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We fabricated a high-performance InAs/GaSb type-II superlattice infrared detector. The tolerance of various sizes of detector irradiated with 1-MeV electrons was characterized. X-Ray Diffraction (XRD) and Atomic Force Microscope (AFM) measurements demonstrated the high quality of the materials. The response spectrum had a 50% cutoff wavelength of 8.85 μm. Irradiation with 1-MeV electrons caused a significant increase in the dark current density from 2.54 × 10−3 to 2.58 × 10−1 A/cm2 at Vb = –0.03 V. The 1-MeV electron irradiation mainly caused displacements in the device, which had a significant impact on the generation-recombination dark current and surface leakage current.

The crystallization of sputter-deposited substrate-free films of amorphous germanium was induced by electron irradiation at SEM-level energies of less than 20 keV at ambient temperature using an electron probe microanalyzer. Instantaneous crystallization, referred to as explosive crystallization, occurred consistently at 2–20 keV; the threshold of electron fluxes is 1015–1016 m−2 s−1, which is five to six orders of magnitude lower than those at 100 keV reported previously. This process is expected to be advantageous in the production of polycrystalline Ge films since it is rapid, requires little energy, and results in negligible damage to the substrate.

When electrons from a plasma enter a water surface, they collide with the water molecules and lose their energy, eventually becoming hydrated electrons, which are an important species for radical formation in liquid water. Although gas discharge plasmas in contact with water are an easy source of hydrated electrons, their production processes are not clearly understood. In this study, Monte Carlo simulations of electrons in liquid water were performed to investigate the production of a hydrated electron and radical species by low-energy electron irradiation of the water surface from an atmospheric-pressure plasma. The incident electrons were assumed to have a Maxwellian energy distribution with mean electron energy ranging from 1 to 10 eV. The production of hydrated electrons by electron irradiation of 3 eV reached a peak near the gas–liquid interface, and the electrons spread to a depth of approximately 17 nm. OH and H are also generated near the water surface.

Actuation of thin polymeric films via electron irradiation is a promising avenue to realize devices based on strain engineered two-dimensional materials. Complex strain profiles demand a deep understanding of the mechanics of the polymeric layer under electron irradiation; in this article, we report a detailed investigation on electron-induced stress on a poly-methyl-methacrylate (PMMA) thin film material. After an assessment of stress values using a method based on dielectric cantilevers, we directly investigate the lateral shrinkage of PMMA patterns on epitaxial graphene, which reveals a universal behavior, independent of the electron acceleration energy. By knowing the stress-strain curve, we finally estimate an effective Young's modulus of PMMA on top of graphene, which is a relevant parameter for PMMA-based electron-beam lithography and strain engineering applications. Published under license by AIP Publishing.

Molecular dynamics simulations were performed to study the susceptibility of carbon atom displacement under electron irradiation. The mapping of threshold displacement energies at different recoiling directions showed that the energies are very sensitive to the layer configurations and positions of neighboring atoms. Carbon atoms on the top and the bottom layers of few-layer graphene are most vulnerable to irradiation damage due to lack of constraints from the neighboring graphene layers. As indirect experiment evidence, transmission electron microscopy was performed on the edge of folded few-layer graphene, which made it possible to reveal “the inside” and compare irradiation tolerance of atoms at different layers, by using an electron analysis beam for both displacement creation and in situ characterization.

The crystallization behavior of sputter-deposited films of amorphous Si (a-Si) and SiGe alloys (a-SiGe) induced by electron irradiation at room temperature and by thermal annealing was investigated by in situ transmission electron microscopy. On electron irradiation at room temperature, extremely rapid crystallization, so-called explosive crystallization, occurred at a higher electron flux but not at a lower electron flux. On in situ thermal annealing, explosive crystallization occurred preferentially and partially at low temperatures in Ge-rich a-SixGe100−x for x 50. These results indicate that the increase of Si content in a-SiGe prevents the occurrence of explosive crystallization. We previously proposed that explosive crystallization can occur in pristine a-Ge films via the interface of a liquid-like, high-density amorphous state at the growth front. An increase in the instability of this high-density amorphous state caused by the increase of Si in a-SiGe apparently gives rise to the suppression of explosive crystallization.

We have studied the formation of color centers in magnesium aluminate spinel (MgAl2O4) by X-ray and electron irradiations near room temperature (RT). For this purpose, Cu Kα radiation and three electron energies (1.0, 1.4, and 2.5 MeV) were used for variable fluences (up to 4.2 × 1018 cm−2). Off-line UV-visible absorption spectra were recorded at RT as well as at low temperature down to 27 K after electron irradiation. The dependence of the production rate of F centers (oxygen vacancies) on the electron energy yields a threshold displacement energy of 190 ± 10 eV for oxygen atoms at RT, which is much higher than the determinations by molecular-dynamics simulations. Such a discrepancy is discussed on the basis of available migration data of point defects in spinel. Equipartition of F0 and F+ centers, i.e., the neutral (VOx) and singly ionized (VO.) oxygen vacancies, is reached for high electron fluences. Moreover, the evolution of the width of color-center absorption bands versus temperature is interpreted with the classical theory for F centers (neutral halogen vacancies) in alkali halides. The Stokes shifts are deduced from the temperature dependence of the absorption bandwidths of color centers like for alkali halides and alkaline-earth oxides. Finally, isothermal annealing data for long annealing time show a non-zero asymptotic behavior for both F0 and F+ centers. This uncommon behavior is interpreted by charge exchange processes leading to an equilibrium state between those two color centers.

