Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “attributes”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Dynamics of asymmetric binary glass formers. I. A dielectric and nuclear magnetic resonance spectroscopy study

Dielectric spectroscopy as well as {sup 2}H and {sup 31}P nuclear magnetic resonance spectroscopy (NMR) are applied to probe the component dynamics of the binary glass former tripropyl phosphate (TPP)/polystyrene (PS/PS-d{sub 3}) in the full concentration (c{sub TPP}) range. In addition, depolarized light scattering and differential scanning calorimetry experiments are performed. Two glass transition temperatures are found: T{sub g1}(c{sub TPP}) reflects PS dynamics and shows a monotonic plasticizer effect, while the lower T{sub g2}(c{sub TPP}) exhibits a maximum and is attributed to (faster) TPP dynamics, occurring in a slowly moving or immobilized PS matrix. Dielectric spectroscopy probing solely TPP identifies two different time scales, which are attributed to two sub-ensembles. One of them, again, shows fast TPP dynamics (α{sub 2}-process), the other (α{sub 1}-process) displays time constants identical with those of the slow PS matrix. Upon heating the α{sub 1}-fraction of TPP decreases until above some temperature T{sub c} only a single α{sub 2}-population exists. Inversely, below T{sub c} a fraction of the TPP molecules is trapped by the PS matrix. At low c{sub TPP} the α{sub 2}-relaxation does not follow frequency-temperature superposition (FTS), instead it is governed by a temperature independent distribution of activation energies leading to correlation times which follow Arrhenius laws, i.e., the α{sub 2}-relaxation resembles a secondary process. Yet, {sup 31}P NMR demonstrates that it involves isotropic reorientations of TPP molecules within a slowly moving or rigid matrix of PS. At high c{sub TPP} the super-Arrhenius temperature dependence of τ{sub 2}(T), as well as FTS are recovered, known as typical of the glass transition in neat systems.

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

Surface plasmon coupled emission studies on engineered thin film hybrids of nano α−Al{sub 2}O{sub 3} on silver

We report the first time engineering and fabrication of a novel thin film hybrid of nano α-alumina doped in a polyvinyl alcohol (PVA) matrix along with rhodamine b (Rh.B) on a silver thin film. Silver films of 50 nm thickness on glass slides were fabricated by thermal evaporation. Nano α-alumina was synthesized through the combustion route and characterized by XRD. The α-alumina was dispersed in the PVA-Rh.B matrix by tip sonication. The resultant solution was spin coated on the Ag thin film at 3000 rpm to generate an overcoat of ∼30 nm. We have designed and constructed an opto-mechanical setup for performing the SPCE studies. Excitation with a 532 nm continuous laser, led to the coupling of the energy of Rh.B emission to the surface plasmon modes of silver. The emission @ 580 nm was recorded using an Ocean Optics(copyright, serif) fiber optic spectrometer. Calculation of the ratio of signal intensity between the directional SPCE and isotropic fluorescence gives us the factor of signal enhancements which SPCE offers. We report an '8 fold' signal enhancement attributed to SPCE arising from the metal oxide doped thin film hybrid. We observed only a '5 fold' signal enhancement in the case of a thin film hybrid without α-alumina. The emission was also 92% P-polarized which is in coherence with the theory of SPCE. The greater degree of signal enhancement observed in the α-alumina doped thin film substrate can be attributed to the surface roughness which alumina offers to silver, which along with the porous nature of alumina enables a greater degree of adsorption of Rh.B which results in a higher emission intensity. Computational modeling was also performed, based on surface plasmon resonance (SPR) calculations to provide theoretical background to observed experimental data. The α-alumina thin film hybrid can be extended as an economical sensing platform towards the high sensitive detection of analytes.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Structural defects induced by Fe-ion implantation in TiO{sub 2}

