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Chalcogenide thin films that undergo reversible phase changes show promise for use in next-generation nanophotonics, microelectronics, and other emerging technologies. One of the many studied compounds, Ge2Sb2Te5, has demonstrated several useful properties and performance characteristics. However, the efficacy of benchmark Ge2Sb2Te5 is restricted by amorphous phase thermal stability below ∼150 °C, limiting its potential use in high-temperature applications. In response, previous studies have added a fourth species (e.g., C) to sputter-deposited Ge2Sb2Te5, demonstrating improved thermal stability. Our current research confirms reported thermal stability enhancements and assesses the effects of carbon on crystalline phase radiation response. Through in situ transmission electron microscope irradiation studies, we examine the effect of C addition on the amorphization behavior of initially cubic and trigonal polycrystalline films irradiated using 2.8 MeV Au to various doses up to 1 × 1015 cm−2. It was found that increased C content reduces radiation tolerance of both cubic and trigonal phases. [ABSTRACT FROM AUTHOR]

Studies of the radiation tolerance and electrical behavior of gallium nitride (GaN) based devices are important for the next generation of high-power and high-voltage electronics that may be subjected to harsh environments such as nuclear reactor and fusion facilities, particle accelerators, and post-denotation environments. In this work, we study the behavior of Ga-polar and N-polar GaN Schottky diodes before and after exposure to fast and thermal + fast neutrons. Temperature-dependent current–voltage (I–V) and circular transmission line method (CTLM) measurements were used to study the electrical characteristics. A strong reduction in reverse leakage current and an increase in differential resistance in forward bias were observed after neutron irradiation. Thermionic emission (TE), Frenkel–Poole (FP) emission, and Fowler–Nordheim (FN) tunneling models were used to explain the forward and reverse I–V characteristics pre- and post-irradiation. The study confirms that Ga-polar and N-polar GaN Schottky diodes exhibit different electrical responses to fast and thermal neutron irradiations. The reverse bias characteristics of N-polar diodes are less affected after the fast neutron irradiation compared to Ga-polar diodes, while in the forward bias region, the electrical behavior after fast and thermal neutron irradiations is similar in Ga-polar and N-polar diodes. The results indicate that the role of orientation should be considered in the design of GaN-based radiation-tolerant electronics. [ABSTRACT FROM AUTHOR]

Ultra-thin solar cells are of significant interest for use in space due to their intrinsic radiation tolerance, which may allow them to be used in particularly harsh radiation environments, where thicker cells would degrade rapidly and enable reduction in cover glass thickness to reduce launch mass. In this study, devices with an 80 nm GaAs absorber layer were irradiated with 3 MeV protons. It is shown that integrated light management in these ultra-thin devices offers enhanced efficiency, in addition to extended lifetime through radiation resilience. Time-resolved cathodoluminescence is employed to map the introduction of radiation-induced defects with increasing proton fluence and characterize a decrease in carrier lifetime from 198 ± 5 ps pre-radiation to 6.2 ± 0.6 ps, after irradiation to 2 × 10 14 c m − 2 fluence. Despite the substantial reduction in carrier lifetime, short-circuit current does not degrade up to a proton fluence of 1 × 10 15 cm − 2 , beyond which a collapse in short-circuit current is observed. This exposure correlates with the point at which the carrier lifetime, extrapolated from cathodoluminescence, becomes comparable to the transit time for carriers to cross the ultra-thin device. Variation in current–voltage behavior with carrier lifetime and fluence shows that the recombination statistics are similar to those of a Shockley–Read–Hall single deep-level trap model, but that bimolecular recombination does not fully describe the observed behavior. An implication of these highly radiation tolerant cells for space power systems is shown to offer significant savings in cover glass mass, compared with a thicker cell. [ABSTRACT FROM AUTHOR]

