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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Adhesion between polymers and evaporated gold and nickel films

To obtain information on the adhesion between metal films and polymeric solids, the adhesion force was measured by means of a tensile pull test. It was found that the adhesion strengths between polymeric solids and gold films evaporated on polymer substrates were (1.11 + or - 0.53) multiplied by 10(6) N/M(2) on PTFE, about 5.49 multiplied by 10(6) N/m(2) on UHMWPE, and 6.54x10(6) on 6/6 nylon. The adhesion strengths for nickel films evaporated on PTFE, UHMWPE, and 6/6 nylon were found to be a factor of 1.7 higher than those for the gold coated PTFE, UHMWPE, and 6/6 nylon. To confirm quantitatively the effect of electron irradiation on the adhesion strength between a PTFE solid and metal films, a tensile pull test was performed on the irradiated PTFE specimens, which were prepared by evaporating nickel or gold on PTFE surfaces irradiated by 2-keV electrons for various times. After irradiation, the adhesion strength increased to (4.92 + or - 0.92)x10(6) N/m(2) for nickel coated PTFE and (1.82 + or - 0.48)x10(6) N/m(2) for gold coated PTFE. The improvement in adhesion for nickel is higher than that for gold.

Yamada, Y.↗
NASA NTRS1984

Gold absorbing film for a composite bolometer

The principles governing the design of metal films are reviewed, with attention also given to the choice of metals. A description is then given of the characteristics of a bolometer with a gold absorbing film. It is demonstrated that gold is effective as an absorbing film for a millimeter bolometer operated at 1.5 K. At 1.5 K, gold is significantly better than bismuth since gold has a lower heat capacity for the absorbing film. At 0.3 K, gold and bismuth are both suitable. It is pointed out that at temperatures below 0.3 K, a superconducting absorbing film can have a heat capacity low enough not to dominate the heat capacity of the detector; for this reason, it may give better performance than a nonsuperconducting absorbing film.

Dragovan, M.↗
NASA NTRS1988

The interaction of gold with gallium arsenide

Gold and gold-based alloys, commonly used as solar-cell contact materials, are known to react readily with gallium arsenide. Experiments designed to identify the mechanisms involved in these GaAs-metal interactions have yielded several interesting results. It is shown that the reaction of GaAs with gold takes place via a dissociative diffusion process. It is shown further that the GaAs-metal reaction rate is controlled to a very great extent by the condition of the free surface of the contact metal, an interesting example of which is the previously unexplained increase in the reaction rate that has been observed for samples annealed in a vacuum environment as compared to those annealed in a gaseous ambient. A number of other hard-to-explain observations, such as the low-temperature formation of voids in the gold lattice and crystallite growth on the gold surface, are also explained by invoking this mechanism.

Weizer, Victor G.↗
NASA NTRS1991

Crystal growth of YBa2Cu3O(7-x) and reaction of gold crucible with Ba-Cu-rich flux

YBa2Cu3O(7-x) crystals are grown in a gold crucible by a self-flux method. The flux moves along the gold surface due to surface wetting and leaves Y123 crystals behind. The obtained crystals are clean and have a size up to two millimeters and a Tc is greater than 90 K. In an effort to recycle the used crucibles, it is found that the used gold is contaminated by copper. A CuO thin film is easily formed on the surface of the crucible that is made of the used gold. This film provides good surface wetting and a buffer layer, which reduces the reaction between gold and the Y-Ba-Cu-oxide melt.

Tao, Y. K.↗
NASA NTRS1999

Transmission Measurement of the Third-Order Susceptibility of Gold

Gold nanoparticle composites are known to display large optical nonlinearities. In order to assess the validity of generalized effective medium theories (EMT's) for describing the linear and nonlinear optical properties of metal nanoparticle composites, knowledge of the linear and nonlinear susceptibilities of the constituent materials is a prerequisite. In this study the inherent nonlinearity of the metal is measured directly (rather than deduced from a suitable EMT) using a very thin gold film. Specifically, we have used the z-scan technique at a wavelength near the transmission window of bulk gold to measure the third-order susceptibility of a continuous thin gold film deposited on a quartz substrate surface-modified with a self-assembled monolayer to promote adhesion and uniformity without affecting the optical properties. We compare our results with predictions which ascribe the nonlinear response to a Fermi-smearing mechanism. Further, we note that the sign of the nonlinear susceptibility is reversed from that of gold nanoparticle composites.

