Low Electron Fluence Research Articles

The effects of electron irradiation on the current-voltage and capacitance-voltage measurements of Sn/p-GaAs/Au diodes

In this study 11 (eleven) Sn/p-GaAs/Au diodes were identically fabricated. Au and Sn metals were used in order to fabricate the ohmic and rectifier contacts, respectively. The effect of electron irradiation of high electron energy of 6, 12, 15 and 18 MeV and low electron fluence of 1 × 1012 electrons/cm2 on the various parameters such as barrier height (BH), ideality factor (IF), series resistance (Rs), and rectification ratio (RR), acceptor concentration (Na), diffusion potential (Vd) obtained from current-voltage (I–V) and capacitance-voltage (C–V) characteristics of Sn/p-GaAs/Au diodes was evaluated. The BH value of one (D2) of the unirradiated 11 Sn/p-GaAs/Au diodes was calculated as 0.82 eV, 0.86 eV and 0.94 eV from ln(I)–V characteristics according to the thermionic emission (TE) theory, modified Norde’s functions, and C–V characteristics, respectively. The BH values calculated ln(I)–V and Norde’s functions were found to be very close to each other. The values of RR, IF, and BH of D2 diode calculated from ln(I)–V according to TE theory were calculated as 1 × 106, 1.09 and 0.82 eV, 1 × 106, 1.06 and 0.81 eV, 1 × 106, 1.09 and 0.82 eV, 1 × 106, 1.12 and 0.83 eV, 1 × 106, 1.13 and 0.82 eV for before and after 6, 12, 15 and 18 MeV electron irradiation, respectively. The Rs value of unirradiated and 6, 12, 15 and 18 MeV electron irradiated D2 diode was calculated from Norde’s function was calculated 29, 30, 30, 27, and 26 Ω, respectively. Since these parameters remain nearly unchanged after electron irradiation, it can be said that electron radiation has no significiant effect on ln (I)–V characteristics and the Sn/p-GaAs/Au diodes are insensitive to high-energy electron -irradiation.

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.

Influence of high-temperature annealing on the characteristics of fast electron-irradiated p-n-structures based on neutron doped silicon

The investigation results of the annealing influence (Тann = 300–800 ºС) on the minority charge currier lifetime tP in the n-base of p-n-structures, manufactured on the base of neutron transmutation doped silicon (NTD) КОФ300, irradiated at room temperature by different fluences (F = 1 · 1014 – 3 · 1016 cm–2) of electrons with the energy of Еe = 4 MeV are presented. It is established that at low electron fluences (F = 1 · 1014 cm–2), the annealing of minority charge currier lifetime tP in the n-base of p-n-structures occurs in two stages: the first – 320–400 ºС and the second – 550–650 ºС. At higher electron fluences (F = 5 · 1015–2 · 1016 cm–2), three annealing stages occur: the first – 400–450 ºС, the second – 520–650 ºС and the third – 710–770 ºС. At this, the structure barrier capacitance C dependences on Тann at high electron fluences show the geometry capacitance up to the annealing temperatures Тann = 400 ºС. In the annealing temperature range of Тann = 420–570 ºС, the increase in С with maximum is seen at Тann = 480 ºС and a subsequent decrease in the geometry capacitance is seen in the annealing temperature range of Тann = 600–670 ºС, and then again the increase in С occurs in the annealing temperature range of Тann = 720–770 ºС reaching the С values corresponding to those of the non-irradiated samples in the annealing temperature range of Тann = 770–800 ºС. The analysis of the DLTS-spectra of the investigated structures has allowed establishing the formation in the annealing process of the deep acceptor level ЕС – 0.68 eV at Тann > 400 ºС, the deep donor level ЕС – 0.32 eV in the annealing temperature range of Тann = 420–570 ºС and the deep acceptor level ЕС – 0.53 eV at Тann > 700 ºС, which satisfactorily explains the dependences of t P and С on Тann obtained in this paper.

