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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$\mathrm{x}$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 themore »utility of this apparatus for observing other forms of coating damage such as cracking and blisters.

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2. Low-loss GaO _x -core/SiO ₂ -cladding planar waveguides on Si substrate

   https://doi.org/10.1364/OE.391036  

   Tan, Si ; Deng, Huiyang ; Urbanek, Karel E. ; Miao, Yu ; Zhao, Zhexin ; Harris, James S. ; Byer, Robert L. ( April 2020 , Optics Express)

   The unique properties of gallium oxide (GaO_x) have drawn increasing interest as a material suitable for high-power electronic and optical applications. Herein, we report the demonstration of low-loss GaO_x-core/SiO₂-cladding waveguides on Si substrate. We present the fabrication process and annealing treatments of the waveguide devices, and we characterize the corresponding effects on optical transmission for 3 common wavelengths: 633 nm, 1064 nm, and 1550 nm. The best propagation loss achieved for these wavelengths is measured to be$-<\#comment/>0.4\pm <\#comment/>0.1\text{dB/cm}$,$-<\#comment/>0.3\pm <\#comment/>0.2\text{dB/cm}$, and$-<\#comment/>2.4\pm <\#comment/>0.5\text{dB/cm}$, respectively. We discuss the major waveguide loss mechanisms, followed by results of pump and probe experiments using visible/IR wavelengths for waveguides treated under various post-fabrication annealing conditions. We also show nonlinear measurements for a 250 fs laser beam to offer additional insights into the loss mechanisms, which are consistent with the linear optical transmission performances. High waveguide laser-induced damage threshold (LIDT) of$>2.5{\text{J/cm}}^2$is measured at this pulse width, making GaO_xa potential candidate for high-power integrated photonic devices.
3. A Hybrid Process for Printing Pure and High Conductivity Nanocrystalline Copper and Nickel on Flexible Polymeric Substrates

   https://doi.org/10.1038/s41598-019-55640-7  

   Bhuiyan, Md Emran Hossain ; Behroozfar, Ali ; Daryadel, Soheil ; Moreno, Salvador ; Morsali, Seyedreza ; Minary-Jolandan, Majid ( December 2019 , Scientific Reports)

   Printing functional devices on flexible substrates requires printing of high conductivity metallic patterns. To prevent deformation and damage of the polymeric substrate, the processing (printing) and post-processing (annealing) temperature of the metal patterns must be lower than the glass transition temperature of the substrate. Here, a hybrid process including deposition of a sacrificial blanket thin film, followed by room environment nozzle-based electrodeposition, and subsequent etching of the blanket film is demonstrated to print pure and nanocrystalline metallic (Ni and Cu) patterns on flexible substrates (PI and PET). Microscopy and spectroscopy showed that the printed metal is nanocrystalline, solid with no porosity and with low impurities. Electrical resistivity close to the bulk (~2-time) was obtained without any thermal annealing. Mechanical characterization confirmed excellent cyclic strength of the deposited metal, with limited degradation under high cyclic flexure. Several devices including radio frequency identification (RFID) tag, heater, strain gauge, and temperature sensor are demonstrated.
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.
5. Atomic-scale characterization of structural damage and recovery in Sn ion-implanted β-Ga ₂ O ₃

   https://doi.org/10.1063/5.0099915  

   Yoo, Timothy ; Xia, Xinyi ; Ren, Fan ; Jacobs, Alan ; Tadjer, Marko J. ; Pearton, Stephen ; Kim, Honggyu ( August 2022 , Applied Physics Letters)

   β-Ga 2 O 3 is an emerging ultra-wide bandgap semiconductor, holding a tremendous potential for power-switching devices for next-generation high power electronics. The performance of such devices strongly relies on the precise control of electrical properties of β-Ga 2 O 3 , which can be achieved by implantation of dopant ions. However, a detailed understanding of the impact of ion implantation on the structure of β-Ga 2 O 3 remains elusive. Here, using aberration-corrected scanning transmission electron microscopy, we investigate the nature of structural damage in ion-implanted β-Ga 2 O 3 and its recovery upon heat treatment with the atomic-scale spatial resolution. We reveal that upon Sn ion implantation, Ga 2 O 3 films undergo a phase transformation from the monoclinic β-phase to the defective cubic spinel [Formula: see text]-phase, which contains high-density antiphase boundaries. Using the planar defect models proposed for the [Formula: see text]-Al 2 O 3 , which has the same space group as β-Ga 2 O 3 , and atomic-resolution microscopy images, we identify that the observed antiphase boundaries are the {100}1/4 ⟨110⟩ type in cubic structure. We show that post-implantation annealing at 1100 °C under the N 2 atmosphere effectively recovers the β-phase; however, nano-sized voids retainedmore »within the β-phase structure and a [Formula: see text]-phase surface layer are identified as remanent damage. Our results offer an atomic-scale insight into the structural evolution of β-Ga 2 O 3 under ion implantation and high-temperature annealing, which is key to the optimization of semiconductor processing conditions for relevant device design and the theoretical understanding of defect formation and phase stability.« less