Enhanced age-hardening response and creep resistance of an Al-0.5Mn-0.3Si (at.%) alloy by Sn inoculation.

Precipitation-strengthening at ambient and high temperatures is examined in Al-0.5Mn-0.3Si (at.%) alloys with and without 0.02 at.% Sn micro-additions. Isochronal aging experiments reveal that Sn inoculation results in a pronounced age-hardening response: a hardening increment of 125 MPa is achieved at peak-aging (475 °C), which is five times greater than that of a Sn-free alloy. Scanning electron microscopy and synchrotron x-ray diffraction analyses demonstrate that, while the structure of the α-Al(Mn,Fe)Si precipitates formed in the peak-aged alloys is identical, their mean radius is smaller (R ~ 25 vs. 100-500 nm) and their number density is greater (~1021 vs. ~1019-20 m -3) in the Sn-modified alloy. Atom-probe tomography analyses reveal that the enhanced dispersion of the α-precipitates is related primarily to the formation of Sn-rich nanoprecipitates at intermediate temperatures, which act as nucleation sites for Mn-Si-rich nanoprecipitates. High-resolution transmission electron microscopy analyses demonstrate that these Mn-Si-rich nanoprecipitates exhibit icosahedral quasicrystal ordering (I-phase), which transform into the cubic-approximant α-phase upon peak aging. Significant Sn segregation at the semi-coherent interfaces of the α-precipitates in the peak-aged Sn-modified alloy is observed via APT, which promotes homogeneous nucleation of the I/α-precipitates at aging temperatures > 400 °C. At 300 °C, creep threshold stresses are observed in both alloys in the peak-aged state, which increases from ~30 MPa in the Sn-free alloy to ~52 MPa in the Sn-modified alloy. This boost in creep resistance is consistent with the enhanced aging response (higher Orowan stress).

Solute-induced strengthening during creep of an aged-hardened Al-Mn-Zr alloy.

We examine the precipitation and creep behavior of Al-0.5Mn-0.02Si (at.%) alloys, with and without the L12-forming elements Zr and Er (0.09 and 0.05 at.%, respectively), utilizing isochronal aging experiments as well as compressive and tensile creep tests performed between 275 and 400 °C. The Al-0.5Mn-0.09Zr-0.05Er-0.05Si alloy exhibits an unusually high creep resistance in the peak-aged state, which is significantly better than that observed generally in its Mn-free L12-strengthened counterparts; for example, the creep threshold stresses at 300 °C are 34-37 MPa, about three times higher than those in a Mn-free Al-0.11Zr-0.005Er-0.02Si alloy. Scanning transmission electron microscopy illustrates that nanoscale Al 3 (Zr,Er) L1 2 -precipitates are formed in the dendritic cores and micron-sized Al(Mn,Fe)Si α-precipitates in the inter-dendritic channels. Moreover, the Al(f.c.c.)-matrix remains supersaturated with randomly distributed Mn solute atoms, as determined by atom-probe tomography and electrical conductivity measurements, for months at creep temperatures. Creep experiments on the Zr- and Er-free Al-0.5Mn-0.02Si solid-solution alloy reveal a small primary creep strain, a high apparent stress exponent, na ~9-7, and a threshold-stress-type behavior. After ruling out other possible mechanisms, we provide evidence that the threshold stress in this precipitate-free alloy originates from dislocation/solute elastic interactions leading to a strong drag force exerted on edge dislocations, hindering their ability to climb. The relatively high creep resistance of Al-0.5Mn-0.09Zr-0.05Er-0.05Si is interpreted in terms of the synergy between this solute-induced threshold stress (SITS, from Mn in solid-solution) and the known precipitate-bypass threshold stress (from the L12-nanoprecipitates).

Laser writing of nitrogen-doped silicon carbide for biological modulation.

Conducting or semiconducting materials embedded in insulating polymeric substrates can be useful in biointerface applications; however, attainment of this composite configuration by direct chemical processes is challenging. Laser-assisted synthesis has evolved as a fast and inexpensive technique to prepare various materials, but its utility in the construction of biophysical tools or biomedical devices is less explored. Here, we use laser writing to convert portions of polydimethylsiloxane (PDMS) into nitrogen-doped cubic silicon carbide (3C-SiC). The dense 3C-SiC surface layer is connected to the PDMS matrix via a spongy graphite layer, facilitating electrochemical and photoelectrochemical activity. We demonstrate the fabrication of arbitrary two-dimensional (2D) SiC-based patterns in PDMS and freestanding 3D constructs. To establish the functionality of the laser-produced composite, we apply it as flexible electrodes for pacing isolated hearts and as photoelectrodes for local peroxide delivery to smooth muscle sheets.

