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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.

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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Controlling magnetic anisotropy in La{sub 0.7}Sr{sub 0.3}MnO{sub 3} nanostructures

We have developed a chlorine based dry etching process for nanopatterning the ferromagnetic oxide La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO). Large arrays of millions of identical structures have been fabricated from thin LSMO films by electron-beam lithography and reactive ion etching. SQUID magnetometry demonstrates that patterned nanostructures with lateral dimensions down to 100 nm retain their full magnetization and the Curie temperature of the bulk layer. In addition, their shape anisotropy is sufficient to overcome the crystalline anisotropy of the bulk. High resolution scanning transmission electron microscopy shows that crystallinity is preserved even at the edges of the nanostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

AlN/Fe/AlN nanostructures for magnetooptic magnetometry

AlN/Fe/AlN/Cu nanostructures with ultrathin Fe grown by sputtering on Si substrates are evaluated as probes for magnetooptical (MO) mapping of weak currents. They are considered for a laser wavelength of λ = 410 nm (3.02 eV) and operate at oblique light incidence angles, φ{sup (0)}, to enable detection of both in-plane and out-of-plane magnetization. Their performance is evaluated in terms of MO reflected wave electric field amplitudes. The maximal MO amplitudes in AlN/Fe/AlN/Cu are achieved by a proper choice of layer thicknesses. The nanostructures were characterized by MO polar Kerr effect at φ{sup (0)} ≈ 5° and longitudinal Kerr effect spectra (φ{sup (0)} = 45°) at photon energies between 1 and 5 eV. The nominal profiles were refined using a model-based analysis of the spectra. Closed form analytical expressions are provided, which are useful in the search for maximal MO amplitudes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

An environment-dependent semi-empirical tight binding model suitable for electron transport in bulk metals, metal alloys, metallic interfaces, and metallic nanostructures. I. Model and validation

Semi-empirical Tight Binding (TB) is known to be a scalable and accurate atomistic representation for electron transport for realistically extended nano-scaled semiconductor devices that might contain millions of atoms. In this paper, an environment-aware and transferable TB model suitable for electronic structure and transport simulations in technologically relevant metals, metallic alloys, metal nanostructures, and metallic interface systems are described. Part I of this paper describes the development and validation of the new TB model. The new model incorporates intra-atomic diagonal and off-diagonal elements for implicit self-consistency and greater transferability across bonding environments. The dependence of the on-site energies on strain has been obtained by appealing to the Moments Theorem that links closed electron paths in the system to energy moments of angular momentum resolved local density of states obtained ab initio. The model matches self-consistent density functional theory electronic structure results for bulk face centered cubic metals with and without strain, metallic alloys, metallic interfaces, and metallic nanostructures with high accuracy and can be used in predictive electronic structure and transport problems in metallic systems at realistically extended length scales.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A close correlation between nanostructure formations and the thickness dependence of the critical current density in pure and BaSnO{sub 3}-added GdBa{sub 2}Cu{sub 3}O{sub 7-δ} films

A close correlation between the nanostructure formations and the thickness dependence of the in-field critical current density (J{sub c}) in GdBa{sub 2}Cu{sub 3}O{sub 7-δ} (GdBCO) films is reported. Pure and 2 wt. % BaSnO{sub 3} (BSO)-added GdBCO films with film thicknesses (d) ranging from 0.2 μm to 1.5 μm were deposited on SrTiO{sub 3} single-crystalline substrates by using a pulsed laser deposition technique. Magnetization data measured at 77 K with the magnetic field applied parallel to the c-axis of the films showed the general trend of decreasing in-field J{sub c} with increasing residual film thickness. The two special inversions, however, were observed at d ∼ 0.6 μm, for which the J{sub c}’s of both the pure and BSO-added GdBCO films were larger than those of the films with d ∼ 0.4 μm. A sequential ion-milling process and scanning electron microscopy studies were employed to examine the microstructural evolution in the 1.5- μm-thick GdBCO films. For the pure GdBCO films, nanosized dislocations were observed to start growing at intersections of perpendicularly connected a-axis-oriented grains in a residual film thickness (t) of ∼ 0.6 μm and the growth persisted to the top surface of the 1.5-μm-thick GdBCO film. For the BSO-added GdBCO films, the density of BSO nanorods was estimated to be decreased versus t with an increase found at t of ∼ 0.6 μm A reason for this inversions of J{sub c} might be the nanostructure formations at t ∼ 0.6 μm, which were proved to serve as effective pinning centers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Synthesis, characterization and electrostatic properties of WS{sub 2} nanostructures