X-ray photoelectron spectroscopy and resonant x-ray emission spectroscopy measurements of pellet and thin film forms of TiO{sub 2} with implanted Fe ions are presented and discussed. The findings indicate that Fe-implantation in a TiO{sub 2} pellet sample induces heterovalent cation substitution (Fe{sup 2+} → Ti{sup 4+}) beneath the surface region. But in thin film samples, the clustering of Fe atoms is primarily detected. In addition to this, significant amounts of secondary phases of Fe{sup 3+} are detected on the surface of all doped samples due to oxygen exposure. These experimental findings are compared with density functional theory calculations of formation energies for different configurations of structural defects in the implanted TiO{sub 2}:Fe system. According to our calculations, the clustering of Fe-atoms in TiO{sub 2}:Fe thin films can be attributed to the formation of combined substitutional and interstitial defects. Further, the differences due to Fe doping in pellet and thin film samples can ultimately be attributed to different surface to volume ratios.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Native and induced triplet nitrogen-vacancy centers in nano- and micro-diamonds: Half-field electron paramagnetic resonance fingerprint

Multiple frequency electron paramagnetic resonance (EPR) study of small (4–25 nm) nanodiamonds obtained by various dynamic synthesis techniques reveals systematic presence in the half-field (HF) region a distinctive doublet fingerprint consisting of resolved g{sub HF1} = 4.26 and g{sub HF2} = 4.00 signals. This feature is attributed to “forbidden” ΔM{sub S} = 2 transitions in EPR spectra of two native paramagnetic centers of triplet (S = 1) origin designated as TR1 and TR2, characterized by zero field splitting values D{sub 1} = 0.0950 ± 0.002 cm{sup −1} and D{sub 2} = 0.030 ± 0.005 cm{sup −1}. Nanodiamonds of ∼50 nm particle size, obtained by crushing of Ib type nitrogen rich synthetic diamonds, show only HF TR2 signal whereas the same sample undergone high energy (20 MeV) electron irradiation and thermal annealing demonstrates rise of HF TR1 signal. The same HF TR1 signals appear in the process of fabrication of fluorescent nanodiamonds from micron-size synthetic diamond precursors. Results obtained allow unambiguous attribution of the half-field TR1 EPR signals with g{sub HF1} = 4.26, observed in nano- and micron-diamond powders, to triplet negatively charged nitrogen-vacancy centers. These signals are proposed as reliable and convenient fingerprints in both qualitative and quantitative study of fluorescent nano- and micron-diamonds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Defects and persistent conductivity in SrTiO{sub 3}

Strontium titanate (SrTiO{sub 3}) is often used as a substrate for oxide thin films such as high-temperature superconductors. It has the perovskite structure and an indirect band gap of 3.25 eV. Our prior work showed that hydrogen impurities form a defect complex that contains two hydrogen atoms. The complex was tentatively attributed to a passivated strontium vacancy. Alternatively, it could be a partially passivated titanium vacancy. In order to create titanium vacancies, we annealed samples in an evacuated ampoule with SrO powder. These samples show unexpected behavior. After illuminating with sub-gap light, the free-electron concentration increases significantly. After the light is turned off, the high conductivity persists at room temperature. We attribute persistent photoconductivity (PPC) to the excitation of an electron from a vacancy into the conduction band, with a low recapture rate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Pulsing frequency induced change in optical constants and dispersion energy parameters of WO{sub 3} films grown by pulsed direct current magnetron sputtering

In this work, we present the pulsing frequency induced change in the structural, optical, vibrational, and luminescence properties of tungsten oxide (WO{sub 3}) thin films deposited on microscopic glass and fluorine doped tin oxide (SnO{sub 2}:F) coated glass substrates by pulsed dc magnetron sputtering technique. The WO{sub 3} films deposited on SnO{sub 2}:F substrate belongs to monoclinic phase. The pulsing frequency has a significant influence on the preferred orientation and crystallinity of WO{sub 3} film. The maximum optical transmittance of 85% was observed for the film and the slight shift in transmission threshold towards higher wavelength region with increasing pulsing frequency revealed the systematic reduction in optical energy band gap (3.78 to 3.13 eV) of the films. The refractive index (n) of films are found to decrease (1.832 to 1.333 at 550 nm) with increasing pulsing frequency and the average value of extinction coefficient (k) is in the order of 10{sup −3}. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion energy (E{sub d}) parameters, dielectric constants, plasma frequency, oscillator strength, and oscillator energy (E{sub o}) of WO{sub 3} films were calculated and reported for the first time due to variation in pulsing frequency during deposition by pulsed dc magnetron sputtering. The E{sub o} is change between 6.30 and 3.88 eV, while the E{sub d} varies from 25.81 to 7.88 eV, with pulsing frequency. The Raman peak observed at 1095 cm{sup −1} attributes the presence of W-O symmetric stretching vibration. The slight shift in photoluminescence band is attributed to the difference in excitons transition. We have made an attempt to discuss and correlate these results with the light of possible mechanisms underlying the phenomena.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Synthesis of highly efficient antibacterial agent Ag doped ZnO nanorods: Structural, Raman and optical properties

