In situ TEM investigation of electron irradiation and aging-induced high-density nanoprecipitates in an Mg-10Gd-3Y-1Zn-0.5Zr alloy

In-situ electron irradiation and aging are applied to introduce high-density precipitates in an Mg-10Gd-3Y-1Zn-0.5Zr(GWZ1031K,wt.%)alloy to improve the hardness.The results show that the hardness of the Mg alloy after irradiation for 10 h and aging for 9 h at 250℃ is 1.64 GPa,which is approximately 64% higher than that of the samples before being treated.It is mainly attributed to γ'precipitates on the basal plane after irradiation and the high-density nanoscale β'precipitates on the prismatic plane after aging,which should be closely related to the irradiation-induced homogenous clusters.The latter plays a key role in precipitation hardening.This result paves a way to improve the mechanical properties of metallic materials by tailoring the precipitation through irradiation and aging.

Deformation defects and electron irradiation effect in nanostructured Al-Mg alloy processed by severe plastic deformation

In order to explore the exact nature of deformation defects previously observed in nanostructured Al-Mg alloys subjected to severe plastic deformation, a more thorough examination of the radiation effect on the formation of the planar defects in the high pressure torsion （HPT） alloys was conducted using high-resolution transmission electron microscopy （HRTEM）. The results show that high density defects in the HRTEM images disappear completely when these images are exposed under the electron beam for some duration of time. At the same time, lattice defects are never observed within no-defect areas even when the beam-exposure increases to the degree that holes appear in the areas. Therefore, it is confirmed that the planar defects observed in the HPT alloys mainly result from the significant plastic deformation and are not due to the radiation effect during HRTEM observation.

Photocarrier radiometry for noncontact evaluation of space monocrystalline silicon solar cell under low-energy electron irradiation

A space monocrystalline silicon（c-Si） solar cell under low-energy（〈 1 MeV） electron irradiation was investigated using noncontact photocarrier radiometry（PCR）. Monte Carlo simulation（MCS） was employed to characterize the effect of different energy electron irradiation on the c-Si solar cell. The carrier transport parameters（carrier lifetime, diffusion coefficient, and surface recombination velocities） were obtained by best fitting the experimental results with a theoretical one-dimensional two-layer PCR model. The results showed that the increase of the irradiation electron energy caused a large reduction of the carrier lifetime and diffusion length. Furthermore, the rear surface recombination velocity of the Si：p base of the solar cell at the irradiation electron energy of 1 Me V was dramatically enhanced due to 1 MeV electron passing through the whole cell. Short-circuit current（I sc） degradation evaluated by PCR was in good agreement with that obtained by electrical measurement.

Charging dynamics of a polymer due to electron irradiation:A simultaneous scattering-transport model and preliminary results

We present a novel numerical model and simulate preliminarily the charging process of a polymer subjected to electron irradiation of several 10 keV. The model includes the simultaneous processes of electron scattering and ambipolar transport and the influence of a self-consistent electric field on the scattering distribution of electrons. The dynamic spatial distribution of charges is obtained and validated by existing experimental data. Our simulations show that excess negative charges are concentrated near the edge of the electron range. However, the formed region of high charge density may extend to the surface and bottom of a kapton sample, due to the effects of the electric field on electron scattering and charge transport, respectively. Charge trapping is then demonstrated to significantly influence the charge motion. The charge distribution can be extended to the bottom as the trap density decreases. Charge accumulation is therefore balanced by the appearance and increase of leakage current. Accordingly, our model and numerical simulation provide a comprehensive insight into the charging dynamics of a polymer irradiated by electrons in the complex space environment.