Localized residual stress and elastic strain concentrations in microelectronic devices often affect the electronic performance, resistance to thermomechanical damage, and, likely, radiation tolerance. A primary challenge for the characterization of these concentrations is that they exist over sub- μ m length-scales, precluding their characterization by more traditional residual stress measurement techniques. Here, we demonstrate the use of synchrotron x-ray-based differential aperture x-ray microscopy (DAXM) as a viable, non-destructive means to characterize these stress and strain concentrations in a depth-resolved manner. DAXM is used to map two-dimensional strain fields between the source and the drain in a gallium nitride (GaN) layer within high electron mobility transistors (HEMTs) with sub- μ m spatial resolution. Strain fields at various positions in both pristine and irradiated HEMT specimens are presented in addition to a preliminary stress analysis to estimate the distribution of various stress components within the GaN layer. γ -irradiation is found to significantly reduce the lattice plane spacing in the GaN along the sample normal direction, which is attributed to radiation damage in transistor components bonded to the GaN during irradiation. [ABSTRACT FROM AUTHOR]

Radiation tolerance of semiconductors depends on the dynamic defect annealing efficiency during irradiation. Consequently, it matters at what temperature one keeps the sample during irradiation, so that elevated temperatures typically result in lower remaining disorder. In the present work, we observed an opposite trend for the nitrogen ion implants into zinc oxide. Combining ion channeling technique, x-ray diffraction, and photoluminescence spectroscopy, we demonstrate that the interaction of nitrogen with radiation defects promotes an inverse dynamic annealing process, so that the increase in irradiation temperature leads to a more efficient defect formation. As a result, the residual radiation disorder is maximized at 650 °C and this state is characterized by the appearance of prominent optical signatures associated with zinc interstitials and strongly reduced strain accumulation as compared to the samples implanted at lower temperatures. However, for higher implantation temperatures, the impact of the inverse annealing decreases correlating with the surface degradation and loss of nitrogen. [ABSTRACT FROM AUTHOR]

Fe–Cr alloys are at the forefront for high radiation tolerant materials with long-standing validated performance. Yet, the detailed mechanism behind their high radiation resistance is in question and understanding the effect of varying Cr percentage is a grand challenge limiting further improvements. Here, we applied depth-resolved positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy to study the effect of Cr alloying on the formation and evolution of atomic size clusters induced by ion-irradiation in Fe. We also used atom probe tomography to investigate the possible presence of Cr clusters or α′ phase precipitates with high Cr composition. The study reveals that the well-known resistance to radiation in Fe–Cr alloys may arise from the stabilization of vacancy clusters around Cr atoms, which act as sinks for radiation-induced defects. This implies that Cr atoms do not provide a direct sink for interstitials; rather defect complexes that consist of Cr atoms and vacancies, in turn, act as sinks for irradiation-induced vacancies and interstitials. we also find that lower amounts of Cr create smaller defect clusters that act as efficient sinks for radiation damage, but larger quantities of Cr form a defect structure that is less homogenous and larger in size, resulting in less efficient damage recombination. No evidence of α′ was found before or after irradiation, which indicates that it does not contribute to the observed radiation tolerance. [ABSTRACT FROM AUTHOR]

Complex-concentrated-alloys (CCAs) are of interest for a range of applications due to a host of desirable properties, including high-temperature strength and tolerance to radiation damage. Their multi-principal component nature results in a vast number of possible atomic environments with the associated variability in chemistry and structure. This atomic-level variability is central to the unique properties of these alloys but makes their modeling challenging. We combine atomistic simulations using many body potentials with machine learning to develop predictive models of various atomic properties of CrFeCoNiCu-based CCAs: relaxed vacancy formation energy, atomic-level cohesive energy, pressure, and volume. A fingerprint of the local atomic environments is obtained combining invariants associated with the local atomic geometry and periodic-table information of the atoms involved. Importantly, all descriptors are based on the unrelaxed atomic structure; thus, they are computationally inexpensive to compute. This enables the incorporation of these models into macroscopic simulations. The models show good accuracy and we explore their ability to extrapolate to compositions and elements not used during training. [ABSTRACT FROM AUTHOR]

