Effect Of High-energy Electron Irradiation Research Articles

Effect of High-Energy Electron Irradiation on the Microstructure and Properties of Polyetherimide

Effect of High-Energy Electron Irradiation on the Microstructure and Properties of Polyetherimide

Electron Beam Induced Enhancement and Suppression of Oxidation in Cu Nanoparticles in Environmental Scanning Transmission Electron Microscopy.

We have investigated the effects of high-energy electron irradiation on the oxidation of copper nanoparticles in environmental scanning transmission electron microscopy (ESTEM). The hemispherically shaped particles were oxidized in 3 mbar of O2 in a temperature range 100-200 °C. The evolution of the particles was recorded with sub-nanometer spatial resolution in situ in ESTEM. The oxidation encompasses the formation of outer and inner oxide shells on the nanoparticles, arising from the concurrent diffusion of copper and oxygen out of and into the nanoparticles, respectively. Our results reveal that the electron beam actively influences the reaction and overall accelerates the oxidation of the nanoparticles when compared to particles oxidized without exposure to the electron beam. However, the extent of this electron beam-assisted acceleration of oxidation diminishes at higher temperatures. Moreover, we observe that while oxidation through the outward diffusion of Cu+ cations is enhanced, the electron beam appears to hinder oxidation through the inward diffusion of O2- anions. Our results suggest that the impact of the high-energy electrons in ESTEM oxidation of Cu nanoparticles is mostly related to kinetic energy transfer, charging, and ionization of the gas environment, and the beam can both enhance and suppress reaction rates.

Reflection high energy electron diffraction (RHEED) study of ice nucleation and growth on Ni(111): influences of adspecies and electron irradiation.

How interfacial molecular interactions influence nucleation and growth processes of water ice is explored using pristine, oxygenated, and CO-adsorbed Ni(111) substrates based on RHEED, together with the effects of high-energy electron irradiation on the crystallization kinetics. A monolayer of amorphous solid water deposited onto the pristine Ni(111) substrate crystallizes into ice Ic at ca. 150 K, whereas ice Ih (Ic) is formed preferentially during water vapor deposition at 135 K (125 K). The ice nucleation tends to be hampered on the oxygenated Ni(111) surface because of the hydrogen bond formation with chemisorbed oxygen, leading to the growth of randomly-oriented ice Ic crystallites via spontaneous nucleation. The amorphization and recrystallization of initially crystalline ices are observed during prolonged RHEED measurements at 20 and 70 K, respectively, signifying that high-energy electron irradiation has both thermal and non-thermal effects on the water phase transition. The epitaxial growth (non-epitaxial growth) of ice occurs during electron irradiation of amorphous solid water formed on the pristine and oxygenated Ni(111) substrates (CO-adsorbed Ni(111) substrate) even at 100 K (120 K) because nucleation and growth are initiated at the substrate interface (in the ASW film interior).

Effects of High-Energy Electron Irradiation on Quantum Emitters in Hexagonal Boron Nitride.

Hexagonal boron nitride (hBN) mono and multilayers are promising hosts for room-temperature single photon emitters (SPEs). In this work we explore high-energy (∼MeV) electron irradiation as a means to generate stable SPEs in hBN. We investigate four types of exfoliated hBN flakes-namely, high-purity multilayers, isotopically pure hBN, carbon-rich hBN multilayers and monolayered material-and find that electron irradiation increases emitter concentrations dramatically in all samples. Furthermore, the engineered emitters are located throughout hBN flakes (not only at flake edges or grain boundaries) and do not require activation by high-temperature annealing of the host material after electron exposure. Our results provide important insights into controlled formation of hBN SPEs and may aid in identification of their crystallographic origin.

High energy electron irradiation effects on Ga-doped ZnO thin films for optoelectronic space applications

Gallium-doped ZnO (GZO) thin films of thickness 394 nm were prepared by a simple, cost-effective sol–gel spin coating method. The effect of 8 MeV electron beam irradiation with different irradiation doses ranging from 0 to 10 kGy on the structural, optical and electrical properties was investigated. Electron irradiation influences the changes in the structural properties and surface morphology of GZO thin films. X-ray diffraction analysis showed that the polycrystalline nature of the GZO films is unaffected by the high energy electron irradiation. The grain size and the surface roughness were found maximum for the GZO film irradiated with 10 kGy electron dosage. The average transmittance of GZO thin films decreased after electron irradiation. The optical band gap of Ga-doped ZnO films was decreased with the increase in the electron dosage. The electrical resistivity of GZO films decreased from 4.83 × 10−3 to 8.725 × 10−4 Ω cm, when the electron dosage was increased from 0 to 10 kGy. The variation in the optical and electrical properties in the Ga-doped ZnO thin films due to electron beam irradiation in the present study is useful in deciding their compatibility in optoelectronic device applications in electron radiation environment.