Characteristics of charge and discharge of PMMA samples due to electron irradiation

In this study, using a comprehensive numerical simulation of charge and discharge processes, we investigate the formation and evolution of negative charge and discharge characteristics of a grounded PMMA film irradiated by a non- focused electron beam. Electron scattering and transport processes in the sample are simulated with the Monte Carlo and the finite-different time-domain （FDTD） methods, respectively. The properties of charge and discharge processes are presented by the evolution of internal currents, charge quantity, surface potential, and discharge time. Internal charge accumulation in the sample may reach saturation by primary electron （PE） irradiation providing the charge duration is enough. Internal free electrons will run off to the ground in the form of leakage current due to charge diffusion and drift during the discharge process after irradiation, while trapped electrons remain. The negative surface potential determined by the charging quantity decreases to its saturation in the charge process, and then increases in the discharge process. A larger thickness of the PMMA film will result in greater charge amount and surface potential in charge saturation and in final discharge state, while the electron mobility of the material has little effects on the final discharge state. Moreover, discharge time is less for smaller thickness or larger electron mobility. The presented results can be helpful for estimating and weakening the charging of insulating samples especially under the intermittent electron beam irradiation in related surface analysis or measurement.

Electron irradiation effects on DC electrical performances of SiGe HBT in a comparison with Si BJT

The DC characteristics of SiGe HBT irradiated at different electron dose havebeen studied in a comparison with those of Si B JT. Generally, I_b and I_b - I_(b0) increase, I_c,I_c -I_(c0) and its +/- transition V_(be) as well as DC current gain ft decreases with increasingdose; increase of I_b -I_(b0) with increasing dose for Si BIT is much larger than that for SiGe HBT;beta increases with V_(be) or I_b, but decreases at I_b < 0.25 mA with I_b, and congregates athigher dose; and a damage factor d(beta) is much less at the same dose for SiGe HBT than for Si BJT.SiGe HBT has much better anti-radiation performance than Si BJT. Some anomalous phenomena forincrease of I_c, I_c -I_(c0), I_b -I_(b0) and beta at low dose have been found. Some electron trapshave been measured. The mechanism of changes of characteristics is discussed.

Electron irradiation-induced change of structure and damage mechanisms in multi-walled carbon nanotubes

Owing to their unique structure and excellent electrical property, carbon nanotubes （CNTs） as an ideal candidate for making future electronic components have great application potentiality. In order to meet the requirements for space appli- cation in electronic components, it is necessary to study structural changes and damage mechanisms of multi-walled carbon nanotubes （MWCNTs）, caused by the irradiations of 70 and 110 keV electrons. In the paper, the changes of structure and damage mechanisms in the irradiated MWCNTs, induced by the irradiations of 70 and 110 keV electrons, are investigated. The changes in surface morphology and structure of the irradiated MWCNT film are characterized using scanning electron microscopy （SEM）, x-ray photoelectron spectroscopy （XPS）, Raman spectroscopy, x-ray diffraction analysis （XRD）, and electron paramagnetic resonance （EPR） spectroscopy. It is found that the MWCNTs show different behaviors in structural changes after 70 and 110 keV electron irradiation due to different damage mechanisms. SEM results reveal that the irra- diation of 70 keV electrons does not change surface morphology of the MWCNT film, while the irradiation of 110 keV electrons with a high fluence of 5 x 1015 cm-2 leads to evident morphological changes, such as the formation of a rough surface, the entanglement of nanotubes and the shrinkage of nanotubes. Based on Raman spectroscopy, XPS, and XRD analyses, it is confirmed that the irradiation of 70 keV electrons increases the interlayer spacing of the MWCNTs and disorders their structure through electronic excitations and ionization effects, while the irradiation of 110 keV electrons obviously reduces the interlayer spacing of the MWCNTs and improves their graphitic order through knock-on atom dis- placements. The improvement of the irradiated MWCNTs by 110 keV electrons is attributed to the restructuring of defect sites induced by knock-on atom displacements. EPR spectroscopic analyses reveal that the MWCNTs exposed to both 70 keV electrons and 110 keV electrons suffer ionization damage to some extent.

