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1. Imaging scatterometer for observing in situ changes to optical coatings during air annealing

   https://doi.org/10.1364/AO.476979  

   Rezac, Michael; Martinez, Daniel; Gleckl, Amy; Smith, Joshua_R (January 2023, Applied Optics)

   Annealing of amorphous optical coatings has been shown to generally reduce optical absorption, optical scattering, and mechanical loss, with higher temperature annealing giving better results. The achievable maximum temperatures are limited to the levels at which coating damage, such as crystallization, cracking, or bubbling, will occur. Coating damage caused by heating is typically only observed statically after annealing. An experimental method to dynamically observe how and over what temperature range such damage occurs during annealing is desirable as its results could inform manufacturing and annealing processes to ultimately achieve better coating performance. We developed a new, to the best of our knowledge, instrument that features an industrial annealing oven with holes cut into its sides for viewports to illuminate optical samples and observe their coating scatter and eventual damage mechanismsin situand in real time during annealing. We present results that demonstratein situobservation of changes to titania-doped tantala coatings on fused silica substrates. We obtain a spatial image (mapping) of the evolution of these changes during annealing, an advantage over x ray diffraction, electron beam, or Raman methods. We infer, based on other experiments in the literature, these changes to be due to crystallization. We further discuss the utility of this apparatus for observing other forms of coating damage such as cracking and blisters. 

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2. Implementation of an Alpha Damage Annealing Model for Zircon (U‐Th)/He Thermochronology With Comparison to a Zircon Fission Track Annealing Model

   https://doi.org/10.1029/2019GC008757  

   Guenthner, William R. (February 2021, Geochemistry, Geophysics, Geosystems)

   Abstract Radiation damage exerts a fundamental control on He diffusion in zircon, which manifests as correlations between (U‐Th)/He date and effective uranium concentration. These correlations can be exploited with modeling to explore long‐term thermal histories. This manuscript focuses on one such model, the zircon radiation damage accumulation and annealing model (ZRDAAM) of Guenthner et al. (2013), https://doi.org/10.2475/03.2013.01, by integrating newly defined alpha damage annealing kinetics measured by Ginster et al. (2019), https://doi.org/10.1016/j.gca.2019.01.033, into ZRDAAM. I explore several consequences of this alpha damage annealing model as it relates to (U‐Th)/He date‐effective uranium (eU) correlations, using representative time‐temperature paths and previously published results. Comparison between the current version of ZRDAAM, which uses fission track annealing, and the new annealing model demonstrates that, for thermal histories with prolonged periods at low temperatures (<50°C), alpha dose annealing kinetics yield slightly younger model dates at low to moderate eU concentrations, older dates at moderate to high eU, and substantially younger dates at the highest eU concentrations. The absolute eU concentrations over which the differences are observed varies for a given thermal history, so these ranges should be interpreted as relative or proportional. Younger model dates at high eU in most thermal histories result from lower amounts of annealing that occur with the Ginster et al. (2019) alpha dose annealing kinetics. This annealing model comparison illustrates that the choice of annealing kinetics has the greatest influence over model output for thermal histories involving either prolonged time periods in the 200–300°C temperature window, or a late‐stage reheating event. 

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3. Forward bias annealing of proton radiation damage in NiO/Ga ₂ O ₃ rectifiers

   https://doi.org/10.1088/1402-4896/ad5514  

   Li, Jian-Sian; Chiang, Chao-Ching; Wan, Hsiao-Hsuan; Rasel, Md_Abu Jafar; Haque, Aman; Kim, Jihyun; Ren, Fan; Chernyak, Leonid; Pearton, S J (June 2024, Physica Scripta)

