Effect Of Electron Irradiation Research Articles

Transformation of a graphene nanoribbon into a hybrid 1D nanoobject with alternating double chains and polycyclic regions.

Molecular dynamics simulations show that a graphene nanoribbon with alternating regions which are one and three hexagons wide can transform into a hybrid 1D nanoobject with alternating double chains and polycyclic regions under electron irradiation in HRTEM. A scheme of synthesis of such a nanoribbon using Ullmann coupling and dehydrogenation reactions is proposed. The reactive REBO-1990EVC potential is adapted for simulations of carbon-hydrogen systems and is used in combination with the CompuTEM algorithm for modeling of electron irradiation effects. The atomistic mechanism of formation of the new hybrid 1D nanoobject is found to be the following. Firstly hydrogen is removed by electron impacts. Then spontaneous breaking of bonds between carbon atoms leads to the decomposition of narrow regions of the graphene nanoribbon into double chains. Simultaneously, thermally activated growth of polycyclic regions occurs. Density functional theory calculations give barriers along the growth path of polycyclic regions consistent with this mechanism. The electronic properties of the new 1D nanoobject are shown to be strongly affected by the edge magnetism and make this nanostructure promising for nanoelectronic and spintronic applications. The synthesis of the 1D nanoobject proposed here can be considered as an example of the general three-stage strategy of production of nanoobjects and macromolecules: (1) precursors are synthesized using a traditional chemical method, (2) precursors are placed in HRTEM with the electron energy that is sufficient only to remove hydrogen atoms, and (3) as a result of hydrogen removal, the precursors become unstable or metastable and transform into new nanoobjects or macromolecules.

Effect of Electron Injection on Minority Carrier Transport Properties in Unintentionally Doped GaN

GaN is a robust and stable wide bandgap material with a bandgap of 3.4eV. It is extensively studied for applications in light emitting diodes, high-power electronics and optoelectronics. Radiation hardness is another attractive attribute of GaN due to its atomic structure and wide bandgap with possible electronic applications in lower Earth satellite orbits. Like other wide bandgap materials, GaN also suffers from short diffusion length, which has been earlier reported to be ~100-300 nm. Minority carrier transport properties such as carrier lifetime (τ) and diffusion length (L) are of vital importance in bipolar and minority-carrier devices. Previously, it was shown that low energy electron beam irradiation (up to 30 keV) for extended duration (up to 3000 seconds) can be used to enhance L by a factor of 4 at room temperature in other wide bandgap materials like p-ZnO and β-Ga2O3 [1-3] . It was suggested that the increase in L is associated with trapping of non-equilibrium electrons on meta-stable trap levels acting as recombination centers. Dependence of L on τ is given by the relation L=√(Dτ) , where D is the diffusion coefficient. Therefore, removal of recombination centers, due to electron trapping on them would, in turn, increase τ, and hence L. Another effect of low energy electron irradiation, apart from increasing τ, is manifested in decrease in the continuous CL intensity. In this work, unintentionally doped GaN was studied using Electron Beam-Induced Current (EBIC), Continuous (CL) and Time-Resolved Cathodoluminescence (TRCL) techniques to independently measure L and τ, and verify the validity of the proposed model[4]. Measurements were conducted on GaN Schottky rectifiers (~400 µm GaN layer grown by Halide Vapor Phase Epitaxy on sapphire) with electron concentration of ~1x1017 cm-3. L was found to increase from 306 nm to 347 nm for a maximum electron injected charge density of 117.5 nC/µm3 and saturating at 60 nC/µm3. For the same maximum and saturation injected charge densities, τ was found to increase from 77 ps to 101 ps. Fig. 1a shows a plot of TRCL streaks for bare region and the region with maximum injected charge density. Slower decay of streak signal indicates longer lifetime in the electron-injected region. Fig. 1b depicts the plot of L and √τ as a function of injected charge density at room temperature. A clear linear dependence (L=√(Dτ)) is seen till saturation charge density of ~60 nC/µm3. Furthermore, mobility values (from the diffusion coefficient) for various charge injection doses were obtained for the ultrafast regime of TRCL spectroscopy.

