Photostimulated Exoelectron Emission Research Articles

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.

METAL SURFACE LAYER ADHESION DESTRUCTION AT TOOL-METAL TORSION CONTACT

Adhesive interaction of metal products with a tool inherent in the process of metal forming. Defects on the products and tools out of the order are the consequences of this. The problem of the choice of material for the instrument has been considered. On the example of mandrel tube drawing mechanism of fracture of adhesive fracture surface layer of metal has been described. Based on an analysis of the solids adhesion hypothesized that the adhesive activity is associated with the electron work function of the material tools. By method of photo-stimulated exoelectron emission electron work function for a number of ceramic materials has been determined. The relationship between the electron work function of the material and surface roughness of workpiece was detected. Criterion for selecting the tool material is formulated and a method of tube drawing fundamentally new quality has been developed.

Optically stimulated exoelectron emission processes in quartz: comparison of experiment and theory

Recent experiments have demonstrated that it is possible to measure optically stimulated exoelectron emission (OSE) signals simultaneously with optically stimulated luminescence (OSL) from quartz samples. These experiments provide valuable information on the charge movement in quartz grains. Two specific experiments measured the temperature dependence of the OSL and OSE signals on preheat and stimulation temperature. This paper provides a quantitative description of these experiments by using a previously published theoretical model for photostimulated exoelectron emission (PSEE). The experimental data yield a value of χ∼1.2 eV for the work function of quartz. The experimental temperature dependence of the OSE signals is interpreted on the basis of a photo-thermostimulated (PTSEE) process involving the main OSL trap at ∼320 °C; this process takes place with a thermal assistance energy estimated at W∼(0.29±0.02) eV. Good quantitative agreement is obtained between theory and experiment by assuming a thermal broadening of the thermal depletion factor for the OSL traps, described by a Gaussian distribution of energies.

Photostimulated exoelectron emission in single crystals of anion‐defective α‐Al 2 O 3 exposed to electrons

In this study methods of exoemission analysis were used to examine main regular features of light and thermally stimulated processes in the near-surface layer of α-Al 2 O 3 crystals excited by electron radiation. The examination by methods of exoelectron spectroscopy showed that if the density of excitations in near-surface layers of α-Al 2 O 3 crystals is large, which is the case with pulsed high-current electron beams, an interactive interaction of trapping centers may show itself in the kinetics of the temperature relaxation of PSEE.

Kinetic modeling of the photo-stimulated exoelectron emission

The phenomenological theories of the non-stationary photostimulated exoelectron emission are demonstrated and described in terms of a kinetic theory close to a luminescence theory. The theory described is shown to be capable of yielding excellent fits to the experimental data and explaining the basic experimental evidence.

SURFACE AND VOLUME CRYSTALLIZATION OF METALLIC GLASS (Ni50Zr50)99.9P0.1 AS INVESTIGATED BY EXOELECTRON EMISSION (EEE) AND DIFFERENTIAL THERMAL ANALYSIS (DTA)

Surface and volume crystallization of amorphous, melt-quenched (Ni50Zr50)99.9P0.1 alloy has been investigated by measurements of the temperature dependencies of the intensity of photostimulated exoelectron emission (EEE) and by differential scanning calorimetry (DSC). A comparison of these dependencies enables one to assess the tendency of the investigated materials to premature surface crystallization. For the (Ni50Zr50)99.9P0.1 alloy the surface crystallization occurs at temperatures distinctly lower than that for the crystallization in bulk. The activation energy for the surface crystallization, determined by the Ozawa method, i.e. from the shift of EEE peak corresponding to the surface crystallization on changing the heating rate, is also much lower than that for the volume crystallization.

The Experimental Criteria for Distinguishing Different Types of Exoelectron Emission Mechanisms

On the basis of classification of exoelectron emission (EE) mechanisms we have proposed some experimental criteria for distinguishing these mechanisms: Bulk–surface criteria and the photon and low-energy electron excitation criterion. To illustrate the application of these criteria we have measured the influence of the precipation procedure on thermostimulated EE (TSEE) of CaSO4 : Mn and the dependence of the TSEE and photostimulated EE (PSEE) intensity of CaSO4 and MgO on exciting electron and photon energy.

The Experimental Criteria for Distinguishing Different Types of Exoelectron Emission Mechanisms

On the basis of classification of exoelectron emission (EE) mechanisms we have proposed some experimental criteria for distinguishing these mechanisms: Bulk–surface criteria and the photon and low-energy electron excitation criterion. To illustrate the application of these criteria we have measured the influence of the precipation procedure on thermostimulated EE (TSEE) of CaSO4 : Mn and the dependence of the TSEE and photostimulated EE (PSEE) intensity of CaSO4 and MgO on exciting electron and photon energy.