We report the direct growth of atomically thin WS{sub 2} nanoplates and nanofilms on the SiO{sub 2}/Si (300 nm) substrate by vapor phase deposition method without any catalyst. The WS{sub 2} nanostructures were systematically characterized by optical microscopy, scanning electron microscopy, Raman microscopy and atomic force microscopy. We found that growth time and growth temperature play important roles in the morphology of WS{sub 2} nanostructures. Moreover, by using Kelvin probe force microscopy, we found that the WS{sub 2} nanoplates exhibit uniform surface and charge distributions less than 10 mV fluctuations. Our results may apply to the study of other transition metal dichalcogenides by vapor phase deposition method.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Site specific isolated nanostructure array formation on a large area by broad ion beam without any mask and resist

We report the formation of isolated nanostructure arrays on a large area via broad ion beam implantation without the aid of any mask or resist. Desired ions have been implanted at specific locations of the prefabricated silicon ripple or triangular structures by exploiting the variation of local ion impact angles. We have shown that the implantation of Fe ions on an O{sup +} ions induced pre fabricated triangular shaped patterned Si surface results in a self-organized periodic array of striped magnetic nanostructures having several micron length and about 50 nm width arranged with a spacial separation of ∼200 nm. The morphology, composition, crystalline structure, and magnetic property of these nanopatterns have been analyzed using high-resolution cross-sectional transmission electron microscopy and atomic force microscopy. A geometrical model has been proposed to explain the fundamental features of such ion-induced nanopattern structures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Spin and phonon anomalies in epitaxial self-assembled CoFe{sub 2}O{sub 4}-BaTiO{sub 3} multiferroic nanostructures

Temperature dependent magnetic and phonon anomalies in epitaxial self-assembled CoFe{sub 2}O{sub 4} (CFO) rods embedded in BaTiO{sub 3} (BTO) matrix nanostructures were investigated. The temperature dependence of A{sub 1}(2TO) phonon frequency of BTO indicates that the BTO matrix experiences structural transformations. The lattice strain produced during the structural transformations drives spin reorientation in CFO rods, resulting in anomalous changes of magnetization. Through correlating the phonon anomalies with the increase of in-plane spin ordering, we show the spin-phonon coupling induces the softening of A{sub 1g} and A{sub 1}(2TO) phonons. It suggests that spin strongly couples with lattice strain and phonons in this nanostructure.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Microstructure and mechanical properties of thermoelectric nanostructured n-type silicon-germanium alloys synthesized employing spark plasma sintering

Owing to their high thermoelectric (TE) figure-of-merit, nanostructured Si{sub 80}Ge{sub 20} alloys are evolving as a potential replacement for their bulk counterparts in designing efficient radio-isotope TE generators. However, as the mechanical properties of these alloys are equally important in order to avoid in-service catastrophic failure of their TE modules, we report the strength, hardness, fracture toughness, and thermal shock resistance of nanostructured n-type Si{sub 80}Ge{sub 20} alloys synthesized employing spark plasma sintering of mechanically alloyed nanopowders of its constituent elements. These mechanical properties show a significant enhancement, which has been correlated with the microstructural features at nano-scale, delineated by transmission electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Communication: Non-additivity of van der Waals interactions between nanostructures

Due to size-dependent non-additivity, the van der Waals interaction (vdW) between nanostructures remains elusive. Here we first develop a model dynamic multipole polarizability for an inhomogeneous system that allows for a cavity. The model recovers the exact zero- and high-frequency limits and respects the paradigms of condensed matter physics (slowly varying density) and quantum chemistry (one- and two-electron densities). We find that the model can generate accurate vdW coefficients for both spherical and non-spherical clusters, with an overall mean absolute relative error of 4%, without any fitting. Based on this model, we study the non-additivity of vdW interactions. We find that there is strong non-additivity of vdW interactions between nanostructures, arising from electron delocalization, inequivalent contributions of atoms, and non-additive many-body interactions. Furthermore, we find that the non-additivity can have increasing size dependence as well as decreasing size dependence with cluster size.