Improved electrical properties of NO-nitrided SiC/SiO2 interface after electron irradiation

Effective improvement in electrical properties of NO passivated SiC/SiO2 interface after being irradiated by electrons is demonstrated.The density of interface traps after being irradiated by 100-kGy electrons decreases by about one order of magnitude,specifically,from 3×1012 cm-2·eV-1 to 4×1011 cm-2·eV-1 at 0.2 eV below the conduction band of 4H-SiC without any degradation of electric breakdown field.Particularly,the results of x-ray photoelectron spectroscopy measurement show that the C-N bonds are generated near the interface after electron irradiation,indicating that the carbon-related defects are further reduced.

Effects of Strain Channel on Electron Irradiation Tolerance of InP-based HEMT Structures

The introduction of strain In_(x)Ga_(1-x)As channel with high In content increases the confinement of the two-dimensional electron gas(2DEG)and further improves the high-frequency performance of InGaAs/InAlAs/InP HEMTs.The effect of In_(x)Ga_(1-x)As channel with different In contents on electron irradiation tolerance of InP-based HEMT structures in terms of 2DEG mobility and density has been investigated.The experiment results show that,after the same high electron irradiation dose,the 2DEG mobility and density in InP-based HEMT structures with strain In_(x)Ga_(1-x)As(x>0.53)channel decrease more dramatically than that without strain In_(0.53)Ga_(0.47)As channel.Moreover,the degradation of 2DEG mobility and density becomes more severe as the increase of In content and strain in the In_(x)Ga_(1-x)As channel.The research results can provide some suggestions for the design of radiation-resistant InP-based HEMTs.

MEASUREMENT OF VACANCY MIGRATION ENERGY BY ELECTRON IRRADIATION

A method together with a new formula were developed for measuring the vacancy migration energy on HVEM considering the effect of surface sink of specimen on point defects.The va- cancy migration energy may be calculated through the loop growth rate under electron irradiation at various temperatures.

The Influence of Pico-Second Pulse Electron Irradiation on the Electrical-Physical Properties of Silicon Crystals

The studies of the influence of pico-second (4 × 10-13 sec.) pulse electron irradiation with energy of 3.5 MeV on the electrical-physical properties of silicon crystals (n-Si) are presented. It is shown that in spite of relatively low electron irradiation energy, induced radiation defects are of cluster type. The behavior of main carrier mobility depending on temperature and irradiation dose is analyzed and charge carriers’ scattering mechanisms are clarified: on ionized impurities, on point radiation defects with transition into cluster formation. Dose dependencies of electrical conductivity and carrier mobility for samples of various specific resistivities are given.

Mechanical properties of multi-scale germanium specimens from space solar cells under electron irradiation

During long-term service in space,Gallium Arsenide(GaAs)solar cells are directly exposed to electron irradiation which usually causes a dramatic decrease in their performance.In the multilayer structure of solar cells,the germanium(Ge)layer occupies the majority of the thickness as the substrate.Due to the intrinsic brittleness of semiconductor material,there exist various defects during the preparation and assembly of solar cells,the influences of which tend to be intensified by the irradiation effect.In this work,first,Ge specimens for mechanical tests were prepared at scales from microscopic to macroscopic.Then,after different doses of electron irradiation,the mechanical properties of the Ge specimens were investigated.The experimental results demonstrate that electron irradiation has an obvious effect on the mechanical property variation of Ge in diverse scales.The four-point bending test indicates that the elastic modulus,fracture strength,and maximum displacement of the Ge specimens all increase,and reach the maximum value at the irradiation dose of 1×10^(15)e/cm^(2).The micrometer scale cantilever and nanoindentation tests present similar trends for Ge specimens after irradiation.Atomic Force Microscope(AFM)also observed the change in surface roughness.Finally,a fitting model was established to characterize the relation between modulus change and electron irradiation dose.