Defects introduced by low fluence arsenic, antimony, erbium, and bismuth ion implantation have been investigated as a function of annealing temperature using deep level transient spectroscopy (DLTS) and Laplace-DLTS. The defects produced by heavy ion implantation are stable up to higher temperatures than those introduced by electron irradiation and low mass ions. This result is attributed to the enhanced defect interactions that take place in the dense collision cascades created by heavy ion implantation. As a consequence, broadened DLTS features are apparent, especially after annealing. Using high energy resolution Laplace-DLTS, the well-known singly charged divacancy and vacancy-donor pair are accompanied by additional apparent defect signals. This shows that Laplace-DLTS is highly sensitive to the type of damage present, and extreme care must be exercised for reliable Arrhenius analysis.

This paper presents a comparative analysis of the structure and photoluminescence (PL) of Si containing dislocations introduced by thermal shock or ion implantation. To study the structure of dislocation cores and their interaction with point defects, we used a high-resolution transmission mode during in situ electron irradiation in the JEM4000EX operating at 400 kV. An appropriate PL spectrum was obtained on dislocated Si after electron irradiation by an external pulse gun operating at 350 kV. This resulted only in an increase in the D2 line intensity that correlated with the formation of metastable interstitial defects on {001}, {111}, and {113} planes near various dislocation cores during in situ electron irradiation, regardless of their types. However, the D1 line relates to a core structure of a shuffle Lomer dislocation consisting of 5/7 atomic rings, which occurs when two shuffle 60° dislocations (so-called S1 type [Pizzagalli et al., Phys. Rev. Lett. 103, 065505 (2009)]) combine with each other in intersecting {111} planes in plastically deformed Si or when an extrinsic Frank partial dislocation transforms into a perfect one in an ion-implanted layer.

Homogeneous films from SiO1.3 (250 nm thick) were deposited on crystalline Si substrates by thermal evaporation of silicon monoxide. A part of the films was further annealed at 700 °C to grow amorphous Si (a-Si) nanoclusters in an oxide matrix, thus producing composite a-Si-SiO1.8 films. Homogeneous as well as composite films were irradiated by 20-MeV electrons at fluences of 7.2 × 1014 and 1.44 × 1015 el/cm2. The film thicknesses and optical constants were explored by spectroscopic ellipsometry. The development of the phase composition of the films caused by the electron-beam irradiation was studied by transmission electron microscopy. The ellipsometric and electron microscopy results have shown that the SiOx films are optically homogeneous and the electron irradiation with a fluence of 7.2 × 1014 el/cm2 has led to small changes in the optical constants and the formation of very small a-Si nanoclusters. The irradiation of the a-Si-SiOx composite films caused a decrease in the effective refractive index a...

The interaction of nitrogen and intrinsic point defects, vacancy (V) and self-interstitial (I), was examined by infrared absorption spectroscopy on the electron irradiated and post-annealed nitrogen doped float zone (FZ) silicon crystal. Various absorption lines were observed, at 551 cm−1 in as-grown samples, at 726 and 778 cm−1 in as-irradiated samples (Ir group), at 689 cm−1 after post-annealing at 400 °C and above (400 °C group), at 762 and 951 cm−1 after annealing at 600 °C (600 °C group), and at 714 cm−1 up to 800 °C (800 °C group). By irradiation, a part of N2 was changed into the Ir group. VN2 is the candidate for the origin of the Ir group. By the post annealing at 400 and 600 °C, a part of N2 and the Ir group were changed into the 400 °C group, to less extent at 600 °C. V2N2 is the candidate for the origin of the 400 °C group. By annealing at 600 °C, most of the Ir group turned into 400 °C and 600 °C groups. By annealing at 800 °C, N2 recovered almost completely, and most other complexes were not observed. Recently, lifetime degradation has been observed in the nitrogen doped FZ Si annealed at between 450 and 800 °C. The N-V interaction in the same temperature range revealed here will help to understand the lifetime degradation mechanism. The behavior of the 689 cm−1 line corresponded well to the lifetime degradation.

Micro-Raman spectroscopy, X-band electron paramagnetic resonance (EPR) spectroscopy, and UV-visible optical absorption spectroscopy were used to study the damage production in cerium dioxide (CeO2) single crystals by electron irradiation for three energies (1.0, 1.4, and 2.5 MeV). The Raman-active T2g peak was left unchanged after 2.5-MeV electron irradiation at a high fluence. This shows that no structural modifications occurred for the cubic fluorite structure. UV-visible optical absorption spectra exhibited a characteristic sub band-gap tail for 1.4-MeV and 2.5-MeV energies, but not for 1.0 MeV. Narrow EPR lines were recorded near liquid-helium temperature after 2.5-MeV electron irradiation; whereas no such signal was found for the virgin un-irradiated crystal or after 1.0-MeV irradiation for the same fluence. The angular variation of these lines in the {111} plane revealed a weak g-factor anisotropy assigned to Ce3+ ions (with the 4f1 configuration) in a high-symmetry local environment. It is conclude...

