The effect of temperature on the sputter yield of indium was predicted based on both previously published and experimentally measured sputter yield data. The increase in the indium sputter yield with temperature can lead to damage when packaged as indium-bump semiconductor structures. Cryogenic (cryo) focused ion beam (FIB) milling, ex situ lift out micromanipulation, and cryogenic scanning transmission electron microscopy (STEM) were used to prepare indium specimens for high-resolution imaging. FIB milling at lower temperatures reduces the sputter yield of indium, preventing heating, damage, and possible void or bubble formation observed in bump structures. In addition, cryo-STEM imaging reduces contamination when imaging In at high resolution. These findings underscore the importance of specimen cooling and cryogenic characterization techniques in preventing thermal sputtering effects and contamination, particularly in low melting point materials, such as indium.

Permanent markers are often used to apply protective layers in FIB specimen preparation. In this work, we used FIB, EXLO and STEM to prepare specimens and analyze the morphology and composition of black, blue, green, and magenta colored ink drawn on a Si substrate. The coating layers are all amorphous. When normalized to the Si substrate, STEM and EDS results indicate noticeable differences in C, N, O, S, Cl between the layers. The presence of these elements is consistent with different organic colorants and/or a combination of multiple colorants. All ink layers are easy to apply and are continuous and thick enough to follow up with additional FIB deposited coatings.

Additive manufacturing (AM) has opened new pathways for producing high-strength aluminum alloy components. However, optimizing their mechanical performance require a detailed understanding of microstructural evolution. In this study, a multi-length-scale microstructural and computational analysis was conducted on a commercially available, precipitation-hardenable aluminum alloy (AA7A77) in the as-fabricated condition. A distinct bimodal microstructure influenced by the solidification process was observed, with fine equiaxed grains near the melt-pool boundaries and coarse elongated grains within the center of the melt pool. Two key metastable phases were identified: the cuboidal L12 Al3Zr phase within fine grains and the icosahedral Mg32(Al, Zn, Cu)49 quasicrystal located within coarse grains and along grain boundaries. Computational simulations provided insight into the formation of the quasicrystals, where a secondary phase was predicted to form at the termination of solidification which is favorable to quasicrystal formation. Nanoindentation demonstrated a hardness comparable to peak-aged AA7075, which leads to the possibility of further improvement through a precipitationhardening heat treatment. This work provides new insights into the microstructural characteristics of highstrength AM aluminum alloys and presents a novel pathway for leveraging quasicrystals for enhanced mechanical performance.

A conduction heat transfer analysis of ex situ lift-out specimen handling under cryogenic conditions (cryo-EXLO) is performed and compared with experimentally determined temperature values using a type K thermocouple. Using a finite-volume solver for heat conduction, the analysis confirms that manipulation of a specimen by a probe above a working surface cooled at liquid nitrogen (LN2) temperatures can remain below the critical vitreous temperature up to several hundreds of micrometers above the working surface, allowing for ample distance for lift out and specimen manipulation. In addition, the temperature above the cryogenic shuttle sample holder working surface remains below the vitreous temperature for several tens of minutes without adding cryogen, yielding sufficient time to complete multiple manipulations. Periodically topping off the cryogen level may allow for unlimited cryo-EXLO manipulations with this hardware and geometry.

In this study, a conjugate radiation/conduction multimode heat transfer analysis of cryogenic focused ion beam (FIB) milling steps necessary for producing ex situ lift out specimens under cryogenic conditions (cryo-EXLO) is performed. Using finite volume for transient heat conduction and enclosure theory for radiation heat transfer, the analysis shows that as long as the specimen is attached or touching the FIB side wall trenches, the specimen will remain vitreous indefinitely, while actively cooled at liquid nitrogen (LN2) temperatures. To simulate the time needed to perform a transfer step to move the bulk sample containing the FIB-thinned specimen from the cryo-FIB to the cryo-EXLO cryostat, the LN2 temperature active cooling is turned off after steady-state conditions are reached and the specimen is monitored over time until the critical devitrification temperature is reached. Under these conditions, the sample will remain vitreous for >3 min, which is more than enough time needed to perform the cryo-transfer step from the FIB to the cryostat, which takes only ∼10 s. Cryo-transmission electron microscopy images of a manipulated cryo-EXLO yeast specimen prepared with cryo-FIB corroborates the heat transfer analysis.

