Exoelectron Research Articles

Explosive desorption from solid methane and methane-containing argon matrices

The total yield of emitted particles from solid CH4 and Ar matrices doped with CH4 was studied under irradiation with electrons. The explosive desorption was detected for these systems. Strong bursts of particles were delayed with respect to the start of irradiation indicating the need for accumulation of radiolysis products. The study was performed using optical and current spectroscopy – cathodoluminescence (CL) together with thermally stimulated exoelectron emission (TSEE) and thermally stimulated post-desorption (TSpD). In the CL spectra, the products of radiation-induced transformation of CH4 molecules were recorded: H, CH, C. Dose dependencies of the optical emissions were measured in a correlated manner with the total yield of particles. It was found that the particles burst correlates with an increase in the concentration of H atoms. Scenario suggested for the delayed particle emission incorporates the recombination of CH3 radicals appearing simultaneously with H atoms in the reaction CH4 → CH3 + H.

Effect of gamma radiation on thermostimulated exoelectron emission from Gd2O3 films

The effect of gamma irradiation on Gd2O3 films was studied using the thermostimulated exoelectron emission (TSEE) technique. The films were deposited on a glass and Si/SiO2 substrates using an extraction-pyrolytic method. Crystalline structure, chemical composition, film thickness and surface morphology were characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The films were irradiated by 10 MeV gamma photons and TSEE was measured from the irradiated films. It was found that gamma irradiation decreases TSEE intensity and the area below TSEE spectral curves. A linear correlation between the relative decrease in the area and the delivered dose was observed in a dose range of 0–10 Gy. These findings suggest that gamma radiation might decrease the density of trapped electrons present in the as-grown Gd2O3 films or create competing electron traps that inhibit TSEE from the films.

Electron-induced delayed desorption of solid argon doped with methane

The total yield of particles desorption from solid Ar doped with CH4 under irradiation with an electron beam was studied at 5 K. The measurements were carried out at a CH4 concentration of 1 and 5%. The effect of explosive delayed desorption from the surface of argon matrix was discovered in both mixtures. With a higher concentration of CH4, it appeared at lower doses and was more pronounced. Two types of self-oscillations were observed: long-period bursts (on a time scale of about 25 min) and short-period oscillations (of about 10 s). In pure solid Ar delayed desorption was not observed despite the accumulation of a significant number of excess electrons, exceeding their number in mixtures of Ar and CH4 as it was found by measurements of thermally stimulated exoelectron emission. This finding discards the model of Coulomb explosion for the phenomenon detected. In this paper we focused on the role of hydrogen (one of the radiolysis products) in delayed desorption. The formation of atomic hydrogen in the matrix was traced via cathodoluminescence by the emission band of the excimer Ar2H* at 166 nm. Desorption of excited hydrogen atoms in the excited state was detected by the Ly-α emission line. A decrease of the Ar2H* band intensity at higher concentration of CH4 was found evidencing bleaching these centers likely due to recombination of H atoms with energy release and formation of molecular hydrogen. The data obtained give additional evidence in favor of the hypothesis that the exothermic reactions of radiolysis products serve as a stimulating factor for delayed desorption.

Effects induced by electron beam in methane ices

The radiation effects and relaxation processes in solid CH4 irradiated by an electron beam were studied with a focus on the beam-induced particle emission. The study was performed using cathodoluminescence (CL), monitoring of the total yield of particle emission and applying activation spectroscopy technique – thermally stimulated exoelectron emission (TSEE). Emissions of photons and particles under beam were monitored in a correlated style. Upon irradiation by 1 keV electron beam of 3 mA cm−2 current density we observed for the first time explosive particle emission which occurred with the delay of an hour with respect to the start of irradiation. Simultaneously with the particles outburst a CL flash was detected. Delay in the giant outburst of particles indicates the need for the accumulation of radiolysis products for this phenomenon. The critical dose for this effect is 100 eV per methane molecule. The outburst of particles is preceded by oscillations of particles emission with increasing amplitude. The period of these oscillations depends on the intensity of the irradiation, it decreases with an increase in the beam current density. Possible mechanisms of low-temperature explosive particle emission are discussed.