With low energy electron irradiation in the 80–250keV range, we were able to create only those intrinsic defects related to the initial displacements of carbon atoms in the silicon carbide lattice. Radiation induced majority and minority carrier traps were analyzed using capacitance transient techniques. Four electron traps (EH1, Z1∕Z2, EH3, and EH7) and one hole trap (HS2) were detected in the measured temperature range. Their concentrations show linear increase with the irradiation dose, indicating that no divacancies or di-interstitials are generated. None of the observed defects was found to be an intrinsic defect–impurity complex. The energy dependence of the defect introduction rates and annealing behavior are presented and possible microscopic models for the defects are discussed. No further defects were detected for electron energies above the previously assigned threshold for the displacement of the silicon atom at 250keV.

Crystallization of amorphous data marks in crystalline Ga15Sb85 and Ge,In doped SbTe phase-change material was studied in situ in a Transmission Electron Microscope (TEM). Electron irradiation induced crystallization was obtained at room temperature using a 120kV beam. In general, electron beam (e−-beam) induced crystallization started from the amorphous-crystalline interface and was growth dominated for both materials. A dependence of growth velocity on electron beam intensity and crystal direction was observed. A comparison with laser-crystallized amorphous marks was made. For laser-induced crystallization also crystal growth from the amorphous-crystalline interface was seen. However, differences in morphology between the e−-beam and laser-recrystallized data marks of the GaSb phase-change material were observed. The electron beam erased data marks contained crystals with (extremely) large periodicities found in three dimensions. For the Ge,In doped SbTe phase-change material identical morphologies were...

A scanning electron microscope has been equipped to study the fundamental aspects of charge trapping in insulating materials, by measuring the secondary electron emission (SEE) yield σ with a high precision (a few percent), as a function of energy, electron current density, and dose. The intrinsic secondary electron emission yield σ0 of uncharged MgO single crystals annealed at 1000 °C, 2 h, has been studied at four energies 1.1, 5, 15, and 30 keV on three different crystal orientations (100), (110), and (111). At low energies (1.1 and 5 keV) σ0 depends on the crystalline orientation wheras at high energies (30 keV) no differentiation occurs. It is shown that the value of the second crossover energy E2, for which the intrinsic SEE yield σ0=1, is extremely delicate to measure with precision. It is about 15 keV±500 eV for the (100) orientation, 13.5 keV±500 eV for the (110), and 18.5 keV±500 eV for the (111) one. At low current density J⩽105 pA/cm2, the variation of σ with the injected dose makes possible t...

This article presents a study performed with a dedicated scanning electron microscope on the electrical property evolution of surfaces of (0001)-oriented sapphire (Al2O3) and (100)-oriented yttria-stabilized zirconia (YSZ) single crystals, during a 1.1 keV electron irradiation at room temperature. The type of charges trapped on the irradiated areas and the charging kinetics are determined by measuring the total secondary electron emission yield σ during the injection process, by means of two complementary detectors. At low current density (

Quenching of the cathodoluminescent (CL) efficiency of La2O2S:Eu3+ prepared by combustion reaction was investigated by measuring the temporal dependence of the CL intensities. While the emission intensity corresponding to the 5D0⇒7F2 electronic transition of Eu3+ did not change at a low current density (e.g., 65 μA/cm2), it decayed over the first 5 s of irradiation at a high current density (e.g., 500 μA/cm2). In addition, the difference between the initial and steady-state emission intensities increased as the current density increased. Based on thermal quenching data for the 5D0⇒7F2 transition, the quenching observed at high current densities was only partially explained by electron-beam heating. In addition to changes in intensity, the ratio of the CL intensities from the 5D1 transition (5D1⇒7F3) and the 5D0 transition (5D0⇒7F2) (designated 5D1/5D0) also decreased with increasing current density during the first ∼5 s of electron irradiation. Based upon measurement of the Auger electron peak energies, i...

The effect of high-energy electron irradiation on poly(vinylidene fluoride-trifluoroethylene) 80/20 mol % copolymers has been studied in a broad dose ranging from 0 to 120 Mrad. It was found that the copolymers transformed from a normal ferroelectric to a relaxor ferroelectric phase (RFE) at high electron doses. For copolymers irradiated at the dose above 90 Mrad, they exhibited typical dielectric behavior of RFE, e.g., whose dielectric constant peaks show strong frequency dispersion. X-ray diffraction patterns showed that the irradiation induced a coexistence of the polar and nonpolar phase in the crystalline regions, leading to nanosized coherent regions in the irradiated copolymer films. Differential scanning calorimetery and polarization hysteresis loops also revealed the reduction in the crystallinity and stability of the ferroelectric state, reflecting significant changes in the ferroelectric-to-paraelectric phase transition due to the effect of high-energy electron irradiation.

