Potentiostatic slow strain rate testing was conducted on stress corrosion cracking (SCC) test specimens exposed to ethanolic environments prepared from pure dehydrated ethanol. The mechanism of SCC in such environments is not well‐understood. Cracks of various types—intergranular and transgranular open cracks, and sharp closed transgranular cracks—were found by altering several testing parameters. The presence of chloride was found to be essential for crack initiation. A scanning electron microscope examination indicated that an “anodic” cracking mechanism, not necessarily slip dissolution, was most likely operating at high elongations. Sharp, closed transgranular cracks, with a maximum depth of 4 µm, were detected at elongations below 3% in ethanol solutions containing 2.5‐mM LiCl. A focused ion beam was used to extract such a transgranular crack tip for analytical transmission electron microscopy using electron energy loss spectroscopy, which confirmed that the crack was in a ferrite grain. The sharp closed transgranular cracks seem to ally with the cracks observed in CO–CO2–H2O and anhydrous ammonia environments, which are proposed to grow by unique cleavage mechanisms. The possibility of embrittlement by carbon interstitials produced by ethanol electro‐oxidation within the crack is discussed.

Graphene is a key material of interest for the modification of physicochemical surface properties. However, its flat surface is a limitation for applications requiring a high specific surface area. This restriction may be overcome by integrating 2D materials in a 3D structure. Here, a strategy for the controlled synthesis of Graphene-Mesoporous Germanium (Gr-MP-Ge) nanomaterials is presented. Bipolar electrochemical etching and chemical vapor infiltration were employed, respectively, for the nanostructuration of Ge substrate and subsequent 3D nanographene coating. While Raman spectroscopy reveals a tunable domain size of nanographene with the treatment temperature, transmission electron microscopy data confirm that the crystallinity of Gr-MP-Ge is preserved. X-ray photoelectron spectroscopy indicates the non-covalent bonding of carbon to Ge for Gr-MP-Ge. State-of-the-art molecular dynamics modeling provides a deeper understanding of the synthesis process through the presence of radicals. The successful synthesis of these nanomaterials offers the integration of nanographene into a 3D structure with a high aspect ratio and light weight, thereby opening avenues to a variety of applications for this versatile nanomaterial.

Environmentally assisted cracking (EAC) initiation tests were carried out by subjecting Alloy 800 tensile specimens to 0.55 mol/kg SO42- solution, pH(280 degrees C) 3, at 280 degrees C using slow rise-time cyclic loading and in-situ crack detection. EAC, intergranular corrosion (IGC), and pitting were observed. Transmission electron microscopy analysis revealed Ti- and Cr-rich oxides in cracks, and sulfur incorporated in oxide(s) or as sulfide compound(s). This oxide/sulfide film is likely impaired, producing a slip dissolution-type EAC mechanism. For pitting, only a nano-scale sulfur layer was identified at pit-metal interfaces. This high surface coverage of adsorbed sulfur limited oxide nucleation and accelerated metal dissolution.

The effect of Pt on the structural evolution of nanoporous gold (NPG) is complex and is controlled by processes including secondary dealloying of Ag, surface diffusion of Au, and Pt segregation. High-resolution studies are carried out to investigate the interplay of the inherent processes. Observations such as Pt segregation at nanoligament surfaces, core-shell structures of nanoligaments, and Ag retention inside individual nanoligaments are seen at unprecedented detail using high resolution characterization techniques, including Atom Probe Tomography (APT) and Electron Energy Loss Spectroscopy (EELS). Quantitative estimates of the surface area-to-volume ratios of nanoporous layers with different Pt content indicate their relative functionalities for surface area driven applications.