Fermi level controlled point defect balance is demonstrated in ion irradiated indium oxide ( In 2 O 3). Specifically, our observations can be sub-divided into the formation of isolated Frenkel pairs and secondary defects, correlated with an increase and decrease in resistance, respectively. Importantly, by considering the net charge contribution from the most energetically stable Frenkel pair configurations, we explain the data trends for low doses and determine an upper limit for the Fermi level pinning. Moreover, by comparing the corresponding number of generated carriers with the ballistic defect generation rates, we estimate the dynamic annealing efficiency. Further irradiation toward higher doses is consistent with the buildup of secondary defects. As such, the present data may be of practical use in a variety of In 2 O 3 device applications requiring predictions of its radiation tolerance. In a broader perspective, the present methodology may be valuable for benchmarking defect simulation data in semiconductors in general. [ABSTRACT FROM AUTHOR]

It is the first time to fabricate the polymethyl methacrylate (PMMA) based compound kinoform lenses (CKLs) for nano-focusing of hard x-rays. The PMMA CKLs with a physical aperture of 160 µm and a focal length of 20 mm are designed and fabricated by x-ray LIGA technology at the Beijing Synchrotron Radiation Facility. To improve the stiffness of the PMMA lines, PMMA sheets with high molecular weight are fabricated, and the results revealed that the PMMA lines with higher molecular weight were much stronger. After optimization, CKLs with the narrowest lines of 4 µm width can achieve 110 µm height and 2.99 nm surface roughness without deformation. The CKLs were tested at the Diamond Light Source, which provided a focal width of 122 nm for 12 keV x rays. Though the PMMA has a poor radiation tolerance, it has a better process tolerance, and it can lay a good foundation for the fabrication of SU8 based CKLs by LIGA technology, which has a better radiation tolerance. Compared to the Si CKLs fabricated by dry etching, the PMMA CKLs are higher in depth, smoother at the sidewall, and have better nanofocusing. [ABSTRACT FROM AUTHOR]

Grain size driven effects on electronic excitation-induced structural modifications have been investigated in nanocrystalline (NC) Nd2Zr2O7 on irradiation with 100 MeV iodine ions. Characterizations have been performed with in situ x-ray diffraction, Raman spectroscopy, and plane-view high-resolution transmission electron microscopy techniques. NC-powders of Nd2Zr2O7 were synthesized by auto gel-combustion and sintered at different temperatures to obtain different grain-sized samples. XRD analysis of the smallest grain-sized sample reveals the highest order–disorder transition (from pyrochlore to a more radiation-resistant phase; anion-deficient fluorite) rate at initial ion fluences followed by least amorphization at higher ion fluences. A strong correlation of the transformation build-up with the double ion impact model confirms the two step amorphization process in NC-Nd2Zr2O7 with the disordered anion-deficient fluorite structure as an intermediate phase. TEM result supports the formation of circular ion track consisting of randomly distributed regions (anion-deficient fluorite structure and amorphous regions), surrounded by a microstrain induced defect-rich pyrochlore superstructure. Lesser ordering at cationic sites and a relatively larger number of grain boundaries are responsible for the highest radiation tolerance exhibited by the smallest grain-sized sample. The present study reports a relatively higher radiation stability of NC-ternary pyrochlore oxide, Nd2Zr2O7, with a grain size of a few tens of nm, which establishes its application as a potential inert matrix for nuclear applications. [ABSTRACT FROM AUTHOR]

Oxygen vacancies are found to play a crucial role in inducing many functional properties at the heterointerfaces in complex oxides. Gaining better control over the properties requires an understanding of the atomic structure of oxygen vacancies at the heterointerfaces. In this paper, we elucidate the effects of the interfacial strain on the oxygen-vacancy ordering in fluorite δ-Bi2O3 and perovskite LaNiO2.5 using first-principles calculations. By applying biaxial strains, we find that the 〈110〉−〈111〉 oxygen vacancy order in δ-Bi2O3 is broken, resulting in a faster diffusion of oxygen ions. Similarly, the biaxial strain is used to leverage both ordered and disordered arrangements of vacancies in LaNiO2.5. Besides the vacancy order, we find that the biaxial strain can also be used to break the cation order in Gd2Ti2O7, where Gd and Ti antisites can be created on the cation sublattice, which leads to enhanced radiation tolerance and higher oxygen diffusivity. These results indicate that the biaxial strain that is commonly present at heterointerfaces can be used to gain control over both ordered and disordered arrangements of defects, potentially opening new opportunities to functionalize complex oxides. [ABSTRACT FROM AUTHOR]

