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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on AgAu by Materials Project

AuAg crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Au1- is bonded to six equivalent Au1- and six equivalent Ag1+ atoms to form distorted AuAg6Au6 cuboctahedra that share corners with eighteen equivalent AuAg6Au6 cuboctahedra, edges with six equivalent AuAg6Au6 cuboctahedra, edges with twelve equivalent AgAg6Au6 cuboctahedra, faces with eight equivalent AuAg6Au6 cuboctahedra, and faces with twelve equivalent AgAg6Au6 cuboctahedra. All Au–Au bond lengths are 2.94 Å. All Au–Ag bond lengths are 2.95 Å. Ag1+ is bonded to six equivalent Au1- and six equivalent Ag1+ atoms to form distorted AgAg6Au6 cuboctahedra that share corners with eighteen equivalent AgAg6Au6 cuboctahedra, edges with six equivalent AgAg6Au6 cuboctahedra, edges with twelve equivalent AuAg6Au6 cuboctahedra, faces with eight equivalent AgAg6Au6 cuboctahedra, and faces with twelve equivalent AuAg6Au6 cuboctahedra. All Ag–Ag bond lengths are 2.94 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgAu(IO3)4 by Materials Project

AuAg(O3I)4 crystallizes in the monoclinic Pc space group. The structure is three-dimensional. Au3+ is bonded in a square co-planar geometry to four O2- atoms. There are one shorter (2.02 Å) and three longer (2.03 Å) Au–O bond lengths. Ag1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ag–O bond distances ranging from 2.41–2.87 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to one Au3+, one Ag1+, and one I5+ atom. The O–I bond length is 1.93 Å. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Au3+, one Ag1+, and one I5+ atom. The O–I bond length is 1.92 Å. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to one Au3+ and one I5+ atom. The O–I bond length is 1.93 Å. In the fourth O2- site, O2- is bonded in a bent 120 degrees geometry to one Au3+ and one I5+ atom. The O–I bond length is 1.93 Å. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one Ag1+ and one I5+ atom. The O–I bond length is 1.89 Å. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to one Ag1+ and one I5+ atom. The O–I bond length is 1.86 Å. In the seventh O2- site, O2- is bonded in a 1-coordinate geometry to one Ag1+ and two I5+ atoms. There are one shorter (1.84 Å) and one longer (2.61 Å) O–I bond lengths. In the eighth O2- site, O2- is bonded in a distorted single-bond geometry to two I5+ atoms. There are one shorter (1.82 Å) and one longer (2.56 Å) O–I bond lengths. In the ninth O2- site, O2- is bonded in a distorted single-bond geometry to two I5+ atoms. There are one shorter (1.83 Å) and one longer (2.55 Å) O–I bond lengths. In the tenth O2- site, O2- is bonded in a distorted single-bond geometry to two I5+ atoms. There are one shorter (1.84 Å) and one longer (2.51 Å) O–I bond lengths. In the eleventh O2- site, O2- is bonded in a single-bond geometry to one I5+ atom. The O–I bond length is 1.80 Å. In the twelfth O2- site, O2- is bonded in a 2-coordinate geometry to one Ag1+ and one I5+ atom. The O–I bond length is 1.81 Å. There are four inequivalent I5+ sites. In the first I5+ site, I5+ is bonded in a 5-coordinate geometry to five O2- atoms. In the second I5+ site, I5+ is bonded in a 5-coordinate geometry to five O2- atoms. In the third I5+ site, I5+ is bonded in a 3-coordinate geometry to three O2- atoms. In the fourth I5+ site, I5+ is bonded in a 3-coordinate geometry to three O2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgAu by Materials Project