The environmental stability of the layered semiconductor black phosphorus (bP) remains a challenge. Passivation of the bP surface with phosphorus oxide, POx, grown by a reactive ion etch with oxygen plasma is known to improve photoluminescence efficiency of exfoliated bP flakes. We apply phosphorus oxide passivation in the fabrication of bP field effect transistors using a gate stack consisting of a POx layer grown by reactive ion etching followed by atomic layer deposition of Al2O3. We observe room temperature top-gate mobilities of 115 cm2 V−1 s−1 in ambient conditions, which we attribute to the low defect density of the bP/POx interface.

Nickel-rich materials such as LiNi1-x-yMnxCoyO2 (NMC) and LiNi1-x-yCoxAlyO2 (NCA) have become attractive compared to LiCoO2 due to their lower cost, increased lifetime and increased safety. Coprecipitation is a common method to synthesize mixed metal hydroxides (M(OH)2: M = divalent transition metals) as the precursor materials to the lithiated metal oxides. While the syntheses of divalent NMC precursor materials are well understood, the introduction of a trivalent cation, such as Al+3, complicates the synthesis and affects the products significantly.1 In order to balance the charge, an extra anion needs to be incorporated into the layered structure, resulting in the formation of a new layered double hydroxide (LDH) phase.1 Increases in the Al content of the precursor result in a larger proportion of LDH phase in the material. Most insidious is that the Al atoms are in the LDH phase and not uniformly distributed as a solid solution in the material. Literature on NCA materials often omit reporting precursor characterization, or obtain commercial precursors that do not have LDH. Even when a group reported precursors with no LDH2 and with LDH3 using the same synthesis method, there was only a brief mention about LDH presence, with no discussion as to its formation or removal. LDH phases have been widely reported in supercapacitor research, even in ­NCA hydroxides.4 Unfortunately, there has been little to no work reported on the conversion of LDH phases with trivalent cations to phases with no intercalated molecules. However, there is a large body of work on the 2 known phases of Ni(OH)2, denoted as α-Ni(OH)2 and β-Ni(OH)2.5 α-Ni(OH)2 is analogous to the LDH phase, with water molecules intercalated between layers of Ni(OH)2; β-Ni(OH)2 does not have any intercalated molecules. It is known that α-Ni(OH)2, can be converted into β-Ni(OH)2 by a process called chemical ageing.5 This is generally performed in concentrated alkaline solutions, usually at higher temperatures. In this work, [Ni0.80Co0.15]0.95-xAl0.05+x(OH)2 (x = 0, 0.05) precursor materials were prepared by the coprecipitation method. The materials with Al contained appreciable amounts of LDH phase. The precursor materials were then washed in a solution of NaOH, filtered and dried. NaOH concentration, initial solution temperature, stirring temperature and stirring time were varied to study their impact on LDH removal. Unwashed and washed samples were characterized by XRD, ICP-OES, and TGA-MS to monitor LDH content, metal ratios and LDH anions. SEM and photographs were also used to monitor morphological and visual changes. Recommended recipes for the production of competitive NCA hydroxide precursors are reported. The competitive hydroxides were reacted with LiOH•H2O at elevated temperature to create NCA materials with excellent electrochemical behavior. (1) Zhao, X.; Zhou, F.; Dahn, J. R. J. Electrochem. Soc. 2008, 155, A642–A647. (2) Duan, J.; Hu, G.; Cao, Y.; Tan, C.; Wu, C.; Du, K.; Peng, Z. J. Power Sources 2016, 326, 322–330. (3) Duan, J.; Wu, C.; Cao, Y.; Huang, D.; Du, K.; Peng, Z.; Hu, G. J. Alloys Compd. 2017, 695, 91–99. (4) Wang, X.; Lin, Y.; Su, Y.; Zhang, B.; Li, C.; Wang, H.; Wang, L. Electrochim. Acta 2017, 225, 263–271. (5) Hall, D. S.; Lockwood, D. J.; Bock, C.; MacDougall, B. R. Proc. R. Soc. A 2014, 471, 20140792(1-65).

