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12 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

CO and H 2 adsorption on Au-Ni bimetallic surfaces: a combined experimental and DFT theoretical study

Au-Ni bimetallic thin films were grown on refractory metal substrates. CO and H 2 adsorption on Au-Ni bimetallic surfaces have been studied by a combination of in situ polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), temperature-programmed desorption (TPD), and density functional theory (DFT) calculations. It is found CO desorption peak shifts from 413 K on pure Ni surfaces to 293 K on the isolated Ni atoms formed by alloying with Au atoms. The sharp decrease of CO desorption temperature on Au-Ni surfaces with increasing Au coverage is caused by the change of the favored CO adsorption sites from bridge/hollow sites on pure Ni surfaces to Ni top sites on Au-Ni bimetallic surfaces. In situ PM-IRRAS shows two CO adsorption bands on Au sites at 2119 cm −1 and 2103 cm −1 on Au-Ni surfaces at 80 K, which are due to CO bound on under-coordinated Au atoms and electron negatively charged Au sites modified with nearby Ni atoms, respectively. Even with the Au-Ni surface temperature at as low as 100 K, CO adsorption induced Ni surface segregation has been observed by in situ PM-IRRAS. Furthermore, DFT calculation results discover the adsorption energy of CO on Ni top sites continues to decrease with increasing Au coverage due to the geometric ensemble effect and the lowered d-band center after Ni alloying with Au. H 2 desorption temperature decreases from 363 K on pure Ni thin films to 302 K with increasing Au coverage to 0.6 ML. A new H 2 peak appears at around 170 K on the Au-Ni surfaces with Au coverages between 0.6 ML and 0.9 ML. This new H 2 TPD peak is assigned to H 2 desorption from the totally isolated Ni sites. With Au coverage above 1.5 ML, there is no any H 2 desorption detected. Finally, the combined surface science studies and DFT calculations provide new insights into the surface structure-activity correlation of Ni-base bimetallic surface alloys.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1992

The achievement of low contact resistance to indium phosphide: The roles of Ni, Au, Ge, and combinations thereof

We have investigated the electrical and metallurgical behavior of Ni, Au-Ni, and Au-Ge-Ni contacts on n-InP. We have found that very low values of contact resistivity rho(sub c) in the E-7 omega-sq cm range are obtained with Ni-only contacts. We show that the addition of Au to Ni contact metallization effects an additional order of magnitude reduction in rho(sub c). Ultra-low contact resistivities in the E-8 omega-sq cm range are obtained with both the Au-Ni and the Au-Ge-Ni systems, effectively eliminating the need for the presence of Ge in the Au-Ge-Ni system. The formation of various nickel phosphides at the metal-InP interface is shown to be responsible for the observed rho(sub c) values in the Ni and Au-Ni systems. We show, finally, that the order in which the constituents of Au-Ni and Au-Ge-Ni contacts are deposited has a significant bearing on the composition of the reaction products formed at the metal-InP interface and therefore on the contact resistivity at that interface.

Fatemi, Navid S.↗
DOE OSTI2022

Effect of applied potential on metal surfaces: Surface energy, Wulff shape and charge distribution

Here we use grand canonical density functional theory to predict the surface energies, Wulff shapes, charge distributions and catalytically active sites of different metal surfaces under electrochemical conditions. We propose a method for computing surface energies from grand canonical density functional theory (GC-DFT) calculations of periodic slab models and use it to compute the surface energies of the facets of Pt, Cu, and Ag crystals to predict their Wulff shapes under electrochemical conditions. GC-DFT predicts that, for the pure metals studied, solvation only slightly affects the Wulff shape while applied potentials considerably affect the surface energies and corresponding Wulff shapes. We used Bader charge analysis of GC-DFT computed electron densities to investigate the effect of applied potential on the distribution of electron density over the atoms of the surfaces of Pt, Cu, Ag, and the 75–25 Ag-Pt and Au-Ni alloys. This analysis shows that, under an applied potential, the electron density is unevenly distributed over the surface atoms and that the charges of atoms more exposed to solvent are more sensitive to bias. Our results show that the most sensitive atom to bias can be used to identify the most favorable adsorption site and thus, the active sites of electrochemical reactions, which is computationally less demanding than calculating the adsorption energies on all possible adsorption sites.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Self-Assembled TiN-Metal Nanocomposites Integrated on Flexible Mica Substrates towards Flexible Devices

The integration of nanocomposite thin films with combined multifunctionalities on flexible substrates is desired for flexible device design and applications. For example, combined plasmonic and magnetic properties could lead to unique optical switchable magnetic devices and sensors. In this work, a multiphase TiN-Au-Ni nanocomposite system with core–shell-like Au-Ni nanopillars embedded in a TiN matrix has been demonstrated on flexible mica substrates. The three-phase nanocomposite film has been compared with its single metal nanocomposite counterparts, i.e., TiN-Au and TiN-Ni. Magnetic measurement results suggest that both TiN-Au-Ni/mica and TiN-Ni/mica present room-temperature ferromagnetic property. Tunable plasmonic property has been achieved by varying the metallic component of the nanocomposite films. The cyclic bending test was performed to verify the property reliability of the flexible nanocomposite thin films upon bending. This work opens a new path for integrating complex nitride-based nanocomposite designs on mica towards multifunctional flexible nanodevice applications.

