Ion-induced Electron Emission Research Articles

Nano-scale modification and doping of diamond: interesting science and promising technology

Diamond is a unique material with outstanding physical and chemical properties. Among these are very unusual properties of the diamond surface; i.e., its negative electron affinity when hydrogen terminated (i.e., 'negative work-function') and the p-type 2D electrical conductivity it shows (when exposed to different atmospheres). These make diamond a material of choice for the fundamental study of a variety of electron-emission processes as well as for their application, on the nano-scale, as point cold electron-emission devices and various nano-size electronic devices. The uniqueness of the diamond surface, when hydrogen terminated are discussed. Results on the emission of electrons from diamond induced by an external electric field (field emission) by electron-impact (secondary electron emission) and by ion-impact (ion-induced electron-emission) are reviewed. Modifications of these properties on the nano-scale by single ion-impacts and by localised electric fields (from a STM tip) are demonstrated. Stunning results on huge ion-induced electron emission and their rapid degradation are presented and explained. The possible application of the electron-emission from diamond utilising its 2D surface conductivity and the resulting quantisation are discussed enabling the realisation of low dimensional (line and point) devices including point sources of cold electrons and for nano scale electronic devices.

Monte Carlo simulation of ion-induced secondary electron emission from MgO film

Kinetic electron emission from MgO film under the impact of 50–300 eV rare-gas ions has been investigated by Monte Carlo simulation. The program includes excitation of the target electrons (by projectile ions, recoiling target atoms and fast primary electrons), subsequent transport and escape of these electrons from the target surface. Potential electron yields due to Auger neutralization of various ions are obtained by comparing the calculated kinetic electron yield with the experimental data. The program generates partial yields of the secondary electrons excited by projectile ions, recoiling target atoms and electron cascades. The partial yields of the electrons excited by projectile ions and electron cascades fluctuate with mass of the projectile ion like the electronic stopping. Moreover, lateral and depth distribution of the electrons excited by three excitation processes were quite different. For the range of investigated ion energies, the average electron escape depth was independent of the mass of the incident ion, which indicates that electron escape depth is a material property.

Electronic interaction of very slow light ions in Au: Electronic stopping and electron emission

Electronic stopping and ion-induced electron emission during the interaction of slow $(v<0.1\text{ }\text{a}\text{.u}\text{.})$ ${\text{H}}^{+}$ and ${\text{D}}^{+}$ ions with polycrystalline Au targets have been investigated. Electronic stopping is deduced from time-of-flight low-energy ion scattering measurements in backscattering geometry using polycrystalline films of several nanometers thick. Current measurements are performed to determine the ion-induced electron emission yield. Both in electronic stopping and in ion-induced electron emission we find a rather sharp, distinctive threshold velocity of $\ensuremath{\sim}0.19\text{ }\text{a}\text{.u}\text{.}$ for specific excitation and emission of $5d$ electrons. Below this threshold the projectiles interact exclusively with the $6s$ electrons.

On the mechanism of the negative differential resistance of a Townsend discharge

The effects leading to the falling behavior of the current–voltage characteristic of a Townsend discharge from ‘zero’ current are considered. The conditions investigated correspond to the breakdown of argon at pd ∼ 1 Torr cm. Using a Monte Carlo method for modeling electron multiplication the probability of ion-induced electron emission is extracted from the experimental breakdown data and the initial negative slopes of the current–voltage characteristic are found. This paper shows that two mechanisms provide the existence of the negative differential resistance R1D. One of them is connected to the decrease in the probability of an electron to return to the cathode due to backscattering when increasing the discharge current; this mechanism was discussed before. The other mechanism is a result of non-equilibrium electron motion in a discharge gap. The higher the current and consequently the electric field at the cathode, the earlier an emitted electron acquires the energy necessary for ionization. This leads to an increase in the electron multiplication. Although this non-equilibrium effect is known, it was not considered previously as the possible cause of the appearance of the negative differential resistance. This paper shows that the role of the second mechanism in the formation of the negative differential resistance turns out to be even higher than that of the first one. The calculated R1D values are in good agreement with the experiment.

Effect of the ion current density on the temperature dependences of ion-induced electron emission from carbon-based materials

The effect of ion current density j on the temperature dependences of the ion-induced electron emission yield γ(T) of carbon-based materials (polycrystalline graphite MPG-8, highly oriented pyrolytic graphite UPV-1T, and some glassy carbons) under irradiation by atomic and molecular nitrogen ions with energies of several tens of keV has been experimentally studied. The most significant effect of the density j on the dependences γ(T) is observed for low-temperature glassy carbons.

Exciton Autoionization in Ion-Induced Electron Emission

We report on measurements of electron emission spectra from surfaces of highly oriented pyrolytic graphite (HOPG) excited by 1-5 keV He+ and Li+ which, for He+, exhibit a previously unreported high-energy structure. Through a full quantum dynamic description that allows for the calculation of neutralization and electron-hole pair excitation, we show that these high-energy electrons can arise from autoionization of excitons formed by electron promotion to conduction band states close to the vacuum level. The same calculation explains the observed absence of high-energy excitons for Li+ on HOPG.