Intergranular oxidation in Alloy 600 exposed to 480 °C hydrogenated steam was examined at the nano-scale level with analytical electron microscopy and atom probe tomography. The fundamental processes of minor element oxidation and diffusion-induced grain boundary migration (DIGM) were explored. Intergranular oxidation was observed, with Ti and Al oxidation preceding Cr oxidation. Extensive DIGM is observed, with concentrations of minor elements far exceeding bulk values. Calculations are performed which support that the mechanism of DIGM causes large-scale segregation of minor elements. Also, discrete oxide particles ahead of the oxide front provide evidence for classical intergranular internal oxidation at temperatures below 500 °C.

Alloy 800 was exposed to a 330 degrees C Pb-containing, mildly caustic (pH(330 degrees C) 9.5) environment producing SCC. High resolution analytical TEM characterization of crack tips provided evidence to elucidate the Pb-caustic SCC mechanism and highlight a continuum of classical caustic SCC, facilitated at lower pH by the presence of Pb. Successive regions of Ni-enrichment and Cr-rich oxides were observed along the crack with selective Fe dissolution ahead of crack tips, de-alloying. Also, Pb is observed at oxide-metal interfaces. A hybrid film-rupture/de-alloying SCC mechanism is proposed, with Pb at oxide-metal interfaces acting to impair the passivity of the metastable Cr-rich oxide.

Quantum bits (qubits) with long coherence times are an important element for the implementation of medium- and large-scale quantum computers. In the case of superconducting planar qubits, understanding and improving qubits' quality can be achieved by studying superconducting planar resonators. In this paper, we fabricate and characterize coplanar waveguide resonators made from aluminum thin films deposited on silicon substrates. We perform three different substrate surface treatments prior to aluminum deposition: one chemical treatment based on a hydrofluoric acid clean; one physical treatment consisting of a thermal annealing at 880 degrees C in high vacuum; and one combined treatment comprising both the chemical and the physical treatments. The aim of these treatments is to remove the two-level state (TLS) defects hosted by the native oxides residing at the various samples' interfaces. We first characterize the fabricated samples through cross-sectional tunneling electron microscopy, acquiring electron energy loss spectroscopy maps of the samples' cross sections. These measurements show that both the chemical and the physical treatments almost entirely remove native silicon oxide from the substrate surface and that their combination results in the cleanest interface. Additionally, we analyze the effects of the various substrate treatments on the roughness of the silicon surface by means of atomic force microscopy surface morphology mapping. We then study the quality of the resonators by means of microwave measurements in the 'quantum regime', i.e., at a temperature T similar to 10 mK and at a mean microwave photon number (n(ph)) similar to 1. In this regime, we find that both surface treatments independently improve the resonator's intrinsic quality factor by approximate to 172%. The highest quality factor is obtained for the combined treatment, Q(i) approximate to 0.82 million, corresponding to an improvement by Finally, we find that the TLS quality factor averaged over a time period of 3 h is similar to 3 million at (n(ph)) similar to 10, indicating that substrate surface engineering can potentially reduce the TLS loss below other losses such as quasiparticle loss and flux noise.

Nanoporous gold (NPG) is usually made by electrochemical dealloying of Ag from binary AgAu alloys. The resulting nanoscale ligaments are not very stable, and tend to coarsen with time by surface self-diffusion, especially in electrolyte, which may lead to inferior electrocatalytic properties. Addition of a small amount of Pt to the precursor alloy is known to refine and stabilize the nanoporous product (NPG-Pt). However, the mechanisms by which Pt serves to refine the microstructure remain poorly understood. The present study aims to expand our knowledge of the role of Pt by examining NPG-Pt at atomic resolution with Atom Probe Tomography (APT), as well as by aberration-corrected Transmission Electron Microscopy. Atomic level observation of Pt enrichment on ligament surfaces sheds light on the underlying mechanisms that give rise to Pt's refining effect. Owing to improved Ag retention with higher Pt content, NPG-Pt1 (made by dealloying Ag77Au22Pt1) was shown to have the highest surface area-to-volume ratio, compared to NPG-Pt3 (made by dealloying Ag77Au20Pt3). Quantitative estimates reveal up to 5-fold enrichment of Pt at nanoligament surfaces, compared to the precursor content, in NPG-Pt. The interface between the dealloyed layer and the substrate was captured by APT, for the first time. The findings of this investigation add insight into the functionality of NPG-Pt and its prospective catalytic performance.

