Characterization of a HPHT boron ion-implanted diamond X-ray mirror following high vacuum annealing
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36 MATERIALS SCIENCE↗
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Results for “surface characterization”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Isopotential Electron Titration: Hydrogen Adsorbate-Metal Charge Transfer
The extent of charge transfer between an adsorbate and thermocatalytic surface plays a key role in determining catalytic activity, but direct and quantitative measures have remained elusive. Here, we report the method of isopotential electron titration (IET), an approach that directly measures charge transfer between adsorbates and catalytic surfaces. Charge transfer between Pt and adsorbed hydrogen adatoms was investigated using a catalytic condenser, where the Pt surface was separated from a p-type silicon layer by a hafnia dielectric film. By forcing the Pt and Si layers into isopotential conditions, charge transfer between the adsorbate and Pt surface was titrated through an external circuit. Hydrogen atoms donated electrons to Pt upon adsorption, which was quantitatively reversed upon desorption. Across a temperature range of 125–200 °C (surface hydrogen fractional coverages of 80–100%), the charge transferred to Pt by an adsorbed hydrogen atom was measured to be 0.19 ± 0.01% |e|/H. Bader charge analysis of the extent of charge transfer was in agreement with experimental measurements, with a calculated net donation of 0.4% |e|/H. The ability to experimentally quantify surface charge transfer provides an electronic-based approach to characterize catalytic surfaces, the adsorbed moieties residing on them, and the chemical reactions they accelerate.
Adsorption↗
A New Approach to Predict Hydrogeological Parameters Using Shear Waves from the Multichannel Analysis of Surface Waves Method
For near-surface contaminant characterization, the accurate prediction of hydrogeological parameters in anisotropic and heterogeneous environments has been a challenge since the last decades. However, recent advances in near-surface geophysics have facilitated the use of geophysical data for hydrogeological characterization in the last few years. A pseudo 3-D high resolution P-wave shallow seismic reflection survey was performed at the P Reactor Area, Savannah River Site, South Carolina in order to delineate and predict migration pathways of a large contaminant plume including trichloroethylene. This contaminant plume originates from the northwest section of the reactor facility that is located within the Upper Atlantic Coastal Plain. The data were collected with 40 Hz geophones, an accelerated weight-drop as seismic source and 1 m receiver spacing with near- and far-offsets of 0.5 and 119.5 m, respectively. In such areas with near-surface contaminants, a detailed subsurface characterization of the vadose zone hydraulic parameters is very important. Indeed, an inexpensive method of deriving such parameters by the use of seismic reflection surveys is beneficial, and our approach uses the relationship between seismic velocity and hydrogeological parameters together with empirical observations relating porosity to permeability and hydraulic conductivity. Shear wave velocity ( V s ) profiles were estimated from surface wave dispersion analysis of the seismic reflection data and were subsequently used to derive hydraulic parameters such as porosity, permeability, and hydraulic conductivity. Additional geophysical data including core samples, vertical seismic profiling, surface electrical resistivity tomography, natural gamma and electrical resistivity logs allowed for a robust assessment of the validity and geological significance of the estimated V s and hydrogeological models. The results demonstrate the usefulness of this approach for the upper 15 m of shallow unconsolidated sediments even though the survey design parameters were not optimal for surface wave analysis due to the higher than desired frequency geophones.
Engineering↗
Evaluation of Flaw Detection with SLDV Methods Before/After Mechanical Patch
This report provides a summary of the testing and the experiments to evaluate the utility of laser ultrasonic testing (UT) in detecting and characterizing defects on the surface of steel plates before and after the application of an engineered composite patch for crack repair. Included are the detection and characterization of defects from a section of welded plate material taken from the Sandia National Laboratories’ full-size mockup of a spent nuclear fuel (SNF) dry storage canister which had been pre-flawed and exposed to deliquescent sea salt conditions for 2 years. The information includes a review of previously reported metallurgical characterization, and new work on detailed surface characterization of the corrosion attack using laser UT.
36 MATERIALS SCIENCE↗
Three-dimensional nucleation and growth of deformation twins in magnesium
At two-thirds the weight of aluminum, magnesium alloys have the potential to reduce the fuel consumption of transportation vehicles. These advancements depend on our ability to optimize the desirable versus undesirable effects of deformation twins, which are three-dimensional (3D) microstructural domains that form under mechanical stresses. Previously only characterized through surface or thin-film measurements, we here present 3D in situ characterization of deformation twinning inside an embedded grain over mesoscopic fields of view using dark-field x-ray microscopy supported by crystal plasticity finite element analysis. The results revealed the role of triple junctions on twin nucleation and the sequence and irregularity of twin growth and showed that twin-grain junctions, twin-twin junctions, and twin boundaries were the sites of localized dislocation accumulation.