The ability of high-entropy alloys to resist radiation damage is rooted in their compositional complexity and associated high configurational entropy. In addition, grain boundaries within all alloys serve as effective sinks for defects. Using atomistic modeling, we investigated defect–grain boundary interaction mechanisms near ordered and amorphous grain boundaries in pure nickel and in a model, quaternary, high-entropy alloy (FeCoCrNi). Our results demonstrate that a combination of compositional complexity with amorphization of the grain boundary leads to much more efficient recombination and annihilation mechanisms. Coupling these two microstructural features results in the lowest amount of residual damage, indicating that these effects compound to increase radiation tolerance. These observations are rooted in locally dependent defect migration barriers in the high-entropy alloy and the strong trapping at both ordered and amorphous grain boundaries. [ABSTRACT FROM AUTHOR]

Owing to their excellent radiation tolerance, some of the high-entropy alloys (HEAs) are considered as potential candidates for structural materials in extreme conditions. In order to shed light on the early-stage irradiation damage in HEAs, we performed positron annihilation spectroscopy on hydrogen implanted equiatomic FeMnNiCoCr and interstitial carbon-containing FeMnNiCoCr HEAs. We reveal primary damage as monovacancies in low dose irradiated HEAs. The enhancement of Frenkel pair recombination by C addition is observed in C-containing HEAs. In addition, the C interstitials suppress the vacancy cluster formation in high dose irradiated HEAs. [ABSTRACT FROM AUTHOR]

Significant resistivity variations have previously been observed in oxides subjected to relatively low ion irradiation doses, nominally insufficient to generate the amount of bulk defects needed to explain the phenomena. In an effort to unveil the underlying mechanisms, we performed a systematic comparative study of the resistivity evolution in In2O3-based oxides as a function of low ion doses and ultraviolet (UV) illumination, observing striking correlations. Specifically, we found that irradiation with ∼3 × 1012 Si/cm2 and ∼18 h UV exposure result in similar resistivity drops, interpreted in terms of irradiation/illumination assisted desorption of oxygen containing species from the surface. This was further proven by post-irradiation exposure of one of the samples to an oxygen atmosphere partially restoring the resistivity. Combining the present results with literature data, we conclude that the radiation tolerance of In2O3-based and similar oxides depends on the surface charge modifications, individual defect contributions, and contributions from defect complexes at low, intermediate, and high doses, respectively. [ABSTRACT FROM AUTHOR]

Yttria stabilized zirconia pellets with different crystallite sizes were irradiated with 80 MeV Ag6+ ions at room temperature and 1000 K to understand the effect of crystallite size/material microstructure and irradiation temperature on the radiation tolerance against high energy heavy ions [where electronic energy loss (Se) dominates]. XRD and Raman spectroscopy measurements reveal that, irrespective of the irradiation temperature, the nano-crystalline samples suffered more damage when compared with the bulk-like sample. A reduction in the irradiation damage, i.e., improvement in the radiation tolerance, was observed for all the samples irradiated at 1000 K. The reduction in the damage, however, was remarkably higher for the nano-crystalline samples compared with the bulk-like sample, and hence the difference in the damage between the bulk-like and nano-crystalline samples was also significantly lower at 1000 K than that at room temperature. The irradiation damage, against Se, was thus found to be critically dependent on the interplay between the irradiation temperature and the crystallite size. These results are explained on the basis of the "in-elastic thermal spike" model by taking into consideration the combined effects of crystallite size and environmental (irradiation) temperature on the electron-phonon coupling strength and the lattice thermal conductivity and hence on the resulting thermal spike. These results, besides being crucial from the fundamental prospect of comprehending the size and temperature dependent radiation damage against Se, may also be important from the perspective of designing highly nano-crystalline materials for applications in various radiation environments. [ABSTRACT FROM AUTHOR]

