defects is proposed in order to explain the electrical behavior of the films.

Properties and structure of vitreous silica. I

Abstract: This review is concerned with the properties and structure of silica glass. The following topics are treated: Types of silica glasses; The vitreous state of silica glasses: thermodynamical approach, atomistic approach; Optical properties; absorption and fluorescence, refractive index and homogeneity; Mechanical and thermal properties: specific volume, volume relaxation, volume and pressure, elastic and internal friction behaviour, heat capacity and heat conduction, strength, crystallization.

Space charge dynamics in thermally poled fused silica

Abstract: Measurements of the transient behavior of both the second-harmonic generation signal and the poling current for type-II fused silica samples under a variety of poling histories are reported. The applied voltage was switched between +5 kV, 0 V, and −5 kV with the sample maintained at 275°C. Observations include: multiple time scales (seconds to minutes) for development of the non-linearity depending on the poling history; a transient second-harmonic signal on the new cathode side of the sample following voltage reversal; and hysteretic incubation intervals before growth of the non-linearity. These observations are incompatible with the usual single mobile ion (e.g. Na+) model for establishing the strong local electric field that leads to the non-linearity. An expanded model including ion-exchange between a high mobility ion (as Na+) and a much lower mobility ion (related to H+) provides a good qualitative fit to the experiments.

Static Space Charge and Capacitance for Two‐Blocking Electrodes

Abstract: A one‐dimensional treatment is presented of space‐charge effects in materials having two charge‐blocking electrodes. Especial attention is given to the situation where univalent, mobile charge carriers of only one sign can recombine bimolecularly with fixed charges of opposite sign; however, the case where noncombining charges of both signs are mobile is also included. Space‐charge potential distributions and differential capacitance cannot be obtained explicitly in the general case but have been accurately calculated using a digital computer. Potential vs distance and capacitance curves are presented which illustrate dependence on applied potential, separation of electrodes, and recombination ratio. The results show features often observed experimentally for a wide variety of materials such as photoconductors, semiconductors, and insulators. The treatment is applicable for much higher applied potentials than is the case for the previously considered one blocking electrode situation with charge accumulati...

Space Charge and Electrode Polarization in Glass, II

Abstract: This is Part I of a two-part series on space charge in glass. This part is primarily a review and covers the general nature of the observed phenomena, the relation of these phenomena to usual concepts such as dielectric constant and electrical conduction, and the present understanding of these phenomena in glass. This review serves to describe the background and motivation for the work set forth in Part 11, which is a discussion of recent theory and experiment on space charge in glass. Areas for further investigation also are suggested.

Space‐Charge Development in Glass

Abstract: Data are given that graphically demonstrate space-charge build-up in a glass containing alkali and in a glass relatively free of alkali. The observed potential distributions show a decided asymmetry and have large potential drops near the electrodes with a linear potential change near the center of the sample. The observations qualitatively fit the expected theoretical distributions, according to Proctor and Sutton, for material having cations mobile and anions essentially immobile. Crude estimates arising from comparison with the theory yield carrier concentration near 2 × 1016 per cm3. mobility of the cation near 3 × 10-6 cm.2 per volt second, and diffusion constant near 2 × 10-6 cm.2 per second. These mobility and diffusion values are two orders of magnitude larger than values computed from conductivity data or computed from measurements of the diffusion coefficient for sodium cations, both in simple alkali silicates. According to the theory, these higher values are perhaps reasonable, since they are associated with only the more mobile portion of the cation population.