Phase transitions in some n-alkanes and petroleum waxes — investigation by photoacoustic and exoelectron emission techniques

The use of the photoacoustic (PA) effect and photostimulated exoelectron emission (EEE) technique in the investigation of first- and second-order phase transitions in pure n-alkanes such as n-C 22, n-C 28 and n-C 32 and in three petroleum waxes having different carbon number distributions, have been examined. Changes in the amplitude and phase of the PA signal with temperature and the temperature dependence of the intensity of photostimulated EEE across the phase transitions have been measured. These measurements have shown that both the polymorphic phase transitions and melting of these hydrocarbons are accompanied by jumps or peaks of the PA amplitude and phase and EEE intensity, thus enabling the detection of the solid–solid and solid–liquid phase transitions. These results are further confirmed by a comparison with those obtained by differential thermal analysis (DTA) control measurements performed at the same heating and/or cooling rate. The PA and EEE results thus obtained are discussed in the light of phase transition temperatures obtained from other techniques.

切削加工に伴うエキソ電子放射挙動に関する研究

A radiation of the electron called exoelectron from the machined surface is observed with less energy than usual work function, and it is known that this phenomenon is sensible to changes of crystal structure and surface structure. This paper describes the result of examining the possibility of photo stimulated exoelectron emission as a method of the process monitoring and surface evaluation. As a result of cutting experiment in vacuum atmosphere, it is confirmed that electron emission is observed during the distruction of materials and that there is a relationship between cutting conditions and emission behavior on the machined surface. These results show the possibility of exoelectron emission for new method of process monitoring and surface evaluation.

Field emission theory of dislocation-sensitized photo-stimulated exo-electron emission from coloured alkali halide crystals

A new field emission theory of dislocation-sensitized photo-stimulated exo-electron emission (DSPEE) is proposed, which shows that the increase in the intensity of photo emission fromF-centres during plastic deformation is caused by the appearance of an electric field which draws excited electrons out of the deeper layer and, therefore, increases the number of electrons which reach the surface. The theory of DSPEE shows that the variation of DSPEE flux intensity should obey the following relation $$\frac{{\Delta J_e \left( \varepsilon \right)}}{{J_e \left( o \right)}} = \left[ {\frac{{Y_s }}{{d_F }}\exp \left( {\frac{\chi }{{kT}}} \right) - 1} \right]$$ . The theory of DSPEE is able to explain several experimental observations like linear increase of DSPEE intensityJ e with the strain at low deformation, occurrence of the saturation inJ e at higher deformation, temperature dependence ofJ e, linear dependence ofJ e on the electric field strength, the order of the critical strain at which saturation occurs inJ e, and the ratio of the PEE intensity of deformed and undeformed crystals. At lower values of the strain, some of the excited electrons are captured by surface traps, where the deformation generated electric field is not able to cause the exo-emission. At larger deformation (in between 2% and 3%) of the crystal, the deformation-generated electric field becomes sufficient to cause an additional exo-electron emission of the electrons trapped in surface traps, and therefore,t here appears a hump in theJ e versuse curves of the crystals.

Tribo- and photo-stimulated exoelectron emission from graphite

Tribo- and photo-stimuated exoelectron emission from reactor graphite has been investigated, because an increase in tribo-stimulated exoelectron emission from graphite signifies large friction. Selective deformation of graphite fibrils was identified with transmission electron microscopy. The exothermic process during the preferred orientation caused emission of tribo-stimulated electrons. Photo-stimulated exoelectron emission from reactor graphite was also detected. However, the mechanisms of photo-stimulated exoelectron emission were different from that of tribo-stimulated exoelectron emission, and photo-stimulated exoelectron emission does not relate to a change in tribological characteristics.

Distribution of trap levels in field stimulated exoelectron emission

Trap levels of exoelectrons in high purity aluminum were estimated from the emission properties of field stimulated exoelectrons. The trap level of exoelectron in 99.9999% pure aluminum was found at about 0.2 eV higher than the Fermi level of aluminum and those in less pure aluminum were distributed in a higher energy region. The observed distribution of exoelectron trap levels agrees with the trap level determined by photostimulated exoelectron emission and also explains the glow curves of field stimulated exoelectron emissions from aluminum specimens of different purities.