Near-threshold irradiation of B-doped synthetic diamonds has been performed using a transmission electron microscope operated at 200 kV. Both chemical vapor deposited and high-pressure high-temperature synthesized samples have been studied. The B levels were in the range 1017–1019 cm−3. After irradiation the samples were studied by low temperature (∼7 K) photoluminescence spectroscopy using various excitation wavelengths. A number of characteristic optical centers have been observed in the spectral range 500–800 nm and these centers are reviewed. Details of the properties of the optical centers have been investigated and the results are summarized. In particular, two zero-phonon lines (ZPLs) at 636 and 666 nm, formed in boron-doped diamond materials after near displacement-threshold electron radiation damage, were found to be related. The nature of this relationship is studied by laser power dependence (at different wavelengths) of their intensities over a wide temperature range. The results are interpret...

Copper migration and surface expansion of irradiated areas are observed in amorphous germanium-based chalcogenide thin films when an electron beam is focused in pulsed or continuous operation on the surface of these thin films. Both phenomena can be explained using a simple model in which the population of D− centers is considered to increase upon electron irradiation. The increase in the D− center population is envisaged as due to the breaking of bonds by the electron radiation and by the constant presence of negative charge in irradiated regions. Changes in copper concentration of 20%–30% and surface expansions of 30%–40% of films thickness have been obtained.

Damaged structures of α-SiC below and above the critical temperature of amorphization (T_c) under high-energy electron irradiation were studied by means of transmission electron microscopy and electron energy-loss spectroscopy. Above T_c , crystal fragmentation takes place due to local lattice strains caused by preferential displacements, subsequent outward diffusion of carbon atoms and formation of silicon nano-clusters. On the other hand, the amorphous structure formed below T_c can be well characterized by the formation of Si–Si, Si–C, and sp^3 C–C covalent bonds with the tetrahedral coordination locally retained and uniformly distributed. The primary amorphization process under electron irradiation can be interpreted by the defect-accumulation model, in which displaced atoms are frozen at interstitial sites before long-distance diffusion by reconstructing the surrounding structure to relax the local strains. Accordingly the amorphization process is controlled essentially by the mobility of displaced carbon and silicon atoms, and chemical disordering seems to play a minor role in triggering the amorphization. A key issue for irradiation induced volume swelling of amorphous SiC is also presented.

Cathodoluminescence (CL) studies have been carried out on a 30 nm GaN/1.5 nmIn0.28Ga0.72N/(0001) GaN single quantum well (SQW) structure in a field emission scanning electron microscope at voltages

Specimens of Zr66.7Cu33.3, Zr65.0Al7.5Cu27.5, and Zr65.0Al7.5Ni10.0Cu17.5 amorphous alloys with different thermal stability were irradiated by high energy electrons at an accelerated voltage of 2000 and 1000 kV. Electron irradiation was performed at 298 and 103 K. Crystallization of three amorphous alloys was accelerated by this irradiation and nanocrystalline structures were obtained. The critical total dose required for crystallization of the amorphous phase by electron irradiation depends strongly on the irradiation temperature and stability of this amorphous phase. The phase stability and crystallization behavior of the amorphous phase are discussed based on the electron irradiation effect.

Electron irradiation induced phase decomposition in an alkaline earth multi-component oxide glass has been observed in a scanning transmission electron microscope. Separate regions that are rich and poor in alkaline earths form rapidly during the initial irradiation. In other words, alkaline earth multi-component oxide glasses are intolerant of high-energy (∼100 kV) electrons. This could result from the characteristics of a nonbridging O atom that bound to both Si (covalent) and alkaline earths (ionic). A modified Knotek–Feibelman model has been introduced to interpret the breakaway of cations from the glass network. Driven by electrostatic forces, the cations prefer to segregate, forming a cation rich region to reduce the amount of nonbridging O.

Electrical conductivity of a 295-μm-thick Wesgo AL995 alumina has been measured before and during 1 MeV electron irradiation in a dc electric field of 300 kV/m at temperatures up to 723 K. The difference between the activation energies before (0.49±0.02 eV) and during (0.19±0.06 eV) irradiation indicates a substantial impact of irradiation on the conductivity of Wesgo AL995 alumina. The electrical conductivity of Wesgo AL995 alumina is lower by approximately 2 orders of magnitude than its requirement for the magnetic coils in the international thermonuclear experimental reactor (ITER). Thermal disruption may not impact on Wesgo AL995 alumina insulating material in ITER because of the absence of thermally stimulated conductivity peaks in it. Although no substantial bulk degradation is observed under irradiation up to a fluence of 7.0×1022 e/m2 (7.97×10−5 dpa) at 723 K, surface degradation is detected that could limit the application of Wesgo AL995 in ITER as a potential insulator.

Neutron-irradiation-induced defects in hydrogenated Si were investigated by detecting optical absorption due to their complexes with hydrogen. Specimens were doped with hydrogen by heating in H2 gas at 1300 °C followed by quenching in water. They were then irradiated with neutrons. The optical absorption spectra were measured at about 5 K with a Fourier transform infrared spectrometer. We investigated the dopant dependence and the annealing behaviors of H–interstitial (I) and H–vacancy (V) complexes. From the dopant dependence, we classified the peaks observed as I-related complexes or V-related complexes. In the annealing experiment, we observed numerous peaks after annealing above 300 °C in the region from 1940 to 2040 cm−1, whereas no such peaks were observed in the case of electron irradiation. This result shows that agglomerations of I and of V form more easily in neutron-irradiated Si than in electron-irradiated Si because of higher local concentrations of V and I in neutron-irradiated specimens.