Defect spectroscopy and non-ionizing energy loss analysis of proton and electron irradiated p-type GaAs solar cells

Admittance spectroscopy combined with non-ionizing energy loss (NIEL) analysis is shown to be a powerful tool for analyzing solar cell radiation degradation, not relying on the change of macroscopic cell parameters. GaAs component cells, representative of the middle sub-cell in Ga0.5In0.5P/GaAs/Ge solar cells, were irradiated with protons and electrons in the 0.5–3 MeV energy range. Four irradiation-induced defects are identified in the p-type base layer. The nature of each defect is assessed by analyzing the dependence of its introduction rate on the NIEL deposited by electrons in the semiconductor. The expected linear relationship is only achieved if a unique threshold energy Ed is ascribed to each defect, which ranges from 9 to 38 eV. An electron NIEL with Ed=21eV, customarily used for GaAs-based solar cell degradation analysis, is an approximation of the relative abundance of these four defects. The 21 eV value is thus a GaAs material-specific parameter, independent of the electrical device design. In addition, the type and energy of the incident particle is correlated with the relative abundance of high Ed defects. The impact of each defect on the macroscopic electrical parameters of the cell, namely, the open-circuit voltage VOC, the short-circuit current density JSC, and the recombination current density J02, is assessed with the help of a Pearson analysis. The different effectiveness of electron and proton irradiation on parameters dominated by recombination in the depleted region, such as VOC or J02, is attributed in part to the influence of the particle recoil spectra on the defect capture cross section.

Photoluminescence study on the optical properties of silicon-vacancy centre in diamond

The optical properties of a silicon-vacancy (Si–V) centre were studied using photoluminescence (PL), including the temperature (80 K–270 K) and excitation power (2.25 W-22.5 mW)-dependent PL measurements and the effect of electron irradiation on the PL signal. The intensity decrease, red shift, and broadening of the line width with increasing temperature were fitted nonlinearly. The thermal quenching activation energy (49.59 meV), Huang-Rhys factor (0.049), and average phonon energy (42.09 meV) of the Si–V centre were obtained using suitable physical formulas. For the excitation power dependence, only the PL intensity of Si–V centre was sub-linear with the increasing power, the radiative recombination was dominated and the impact of Auger recombination was negligible. In addition, Fermi level shifted below the ground state level of Si–V in irradiation region due to the introduction of neutral single vacancy (GR1) centre, the PL signal of the Si–V centre was suppressed.

Electron irradiation induced molecular changes in PMMA: A positron spectroscopy study

To examine the positron annihilation parameters with regard to microstructural changes, the positron annihilation lifetime spectroscopy and measurements of the Doppler broadening of annihilation radiation (DBAR) of electron‐irradiated poly(methyl methacrylate) were carried out at room temperature. Trapping rate equations were applied in terms of the positron bulk lifetime as well as the positron lifetime fitting results to investigate the molecular changes due to electron irradiation effects. It was found that the mean positron lifetime shows the same trend as the o‐Ps intensity. In disordered regions, the positronium trapping rate suggests that trapping of o‐Ps increases with increasing electron irradiation fluence until electron fluence reached 5.9 × 1013 electrons/cm2, after which it begins to decrease. The line shape S‐parameter was found to have similar behavior as the o‐Ps intensity, and suggests that poly(methyl methacrylate) undergoes chain scission, followed by cross‐linking, and eventually degradation, due to the electron radiation effects. The results of positron annihilation spectroscopy were verified by X‐ray results, mechanical, and electrical measurements.

