Douglas J. Safarik

Designs for two automated atomic layer deposition (ALD) flow reactors are presented, and their capabilities for coating additively manufactured (AM) metal prints are described. One instrument allows the coating of several AM parts in batches, while the other is useful for single part experiments. To demonstrate reactor capabilities, alumina (Al2O3) was deposited onto AM 316L stainless steel by dosing with water (H2O) vapor and trimethylaluminum (TMA) and purging with nitrogen gas (N2). Both instruments are controlled by custom-programmed LabVIEW software that enables in situ logging of temperature, total pressure, and film thickness using a quartz crystal microbalance. An initial result shows that 150 ALD cycles led to a film thickness of ∼55 nm, which was verified with Rutherford backscattering spectroscopy. This indicates that the reactors were indeed depositing single atomic layers of Al2O3 per ALD cycle, as intended.

We describe the design, construction, operation, and performance of a simple and versatile semi-batch reactor that is especially useful for measurement of gas/solid reaction rates at pressures in the range of 1 mTorr to 1500 Torr. The reactor operates by repeatedly imposing small AC modulations of reactant gas pressure on top of a much larger DC pressure background. Based on the rate of pressure relaxation following each AC pulse, the reaction rate is determined. Our design is characterized by modular construction from off-the-shelf, ultra-high-vacuum-compatible components, which facilitate easy retrofitting and adaptation to a range of experimental conditions. Automated experiment control and data acquisition is accomplished via a custom National Instruments^© LabView virtual instrument. Data analysis is automated using a custom series of Mathworks^© Matlab scripts. We demonstrate reactor performance through measurements of hydrogenation kinetics for a composite H₂ getter material consisting of 1,4-bis(phenylethynyl)benzene mixed with a palladium/carbon catalyst.

The U.S. Department of Energy's Office of Scientific and Technical Information

The U.S. Department of Energy's Office of Scientific and Technical Information

The thermal conductivity of uranium dioxide has been studied for over half a century, as uranium dioxide is the fuel used in a majority of operating nuclear reactors and thermal conductivity controls the conversion of heat produced by fission events to electricity. Because uranium dioxide is a cubic compound and thermal conductivity is a second-rank tensor, it has always been assumed to be isotropic. We report thermal conductivity measurements on oriented uranium dioxide single crystals that show anisotropy from 4 K to above 300 K. Our results indicate that phonon-spin scattering is important for understanding the general thermal conductivity behaviour, and also explains the anisotropy by coupling to the applied temperature gradient and breaking cubic symmetry.