Here, synthesis, structural, morphological, Raman, optical properties and antibacterial activity of undoped and Ag doped ZnO nanorods by chemical co-precipitation technique have been reported. Structural analysis has revealed that Ag doping cannot deteriorate the structure of ZnO and wurtzite phase is maintained. Lattice constants are found to be decreased with the Ag doping. Fourier transform infrared and Raman spectroscopy also confirm the X-ray diffraction results. Scanning electron microscopy results have demonstrated the formation of ZnO nanorods with average diameter and length of 96 nm and 700 nm, respectively. Raman spectroscopy results suggest that the Ag doping enhances the number of defects in ZnO crystal. It has been found from optical study that Ag doping results in positional shift of band edge absorption peak. This is attributed to the successful incorporation of Ag dopant into ZnO host matrix. The antibacterial activity of prepared nanorods has been determined by two different methods and compared to that of undoped ZnO nanorods. Ag doped ZnO nanorods exhibit excellent antibacterial activity as compared to that of undoped ZnO nanorods. This excellent antibacterial activity may be attributed to the presence of oxygen vacancies and Zn{sup 2+} interstitial defects. Our preliminary findings suggest that Ag doped ZnO nanorods can be used externally to control the spreading of infections related with tested bacterial strains.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Structural phase transitions of robust insulating Bi{sub 1-x}La{sub x}Fe{sub 1-y}Ti{sub y}O{sub 3} multiferroics

In contrast to leaky BiFeO{sub 3}, of which two structural phase transitions of cycloidal modulated antiferromagnetic-paramagnetic and ferroelectric-paraelectric are observed below 850 °C, chemical co-substitution to form Bi{sub 1−x}La{sub x}Fe{sub 1−y}Ti{sub y}O{sub 3} ternary solid solution makes these multiferroic ceramics become robust insulating low dielectric loss and exhibit rich structural phase transitions. Differential thermal analysis and temperature-dependent X-ray diffraction measurements probe four first-order structural phase transitions, e.g., T{sub H} = 305 °C, T{sub N} = 365 °C, T{sub C} = 810 °C, and T{sub S} = 830 °C observed in the Bi{sub 0.98}La{sub 0.02}Fe{sub 0.99}Ti{sub 0.01}O{sub 3} system, which are reasonably attributed to Brazovskii-type cycloidal modulated antiferromagnetic-helimagnetic (at T{sub H}) and helimagnetic-paramagnetic (at T{sub N}) magnetic phase transitions, ferroelectric-paraelectric (at T{sub C}) and rhombohedral-cubic (at T{sub S}) structural phase transitions, respectively. Magnetic phase transition temperatures change a little but ferroelectric and lattice structural phase transition temperatures decrease gradually with increasing co-substitution up to composition-induced rhombohedral-(pseudo-)cubic structural phase boundary. The first-order nature of magnetic phase transition and emergence of helimagnetic phase were attributed to Ti{sup 3+} d{sup 1} magnetic disorder distribution in the Fe{sup 3+} d{sup 5}-O-Fe{sup 3+} d{sup 5} chains, while the first-order nature becomes weak with increasing co-substitution, owing to decreased ferroelectric rhombohedral lattice distortion. An intermediate rhombohedral paraelectric phase is discovered intervening between ferroelectric rhombohedral and paraelectric cubic phase, of which the temperature range defined by difference between T{sub C} and T{sub S} increases with increasing co-substitution. It was found that T{sub C} and T{sub S} are able to be predicted quantitatively by reduced mass of unit cell. These findings enrich our understanding of ferroic phase transitions and advance designing novel high temperature multiferroic compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Optical and phonon properties of ZnO:CuO mixed nanocomposite