Electron, Neutron, and Proton Irradiation Effects on SiC Radiation Detectors

Owing to their low dark current, high transparency, high thermal conductivity, and potential radiation hardness, there is a special interest in silicon carbide (SiC) devices for radiation monitoring in radiation harsh environments and with elevated temperatures and, especially, for the plasma diagnostic systems in future nuclear fusion reactors. In this work, four-quadrant p-n junction diodes produced on epitaxial 4H-SiC substrates are studied. The impact of electron, neutron, and proton irradiations (up to fluences of $1 \times 10^{16}$ electrons (e)/cm2, $2 \times 10^{15}$ neutrons (n)/cm2, and $2.5\times 10^{15}$ protons (p)/cm2, respectively) on the electrical characteristics is studied by means of current–voltage ( $I$ – $V$ ) and capacitance–voltage ( $C$ – $V$ ) techniques. Regardless of the particle type and applied fluences, the results show similar low reverse currents for irradiated SiC devices, which are at least about four orders of magnitude lower than comparable Si devices. The effects of irradiation on interquadrant resistance and charge build-up in the interquadrant isolation are assessed. Furthermore, device performance as a radiation detector is investigated upon exposure to a collimated 239Pu–241Am–244Cm tri-alpha source. The performance at room temperature is preserved even for the highest irradiation fluences, despite the fact that the rectification character in electrical characteristics is lost. From the results, advantages of using SiC devices in alpha particle detection in harsh environments can be envisaged.

Electron Irradiation Effects and Defects Analysis of the Inverted Metamorphic Four-Junction Solar Cells

The degradation of inverted metamorphic four-junction (GaInP/GaAs/In0.3Ga0.7As/In0.58Ga0.42As, IMM4J) solar cells irradiated by 1-MeV electrons was investigated via their spectral responses and the characterization of their electrical properties. As in the case of traditional three-junction (TJ) GaInP/GaAs/Ge solar cells, the electrical properties ( I sc, V oc, and P max) decrease with the logarithmic change of the electron fluence. The degradation of open-circuit voltage ( V oc) is slightly more pronounced than that of I sc in IMM4J solar cells because of the sum rule for V oc and the limit rule for I sc. The spectral response analysis showed that an In0.3Ga0.7As subcell was the most damaged subcell in the irradiated IMM4J solar cell, but an In0.58Ga0.42As subcell had the lowest initial short-circuit current density (Jsc), which was maintained throughout the irradiation test. We therefore focused on the In0.58Ga0.42As subcell. Deep-level transient spectroscopy (DLTS) experiments were realized to study emission and capture processes in two special full configurations of In0.58Ga0.42As and In0.3Ga0.7As subcells of the IMM4J solar cell. DLTS measurements reveal a dominant electron trap at 0.52 eV below the conduction band (Ec) of In0.58Ga0.42As, and the electron trap gradually evolved into Ec-0.46eV and Ec-0.58eV after 1-MeV electron irradiation. Based on the first-principles calculation, Ec-0.46 eV and Ec-0.58 eV can be assigned as ${\bf V}_{{\bf Ga}}^{\bf 0}/{\bf V}_{{\bf Ga}}^{{\rm{ - }}1}$ and ${\bf V}_{{\bf In}}^{\bf 0}/{\bf V}_{{\bf In}}^{{\bf - 1}}$ , respectively. However, only one shallow level Ec-0.03eV was observed within the bandgap of In0.3Ga0.7As after irradiation with DLTS detection. We summarize the issues faced for the space application of IMM4J solar cells by comparing the spectral responses of IMM3J, IMM4J, and TJ solar cells. Finally, the optimization of the design and fabrication of IMM solar cells are proposed.

Composition variation and electron irradiation effects on the fluctuation conductivity in Y1\u2013zPrzBa2Cu3O7\u2212\u03b4 single crystals