In this work, the decay of secondary-electron emission (SEE) intensity and charging of hydrogenated and hydrogen-free diamond film surfaces subjected to incident electron irradiation at energies between 5 and 20 eV are investigated. Electron emission curves as a function of incident electron energy were measured. For the hydrogenated films, it was found that the SEE intensity decays in intensity under continuous electron irradiation, albeit maintains a nearly constant onset. The decay in time of the SEE intensity was measured for various incident electron energies. From these measurements, the SEE intensity decay rate from the hydrogenated diamond surface was calculated as a function of incident electron energy and found to display a broad peak at ∼9 eV. The decay of the SEE intensity is explained as due to electron trapping in the near-surface region of the hydrogenated diamond films resulting in the formation of a depletion layer and upward surface band bending while overall charge neutrality is maintai...

We report on the properties of electric fields generated as a result of electron irradiation of dielectrics in a low vacuum scanning electron microscope. Individual field components produced by (i) ionized gas molecules located outside the sample surface and (ii) subsurface trapped charge were detected by measurements of changes in (i) primary electron landing energy and (ii) secondary electron (SE) emission current, respectively. The results provide experimental evidence for a recently proposed model of field-enhanced SE emission from electron irradiated insulators in a low vacuum environment [Toth et al., J. Appl. Phys. 91, 4479 (2002)]. Errors introduced into x-ray microanalysis by the electric fields generated by ionized gas molecules can be alleviated by minimizing the steady state ion concentration by the provision of efficient ion neutralization routes. It is demonstrated how this can be achieved using simple sample-electrode geometries. © 2002 American Institute of Physics. © 2002 American Institute of Physics.

We demonstrate that if charging caused by electron irradiation of an insulator is controlled by a defocused flux of soft-landing positive ions, secondary electron (SE) images can contain contrast due to lateral variations in (i) changes in the SE yield caused by subsurface trapped charge and (ii) the SE-ion recombination rate. Both contrast mechanisms can provide information on microscopic variations in dielectric properties. We present a model of SE contrast formation that accounts for localized charging and the effects of gas ions on the SE emission process, emitted electrons above the sample surface, and subsurface trapped charge. The model explains the ion flux dependence of charge-induced SE contrast, an increase in the sensitivity to surface contrast observed in SE images of charged dielectrics, and yields procedures for identification of contrast produced by localized sample charging.

The study presents detailed isothermal and isochronal annealing recovery of photovoltaic parameters in n+/p InGaP solar cells after 1 MeV electron irradiation. Correlation of the solar cells characteristics with changes in the deep level transient spectroscopy data observed in irradiated and annealed n+/p InGaP diodes and solar cells shows that the H2 (Ev+0.50 eV) and H3 (Ev+0.76 eV) defects have a dominant role in governing the minority-carrier lifetime as well as carrier removal. However, capacitance–voltage measurements indicate that other defects must also play a role in the carrier removal process. In addition, the concentration of the H2 defect is found to decay significantly as a result of room temperature storage for 40 days, suggesting that InGaP-based solar cells will display superior radiation tolerance in space. Finally, the deep donor-like-defect H2 is tentatively identified as a phosphorus Frenkel pair.

The formation of Au nanoparticles (NPs) in Auþ ion-implanted silicon nitride thin films and membranes was investigated as a function of post-implantation thermal treatments or room temperature electron irradiation at energies of 80, 120, 160, and 200 keV. The samples were characterized by Rutherford Backscattering Spectrometry and Transmission Electron Microscopy. High-temperature thermal annealing (1100 C, 1 h) resulted in the formation of Au particles with a mean diameter of 1.3 nm. In comparison, room-temperature electron irradiation at energies from 80 to 200 keV caused the formation of larger Au particles according to two growth regimes. The first regime is characterized by a slow growth rate and occurs inside the silicon nitride membrane. The second regime presents a fast growth rate and starts when Au atoms become exposed to the back free surface of the membrane. Realistic binary electron-atom elastic collision cross-sections were used to analyze the observed nanoparticle growth and membrane sputtering phenomena. The results obtained demonstrate that binary electron-atom elastic collisions can account for the microstructure modifications if the critical displacement energies for the sputtering of N and Si atoms are around 1463 eV, and the displacement energy for surface located Au atoms is approximately 1.2560.2 eV. Irradiation experiments using focused electron probes demonstrate that the process provides fine control of nanoparticle formation, resulting in well-defined sizes and locations. Published by AIP Publishing.