An electron beam irradiation-assisted coating method for the regulation of hydrophilicity and hydrophobicity

Developing a stable,reliable,and industrially compatible method to control hydrophobicity is crucial for separation,transportation,and the generation of special surfaces.An e-HMS-PDMS silica gel nanoparticle coating was prepared using a two-step electron beam irradiation(EBI)process,consisting of(i)grafting of two organic groups onto thiol-functionalized hollow mesoporous silica(HMS-SH)with 10 MeV EBI and(ii)curing of polydimethylsiloxane(PDMS)onto silicone rubber using the HMS hybrid materials prepared in step i as an additive with 200 keV EBI.The tuneable grafting of functional groups and the surface properties of the silica,which was embedded in the PDMS layer,allowed us to precisely control the hydrophilicity of the PDMS layer by means of altering the grafting gradient of the silica and the loading ratio of the monomers.A diverse range of vinyl-structured monomers can be used in this method,and the selection of suitable monomers is vital in determining the physical properties of the coating layer.The hydrophilicity of the coating can be linearly controlled within a specific range(50°to 155°)by using suitable monomers,allowing for the design of surfaces with specific hydrophilic and hydrophobic requirements.

Effect of electron beam irradiation on multi-walled carbon nanotubes

Multi-walled carbon nanotubes （MWCNTs） were irradiated with focused electron beams in a transmission electron microscope at room temperature. The results showed that carbon nanotubes had no obvious structural damages but only shell bending under 100 keV electron beam irradiation. However, when the electron energy increased to 200 keV, the nanotubes were damaged and amorphization, pits and gaps were detected. Furthermore, generating of carbon onions and welding between two MWCNTs occurred under 200 keV electron irradiation. It was easy to destroy the MWCNTs as the electron beams exceeded the displacement threshold energy that was calculated to be 83-110 keV. Conversely, the energy of electron beams below the threshold energy was not able to damage the tubes. The damage mechanism is sputtering and atom displacement.

Zigzag Zinc Blende ZnS Nanowires:Large Scale Synthesis and Their Structure Evolution Induced by Electron Irradiation

Large scale zigzag zinc blende single crystal ZnS nanowires have been successfully synthesized during a vapor phase growth process together with a small yield of straight wurtzite single crystal ZnS nanowires.AuPd alloy nanoparticles were utilized to catalyze a vapor-solid-solid growth process of both types of ZnS nanowires,instead of the more common vapor-liquid-solid growth process.Surprisingly,the vapor-phase grown zigzag zinc blende ZnS nanowires are metastable under high-energy electron irradiation in a transmission electron microscope,with straight wurtzite nanowires being much more stable.Upon exposure to electron irradiation,a wurtzite ZnO nanoparticle layer formed on the zigzag zinc blende ZnS nanowire surface with concomitant displacement damage.Both electron inelastic scattering and surface oxidation as a result of electron-beam heating occur during this structure evolution process.When prolonged higher-voltage electron irradiation was applied,local zinc blende ZnS nanowire bodies evolved into ZnS-ZnO nanocables,and dispersed ZnS-ZnO nanoparticle networks.Random AuPd nanoparticles were observed distributed on zigzag ZnS nanowire surfaces,which might be responsible for a catalytic oxidation effect and speed up the surface oxidation-induced structure evolution.

Improving the NV generation efficiency by electron irradiation

The nitrogen vacancy(NV)center in diamond has been well applied in quantum sensing of electromagnetic field and temperature,where the sensitivity can be enhanced by the number of NV centers.Here,we used electron beam irradiation to increase the generation rate of NV centers by nearly 22 times.We systematically studied the optical and electronic properties of the NV center as a function of an electron irradiation dose,where the detection sensitivity of magnetic fields was improved.With such samples with dense NV centers,a sub-pico-Tesla sensitivity in magnetic fields detection can be achieved with optimal controls and detections.