A comparative analysis of the changes in the fluctuation conductivity and characteristics of the superconducting state of YBa2Cu3O7–δ single crystals caused by various types of defects is carried out. These defects appeared due to irradiation with high-energy electrons (radiation doses from 1.4 to 8.8 1018 cm–2), changes in oxygen deficiency (0.08 ≤ δ ≤ 0.23) due to annealing at different temperatures, or doping with praseodymium (Y1–zPrzBa2Cu3O7−δ, 0 ≤ z ≤ 0.5 at optimal oxygen concentration). It is shown that the introduction of such defects leads to a significant expansion of the temperature range of the existence of excess conductivity, and upon doping with praseodymium, it also leads to the appearance of a thermally activated deflection on the temperature dependence of the electrical resistance. The effect of such defects on the superconducting transition temperature, Tc, and the coherence length along the c axis, ξc(0), is studied. In particular, ξc(0) more than quadruples (at z = 0.43), while the 2D-3D crossover point shifts towards higher temperatures. Possible reasons for the suppression of superconductivity in YBa2Cu3O7–δ upon irradiation with fast electrons and the qualitatively different temperature dependences of its resistivity in the basal plane, ρab (T), are discussed.

Operation experience of ionization-proportional chamber for low-current beam measurements at INR RAS proton linac

A Proton Irradiation Facility has been commissioned at INR RAS linac to study radiation effects in electronics. One of the used diagnostic devices for low intensity proton beams is Multianode Gas Counter. The device consists of ionization chamber to measure beam current and two proportional chambers, based on stripe geometry, to measure beam profiles. The data is processed with Labview software. The models and methods predicting operational characteristics of the counter in ionization and proportional mode are presented. An analytical model of recombination was tested to find the saturation voltage of ionization mode. Beam test results and experimental characteristics of the counter are presented as well as results of investigations of counter degradation under the beam. A new design of a gas filled counter is also discussed.

Quantitative Measurement and Utilization of Electron Irradiation Effects in 2D Materials

Quantitative Measurement and Utilization of Electron Irradiation Effects in 2D Materials

Effect of Proton and Electron Irradiation on Current-Voltage Characteristics of Rectifying Diodes Based on 4H-SiC Structures with Schottky Barrier

Forward and reverse current-voltage (I-V) characteristics of commercial rectifying Schottky diodes (SDs) based on silicon carbide (4H-SiC, base layer doping level 3·1015 cm-3) have been studied under irradiation with 0.9 MeV electrons and 15 MeV protons. The starting diodes were characterized by a barrier height of ~1.5 eV and nearly ideal forward and reverse I-V characteristics. It was found that, at doses exceeding the threshold dose Dth, the series differential resistance Rs of the diodes grows as Rs ~ Dm (m = 10-15) and shows no tendency toward saturation. Dth ≈7·1015 cm-2 under electron irradiation, and Dth ≈ 4·1013 cm-2 in the case of irradiation with protons. Heating to 200oC results in that Rs decreases with activation energy of ~1.1 eV and Rs is partly annealed-out with activation energy of ~0.7 eV. The starting Schottky diodes changes only slightly under irradiation, but, possibly, the irradiation leads to an over-compensation of the n-type layer and formation of an additional barrier in the form of a pn junction.

Effect of TID electronradiation on SiGe BiCMOS LNAs at V-band

We investigate the effect of TID electron irradiation on a 65 GHz LNA in 130 nm SiGe BiCMOS. The LNA is exposed to a Sr-90 radiation source and irradiated at a rate of 200 krad (Si)/hr to a total dose of 15 Mrad (Si), with S-parameter and NF measurements taken at regular intervals. It is found that TID produces and increase in the input impedance, especially in the reactive component. The damage results in 2.3 dB reduction in midband gain, 2.97 dB increase in midband NF and up to 8.19 dB increase in midband S11, although the device remains matched across the band of interest. The degradation is found most pronounced at the band-edges, yielding a 1 dB gain flatness bandwidth reduction of 32%.

1 meV electron irradiation and post-annealing effects of GaInAsN diluted nitride alloy with 1 eV bandgap energy

1 meV electron irradiation and post thermal annealing effects of GaInAsN bulk material with bandgap energy of 1 eV was studied by low-temperature photoluminescence (PL). The nitrogen proportion of the samples was confirmed by high-resolution X-ray diffraction measurement as 0.26%. The result shows that the PL intensity and high activation energy non-radiative centers of GaInAsN materials degraded seriously due to the irradiation induced large number of defects. The PL enhancement phenomena were observed in all samples after rapid thermal annealing (RTA) at 650 ∘C for five minutes. The irradiation and RTA caused PL peak red-shift and blue-shift have been discussed.