The role of Shockley-Read-Hall non-radiative recombination centers on electroluminescence (EL) efficiency in blue multi-quantum-well (MQW) 436 nm GaN/InGaN light emitting diodes (LEDs) was examined by controlled introduction of point defects through 6 MeV electron irradiation. The decrease in the EL efficiency in LEDs subjected to irradiation with fluences above 5 × 1015 cm−2 was closely correlated to the increase in concentration of Ec-0.7 eV electron traps in the active MQW region. This increase in trap density was accompanied by an increase in the both diode series resistance and ideality factor (from 1.4 before irradiation to 2.1 after irradiation), as well as the forward leakage current at low forward voltages that compromise the injection efficiency. Hole traps present in the blue LEDs do not have a significant effect on EL changes with radiation because of their low concentration.

Using in situ transmission electron microscopy (TEM), we studied boron diffusion and segregation in CoFeB/SiO2 nanostructured thin film stacks. We also investigated how these phenomena affected the phase and microstructure of CoFeB thin films under electron beam irradiation at 300 kV. A unique phase transformation was observed in CoFeB thin films under high-dose electron irradiation, from a polycrystalline Co3Fe to a unilateral amorphous phase of Co3Fe and nanocrystalline FexCo23−xB6. The unilateral amorphization of the Co3Fe film showed an electron-dose-rate sensitivity with a threshold dose rate. Detailed in situ TEM studies revealed that the unilateral amorphization of the Co3Fe film arose from boron segregation at the bottom of the Co3Fe thin film induced by radiation-enhanced diffusion of boron atoms that were displaced by electron knock-on effects. The radiation-induced nanocrystallization of FexCo23−xB6 was also found to be dose-rate sensitive with a higher electron beam current leading to earlier ...

Electrical properties of nonirradiated and electron-irradiated thin layers of CdSe, sandwiched between two gold electrodes, were investigated. Thin films of CdSe, prepared by thermal-vacuum evaporation on glass substrate at a temperature of 220 °C, were subjected to two sessions of irradiation with 7 MeV electrons to the fluences of 2×1015 and 4×1015 e/cm2, respectively. The current–voltage characteristics, recorded at temperatures in the range 150–350 K, showed that the Ohm’s law is followed at low-applied voltages, in both nonirradiated and irradiated CdSe layers. In the range of high-applied voltages, the space-charge-limited current (SCLC), controlled by a Gaussian trap distribution, placed in the vicinity of the Fermi level, has been identified as the dominant conduction mechanism. An analysis in the frame of SCLC theory allowed us to obtain the parameters characterizing the trap distribution and their changes induced by electron irradiation.

The refractive index change caused by electron irradiation was measured in amorphous As–S and As–Se thin films coated with different metals. Metal atoms/ions diffused into the films during irradiation. The diffusion was dependent on the metal and influenced the refractive index. The influence was smallest in As40S60 films although these films possessed the highest overall refractive index changes. Au atoms/ions were almost immobile in all films while Ag atoms/ions had the highest mobility. Their high mobility allowed them to diffuse laterally within the film.

We investigate irradiation-induced defects in high-efficiency Cu(In,Ga)Se2/CdS/ZnO heterojunction solar cells after electron irradiation with energies of 0.5, 1, and 3 MeV and after 4 MeV proton irradiation. We use electron and proton fluences of more than 1018 cm−2 and up to 1014 cm−2, respectively. The reduction of the solar cell efficiency in all experiments is predominantly caused by a loss ΔVOC of the open circuit voltage VOC. An analytical model describes ΔVOC in terms of radiation-induced defects enhancing recombination in the Cu(In,Ga)Se2 absorber material. From our model, we extract defect introduction rates for recombination centers in Cu(In,Ga)Se2 for the respective particles and energies. We directly monitor the defect generation of these radiation-induced defects by admittance spectroscopy. The decrease of effective doping density in the Cu(In,Ga)Se2 absorber layer under particle irradiation is analyzed with capacitance voltage measurements at low temperatures. Furthermore, data on the relati...

The formation process of point defect clusters in high-purity (99.999%) iron as a typical bcc metal under the irradiation with low-energy (5 keV)He+ is studied by in situ transmission electron microscopy (TEM). Using conventional TEM techniques, clusters induced by the irradiation are determined to be interstitial-type dislocation loops (I loops) at temperatures ranging from 85 to 770 K and cavities from 300 to 770 K. Most of the I loops are determined to lie on {100} planes, and their Burgers vector are determined to be a[100]. The temporal variation in the volume density of I loops is measured by stereomicroscopy at several temperatures. The volume density of I loops is about two orders of magnitude higher in comparison with the case of high-energy electron irradiation at the same dpa rate; hence, it is deduced that helium atoms have an effect enhancing the nucleation of I loops. The depth distribution of the loop densities becomes broad above around 235 K at which vacancies become thermally mobile, and...

Nanostructures of dielectric materials decorated with metal nanoparticles are of great scientific interest; however, the involved synthesis methods are complicated and require multistep chemical processing, including functionalization of the dielectric surfaces. In the present work, without chemical processes, silver nanoparticles of average sizes in the range of 11 to 15 nm were in-situ synthesized and decorated on SiO2 nanospheres in a single step process by irradiating a solution (AgNO3–polyvinylpyrrolidone (PVP)–SiO2 nanospheres) with 6 MeV electrons at 1.5 × 1015 e−/cm2, 3.0 × 1015 e−/cm2, and 4.5 × 1015 e−/cm2 fluences. The electron irradiated solutions were characterized with different surface and other techniques. The results revealed that the SiO2 nanospheres were uniformly decorated with Ag nanoparticles, and the prominent chemical bonds involved were Ag–O, Si–O–Ag, and Si–Ag. Moreover, the sizes and the decoration density of Ag nanoparticles could be tailored by varying electron fluence. The Su...