In this Letter, trapping effects of a Schottky lightly Mg-doped p-GaN gate stack for low-power applications have been investigated, and further analysis focusing on AlGaN/GaN interface traps under γ-ray irradiation has been carried out. A negligible shift in the flatband voltage with γ-ray irradiation dose up to 800 krad indicates the superior radiation tolerance of the p-GaN gate structure. The difference between capacitance dispersion at the measurement frequency below and above 500 kHz is observed, which is attributed to trapping effects in different locations with varying gate voltage. Moreover, the frequency-dependent conductance method is put forward to assess the effects of different doses of γ-ray irradiation on the AlGaN/GaN interface traps. Based on that method, aside from the shallow trap states [the trap activation energy (ET) is about 0.334–0.338 eV] previously found in the traditional normally on high electron mobility transistor (HEMT), another type of deeper trap states at the AlGaN/GaN interface (ET is about 0.467–0.485 eV) is detected. It is observed that the ET of shallow trap states distributes at a deeper and broader range as the irradiation dose increases. Additionally, the trap density decreased after 600 krad doses irradiation but increased after 800 krad doses irradiation for both deep and shallow ET. Transmission electron microscopy and atomic force microscopy are used to demonstrate the smooth AlGaN/GaN interface morphology, which will not be greatly damaged after 800 krad doses of γ-ray irradiation. This work can provide a further understanding of radiation tolerance and trapping effects of p-GaN gate HEMTs for low-voltage applications. [ABSTRACT FROM AUTHOR]

Radiation and temperature hardness are important for electronic devices operating in harsh environments such as modern medical equipment, outer space, and nuclear energy industries. In this work, we report radiation and temperature-hardened flexible ferroelectric Pb(Zr0.53Ti0.47)O3 epitaxial films that were grown on flexible inorganic mica substrates via van der Waals heteroepitaxy and can be further used for building high-performance electronic devices. We systematically investigated the effect of 60Co-gamma radiation and temperature on the ferroelectric properties of Pb(Zr0.53Ti0.47)O3 films and their flexibility as well. Pb(Zr0.53Ti0.47)O3 films exhibit a radiation and temperature tolerance of up to 20 Mrad and 175 °C, respectively. In particular, the 20 Mrad-irradiated Pb(Zr0.53Ti0.47)O3 film has an excellent retention even after 105 s with extrapolate retention time longer than 10 years and polarization fatigue up to 1010 cycles as well as moderate flexibility and bending stability after bending 105 cycles. Furthermore, we identified that the degradation of macroscopic ferroelectric properties of irradiated Pb(Zr0.53Ti0.47)O3 films originates from the ferroelectric domain pinning effect induced by the ionization effect. Our work demonstrates that flexible ferroelectric Pb(Zr0.53Ti0.47)O3 films are promising for developing novel flexible electronic devices for applications in harsh environments. [ABSTRACT FROM AUTHOR]

We report the effect of 60Co gamma-ray irradiation on the ferroelectric properties of metal–ferroelectric Hf0.5Zr0.5O2–metal thin film structures. The pristine Hf0.5Zr0.5O2 films showed strong radiation tolerance against gamma-rays with stable remanant polarization values. When Hf0.5Zr0.5O2 films were exposed to electric field cycling, or "wake-up" process, prior to irradiation, however, their ferroelectricity demonstrated a clear degradation of remanant polarization and coercive voltage shift of the hysteresis curves. The analysis of ferroelectric switching dynamics revealed faster polarization switching with broadening of Lorentzian distribution of characteristic switching time for higher radiation doses, which is contrary to the wake-up behavior. The relationship between the wake-up process and gamma-ray irradiation on the stability of ferroelectric Hf0.5Zr0.5O2 films was discussed in light of domain alignment and defect mechanisms, considering both the redistribution and trapping of defect charges. [ABSTRACT FROM AUTHOR]