Photoresists as a high spatial resolution autoradiography substrate for quantitative mapping of intra- and sub-cellular distribution of Auger electron emitting radionuclides

Purpose: To explore poly(methyl methacrylate) (PMMA950) as an autoradiography substrate.Materials and methods: PMMA950 was spin coated onto a silicon substrate. Resists were exposed to either a 25 or 50 keV electron beam (e-beam) with fluences of 0.1–33.6 μC/cm2. The resulting patterns were analyzed by atomic force microscopy (AFM). The dependence of pattern sensitivity and resolution on resist thickness, development time and electron energy was evaluated and correlated with Monte Carlo (MC) modeling. Conventional micro-autoradiography (MAR) images were compared to AFM images of photoresist patterns obtained following exposure from 111In-diethylenetriaminepentaacetic acid (DTPA)-human epidermal growth factor (hEGF) (4–6 MBq/μg, 40 nM DTPA-hEGF)-treated human breast cancer cells MDA-MB-468.Results: MC simulation results confirmed the similarity of particle transport in PMMA950 exposed to either an 111In point source or a 25 keV e-beam. Sensitivity was inversely related to resist thickness. Development conditions of the resists greatly affected image quality. Sensitivity of PMMA950 was similar to the UVIII™ resist (consisting of a copolymer of 4-hydroxystyrene and t- butylacrylate) at low electron fluence for both 25 and 50 keV e-beam exposure. AFM evaluation of the exposure patterns from 111In-DTPA-hEGF treated cells and nuclei provides more detailed information in comparison with that from MAR.Conclusions: Photoresist autoradiography can provide information on both the distribution of radiation sources and their strengths within a biological sample; however, the choice of photoresist material and processing conditions greatly affects the outcome.

Low-electron fluence STEM-EELS analysis of ferrihydrite nano-particles approaching the Ångstrom scale

We present here the preliminary results from a modified low electron-fluence (< 107electron nm−2) mode of electron energy-loss spectroscopy (EELS) combined with scanning transmission electron microscopy (viz. Smart-acquisition) as applied to ferrihydrite nanoparticles. Ferrihydrites of two different crystallinities (2-line and 6-line ferrihydrite) have been synthesised and characterised by bulk techniques and then comparing Fe-EELS from the surface and bulk of individual particles (crystallites of 2-6 nm diameter). Thus far we have been able to isolate the first 0.1-0.5 nm of surface EEL-signal specific to both oxygen and iron and detect no differences between the surface and bulk within a particle. The Fe-EEL signal of the 6-line ferrihydrite is consistent with previously published work however we do observe a broadening in the Fe-L3 peak of the less crystalline 2-line ferrihydrite and tentatively attribute this to distortion of the iron co-ordination in the more disordered structure.

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.

Experimental investigation of the effect of the internal space charge accumulation on the electron emission yield of insulators submitted to e-irradiation: application to polycrystalline MgO

Experiments are performed on polycrystalline MgO in order to investigate the internal effects of positive charging on the total electron emission yield (TEEY) under low incident electron fluence (a few to hundreds of fC mm−2) at 200 eV electron irradiation energy. It is experimentally shown that the Coulomb-attractive recombination of electrons undergoing emission with holes generated by the previously emitted electrons significantly affects the TEEY. Furthermore, quantitative analyses of experimental data are done to deduce the electron–hole recombination cross-section which is found to be of a few 10−11 cm−2.

Effects of radiation-induced defects on device performance in electron-irradiated SiC-MESFETs

The impact of radiation damage on the device performance of 4H-SiC metal semiconductor field effect transistors (MESFETs), which are irradiated at room temperature with 2-MeV electrons and 20-MeV protons, is studied. Different degradation behaviour with increasing fluence is observed for electron and proton irradiation. The degradation for low electron fluence is mainly attributed to the radiation-induced decrease of the Schottky barrier height at the gate contact. While no electron capture levels are observed before irradiation, three electron capture levels (E 1, E 2 and E 3) are induced after irradiation. The observed increase of the channel resistance is due to the induced lattice defects creating electron traps.

Radiation-induced defects in SiC-MESFETs after 2-MeV electron irradiation

The impact of radiation damage on the device performance of 4H-SiC metal Schottky field effect transistors, which are irradiated at room temperature with 2-MeV electrons, is studied. No performance degradation is observed by 1 × 10 15 e / cm 2 , while a slight increase of the linear drain current together with a decrease of the threshold voltage are noticed for 1 × 10 16 e / cm 2 . The degradation for low electron fluence is mainly attributed to the radiation-induced decrease of the Schottky barrier height at the gate contact. For exposures over 1 × 10 16 e / cm 2 , the drain current and transconductance decrease. The maximum transconductance for 1 × 10 17 e / cm 2 is only 18% of the value before irradiation. Although no electron capture levels are observed before irradiation, three electron capture levels ( E 1 – E 3 ) are induced after irradiation. The observed increase of the channel resistance is due to the induced lattice defects creating electron traps.