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

Thermal transport in 2- and 3-dimensional periodic “holey” nanostructures

Understanding thermal transport in two- and three-dimensional periodic “holey” nanostructures is important for realizing applications of these structures in thermoelectrics, photonics and batteries. In terms of continuum heat diffusion physics, the effective medium theory provides the framework for obtaining the effective thermal conductivity of such structures. However, recently measured nanostructures possess thermal conductivities well below these continuum predictions. In some cases, their thermal conductivities are even lower than predictions that account for sub-continuum phonon transport. We analyze current understanding of thermal transport in such structures, discussing the various theories, the measurements and the insights gained from comparing the two.

36 MATERIALS SCIENCE↗
DOE OSTI2015

First principles study of thermal conductivity cross-over in nanostructured zinc-chalcogenides

Systematic first principles studies of zinc-chalcogenides have been performed to understand their thermal transport behaviour. We have applied the Boltzmann transport equation in the relaxation time approximation to calculate the thermal conductivity of ZnS, ZnSe, and ZnTe. We find a thermal conductivity cross-over between ZnS and ZnSe at nanostructure sizes around 0.1–0.2 μm and explain this in terms of the different contributions of phonon modes in these materials. We study the effect of nanostructuring using both the diffusive boundary scattering and confined mean free path limit and discuss the variations in the results. Furthermore, we show the strong influence of isotope scattering on the thermal conductivity. The calculated thermal conductivity is found to be strongly dependent on the volume and we explain the observed differences between local density and generalized gradient approximation calculations. We compare further calculated thermal properties, such as the thermal expansion coefficient, to experiment to validate our approach.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Picosecond ultrasonic study of surface acoustic waves on titanium nitride nanostructures

We have measured surface acoustic waves on nanostructured TiN wires overlaid on multiple thin films on a silicon substrate using the ultrafast pump-probe technique known as picosecond ultrasonics. We find a prominent oscillation in the range of 11–54 GHz for samples with varying pitch ranging from 420 nm down to 168 nm. We find that the observed oscillation increases monotonically in frequency with decrease in pitch, but that the increase is not linear. By comparing our data to two-dimensional mechanical simulations of the nanostructures, we find that the type of surface oscillation to which we are sensitive changes depending on the pitch of the sample. Surface waves on substrates that are loaded by thin films can take multiple forms, including Rayleigh-like waves, Sezawa waves, and radiative (leaky) surface waves. We describe evidence for detection of modes that display characteristics of these three surface wave types.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Electrodeposition of Zn based nanostructure thin films for photovoltaic applications

We present here a systematic study on the synthesis thin films of various ZnO, CdO, Zn{sub x}Cd{sub 1-x} (O) and ZnTe nanostructures by electrodeposition technique with ZnCl{sub 2,} CdCl{sub 2} and ZnSO{sub 4} solution as starting reactant. Several reaction parameters were examined to develop an optimal procedure for controlling the size, shape, and surface morphology of the nanostructure. The results showed that the morphology of the products can be carefully controlled through adjusting the concentration of the electrolyte. The products present well shaped Nanorods arrays at specific concentration and temperature. UV-VIS spectroscopy and X-ray diffraction results show that the product presents good crystallinity. A possible formation process has been proposed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

pH effect on structural and optical properties of nanostructured zinc oxide thin films

ZnO nanostructures were Deposited on Objekttrager glasses for various pH values by chemical bath deposition method using Zn (NO3)2·6H2O (zinc nitrate hexahydrate) solution at 75°C reaction temperature without any posterior treatments. The ZnO nanostructures obtained were characterized by X-ray Diffraction (XRD, UV). The structure was hexagonal and it was found that some peaks disappear with various pH values. The grain sizes of ZnO films increases from 22-to-29nm with increasing pH. The transmission of the films was (85-95%)

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Toxicity evaluation of ZnO nanostructures on L929 fibroblast cell line using MTS assay

ZnO has wide applications in medical and dentistry apart from being used as optoelectronic devices such as solar cells, photodetectors, sensors and light emitting diodes (LEDs). Therefore, the toxicity evaluation is important to know the toxicity level on normal cell line. The toxicity of two grades ZnO nanostructures, ZnO-4 and ZnO-8 have been carried out using cytotoxicity test of MTS assay on L929 rat fibroblast cell line. Prior to that, ZnO-4 and ZnO-8 were characterized for its morphology, structure and optical properties using FESEM, X-ray diffraction, and Photoluminescence respectively. The two groups revealed difference in morphology and exhibit slightly shifted of near band edge emission of Photoluminescence other than having a similar calculated crystallite size of nanostructures. The viability of cells after 72h were obtained and the statistical significance value was calculated using SPSS v20. The p value is more than 0.05 between untreated and treated cell with ZnO. This insignificant value of p>0.05 can be summarized as a non-toxic level of ZnO-4 and ZnO-8 on the L929 cell line.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Multiferroic properties of Pb{sub 0.90}Sr{sub 0.10}TiO{sub 3}-CoFe{sub 2}O{sub 4} nanostructured bilayered thin film