AuAg crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Au1- sites. In the first Au1- site, Au1- is bonded to six equivalent Au1- and six Ag1+ atoms to form distorted AuAg6Au6 cuboctahedra that share corners with twelve AuAg6Au6 cuboctahedra, edges with twelve AuAg6Au6 cuboctahedra, edges with twelve AgAg6Au6 cuboctahedra, faces with six equivalent AuAg6Au6 cuboctahedra, and faces with twelve AgAg6Au6 cuboctahedra. All Au–Au bond lengths are 2.95 Å. All Au–Ag bond lengths are 2.94 Å. In the second Au1- site, Au1- is bonded to ten equivalent Au1- and six Ag1+ atoms to form distorted AuAg6Au10 cuboctahedra that share corners with ten AgAg6Au6 cuboctahedra, corners with twelve AuAg6Au6 cuboctahedra, edges with eight AgAg6Au6 cuboctahedra, edges with sixteen AuAg6Au6 cuboctahedra, faces with sixteen equivalent AuAg6Au10 cuboctahedra, and faces with eighteen AgAg6Au6 cuboctahedra. There are a spread of Au–Au bond distances ranging from 2.95–5.89 Å. All Au–Ag bond lengths are 2.94 Å. There are three inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded to six equivalent Au1- and six equivalent Ag1+ atoms to form distorted AgAg6Au6 cuboctahedra that share corners with twelve AgAg6Au6 cuboctahedra, edges with twelve equivalent AuAg6Au6 cuboctahedra, edges with twelve AgAg6Au6 cuboctahedra, faces with six equivalent AgAg6Au6 cuboctahedra, and faces with twelve equivalent AuAg6Au6 cuboctahedra. All Ag–Ag bond lengths are 2.95 Å. In the second Ag1+ site, Ag1+ is bonded to six Au1- and six equivalent Ag1+ atoms to form distorted AgAg6Au6 cuboctahedra that share corners with five equivalent AuAg6Au10 cuboctahedra, corners with twelve AgAg6Au6 cuboctahedra, edges with ten AuAg6Au6 cuboctahedra, edges with twelve AgAg6Au6 cuboctahedra, faces with six equivalent AgAg6Au6 cuboctahedra, and faces with fifteen AuAg6Au6 cuboctahedra. All Ag–Au bond lengths are 2.94 Å. All Ag–Ag bond lengths are 2.95 Å. In the third Ag1+ site, Ag1+ is bonded to six Au1- and six equivalent Ag1+ atoms to form distorted AgAg6Au6 cuboctahedra that share corners with five equivalent AuAg6Au10 cuboctahedra, corners with twelve AgAg6Au6 cuboctahedra, edges with ten AuAg6Au6 cuboctahedra, edges with twelve AgAg6Au6 cuboctahedra, faces with six equivalent AgAg6Au6 cuboctahedra, and faces with fifteen AuAg6Au6 cuboctahedra. All Ag–Ag bond lengths are 2.95 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mapping the effects of physical and chemical reduction parameters on local atomic distributions within bimetallic nanoparticles

Bimetallic nanoparticles prove advantageous over their monometallic counterparts due to the tunable, hybrid properties that result from combining different atomic species in a controlled way. The favorable optical and catalytic properties resulting from AgAu nanoparticle formation have been widely attributed to the existence of Ag–Au bonds, the maximization of which assumes the formation of a homogeneous alloy. Despite the importance of atomic scale structure in these systems, synthetic studies are typically not paired with structural characterization at the atomic scale. Herein, a comprehensive synthetic exploration of physical and chemical reduction parameters of resulting nanoparticle products is complemented with thorough X-ray characterization to probe how these parameters affect atomic scale alloy distributions within AgAu nanoparticles. Presented evidence shows Ag is substantially underincorporated into nanoparticle constructs compared with solution Ag : Au ratios regardless of precursor :reductant ratio or volume of reductant added. Both Ag and Au exhibit significant local clustering, with Ag distributed preferentially towards the nanoparticle surface. Most significantly, the results of this investigation suggest that reduction parameters alone can affect the local alloy distributions and homogeneity within bimetallic nanoparticles, even when the ratio of metallic precursors remains constant. Overall, this investigation presents the ability to control alloy distributions using kinetics and provides new considerations for optimizing synthetic methods to produce functional bimetallic nanoparticles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Effect of Gold Catalyst Surface Morphology on Wetting Behavior and Electrochemical CO 2 Reduction Performance in a Large-Area Zero-Gap Gas Diffusion Electrolyzer

We report catalyst surface area and wetting behavior are key factors in determining the performance of gas diffusion electrode (GDE) electrolyzers for electrochemical CO 2 reduction. In this work, we report the integration of sub-1 μm thick nanoporous gold (npAu) catalyst coatings into a large-area (25 cm 2 ) zero-gap electrolyzer. The npAu coatings were prepared by magnetron sputtering (MS) of thin AgAu alloy films on the microporous carbon layer of a gas diffusion layer (GDL) followed by Ag leaching. Compared to MS Au films of the same thickness, npAu catalyst coatings enable higher Faradaic efficiencies and improved catalyst stability for CO 2 -to-CO reduction with Faradaic efficiencies of up to 88% at 100 mA/cm 2 . For a 800 nm npAu coating, the device level energy efficiency for CO 2 to CO conversion reaches 45% (52% for CO + H 2 ) at 100 mA/cm 2 with a single pass CO 2 conversion efficiency of ~12%. Contact angle measurements reveal that npAu coatings provide a more hydrophobic electrode interface compared to MS Au coatings, suggesting that the more hydrophobic interfacial environment of npAu coatings helps mitigating electrode flooding which is associated with performance deterioration over time.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2025

