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At least 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Rotating copper plasmoid in external magnetic field

Effect of nonuniform magnetic field on the expanding copper plasmoid in helium and argon gases using optical emission spectroscopy and fast imaging is presented. We report a peculiar oscillatory rotation of plasmoid in magnetic field and argon ambient. The temporal variation and appearance of the dip in the electron temperature show a direct evidence of the threading and expulsion of the magnetic field lines from the plasmoid. Rayleigh Taylor instability produced at the interface separating magnetic field and plasma is discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Low temperature plasma-enhanced atomic layer deposition of thin vanadium nitride layers for copper diffusion barriers

Thin vanadium nitride (VN) layers were grown by atomic layer deposition using tetrakis(ethylmethylamino)vanadium and NH{sub 3} plasma at deposition temperatures between 70 Degree-Sign C and 150 Degree-Sign C on silicon substrates and polymer foil. X-ray photoelectron spectroscopy revealed a composition close to stoichiometric VN, while x-ray diffraction showed the {delta}-VN crystal structure. The resistivity was as low as 200 {mu}{Omega} cm for the as deposited films and further reduced to 143 {mu}{Omega} cm and 93 {mu}{Omega} cm by annealing in N{sub 2} and H{sub 2}/He/N{sub 2}, respectively. A 5 nm VN layer proved to be effective as a diffusion barrier for copper up to a temperature of 720 Degree-Sign C.

36 MATERIALS SCIENCE↗
DOE OSTI2013

The Influence of spot size on the expansion dynamics of nanosecond-laser-produced copper plasmas in atmosphere

Laser produced copper plasmas of different spot sizes in air were investigated using fast photography and optical emission spectroscopy (OES). The laser energy was 33 mJ. There were dramatic changes in the plasma plume expansion into the ambient air when spot sizes changed from {approx}0.1 mm to {approx}0.6 mm. A stream-like structure and a hemispherical structure were, respectively, observed. It appeared that the same spot size resulted in similar expansion dynamics no matter whether the target was located in the front of or behind the focal point, although laser-induced air breakdown sometimes occurred in the latter case. Plasma plume front positions agree well with the classic blast wave model for the large spot-size cases, while an unexpected stagnation of {approx}80 ns occurred after the laser pulse ends for the small spot size cases. This stagnation can be understood in terms of the evolution of enhanced plasma shielding effects near the plasma front. Axial distributions of plasma components by OES revealed a good confinement effect. Electron number densities were estimated and interpreted using the recorded Intensified Charge Coupled Device (ICCD) images.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Structural and optical properties of Ag-doped copper oxide thin films on polyethylene napthalate substrate prepared by low temperature microwave annealing

Silver doped cupric oxide thin films are prepared on polyethylene naphthalate (flexible polymer) substrates. Thin films Ag-doped CuO are deposited on the substrate by co-sputtering followed by microwave assisted oxidation of the metal films. The low temperature tolerance of the polymer substrates led to the search for innovative low temperature processing techniques. Cupric oxide is a p-type semiconductor with an indirect band gap and is used as selective absorption layer solar cells. X-ray diffraction identifies the CuO phases. Rutherford backscattering spectrometry measurements confirm the stoichiometry of each copper oxide formed. The surface morphology is determined by atomic force microscopy. The microstructural properties such as crystallite size and the microstrain for (-111) and (111) planes are calculated and discussed. Incorporation of Ag led to the lowering of band gap in CuO. Consequently, it is determined that Ag addition has a strong effect on the structural, morphological, surface, and optical properties of CuO grown on flexible substrates by microwave annealing. Tauc's plot is used to determine the optical band gap of CuO and Ag doped CuO films. The values of the indirect and direct band gap for CuO are found to be 2.02 eV and 3.19 eV, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Evidence of enhanced electron-phonon coupling in ultrathin epitaxial copper films

Electron phonon (el-ph) coupling is a fundamental quantity that controls the electron transport through a conductor. We experimentally determined the el-ph coupling strength of epitaxial copper (Cu) films ranging from 5 to 1000 nm thick using both ultra-fast, optical pump-probe reflectivity and temperature-dependent resistivity measurements. An enhancement of the el-ph coupling strength was observed when the thickness of the films was reduced to below 50 nm. We suggest that this unexpected enhancement of the el-ph coupling strength is partially responsible for the observed increase of resistivity in the films below 50 nm thick.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Percolating porosity in ultrafine grained copper processed by High Pressure Torsion

Defect structures in copper of different purity (nominally 99.99 and 99.999 wt. %) deformed via High Pressure Torsion (HPT) with varying processing parameters are investigated utilizing the radiotracer diffusion technique. While the degree of deformation is kept constant, the effects of applied quasi-hydrostatic pressure, processing temperature, post-deformation annealing treatments, and of the impurity concentration on the deformed samples are analyzed in terms of the formation of interconnected internal porosity. Furthermore, the anisotropy of the developing porosity network is examined. The porosity channels occurred to be interconnected along the direction parallel to the surface normal with a volume fraction of the order of a few ppm while no long-range penetration along the internal porosity could be detected when measured along the azimuthal or radial directions of a HPT processed sample.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Plasticity mechanism for copper extrusion in through-silicon vias for three-dimensional interconnects