Lee, Sangwon [Univ. of Michigan, Ann Arbor, MI (Un↗
Degradation mechanism of lead-vanado-iodoapatite in NaCl solution
Degradation mechanism of lead-vanado-iodoapatite (IAPT) in NaCl solution at 90 °C was investigated through systematic characterization of surface morphology, microstructure and microchemistry evolution of the alteration layer. Nano-scale characterization indicated that IAPT crystals degraded from grain boundaries toward inner grains, forming ultrafine Cl-bearing crystallites. A coupled interface dissolution-reprecipitation replacement mechanism and the ion exchange between Cl - and I - across the degradation zone may together play roles in determining the nano-scale degradation behavior of IAPT. This work highlights the degradation through multiple reactions and elemental transport across the liquid-solid and solid-solid interfaces at length scales from sub-millimeter to nanoscale.
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
Surface stress tensor and junction conditions on a rotating null horizon
The general form of the surface stress tensor of an infinitesimally thin shell located on a rotating null horizon is derived, when different interior and exterior geometries are joined there. Even though the induced metric on the surface must be the same approached from either side, the first derivatives of the metric need not be. Such discontinuities lead to a Dirac δ-distribution in the Einstein tensor localized on the horizon. For a general stationary axisymmetric geometry the surface stress tensor can be expressed in terms of two geometric invariants that characterize the surface, namely the discontinuities [κ] and [J] of the surface gravity κ and angular momentum density J. The Komar energy and angular momentum are given in coordinates adapted to the Killing symmetries, and the surface contributions to each determined in terms of [κ] and [J] . Guided by these, a simple modification of the original Israel junction conditions is verified directly from the Einstein tensor density to give the correct finite result for the surface stress, when the normal n to the surface is allowed to tend continuously to a null vector. The relation to Israel’s original junction conditions, which fail on null surfaces, is given. The modified junction conditions are suitable to the matching of a rotating “black hole” exterior to any interior geometry joined at the Kerr null horizon surface, even when the surface normal is itself discontinuous and the Barrabès-Israel formalism is also inapplicable. This joining on a rotating null horizon is purely of the matter shell type and does not contain a propagating gravitational shock wave.
79 ASTRONOMY AND ASTROPHYSICS↗
Tuning Surface Adhesion Using Grayscale Electron-beam Lithography
Surface texturing of manufactured products tailors their properties, such as friction, adhesion, biocompatibility, or fluid interactions. However, advancements in this area are largely the result of trial-and-effort testing and generally lack a science-guided framework for determining the surface topography that will optimize performance. The present investigation explores grayscale electron-beam lithography as a means to create multiscale surface patterns to control surface performance. Here, we created and characterized a set of surface textures on a silicon wafer; the textures were superpositions of sine waves of varying wavelengths and amplitudes. First, the multiscale topography of the patterned surface was characterized, using profilometry and atomic force microscopy, to understand its fidelity to the designed-in pattern. The results of this analysis demonstrated how grayscale lithography accurately controlled the lateral size of features but was less precise on the vertical height of the surface, and also introduced inherent roughness below the scale of patterning. Second, a micromechanical tester was used to characterize the adhesion of the surfaces with large-scale polished silicon spheres. The results showed that adhesion could be tailored, with significant contribution from all of the designed-in length scales of topography. The strength of adhesion did not correlate with conventional roughness parameters but could be accurately modeled using simple numerical integration. Taken together, this investigation demonstrates the promise and challenges of grayscale e-beam lithography with multiscale patterns as a method for the tailoring of surface performance.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Surface Chemistry of Liquid Bismuth under Oxygen and Water Vapor Studied by Ambient Pressure X-ray Photoelectron Spectroscopy
Bismuth (Bi) has a fairly low melting point of 544 K making it practical as a liquid metal medium in a number of applications. Under ambient atmospheric conditions the surface of solid Bi oxidizes. While the solid Bi interface has been fairly well characterized with surface science studies upon exposure to oxygen, to date little is known about the molecular level reactivity of the liquid interface. Here, using ambient pressure X-ray photoelectron spectroscopy the liquid-gas interfacial chemistry of Bi was examined upon exposure to oxygen gas and water vapor at 550 K up to a maximum pressure of 0.5 Torr. Water vapor remained unreactive towards the liquid interface over the entire pressure range. Oxygen remined unreactive up to 10 –4 Torr, whereas above this pressure oxidation was observed forming Bi 2 O 3 . The oxidation exposure onset was > 5 x 10 5 Langmuirs, significantly higher than what is required for solid Bi interfaces.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Surface oxidation and crystallization of FeNi-Based soft magnetic nanocrystalline and amorphous nanocomposite alloys