Pb{sub 0.90}Sr{sub 0.10}TiO{sub 3}-CoFe{sub 2}O{sub 4}(PST10-CFO) nanostructured bilayered thin film were grown on Si (100) substrate by using metallo-organic decomposition chemical route and spin coating technique. Results show that PST (pervoskite structure) and CFO (spinel) phase coexist in the bilayered thin films, annealed at 650°C for 2hr and no obvious impurity phase can be detected. The structural, surface morphology and micro structural properties were confirmed by X-Ray diffraction (XRD), atomic force microscope (AFM) respectively. Excellent ferroelectric behavior at different voltage was observed, with two platinum electrodes only at surface of the bilayer thin film. A room temperature ferromagnetic behavior was observed in the bilayered Pb{sub 0.90}Sr{sub 0.10}TiO{sub 3}-CoFe{sub 2}O{sub 4} nanostructured thin film. The saturation magnetization and variation in coercivity value of the bilayer thin film is lower than that of the pure CFO film in the presence of non ferromagnetic PST layer which is the attributed that the significant coupling between the two phases.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Characteristics of titanium dioxide nanostructures synthesized via electrochemical anodization at different applied voltages

This paper presents the study of the growth of nanostructure titanium dioxide (TiO{sub 2}) via electrochemical anodization method. Both constant and alternating anodization voltage would be applied in this study. The effects of applied voltage on the morphological and structural properties were studied. Images of field emission scanning electron microscope (FE-SEM) revealed that morphology of nanostructure could be manipulated by changing the type and amount of applied voltage. Besides that, X-ray diffraction (XRD) results indicated that crystalline structures (anatase and rutile) could be obtained after being annealed at 700°C for 60 minutes. By analysing the data in XRD measurements, crystallite size of the TiO{sub 2} could be calculated by using the Scherrer method. Besides that, the relationship between mean crystallites sizes and anodization voltage would also be further studied in this paper.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Nanostructure investigation of magnetic nanomaterial Ni{sub 0.5}Zn{sub 0.3}Cu{sub 0.2}Fe{sub 2}O{sub 4} synthesized by sol-gel method

Magnetic nanomaterial Ni{sub 0.5}Zn{sub 0.3}Cu{sub 0.2}Fe{sub 2}O{sub 4} was successfully prepared by using sol-gel method. Heat treatment on material is always giving defect on properties of material. This paper investigates the effect of heat treatment on nanostructure of magnetic nanomaterial Ni{sub 0.5}Zn{sub 0.3}Cu{sub 0.2}Fe{sub 2}O{sub 4}. According to thermo gravimetric analysis (TGA) that after 600°C there is no more weight loss detected and it was decided as minimum calcination temperature. Intensity, crystallite size, structure, lattice parameter and d-spacing of the material were investigated by using X-ray diffraction (XRD). High resolution transmission electron microscope (HRTEM) was used to examine nanostructure, nanosize, shape and distribution particle of magnetic material Ni{sub 0.5}Zn{sub 0.3}Cu{sub 0.2}Fe{sub 2}O{sub 4} and variable pressure field emission scanning electron microscope (VP-FESEM) was used to investigate the surface morphology and topography of the material. The XRD result shows single-phase cubic spinel structure with average crystallite size in the range of 25.6-95.9 nm, the value of the intensity of the material was increased with increasing temperature, and followed by lattice parameter was increased with increasing calcination temperature, value of d-spacing was relatively decreased with accompanied increasing temperature. From HRTEM result the distribution of particles was tend to be agglomerates with particle size of 7.8-17.68 nm. VP-FESEM result shows that grain size of the material increases with increasing calcination temperature and the surface morphology shows that the material is in hexagonal shape and it was also proved by mapping result which showing the presence each of constituents inside the compound.

77 NANOSCIENCE AND NANOTECHNOLOGY↗