In this paper, we demonstrated the plasticity mechanism for copper (Cu) extrusion in through-silicon via structures under thermal cycling. The local plasticity was directly observed by synchrotron x-ray micro-diffraction near the top of the via with the amount increasing with the peak temperature. The Cu extrusion was confirmed by Atomic Force Microscopy (AFM) measurements and found to be consistent with the observed Cu plasticity behavior. A simple analytical model elucidated the role of plasticity during thermal cycling, and finite element analyses were carried out to confirm the plasticity mechanism as well as the effect of the via/Si interface. The model predictions were able to account for the via extrusions observed in two types of experiments, with one representing a nearly free sliding interface and the other a strongly bonded interface. Interestingly, the AFM extrusion profiles seemed to contour with the local grain structures near the top of the via, suggesting that the grain structure not only affects the yield strength of the Cu and thus its plasticity but could also be important in controlling the pop-up behavior and the statistics for a large ensemble of vias.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Heat treatment effect on the mechanical properties of industrial drawn copper wires

In this present investigation, the mechanical properties of industrial drawn copper wires have been studied by tensile tests. The effect of prior heat treatments at 500°C on the drawn wires behavior was the main goal of this investigation. We have found that the mechanical behavior of drawn wires depends strongly on those treatments. SEM observations of the wire cross section after tensile tests have shown that the mechanism of rupture was mainly controlled by the void formation.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Ultrahigh strain-rate bending of copper nanopillars with laser-generated shock waves

An experimental study to bend FIB-prepared cantilevered single crystal Cu nanopillars of several hundred nanometers in diameter and length at ultrahigh strain rate is presented. The deformation is induced by laser-generated stress waves, resulting in local strain rates exceeding 10{sup 7} s{sup −1}. Loading of nano-scale Cu structures at these extremely short loading times shows unique deformation characteristics. At a nominal stress value of 297 MPa, TEM examination along with selected area electron diffraction characterization revealed that twins within the unshocked Cu pillars interacted with dislocations that nucleated from free surfaces of the pillars to form new subgrain boundaries. MD simulation results were found to be consistent with the very low values of the stress required for dislocation activation and nucleation because of the extremely high surface area to volume ratio of the nanopillars. Specifically, simulations show that the stress required to nucleate dislocations at these ultrahigh strain rates is about one order of magnitude smaller than typical values required for homogeneous nucleation of dislocation loops in bulk copper single crystals under quasi-static conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Influence of the interface on the magnetic properties of ferromagnetic ultrathin films with various adjacent copper thicknesses

The interface and magnetic properties of two series of films with Ta(5 nm)/Fe{sub 20}Ni{sub 80}Nd{sub 0.017}(3 nm)/Cu(t nm) and Ta(5 nm)/Cu(t nm)/Fe{sub 50}Co{sub 50}Gd{sub 0.07}(3 nm)/Cu(2 nm) structures have been investigated by atomic force microscopy, vibrating sample magnetometer, and ferromagnetic resonance (FMR). The roughness of all films increases with increasing copper thickness, which causes the different grain sizes in the surface of films. The coercivity of FeCo-Gd films increases with increasing thickness of inserted Cu layer while decreases with increasing thickness of Cu capping layer for FeNi-Nd films. FMR linewidth exhibits huge dependence on the thickness of inserted Cu layer for FeCo-Gd films, increasing from 2270 to 3680 Oe, which comes from the additional contribution of effect of the two-magnon scattering. And the thickness of Cu capping layer shows also an influence on FMR linewidth of FeNi-Nd films, increasing from 190 to 320 Oe, which mainly comes from intrinsic FMR linewidth and plus minor inhomogeneous broadening. All of these extrinsic linewidth broadening are related to the interface roughness.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Revisiting the adsorption of copper-phthalocyanine on Au(111) including van der Waals corrections

We have studied the adsorption of copper-phthalocyanine on Au(111) by means of van der Waals corrected density functional theory using the Tkatchenko-Scheffler method. We have compared the element and site resolved adsorption distances to recent experimental normal-incident X-ray standing wave measurements. The measured adsorption distances could be reproduced within a deviation of 1% for the Cu atom, 1% for the C atoms, and 2% for the N atoms. The molecule was found to have a magnetic moment of 1 μ{sub B} distributed over the Cu and the N atoms of the pyrrole ring. Simulated scanning tunnel microscopy images based on the total and on the spin-resolved differential charge densities are provided for bias voltages of −1.45 and 1.45 eV.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Synthesis of silver particles on copper substrates using ethanol-based solution for surface-enhanced Raman spectroscopy