Smith, David D.↗
NASA NTRS2008

Gold Nanoparticle Labels Amplify Ellipsometric Signals

The ellipsometric method reported in the immediately preceding article was developed in conjunction with a method of using gold nanoparticles as labels on biomolecules that one seeks to detect. The purpose of the labeling is to exploit the optical properties of the gold nanoparticles in order to amplify the measurable ellipsometric effects and thereby to enable ultrasensitive detection of the labeled biomolecules without need to develop more-complex ellipsometric instrumentation. The colorimetric, polarization, light-scattering, and other optical properties of nanoparticles depend on their sizes and shapes. In the present method, these size-and-shape-dependent properties are used to magnify the polarization of scattered light and the diattenuation and retardance of signals derived from ellipsometry. The size-and-shape-dependent optical properties of the nanoparticles make it possible to interrogate the nanoparticles by use of light of various wavelengths, as appropriate, to optimally detect particles of a specific type at high sensitivity. Hence, by incorporating gold nanoparticles bound to biomolecules as primary or secondary labels, the performance of ellipsometry as a means of detecting the biomolecules can be improved. The use of gold nanoparticles as labels in ellipsometry has been found to afford sensitivity that equals or exceeds the sensitivity achieved by use of fluorescence-based methods. Potential applications for ellipsometric detection of gold nanoparticle-labeled biomolecules include monitoring molecules of interest in biological samples, in-vitro diagnostics, process monitoring, general environmental monitoring, and detection of biohazards.

Venkatasubbarao, Srivatsa↗
DOE OSTI2026

Site-Selective Doping and Oxidation State Control of Copper in Gold Nanorods

We report the synthesis of plasmonic gold–copper nanostructures with tunable copper spatial distribution and oxidation state. Au–Cu alloy shells were deposited in aqueous solution onto colloidal gold nanorods that functioned as seeds, and the resulting shell morphology was found to depend strongly on the nanorod aspect ratio. For relatively fat gold nanorods (16 x 31 nm), Au–Cu growth was preferentially localized near the rod midsections, forming belt-like structures, whereas for skinnier nanorods (9 x 32 nm), Au–Cu growth produced patchy surface coverage around the entire rod. The shell thickness was tuned from 1 to 4 nm; upon air exposure, thicker shells exhibited a higher Cu(I) fraction compared to the initial shell. Incorporation of the Au–Cu shell led to pronounced shifts in the plasmonic features of the gold nanorods. These tunable plasmonic Au–Cu nanorods provide a materials basis for Cu-based plasmonic materials in the context of electrochemical CO₂ reduction.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Au147(SPh)30(PPh3)12: A Geometrically Closed, but Electronically Open Triple‐Shell Icosahedral Gold Cluster and its Geometrically Open Counterpart

The aesthetic platonic solids have been known since ancient times, and the structure of all five platonic solids is also found in chemical compounds. While gold sub-nanometer clusters and gold nanoparticles with an icosahedral structure have been known for a long time to exist, a multi-shell icosahedral gold cluster at the intermediate size between 13 and thousands of atoms has been elusive. Here we present the synthesis and crystallographic characterization of the first triple-shell icosahedral metal cluster, Au147(SPh)30(PPh3)12 1. The gold core in 1 is stabilized by phosphines and thiolates, but surprisingly no staple motifs are formed. A second cluster, Au146(SPh)30(PPh3)12 2, cocrystallizes and is identified as having a closed electronic shell but can be considered as a geometrically open pendant of 1. The unique clusters are characterized experimentally by EDX, UV/vis, DLS, and EPR and theoretically by quantum chemical calculations.

Strienz, Markus↗
DOE OSTI2025

Scanning transmission election microscopy observations of twisted epitaxial gold nanodiscs in twisted molybdenum disulfide bilayers

Atomic scale, scanning transmission electron microscopy (STEM) analysis of the moiré structures in twisted epitaxial gold nanodiscs encapsulated in twisted bilayer molybdenum disulfide is presented. High angle annular dark field STEM imaging reveals that the period of the moiré patterns between gold and molybdenum disulfide varies with different twist angles of the bilayer molybdenum disulfide, ranging from 1.80 nm (epitaxial alignment of gold) to 1.53 nm (twisted epitaxial alignment of gold). Additionally, bright field STEM imaging reveals a faint, larger "moiré of moiré" structure in cases where the bilayer molybdenum disulfide twist angle is small (~6°), arising from the overlapping three-layers, which is not visible in conventional transmission electron microscopy images. In conclusion, our experiments indicate that scanning transmission electron microscopy as a suitable tool for moiré analysis of twisted multilayer planar heterostructures, complementary to information provided by conventional transmission electron microscopy and diffraction.