42 ENGINEERING↗
NASA NTRS1975

Oxygen reduction of several gold alloys in 1-molar potassium hydroxide

With rotated disk-and-ring equipment, polarograms and other electrochemical measurements were made of oxygen reduction in 1-molar potassium hydroxide on an equiatomic gold-copper (Au-Cu) alloy and a Au-Cu alloy doped with either indium (In) or cobalt (Co) and on Au doped with either nickel (Ni) or platinum (Pt). The results were compared with those for pure Au and pure Pt. The two-electron reaction dominated on all Au alloys as it did on Au. The polarographic results at lower polarization potentials were compared, assuming exclusively a two-step reduction. A qualified ranking of cathodic electrocatalytic activity on the freshly polished reduced disks was indicated: anodized Au Au-Cu-In Au-Cu Au-Cu-Co is equivalent or equal to Au-Pt Au-Ni. Aging in distilled water improved the electrocatalytic efficiency of Au-Cu-Co, Au-Cu, and (to a lesser extent) Au-Cu-In.

Miller, R. O.↗
NASA NTRS1986

A nonmagmatic origin of group-IIE iron meteorites

New neutron activation data on 10 elements in 12 IIE and IIE-related irons lead to a reclassification of several irons. Seymchan and Lonaconing are removed from IIE, and Leshan added. Four IIE members are designated IIE-An to call attention to some anomalous properties. The eight normal IIE members define element-Ni trends generally similar to those in the nonmagmatic group IAB; the small negative slopes on W-Ni and Ir-Ni diagrams are strongly indicative of a nonmagmatic origin of the IIE irons. It is proposed that IIE irons like IAB irons originated as individual pools of impact-produced melt in the near-surface region of a chondritic parent body. The positive As-Ni and Au-Ni trends are the only evidence suggesting fractional crystallization, but their slopes are lower than those in magmatic group IIIAB, and only slightly higher than those of Cu and Sb in IAB. It is suggested that the S and C contents of the IIE precursor materials were much lower than those of the IAB precursors, thus higher temperatures were required to generate enough metallic melt to segregate into pools. These higher temperatures are also reflected in the nonchondritic compositions of the silicate inclusions.

Wasson, J. T.↗
NASA NTRS2000

Surface Segregation in Ternary Alloys

Surface segregation profiles of binary (Cu-Ni, Au-Ni, Cu-Au) and ternary (Cu-Au-Ni) alloys are determined via Monte Carlo-Metropolis computer simulations using the BFS method for alloys for the calculation of the energetics. The behavior of Cu or Au in Ni is contrasted with their behavior when both are present. The interaction between Cu and Au and its effect on the segregation profiles for Cu-Au-Ni alloys is discussed.

Good, Brian↗
DOE OSTI2020

Materials Data on NiAu3 by Materials Project

Au3Ni is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ni3+ is bonded to twelve equivalent Au1- atoms to form NiAu12 cuboctahedra that share corners with twelve equivalent NiAu12 cuboctahedra, edges with twenty-four equivalent AuNi4Au8 cuboctahedra, faces with six equivalent NiAu12 cuboctahedra, and faces with twelve equivalent AuNi4Au8 cuboctahedra. All Ni–Au bond lengths are 2.85 Å. Au1- is bonded to four equivalent Ni3+ and eight equivalent Au1- atoms to form distorted AuNi4Au8 cuboctahedra that share corners with twelve equivalent AuNi4Au8 cuboctahedra, edges with eight equivalent NiAu12 cuboctahedra, edges with sixteen equivalent AuNi4Au8 cuboctahedra, faces with four equivalent NiAu12 cuboctahedra, and faces with fourteen equivalent AuNi4Au8 cuboctahedra. All Au–Au bond lengths are 2.85 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NiAu3 by Materials Project

