Positive Ion Bombardment Research Articles

Emission of negative ions of oxygen during the activation of oxide-coated cathodes

Oxide-coated cathodes have been used as ion sources in a simple mass spectrometer and have been found to emit atomic negative ions of oxygen during their activation at high temperatures (1150-1275° K). A retarding potential at the collector was used to separate the ions emitted by the cathode from the ions formed in the residual gas. Most of the oxygen ions from the cathode arrived at the collector with more energy than they could have obtained from the potential difference across the electron gun, and their number increased as the cathode became more active. The evidence suggests that the ions were formed by dissociation of the oxide coating, then diffused to the surface and were removed by positive ion bombardment. Such a process would leave oxygen vacancies in the oxide which would act as electron donors and increase its electron emission.

Surface properties of vacuum cleaned silicon

Measurement of conductivity, photoconductivity and change in contact potential with light have been made on a sample of floating zone single crystal silicon cleaned by positive ion bombardment and annealed. The absence of a conducting p-film after such treatment has been demonstrated. The annealing after bombardment has been measured as a function of time at various temperatures. Changes in the bulk carrier concentration have been studied after various heating treatments. Changes in conductivity produced by argon ions indicate that in the clean condition the Fermi level is about 0.1–0.2 eV above the valence band edge. Adsorption of atomic hydrogen decreases the conductivity of both heated and bombarded and annealed samples. At the same time Δ CP becomes more negative indicating a downward movement of the energy bands at the surface.

H1−Production by Hydrogen Positive Ion Bombardment of a Tungsten Surface

A study of the energy distribution of the negative ions is described. One-kilovolt ions are used. The double mass spectrograph used allows analysis of both the incoming positive- and outgoing negative-ion beams. Two peaks are studied: a low-energy peak of negative hydrogen ions created by the bombardment of a dirty surface by an assortment of positive ions, and a high-energy peak of negative hydrogen ions created only under bombardment of a surface by ${\mathrm{H}}_{2}^{+}$ and ${\mathrm{H}}_{1}^{+}$. The height of the low-energy peak is found to be proportional to the amount of hydrogen on the surface. The curve has a peak three volts wide at its half-maximum, and a tail 25 volts long on the high self-energy side. The high-energy peak ranges from zero self-energy to a value resulting from a head-on collision between a proton in the incoming ion beam and one of the atoms in the surface. This curve is flat over its whole-energy range, dropping to zero at the low self-energy end independent of incident ion energy. On a clean surface the shape of this curve is independent of target temperature.The shape of the high-energy curve is compared with curves predicted by a random walk-collision theory and a theory based on the loss and gain, due to scattering, of particles in velocity groups. The shape of the low-energy curve is compared with curves predicted by a theory of thermal desorption of ions from a surface coupled with a mechanism for neutralization of ions as they leave the surface.

Study on the Secondary Electron Multiplier TubeI.Secondary Electron Yield for Cu-Be(4%)Surface sby Bombardment of Low Energy Positive Ions

Study on the Secondary Electron Multiplier TubeI.Secondary Electron Yield for Cu-Be(4%)Surface sby Bombardment of Low Energy Positive Ions

Electron Ejection from Metal Targets due to Positive Ion Bombardment

A mass spectromerter has been used for the investigation of secondary electron emission from metal surfaces by the impact of ions. The total yield, the ratio of the number of secondary electrons to the number of incident ions, has been measured for electrons ejected from Pt, Au, Ni, and Mo targets without special cleaning by the ions A+, A++, Kr+, Kr++, and C3H7+ (dissociated from n-butane) with the kinetic energy between 800 to 2500 eV.The total yield increases almost linearly with the increase of ion energy in the range above mentioned.

Pulse Technique for Probe Measurements in Gas Discharges

A pulse technique for making Langmuir probe measurements in gas discharges has been developed. The basic procedure consists in operating the probe 40–50 v negative with respect to the discharge, and pulsing it positive at a repetition rate of 60 cps. The probe current-voltage characteristic during the positive-going pulse is presented on an oscilloscope and the resulting trace is photographed. The phase of the pulse may be varied, so that the method is useful for studying 60 cps ac discharges as well as dc discharges. Positive-ion bombardment while the probe is strongly negative tends to sputter away contamination and make it possible to keep the probe clean while making measurements within one mm of an oxide cathode at 1000°C, despite rapid evolution of contaminants from the cathode. Together with the small size of the probes that can be used, this permits meaningful measurements to be made in the negative glow of an oxide-cathode low-pressure discharge of the fluorescent-lamp type. Measurements on such lamps are described which demonstrate the presence of energetic primary electrons from the cathode as well as secondary electrons in the negative glow.

Errata: “Changes in Trapping Levels of Zinc Sufide Phosphors Resulting from Positive Ion Bombardment” [J. Electrochem. Soc., 106, 213 (March 1959)

not Available.