Optical and phonon properties of ZnO:CuO nanocrystals which are prepared through sol-gel method are reported here. From X-ray diffraction studies, observed that Cu doping replaces the Zn and also forms secondary phase. Optical absorption spectral studies shows that the exciton and plasmon related bands of ZnO and CuO phase, respectively. Fluorescence studies of the prepared samples shows that green emission from ZnO is completely depleted and the same is attributed to CuO Plasmon. Raman spectral studies reveal that secondary phase (impurity) induced profile changes in 1LO and E{sub 2High} modes. Asymmetry in peak shape is analyzed using Fano profile with the combination of Lorentzian profile. Moreover, the monotonic increase of Fano factor and full width at half maxima is hopefully attributed to the continuum arises by the plasmons of Cu-O phase in ZnO nanosystem.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Domain wall motion and electromechanical strain in lead-free piezoelectrics: Insight from the model system (1 - x)Ba(Zr 0.2 Ti 0.8 )O 3 -x(Ba 0.7 Ca 0.3 )TiO 3 using in situ high-energy X-ray diffraction during application of electric fields

The piezoelectric compositions (1 - x)Ba(Zr 0.2 Ti 0.8 )O 3 –x(Ba 0.7 Ca 0.3 )TiO 3 (BZT-xBCT) span a model lead-free morphotropic phase boundary (MPB) between room temperature rhombohedral and tetragonal phases at approximately x = 0.5. In the present work, in situ X-ray diffraction measurements during electric field application are used to elucidate the origin of electromechanical strain in several compositions spanning the tetragonal compositional range 0.6 ≤ x ≤ 0.9. As BCT concentration decreases towards the MPB, the tetragonal distortion (given by c/a-1) decreases concomitantly with an increase in 90° domain wall motion. The increase in observed macroscopic strain is predominantly attributed to the increased contribution from 90° domain wall motion. The results demonstrate that domain wall motion is a significant factor in achieving high strain and piezoelectric coefficients in lead-free polycrystalline piezoelectrics.

Tutuncu, Goknur↗
DOE OSTI2014

Investigation of combinatorial coevaporated thin film Cu{sub 2}ZnSnS{sub 4}. I. Temperature effect, crystalline phases, morphology, and photoluminescence

Cu{sub 2}ZnSnS{sub 4} is a promising low-cost, nontoxic, earth-abundant absorber material for thin-film solar cell applications. In this study, combinatorial coevaporation was used to synthesize individual thin-film samples spanning a wide range of compositions at low (325 °C) and high (475 °C) temperatures. Film composition, grain morphology, crystalline-phase and photo-excitation information have been characterized by x-ray fluorescence, scanning electron microscopy, x-ray diffraction, Raman spectroscopy, and photoluminescence imaging and mapping. Highly textured columnar grain morphology is observed for film compositions along the ZnS-Cu{sub 2}ZnSnS{sub 4}-Cu{sub 2}SnS{sub 3} tie line in the quasi-ternary Cu{sub 2}S-ZnS-SnS{sub 2} phase system, and this effect is attributed to structural similarity between the Cu{sub 2}ZnSnS{sub 4}, Cu{sub 2}SnS{sub 3}, and ZnS crystalline phases. At 475 °C growth temperature, Sn-S phases cannot condense because of their high vapor pressures. As a result, regions that received excess Sn flux during growth produced compositions falling along the ZnS-Cu{sub 2}ZnSnS{sub 4}-Cu{sub 2}SnS{sub 3} tie line. Room-temperature photoluminescence imaging reveals a strong correlation for these samples between film composition and photoluminescence intensity, where film regions with Cu/Sn ratios greater than ∼2 show strong photoluminescence intensity, in comparison with much weaker photoluminescence in regions that received excess Sn flux during growth or subsequent processing. The observed photoluminescence quenching in regions that received excess Sn flux is attributed to the effects of Sn-related native point defects in Cu{sub 2}ZnSnS{sub 4} on non-radiative recombination processes. Implications for processing and performance of Cu{sub 2}ZnSnS{sub 4} solar cells are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Measurements of the force fields within an acoustic standing wave using holographic optical tweezers

