We present and analyze a three-dimensional (3D) volume of nanoscale helium bubbles in a tritium-exposed palladium alloy that we have reconstructed by transmission electron tomography. Helium nanobubbles commonly form within metals during exposure to radiation and radioactive substances. The radioactive decay of tritium stored in metal tritides often results in a high density of these nanoscale helium bubbles. A persistent question about the mechanisms of bubble nucleation and growth has been the role of lattice defects and impurities. To address this matter, we have determined the 3D positions of helium nanobubbles in a palladium-nickel alloy exposed to tritium for 3.8 years. We introduce methods to determine the 3D shapes, volumes, and spatial positions of helium bubbles as small as 1 nm within solids. We find that the size and spacing of observed nanobubbles are not correlated. Our results suggest that previous models, which hypothesize initial, rapid homogeneous nucleation of nanobubbles followed by diffusion-limited growth as helium atoms join the nearest bubble, are inadequate. We propose that the lack of size and spacing correlation is due to traps of atomic helium in the metal lattice that allow bubbles to nucleate even at low average helium concentration. This work will facilitate the development of high-fidelity models of helium nanobubble formation in radiation-exposed metals.

A direct comparison between electron transparent transmission electron microscope (TEM) samples prepared with gallium (Ga) and xenon (Xe) focused ion beams (FIBs) is performed to determine if equivalent quality samples can be prepared with both ion species. We prepared samples using Ga FIB and Xe plasma focused ion beam (PFIB) while altering a variety of different deposition and milling parameters. The samples' final thicknesses were evaluated using STEM-EELS t/lambda data. Using the Ga FIB sample as a standard, we compared the Xe PFIB samples to the standard and to each other. We show that although the Xe PFIB sample preparation technique is quite different from the Ga FIB technique, it is possible to produce high-quality, large area TEM samples with Xe PFIB. We also describe best practices for a Xe PFIB TEM sample preparation workflow to enable consistent success for any thoughtful FIB operator. For Xe PFIB, we show that a decision must be made between the ultimate sample thickness and the size of the electron transparent region.

We present Keck Planet Imager and Characterizer (KPIC) high-resolution (R similar to 35,000) K-band thermal emission spectroscopy of the ultrahot Jupiter WASP-33b. The use of KPIC's single-mode fibers greatly improves both blaze and line-spread stabilities relative to slit spectrographs, enhancing the cross-correlation detection strength. We retrieve the dayside emission spectrum with a nested-sampling pipeline, which fits for orbital parameters, the atmospheric pressure-temperature profile, and the molecular abundances. We strongly detect the thermally inverted dayside and measure mass-mixing ratios for CO (logCO(MMR) = -1.1(-0.6)(+0.4)), H2O (logH(2)O(MMR) = -4.1(-0.9)(+0.7)), and OH (logOH(MMR) = -2.1(-1.1)(+0.5)), suggesting near-complete dayside photodissociation of H2O. The retrieved abundances suggest a carbon- and possibly metal-enriched atmosphere, with a gas-phase C/O ratio of 0.8(-0.2)(+0.1), consistent with the accretion of high-metallicity gas near the CO2 snow line and post-disk migration or with accretion between the soot and H2O snow lines. We also find tentative evidence for (CO)-C-12/(CO)-C-13 similar to 50, consistent with values expected in protoplanetary disks, as well as tentative evidence for a metal-enriched atmosphere (2-15 x solar). These observations demonstrate KPIC's ability to characterize close-in planets and the utility of KPIC's improved instrumental stability for cross-correlation techniques.

We present high-resolution K-band emission spectra of the quintessential hot Jupiter HD 189733 b from the Keck Planet Imager and Characterizer. Using a Bayesian retrieval framework, we fit the dayside pressure-temperature profile, orbital kinematics, mass-mixing ratios of H2O, CO, CH4, NH3, HCN, and H2S, and the (CO)-C-13/(CO)-C-12 ratio. We measure mass fractions of logH(2)O = -2.0(-0.4)(+0.4) and logCO = -2.2(-0.5)(+0.5), and place upper limits on the remaining species. Notably, we find logCH(4) < -4.5 at 99% confidence, despite its anticipated presence at the equilibrium temperature of HD 189733 b assuming local thermal equilibrium. We make a tentative (similar to 3 sigma) detection of (CO)-C-13, and the retrieved posteriors suggest a C-12/C-13 ratio similar to or substantially less than the local interstellar value. The possible C-13 enrichment would be consistent with accretion of fractionated material in ices or in the protoplanetary disk midplane. The retrieved abundances correspond to a substantially substellar atmospheric C/O = 0.3 +/- 0.1, while the carbon and oxygen abundances are stellar to slightly superstellar, consistent with core-accretion models which predict an inverse correlation between C/O and metallicity. The specific combination of low C/O and high metallicity suggests significant accretion of solid material may have occurred late in the formation process of HD 189733 b.

Tension remains between the observed and modeled properties of substellar objects, but objects in binary orbits, with known dynamical masses, can provide a way forward. HD 72946 B is a recently imaged brown dwarf companion to a nearby, solar-type star. We achieve similar to 100 mu as relative astrometry of HD 72946 B in the K band using VLTI/GRAVITY, unprecedented for a benchmark brown dwarf. We fit an ensemble of measurements of the orbit using orbitize! and derive a strong dynamical mass constraint M B = 69.5 +/- 0.5 M Jup assuming a strong prior on the host star mass M A = 0.97 +/- 0.01 M circle dot from an updated stellar analysis. We fit the spectrum of the companion to a grid of self-consistent BT-Settl-CIFIST model atmospheres, and perform atmospheric retrievals using petitRADTRANS. A dynamical mass prior only marginally influences the sampled distribution of effective temperature, but has a large influence on the surface gravity and radius, as expected. The dynamical mass alone does not strongly influence retrieved pressure-temperature or cloud parameters within our current retrieval setup. Independently of the cloud prescription and prior assumptions, we find agreement within +/- 2 sigma between the C/O of the host (0.52 +/- 0.05) and brown dwarf (0.43-0.63), as expected from a molecular cloud collapse formation scenario, but our retrieved metallicities are implausibly high (0.6-0.8) in light of the excellent agreement of the data with the solar-abundance model grid. Future work on our retrieval framework will seek to resolve this tension. Additional study of low surface gravity objects is necessary to assess the influence of a dynamical mass prior on atmospheric analysis.