Changes in Trapping Levels of Zinc Sulfide Phosphors Resulting from Positive Ion Bombardment

Utilizing a decay method which consisted of measuring the amount of visible light emitted by the phosphor 5.0 msec after excitation by weak ultraviolet, studies were made of the changes in trap distribution on the surface of phosphor crystals which previously had been bombarded by Ar+, , and ions. Interpretation of results was limited to first order kinetics.The results showed that bombardment by ions caused an increase in the number of traps at the lowest trapping level, 0.28 ev deep, as well as the creation of new traps at depths slightly greater and slightly less than 0.28 ev. This effect was independent of the ion used for bombardment.In addition, ion bombardment caused new traps to appear at deeper trapping levels: 0.37 ev for Ar+ ion bombardment, 0.38 ev for ion bombardment, and 0.39 ev for ion bombardment. For the latter, the peak in the difference curve is quite sharp and clearly located at 345°K, locating its depth at 0.39 ev. This corresponds to the next trapping level with increasing depth reported in the literature and thus may indicate that this trapping level is caused by the presence of oxygen in phosphors.

Positive-Ion Bombardment of Germanium and Silicon

A very sensitive vacuum microbalance has been used to study the sputtering of germanium and silicon by argon ion bombardment. Current densities of 1 to 12 \ensuremath{\mu}a/${\mathrm{cm}}^{2}$ were used.The rates of sputtering of these materials were observed as a function of ion energy. A sputtering threshold energy of 46 ev was determined for germanium. The bombardment data are discussed in terms of the nature of the target surface. Oxidation data at 3 mm oxygen pressure are offered as evidence of the cleanliness of the bombarded surface. Approximately ${10}^{15}$ argon atoms/${\mathrm{cm}}^{2}$ were trapped or adsorbed by the target during the bombardment process.

Radiation Effect of Positive Ion Bombardment on Glass

Bombardment of a silica-soda-lime glass (nD=1.5246) by more than 5×1016 A+ ions/cm2 with an energy of 33.5 kev reduces the reflection coefficient to 0.36 of its normal value for light of wavelength λ=0.6 μ. The change in reflection coefficient is attributed to the formation of an altered glass layer. For a bombardment by 40-kev A+ ions, the layer has a thickness of 0.095 μ and an effective refractive index of 1.343. The depth of the layer is determined by the ion energy and agrees approximately with the theoretical range of the incident ions. The refractive index of the altered layer is determined by the integrated flux of positive ions and the type of ion. The magnitude of the positive ion flux employed here is shown to be orders of magnitude larger than the flux of primary ``knocked-on'' atoms produced by fast neutron bombardment in a reactor.

Vacuum Ultraviolet Photochemistry. Part IV. NO at 1236 A

Dissociative recombination of NO+ ions with electrons was shown to take place when NO is irradiated with krypton resonance radiation at 1236 A. Application of a dc voltage across the reaction cell produces an increased rate of decomposition by electron or positive ion bombardment of neutral NO molecules.

The Gas-Multiplier: a New Type of Electron Multiplier

I HAVE recently investigated the possibility of using the Townsend electron avalanche process in a gas in a stage-by-stage system to give a highly stable electron-multiplication factor, and have constructed for this purpose a new form of electron-multiplier referred to as a gas-multiplier1. This device is designed to permit electron-multiplication by the Townsend α-process, while restricting the accompanying processes which cause positive feedback by releasing further electrons in the input region. As is well known, the latter processes, particularly photoelectric effects and positive ion bombardment of the cathode, have set an upper limit of about 104 to the gas-amplification which has been practicable in single-stage devices such as proportional counters and gas-filled photoelectric cells, owing to the imminence of breakdown. The gas-multiplier is designed to be free from this limitation, by operating under conditions that are stable for any number of stages.

Deterioration of Luminescent Phosphors under Positive Ion Bombardment

The reduction of cathodoluminescence efficiency of phosphors has been observed after bombarding with H+, H2+, He+, Ne+, N2, and A+ ions having energies from 1 to 25 kev. Detectable deterioration could be observed after a bombardment of less than 10−9 coul/mm2 of ions (5×1011 ions/cm2). The deterioration could be annealed out at temperatures between 450° and 700°C. Results indicate that light 25-kev ions probably penetrate 0.1μ to 0.2μ into the phosphor.

Desorption of gas in the cold cathode ionization gauge

In this work desorption of gas in the cold cathode ionization gauge by positive ion bombardment has been studied. Mass spectrometer measurements have shown an interesting exchange process to take place at the cathode of the gauge. Incident ions with an energy of the order of 1000 eV drive off molecules already trapped at the surface and are themselves adsorbed. In addition to a careful study of this phenomenon a further clean-up mechanism has been noticed, in which gas is held in the interior of the electrodes. These two clean-up reactions take place simultaneously. These phenomena are probably not confined to the cold cathode ionization gauge but take place whenever surfaces are exposed to ion bombardment and are therefore of fairly general interest.