Electron and ion irradiation of zeolites

Three zeolites (analcime, natrolite, and zeolite-Y) were irradiated with 200 and 400 keV electrons. All zeolites amorphized at a relatively low electron fluence. The electron fluences for amorphization by the 200 keV electron irradiation at room temperature were: 7.0×10 19 e −/ cm 2 (analcime), 1.8×10 20 e −/ cm 2 (natrolite), and 3.4×10 20 e −/ cm 2 (zeolite-Y). These doses are equivalent to an energy deposition between 2.6×10 10 and 1.27×10 11 Gy. An inverse temperature dependence of amorphization dose was observed for all three zeolites, i.e., amorphization dose decreased with increasing temperature. Analcime was also irradiated with 1.5 MeV Kr + from 300 to 973 K. The amorphization dose by the ion irradiation was constant, ∼1×10 14 ions / cm 2 , which is ∼0.1 dpa of collisional damage and ∼6.25 × 10 8 Gy of ionizing energy deposition.

Chemistry of Cyclopropane on Pt(111): Thermal, Electron, and Photon Activation

The thermal, electron, and photon-induced chemistry of cyclopropane, c-C3H6, adsorbed on Pt(111) at 100 K has been studied. The thermal chemistry is simple. Adsorption is saturable, no multilayer accumulates, and thermal desorption exhibits only c-C3H6 with one peak at 144 K. High-resolution electron energy loss spectra results indicate that c-C3H6 adsorbs with the plane of the ring tilted away from the surface normal. The electron-induced chemistry is more complex. Irradiation with 50 eV electrons activates dissociation of adsorbed c-C3H6 at 100 K, and there are thermally activated reactions during subsequent temperature-programmed desorption. The total cross-section for destruction of c-C3H6 is 8.2 (±0.2) × 10-17 cm2. For low electron fluences, <1016 cm-2, the chemistry involved is describable in terms of C−C bond breaking to open the ring and form metallacyclic species, some of which promptly lose H to form allylic (C3H5) moieties. In subsequent thermally activated reaction-limited processes, propylene...

Thermal and electron driven chemistry of CCl4 on oxidized Si(100)

Dosed on oxidized Si(100) at 100 K, carbon tetrachloride adsorbs and desorbs without dissociation. The monolayer desorbs at 135 K, 10 K lower than the multilayer. This unusual behavior is attributed to stronger interactions between condensed CCl4 molecules than between CCl4 and SiO2. Irradiation with either low-energy (⩽50 eV) electrons or Mg Kα x rays causes C–Cl cleavage. For 50 eV incident electrons, the decay of the CCl4 temperature programmed desorption peak area occurs with an effective cross section of (2.0±0.1)×10−16 cm2. The same cross section characterizes the ejection of CCl (CCl+) during electron irradiation. After low electron fluences, C2 and C3 molecules desorb reflecting both electron-induced C–Cl bond dissociation and C–C bond formation. At 2.5 eV incident electron energy, the cross section is still high—10−17 cm2. Electron activation is attributed to a combination of impact ionization and electron attachment mechanisms.

Coupled charge trapping dynamics in thin SiO2 gate oxide under Fowler–Nordheim stress at low electron fluence