In-situ Observation of Point Defect and Precipitate Evolvement of CLAM Steel under Electron Irradiation

The point defect and precipitate evolution of China low activation martensitic steel （CLAM） under electron beam irradiation were characterized by high voltage electron microscopy. The process was recorded in-situ on electronsensitive films. The irradiation dose rate was 1.78 × 10-3 dpa/s and the highest dose was 2.12 dpa/s. Irradiation introduced dislocation loops into the sub-grain, which increased density when the irradiation dose was increased from 0.53 dpa to 1.59 dpa at 723 K. The precipitate, found to be an M6C type, was irradiated at 773 K at the [011] plane direction. The precipitate morphology and structure were unchanged when the irradiation dose was increased to 2.12 dpa. Compared with the irradiation at 723 K in the sub-grain, no other defects were generated at the nearby grain boundary at 773 K.

Dose rate effects on shape memory epoxy resin during 1 Me V electron irradiation in air

The effects of 1 Me V electron irradiation in air at a fixed accumulated dose and dose rates of 393.8,196.9,78.8,and 39.4 Gy s^(-1)on a shape memory epoxy(SMEP)resin were studied.Under low-dose-rate irradiation,accelerated degradation of the shape memory performance was observed;specifically,the shape recovery ratio decreased exponentially with increasing irradiation time(that is,with decreasing dose rate).In addition,the glass transition temperature of the SMEP,as measured by dynamic mechanical analysis,decreased overall with decreasing dose rate.The dose rate effects of 1 Me V electron irradiation on the SMEP were confirmed by structural analysis using electron paramagnetic resonance(EPR)spectroscopy and Fourier transform infrared(FTIR)spectroscopy.The EPR spectra showed that the concentration of free radicals increased exponentially with increasing irradiation time.Moreover,the FTIR spectra showed higher intensities of the peaks at 1660 and 1720 cm^(-1),which are attributed to stretching vibrations of amide C=O and ketone/acid C=O,at lower dose rates.The intensities of the IR peaks at 1660 and 1720 cm^(-1) increased exponentially with increasing irradiation time,and the relative intensity of the IR peak at 2926 cm^(-1)decreased exponentially with increasing irradiation time.The solid-state13 C nuclear magnetic resonance(NMR)spectra of the SMEP before and after 1 Me V electron irradiation at a dose of 1970 k Gy and a dose rate of 78.8 Gy s^(-1) indicated damage to the CH_(2)–N groups and aliphatic isopropanol segment.This result is consistent with the detection of nitrogenous free radicals,a phenoxy-type free radical,and several types of pyrolytic carbon radicals by EPR.During the subsequent propagation process,the free radicals produced at lower dose rates were more likely to react with oxygen,which was present at higher concentrations,and form the more destructive peroxy free radicals and oxidation products such as acids,amides,and ketones.The increase in peroxy free radicals at lower dose rates was thought to accelerate the degradation of the macroscopic performance of the SMEP.

Phase Separation and Crystallization Induced by Electron Irradiation in Nanoscale Fe_(56.5)Mn_(11)Cr_(8.5)Ni_4Si_(10)C_(10) Metallic Glass

A nanoscale Fe56.5Mn11Cr8.5Ni4Si10C10 metallic glass was irradiated by electron beam in a 200 kV trans- mission electron microscope. Structure evolution in the metallic glass was investigated in situ during continuous irradi- ation, where phase separation was observed after irradiation for 5 min and crystallization was observed after 33.5 min. Based on the analysis of irradiation effect, atomic displacement is believed to be the main reason for the structure rearrangement. Accumulation of atomic displacement increases the energy of the sample and promotes atomic diffusion during transformation. On the other hand, the large specific surface area of the sample also contributes to increasing free energy and atomic diffusion.

Influence of electron irradiation on the switching speed in insulated gate bipolar transistors

The influence of electron irradiation on the switching speed in insulated gate bipolar transistors（IGBT） with different epitaxial layer thicknesses is discussed in detail.The experimental results prove that the fall time of IGBT increases when increasing the thickness of the epitaxial layer.However,there is no obvious difference between the ratios of the fall time after irradiation to those before irradiation for different epitaxial layer thicknesses.The increase in switching speed of the IGBT is accompanied by an increase in the forward drop,and a trade-off curve between forward voltage drop and fall time of IGBT is presented.