Relaxation processes in solid methane pre-irradiated with an electron beam

Abstract The relaxation processes in CH4 solids irradiated by an electron beam were studied with a focus on post-irradiation phenomena. Because of absence of thermally stimulated luminescence (TSL) from pure solid methane we applied current activation spectroscopy method – thermally stimulated exoelectron emission (TSEE). Two broad features were detected near 18 and 43 K. Their relative intensity appeared to depend on irradiation time. The experiments performed with a variable voltage applied to an electrode for current detection first revealed significant accumulation of uncompensated negative charge in pre-irradiated methane films. The TSEE current was detected at negative voltages up to −35 V. Concurrently with thermally stimulated yield of electrons the total yield of thermally stimulated post-desorption (TSpD) from pre-irradiated solid methane film was detected. Correlation of TSEE and TSpD yields is discussed and compared with the temperature behavior of solid methane subjected to a neutron flux.

Evaluation of the thermally and optically stimulated response of an Italian Obsidian irradiated in 60Co beams

From Obsidian silicate, in its natural form, pellets were manufactured adding Teflon to the material in powder. These pellets were exposed to the gamma radiation beams of a 60Co source in a dose interval from 10 Gy to 10 kGy. The Obsidian in powder was investigated in relation to its physical and chemical characteristics, by means of the X-ray diffraction, scanning electronic microscopy and energy-dispersive X-ray spectroscopy techniques. After the irradiation procedure, the signal of the samples was evaluated by means of three techniques: thermoluminescence (TL), optically stimulated luminescence (OSL) and thermally stimulated exoelectron emission (TSEE). The objective of this work was to verify the TL, OSL and TSEE response of the Obsidian+Teflon pellets after exposure to high doses of gamma radiation. Different response characterization tests were performed, as TL and TSEE emission curves, OSL signal decay, reproducibility, dose-response curves, lower detection limits and fading. From these results, it can be observed that the Obsidian+Teflon pellets present good conditions to be used as high dose gamma radiation detectors; the results obtained with the OSL technique were the most adequate in terms of response in function of absorbed dose. The fading of the signals, varying from about 26% (TSEE) to 44% (OSL), in a time interval of 360 h post-irradiation, also showed favorable results for the use of this material as radiation detector, when the measurements are taken after a defined time interval.

Apparatus for measurements of thermal and optical stimulated exo-electron emission and luminescence

The purpose of the design, construction and implementation of vacuum apparatus for measuring simultaneously three or more stimulated phenomena in dielectrics and eventually semiconductors is to investigate those phenomena as a function of temperature and wavelength. The test of equipment and its functionality were carried out step by step (apparatus, components and control sample) and associated with the calculation of the main physical parameters. The tests of individual parts of the apparatus clearly confirmed that the design, construction and selected components fulfil or even exceed the required properties. On the basis of the measurement of selected sample, it was shown that even weak signals from the material can be detected from both thermally stimulated luminescence and thermally stimulated exo-electron emission moreover transmission and desorption can be measured. NaCl:Ni (0.2%) was chosen as the test material. The activation energies and frequency factor were calculated using the methods of different authors.

Radiation effects in nitrogen and methane “ices”

Abstract The radiation effects and relaxation processes in N2 and CH4 solids irradiated by an electron beam were studied with a focus on post-irradiation phenomena. The study was performed using optical and current spectroscopy methods: cathodoluminescence (CL) and developed by our group nonstationary luminescence (NSL) as well as nonstationary desorption (NSD) methods, together with activation spectroscopy techniques – spectrally resolved thermally stimulated luminescence (TSL), and thermally and photostimulated exoelectron emission (TSEE/PSEE). An afteremission of electrons was observed from N2 and CH4 solids pointing to an electrostatic charging of both films. The PSEE and TSEE from methane films were detected for the first time demonstrating important role of charge centers in radiation effects. Formation of negatively charged ions in methane by electron attachment was verified via PSEE followed by TSEE. Possible scenarios of N4+ and N3+ neutralization via dissociative recombination are discussed and data indicating space distribution of these centers are presented.

Exo-Electron Emission From MgO Nanopowders on MgO Thin Film of Alternating Current Plasma Display Panels—Part I. Mechanism of Exo-Electron Emission

Exo-electron emission from MgO nanopowders sprayed on MgO thin film of alternating current plasma display panels was measured experimentally. Effects of several key parameters including panel temperature on the emission currents were measured and compared with a thermostimulated exo-electron emission model with three energy levels proposed in this paper. The results indicate that the exo-electron emission phenomenon is controlled by a thermal excitation of trapped electrons at shallow levels, ~0.2 ~ 0.3 eV below the conduction band edge. The MgO nanopowders increases the emission current significantly over the MgO thin film, possibly due to a higher concentration of recombination centers at deeper energy levels.