Degradation of thermally grown silicon dioxide (SiO2) in metal-oxide-semiconductor capacitors due to bulk trapped positive charges has been theoretically investigated under Fowler–Nordheim (FN) stress at a low electron fluence Qinj (⩽0.01 C/cm2) from the accumulated layer of (100) n-Si. n+-polySi gate capacitors with 22-, 27-, and 33-nm-thick SiO2 dielectrics were studied under FN stress over a wide range of cathode electric fields (6–12.5 MV/cm). The present numerical simulation is based on the tunneling electron initiated trap-to-band ionization and band-to-band ionization as the possible coupled mechanisms for the generation of positive charges and holes, respectively. Our theoretical analysis is carried out with a Gaussian and a uniform distribution of trapped holes in the oxide in addition to the widely used constant value (5 nm from the Si–SiO2 interface) of the centroid of the trapped holes. Utilizing the available experimental data, the estimated values of various trapping parameters obtained from the present coupled dynamics differ by ∼35%–40% from those obtained by the traditional analysis based on either one of the above two mechanisms. The results obtained from the present model are in good agreement with the experimental data of FN voltage shift as a function of electron fluence Qinj reported by Fazan et al. [Solid State Electron. 30, 829 (1987)]. By recourse to estimation of the trapping parameters from the experimental data under constant current stress, a comparative study of degradation under various modes of FN stressing (constant current and constant gate voltage) is also presented. The present simulation predicts the occurrence of plateau level consistent with earlier experimental observations in various measurables (FN voltage shift and FN tunneling current transient, under constant current and field stress, respectively) at a Qinj around 2×10−3 C/cm2 independent of oxide thickness and mode of stressing.

Electron Irradiation of Zeolites

AbstractThree different zeolites (analcime, natrolite, and zeolite-Y) were irradiated with 200 keV and 400 keV electrons. All zeolites amorphized under a relatively low electron fluence. The transformation from the crystalline-to-amorphous state was continuous and homogeneous. The electron fluences for amorphization of the three zeolites at room temperature were: 7.0× 1019 e/cm2 (analcime), 1.8×1020 e/cm2 (natrolite), and 3.4×1020 e/cm2 (zeolite-Y). The different susceptibilities to amorphization are attributed to the different channel sizes in the structures which are the pathways for the release of water molecules and Na+. Natrolite formed bubbles under electron irradiation, even before complete amorphization. Analcime formed bubbles after amorphization. Zeolite-Y did not form bubbles under irradiation. The differences in bubble formation are attributed to the different channel sizes of the three zeolites. The amorphization dose was also measured at different temperatures. An inverse temperature dependence of amorphization dose was observed for all three zeolites: electron dose for amorphization decreased with increasing temperature. This unique temperature effect is attributed to the fact that zeolites are thermally unstable. A semi-empirical model was derived to describe the temperature effect of amorphization in these zeolites.

A new approach to investigate gate oxide degradation of MOS capacitors during Fowler–Nordheim stress at low electron fluence

A new rate equation formalism is proposed to analyze the gate oxide degradation of metal-oxide-semiconductor (MOS) capacitors under low fluence (⩽0.01 C/cm 2) Fowler–Nordheim (FN) stress over a wide range of cathode electric field (6–12.5 MV/cm). Our present model is theoretically verified during constant current FN injection from the (100) n-Si substrate of n +-poly-Si-gate MOS capacitors with 22, 27 and 33 nm thick thermally grown SiO 2 gate oxides. The present numerical simulation is based on the tunneling electron initiated trap-to-band ionization (TTBI) and band-to-band ionization (BTBI) as the possible coupled mechanisms for the generation of the trapped positive oxide charges near both interfaces of the samples studied here. Adopting the above coupled rate equation formalism, the trapping parameters are estimated utilizing the experimental data of FN voltage shift with injection time. The parameter values obtained from our present rigorous model differ in magnitude by ∽35–40% from those obtained by the traditional analysis based on either one of the above two mechanisms. The results obtained from the coupled dynamics are in good agreement with the experimental data of FN voltage shift as a function of electron fluence Q inj by Fazan et al. The present simulation gives an interesting feature that a steady-state plateau level in the FN voltage shift, Δ V FN, occurs at Q inj around 2×10 −3 C/cm 2 independent of oxide thickness and stress current density, consistent with earlier experimental observations.