Phase Segmentation in Atom-Probe Tomography Using Deep Learning-Based Edge Detection.

Atom-probe tomography (APT) facilitates nano- and atomic-scale characterization and analysis of microstructural features. Specifically, APT is well suited to study the interfacial properties of granular or heterophase systems. Traditionally, the identification of the interface between, for precipitate and matrix phases, in APT data has been obtained either by extracting iso-concentration surfaces based on a user-supplied concentration value or by manually perturbing the concentration value until the iso-concentration surface qualitatively matches the interface. These approaches are subjective, not scalable, and may lead to inconsistencies due to local composition inhomogeneities. We introduce a digital image segmentation approach based on deep neural networks that transfer learned knowledge from natural images to automatically segment the data obtained from APT into different phases. This approach not only provides an efficient way to segment the data and extract interfacial properties but does so without the need for expensive interface labeling for training the segmentation model. We consider here a system with a precipitate phase in a matrix and with three different interface modalities-layered, isolated, and interconnected-that are obtained for different relative geometries of the precipitate phase. We demonstrate the accuracy of our segmentation approach through qualitative visualization of the interfaces, as well as through quantitative comparisons with proximity histograms obtained by using more traditional approaches.

Broad-band high-gain room temperature photodetectors using semiconductor-metal nanofloret hybrids with wide plasmonic response.

Semiconducting nanowires are widely studied as building blocks for electro-optical devices; however, their limited cross-section and hence photo-response hinder the utilization of their full potential. Herein, we present an opto-electronic device for broad spectral detection ranging from the visible (VIS) to the short wavelength infra-red (SWIR) regime, using SiGe nanowires coupled to a broadband plasmonic antenna. The plasmonic amplification is obtained by deposition of a metallic nanotip at the edge of a nanowire utilizing a bottom-up synthesis technique. The metallic nanotip is positioned such that both optical plasmonic modes and electrical detection paths are coupled, resulting in a specific detectivity improvement of ∼1000 compared to conventional SiGe NWs. Detectivity and high gain are also measured in the SWIR regime owing to the special plasmonic response. Furthermore, the temporal response is improved by ∼1000. The fabrication process is simple and scalable, and it relies on low-resolution and facile fabrication steps with minimal requirements for top-down techniques.

Strain-Energy Release in Bent Semiconductor Nanowires Occurring by Polygonization or Nanocrack Formation.

Strain engineering of semiconductors is used to modulate carrier mobility, tune the energy bandgap, and drive growth of self-assembled nanostructures. Understanding strain-energy relaxation mechanisms including phase transformations, dislocation nucleation and migration, and fracturing is essential to both exploit this degree of freedom and avoid degradation of carrier lifetime and mobility, particularly in prestrained electronic devices and flexible electronics that undergo large changes in strain during operation. Raman spectroscopy, high-resolution transmission electron microscopy, and electron diffraction are utilized to identify strain-energy release mechanisms of bent diamond-cubic silicon (Si) and zinc-blende GaAs nanowires, which were elastically strained to >6% at room temperature and then annealed at an elevated temperature to activate relaxation mechanisms. High-temperature annealing of bent Si-nanowires leads to the nucleation, glide, and climb of dislocations, which align themselves to form grain boundaries, thereby reducing the strain energy. Herein, Si nanowires are reported to undergo polygonization, which is the formation of polygonal-shaped grains separated by grain boundaries consisting of aligned edge dislocations. Furthermore, strain is shown to drive dopant diffusion. In contrast to the behavior of Si, GaAs nanowires release strain energy by forming nanocracks in regions of tensile strain due to the weakening of As-bonds. These insights into the relaxation behavior of highly strained crystals can inform the design of nanoelectronic devices and provide guidance on mitigating degradation.

Atomically resolved calcium phosphate coating on a gold substrate.