In situ metal transfer monitoring using photostimulated exoelectron emission

In situ monitoring of metal transfer on various material surfaces has been studied using photostimulated exoelectron emission (PSEE) characteristics of aluminium transfer. The transfers studied were obtained with an aluminium pin sliding on disc surfaces of various ceramics, such as SiC, Si 3N 4, A1 2O 3, ZrO 2, and a polymer of nylon. For each material, the metal transfers were sensitively detected, demonstrating the usefulness of the PSEE technique for in situ monitoring of metal fragments transferred during sliding. The PSEE characteristics of the transfer were influenced by the UV spot size stimulating the electron emission and the intermittent time of the UV illumination. The intensity of the electron emission from the metallic transfer correlated well with the friction coefficient for a small number of repeated sliding traversals. The electron emission intensity increased linearly with increase in repeated sliding traversals.

Thermoluminescent and Exoemission Properties of New High-Sensitivity TLD a-Al2O3:C Crystals

To determine the mechanisms of the electron-hole processes in a-Al2O3:C crystals, characteristics of their thermo- and photo-stimulated exoelectron emission (TSEE, PSEE) and luminescence have been studied. It is shown that the emission of F+ centres takes place with the temperature shift relative to the emission of F centres, and the hole-induced TSEE takes place synchronously with the emission of F centres. The electron energy distribution parameters at PSEE do not depend on the energy of stimulating light photons, which testifies to thermalisation of the released holes before their recombination. Parameters determined for doped anion-deficient corundum crystals are considered within the framework of the two-stage Auger process model.

Thermoluminescent and Exoemission Properties of New High-Sensitivity TLD a-Al2O3:C Crystals

Abstract To determine the mechanisms of the electron-hole processes in a-Al2O3:C crystals, characteristics of their thermo- and photo-stimulated exoelectron emission (TSEE, PSEE) and luminescence have been studied. It is shown that the emission of F+ centres takes place with the temperature shift relative to the emission of F centres, and the hole-induced TSEE takes place synchronously with the emission of F centres. The electron energy distribution parameters at PSEE do not depend on the energy of stimulating light photons, which testifies to thermalisation of the released holes before their recombination. Parameters determined for doped anion-deficient corundum crystals are considered within the framework of the two-stage Auger process model.

Temperature dependences of the contact potential difference relative to platinum and exoelectron emission intensity for metallic glasses Ni73TM5Si10B12

The temperature dependences of the contact potential difference relative to platinum and of the intensity of photostimulated exoelectron emission from metallic glasses Ni73TM5Si10B12(TM = Co, Ni, V, Mn, Cr, Cu) have been investigated. It has been found that although the shapes of the CPD and EEE curves are distinctly different, both of them show anomalies corresponding to the structural transformations in the surface layer of the investigated materials.

Exoelectron emission during polymorphic phase transitions of some ammonium salts

Results of experimental investigations of the photostimulated exoelectron emission (EEE) accompanying polymorphic phase changes in ammonium chloride, ammonium bromide and ammonium iodate are reported for the first time. The temperature-dependences of the intensity of photostimulated EEE from reagent grade powder materials were measured in air at atmospheric pressure, the exoelectrons being detected with an open air point counter with saturated ethanol quenching vapour. The DTA control measurements were performed at the same heating rate, with reagent grade Al2O3 as a reference. A comparison of the results of the EEE and DTA measurements shows clearly that the polymorphic phase transitions of the investigated materials are accompanied by peaks of the EEE intensity, thereby allowing the detection of solid-solid phase transitions in inorganic compounds with the EEE technique.

Exoelectron emission accompanying the phase transformations in some silver salts

Results of experimental investigations of the photostimulated exoelectron emission (EEE) accompanying polymorphic phase changes in silver iodide, silver nitrate and silver sulphate are reported. The measurements of the temperature dependence of the intensity of photostimulated EEE from reagent grade powder materials were performed in air at atmospheric pressure, the exoelectrons being detected with an open air point counter with saturated ethanol quenching vapour. The differential thermal analysis (DTA) control measurements were performed at the same heating rate. A comparison of the results of the EEE and DTA measurements shows clearly that the polymorphic phase transitions in the investigated materials are accompanied by enhancement (peaks) of the EEE intensity. This enables the detection of the solid-solid phase transitions in inorganic compounds to be made by the EEE technique.

Exoelectron emission accompanying the phase transformations in the AgI-type superionic conductors

Results of experimental investigations of the photostimulated exoelectron emission (EEE) accompanying the polymorphic phase changes in some superionic conductors (silver, copper and mercury iodides) are reported for the first time. The measurements of the temperature dependence of the intensity of photostimulated EEE were performed in air at atmospheric pressure, the (exo)electrons being detected with an open air point-counter with saturated ethanol quenching vapour. The DTA control measurements were performed at the same heating and/or cooling rate. A comparison of the results of the EEE and DTA measurements shows clearly that the polymorphic phase transitions and melting of investigated materials are accompanied by an enhancement (peak) of the EEE intensity. This enables the detection of the phase transformations in inorganic compounds by the EEE technique.