Control of Radiation Defects and Na Clusters in the Process of Radiation Degradation of Natural Stone Salt Single Crystals

Using the methods of positron annihilation and optical spectroscopy, the effect of gamma (Co60) and electron irradiation (Cockcroft–Walton accelerator) on NaCl single crystals, followed by annealing at various temperatures. It was found that electron color centers are effective traps of positrons diffusing in the lattice. At the same time, hole centers do not capture positrons. It was shown that positrons are captured by sodium clusters formed in the bulk of NaCl crystals upon annealing (443 K) of irradiated (2650 Mrad) samples. The annihilation characteristics of captured positrons allow us to estimate size of sodium clusters R = 23.0 nm and their concentration Nx = 5.3 × 1017 cm–3. Taking into account the fact that modern optical and positron spectrometers are quite compact and sensitive instruments, the monitoring of the processes of radiation degradation of the geological rock of rock salt can be carried out directly at the disposal sites of radioactive waste rather quickly and with the necessary degree of sensitivity to the accumulation of radiolytic products.

Polyamide Surface Layer Nano-Indentation and Thermal Properties Modified by Irradiation.

This study describes the effect of electron radiation on the nano-mechanical properties of surface layers of selected polyamide (PA) types. Electron radiation initiates the cross-linking of macromolecules in the polyamide structure, leading to the creation of a 3D network which fundamentally changes the properties of the tested polymers. Selected types of polyamide (PA 6, PA 66 and PA 9T) were exposed to various intensities of electron radiation (33 kGy, 66 kGy, 99 kGy, 132 kGy, 165 kGy and 198 kGy). The cross-linked polyamides’ surface properties were measured by means of the modern nano-indentation technique (Depth Sensing Indentation; DSI), which operates on the principle of the immediate detection of indenter penetration depth in dependence on the applied load. The evaluation was preformed using the Oliver–Pharr method. The effect of electron radiation on the tested polyamides manifested itself in the creation of a 3D network, which led to an increase of surface layer properties, such as indentation hardness, elastic modulus, creep and temperature resistance, by up to 93%. The increase of temperature and mechanical properties substantially broadens the field of application of these materials in technical practice, especially when higher temperature resistance is required. The positive changes to the nano-mechanical properties as well as mechanical and temperature capabilities instigated by the cross-linking process were confirmed by the gel volume test. These measurements lay the foundation for a detailed study of this topic, as well as for a more effective means of modifying chosen properties of technical polyamide products by radiation.

Effects of 1-MeV Electron Irradiation on the Photoluminescence of GaInNAs|GaAs Single Quantum Well Structure

Minimizing the impact of radiation-induced degradation in dilute nitride based optoelectronic devices is crucial in its applications. The effects of 1-MeV electron irradiation (of 1 × 1014–1 × 1016 e/cm2 range) on undoped GaInNAs|GaAs single quantum-well (QW) structure has been studied by low-temperature photoluminescence (PL). PL spectra of GaInNAs|GaAs QW are measured before and after electron irradiation. The results show a slight enhancement of the PL intensity in relatively low electron fluence, and then subsequent deterioration of PL with the increase of cumulative electron fluences. The enhancement in PL intensity at low electron doses is explained by recombination-enhanced defect reaction model, and the degradation at high electron doses is explained by irradiation-induced defects in the lattice.