A new method of measuring electron emission induced by low energy ions from solids

A newly developed experimental system for measurements of electron emission induced by low energy ions at below low ion flux (105 ions s−1 cm−2) avoiding the fast emission degradation caused by high ion fluxes (usually applied 1010–1013 ions s−1 cm−2) has been established. The method, based on an event-by-event recording of the emitted cluster of electrons for each impinging ion event, overcomes the difficulty of measurement of reliable ion-induced secondary electron emission (IIEE) yield, associated with fast degradation of the electron yield. This method provides not only the average number (γ) of IIEE under a given ionic impact, but actually higher moments of their distribution, which contains more information on the physical processes involved in the IIEE phenomenon. The secondary electron emission coefficients showed a dependence on the kinetic energy of incident argon ions and protons ranging from 1 keV to 10 keV on hydrogenated diamond film surfaces.

10.1007/s11700-008-1009-x

Recently obtained experimental results on sputtering, ion-induced electron emission, elemental composition, structure, and topography of modified surface layers of carbon-based materials (polycrystalline graphites, highly oriented pyrolitic graphite, glassy carbons, et al.) under high-dose ion irradiation are presented and discussed.

Performance of the SIRAD ion electron emission microscope

An axial ion electron emission microscope (IEEM) is now working at the SIRAD irradiation facility of the INFN Laboratories of Legnaro (Italy). The IEEM is used to precisely reconstruct the impact points of single ions, information that may be used to determine the areas of a microelectronic device under test that are sensitive to single event effects (SEE). After describing the setup briefly reviewing its working principles, we show our first time resolved ion induced electron emission images of standard calibration targets. We also discuss a preliminary measurement of ion impact detection efficiency of the IEEM system and the available trigger signals for SEE studies. We finally make an assessment of ion electron emission microscopy at SIRAD and indicate future developments.

Incident-angle dependence of ion-induced electron emission from Al & Co films using swift heavy ion

The interaction of charged particles with solid surfaces leads to ion induced electron emission (IIEE). The study of emission of electrons has been a subject of interest in the field of ion-solid collisions. In the present experiment we have measured electron emission yields for Al and Co targets as a function of angle of incidence in the range 0°–30° using swift heavy ions. We observed that the inverse cosine law is not followed in case of swift heavy ions. The possible reasons for deviation from inverse cosine law are discussed. The aim of this work is to show how the variation of the electron yield with the angle of ion incidence reveals proportionality between the yield and the amount of the energy deposited in the electronic excitation near the target surface.

The effect of crystalline structure on molecular effect in ion-induced electron emission

The results of experimental and theoretical study of the molecular effect in ion-induced electron emission from single crystal and polycrystalline materials are presented. It has been found that the electron emission yield γ 2 under N 2 + bombardment of a single crystal shows a dependence on ion incidence angle θ, which is analogous to the anisotropy of the yield γ 1 under N + impact. The ratio R 2( θ)= γ 2/2 γ 1<1 exhibits, for single crystals, a drastic angular dependence, which was successfully described on the basis of electron sweeping-out mechanism by conjunction of both the sharp channeling at θ< ψ L and the shadowing-caused bell-like pattern at θ> ψ L, the Lindhard angle.

Plasma Density, Electron Temperature, Excited Xenon Density and Ion-Induced Secondary Electron Emission Coefficient for the Vacuum Ultraviolet Luminous Efficiency in an Alternating Current Plasma Display Panel

Plasma Density, Electron Temperature, Excited Xenon Density and Ion-Induced Secondary Electron Emission Coefficient for the Vacuum Ultraviolet Luminous Efficiency in an Alternating Current Plasma Display Panel

Excited xenon density and ion-induced secondary electron emission coefficient for vacuum ultraviolet luminous efficiency in alternating current plasma display panel

It is shown for Xe content ratio of 10% that the excited xenon atom density for the 1s 5 metastable state is 3.0 × 10 12 cm − 3 with a gap distance of 50 μm under a fixed gas pressure of 5.3 × 10 4 Pa in alternating current plasma display panels. It is observed that the VUV emission of 173 nm continues after its peak and lasts much longer than 147 nm emission. We also found that the time of VUV peak emission intensity for higher xenon mole fraction is longer. It is also concluded that the luminous efficiency is strongly dependent on the ion-induced secondary electron emission coefficient.

Neutralization mechanisms in He +–Al surface collisions

From a quantum mechanical calculation where the populations of He ground and first excited states are properly taken into account, we can identify for the first time the neutralization to the He first excited state as an operative mechanism in He +–Al surface collisions. This identification allows us to understand the presence of high energy electrons in the ion induced electron emission spectra, through the inclusion of Auger deexcitation as an electron emission source, as well as to suggest a possible cause for the disagreement still found between theory and experiments in low energy ion scattering (LEIS) for this system.