Site-specific focused ion beam (FIB) specimens have been successfully prepared at cryogenic conditions and analyzed using cryogenic scanning/transmission electron microscopy (cryo-S/TEM) and cryogenic electron tomography (cryo-ET) [1][2][3][4][5][6][7][8][9][10][11][12][13].We recently showed that cryogenic ex situ lift out (cryo-EXLO) specimen handling methods can be used to successfully manipulate cryo-FIB prepared specimens outside of the FIB in a humidity-controlled environment [13].These cryo-EXLO techniques were applied to beam-sensitive polymer samples and plunge-frozen yeast specimens [13].In this work, we apply cryo-EXLO to high pressure frozen Yarrowia lipolytica yeast samples.Cryo-FIB specimens were milled and manipulated using a cryo-EXLO station (e.g., an EXpressLO Nicola CRYO™) installed inside an environmentally controlled glovebox.The upgraded Nicola CRYO TM uses semi-automated remote controls, enabling computer-controlled specimen manipulation from outside the glovebox to facilitate ease of use.Cryo-ET analysis of cryo-EXLO manipulated specimens were conducted, showing that EXLO manipulation and transfer of FIB milled specimens induced no significant ice contamination and retained the vitreous phase of the high-pressure frozen specimens.In addition, thermal modeling of the cryo-FIB milling and cryo-EXLO process is consistent with our experimental cryo-ET results [14].

Journal Article Semi-Automated EXLO for Ambient and Cryogenic TEM Specimen Manipulation Get access Ahmed A Darwish, Ahmed A Darwish EXpressLO LLC, Lehigh Acres, FL, United States Search for other works by this author on: Oxford Academic Google Scholar Thomas E Dougherty, Thomas E Dougherty EXpressLO LLC, Lehigh Acres, FL, United States Search for other works by this author on: Oxford Academic Google Scholar Brandon J Heck, Brandon J Heck EXpressLO LLC, Lehigh Acres, FL, United States Search for other works by this author on: Oxford Academic Google Scholar Michael Colletta, Michael Colletta Applied and Engineering Physics, Cornell University, Ithaca, NY, United States Search for other works by this author on: Oxford Academic Google Scholar Yue Yu, Yue Yu Applied and Engineering Physics, Cornell University, Ithaca, NY, United States Search for other works by this author on: Oxford Academic Google Scholar Lena F Kourkoutis, Lena F Kourkoutis Applied and Engineering Physics, Cornell University, Ithaca, NY, United StatesKavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NYUnited States Search for other works by this author on: Oxford Academic Google Scholar Kyle Beggs, Kyle Beggs Centecorp LLC, Longwood, FL, United States Search for other works by this author on: Oxford Academic Google Scholar Alain J Kassab, Alain J Kassab Centecorp LLC, Longwood, FL, United States Search for other works by this author on: Oxford Academic Google Scholar Alice Dohnalkova, Alice Dohnalkova Pacific Northwest National Laboratory, Richland, WA, United States Search for other works by this author on: Oxford Academic Google Scholar Lucille A Giannuzzi Lucille A Giannuzzi EXpressLO LLC, Lehigh Acres, FL, United States Corresponding author: Lucille.Giannuzzi@EXpressLO.com Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Page 553, https://doi.org/10.1093/micmic/ozad067.262 Published: 22 July 2023

This work describes cryogenic ex situ lift out (cryo-EXLO) of cryogenic focused ion beam (cryo-FIB) thinned specimens for analysis by cryogenic transmission electron microscopy (cryo-TEM). The steps and apparatus necessary for cryo-EXLO are described. Methods designed to limit ice contamination include use of an anti-frost lid, a vacuum transfer assembly, and a cryostat. Cryo-EXLO is performed in a cryostat with the cryo-shuttle holder positioned in the cryogenic vapor phase above the surface of liquid N-2 (LN2) using an EXLO manipulation station installed inside a glove box maintained at < 10% relative humidity and inert (e.g., N-2 gas) conditions. Thermal modeling shows that a cryo-EXLO specimen will remain vitreous within its FIB trench indefinitely while LN2 is continuously supplied. Once the LN2 is cut off, modeling shows that the EXLO specimen will remain vitreous for over 4 min, allowing sufficient time for the cryo-transfer steps which take only seconds to perform. Cryo-EXLO was applied successfully to cryo-FIB-milled specimen preparation of a polymer sample and plunge-frozen yeast cells. Cryo-TEM of both the polymer and the yeast shows minimal ice contamination with the yeast specimen maintaining its vitreous phase, illustrating the potential of cryo-EXLO for cryo-FIB-TEM of beam-sensitive, liquid, or biological materials.

Abstract: Low-Z nanocrystalline diamond (NCD) grids have been developed to reduce spurious fluorescence and avoid X-ray peak overlaps or interferences between the specimen and conventional metal grids. The low-Z NCD grids are non-toxic and safe to handle, conductive, can be subjected to high-temperature heating experiments, and may be used for analytical work in lieu of metal grids. Both a half-grid geometry, which can be used for any lift-out method, or a full-grid geometry that can be used for ex situ lift-out or thin film analyses, can be fabricated and used for experiments.

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The focused ion beam (FIB) instrument is designed to provide the removal of material with nanometer-scale precision. However, one often needs to remove a substantial amount of material to expose the region of interest or prepare a specimen for transmission electron microscopy analysis. The maximum current available on Ga+ FIB sources is less than 100 nA, and this is a limiting factor when removal on the millimeter scale is desired. Any improvement in the removal rate reduces the analysis time and increases the range of samples that can be analyzed. Optimization of ion beam parameters, such as dwell time and overlap, can improve material removal and reduce redeposition. Since sputtering occurs faster at an edge, the use of a nested arrangement of raster patterns to more frequently present an edge to the ion beam was able to improve the removal of material at the region of interest by over 30% in the silicon and polycrystalline copper substrates used for this study. A confocal laser scanning microscope made possible an accurate determination of the material removed.