The preparation of TEM samples using focused-ion beam (FIB) techniques allows for characterization of electron-transparent site-specific areas, such as oxide-metal interfaces and crack tips, leading to improved understanding of material degradation mechanisms. Using conventional FIB techniques to prepare zirconium alloy TEM samples results in the production of artefact delta hydrides during the final thinning stage, which can confound analyses and mechanistic interpretation, especially when understanding hydride morphology and crystallography is critical. A comparison of various preparation methods was performed to determine their influence on artefact hydrides in TEM samples. As-received Zircaloy-4 material with <10 mu g/g hydrogen was quenched, fabricated into electropolished (EP) foils, TEM lamella were extracted using FIB, then the lamella were final thinned using different ion beam preparation techniques. Low-loss electron energy loss spectroscopy (EELS) was performed on the EP and FIB-prepared samples before and after final thinning. The expected post-quench distribution of gamma hydrides was present in the EP and FIB samples before final thinning, however, after FIB or broad ion beam final thinning at room temperature the hydride phase was predominately delta with a larger volume fraction. After TEM lamella were cooled with liquid nitrogen during FIB or broad ion beam final thinning only gamma hydrides were present, which was confirmed with diffraction analysis by observing gamma hydride super-lattice reflections. The large surface area to volume ratio, reactive surface, and beam heating during conventional FIB final thinning is believed to cause hydrogen-containing impurities in the vacuum chamber to dissociate and allow hydrogen to enter the specimen. Specimen cooling and the presence of a nearby cold finger reduce the hydrogen partial pressure near the sample surface and significantly reduce the hydrogen adsorption, absorption, and diffusion kinetics. Future investigations using FIB-prepared TEM samples of zirconium should apply cryo-techniques to prevent artefact hydrides. (C) 2018 Elsevier B.V. All rights reserved.

At an implant biointerface, where an engineered material merges into a biological environment, complex biophysicochemical interactions occur. One typical biointerface is the bond between human bone and dental or orthopedic implants, which is based on the biomineralization of essential bone components such as hydroxyapatite, at the implant surface. However, the exact bonding mechanism between bone and implants is still unclear. The distribution of both the mineralized and organic components of bone at the interface, and their origins, requires improved characterization. Here, the first correlative characterization is reported using multiple-length-scale tomography and spectroscopy techniques to probe the chemical structure of the biointerface between human bone and commercial titanium dental implant down to the atomic scale in four dimensions (4D). The existence of an intervening transition zone bonding mature bone tissue is demonstrated to implant at multiple length scales, where the phase of bone mineral differs immediately adjacent to the implant and atomic-scale osseointegration is confirmed. The correlative 4D electron energy loss spectroscopy tomography and atom probe tomography workflow established herein is transferable to other applications in materials or biological sciences.

Microalloying additions to Mg-Zn base alloys can refine precipitation and improve hardening, but their effect on the microstructure at the grain boundary regions are seldom analyzed. Here the grain boundary microstructure is examined in an Mg-4Zn (wt.%) alloy, which has been microalloyed with Ce-Ca. This combination of elements has previously been shown to successfully enhance ductility, texture, and precipitation hardening, compared to binary Mg-Zn. Coarse grain boundary precipitates are found with or without microalloying, but precipitate-free zones (PFZs) for β′1 that surround the boundaries are far narrower with Ce-Ca microalloying additions. Furthermore, fine basal precipitates containing Ca are found uniformly distributed up to the boundary, making those zones devoid of β′1 not truly precipitate-free. Electron microscopy and atom probe analysis of early-stage ageing conditions reveals that Ca readily forms clusters with Zn, and forms fine ordered GP zones, while Zn also segregates to the grain boundaries. The tendency of Ca to homogeneously form clusters and precipitates reduces Ca migration to the grain boundaries, which has a beneficial effect on producing the refined precipitate distributions at the grain boundary regions.