Au↗
DOE OSTI2024

Scalable and adaptable two-ligand co-solvent transfer methodology for gold bipyramids to organic solvents

Large and faceted nanoparticles, such as gold bipyramids, presently require synthesis using alkyl ammonium halide ligands in aqueous conditions to stabilize the structure, which impedes subsequent transfer and suspension of such nanoparticles in low polarity solvents despite success with few nanometer gold nanoparticles of shapes such as spheres. Phase transfer methodologies present a feasible avenue to maintain colloidal stability of suspensions and move high surface energy particles into organic solvent environments. Here, we present a method to yield stable suspensions of gold bipyramids in low-polarity solvents, including methanol, dimethylformamide, chloroform, and toluene, through the requisite combination of two capping agents and the presence of a co-solvent. By utilizing PEG-SH functionalization for stability, dodecanethiol (DDT) as the organic-soluble capping agent, and methanol to aid in the phase transfer, gold bipyramids with a wide-range of aspect ratios and sizes can be transferred between water and chloroform readily and maintain colloidal stability. Subsequent transfer to various organic and low-polarity solvents is then demonstrated for the first time.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Potentiometric Studies on Ion-Transport Selectivity in Charged Gold Nanotubes

Under ideal conditions, nanotubes with a fixed negative tube-wall charge will reject anions and transport-only cations. Because many proposed nanofluidic devices are optimized in this ideally cation-permselective state, it is important to know the experimental conditions that produce ideal responses. A parameter called Ccrit, the highest salt concentration in a contacting solution that still produces ideal cation permselectivity, is of particular importance. Pioneering potentiometric studies on gold nanotubes were interpreted using an electrostatic model that states that Ccrit should occur when the Debye length in the contacting salt solution becomes equivalent to the tube radius. Since this “double-layer overlap model” (DLOM), treats all same-charge ions as identical point charges, it predicts that all same-charged cations should produce the same Ccrit. However, the effect of cation on Ccrit in gold nanotubes was never investigated. This knowledge gap has become important because recent studies with a polymeric cation-permselective nanopore membrane showed that DLOM failed for every cation studied. To resolve this issue, we conducted potentiometric studies on the effect of salt cation on Ccrit for a 10 nm diameter gold nanotube membrane. Ccrit for all cations studied were, within experimental error, the same and identical, with values predicted by DLOM. The reason DLOM prevailed for the gold nanotubes but failed for the polymeric nanopores stems from the chemical difference between the fixed negative charges of these two membranes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1977

Quantitative analysis of the Dermott-Gold theory for Uranus's rings

A summary is presented of an investigation which supplements the largely qualitative analysis conducted by Dermott and Gold (1977). Dermott and Gold have attempted to explain the locations of Uranus's rings in terms of resonances between ring particles and pairs of satellites. An equation of motion, analogous to that of a pendulum, is derived, taking into account a study by Wilkens (1933) of possible three-body resonances involving one minor and two major planets. Dermott and Gold had concluded that the observed pattern is probably due primarily to the effect of Ariel-Titania and Ariel-Oberon pairs. However, on the basis of the values derived in the reported investigation it is seen that Miranda plays the key role rather than Ariel, in spite of the small mass of the former. It is concluded that a decisive test of the Dermott-Gold theory has to await further observational details concerning the Uranus's rings.

Aksnes, K.↗
NASA NTRS1983

Friction and hardness of gold films deposited by ion plating and evaporation

Sliding friction experiments were conducted with ion-plated and vapor-deposited gold films on various substrates in contact with a 0.025-mm-radius spherical silicon carbide rider in mineral oil. Hardness measurements were also made to examine the hardness depth profile of the coated gold on the substrate. The results indicate that the hardness is influenced by the depth of the gold coating from the surface. The hardness increases with an increase in the depth. The hardness is also related to the composition gradient in the graded interface between the gold coating and the substrate. The graded interface exhibited the highest hardness resulting from an alloy hardening effect. The coefficient of friction is inversely related to the hardness, namely, the load carrying capacity of the surface. The greater the hardness that the metal surface possesses, the lower is the coefficient of friction. The graded interface exhibited the lowest coefficient of friction.