Efficient Modeling of Structural, Electronic, and Optical Properties of Silver and Gold Metal Nanoclusters and Alloys Using Optimized SCC-DFTB Parameters

Computation of optical properties using conventional time-dependent density functional theory (TD-DFT) is time-consuming and memory-intensive. In this study, we investigate the accuracy and efficiency of the density functional tight binding (DFTB) framework with newly optimized Slater–Koster (SK) parameters for modeling the structural, electronic properties, and absorption spectra of silver and gold nanoclusters and their alloys. Our investigation of the ground state (GS) properties demonstrates that the newly developed GS-SK parameters enable DFTB to closely approximate DFT-calculated bond lengths for octahedron, tetrahedron, icosahedra, and truncated octahedron with sizes Ag n /Au n (n = 19, 20, 38, 55), nanoclusters and Ag 20 /Au 20 nanoalloys, with a maximum deviation of approximately 0.15 Å. Formation energy results indicate that the GS-SK parameters can closely estimate changes in formation energies with alloy composition, and the comparison of electronic structures for Ag 20 , Au 20 , and AgAu alloy nanoclusters using the DFTB approximation reveals good agreement in the projected density of states (DOS) profiles and energy levels. A second set of SK parameters, ES-SK, has been developed to describe excited state (ES) properties, including the absorption spectra of silver octahedron Ag 19 , tetrahedral Ag n (n = 20, 56, 84), truncated octahedron Ag 38 , and icosahedra Ag 55 closed-shell clusters and their gold and alloy counterparts over a broad range of alloy compositions. This parametrization uses TD-DFTB calculations and fine-tunes the d and p eigenvalues by comparing them to reference absorption spectra from first-principles TD-DFT. This enables the generation of absorption spectra that closely match the reference spectra when plasmon excitation is dominant, as demonstrated by studying the plasmonic properties of icosahedral Ag n and Au n (n = 309 and 561) nanoparticles. This includes the rapid loss in plasmon quality when Au partially replaces Ag in alloy clusters. Furthermore, these results provide a foundation for addressing computational bottlenecks in plasmonics and with new prospects for applications in the quantum plasmonics for bimetallic alloys.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2004

A Comparison of Experimental EPMA Data and Monte Carlo Simulations

Monte Carlo (MC) modeling shows excellent prospects for simulating electron scattering and x-ray emission from complex geometries, and can be compared to experimental measurements using electron-probe microanalysis (EPMA) and phi(rho z) correction algorithms. Experimental EPMA measurements made on NIST SRM 481 (AgAu) and 482 (CuAu) alloys, at a range of accelerating potential and instrument take-off angles, represent a formal microanalysis data set that has been used to develop phi(rho z) correction algorithms. The accuracy of MC calculations obtained using the NIST, WinCasino, WinXray, and Penelope MC packages will be evaluated relative to these experimental data. There is additional information contained in the extended abstract.

Carpenter, P. K.↗
NASA NTRS2005

Calculated X-ray Intensities Using Monte Carlo Algorithms: A Comparison to Experimental EPMA Data

Monte Carlo (MC) modeling has been used extensively to simulate electron scattering and x-ray emission from complex geometries. Here are presented comparisons between MC results and experimental electron-probe microanalysis (EPMA) measurements as well as phi(rhoz) correction algorithms. Experimental EPMA measurements made on NIST SRM 481 (AgAu) and 482 (CuAu) alloys, at a range of accelerating potential and instrument take-off angles, represent a formal microanalysis data set that has been widely used to develop phi(rhoz) correction algorithms. X-ray intensity data produced by MC simulations represents an independent test of both experimental and phi(rhoz) correction algorithms. The alpha-factor method has previously been used to evaluate systematic errors in the analysis of semiconductor and silicate minerals, and is used here to compare the accuracy of experimental and MC-calculated x-ray data. X-ray intensities calculated by MC are used to generate a-factors using the certificated compositions in the CuAu binary relative to pure Cu and Au standards. MC simulations are obtained using the NIST, WinCasino, and WinXray algorithms; derived x-ray intensities have a built-in atomic number correction, and are further corrected for absorption and characteristic fluorescence using the PAP phi(rhoz) correction algorithm. The Penelope code additionally simulates both characteristic and continuum x-ray fluorescence and thus requires no further correction for use in calculating alpha-factors.

Carpenter, P. K.↗