Some articles have revealed that the electrodeposition of calcium phosphate (CaP) coatings entails a precursor phase, similarly to biomineralization in vivo. The chemical composition of the initial layer and its thickness are, however, still arguable, to the best of our knowledge. Moreover, while CaP and electrodeposition of metal coatings have been studied utilizing atom-probe tomography (APT), the electrodeposition of CaP ceramics has not been heretofore studied. Herein, we present an investigation of the CaP deposition on a gold substrate. Using APT and transmission electron microscopy (TEM) it is found that a mixture of phases, which could serve as transient precursor phases to hydroxyapatite (HAp), can be detected. The thickness of these phases is tens of nanometers, and they consist of amorphous CaP (ACP), dibasic calcium phosphate dihydrate (DCPD), and octacalcium phosphate (OCP). This demonstrates the value of using atomic-resolved characterization techniques for identifying the precursor phases. It also indicates that the kinetics of their transformation into the more stable HAp is not too fast to enable their observation. The coating gradually displays higher Ca/P atomic ratios, a porous nature, and concomitantly a change in its density.

Systematic approaches for targeting an atom-probe tomography sample fabricated in a thin TEM specimen: Correlative structural, chemical and 3-D reconstruction analyses.

Atom-probe tomography (APT) is a unique analysis tool that enables true three-dimensional (3-D) analyses with sub-nano scale spatial resolution. Recent implementations of the local-electrode atom-probe (LEAP) tomograph with ultraviolet laser pulsing have significantly expanded the research applications of APT. The small field-of-view of a needle-shaped specimen with a less than 100 nm diam. is, however, a major limitation for analyzing materials. The systematic approaches for site-specific targeting of an APT nanotip in a transmission electron microscope (TEM) of a thin sample are introduced to solve the geometrical limitations of a sharpened APT nanotip. In addition to "coupling APT to TEM", the technique presented here allows for targeting the preparation of an APT tip based on TEM observation of a much larger area than what is captured in the APT tip. The correlative methods have synergies for not only high-resolution structural analyses but also for obtaining chemical information. Chemical analyses in a TEM, both energy-dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS), are performed and compared with the APT chemical analyses of a carbide phase (M7C3) precipitate at a grain boundary in a Ni-based alloy. Additionally, a TEM image of a sharpened APT nanotip is utilized for calculation of the detection area ratio of an APT nanotip by comparison with a TEM image for precise tomographic reconstructions. A grain-boundary/carbide precipitate triple junction is used to attain precise positioning of an APT nanotip in an analyzed TEM specimen.

Criteria and considerations for preparing atom-probe tomography specimens of nanomaterials utilizing an encapsulation methodology.

Atom-probe tomography (APT) is a powerful method for characterization of nanomaterials due to its atomic-ppm level detection limit and Angstrom spatial resolution. Sample preparation for nanomaterials is, however, challenging because of their small dimensions and complicated geometries. Nanowires, with their high geometrical aspect ratio and nanowire length, 10 to 100 times their typical diameters, are highly suitable specimens for APT analyses, which can be transferred to silicon microposts using a nanomanipulator for direct APT measurements. This method is, however, prone to poor alignment and a limited field-of-view (FOV). Most importantly, direct implementation of APT with high aspect ratio nanowires may yield a low success rate of ∼30%, due to the high electric fields (10-40 V nm-1) associated with APT. While this is acceptable for samples analyzed solely by APT, a low sample yield makes it challenging to perform correlative experiments on the same nanowire specimen, utilizing other sophisticated characterization instruments. Herein, we introduce a general strategy for preparing high-yield APT specimens by encapsulating the nanowires utilizing a conformal atomic-layer deposition (ALD) coating followed by site-specific lift-out using a dual-beam focused-ion beam microscope. The ALD deposited coating forms strong chemical bonds with the Si nanowires yielding a high-quality and robust interface. The evaporation electric fields of the ALD coating and the nanowires are tuned by changing laser energy to obtain a uniform evaporation rate. The strong adhesion of the ALD-coating/nanowire interface and uniform evaporation rate produce a >90% specimen yield, with small concentration of reconstruction artifacts in 3-D. Simultaneously, the field-of-view is enhanced and the surface of the nanowire becomes visible, which makes the study of surface adsorption, segregation and oxidation possible. We utilized ALD-ZnO coated silicon nanowires as an example for investigating the criteria for choosing coating materials, laser pulse energy, laser direction, sample geometry, and substrate materials. The same criteria and considerations are applicable for preparing specimens of nanoparticles and 2-D material.

Alloy-assisted deposition of three-dimensional arrays of atomic gold catalyst for crystal growth studies.