Miyoshi, K.↗
NASA NTRS1986

Mid-infrared reflectlance spectra (2.3-22 micions) of sulfur, gold, KBr, MgO, and halon

Biconical diffuse reflectance spectra in the mid-infrared are presented for powder and other solid forms of sulfur, gold, potassium bromide, magnesium oxide, and halon. Comparisons are made with previously published results of other investigators, and recommendations are made regarding the relative usefulnees of these materials as reflectance standards in the mid-IR. Sulfur has strong intrinsic bands at wavelengths greater than 7 microns that must be taken into account for its use as a reflectance standard. Some sulfur samples have hydrocarbon contaminants and in powder form may have adsorbed water, both of which produce bands in the 3-4-micron region. Potassium bromide has several weak intrinsic bands and is very sensitive to adsorbed water contamination; otherwise it is a good IR reference material. Magnesium oxide and halon have major bands structure and low reflectivity at wavelengths greater than 2.6 microns and thus are unsuitable as reference materials in the mid-IR. Vapor-deposited gold on fine sandpaper (600 grit) is very bright, spectrally flat, and fairly diffuse, so it is the superior material (of those examined) for reflectance reference material throughout the IR. Fine gold powder, on the other hand, is much less bright than evaporated gold, and its reflectivity at wavelengths greater than its particle size is highly sensitive to particle packing density.

Nash, D. B.↗
NASA NTRS1986

Airborne Thermal Infrared Multispectral Scanner (TIMS) images over disseminated gold deposits, Osgood Mountains, Humboldt County, Nevada

The U.S. Geological Survey (USGS) acquired airborne Thermal Infrared Multispectral Scanner (TIMS) images over several disseminated gold deposits in northern Nevada in 1983. The aerial surveys were flown to determine whether TIMS data could depict jasperoids (siliceous replacement bodies) associated with the gold deposits. The TIMS data were collected over the Pinson and Getchell Mines in the Osgood Mountains, the Carlin, Maggie Creek, Bootstrap, and other mines in the Tuscarora Mountains, and the Jerritt Canyon Mine in the Independence Mountains. The TIMS data seem to be a useful supplement to conventional geochemical exploration for disseminated gold deposits in the western United States. Siliceous outcrops are readily separable in the TIMS image from other types of host rocks. Different forms of silicification are not readily separable, yet, due to limitations of spatial resolution and spectral dynamic range. Features associated with the disseminated gold deposits, such as the large intrusive bodies and fault structures, are also resolvable on TIMS data. Inclusion of high-resolution thermal inertia data would be a useful supplement to the TIMS data.

Krohn, M. Dennis↗
NASA NTRS1987

Ion plated gold films: Properties, tribological behavior and performance

The glow discharge energizing favorably modifies and controls the coating/substrate adherence and the nucleation and growth sequence of ion plated gold films. As a result the adherence, coherence, internal stresses, and morphology of the films are significantly improved. Gold ion plated films because of their graded coating/substrate interface and fine uniform densely packed microstructure not only improve the tribological properties but also induce a surface strengthening effect which improves the mechanical properties such as yield, tensile, and fatigue strength. Consequently significant improvements in the tribological performance of ion plated gold films as compared to vapor deposited gold films are shown in terms of decreased friction/wear and prolonged endurance life.

Spalvins, Talivaldis↗
NASA NTRS1993

Deposition and characterization of far-infrared absorbing gold black films

A process is described for producing gold black films with high absorptance in the far IR. The optical and electrical properties of these films have been studied with particular emphasis on the absorptance of films at wavelengths as long as 50 microns. A substantial decrease in absorptance near 50 microns has been observed for pure gold black films on aging in air. This degradation can be largely avoided by alloying the gold with a small percentage of copper during the deposition. Preliminary results on two methods for delineating gold black films are also presented.

Advena, Donna J.↗
NASA NTRS2009

Detecting Airborne Mercury by Use of Gold Nanowires

Like the palladium chloride (PdCl2) films described in the immediately preceding article, gold nanowire sensors have been found to be useful for detecting airborne elemental mercury at concentrations on the order of parts per billion (ppb). Also like the PdCl2 films, gold nanowire sensors can be regenerated under conditions much milder than those necessary for regeneration of gold films that have been used as airborne-Hg sensors. The interest in nanowire sensors in general is prompted by the expectation that nanowires of a given material covering a given surface may exhibit greater sensitivity than does a film of the same material because nanowires have a greater surface area. In preparation for experiments to demonstrate this sensor concept, sensors were fabricated by depositing gold nanowires, variously, on microhotplate or microarray sensor substrates. In the experiments, the electrical resistances were measured while the sensors were exposed to air at a temperature of 25 C and relative humidity of about 30 percent containing mercury at various concentrations from 2 to 70 ppb (see figure). The results of this and other experiments have been interpreted as signifying that sensors of this type can detect mercury at ppb concentrations in room-temperature air and can be regenerated by exposure to clean flowing air at temperatures <40 C.

Ryan, Margaret↗