The displacement reaction of AgNO{sub 3} and copper metal is an effective and economical way to fabricate Ag-Cu surface enhanced Raman scattering (SERS) substrates. Aqueous solutions of AgNO{sub 3} are usually used for substrate preparation. In this work, a new method for Ag-Cu SERS substrate preparation is proposed, which uses an ethanol solution rather than an aqueous AgNO{sub 3} solution. Analysis of the surface morphologies of sample substrates by field emission scanning electron microscopy (FESEM) showed that the silver nanoparticles prepared by this new method were more regular than those prepared in the traditional aqueous solution. The SERS spectra of Rhodamine 6G (R6G) adsorbed on these Ag-Cu substrates were then investigated and compared. It was found that the Ag-Cu substrates prepared by this method provide significant improvements in Raman signal sensitivity and large-area uniformity. The enhancement factor of this new substrate is about 330 times higher than that prepared using an aqueous AgNO{sub 3} solution under identical experimental conditions. It was also found that 70% of the original sensitivity of the substrate remains after 15 days of exposure to air.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Liquid phase synthesis of copper indium diselenide nanoparticles

Nanoparticles of Copper Indium diselenide (CuInSe{sub 2}), belongs to I-III-VI{sub 2} family has been synthesized via liquid phase route using ethylenediamine as a solvent. Characterization of as-grown particles is done by XRD, HRTEM, DLS, optical microscopy and UV-Vis spectroscopy. X-ray diffraction pattern confirmed that the CuInSe2 nanoparticles obtained reveals chalcopyrite structure. Particle size evaluated from dynamic light scattering of as grown particle possessing radius of 90 nm. The bandgap of 1.05eV is obtained from UV-Vis spectrum which will applicable to the solar cell devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Plasma-enhanced chemical vapor deposition of graphene on copper substrates

A plasma enhanced vapor deposition process is used to synthesize graphene from a hydrogen/methane gas mixture on copper samples. The graphene samples were transferred onto SiO{sub 2} substrates and characterized by Raman spectroscopic mapping and atomic force microscope topographical mapping. Analysis of the Raman bands shows that the deposited graphene is clearly SLG and that the sheets are deposited on large areas of several mm{sup 2}. The defect density in the graphene sheets is calculated using Raman measurements and the influence of the process pressure on the defect density is measured. Furthermore the origin of these defects is discussed with respect to the process parameters and hence the plasma environment.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Eutectic structures in friction spot welding joint of aluminum alloy to copper

A dissimilar joint of AA5083 Al alloy and copper was produced by friction spot welding. The Al-MgCuAl{sub 2} eutectic in both coupled and divorced manners were found in the weld. At a relatively high temperature, mass transport of Cu due to plastic deformation, material flow, and atomic diffusion, combined with the alloy system of AA5083 are responsible for the ternary eutectic melting.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine

Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-1/2 ) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by the long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localized spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Ultrashort laser ablation of bulk copper targets: Dynamics and size distribution of the generated nanoparticles

We address the role of laser pulse fluence on expansion dynamics and size distribution of the nanoparticles produced by irradiating a metallic target with an ultrashort laser pulse in a vacuum, an issue for which contrasting indications are present in the literature. To this end, we have carried out a combined theoretical and experimental analysis of laser ablation of a bulk copper target with ≈50 fs, 800 nm pulses, in an interval of laser fluencies going from few to several times the ablation threshold. On one side, molecular dynamics simulations, with two-temperature model, describe the decomposition of the material through the analysis of the evolution of thermodynamic trajectories in the material phase diagram, and allow estimating the size distribution of the generated nano-aggregates. On the other side, atomic force microscopy of less than one layer nanoparticles deposits on witness plates, and fast imaging of the nanoparticles broadband optical emission provide the corresponding experimental characterization. Both experimental and numerical findings agree on a size distribution characterized by a significant fraction (≈90%) of small nanoparticles, and a residual part (≈10%) spanning over a rather large size interval, evidencing a weak dependence of the nanoparticles sizes on the laser pulse fluence. Numerical and experimental findings show a good degree of consistency, thus suggesting that modeling can realistically support the search for experimental methods leading to an improved control over the generation of nanoparticles by ultrashort laser ablation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Cost effective nanostructured copper substrates prepared with ultrafast laser pulses for explosives detection using surface enhanced Raman scattering

Ultrafast laser pulses induced surface nanostructures were fabricated on a copper (Cu) target through ablation in acetone, dichloromethane, acetonitrile, and chloroform. Surface morphological information accomplished from the field emission scanning electron microscopic data demonstrated the diversities of ablation mechanism in each case. Fabricated Cu substrates were utilized exultantly to investigate the surface plasmon (localized and propagating) mediated enhancements of different analytes using surface enhance Raman scattering (SERS) studies. Multiple utility of these substrates were efficiently demonstrated by collecting the SERS data of Rhodamine 6G molecule and two different secondary explosive molecules such as 5-amino-3-nitro-l,2,4-triazole and trinitrotoluene on different days which were weeks apart. We achieved significant enhancement factors of >10{sup 5} through an easily adoptable cleaning procedure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