Electrical characterization of electron irradiated and annealed lowly-doped 4H-SiC

The effect of high energy electron (HEE) irradiation on nickel Schottky contacts fabricated on lowly-doped n-type 4H-SiC was investigated by deep level transient spectroscopy (DLTS) and high resolution Laplace-DLTS. The Schottky contacts were deposited by resistive evaporation of nickel and were observed to be of good rectification quality from current-voltage measurements. DLTS was performed up to 350K to investigate the presence of defects before and after HEE irradiation. HEE irradiation was observed to induce three deep level defects below 350K at 0.42eV, 0.62eV and 0.76eV below the conduction band minimum. These deep level defects are labelled E0.42, E0.62 and E0.76. Defects E0.42 and E0.76 were observed after the same electron fluence and were annealed out at the same temperature, suggesting that the defects could be strongly related. The effect of HEE irradiation and annealing on as-grown defects was also investigated and is reported.

The Effect of an Incident Electron Beam on the I–V Characteristics of a Au-ZnSe Nanowire-Au Nanostructure

In order to the modify electron transport property of a metal-semiconductor nanowire(NW)-metal (M-S-M) nanostructure, the effect of high-energy electron irradiation on the current-voltage (I–V) characteristics of M-S-M nanostructure is investigated by in situ transmission electron microscopy. Experimentally measured I–V characteristics of an M-S-M nanostructure can be obviously modified under electron beam irradiation. The current increases rapidly due to increase of the carrier densities resulting from the electron-hole pair excitation in the NW irradiated by the electron beam. If the electron beam is focused on the NW (M-S) nanocontact, the electrons in the Au electrode are excited to higher energy states above the height of the Schottky barrier that becomes transparent to the conduction electrons. As a result, the nonlinear to linear I–V characteristics can be observed. The experimentally revealed I–V characteristics corresponding to transformation from the rectification to Ohm strongly suggest that the intrinsic transport property of the M-S nanocontact can be completely modified by irradiation of the high-energy electron beam.

Effect of high-energy electron irradiation on forsterite laser crystals

The effect of 21-MeV electron irradiation on the optical absorption characteristics of Czochralski-grown forsterite (Mg2SiO4) single crystals (both undoped and chromium-doped) has been investigated. The irradiation is found to induce additional optical absorption (AOA) in the crystals in the range of 225–1200 nm due to the formation of color centers based on intrinsic host point defects and the change in the oxidation state of chromium ions. The AOA spectra have been decomposed into elementary bands. The influence of the chromium concentration in crystals, the oxygen content in the growth atmosphere, and additional doping with lithium on the behavior of these bands has been analyzed. A possible structure of the color centers responsible for the AOA is discussed. It is shown that the electron irradiation somewhat decreases the intensity of the characteristic absorption bands of tri- and tetravalent chromium ions and gives rise to a new absorption band in Mg2SiO4:Cr and Mg2SiO4:Cr,Li crystals heavily doped with chromium.

Effect of high-energy electron irradiation in an electron microscope column on fluorides of alkaline earth elements (CaF2, SrF2, and BaF2)

The effect of high-energy (150 eV) electron irradiation in an electron microscope column on crystals of fluorides of alkaline earth elements CaF2, SrF2, and BaF2 is studied. During structural investigations by electron diffraction and electron microscopy, the electron irradiation causes chemical changes in MF2 crystals such as the desorption of fluorine and the accumulation of oxygen in the irradiated area with the formation of oxide MO. The fluorine desorption rate increases significantly when the electron-beam density exceeds the threshold value of ∼2 × 103 pA/cm2). In BaF2 samples, the transformation of BaO into Ba(OH)2 was observed when irradiation stopped. The renewal of irradiation is accompanied by the inverse transformation of Ba(OH)2 into BaO. In the initial stage of irradiation of all MF2 compounds, the oxide phase is in the single-crystal state with a lattice highly matched with the MF2 matrix. When the irradiation dose is increased, the oxide phase passes to the polycrystalline phase. Gaseous products of MF2 destruction (in the form of bubbles several nanometers in diameter) form a rectangular array with a period of ∼20 nm in the sample.

