Pulsed Electron Beam Irradiation Research Articles

Pulsed electron beam irradiation of vanadium single crystals

Abstract The damage produced by pulsed electron beam irradiation of vanadium single crystals has been studied by the channeling technique and by thin film X-ray analysis. A surface disorder peak and a small dechanneling component was produced by applying electron energy densities below the melting threshold. The structure of the surface disorder was microcrystalline or amorphous and the dechanneling component could be described by small angle boundaries. After melting of the crystal surface to a depth of approximately 2 μm, epitaxial regrowth with a high defect density took place.

Relaxation Processes from Higher Excited States of Self-Trapped Excitons in Condensed Neon

Higher excited states (2p 5 3p) of the atomic-type self-trapped excitons (STE) are produced by a pulsed electron beam irradiation and a subsequent laser pulse excitation in solid and liquid neon. The decay processes from these states are investigated by absorption and luminescence spectra. Luminescence corresponding to 3p →3s transitions in Ne atom and conversion of the atomic-type STE to molecular-type STE are observed. The bubble formation around the molecular-type STE is concluded from the time evolution of absorption spectra after pulsed electron irradiation.

Superconducting Effects in Rapidly Quenched Materials Formed by Ion and Laser Bombardment

ABSTRACTThe application of low temperature ion bombardment and pulsed laser or electron beam irradiation for the production of rapidly quenched superconducting alloys is described and compared with other more conventionally used non-equilibrium techniques. The comparison is based on the identification of the metastable phases produced by their specific electrical and superconducting properties. It is concluded that low temperature heavy ion bombardment is comparable with vapor quenching whereas laser quenching yields results similar to liquid quenching. Finally, the interesting superconducting properties of these rapidly quenched metastable alloys are discussed.

Pulsed electron beam irradiation of ion-implanted copper single crystals

The effect of an intense, pulsed electron beam on high-dose implanted Cu single crystals has been studied. Rutherford backscattering and channeling have been used to obtain the depth concentration profiles and lattice locations of the implanted species (Au, Ag, and Ta) before and after pulsed electron beam irradiation. Channeling and secondary electron microscopy measurements show that the Cu surface melts during pulsed irradiation followed by an epitaxial lattice growth resulting in (i) a redistribution of the implanted species, (ii) some species (e.g., Au and Ag) remaining on lattice sites, and (iii) Ta leaving substitutional sites.

Electron-beam-induced conduction in polyethylene

The electrical conduction in polyethylene induced by the irradiation of the short pulsed electron beam (100-nsec time width) consists of the fast and the slow components. The former is attributed to the carrier transport in the crystalline part and the latter to that in the amorphous part. A logarithmic plot (Scher-Montroll plot) of the slow part of the induced current versus time gives a knee at time Tr, which is thought to be the transit time of the carrier front between electrodes. Simple calculation by the formula μ=L/TrE gives the apparent slow carrier mobility μ of 5.6×10−7 and 3.2×10−7 cm2/V sec for the electron and the hole, respectively, at 343 K under a field E of 1.2 MV/cm for sample thickness L of 12 μm. These apparent slow carrier mobilities are dependent on both the thickness and the field strength. These behaviors are discussed in terms of Scher-Montroll theory on transport in amorphous substances. The activation energy of the mobility is in good agreement with the apparent trap depth obtained from the TSC measurement.

Enhanced Flatband Voltage Recovery in Hardened Thin MOS Capacitors

The short-term recovery of hardened pyrogenic SiO2 MOS capacitors exposed to pulsed electron-beam irradiation was studied as a function of oxide thickness between 200 and 1000 Å. Two sets of samples were studied: one set grown to a single thickness and then etched back to various thicknesses, and the other set grown for different lengths of time to varying thicknesses. In both cases, the recovery time was observed to vary approximately as the fourth power of oxide thickness. This anomalous superlinear dependence of recovery time on the SiO2 thickness agrees with the predictions of the stochastic model of hole transport based on a continuous-time random walk. Combining the highly field activated character of hole transport in SiO2 with the thickness dependence reported here demonstrates that very significant gains in the short-term recovery speed can be made by reducing the oxide thickness and/or increasing the oxide field.

F Center Formation in KCl and KBr Crystals below 4.2 K

The efficiencies of the F center formation, η F , and of the intrinsic luminescence, η L , in KCl and KBr crystals have been studied under the irradiation of a pulsed electron beam at temperatures mainly below 4.2 K. η F at 1.7 K was about 1/5 of that at 4.2 K, while η L was almost a constant value down to 1.7 K, suggesting no change of the efficiency of the V k type relaxation of the self trapped hole. The decrease of η F follows an Arrhenius' equation with a thermal activation energy of ∼2 meV and ∼1 meV in KCl and KBr crystals, respectively. A tentative mechanism of the F center formation is discussed.

Role Transport and Charge Relaxation in Irradiated SiO2 MOS Capacitors

The transient response of SiO2 gate-insulator MOS capacitors to pulsed electron beam irradiation was studied. The radiation-induced flatband voltage shift (Δ VFB) in SiO2 MOS capacitors was measured with a fast C-V technique from 70 μsec to 1000 sec after a 60 krad radiation pulse for temperatures from 80 to 293 K. In complementary experiments, the post-irradiation charge displacement in the MOS capacitors was measured with an integrating picoammeter. By correlating the relaxation of the flatband voltage with integrated current measurements, it was established that the measured response is dominated by hole transport and trapping in the SiO2 film. The temporal and temperature dependences of the hole transport are well described by a stochastic hopping model based on a continuous time random walk (CTRW). The essential feature of the CTRW is that the transport occurs via a carrier hopping (phonon assisted) process between localized sites randomly distributed in the amorphous SiO2. Since the carriers do not require excitation to the band edges in order to be mobilized, the activation energy for conduction (tunneling) is independent of the optical excitation energy.

Color Center Studies in Alkali Halides by Pulsed Electron Beam Irradiation

The formation and decay of color centers in alkali halides have been studied using a pulsed electron beam. The F and V -type bands reach maximum heights in optical density at the end of the radiation pulse. V k and V 1 bands in KBr appear to show the first order decay kinetics; their room temperature life times are 1.3 and 3.8 µsec, respectively. A fraction of F and F ' bands bleach by the annihilation with migrating V k centers. The activation energies for the disappearance of H , V 1 and V k centers in KBr are found to be 0.09, 0.25 and 0.39±0.02 eV, respectively. A fraction of H centers in KCl decays with a temperature independent time constant (∼0.13 µsec) which is due to the tunneling with nearby F centers. In crystals containing U -centers (H - ions) the F band continues to grow for several microseconds after the pulse. Absorption bands which decay with the same time constant as the F band growth have been found at 775 mµ (KBr) and 725 mµ (KCl).