Knowledge of solute interaction with the interface during the transformation of austenite into ferrite is fundamental in predicting its kinetics in multicomponent steel. This interaction notably translates in segregation, or depletion, of the solutes at the transformation interface. Here, this segregation was successfully quantified by atom probe tomography (APT) in four ternary Fe-X-C systems involving substitutional solutes commonly found in modern steel grades (X = Cr, Mn, Ni, Mo). Controlled decarburization was used to grow a uniform, planar and incoherent ferrite layer at the surface of fully austenitic samples. In the case of Fe-Cr-C and Fe-Mo-C, the interfacial concentrations permitted the evaluation of the binding energy of each substitutional solute to the interface, which was found to be comparable to its respective grain boundary binding energy. In the case of Fe-Mn-C and Fe-Ni-C, undesirable motion of the interface during the quench of the samples could not be avoided, preventing a reliable estimation of their binding energy since temperature and interface velocity were unknown. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Ammonia electro-oxidation activity is promoted at Pt nanostructured catalysts which combine high surface area values and a high proportion of (1 0 0) surface atoms. The latter is extensively known to be the most active surface arrangement of atoms for NH3 oxidation. In the present study, Pt(1 0 0) nanostructured thin films were prepared and subsequently modified by surface functionalization with rhodium through pulsed electrodeposition. Rh surface coverage was varied by modifying the number of applied electrodeposition pulses, and was found to modify the voltammetric H-upd features. When Rh surface content was assessed by H-upd deconvolution analyses, it was revealed that Rh nucleation first occurred at (1 0 0) Pt step sites in the form of Rh(1 0 0) sub-monolayers, and subsequently grew further to form Rh multilayer species. For minute amounts of rhodium, NH3 activity is increased slightly, provided that long range (1 0 0) Pt wide domains were not shortened. The lower onset potential for NH3 oxidation in the presence of Rh surface atoms, which is shifted negatively by more than 50 mV as compared to Pt, is attributed to the NH3 oxidative dehydrogenation processes at lower potential values. For similar Rh coverage (around 20%), similar NH3 activity is obtained at pseudomorphic Rh(1 00) adlayers and Rh 3D islands, a finding which emphasizes the non-specific NH3 activity of Rh(1 0 0) atoms. (C) 2017 Elsevier Inc. All rights reserved.

To evaluate the beneficial effects of intergranular carbides on inhibiting stress corrosion cracking (SCC), Alloy 600 samples in the thermally-treated (TT) and solution-annealed (SA) conditions were analyzed after exposure to 480 degrees C hydrogenated steam. Intergranular oxidation was observed in both samples, along with diffusion-induced grain boundary migration (DIGM). Compositional mapping revealed DIGM to be more severe in 600SA, while conventional intergranular solute diffusion involving static boundaries appeared dominant in 600TT. 3D serial sectioning of the boundaries revealed strong variations in the intergranular oxide for 600TT, particularly in the depth of oxide penetration. This was attributed to Cr carbide precipitates, present due to the thermal treatment, pinning against DIGM. Immobilizing the boundary via carbide pinning reduces oxide growth by effectively starving it of the ready solute supply otherwise available to a migrating boundary. Because of this interaction between boundary migration, carbide pinning, and oxide growth, the intergranular oxidation in 600TT is highly variable and discontinuous compared to 600SA, where DIGM is unchecked and easier oxide growth produces near-uniform coverage of the boundary. This marked decrease in boundary oxide coverage likely contributes to the improved SCC resistance of 600TT. These results demonstrate the necessity of investigating such phenomena using 3D analysis methods. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Deterioration of nickel-based alloy components in fission reactors is associated with the generation of helium from neutron-induced nuclear reactions. In tests at the macroscopic scale, deleterious effects of helium on the mechanical properties of nickel alloys are observed upon the formation and growth of helium bubbles. In order to enhance the understanding of helium effects in nickel, the properties of helium bubbles can be investigated by atomistic scale simulations. In the present work, we have studied helium bubbles in pure nickel, with diameters from 1.0 to 5.0 nm, using molecular dynamics (MD) simulations. The properties of nano-sized helium bubbles as a function of the helium-to-vacancy ratio are calculated at 600 K. The conditions for helium bubbles in mechanical equilibrium with the nickel matrix are determined. The results from simulations are found to be in good agreement with experimental data. Crown Copyright (C) 2017 Published by Elsevier B.V. All rights reserved.