Ionic bombardment heating of magnetron cathodes

A novel method of heating thermionic cathodes in transverse electric and magnetic fields is described. Hydrogen at an accurately controlled pressure is admitted into the vacuum envelope from a hybride replenisher (consisting of an indirectly heated nickel pellet coated with a suspension of zirconium hydride). Following the initiation of a low-pressure gas discharge in the interelectrode space, the cathode is heated by positive ion bombardment until it reaches the temperature required for thermionic electron emission. The hydrogen is then reabsorbed by the replenisher and high-vacuum conditions are restored, while the cathode is maintained hot by electron back-bombardment alone. Following a section dealing with physical phenomena, practical applications of the method are discussed, such as the processing and starting of oxide-coated as well as high-temperature magnetron cathodes.

Secondary Emission by Positive Ion Bombardment

Secondary Emission by Positive Ion Bombardment

Secondary Emission from Nichrome V, CuBe, and AgMg Alloy Targets Due to Positive Ion Bombardment

A mass spectrometer ion collector system has been devised for the investigation of secondary electron emission by impact of ions on surfaces. Results are reported for various ions incident on clean, baked (but not atomically clean) surfaces of AgMg, CuBe, and Nichrome V targets. For rare gas isotopic ions it is found that for a given energy ion the value of γ varies approximately inversely with the square root of the mass.

Fast Time Analysis of Intermittent Point-to-Plane Corona in Air. III. The Negative Point Trichel Pulse Corona

Fast oscilloscopic time analysis of the negative point Trichel pulse corona in room air at various pressures and gap geometries reveals the following data. The very short rise and quenching time of the pulse at atmospheric pressure observed by English is confirmed. Under these conditions the secondary action is a photoelectric liberation from the cathode and discharge extinguishes by dissociative attachment to give O− ions. Decreasing pressures reduces space charge density, prolongs the discharge and brings in a secondary liberation by positive ion bombardment. Increasing potential at constant pressure at first decreases clearing time, leaving pulses unchanged and current increases proportional to repeat rate. At higher potentials, photon action is reduced relative to positive ion impact at the cathode, the discharge extends further into the gap, and quenching is very effective with less total ions reducing pulse size. With increasing repeat rate, current no longer increases proportional to repeat rate in consequence of smaller pulse height. The effects of increased point diameter are increased pulse size. Comparable clearing times for large and small points require higher potentials for the former. Thus, at constant pressure and potential, increase in point radius produces a decrease in frequency and increase in total charge per pulse. Conditioning of the point at high-current densities and repeat rates decreases the number of ions per pulse, which is of the order of 109 under normal circumstances, and shortens the pulse by reducing cathode work function and increasing photoelectric liberation, so that choking occurs with little ion action. Since repeat rate is slightly decreased by the charge liberation, the reduced pulse charge yields a reduced current through a conditioning that decreases work function. Comparison of ion movement across the gap during clearing time, with that for O2+ ions of known mobility in air, indicates that the rapid ion transit in Trichel pulses is caused by a majority of O− ions with a mobility of about 4 cm2/volts second from near the cathode with some formation of O2− ions in transit.

Formative Time Lags of Uniform Field Breakdown in Argon

The nature of the uniform field breakdown in argon has been investigated by measuring the formative time lags of breakdown as a function of overvoltage (from about 5 to 100 percent), pressure (150- to 700-mm Hg) and electrode separation (0.3 to 3.0 cm). Formative time lags in argon at a given percent overvoltage are very long compared to the values previously obtained in air and nitrogen. For most values of pressure and electrode separation studied in argon, an overvoltage of 100 percent must be applied before the time lags decrease to the order of 1\ensuremath{\mu}sec. The results in argon (like those in air and nitrogen) indicate a Townsend buildup before breakdown. For the range of variables studied in argon, the data cannot be accounted for satisfactorily by buildup as a result of metastable action at the cathode, positive ion bombardment of the cathode, or photoelectric emission from the cathode by photons crossing the gap with a velocity close to $c$. There is a possibility that the results may be explained by a photoelectric effect at the cathode if delays are introduced due to the diffusion of resonance radiation; this conjecture remains to be verified. At this time the positive identification of the effective secondary mechanism in the breakdown of argon cannot be made. The present results indicate the universality of the Townsend buildup before breakdown, but the buildup may proceed by different mechanisms in different gases.

Secondary Electron Emission from Metals under Positive Ion Bombardment in High Extractive Fields

In the further study of breakdown mechanisms in high vacuum, experiments show that secondary electron emission from metals under positive hydrogen ion bombardment is small and increases only slowly with the electric field strength at the bombarded surface. Although more significant emission may yet be found with the heavier ions obtained in an actual vacuum gap, the particle interchange component of the breakdown process appears to be quantitatively inadequate on the basis of present measured electron and positive ion emission coefficients. The possible importance of negative ion emission deserves consideration in the particle exchange process.