Exo-Electron Emission From MgO Nanopowders on MgO Thin Film of Alternating Current Plasma Display Panels—Part II. Relationship Between Exo-Electron Currents and Statistical Delay

The relationship between exo-electron currents and statistical delay is examined at the pixels of alternating currents plasma display panels. The delay was described using a reciprocal function of exo-electron emission current, irrespective of MgO nanopowder coating on MgO thin film. Shorter discharge delays in a panel with MgO nanopowder coating is mainly due to increased exo-electron currents associated with the coating. Dependence of the delays on panel temperature is examined as well in this paper.

Applying the TSEE technique to Spectrolite and Opal pellets irradiated with high doses of gamma radiation

Spectrolite + Teflon and Opal + Teflon pellets were studied in this work in relation to their dosimetric properties, using the thermally stimulated exoelectron emission (TSEE) phenomenon. The purpose of this work was to study these materials to be used in high-dose dosimetry of 60Co irradiators, which are employed for several industrial applications. The basic physical principle of this technique is the emission of low energy electrons from the surface of different crystals. For this reason, it is very employed in work with specially radiation sources of low penetrating power, as alpha and beta radiation, but also with gamma sources. Both materials had already their dosimetric chatacteristics verified in previous works after exposure to high doses of a 60Co source and measurements by means of thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques. The TSEE response was investigated in terms of the following tests: TSEE emission curves, reproducibility, minimum detectable doses and dose-response curves.

Visible light effects in plasma plume ignition

The breakdown delay time of a closed plasma plume excited by a high-voltage pulse is investigated. The visible monochromatic light of 404, 532, and 662 nm wavelength and narrow-waveband light at a central wavelength of 400, 430, 450, 470, 500, 530, 570, 610, and 630 nm are used to pre-ionize the gas. It is found that the breakdown delay time decreases when the visible light illuminates the discharge tube. The light is most effective when it is applied at the position near the high-voltage electrode. Besides, the tube material and size are important for enhancing the effect. The jet using quartz tube and larger inner diameter make the effect stronger. The effect of visible light is found to inversely relate to the wavelength, manifested by the longer breakdown delay times for longer wavelengths. With increasing the frequency and the pulse width of the voltage, the visible light shortens the delay time more effectively. These observations can be explained by the visible light-enhanced generation of free electrons before the ignition. The proposed mechanisms of free-electron generation are the optically stimulated exoelectron emission from the inner surface of the discharge tube wall and the vibrational excitation of nitrogen molecules. The effects of visible light weaken with the addition of oxygen as a result of electron affinity to oxygen.

Analysis on electron emission characteristics of MgO layer with MgO crystal powder under various panel temperatures in ac-plasma display panels

ABSTRACTThis paper examines the electron emission characteristics of the MgO layer in the case of spraying the MgO crystal powders based on the two monitoring parameters such as the electric field strength and the panel temperature. In particular, in order to analyze the effects of the electric field strength on the electron emission characteristics of the MgO layer with MgO crystal powders, the variations in the wall voltage induced by the electron emission are measured relative to the electric field strength between the address-sustain electrodes during an address period under various panel temperature conditions ranging from −5 to 65°C. As a result, it is observed that the electron emission characteristics of the MgO layer with MgO crystal powder strongly depend on the electric field strength rather than the thermal effect of exo-electron emission, which is confirmed by the measurement result of the wall voltage variation relative to the electric field strength under the low panel temperature of −5°C.

Excitation-induced processes in model molecular solid – N2

Recent findings on electronically induced processes in N2 molecular solids monitored by luminescence methods are presented with a focus on the electronically induced desorption. Low-energy electron beam was used for excitation to avoid the knock-on defect formation and sputtering. The samples were probed with depth by varying electron energy. VUV photon emissions from desorbing N* atoms (the 4P1/2–5/2→4S3/2 transitions) under irradiation by electrons of subthreshold energy were observed for the first time. Their distinctive feature is a coincidence with the gas phase lines within the experimental error. New data on electronically stimulated desorption of N2* molecules in the electronic excited state C3Πu are reported. Monitoring of nonstationary desorption NsD in combination with the detection of thermally stimulated exoelectron emission TSEE and post-desorption reveal the contribution of charge recombination reactions in the electronically induced particles ejection. Fresh approach to study of electronically induced desorption opens new type of greatly delayed desorption associated with the entry of freeing electrons in recombination process.