Large-scale assembly of individual atoms over smooth surfaces is difficult to achieve. A configuration of an atom reservoir, in which individual atoms can be readily extracted, may successfully address this challenge. In this work, we demonstrate that a liquid gold-silicon alloy established in classical vapor-liquid-solid growth can deposit ordered and three-dimensional rings of isolated gold atoms over silicon nanowire sidewalls. We perform ab initio molecular dynamics simulation and unveil a surprising single atomic gold-catalyzed chemical etching of silicon. Experimental verification of this catalytic process in silicon nanowires yields dopant-dependent, massive and ordered 3D grooves with spacing down to ~5 nm. Finally, we use these grooves as self-labeled and ex situ markers to resolve several complex silicon growths, including the formation of nodes, kinks, scale-like interfaces, and curved backbones.

1-D Metal Nanobead Arrays within Encapsulated Nanowires via a Red-Ox-Induced Dewetting: Mechanism Study by Atom-Probe Tomography.

Metal nanoparticle arrays are excellent candidates for a variety of applications due to the versatility of their morphology and structure at the nanoscale. Bottom-up self-assembly of metal nanoparticles provides an important complementary alternative to the traditional top-down lithography method and makes it possible to assemble structures with higher-order complexity, for example, nanospheres, nanocubes, and core-shell nanostructures. Here we present a mechanism study of the self-assembly process of 1-D noble metal nanoparticles arrays, composed of Au, Ag, and AuAg alloy nanoparticles. These are prepared within an encapsulated germanium nanowire, obtained by the oxidation of a metal-germanium nanowire hybrid structure. The resulting structure is a 1-D array of equidistant metal nanoparticles with the same diameter, the so-called nanobead (NB) array structure. Atom-probe tomography and transmission electron microscopy were utilized to investigate the details of the morphological and chemical evolution during the oxidation of the encapsulated metal-germanium nanowire hybrid-structures. The self-assembly of nanoparticles relies on the formation of a metal-germanium liquid alloy and the migration of the liquid alloy into the nanowire, followed by dewetting of the liquid during shape-confined oxidation where the liquid column breaks-up into nanoparticles due to the Plateau-Rayleigh instability. Our results demonstrate that the encapsulating oxide layer serves as a structural scaffold, retaining the overall shape during the eutectic liquid formation and demonstrates the relationship between the oxide mechanical properties and the final structural characteristics of the 1-D arrays. The mechanistic details revealed here provide a versatile tool-box for the bottom-up fabrication of 1-D arrays nanopatterning that can be modified for multiple applications according to the RedOx properties of the material system components.

Analysis of Nanoprecipitates in a Na-Doped PbTe-SrTe Thermoelectric Material with a High Figure of Merit.

The dimensionless figure of merit, ZT, of bulk thermoelectric materials depends mainly on the transport properties of charge carriers and heat-carrying phonons. PbTe-4 mol % SrTe doped with 2 mol % Na (Pb0.94Na0.02Sr0.04Te) is a nanostructured material system that exhibits a ZT higher than 2. The precipitate size distribution of SrTe precipitates is believed to play a key role. This raises the question of whether its performance is limited by precipitate coarsening (Ostwald ripening) at elevated temperatures. Herein, we utilize an atom-probe tomography (APT) to study the number density and mean radii of precipitates in concert with partial radial distribution functions (RDFs) of individual atoms. We find that the SrTe precipitates actually contain oxygen: SrTe1-xOx. We correlate this information with the overall ZT performance, specifically focusing on the electrical and lattice thermal conductivities after isothermal heat treatments at 300 and 400 °C for 7 days, followed by furnace cooling. Comparison of the samples annealed at 400 and 300 °C demonstrates significant coarsening of SrTe1-xOx precipitates as well as strong segregation of oxygen impurities in the SrTe1-xOx precipitates. Additionally, on the basis of the partial RDFs, the Na dopant atoms cluster with other Na atoms as well as with Pb, Te, and Sr atoms; clustering depends strongly on the annealing temperature and concomitantly affects the overall ZT values. We found that the coarsening slightly increases the lattice thermal conductivity and also increases the electrical conductivity, thereby having little or even a beneficial effect on the ZT values. Importantly, these findings demonstrate that APT enables quantitative analyses in three dimensions of the PbTe-4 mol % SrTe samples in addition to correlation of their properties with the thermoelectric performance.

Nanowire Kinking Modulates Doping Profiles by Reshaping the Liquid-Solid Growth Interface.

Dopants modify the electronic properties of semiconductors, including their susceptibility to etching. In semiconductor nanowires doped during growth by the vapor-liquid-solid (VLS) process, it has been shown that nanofaceting of the liquid-solid growth interface influences strongly the radial distribution of dopants. Hence, the combination of facet-dependent doping and dopant selective etching provides a means to tune simultaneously the electronic properties and morphologies of nanowires. Using atom-probe tomography, we investigated the boron dopant distribution in Au catalyzed VLS grown silicon nanowires, which regularly kink between equivalent ⟨112⟩ directions. Segments alternate between radially uniform and nonuniform doping profiles, which we attribute to switching between a concave and convex faceted liquid-solid interface. Dopant selective etching was used to reveal and correlate the shape of the growth interface with the observed anisotropic doping.