InP-based high electron mobility transistors (HEMTs) are potential candidates for sub-millimeter wave and terahertz satellite communications due to their ultrahigh frequency performance. Therefore, the study of their irradiation reliability is extremely urgent. In this paper, a 2 MeV proton irradiation experiment has been carried out in InP-based HEMTs, and damage mechanisms have been systematically studied, including dc and rf characteristics. The experimental results show that InP-based HEMTs have wondrously excellent radiation tolerance. The degradation of electrical characteristics occurs only when the irradiation fluence is higher than 1 × 1013 H+/cm2. The drain saturation current and the maximum transconductance have, respectively, decreased by 7.1% and 5.4% at a fluence of 1 × 1014 H+/cm2. Different from the other III–V HEMTs, the irradiated InP-based HEMTs exhibited an abnormality in the "peak collapse" of transconductance. Rf characteristics' parameters demonstrate slighter degradation compared to dc transconductance. Transmission line model (TLM) measurement and Schottky barrier calculation have shown that there is no noticeable degradation of an Ohmic contact and a Schottky contact; therefore, the main possible reason for device degradation comes from the interior of a semiconductor structure. Furthermore, device simulation indicates that defects introduced by irradiation on the upper and lower heterojunction interface of the channel and the interface of the gate recess should be responsible for degradation. Our experiments show that InP-based HEMTs have excellent radiation resistance, and they have good prospects for applications in radiation environments. [ABSTRACT FROM AUTHOR]

Understanding of radiation tolerance and hydrogen accumulation in nanomaterials is an urgent challenge since it may open new perspectives to design advanced materials for extreme conditions, for example, nuclear energy systems. In this work, intrinsic defects in nanostructured tungsten (W) films with different grain sizes were studied by decoration with deuterium (D). This method was also successfully applied to detect defects at the interface between the coating and the substrate, as well as radiation-induced defects. The build-up of D at the interface between the coating and the substrate was observed, which can be a concern for both un-irradiated and neutron-irradiated materials. It was found that the concentration of D in W materials drastically increases with decreasing mean grain size. However, the D concentration at radiation-induced defects produced by self-ion irradiation at room temperature to 3 displacements per atom is the same for all types of coatings, and it is the same as for polycrystalline W. This implies that the density of radiation-induced defects is the same for all types of W coatings, regardless of the crystalline structure of a W material. In this respect, a compromise in the development of new promising nanostructured tungsten films is necessary to ensure the radiation resistance, keeping the hydrogen concentration at an acceptable level and reducing/preventing high density of defects at the interface between the nanostructured coating and the substrate. [ABSTRACT FROM AUTHOR]

The aim of the present paper is to report the effect of radiation on the Er3+-doped sol-gel silica glasses. A possible application of these sol-gel glasses could be their use in harsh radiation environments. The sol-gel glasses are fabricated by densification of erbium salt-soaked nanoporous silica xerogels through polymeric sol-gel technique. The radiation-induced attenuation of Er3+- doped sol-gel silica is found to increase with erbium content. Electron paramagnetic resonance studies reveal the presence of E'δ point defects. This happens in the sol-gel aluminum-silica glass after an exposure to γ-rays (kGy) and in sol-gel silica glass after an exposure to electrons (MGy). The concentration levels of these point defects are much lower in c-ray irradiated sol-gel silica glasses. When the samples are co-doped with Al, the exposure to γ-ray radiation causes a possible reduction of the erbium valence from Er3+ to Er2+ ions. This process occurs in association with the formation of aluminum oxygen hole centers and different intrinsic point defects. [ABSTRACT FROM AUTHOR]

Mn+1AXn phases exhibit unique laminated atomic structures that result in properties typical of both ceramics and metals. Due to their unusual characteristics, these materials have been proposed for use in a wide variety of industrial applications, including in nuclear reactors—both fission and fusion systems—where they will be exposed to extreme irradiation conditions and high temperatures. Recently, numerous studies have investigated radiation effects on the Mn+1AXn phases, revealing complex behavior—phase transformations, surface modification, and mechanical property changes—induced by ion or neutron irradiation over a range of temperatures. This review summarizes recent experimental and theoretical work on the response of the Mn+1AXn phases to irradiation and discusses the intrinsic controls on the radiation tolerance of these materials. Based on the review of the present body of work, a comprehensive understanding of the mechanisms of irradiation-induced structural modification and defect evolution in Mn+1AXn phases is developed, as well as proposed strategies for designing novel Mn+1AXn phases with enhanced performance under extreme irradiation conditions. [ABSTRACT FROM AUTHOR]