Radiation-induced defects, energy storage and release in nitrogen solids

New trends in the study of radiation effects in nitrogen solids with a focus on the defect-induced processes are presented. An electron beam of subthreshold energy was used to generate radiation defects via electronic subsystem. Experimental techniques developed enabled us to detect neutral and charged defects of both signs. Defect production and desorption were monitored using optical and current emission spectroscopy: cathodoluminescence CL, thermally stimulated luminescence TSL and exoelectron emission TSEE along with the detection of postdesorption. Our results show stabilization and accumulation of radiation defects – ionic centres of both signs (N4+, N3+, N3-), trapped electrons and radicals (N, N3). The neutralization reactions: N4++e-→N4*→N2*(a‘1Σu-)+N2*(a‘1Σu-) +ΔE1 →N2 +N2 +2hν+ΔE2 and N3++e-→N*(2D)+N2(1Σg+)+ΔE3→N(4S)+N2(1Σg+)+hγ+ΔE3 are shown to be the basis of defect production and anomalous low-temperature post-desorption ALTpD. The part played by pre-existing and radiation-induced defects in energy storage is discussed.

Radiation Effects in Solid Nitrogen

The radiation effects and relaxation processes in pre-irradiated by an electron beam solid $$\hbox {N}_{2}$$ have been studied with a focus on the behavior of the so far unidentified emission band at 360 nm. The study was performed using optical and current spectroscopy methods: cathodoluminescence and developed by our group nonstationary luminescence, as well as spectrally resolved thermally stimulated luminescence, and thermally stimulated exoelectron emission. The measurements cover the temperature range of the $$\alpha $$ -phase existence. Activation spectroscopy evidenced connection of the 360 nm band with the neutralization reaction. Possible scenarios of $$\hbox {N}_{4}^{+}$$ neutralization via dissociative recombination are discussed, and interpretation of the 360 nm band is suggested.

Defect states in amorphous SiNx:H compounds using thermally stimulated exo-electron emission

Defect states of hydrogenated amorphous silicon nitride (a-SiNx:H) thin films were measured using the thermally stimulated exoelectron emission spectroscopic method. The defect states of films with nitrogen to silicon composition ratios (x) of 0.92, 1.21, and 1.44 were found to be located 1.66, 1.77, and 1.82eV below the conduction band minimum, respectively.We confirmed that the hydrogen concentration decreased as x was increased via an elastic recoil detection analysis experiment, while as the hydrogen concentration increased, the defect concentration decreased. From these results, we concluded that the defect centers could be related to dangling bonds, the so-called K centers, in silicon nitride. Furthermore, as the concentration of SiH was increased with decreasing x via the infrared spectroscopy, the defect density was reduced through the defect passivation.

Defect‐induced electrostatic charging of nitrogen films

Electrostatic charging of nanostructured N2 films was studied employing optical and a current set of emission spectroscopy methods: cathodoluminescence CL, thermally and photon‐stimulated exoelectron emission TSEE, PSEE as well as thermally and photon‐stimulated luminescence TSL, PSL. Concurrently with thermally stimulated yield of electrons the yield of nitrogen particles was detected, so‐called “postdesorption.” An enhancement of the optical emission stemmed from the neutralization reaction N4+ + e → N2* + N2* → N2 + N2 + hν was observed with an exposure to an electron beam. The experiments performed with a variable voltage applied to an electrode for current detection demonstrated significant accumulation of negative charge. The TSEE current in the low‐temperature range was detected at negative voltages up to −30 V. An accumulation of trapped electrons (up to 1016 cm−3) was detected. A possible contribution of N3− in electrostatic charging was assumed.Thermally stimulated yield of negatively charged particles from a N2 film subjected to an electron beam.

Emission spectroscopy of solid nitrogen

Monitoring of the cathodoluminescence spectra temporal evolution and concurrent measurements of optical and current relaxation emissions revealed stabilization and accumulation of the radiation-induced charged species. New results in favor of hole self-trapping with the tetranitrogen cation N4+ formation are presented. “Fingerprints” of N3− species are detected by the photon-stimulated exoelectron emission.

Estimation of tension of the surface layer of parts after hardening by different methods of surface plastic deformation

A method of control of shot impact methods of surface plastic deformation is presented in the paper. The possibility of controlling the hardening process of parts made of titanic alloys in terms of deflection of plates made of carbon steels is shown. Because of differences in the resilient and plastic properties of materials and as they show different tendencies to hardening their deformation will occur with different speed and intensity over time. In the case of the greatest deflection of the testplate it may not be up to the required degree of hardening of the part made of another material. Cases of insufficient hardening or rehardening of the part’s surface layer may occur in controlling the hardening on plates made of U8A steel. One of the indices of the surface layer is its energy level, therefore the intensity of exoelectronic emission of the surface of the part treated can be used as a criterion of estimation of the stress-strain state of the surface layer. Non-destructive testing of hardening and finishing of the surface layer can be accomplished comparing the part tested with the reference standard.