True Atomic-Scale Imaging in Three Dimensions: A Review of the Rebirth of Field-Ion Microscopy.

This article reviews recent advances utilizing field-ion microscopy (FIM) to extract atomic-scale three-dimensional images of materials. This capability is not new, as the first atomic-scale reconstructions of features utilizing FIM were demonstrated decades ago. The rise of atom probe tomography, and the application of this latter technique in place of FIM has unfortunately severely limited further FIM development. Currently, the ubiquitous availability of extensive computing power makes it possible to treat and reconstruct FIM data digitally and this development allows the image sequences obtained utilizing FIM to be extremely valuable for many material science and engineering applications. This article demonstrates different applications of these capabilities, focusing on its use in physical metallurgy and semiconductor science and technology.

Dopant Diffusion and Activation in Silicon Nanowires Fabricated by ex Situ Doping: A Correlative Study via Atom-Probe Tomography and Scanning Tunneling Spectroscopy.

Dopants play a critical role in modulating the electric properties of semiconducting materials, ranging from bulk to nanoscale semiconductors, nanowires, and quantum dots. The application of traditional doping methods developed for bulk materials involves additional considerations for nanoscale semiconductors because of the influence of surfaces and stochastic fluctuations, which may become significant at the nanometer-scale level. Monolayer doping is an ex situ doping method that permits the post growth doping of nanowires. Herein, using atom-probe tomography (APT) with subnanometer spatial resolution and atomic-ppm detection limit, we study the distributions of boron and phosphorus in ex situ doped silicon nanowires with accurate control. A highly phosphorus doped outer region and a uniformly boron doped interior are observed, which are not predicted by criteria based on bulk silicon. These phenomena are explained by fast interfacial diffusion of phosphorus and enhanced bulk diffusion of boron, respectively. The APT results are compared with scanning tunneling spectroscopy data, which yields information concerning the electrically active dopants. Overall, comparing the information obtained by the two methods permits us to evaluate the diffusivities of each different dopant type at the nanowire oxide, interface, and core regions. The combined data sets permit us to evaluate the electrical activation and compensation of the dopants in different regions of the nanowires and understand the details that lead to the sharp p-i-n junctions formed across the nanowire for the ex situ doping process.

Heterogeneous silicon mesostructures for lipid-supported bioelectric interfaces.

Silicon-based materials have widespread application as biophysical tools and biomedical devices. Here we introduce a biocompatible and degradable mesostructured form of silicon with multi-scale structural and chemical heterogeneities. The material was synthesized using mesoporous silica as a template through a chemical vapour deposition process. It has an amorphous atomic structure, an ordered nanowire-based framework and random submicrometre voids, and shows an average Young's modulus that is 2-3 orders of magnitude smaller than that of single-crystalline silicon. In addition, we used the heterogeneous silicon mesostructures to design a lipid-bilayer-supported bioelectric interface that is remotely controlled and temporally transient, and that permits non-genetic and subcellular optical modulation of the electrophysiology dynamics in single dorsal root ganglia neurons. Our findings suggest that the biomimetic expansion of silicon into heterogeneous and deformable forms can open up opportunities in extracellular biomaterial or bioelectric systems.

Evidence of sub-10 nm aluminum-oxygen precipitates in silicon.

In this research, ultraviolet laser-assisted atom-probe tomography (APT) was utilized to investigate precisely the behavior at the atomistic level of aluminum impurities in ultrathin epitaxial silicon layers. Aluminum atoms were incorporated in situ during the growth process. The measured average aluminum concentration in the grown layers exceeds by several orders of magnitude the equilibrium bulk solubility. Three-dimensional atom-by-atom mapping demonstrates that aluminum atoms precipitate in the silicon matrix and form nanoscopic precipitates with lateral dimensions in the 1.3 to 6.2 nm range. These precipitates were found to form only in the presence of oxygen impurity atoms, thus providing clear evidence of the longhypothesized role of oxygen and aluminum-oxygen complexes in facilitating the precipitation of aluminum in a silicon lattice. The measured average aluminum and oxygen concentrations in the precipitates are ∼10 ± 0.5 at.% and ∼4.4 ± 0.5 at.%, respectively. This synergistic interaction is supported by first-principles calculations of the binding energies of aluminum-oxygen dimers in silicon. The calculations demonstrate that there is a strong binding between aluminum and oxygen atoms, with Al-O-Al and O-Al-Al as the energetically favorable sequences corresponding to precipitates in which the concentration of aluminum is twice as large as the oxygen concentration in agreement with APT data.