Effects of high-energy electron irradiation on blue luminescence of unintentionally doped GaN heterostructure

The unintentionally doped epitaxial GaN was grown on (0001) sapphire by metal organic chemical vapor deposition (MOCVD). The effects of 2MeV electron irradiation with the doses of 1×1015/cm2 and 5×1015/cm2 on the GaN epilayers were investigated by photoluminescence (PL) and Rutherford backscattering spectroscopy (RBS). The blue luminescence (BL) from the GaN epitlayers decreases significantly after the dose of 1×1015/cm2 electron irradiation. This is attributed to complex formation of BL-related defects with other point defects. On the contrary, the BL intensity from the GaN epilayers subjected to electron irradiation with the dose of 5×1015/cm2 increases beyond the BL intensity from the low-dose irradiated one. It is deduced that the surplus gallium vacancies in 1− charge state (VGa1-) could lead to the BL intensity rebounding as electron irradiation damage accumulated.

Evolution of High-Energy Electron Beam Irradiation Effects on Zeolite Supported Catalyst: Metal Nanoprecipitation

The high-energy electron irradiation effects on Fe-loaded, zeolite-supported catalyst were examined by transmission electron microscopy. In the original sample under little beam irradiation, no nanoparticles larger than 1 nm can be observed, and about half of the loaded Fe is identified as being in a positive ion state (i.e., iron oxides). Metal Fe nanoparticles in neutral state Fe0 were then found to precipitate quickly under beam illumination with an electron dose of ∼2.4 × 107 nm–2 or above at room temperature. Since electron microscopy is widely applied in the characterization of all sorts of catalysts supported on zeolites, the current observations could be treated as a model system to distinguish the metal nanoparticles existing in the original catalyst from those precipitated by electron beam irradiation. It was the ionization effect of electron radiation, other than temperature rise, that played an important role in the formation and growth of the metal precipitates. In the current system, the induced nanoprecipitations were identified as pure Fe metal clusters by electron energy loss spectroscopy (EELS), high-resolution transmission electron microscopy (HRTEM), and electron diffraction. As in current modeling system, although only metal Fe nanoparticles can be observed by EELS if the irradiation effect is ignored at the first place, the functional component in the loaded catalyst is actually a mixture of Fe-oxide and Fe.

Effect of high-energy electron irradiation of a multilayer W-Mo system on the spectral characteristics of thermowave processes

A method is developed to analyze the state of the interface in a multilayer metallic system; it is based on spectral analysis of a heat-transfer coefficient. A coefficient of correlation is used to find the relation between the spectral characteristics and the thermal conductivity of the interphase interface. The change in the coefficient of correlation induced by 10-MeV electron irradiation of a multilayer W-Mo system is studied.

Effects of High-Energy Electron Irradiation on ZnO/Si MSM Photodetectors

ZnO/Si metal–semiconductor–metal photodetectors (MSM-PDs) were subjected to high-energy electron irradiation (HEEI) to total fluence of 2 × 1013 cm−2. ZnO/Si MSM-PDs demonstrated at least 43% greater radiation resistance than similar Si devices. Room-temperature annealing of radiation damage was observed as 63% recovery of photocurrent over 47 days. The current transport mechanism for ZnO/Si MSM-PDs was dominated by space-charge-limited conduction (SCLC) with minimal effect on conduction regime due to HEEI. Analysis of photoluminescence (PL) data indicates that the radiation-induced defects are likely oxygen and zinc vacancies, i.e., (V 0 + ) and $$ (\hbox{V}_{\rm{Zn}}^{ - } - \hbox{H}^{ + } )^{0} $$ , respectively.

Electron-beam-induced reduction of Fe 3+ in iron phosphate dihydrate, ferrihydrite, haemosiderin and ferritin as revealed by electron energy-loss spectroscopy

The effect of high-energy electron irradiation on ferritin/haemosiderin cores (in an iron-overloaded human liver biopsy), its mineral analogue; six-line ferrihydrite (6LFh), and iron phosphate dihydrate (which has similar octahedral ferric iron to oxygen coordination to that in ferrihydrite and ferritin/haemosiderin cores) has been investigated using electron energy-loss spectroscopy (EELS). Fe L 2,3-ionisation edges were recorded on two types of electron microscope: a 200 keV transmission electron microscope (TEM) and a 100 keV scanning transmission electron microscope (STEM), in order to investigate the damage mechanisms in operation and to establish a methodology for minimum specimen alteration during analytical electron microscopic characterisation. A specimen damage mechanism dominated by radiolysis that results in the preferential loss of iron co-ordinating ligands (O, OH and H 2O) is discussed. The net result of irradiation is structural re-organisation and reduction of iron within the iron hydroxides. At sufficiently low electron fluence and particularly in the lower incident energy, finer probe diameter STEM, the alteration is shown to be minimal. All the materials examined exhibit damage which as a function of cumulative fluence is best fitted by an inverse power-law, implying that several chemical and structural changes occur in response to the electron beam and we suggest that these are governed by secondary processes arising from the primary ionisation event. This work affirms that electron fluence and current density should be considered when measuring mixed valence ratios with EELS.