Au3Ni is Uranium Silicide-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ni3+ is bonded to twelve equivalent Au1- atoms to form NiAu12 cuboctahedra that share corners with six equivalent NiAu12 cuboctahedra, corners with twelve equivalent AuNi4Au8 cuboctahedra, edges with eighteen equivalent AuNi4Au8 cuboctahedra, faces with eight equivalent NiAu12 cuboctahedra, and faces with twelve equivalent AuNi4Au8 cuboctahedra. All Ni–Au bond lengths are 2.84 Å. Au1- is bonded to four equivalent Ni3+ and eight equivalent Au1- atoms to form distorted AuNi4Au8 cuboctahedra that share corners with four equivalent NiAu12 cuboctahedra, corners with fourteen equivalent AuNi4Au8 cuboctahedra, edges with six equivalent NiAu12 cuboctahedra, edges with twelve equivalent AuNi4Au8 cuboctahedra, faces with four equivalent NiAu12 cuboctahedra, and faces with sixteen equivalent AuNi4Au8 cuboctahedra. There are a spread of Au–Au bond distances ranging from 2.78–2.89 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni3Au by Materials Project

Ni3Au is Uranium Silicide-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Ni sites. In the first Ni site, Ni is bonded to eight Ni and four equivalent Au atoms to form distorted NiNi8Au4 cuboctahedra that share corners with twelve equivalent NiNi8Au4 cuboctahedra, edges with eight equivalent AuNi12 cuboctahedra, edges with sixteen NiNi8Au4 cuboctahedra, faces with four equivalent AuNi12 cuboctahedra, and faces with fourteen NiNi8Au4 cuboctahedra. There are four shorter (2.60 Å) and four longer (2.62 Å) Ni–Ni bond lengths. All Ni–Au bond lengths are 2.62 Å. In the second Ni site, Ni is bonded to eight equivalent Ni and four equivalent Au atoms to form distorted NiNi8Au4 cuboctahedra that share corners with four equivalent NiNi8Au4 cuboctahedra, corners with eight equivalent AuNi12 cuboctahedra, edges with twenty-four NiNi8Au4 cuboctahedra, faces with six equivalent AuNi12 cuboctahedra, and faces with twelve NiNi8Au4 cuboctahedra. All Ni–Au bond lengths are 2.60 Å. Au is bonded to twelve Ni atoms to form AuNi12 cuboctahedra that share corners with four equivalent AuNi12 cuboctahedra, corners with eight equivalent NiNi8Au4 cuboctahedra, edges with eight equivalent AuNi12 cuboctahedra, edges with sixteen equivalent NiNi8Au4 cuboctahedra, faces with four equivalent AuNi12 cuboctahedra, and faces with fourteen NiNi8Au4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni3Au by Materials Project

Ni3Au is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are three inequivalent Ni sites. In the first Ni site, Ni is bonded to eight Ni and four equivalent Au atoms to form distorted NiNi8Au4 cuboctahedra that share corners with four equivalent AuNi12 cuboctahedra, corners with fourteen equivalent NiNi8Au4 cuboctahedra, edges with six equivalent AuNi12 cuboctahedra, edges with twelve NiNi8Au4 cuboctahedra, faces with four equivalent AuNi12 cuboctahedra, and faces with sixteen NiNi8Au4 cuboctahedra. There are a spread of Ni–Ni bond distances ranging from 2.49–2.74 Å. There are two shorter (2.62 Å) and two longer (2.65 Å) Ni–Au bond lengths. In the second Ni site, Ni is bonded to eight Ni and four equivalent Au atoms to form distorted NiNi8Au4 cuboctahedra that share corners with four equivalent AuNi12 cuboctahedra, corners with fourteen NiNi8Au4 cuboctahedra, edges with six equivalent AuNi12 cuboctahedra, edges with twelve NiNi8Au4 cuboctahedra, faces with four equivalent AuNi12 cuboctahedra, and faces with sixteen NiNi8Au4 cuboctahedra. There are a spread of Ni–Ni bond distances ranging from 2.49–2.74 Å. There are two shorter (2.62 Å) and two longer (2.65 Å) Ni–Au bond lengths. In the third Ni site, Ni is bonded to eight Ni and four equivalent Au atoms to form distorted NiNi8Au4 cuboctahedra that share corners with four equivalent AuNi12 cuboctahedra, corners with fourteen NiNi8Au4 cuboctahedra, edges with six equivalent AuNi12 cuboctahedra, edges with twelve NiNi8Au4 cuboctahedra, faces with four equivalent AuNi12 cuboctahedra, and faces with sixteen NiNi8Au4 cuboctahedra. There are two shorter (2.62 Å) and two longer (2.65 Å) Ni–Au bond lengths. Au is bonded to twelve Ni atoms to form AuNi12 cuboctahedra that share corners with six equivalent AuNi12 cuboctahedra, corners with twelve NiNi8Au4 cuboctahedra, edges with eighteen NiNi8Au4 cuboctahedra, faces with eight equivalent AuNi12 cuboctahedra, and faces with twelve NiNi8Au4 cuboctahedra.

36 MATERIALS SCIENCE↗