Laser-Assisted Field Evaporation and Three-Dimensional Atom-by-Atom Mapping of Diamond Isotopic Homojunctions.

It addition to its high evaporation field, diamond is also known for its limited photoabsorption, strong covalent bonding, and wide bandgap. These characteristics have been thought for long to also complicate the field evaporation of diamond and make its control hardly achievable on the atomistic-level. Herein, we demonstrate that the unique behavior of nanoscale diamond and its interaction with pulsed laser lead to a controlled field evaporation thus enabling three-dimensional atom-by-atom mapping of diamond (12)C/(13)C homojunctions. We also show that one key element in this process is to operate the pulsed laser at high energy without letting the dc bias increase out of bounds for diamond nanotip to withstand. Herein, the role of the dc bias in evaporation of diamond is essentially to generate free charge carriers within the nanotip via impact ionization. The mobile free charges screen the internal electric field, eventually creating a hole rich surface where the pulsed laser is effectively absorbed leading to an increase in the nanotip surface temperature. The effect of this temperature on the uncertainty in the time-of-flight of an ion, the diffusion of atoms on the surface of the nanotip, is also discussed. In addition to paving the way toward a precise manipulation of isotopes in diamond-based nanoscale and quantum structures, this result also elucidates some of the basic properties of dielectric nanostructures under high electric field.

Microstructure and Creep Properties of Boron- and Zirconium-Containing Cobalt-based Superalloys.

The effects of micro-additions of boron and zirconium on grain-boundary (GB) structure and strength in polycrystalline γ(f.c.c.) plus γ'(L12) strengthened Co-9.5Al-7.5W-X at. % alloys (X = 0-Temary, 0.05B, 0.01B, 0.05Zr, and 0.005B-0.05Zr at. %) are studied. Creep tests performed at 850 °C demonstrate that GB strength and cohesion limit the creep resistance and ductility of the ternary B- and Zr-free alloy due to intergranular fracture. Alloys with 0.05B and 0.005B-0.05Zr both exhibit improved creep strength due to enhanced GB cohesion, compared to the baseline ternary Co-9.5Al-7.5W alloy, but alloys containing 0.01B or 0.05Zr additions displayed no benefit. Atom-probe tomography is utilized to measure GB segregation, where B and Zr are demonstrated to segregate at GBs. A Gibbsian interfacial excess of 5.57 ± 1.04 atoms nm-2 was found for B at a GB in the 0.01B alloy and 2.88 ± 0.81 and 2.40 ± 0.84 atoms nm-2 for B and Zr, respectively, for the 0.005B-0.05Zr alloy. The GBs in the highest B-containing (0.05B) alloy exhibit micrometer-sized boride precipitates with adjacent precipitate denuded-zones (PDZs), whereas secondary precipitation at the GBs is not present in the other four alloys. The 0.05B alloy has the smallest room temperature yield strength, by 6 %, which is attributed to the PDZs, but it exhibits the largest increase in creep strength (with an ~2.5 order of magnitude decrease in the minimum strain rate for a given stress at 850 °C) over the baseline Co-9.5Al-7.5W alloy.

An Atomistic Tomographic Study of Oxygen and Hydrogen Atoms and their Molecules in CVD Grown Graphene.

The properties and growth processes of graphene are greatly influenced by the elemental distributions of impurity atoms and their functional groups within or on the hexagonal carbon lattice. Oxygen and hydrogen atoms and their functional molecules (OH, CO, and CO2 ) positions' and chemical identities are tomographically mapped in three dimensions in a graphene monolayer film grown on a copper substrate, at the atomic part-per-million (atomic ppm) detection level, employing laser assisted atom-probe tomography. The atomistic plan and cross-sectional views of graphene indicate that oxygen, hydrogen, and their co-functionalities, OH, CO, and CO2 , which are locally clustered under or within the graphene lattice. The experimental 3D atomistic portrait of the chemistry is combined with computational density-functional theory (DFT) calculations to enhance the understanding of the surface state of graphene, the positions of the chemical functional groups, their interactions with the underlying Cu substrate, and their influences on the growth of graphene.