Direct measurement of the forces experienced by micro-spheres in an acoustic standing wave device have been obtained using calibrated optical traps generated with holographic optical tweezers. A micro-sphere, which is optically trapped in three dimensions, can be moved through the acoustic device to measure forces acting upon it. When the micro-sphere is subjected to acoustic forces, it's equilibrium position is displaced to a position where the acoustic forces and optical forces are balanced. Once the optical trapping stiffness has been calibrated, observation of this displacement enables a direct measurement of the forces acting upon the micro-sphere. The measured forces are separated into a spatially oscillating component, attributed to the acoustic radiation force, and a constant force, attributed to fluid streaming. As the drive conditions of the acoustic device were varied, oscillating forces (>2.5 pN{sub pp}) and streaming forces (<0.2 pN) were measured. A 5 μm silica micro-sphere was used to characterise a 6.8 MHz standing wave, λ = 220 μm, to a spatial resolution limited by the uncertainty in the positioning of the micro-sphere (here to within 2 nm) and with a force resolution on the order of 10 fN. The results have application in the design and testing of acoustic manipulation devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Electronic state spectroscopy of diiodomethane (CH{sub 2}I{sub 2}): Experimental and computational studies in the 30 000–95 000 cm{sup −1} region

The electronic absorption spectrum of diiodomethane in the 30 000–95 000 cm{sup −1} region is investigated using synchrotron radiation; the spectrum in the 50 000–66 500 cm{sup −1} region is reported for the first time. The absorption bands in the 30 000–50 000 cm{sup −1} region are attributed to valence transitions, while the vacuum ultraviolet (VUV) spectrum (50 000–95 000 cm{sup −1}) is dominated by several Rydberg series converging to the first four ionization potentials of CH{sub 2}I{sub 2} at 9.46, 9.76, 10.21, and 10.56 eV corresponding to the removal of an electron from the outermost 3b{sub 2}, 2b{sub 1}, 1a{sub 2}, and 4a{sub 1} non-bonding orbitals, respectively. Rydberg series of ns, np, and nd type converging to each of the four ionization potentials are assigned based on a quantum defect analysis. Time dependent density functional theory calculations of excited states support the analysis and help in interpretation of the Rydberg and valence nature of observed transitions. Density functional theory calculations of the neutral and ionic ground state geometries and vibrational frequencies are used to assign the observed vibronic structure. Vibronic features accompanying the Rydberg series are mainly due to excitation of the C-I symmetric stretch (ν{sub 3}) and CH{sub 2} wag (ν{sub 8}) modes, with smaller contributions from the C-H symmetric stretch (ν{sub 1}). UV absorption bands are assigned to low lying valence states 1{sup 1}B{sub 2}, 1{sup 1}B{sub 1}, 2{sup 1}A{sub 1}, 3{sup 1}A{sub 1}, 2{sup 1}B{sub 1}, and 2{sup 1}B{sub 2} and the unusually high underlying intensity in parts of the VUV spectrum is attributed to valence states with high oscillator strength. This is the first report of a comprehensive Rydberg series and vibronic analysis of the VUV absorption spectrum of CH{sub 2}I{sub 2} in the 50 000–85 000 cm{sup −1} region. The VUV absorption spectrum of CD{sub 2}I{sub 2} which serves to verify and consolidate spectral assignments is also reported here for the first time.

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

Uniform nano-ripples on the sidewall of silicon carbide micro-hole fabricated by femtosecond laser irradiation and acid etching

Uniform nano-ripples were observed on the sidewall of micro-holes in silicon carbide fabricated by 800-nm femtosecond laser and chemical selective etching. The morphology of the ripple was analyzed using scanning electronic microscopy. The formation mechanism of the micro-holes was attributed to the chemical reaction of the laser affected zone with mixed solution of hydrofluoric acid and nitric acid. The formation of nano-ripples on the sidewall of the holes could be attributed to the standing wave generated in z direction due to the interference between the incident wave and the reflected wave.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Experimental verification of the high pressure crystal structures in NH{sub 3}BH{sub 3}