In this work, we present characterization of surface oxidation and crystallization behavior of Metal Amorphous Nanocomposite (MANC) (Fe 70 Ni 30 ) 80 Nb 4 Si 2 B 14 alloys via complementary x-ray diffraction, electron microscopy, and x-ray photoelectron spectroscopy techniques. An adherent amorphous oxide of roughly 15–20 nm in thickness is observed on the wheel side of the ribbon, enriched in Fe relative to Ni and with significant content of Si and Nb as would be expected based upon a comparison of the Gibbs free energy of formation of the stable oxide phases. The amorphous character of the oxide is likely to result from the significant Si-content coupled with the amorphous and nanocrystalline character of the underlying metallic layer. Higher density of FeNi-enriched nanocrystals is also observed within ~100 nm of the wheel-side surface, presumably due to reduction in local glass former concentration. A rough, crystalline copper oxide layer is also present and forms through contact between the copper wheel and the solidifying melt during the rapid solidification process. On the air side of the ribbon, a crystalline oxide layer of ~15–20 nm is formed as well as intergranular oxidation that penetrates along the grain boundaries between highly textured surface crystallites of ~50–100 nm in size. The crystalline nature of the oxide on these surfaces is asserted to result from the lack of significant Si-content and the pre-existing surface crystallites that form during the rapid solidification process which promote a crystalline oxide surface layer. Furthermore, these results shed new insights into the details of surface oxidation and can help to inform processing and alloy composition adjustments which seek to tailor surface properties.
36 MATERIALS SCIENCE↗
New experimental approach to understanding the chemical reactivity of oxide surfaces
Metal oxides have been an attractive option for a range of applications, including hydrogen sensors, microelectronics, and catalysis, due to their reactivity and tunability. The properties of metal oxides can vary greatly on their precise surface structure; however, few surface science techniques can achieve atomistic-level determinations of surface structure, and fewer yet can do so for insulator surfaces. Low energy ion beam analysis offers a potential insulator-compatible solution to characterizing the surface structure of metal oxides. As a feasibility study, we apply low energy ion beam analysis to investigate the surface structure of a magnetite single crystal, Fe 3 O 4 (100). We obtain multi-angle maps using both forward-scattering low energy ion scattering (LEIS) and backscattering impact-collision ion scattering spectroscopy (ICISS). Both sets of experimental maps have intensity patterns that reflect the symmetries of the Fe 3 O 4 (100) surface structure. However, analytical interpretation of these intensity patterns to extract details of the surface structure is significantly more complex than previous LEIS and ICISS structural studies of one-component metal crystals, which had far more symmetries to exploit. To gain further insight into the surface structure, we model our experimental measurements with ion-trajectory tracing simulations using molecular dynamics. Our simulations provide a qualitative indication that our experimental measurements agree better with a subsurface cation vacancy model than a distorted bulk model.
36 MATERIALS SCIENCE↗
Chemical and Radiological Compatibility Testing of 3D Printed Materials
To dramatically increase the adaptability, performance, and safety of processes in support of the Defense Waste Processing Facility (DWPF), Savannah River National Lab (SRNL) plans to perform chemical and radiological compatibility testing on a wide variety of 3D printed materials of interest. The 3D printing process provides numerous strategic operational benefits such as rapid prototyping of complex designs and geometry specific to the needs of the nuclear waste disposition process, as well as on-demand rapid prototyping and iteration with materials that aren’t as accessible through traditional manufacturing methods. Reaction chemistry in simulated waste batches can be matched closely to its radioactive counterpart, but glass reactor vessels have limitations. Vessel geometry can play a big factor in mixing transport limitations, process chemistry, and degradation reaction kinetics. In addition, additive manufacturing allows for much more detailed vessel design than traditional alternatives. Waste processing techniques in DWPF also encounter extreme chemical environments including high pH, strong acids, abrasive slurries, and significant irradiation. To meet these challenges, a matrix of various polymer, ceramic, and metal additive manufacturing materials have been exposed to a suite of chemical environments of interest as well as radioactive dose (such as gamma radiation from 60 Co) to properly test their durability under these conditions. Mass change has been monitored over a period of up to a week in these conditions, as well as added characterization for surface modification through Scanning Electron Microscopy/Electron Dispersive X-ray analysis (SEM/EDX). Further chemical characterization has been monitored through Fourier-Transform InfraRed Spectroscopy (FTIR), with planned investigation via thermal and tensile strength degradation. While the direct product of this research is identification of material(s) that can withstand specific hazardous environments encountered by the mercury water wash tank in DWPF process simulation experiments, the reference base of materials will be used for many other nuclear processes in the pursuit of rapidly developed, cost-efficient, and highly specific devices for environmental remediation and much more.