The stability and reliability of emerging two-dimensional (2D) quantum materials subjected to harsh environments, such as high-energy radiation, are of high importance, particularly in the fields of space, defense, and energy applications. In this work, we explored the effects of gamma radiation on the structural and optical properties of monolayer WSe2 and WS2 crystals. Raman and photoluminescence spectroscopies were employed to study and probe radiation-induced changes to the samples after exposure to intense gamma radiation (from a 60Co source) in a high-vacuum environment (∼1 × 10−6 Torr) and with various exposure times to vary the total accumulated dosage (up to ∼56 Mrad). In general, very small changes in optical or vibrational properties were observed compared to pristine samples, suggesting noteworthy stability even for high dosages of gamma radiation. Moreover, we found that WSe2 monolayer samples exhibited higher tolerance to gamma radiation compared to WS2 samples. These findings highlight the inherent stability of these 2D quantum materials in harsh radioactive environments, which motivates further investigation of their optical, electrical, and structural properties and exploration for use in future space, energy, and defense applications. [ABSTRACT FROM AUTHOR]

First-principles calculations have been carried out to study the electronic properties of A2Ti2O7 (A=Sm, Gd, Er) pyrochlores. It was found that f electrons have negligible effect on the structural and energetic properties, but have significant effect on the electronic properties. Density of state analysis shows that A-site 4f electrons do take part in the chemical bonding. Also, we found that bond is less covalent than and bonds, while bond in Gd2Ti2O7 is more covalent. It was proposed that for A2Ti2O7 (A=Sm, Gd, Er) pyrochlores, bonds may play more significant role in determining their radiation resistance to amorphization. [ABSTRACT FROM AUTHOR]

The viability of InGaP diodes coupled with α-particle sources as radioisotope power supplies is investigated both theoretically and experimentally. The electrical power output of epitaxially grown InGaP p-type/n-type (p/n) junction diodes coupled with 241Am and 210Po α-particle sources was measured. A theoretical model was developed that determines the α-particle energy deposition profile within an InGaP diode when irradiated by an omnidirectional α-particle source. The results of the model illustrate the dramatic influence the radiation source/diode configuration has on the α-particle energy deposition profile within a device. Progress has been shown towards increasing the radiation tolerance of the InGaP devices, which included utilizing an intrinsic region and reducing the junction thickness. Introduction of the intrinsic region within a conventional n/p diode to form a n-type/intrinsic/p-type diode enabled the device to withstand a ten times greater fluence of 4.2 MeV α particles before decreasing to 50% of its original power output under simulated air mass zero illumination, when compared to an abrupt junction device with the same active region thickness. [ABSTRACT FROM AUTHOR]

The study presents detailed isothermal and isochronal annealing recovery of photovoltaic parameters in n[sup +]/p InGaP solar cells after 1 MeV electron irradiation. Correlation of the solar cells characteristics with changes in the deep level transient spectroscopy data observed in irradiated and annealed n[sup +]/p InGaP diodes and solar cells shows that the H2 (E[sub v]+0.50 eV) and H3 (E[sub v]+0.76 eV) defects have a dominant role in governing the minority-carrier lifetime as well as carrier removal. However, capacitance–voltage measurements indicate that other defects must also play a role in the carrier removal process. In addition, the concentration of the H2 defect is found to decay significantly as a result of room temperature storage for 40 days, suggesting that InGaP-based solar cells will display superior radiation tolerance in space. Finally, the deep donor-like-defect H2 is tentatively identified as a phosphorus Frenkel pair. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This work investigates the role of Mn-doping of ferroelectric lead zirconate titanate (PZT) thin films exposed to a range of ionizing radiation doses. PZT thin films were fabricated with both undoped and 4% Mn-doped compositions, and the functional response was compared both before and after exposure to gamma radiation doses up to 10 Mrad. A phenomenological model was applied to quantify defect interactions and compare trends in the degradation of the functional response. Mn-doped PZT samples demonstrate reduced magnitude of functional response in nonirradiated samples but exhibit vastly superior radiation tolerance of dielectric and ferroelectric properties across the range of gamma doses studied here. Strong MnZr/Ti" - VÖ defect dipoles pin domain walls, resulting in a lower initial functional response and mitigating the deleterious effects of irradiation on extrinsic contributions to the said response. Piezoelectric response trends as a function of radiation dose are highly nonlinear. The results of this work can be leveraged to engineer next-generation radiation-tolerant ferroelectric materials for applications where high levels of functional response stability are required, especially at elevated ionizing radiation dose. [ABSTRACT FROM AUTHOR]