Observations on deep levels introduced in silicon by 1 MeV electron irradiation are reported using boron- or gallium-doped Czochralski (CZ) grown Si space solar cells with different doping concentrations, deep level transient spectroscopy analysis has been carried out to detect the radiation-induced deep levels. Present results provide evidence for new defect states in addition to those previously reported in gallium- and boron-doped Si. The combined boron and gallium data provide enough information to gain valuable insight into the role of the dopants on radiation induced defects in Si. The dominant donor-like electron level at EC−0.18 eV in boron-doped Si has not been observed in gallium-doped CZ-grown Si. A noticeable suppressing generation of the radiation-induced defects in gallium-doped Si is also observed, especially hole level EV+0.36 eV, which is thought to acts as a recombination center.

Using Rutherford backscattering spectroscopy, nuclear elastic resonance analysis, atomic force microscopy, transmission electron microscopy, and wear resistance and microhardness tests, the alloy Ti41–V41–Al18 was investigated after Fe ion (60 kV) and Zr (40 kV) ion implantation and subsequent high-current electron beam (HCEB) irradiation at an energy flow density of 6 J/cm2, called duplex treatment. Profiles show that the maximum concentration of Fe ions was 16.5 at. % at 85 nm from sample surface and that of Zr ions was 0.85 at. % at 56 nm. The maximum of the Fe concentration profile was found to shift to the large sample depth toward after increasing the implantation dose. The surface alloy layer is composed of a number of structures: grains of dislocation substructure (2×1010 cm−2), grains with plates, and grains with packed martensite. The disorientation of regions is observed. After HCEB treatment, the disorientation of microregions increases (Δα=7.5°) and particles of Ti2Fe are formed. After double...

The effect of high-energy electron irradiation on structural and polarization properties of 50/50 mol % copolymer of poly(vinylidene fluoride-trifluoroethylene) was investigated for both mechanically stretched and unstretched films. Although stretching can significantly enhance the polarization and dielectric responses in unirradiated films, it was observed that this enhancement was not significant in irradiated films. In addition, the polarization in both types of films after irradiation can be described quite well by a logarithmic mixing law of composites, which consist of crystallites embedded in an amorphous matrix with nearly the same fitting parameters. On the other hand, the enhancement of the mechanical properties from stretching persists after the irradiation, and the elastic modulus along the stretching direction remains high after irradiation in comparison with unstretched films. It was found that the dielectric dispersion in both types of films after irradiation fits well to the Vogel–Fulcher law. It was also observed that the crystallinity decreases and the crosslinking coefficient increases continuously with dose. However, there was no direct one to one type relationship between the crystallinity and the crosslinking coefficient. Although stretching can reduce the rate of crosslinking, the reduction of crystallinity with dose for stretched and unstretched films does not show a marked difference.

We analyze the problems associated with the generation of coherent radiation by an e beam, traversing an undulator magnet, with an initial energy-phase correlation. The mechanisms of the process are explained and the role played by the bunching is clarified. The effect of the correlation on the stimulated part of the emission is also discussed.

Synthetic α-quartz is shown to contain a significant concentration (several ppm) of vacancies. The major concentration of vacancies is suggested to be in the form of divacancies, giving rise to a positron lifetime of 285±5 ps, but in addition, there is a much smaller concentration of large vacancy clusters that are observable only after electron irradiation, whereupon they give rise to a positron lifetime close to 425 ps. Annealing between 900 and 1000 °C causes disappearance of divacancies and formation of vacancy clusters giving rise to a positron lifetime close to 300 ps. Above ∼950 °C positronium is formed with an exceptionally long lifetime (3–5 ns) ascribable to the formation of an amorphous phase connected with the thermal instability of β-quartz. Electron irradiation (2.3 MeV at 8 °C) gave rise to a 250±5 ps lifetime component interpreted to signify formation of neutral monovacancies, V0 and/or VSi. Their introduction rate is nonlinear, decreasing abruptly by a factor of ∼5 above a dose of 1×1017 ...

The fluence-dependent properties and the annealing behavior of electron-irradiation-induced deep levels in n-type 6H–SiC have been studied using deep-level transient spectroscopy (DLTS). Sample annealing reveals that the dominant DLTS signal at EC−0.36 eV (labeled as E1 by others) consists of two overlapping deep levels (labeled as ED3L and ED3H). The breakup temperature of the defect ED3L is about 700 °C. The ED3H center together with another deep level located at EC−0.44 eV (so-called E2) can withstand high-temperature annealing up to 1600 °C. It is argued that the involvement of the defect ED3L is the reason that various concentration ratios of E1/E2 were observed in the previous work. The revised value of the capture cross section of the deep-level ED3H has been measured after removing ED3L by annealing. A deep level found at EC−0.50 eV is identified as a vacancy–impurity complex since it was found to have a lower saturated concentration and weak thermal stability. Two other deep levels, EC−0.27 eV an...