The effects of irradiation on Inconel® (Inconel is a registered trademark of Special Metals Corporation and its subsidiaries) X-750, have been shown to lead to embrittlement and intergranular fracture. This is now widely accepted to be a result of intergranular helium bubbles over the fluence range studied. This paper provides a quantitative assessment and a detailed discussion of the radiation-induced defects including; helium bubbles (size and density distribution, and grain boundary area fraction), dislocation loops and stacking fault tetrahedra, and the disordering and dissolution of secondary gamma prime precipitates. The microstructural evolution will be presented and discussed as a function of dose (from ~5.5 to ~80 dpa), helium concentration (~1300 to ~25,000 appm helium), and irradiation temperature (~120–280 to ~300–330 °C).

The primary heat transport system of modern CANDU® (CANDU is a registered trademark of Atomic Energy of Canada Limited) reactors uses A106B piping (i.e., feeder pipes). Feeder cracking has only affected tight-radius bends at outlet feeders (higher temperature), and cracking is limited to regions with high residual stress suffering from wall-thinning by flow accelerated corrosion. To date, the mechanism of feeder cracking has not been identified. This paper includes high-resolution transmission electron microscopy and electron energy loss near edge structure characterization of inside and outside surface intergranular cracks from ex-service CANDU feeders. Prior to this work, no high resolution characterization has been performed for CANDU feeder cracking. All intergranular cracks show evidence of cementite decomposition, leading to decoration of grain boundaries with amorphous carbon, and carbon diffusion along un-cracked boundaries ahead of crack tips. Sulfur has been found on the oxide-metal interface of all intergranular cracks, but is not observed ahead of the crack tips. Sulfur is believed to be from the breakdown of manganese sulfides during service. The cementite decomposition and breakdown of manganese sulfides are believed to be accelerated in the presence of hydrogen produced from the flow accelerated corrosion. Small (<15 nm) voids are also present ahead of some intergranular crack-tips along the ferrite-ferrite boundaries, indicating that hydrogen enhanced, low temperature creep-cracking, may also contribute to intergranular fracture.

We have physicochemically characterized the formation of PtRu nanoparticles, deposited by evaporation onto highly oriented pyrolytic graphite, using in situ X-ray photoelectron spectroscopy, ex situ high-angle annular dark-field/scanning transmission electron microscopy, electron energy loss spectroscopy, and time-of-flight secondary ion mass spectrometry. We used three different orders of metal deposition: Pt evaporated onto Ru, Ru evaporated onto Pt and both metals evaporated simultaneously, and then followed the evolutions of the alloys as a function of annealing temperature. The C 1s, O 1s, Ru 3d, and Pt 4f core level spectra were employed to describe the alloying interactions between the metals. For all deposition methods, Ru diffuses to the NP surface through the Pt, and not the reverse. Each of the preparation methods produces surface and volume structures that differ from those of the others, even after prolonged annealing at temperatures over 700 degrees C, indicating the source of confusion in the literature concerning the physicochemical characterization of PtRu nanoparticles.