   Abstract 17 MeV proton irradiation at fluences from 3–7 × 10¹³cm⁻²of vertical geometry NiO/β-Ga₂O₃heterojunction rectifiers produced carrier removal rates in the range 120–150 cm⁻¹in the drift region. The forward current density decreased by up to 2 orders of magnitude for the highest fluence, while the reverse leakage current increased by a factor of ∼20. Low-temperature annealing methods are of interest for mitigating radiation damage in such devices where thermal annealing is not feasible at the temperatures needed to remove defects. While thermal annealing has previously been shown to produce a limited recovery of the damage under these conditions, athermal annealing by minority carrier injection from NiO into the Ga₂O₃has not previously been attempted. Forward bias annealing produced an increase in forward current and a partial recovery of the proton-induced damage. Since the minority carrier diffusion length is 150–200 nm in proton irradiated Ga₂O₃, recombination-enhanced annealing of point defects cannot be the mechanism for this recovery, and we suggest that electron wind force annealing occurs. 

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4. Non-Thermal Annealing of Gamma Irradiated GaN HEMTs with Electron Wind Force

   https://doi.org/10.1149/2162-8777/ac7f5a  

   Rasel, Md Abu; Stepanoff, Sergei; Haque, Aman; Wolfe, Douglas E.; Ren, Fan; Pearton, Stephen (July 2022, ECS Journal of Solid State Science and Technology)

   Radiation damage mitigation in electronics remains a challenge because the only established technique, thermal annealing, does not guarantee a favorable outcome. In this study, a non-thermal annealing technique is presented, where electron momentum from very short duration and high current density pulses is used to target and mobilize the defects. The technique is demonstrated on 60 Co gamma irradiated (5 × 10 6 rad dose and 180 × 10 3 rad h −1 dose rate) GaN high electron mobility transistors. The saturation current and maximum transconductance were fully and the threshold voltage was partially recovered at 30 °C or less. In comparison, thermal annealing at 300 °C mostly worsened the post-irradiation characteristics. Raman spectroscopy showed an increase in defects that reduce the 2-dimensional electron gas (2DEG) concentration and increase the carrier scattering. Since the electron momentum force is not applicable to the polymeric surface passivation, the proposed technique could not recover the gate leakage current, but performed better than thermal annealing. The findings of this study may benefit the mitigation of some forms of radiation damage in electronics that are difficult to achieve with thermal annealing. 

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5. Ion velocity effect governs damage annealing process in defective KTaO ₃

   https://doi.org/10.1088/1361-6463/ad53da  

   Velişa, G.; Iancu, D.; Zarkadoula, E.; Tong, Y.; Zhang, Y.; Weber, W_J (June 2024, Journal of Physics D: Applied Physics)

   Abstract Effects of electronic to nuclear energy losses (S_e/S_n) ratio on damage evolution in defective KTaO₃have been investigated by irradiating pre-damaged single crystal KTaO₃with intermediate energy O ions (6 MeV, 8 MeV and 12 MeV) at 300 K. By exploring these processes in pre-damaged KTaO₃containing a fractional disorder level of 0.35, the results demonstrate the occurrence of a precursory stage of damage production before the onset of damage annealing process in defective KTaO₃that decreases with O ion energy. The observed ionization-induced annealing process by ion channeling analysis has been further mirrored by high resolution transmission electron microscopy analysis. In addition, the reduction of disorder level is accompanied by the broadening of the disorder profiles to greater depth with increasing ion fluence, and enhanced migration is observed with decreasing O ion energy. SinceS_e(∼3.0 keV nm⁻¹) is nearly constant for all 3 ion energies across the pre-damaged depth, the difference in behavior is due to the so-called ‘velocity effect’: the lower ion velocity below the Bragg peak yields a confined spread of the electron cascade and hence an increased energy deposition density. The inelastic thermal spike calculation has further confirmed the existence of a velocity effect, not previously reported in KTaO₃or very scarcely reported in other materials for which the existence of ionization-induced annealing has been reported. In other words, understanding of ionization-induced annealing has been advanced by pointing out that ion velocity effect governs the healing of pre-existing defects, which may have significant implication for the creation of new functionalities in KTaO₃through atomic-level control of microstructural modifications, but may not be limited to KTaO₃. 

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