Study on breakdown characteristics of a low-pressure dielectric barrier discharge

AbstractThe breakdown characteristics of a low-frequency dielectric barrier discharge (DBD) at low pressure are investigated experimentally in He, Ne and Ar. The current waveform of this DBD, a series of pulses, is caused by the results of the electron avalanches under the action of the applied field and the quenching effect of the wall-charge field on the avalanches. Taking into consideration the diffusion loss of the charged particles in the breakdown processes, the experimental investigation and the theoretical analysis of its breakdown characteristics indicate that its breakdown voltage is higher than the calculation by the Paschen law and depends on the filled-gas pressure and the distance between the electrodes, instead of their product. The ion-induced secondary electron emission coefficient and the mean electron energy at the moment of breakdown can also be determined approximately by measuring the breakdown characteristics of the discharge tubes with different distances between the electrodes and combining the theoretical deductions. The experimental results and the theoretical analysis of the breakdown characteristics of this DBD are discussed.

Temperature dependences of the ion-electron emission of glassy carbons under 30-keV argon ion irradiation

The temperature dependences (−200°C < T ≤ 350°C) of the ion-induced electron emission yield γ and the structures of modified surface layers have been studied experimentally for SU-850, SU-1000, SU-1300, SU-2000, and SU-2500 glassy carbons under high-dose 30-keV Ar+ and N 2 + ion irradiation. Glassy carbons manufactured using a relatively high heat-treatment temperature T ht exhibit a stepwise increase in the electron yield at certain annealing temperatures T a. The same behavior is observed for graphitized carbon materials. For low-temperature glassy carbons, the electron yield exhibits a monotonic increase with increasing irradiation temperature. The observed differences are related to the occurrence of different structural types of fullerene-like nanoparticles in the low-and high-temperature glassy carbons.

Correlation between electron and negative O− ion emission during reactive sputtering of oxides

The energy distribution of negative O− ions has been measured during the reactive magnetron sputtering of 13 different target materials by the means of energy resolved mass spectrometry. For the same series of target materials the ion-induced secondary electron emission coefficient was determined in an earlier published research. A correlation between this ion-induced secondary electron emission coefficient and the emission of the high energetic negative O− ions was observed. This correlation should be taken into consideration in the selection of oxides for their high electron emission coefficients as these materials will emit at the same time negative O− ions.

Ion-induced electron emission (IIEE) from undoped and B-doped diamond films induced by 1–10 KeV H + and Ar +

A newly developed experimental system enables measurements of IIEE at a very low ion flux (10 5 ions/s cm 2) avoiding the fast emission degradation caused by high ion fluxes (usually applied 10 10–10 13 ions/s cm 2). The method overcomes the difficulty of measurement of reliable ion-induced secondary electron emission (IIEE) yield, associated with fast degradation of the IIEE yield. We report on the investigation of the IIEE from hydrogenated undoped and B-doped diamond films as a function of (i) moderate heating in vacuum prior to the measurements, (ii) H + and Ar + energy in the range of 1–10 KeV, and (iii) film thickness and microstructure. An IIEE yield ( γ) enhancement was typically detected when the films were heated to 300 °C in vacuum. In the B-doped diamond film heated to 300 °C, γ rose nearly linearly from ∼ 20 to ∼ 100 electrons/ion, for 1 to 10 KeV Ar + ions, respectively. The values of γ obtained with H + showed a more moderate, nonlinear increase from ∼ 8 electrons/ion at 1 KeV up to ∼ 90 electrons/ion at 10 KeV. In heated undoped diamond films of different thicknesses the measured values of γ were similar for all the studied films and somewhat lower than in B-doped film: from ∼ 10–16 to 60–70 electrons per 1 to10 KeV Ar +, respectively, and from 14–26 to 50–60 electrons per 1 to10 KeV H +, respectively. The experimental results were interpreted using TRIM calculations.

Fermi edge singularities in ion-induced electron emission from plane metal surfaces

Auger electron emission – following low energy monoatomic ion impact on metal surfaces – is studied with a many body theory that includes both the band structure and the Fermi singular response of metal electrons (to the sudden neutralization of the projectiles). Application is made to the experimental kinetic energy distributions of electrons ejected from polycrystalline Al by Ar+-projectiles at varying incident energies and angles. Excellent agreement is found between the theory and the measurements.

Differential multi-electron emission induced by swift highly charged gold ions penetrating carbon foils

First results on swift heavy ion induced electron emission from solids obtained with a reaction microscope are presented. This advanced technique, which is successfully used since quite some time to study electron ejection in ion–atom collisions, combines the measurement of the time-of-flight of electrons with imaging techniques. A combination of electric and magnetic fields guides the ejected electrons onto a position sensitive detector, which is capable to accept multiple hits. From position and time-of-flight measurement the full differential emission characteristics of up to 10 electrons per single incoming ion can be extracted. As a first example, we show energy spectra, angular distributions and the multiplicity distribution of electrons from impact of Au24+ (11MeV/u) on a thin carbon foil (28μg/cm2).