Radiation tolerance is a critical performance criterion of photovoltaic devices for space power applications. In this paper we demonstrate the intrinsic radiation tolerance of an ultra-thin solar cell geometry. Device characteristics of GaAs solar cells with absorber layer thicknesses 80 nm and 800 nm were compared before and after 3MeV proton irradiation. Both cells showed a similar degradation in Voc with increasing fluence; however, the 80 nm cell showed no degradation in Isc for fluences up to 1014 p+ cm–2. For the same exposure, the Isc of the 800 nm cell had severely degraded leaving a remaining factor of 0.26. [ABSTRACT FROM AUTHOR]

Nanostructuring has been proposed as a method to enhance radiation tolerance, but many metallic systems are rejected due to significant concerns regarding long term grain boundary and interface stability. This work utilized recent advancements in transmission electron microscopy (TEM) to quantitatively characterize the grain size, texture, and individual grain boundary character in a nanocrystalline gold model system before and after in situ TEM ion irradiation with 10MeV Si. The initial experimental measurements were fed into a mesoscale phase field model, which incorporates the role of irradiation-induced thermal events on boundary properties, to directly compare the observed and simulated grain growth with varied parameters. The observed microstructure evolution deviated subtly from previously reported normal grain growth in which some boundaries remained essentially static. In broader terms, the combined experimental and modeling techniques presented herein provide future avenues to enhance quantification and prediction of the thermal, mechanical, or radiation stability of grain boundaries in nanostructured crystalline systems. [ABSTRACT FROM AUTHOR]

Helium implantation from transmutation reactions is a major cause of embrittlement and dimensional instability of structural components in nuclear energy systems. Development of novel materials with improved radiation resistance, which is of the utmost importance for progress in nuclear energy, requires guidelines to arrive at favorable parameters more efficiently. Here, we present a methodology that can be used for the design of radiation tolerant materials. We used synchrotron X-ray reflectivity to nondestructively study radiation effects at buried interfaces and measure swelling induced by He implantation in Cu/Nb multilayers. The results, supported by transmission electron microscopy, show a direct correlation between reduced swelling in nanoscale multilayers and increased interface area per unit volume, consistent with helium storage in Cu/Nb interfaces in forms that minimize dimensional changes. In addition, for Cu/Nb layers, a linear relationship is demonstrated between the measured depth-dependent swelling and implanted He density from simulations, making the reflectivity technique a powerful tool for heuristic material design. [ABSTRACT FROM AUTHOR]

The radiation tolerance characterization of dual band InAs/GaSb type-II strain-layer superlattice pBp detectors of varying size using 63 MeV proton irradiation is presented. The detectors' mid-wave infrared performance degraded with increasing proton fluence [uppercase_phi_synonym]P up to 3.75 × 1012 cm-2 or, equivalently, a total ionizing dose = 500 kRad (Si). At this [uppercase_phi_synonym]P, an ∼31% drop in quantum efficiency η, ∼2 order increase in dark current density JD, and consequently, >1 order drop in calculated detectivity D* were observed. Proton damage factors were determined for η and D*. Arrhenius-analysis of temperature-dependent JD measurements reflected significant changes in the activation energies following irradiation. [ABSTRACT FROM AUTHOR]

The authors demonstrate a substantial enhancement in radiation-induced amorphization resistance for single-phased nanocrystalline (NC) versus large-grained polycrystalline MgGa2O4. NC and large-grained MgGa2O4 were irradiated at ∼100 K with 300 keV Kr++ ions to fluences ranging between 5×1019 and 4×1020 Kr/m2. Large-grained MgGa2O4 samples began to amorphize by a fluence of 5×1019 Kr/m2, while NC MgGa2O4 remained crystalline with no evidence for structural changes (other than moderate grain growth in the lowermost implanted region), to a fluence of 4×1020 Kr/m2. To our knowledge, this is the first experimental study to reveal enhanced amorphization resistance in an irradiated, single-phase, NC material. [ABSTRACT FROM AUTHOR]