The response of n-channel EPROMs to radiation and annealing

The performance of n-channel EPROMs, type 2716 and 2732, under different types of radiation environment and high temperature annealing was studied. Variations in the number of programmed logic “0” states and unprogrammed logic “1” states of memory MOS transistors of EPROMs were measured as functions of doses of CO-60 gamma-rays, fluences of 1 and 6 MeV electrons and EPROM temperature up to 500°C. In the EPROMs, when they were exposed to radiation, the programmed “0” states gradually underwent a transition to “1” states, and finally the stored data was erased. With increased radiation doses, though all the memory MOS transistors appeared to be in “1” states, the EPROM was not programmable. After this stage when the exposure to radiation was continued, at a dose of 116 krad (Si) of Co-60 gamma-rays or at a fluence of, 2.2 × 10 13 e/cm 2 of 1 MeV electrons or 8 × 10 12 e/cm 2 of 6 MeV electrons, all the “1” states transitioned to “0” states. The transition from the “1” to the “0” states was also seen in the biased EPROMs. This rebound phenomenon for the “0” states was observed for the first time in the EPROMs irradiated either at room temperature or at liquid nitrogen temperature. Since in the case of cooled EPROMs the transition from “1” state to “0” state was observed at relatively low electron fluence, it is shown that negatively charged interface states do not influence the observed rebound phenomenon. Detailed analysis of the results and observations lead to conclusion that the positive oxide-trap charge, in the memory MOS transistors is responsible for the observed unprogrammable “1” states and that in the MOS transistors of the control circuitry for the observed radiation induced “0” states. An irradiated EPROM, when annealed at 450°C for 30 min, all its radiation-induced “0” states recovered to “1” states and the EPROM was found functioning normally. The activation energy of 1.2 eV is found to be effective for removal of the induced damage in an EPROM.

Comparison between deep level defects in GaAs induced by gamma, 1 MeV electron, and neutron irradiation

The deep level transient spectroscopy technique has been employed to follow closely the effect of 1–300 Mrad 60Co γ irradiation on the deep electron traps in undoped vapor-phase-epitaxy n-type GaAs. The 1 Mrad γ-irradiated Schottky device was identical to the as-grown or control device, with only two electron traps EL2 (Ec−0.820 eV) and EL3 (Ec−0.408 eV) detected. At a γ dose of 5 Mrad, two additional electron traps EL6 (Ec−0.336 eV) and E2 (Ec−0.128 eV) were observed. As the γ doses were increased to ≥10 Mrad, a third electron trap E1 (Ec−0.033 eV) was observed, and the single exponential EL2 capacitance transient became a double exponential, indicating two deep levels lying at Ec−0.820 eV (EL2/EL2-A) and Ec−0.843 eV (EL2-B). The trap concentration of EL2-A remained unchanged up to a γ dose of 50 Mrad before starting to increase slowly as the γ dose was increased to ≥100 Mrad. In contrast, the EL2-B trap concentration was found to increase by 32 times, reaching 2.6×1014 cm−3 at 300 Mrad from a low 8.0×1012 cm−3 at 10 Mrad when it was first observed, whereas for the 1 MeV electron irradiation with low electron fluence of 1014 e cm−2, the EL6, E2, E1, and the double exponential EL2 were detected at the same time. There was no sign of EL2-B, EL3, EL6, E2, or E1, but an additional broad U band was observed after irradiation with 1 MeV neutrons. The results of the γ and neutron irradiation suggest that the presence of the double exponential EL2 transients is not related to either EL6, E2, E1, or the U band, and is unlikely to be due AsGa→VGa+Asi but is probably caused by the AsGa complex defects involving an irradiation defect. The defect concentration of trap E1 increased strongly from 5.4×1013 cm−3 at 10 Mrad to 9.3×1014 cm−3 at 100 Mrad, and E2 increased from 2.1×1013 cm−3 at 5 Mrad to 6.7×1014 cm−3 at 100 Mrad.

European domestic heating update — United Kingdom radiators and domestic heat emitters

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 L2,3-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 H2O) 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.

The effect of electron radiation on CdS/Cu2S thin film solar cells

Abstract Encapsulated and unencapsulated CdS/Cu2S thin film solar cells have been irradiated with monoenergetic electrons having energies in the range 100–425 keV. The current-voltage characteristics of the solar cells have been analysed in terms of a five parameter model. A study has been made of the way in which these parameters (and Ig , Voc and cell efficiency) depended on energy and fluence of the electron beam. The degradations of the encapsulated cells have been shown to be due mainly to the darkening of the Mylar encapsulant. A mechanism for the reduction of the open circuit voltage (Voc ) on irradiation under high and low electron fluences has been proposed.

The Fluence of Low Energy Electrons established within and emitted from Irradiated Conducting Materials

A parallel-plate vacuum chamber has been used to measure the low energy electron fluence emitted from and established within irradiated materials. The variation of the electron fluence with photon energy and atomic number of the material has been studied and implications for dosimetry discussed. The low energy electron fluence within soft tissues irradiated by photons is estimated as 4 × 106 electrons cm−2 sec−1.