High energy electron irradiation effects on polystyrene films

The effect of an 8 MeV electron-beam on the structural, optical and dielectric properties of polystyrene films has been investigated respectively by means of Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–VIS) spectroscopy and electrical impedance (LCR) analysis over a radiation dose in the range of 50–250 kGy using a Microtron accelerator. The FTIR spectral analysis shows no change in the overall structure of the irradiated polystyrene films, except a minor change in the intensity of a few peaks in the FTIR spectrum, indicating that polystyrene is resistant to electron-beam irradiation over the range of radiation doses investigated. The optical band gap analysis using the UV–VIS absorption spectra of the polystyrene shows a small decrease in the optical band gap (E g) and the activation energy with an increase in electron doses. Further, the dielectric measurements over a frequency range of 100 Hz to 1 MHz for the electron-beam-irradiated polystyrene films show that both the dielectric constant and the dielectric loss increase with an increase in electron radiation dose, which may be ascribed to the formation of defect sites in the band gap of polystyrene as a consequence of molecular chain scission in the polymer films upon irradiation.

Electron irradiation effects on the organic-on-inorganic silicon Schottky structure

In this study, the effects of high-energy electron irradiation on the electrical characteristics of a Rhodamine-101(Rh101)/p-Si Schottky structure were investigated. Some contact parameters such as barrier height, ideality factor and series resistance were calculated from the current–voltage ( I– V) characteristics. It was seen that these three parameters were increased by the electron irradiation. After the electron irradiation, it was also seen that the carrier concentration, the reverse bias current and the capacitance of the device decreased.

The effect of high-energy electron irradiation on ZnO-based ohmic and Schottky contacts

A systematic study of radiation effects on the major parameters of ohmic and Schottky contacts based on n-ZnO is introduced. Al and Au metals were used as contact elements in order to fabricate the ohmic and Schottky structures, respectively. The transmission line method (TLM) measurements on Al/n-ZnO have revealed that high-energy (6, 9, 12 MeV) and relatively low-dose (3 × 1012 e− cm−2) electron irradiation produced lower specific ohmic contact resistivity values as compared with the reference sample. The current–voltage (I–V) and capacitance–voltage (C–V) measurements on the Au/n-ZnO structures are shown to increase in ideality and to decrease in the Schottky barrier heights with increasing electron energy. These findings have been interpreted based on the assumption that the atoms of the contact elements diffused into the semiconductor material, thus turning the rectifying character to ohmic behaviour with the influence of radiation–matter interaction and subsequent annealing effects.

Relaxor ferroelectric behavior and structural evaluation in electron-irradiated P (vinylidene fluoride-trifluoroethylene) copolymer blends

The effect of high-energy electron-irradiation on binary ferroelectric blends of poly(vinylidene fluoride-trifluoroethylene) 56/44 and 80/20 mol% has been studied in a broad dose ranging from 0 to 120 Mrad. It was found that the blends transformed from a normal ferroelectric to relaxor ferroelectric, obeying the Vogel-Fulcher law, after a proper electron dose by dielectric constants and loss measurements. X-ray diffraction shows significant changes in the ferroelectric-to-paraelectric phase transition behavior from all-trans to trans-gauche conformation after irradiation. In differential scanning calorimetry (DSC) thermograms, the Curie temperature and melting temperature decrease with the dose, indicating that there exists a strong lattice coupling between the two copolymers.

Effects of high-energy electron irradiation on heavy-metal fluoride glass

The effects of high-energy (100keV) electron irradiation have been observed in a heavy-metal fluoride glass using in situ time-resolved electron energy loss spectroscopy in a scanning transmission electron microscope. Formation of F2 has been observed. The irradiation-induced changes of configuration and composition are discussed based on the evolution of the near-edge fine structures of F K edge. We suggest that the high sensitivity to electron irradiation is due to the existence of nonbridging F in heavy-metal fluoride glasses so that is there is a tendency of the electron irradiation to eliminate nonbridging F in the irradiated region.

High-energy electron irradiation and B coordination in Na2O–B2O3–SiO2 glass

The effects of high-energy electron irradiation and the fractions of B atoms in particular sites in a Na borosilicate glass have been studied using time resolved electron energy loss spectroscopy in a scanning transmission electron microscope. Conversion of B atoms from the tetrahedral into trigonal coordination under irradiation has been observed. A mechanism for high-energy electron irradiation processes in Na borosilicate glasses is proposed based on the evolution of the near-edge fine structures of the B K, Si L and O K-edges.