Spatially resolved characterization of thermally grown oxides using time-domain thermoreflectance

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Cal Poly Satellite Positioning Systems: Thrust or Bust!

Satellites need a way to make precise corrections to their orbit and positioning. The purpose of this project is to design a gimbal mechanism for Astranis that orients an ion thruster along a requested vector. The gimbal must produce any vector within a 2.5° cone in a thirty-minute window. Current systems are expensive and not well suited to this application. The design must be operable in a space environment and optimize mass, size, and reliability. Our design toggles between four discrete positions to achieve an average thrust vector. The gimbal accomplishes this using four solenoids that tilt a plate about a central hinge. The hinge allows for low friction rotation in only two axes. It also contains an integrated restoring force, which will passively restore the thruster to center in event of actuator failure. A linkage assembly connects the solenoids to the thruster plate, allowing for mechanical advantage and a low profile. Four hard stops in the linkage assembly physically define the actuation angles. We initially pursued several designs in parallel before narrowing down to a single design for our confirmation prototype. After manufacturing this prototype, we tested our design to verify range and accuracy of the vector and the ability of the gimbal to move an ion thruster on Earth. The gimbal produced a 2.445° cone with a vector precision of ±0.01° and successfully actuated a 5kg load with a similar center of mass. The gimbal has an envelope of 199x199x44mm and a total mass of 0.926kg. Future testing should include environment tests and complete system tests to ensure full functionality in the intended application. Although our final prototype is not intended to be launch ready, the work accomplished for this project will benefit Astranis as they pursue a flight ready design

Validation of the Wiedemann-Franz Law in solid and molten tungsten above 2000 K through thermal conductivity measurements via steady state temperature differential radiometry

We measure the thermal conductivity of solid and molten tungsten using Steady State Temperature Differential Radiometry. We demonstrate that the thermal conductivity can be well described by application of Wiedemann-Franz Law to electrical resistivity data, thus suggesting the validity of Wiedemann-Franz Law to capture the electronic thermal conductivity of metals in their molten phase. We further support this conclusion using ab initio molecular dynamics simulations with a machine-learned potential. Our results show that at these high temperatures, the vibrational contribution to thermal conductivity is negligible compared to the electronic component

Organic-component dependent thermal conductivity reduction in ALD/MLD grown ZnO: organic superlattice thin films

This project has received funding from the European Union's Horizon 2020 Research and Innovation programme under the Marie Skłodowska-Curie Grant Agreement (No. 765378) and the Academy of Finland (Profi 3). We acknowledge the use of the RawMatters Finland Infrastructure (RAMI) at Aalto University. We appreciate support from the Army Research Office Grant (No. W911NF-16-1-0406).Inorganic-organic superlattice (SL) thin films are intriguing candidates for flexible thermoelectric applications; in such SLs, the heat conduction can be efficiently blocked at the inorganic/organic interfaces. Fabrication of these materials using the atomic/molecular layer deposition (ALD/MLD) technique allows precise layer-sequence manipulation. Another unique advantage of ALD/MLD is its capability to yield conformal coatings even on demanding substrates such as textiles. These benefits have been demonstrated in previous works for SL thin films where ZnO serves as the inorganic matrix and hydroquinone as the organic component. In this work, we extend the study to three other organic components, i.e., p-phenylenediamine, terephthalic acid, and 4,4 '-oxydianiline, to address the importance of the bonding structure and the density difference at the inorganic/organic interface, and the thickness of the monomolecular organic blocking layer.Peer reviewe

Simultaneously enhanced electrical conductivity and suppressed thermal conductivity for ALD ZnO films via purge-time controlled defects

| openaire: EC/H2020/765378/EU//HYCOAT Funding Information: The authors acknowledge the extensive use of the RawMatters Finland Infrastructure (RAMI) at Aalto University. Funding was received from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement (No. 765378), and also from Academy of Finland (Profi-3, PREIN) and the Army Research Office (No. W911NF-16-1-0406). Publisher Copyright: © 2022 Author(s).We demonstrate the simultaneous manipulation of electrical and thermal transport characteristics of ZnO thin films fabricated via the prototype atomic layer deposition (ALD) process from diethyl zinc (DEZ) and water precursors. The key ALD process parameter is the length of the N2 purge applied after the DEZ precursor pulse. We characterize the thin films with x-ray reflectivity measurements for the film growth characteristics, with photoluminescence spectroscopy for structural defects, with electrical transport measurements for carrier density, electrical resistivity, and Seebeck coefficient, and with time-domain thermoreflectance measurements for thermal conductivity. Photoluminescence spectroscopy data suggest that elongation of the purge period creates structural defects, which increase the electron carrier density; this would explain the enhanced electrical conductivity of the films. At the same time, the defects are likely to hinder the thermal transport in the films. The, thus, realized simultaneous increase in electrical conductivity and decrease in thermal conductivity are of fundamental importance in thermoelectrics. Moreover, the simple control of the intrinsic electrical transport properties is highly desired for the semiconducting ZnO films in optics and microelectronics.Peer reviewe