Effect of electron irradiation on some physical, chemical and digestion properties of pistachio by-products

In the present study pistachio by-products (PB) were treated with various doses of electron irradiation (10–100 kGy). The results indicated that applied doses of electron irradiation had no effect on organic matter (OM), crude protein (CP) and ether extract content of PB. Irradiation increased (P < 0.01) total phenol content; while decreased cell wall compartment, tannin (P = 0.05) and condensed tannin (P = 0.03) contents. Irradiation decreased (P = 0.04) water binding capacity (WBC), but increased (P < 0.05) solubility of dry mater (DM), OM and protein of PB with increasing in irradiation dose. Electron irradiation effectively increased rapidly degradable fraction (a) and decreased potentially degradable fraction (b) of DM and OM of PB in the rumen of sheep compared to the control. The FTIR spectra of samples revealed similar pattern without any changes in the functional group status with a decrease in relative transmittance of peaks in irradiated groups. In conclusion, this study showed that electron irradiating can effectively change physical and chemical; and digestive properties of PB.

Electron irradiation and annealing effects on the pseudogap in optimally doped YBCO single crystals

The effect of room-temperature annealing on the basal-plane conductivity of YBCO single crystals is investigated after their irradiation with fast electrons. It is revealed that the excess conductivity [Formula: see text] of the samples obeys an exponential temperature dependence in a broad temperature range [Formula: see text]. Here, [Formula: see text] is the crossover temperature from the pseudogap to the fluctuation conductivity regime. The description of the excess conductivity with the expression [Formula: see text] can be interpreted in terms of the mean-field theory where [Formula: see text] corresponds to the mean-field transition temperature to the pseudogap state and the dependence [Formula: see text] is described within the framework of the BCS-BEC crossover theory.

Electron Irradiation Effects on the Optical and Electrical Properties of ZnO/Ag/SnO&lt;sub&gt;2&lt;/sub&gt; Thin Films

Transparent conductive ZnO 50 nm/Ag 10 nm/SnO&lt;sub&gt;2&lt;/sub&gt; 50 nm (ZAS) tri-layer films were deposited on glass substrates by magnetron sputtering, and then the surface was subjected to intense electron beam irradiation to investigate the effects of electron irradiation on the structural, optical, and electrical properties of the films. After deposition, the ZAS thin films were electron-irradiated for 10 minutes, with varying electron incident energies of 300, 600, and 900 eV. The films that were electron irradiated at 900 eV showed higher optical transmittance of 83.6% in the visible wavelength region, and lower resistivity, of 4.75 × 10&lt;sup&gt;-5&lt;/sup&gt; Ωcm, than the other films. From the observed electrical properties and optical band gap, it was concluded that the optical band gap increased with the incident electron energy up to 600 eV. The optical band gap increased from 4.12 to 4.23 eV, with carrier density increasing from 7.09 to 8.55 × 10&lt;sup&gt;21&lt;/sup&gt; cm&lt;sup&gt;−3&lt;/sup&gt;. However, the film electron irradiated at 900 eV showed a decrease in optical band gap energy of 4.16 eV due to the decreased carrier density of 8.25 × 10&lt;sup&gt;21&lt;/sup&gt; cm&lt;sup&gt;−3&lt;/sup&gt;. The figure of merit revealed that the ZAS thin films electron-irradiated at 900 eV had higher optical and electrical performance than the other films prepared in this study.

Effect of electron radiation on small-signal parameters of NMOS devices at mm-wave frequencies

The effect of electron radiation on the forward-active small-signal model parameters for 0.35 μm CMOS devices is reported. Four devices with different gate widths were exposed to electron radiation using a Strontium 90 (Sr 90) radiation source at dose rates of 200 kRad (Si)/hr up to a total radiation dose of 2.7 MRad. S-parameters were measured, and small-signal models extracted, both pre-irradiation and at regular dose intervals. Relationships between small-signal model parameters and total radiation dose d were derived and used to calculate small-signal parameters. The major model variations due to total ionizing dose exposure were increases in the gate resistance (Rg), gate drain capacitance (Cgd) and gate source capacitance (Cgs), with a reduction in transconductances (gm and gds). This results in S11 and S22 becoming more resistive as d is increased, with a decrease in the unilateral gain, fT and fmax. The application of the data in predictive modelling of radiation damage is demonstrated.