With negligible quantities of nitrogen, wrought and welded solid solution strengthened nickel superalloys usually contain carbides and topologically close-packed phases, such as Laves phase. However, appreciable nitrogen levels on the order of 0.1 % mass fraction drove the precipitation of a range of unanticipated nitride phases in additively manufactured Inconel 625 in the as-deposited and post process hot isostatically pressed conditions. Different nitride phases were observed with small changes in alloy chemistry. Cubic metal nitrides (MN), tetragonal Z-phase (CrNbN), and diamond-cubic metal eta-nitrides (M6N) were found within the gamma matrix of Inconel 625 containing relatively low Fe (1 %), low Ti (0.02 %), and high Si (0.39 %) mass fractions. Conversely, these phases were replaced by only MN nitrides in a similar Inconel 625 alloy with elevated mass fractions of Ti (0.21 %) and Fe (4 %). These various phases, however, were not fully predicted using state-of-the-art computational thermodynamic tools and databases, indicating a sparsity of data for nickel superalloys. Even after hot isostatic pressing, many nitrides persisted and only experienced slight changes in composition and lattice parameters in both materials. The stability of these nitride phases presents a potential pathway for achieving enhanced high temperature and creep properties within this and similar alloy systems. Published by Elsevier B.V.

This article investigates the integrity of laser welds on neutron irradiated, He-containing steels. Life extension of the current fleet of light water reactors could necessitate repair of cracks on irreplaceable internal components, but heat input of weld repairs exacerbates the problem by initiating He-induced cracking. Laser welding is a promising low-heat-input technology thought to limit the extent of He-induced cracking. In this study, we produce laser welds in a hot cell on AISI 304L stainless steel plates previously irradiated in the Experimental Breeder Reactor (EBR)-II. We select a systematic set of three specimens spanning fluences ~1–28 displacements per atom (dpa) at ~415–430 °C and He concentrations ~0.2–8 atomic parts per million (appm) amounting to ~0.2–2.8% swelling. He-induced cracking is observed only in specimens containing ≥3 appm He. Laser welding nearly eliminates all irradiation-induced cavities and reduces the dislocation loop number density, similar to conventional post-irradiation annealing. Microchemically, laser welding induces Cr-rich precipitation and suppresses grain boundary radiation-induced segregation. The mechanism of He-induced cracking is discussed in the context of these microchemical changes. The weld heat input is calculated and suggests that further refinement of laser welding parameters may improve the cracking resistance for higher dose and He conditions.

Super-duplex stainless steel powder feedstocks specified for use in directed energy deposition additive manufacturing processes can have an oxygen composition nearly five times higher than that present in comparable wrought forms. A combination of computational thermodynamic calculations and experimental validation showed that high levels of oxygen promoted the formation of oxygen-rich inclusions during directed energy deposition additive manufacturing. These inclusions play an important role in microstructural evolution during the rapid heating and cooling cycles prevalent in additive manufacturing and impact mechanical and corrosion properties. Inclusions observed across the powder feedstock and additively manufactured and post-processed materials exhibited complex structures with a combination of amorphous, metastable, and stable phases. The powder feedstock, which experiences rapid cooling rates during the gas atomization process, yielded amorphous inclusions that were rich in manganese, chromium, silicon, and oxygen surrounded by small crystalline MnS particles. After additive manufacturing, inclusions transformed to a combination of rhodonite (MnSiO3) and spinel (MnCr2O4) with amorphous regions around the exterior. Post-process hot isostatic pressing treatments, which replicate conditions most similar to equilibrium, resulted in the formation of a stable spinel oxide with MnS particles around the exterior, matching the results predicted by thermodynamic equilibrium calculations.

The transformation of unstable austenite to ferrite or α′ martensite as a result of exposure to Xe+ or Ga+ ions at room temperature was studied in a 304 stainless steel casting alloy. Controlled Xe+ and Ga+ ion beam exposures of the 304 were carried out at a variety of beam/sample geometries. It was found that both Ga+ and Xe+ ion irradiation resulted in the transformation of the austenite to either ferrite or α′ martensite. In this paper, we will refer to the transformation product as a BCC phase. The crystallographic orientation of the transformed area was controlled by the orientation of the austenite grain and was consistent with either the Nishiyama–Wasserman or the Kurdjumov–Sachs orientation relationships. On the basis of the Xe+ and Ga+ ion beam exposures, the transformation is not controlled by the chemical stabilization of the BCC phase by the ion species, but is a result of the disorder caused by the ion-induced recoil motion and subsequent return of the disordered region to a more energetically favorable phase.

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