Wilson, Nathan W. [Savannah River National Laborat↗
Advanced nanoscale characterization of aluminum nanoparticles with modified surface morphology via atmospheric helium and carbon monoxide plasmas
Aluminum nanoparticles (nAl) have the potential as energetic additives in explosive/propellant formulations. Scalable methodologies must be pursued to mitigate the inactive amorphous alumina shell surrounding the active aluminum (Al) core with modified surface morphology and chemistry for increased combustion effects. This work explores the feasibility of making reactive core/shell nAl with thinned oxide shells and modified surface coatings via a two-step atmospheric plasma surface treatment process in a custom dielectric barrier discharge plasma reactor. The commercial nAl of nominal average size similar to 40-60nm was first treated with helium (He) followed by He/carbon monoxide (CO) plasmas for different durations. The resultant samples were characterized via high-resolution transmission electron microscopy (HRTEM) and Fourier transform IR (FTIR) spectra. HRTEM images revealed sporadic patchy gamma -alumina deposits on particle surfaces and in gaps among particles for all samples, suggesting the non-uniform plasma effects of the He/CO glow. Nanoscale chemical analyses via scanning transmission electron microscopy elemental mapping and x-ray energy dispersive spectroscopy were further performed. Although no carbon-associated structure appeared in electron energy loss spectroscopy (EELS) spectra, the presence of carbonaceous materials was confirmed as a thin dispersive layer evenly distributed on the nAl surface suggesting either its amorphous nature or is present at a level insufficient to generate satisfactory EELS spectra. The trend of intensity profiles for key elements acquired by drawing lines across a single particle on the elemental maps confirmed that carbonaceous materials only existed on the surface and they were most likely carboxylates that increased with increased He/CO treatment duration, as evident by FTIR results. Finally, this work demonstrated the success of atmospheric plasma-treated reactive nAl with comprehensively characterized surface features via advanced microscopy and spectroscopy.
36 MATERIALS SCIENCE↗
Build orientation, surface roughness, and scan path influence on the microstructure, mechanical properties, and flexural fatigue behavior of Ti–6Al–4V fabricated by electron beam melting
In the present work, microstructure and fatigue behavior of Electron Beam Melted (EBM) Ti–6Al–4V have been systematically studied. Fatigue behavior was investigated using four-point bend tests of rectangular bars with internal features fabricated with different build orientations, scan paths, and surface conditions. Microstructural variations were evaluated by optical microscopy and Vickers micro-hardness indentations, both of which were found to be consistent throughout the build and within ranges reported in the literature. The fatigue performance of the EBM material was comparable to wrought Ti–6Al–4V when the loading direction was parallel to the build direction, but severely limited when loaded perpendicular to the build direction or if surface roughness defects were present. Scanning electron microscopy and interrupted fatigue tests were utilized to characterize fracture surfaces, failure mechanisms, crack initiation, and propagation behavior. Crack initiation sites in the vertically-oriented specimens were identified to be melt-related defects formed by insufficient melting.