A detailed high-pressure study on NH{sub 3}BH{sub 3} has been carried out using in situ synchrotron X-ray diffraction (XRD) and Raman scattering with a diamond anvil cell up to 20 and 33 GPa, respectively. The Rietveld refinement based on the XRD pattern and analysis of Raman data indicate two first-order phase transitions from the ambient pressure I4 mm structure (α-NH{sub 3}BH{sub 3}) to a high pressure Cmc2{sub 1} phase (β-NH{sub 3}BH{sub 3}) at 2.14 GPa, and further into a monoclinic P2{sub 1} (Z = 2) phase (γ-NH{sub 3}BH{sub 3}) at 9.67 GPa. Fitting the measured volumetric compression data to the third order Birch-Murnaghan equation of state reveals a bulk modulus of B{sub 0} = 9.9 ± 0.5 and 17.0 ± 3.0 GPa (with fixed B{sub 0}{sup ′} = 4) for the β-NH{sub 3}BH{sub 3} below and above 5 GPa, respectively. Still, with the splitting of the NBH rock mode in Raman experiment, it is concluded that a second-order isostructural phase transition occurs at 5 GPa. By analyzing the dihydrogen bonding framework, the origin of the isostructural phase transition is attributed to the number of dihydrogen bondings per molecule in the Cmc2{sub 1} phase increasing from 12 to 14 at 5 GPa.

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

Synchrotron-based measurement of the impact of thermal cycling on the evolution of stresses in Cu through-silicon vias

One of the main causes of failure during the lifetime of microelectronics devices is their exposure to fluctuating temperatures. In this work, synchrotron-based X-ray micro-diffraction is used to study the evolution of stresses in copper through-silicon via (TSV) interconnects, “as-received” and after 1000 thermal cycles. For both test conditions, significant fluctuations in the measured normal and shear stresses with depth are attributed to variations in the Cu grain orientation. Nevertheless, the mean hydrostatic stresses in the “as-received” Cu TSV were very low, at (16 ± 44) MPa, most likely due to room temperature stress relaxation. In contrast, the mean hydrostatic stresses along the entire length of the Cu TSV that had undergone 1000 thermal cycles (123 ± 37) MPa were found to be eight times greater, which was attributed to increased strain-hardening. The evolution in stresses with thermal cycling is a clear indication that the impact of Cu TSVs on front-end-of-line (FEOL) device performance will change through the lifetime of the 3D stacked dies, and ought to be accounted for during FEOL keep-out-zone design rules development.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Local vibrational modes competitions in Mn-doped ZnO epitaxial films with tunable ferromagnetism

We reported spectroscopic investigations of high quality Mn-doped ZnO (ZnMnO) films grown by oxygen plasma-assisted molecular beam epitaxy. Raman scattering spectra revealed two local vibrational modes (LVMs) associated with Mn dopants at 523 and 712 cm{sup −1}. The LVMs and magnetic properties of ZnMnO films can be synchronously modulated by post annealing processing or by introducing tiny Co. The relative intensity of two LVMs clearly shows competitions arising from uncompensated acceptor and donor defects competition for ferromagnetic and nonmagnetic films. The experimental results indicated that LVM at 523 cm{sup −1} is attributed to Mn—(Zinc-vacancy) complexes, while LVM at 712 cm{sup −1} is attributed to Mn—(Oxygen-vacancy) complexes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Growth-induced non-planar magnetic anisotropy in FeCoZr-CaF{sub 2} nanogranular films: Structural and magnetic characterization

The relation between nanoscale structure, local atomic order and magnetic properties of (FeCoZr){sub x}(CaF{sub 2}){sub 100−x} (29 ≤ x ≤ 73 at. %) granular films is studied as a function of metal/insulator fraction ratio. The films of a thickness of 1–6 μm were deposited on Al-foils and glass-ceramic substrates, by ion sputtering of targets of different metal/insulator contents. Structural characterization with X-ray and electron diffraction as well as transmission electron microscopy revealed that the films are composed of isolated nanocrystalline bcc α-FeCo(Zr) alloy and insulating fcc CaF{sub 2} matrix. They grow in a columnar structure, where elongated metallic nanograins are arranged on top of each other within the columns almost normal to the substrate surface. Mössbauer spectroscopy and magnetometry results indicate that their easy magnetization axes are oriented at an angle of 65°–74° to the surface in films with x between 46 and 74, above the electrical percolation threshold, which is attributed to the growth-induced shape anisotropy. Interatomic distances characteristic for metallic state of α-FeCo(Zr) nanograins were revealed by X-ray Absorption Spectroscopy. The results show a lack of surface oxidation of the alloy nanograins, so the growth-induced orientation of nanograins in the films cannot be attributed to this effect. The study is among the first to report a growth-induced non-planar magnetic anisotropy in metal/insulator granular films above the percolation threshold and to reveal the origin of it.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