We have conducted a detailed in situ study of phase formation in Zr–Fe metallic multilayers using irradiation and thermal annealing. Metallic multilayers with near equiatomic and Fe-rich overall compositions and with repetition thicknesses ranging from 7.4 to 33 nm were either irradiated with 300 keV Kr ions at various temperatures (from 17 to 623 K) or thermally annealed at 773 K while being observed in situ. The kinetics of multilayer reaction were monitored by following the diffraction patterns. For near equiatomic samples, irradiation causes complete amorphization. The dose to amorphization increases in proportion to the square of the wavelength, indicating a process controlled by atomic transport. Amorphization was also achieved by 900 keV electron irradiation at 25 K showing that displacement cascades are not required. The critical dose to amorphization was independent of temperature below room temperature and decreased above room temperature. The activation energy for this second process is 0.17 eV...

Platinum has been diffused at 300–800 °C for 30 min into n-type epitaxial silicon samples during 2 MeV electron irradiation using a dose of 1×1017 e− cm−2. Thereafter the samples were characterized by capacitance–voltage measurements and deep level transient spectroscopy. The samples with irradiation temperatures of 500, 600, and 700 °C could be analyzed, while the compensation in the others was too high. Most of the observed deep levels were characterized using the Arrhenius method. Their possible identities are discussed. The deep level of substitutional platinum first appears in the sample irradiated at 600 °C and is the dominant defect level at even higher temperatures. We observe that at a chosen distance from the sample surface (17 μm), the concentration of electrically active platinum after an irradiation at 700 °C is a factor of 1000 higher than in an ordinarily diffused sample. Taking into account experiments where platinum was diffused into pre-irradiated samples, the observed behavior is attrib...

An investigation of electron irradiation induced deep levels in 6H–SiC p+n diodes grown by chemical vapor deposition has been performed. Deep level transient spectroscopy (DLTS) reveals several overlapping peaks in the temperature range 140–650 K. The electron capture cross sections have been measured by directly observing the variation of the DLTS peak height with the duration of the filling pulse and fitting the capacitance transient using multiple linear regression. Temperature dependence studies of the electron capture cross section were performed on three of the observed levels.

The electrical properties of nonirradiated and electron irradiated structures, containing a polycrystalline thin layer of CdS, sandwiched between two gold electrodes, were investigated. The thin films of CdS, obtained through thermal-vacuum evaporation on the glass substrate at a temperature of 220 °C, were subjected to two sessions of irradiation with 7 MeV electrons to the fluences of 4×1015 and 6×1015 e/cm2, respectively. In the case of nonirradiated structures, under low voltages, the Ohm’s law is followed with a thermally activated electron concentration of n0≅3×1016 cm−3, an electron mobility μ0≅0.1 cm2/V s and a room temperature electrical conductivity σ0≅4×10−4 Ω−1 cm−1. In this range of voltage the electron irradiation induces a small increase in the activation energy of mobility, determining, of course, a small decreasing of the mobility. At high-applied voltage, there is a space-charge-limited conductivity controlled by a single trap level having the depth of Ec−Et≅0.086 eV and the total trap c...

We studied the process of generation and some properties of shallow donors generated by annealing a hydrogen-doped Czochralski-grown silicon crystal after electron irradiation. Hydrogen was doped by annealing specimens at 1200 °C in hydrogen atmosphere followed by quenching. Specimens were irradiated with 3 MeV electrons. Three kinds of shallow donors, termed D1–D3, were generated and annihilated due to isochronal annealing between 300 and 650 °C as shown by the measurement of optical absorption at 6 K. The generation process of D1 was well described by the first order reaction. The activation energy for the generation of D1 was about 1.8 eV. This agreed well with the migration energy of a vacancy-oxygen pair (VO pair). Hence, it is proposed that D1 is a complex of one VO pair and a hydrogen aggregate. Neutral D1 is in a metastable state. The optical threshold energy for the excitation of the neutral charge state of D1 was about 0.36 eV. The energy barrier from the neutral to the stable state of D1 was estimated to be about 0.13 eV.

The vacancy production in 6H-SiC by 3 MeV electron irradiation at room temperature was studied using positron lifetime spectroscopy combined with annealing experiments. It was found that the trapping rates of positrons in vacancies increased linearly with the fluence in the initial stage of irradiation. After the linear increase, the trapping rates were found to be proportional to the square root of the fluence. The linear and nonlinear fluence dependences of the trapping rates are explained by the reduction of vacancies due to recombination with interstitials during irradiation. The positron trapping rate for the admixture of silicon vacancies and divacancies showed a tendency to saturate in the higher fluence range. The trapping rate for carbon vacancies decreased after reaching a maximum. These results are explained in terms of the shift of the Fermi level due to the irradiation process. It was found that, for the lightly irradiated specimen, an annealing stage caused by recombination between close vacancies and interstitials was observed. However, such an annealing stage was not observed when using a heavily irradiated specimen. These different results are explained as the reduction of interstitials due to the recombination with vacancies and long-range migration of interstitials to sinks during irradiation.