36 MATERIALS SCIENCE↗
Viscosity of the Mercurian Magma Ocean: Implications of Sulfur-Free and Sulfur-Bearing Magma Oceans for Differentiation and Crustal Petrogenesis
Mercury is believed to have had a magma ocean in its early evolution whose solidification dynamics contributed to the planet’s present day surface composition. The surface is characterized by two main geological provinces; the Northern Smooth Plains (NSP),and the Heavily Cratered Terrain (HCT) and Intercratered Terrian (IcT). These provinces are defined by the differences in morphology, composition, and age. The NSP are located in the northern hemisphere and have low Mg/Si, Ca/Si, and S/Si ratios and high Al/Si ratios, and are compositionally analogous to a magnesian alkali basalt. The HCT/IcT cover the majority of the planet and are older than the NSP, and are characterized by high Mg/Si, Ca/Si, and S/Si ratios and low Al/Si ratios. The dichotomy in surface composition motivates the study into the structure of the mantle as a product of magma ocean solidification. Two important and interrelated parameters that determine the efficiency of crystal fractionation during magma ocean solidification are convection vigor and viscosity of the magma ocean. Crystal suspension in a cooling magma ocean could be efficient or inefficient which suggests two end member possibilities for magma ocean solidification. The first is the formation of a compositionally stratified mantle reflecting a cumulate sequence produced along a fractional liquid line of descent. The second is the formation of a well-mixed, batch crystallized mantle by high viscosity and/or vigorously convecting magma ocean. Determining which of these end members, or where on the spectrum between them is most relevant to Mercury’s magma ocean can be experimentally constrained through high P-T falling-sphere viscometry experiments.
Mouser, M. D.↗
Quantitative Infrared-to-Terahertz Nanospectroscopy of Semiconductors
Semiconductor technology now employs few-nanometer features, necessitating tools probing electronic properties on the same length scale. While the concentration of free charge carriers is routinely measured, the scattering rate remains challenging to access at the nanoscale. Here, we present ultrabroadband (5–50 THz) synchrotron infrared nanospectroscopy as a quantitative metrology tool for semiconductors. This technique can determine both the charge carrier concentration and scattering rate with percent-level accuracy, and it is inherently capable of ∼10 nm spatial resolution. We study silicon with different doping levels and confirm the method’s accuracy by statistical analysis and comparison with established far-field infrared spectroscopy. Near-field measurements systematically reveal charge-carrier concentrations ∼30% lower than far-field values, consistent with increased surface sensitivity and surface depletion. Our work establishes synchrotron infrared nanospectroscopy as a precise tool for quantitative nanoscale semiconductor characterization and paves the way toward all-optical characterization of surface depletion effects.
36 MATERIALS SCIENCE↗
Impacts of the Additive Manufacturing Process on the Roughness of Engine Scale Vanes and Cooling Channels
Abstract By leveraging the additive manufacturing (AM) platform, development time and costs for turbine component testing can be reduced relative to traditional investment casting. Surface roughness is a key characteristic of the additive manufacturing process that can impact flow, heat transfer, and mechanical integrity of printed components. There are multiple design and build considerations that result in variability in surface roughness, especially when additively fabricating complicated three-dimensional vanes and internal cooling passages. This study characterizes the surface roughness of internal cooling passages, vanes, and flat external surface samples made using additive manufacturing, specifically the direct metal laser sintering process. The samples were manufactured with various wall thicknesses, layer thicknesses, build locations, build directions, and on different AM machines. A combination of computed tomography scanning and optical profilometry was used to evaluate surface roughness levels. The data indicate that the dominant factors in roughness for a given layer thickness are a function of wall thickness, build location, and build direction.
Engineering↗
Journal Pre-proof3D printed polylactic acid and acrylonitrile butadiene styrene fluidicstructures for biological applications: tailoring bio-material interfaceviasurface modification
Three-dimensional (3D) printing is a rapidly growing technology that best fits for cell culture and other biological applications due to its potential to build immensely complex structures from customized designs. However, use of 3D printed structures for cell adhesion, proliferation, and activation requires tailoring of surface characteristics. In this context, this work investigates the use of two biocompatible 3D printable polymer materials, Poly-L-lactic Acid (PLA) and Acrylonitrile Butadiene Styrene (ABS) for bio applications, and the effect of their post-printing surface modification processes to achieve desired bio functionality. Three post-printing surface modification techniques, alkaline hydrolysis, ultraviolet ozone plasma irradiation and gold thin film deposition are performed with the objective of introducing useful levels of surface functionalities. Poly-L-lysine (PLL) labelled with FITC chromophore is immobilized on the surface modified samples following standard protocols. The effect of surface roughness and porosity of the 3D printed structures on the polypeptide immobilization is compared on as-printed versus mechanically polished surfaces. Different characterization methods, viz., Fluorescence microscopy, Raman Spectroscopy and UV–vis spectroscopy, are used to study the efficacy of the surface modification and PLL immobilization techniques. Our results demonstrated denser PLL attachment on polished hydrolyzed PLA and ABS surfaces which enables the use of these printable polymers for a range of applications such as tissue scaffolds and microfluidics.
3D Printing, PLA, ABS, Biodegradable Polymer, Surf↗