Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “nanostructures”

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 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Control of SPP propagation and focusing through scattering from nanostructures

Measuring the characteristics of radiation scattered by surface plasmon polariton waves and detecting them in the far field is the only efficient method for studying the directivity of propagation, wave vector magnitude, and propagation length of such waves. In the present work, we demonstrate that it is possible to control the properties of surface plasmon polaritons propagating along the surface of metal nanofilms by scattering from nanoobjects, namely, nanogrooves and nanopits, formed in the nanofilms. It is shown that this technique allows the main parameters of surface plasmon polaritons to be measured. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Sub-10 nm patterning with DNA nanostructures: a short perspective

DNA is the hereditary material that contains our unique genetic code. Since the first demonstration of two-dimensional (2D) nanopatterns by using designed DNA origami ~10 years ago, DNA has evolved into a novel technique for 2D and 3D nanopatterning. It is now being used as a template for the creation of sub-10 nm structures via either 'top-down' or 'bottom-up' approaches for various applications spanning from nanoelectronics, plasmonic sensing, and nanophotonics. This paper starts with an histroric overview and discusses the current state-of-the-art in DNA nanolithography. Finally, emphasis is put on the challenges and prospects of DNA nanolithography as the next generation nanomanufacturing technique.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2026

Dynamic evolution of ultracold electron beams from nanostructured cathodes

Dynamic Coulomb expansion of dense, nonuniform particle beamlets can lead to causticlike formations in the charge density profile of the resultant beam. Such features only occur for cold beams where thermal diffusion of the particles is minimized. These phenomena have been observed experimentally for select cases with ion beams but not yet for electron beams as the electron dynamics occur over far faster timescales. We simulate the interaction of electron bunches while varying the initial transverse temperature and density profiles to determine the thresholds that characterize this pattern formation. Furthermore, we extend the simulations to geometric arrangements that are more pertinent to the nanotip cathode application and consider the effects of asymmetries and the impact of a low-density halo on the overall process. The simulations are conducted using a previously documented high-fidelity algorithm for collisional particle dynamics. These studies identify the temperature and density thresholds required for caustic formation and provide guidance for optimizing the design of nanoscale structured cathodes. We also demonstrate that the correlation between the final density patterns and the underlying beam parameters enables a virtual diagnostic tool for measuring ultralow emittance beams solely based on a transverse charge density profile.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Nanostructures of Liquid Crystal Phases in Mixtures of Bent-core and Rod-shaped Molecules

We report small angle x-ray scattering (SAXS) studies of isotropic, nematic, and smectic mesophases formed by binary mixtures of bent-core (BC) and rod-shaped (RS) molecules. While optical studies indicate that the components are fully miscible, SAXS reveals fascinating structures that are consistent with segregation on a nanoscopic scale. We find that tilted smectic clusters, which have been previously reported in both the nematic and isotropic states of the pure BC materials, are also present in mixtures with up to 50 wt% of the RS compound; this is consistent with previous dielectric and flexoelectric studies on such mixtures. Unexpectedly in this concentration range the clusters are present in the isotropic and in the induced smectic phase range, as well as throughout the nematic phase. The results in the smectic phase also reveal complex layering phenomena, providing important insight into the interaction between bent and rod-shaped molecules. These studies will be crucial in the design of promising new functional nanomaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2015

DShaper: An approach for handling missing low-Q data in pair distribution function analysis of nanostructured systems

In this work we discuss the potential problems and currently available solutions in modeling powder-diffraction based pair-distribution function (PDF) data from systems where morphological feature information content includes distances in the nanometer length scale, such as finite nanoparticles, nanoporous networks, and nanoscale precipitates in bulk materials. The implications of an experimental finite minimum Q-value are addressed by simulation, which also demonstrates the advantages of combining PDF data with small angle scattering data (SAS). In addition, we introduce a simple Fortran90 code, DShaper , which may be incorporated into PDF data fitting routines in order to approximate the so-called shape-function for any atomistic model.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Co-Pt core-shell nanostructured catalyst prepared by selective chemical vapor pulse deposition of Pt on Co as a cathode in polymer electrolyte fuel cells

A new type of PtCo/C catalyst for use as a cathode in polymer electrolyte fuel cells was prepared by selective chemical vapor pulse deposition (CVPD) of Pt on the surface of Co. The activity of the prepared catalyst for oxygen reduction was higher than that of a catalyst prepared by sequential impregnation (IMP) with the two metallic components. This catalytic activity difference occurs because the former catalyst has smaller Pt crystallites that produce stronger Pt-Co interactions and have a larger Pt surface area. Consequently, the CVPD catalyst has a great number of Co particles that are in close contact with the added Pt. The Pt surface was also electronically modified by interactions with Co, which were stronger in the CVPD catalyst than in the IMP catalyst, as indicated by X-ray diffraction, X-ray photoemission spectroscopy, and cyclic voltammetry measurements of the catalysts.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Ascorbic Acid Additions on the Mechanism Underlying the Growth of Nanostructured PbSe Films via Hydrochemical Deposition

The effect of ascorbic acid additions on the growth mechanism of thin PbSe films produced by hydrochemical deposition has been studied by atomic force microscopy (AFM). A fractal analysis of AFM images of the lead selenide films has shown that their formation follows the “cluster–particle” aggregation mechanism. The fractal dimension assessed by the box-counting method is 2.26 at an average grain size of ~150 nm. From the transmission spectra of the films grown at deposition times from 20 to 120 min, we have evaluated their optical band gap, which has been shown to decrease from 0.595 to 0.53 eV with increasing deposition time. These values are attributable to the manifestation of quantum size effects in the grown PbSe films.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Nanostructured crystals of Sr{sub 1-x}R{sub x}F{sub 2+x} fluorite phases and their ordering: 6. Microindentation analysis of crystals

Hardness, crack resistance, brittleness, and effective fracture energy have been studied for crystals of 24 fluorite phases Sr{sub 1-x}R{sub x}F{sub 2+x} (R are 14 rare earth elements (REEs); 0 < x {<=} 0.5) and SrF2 grown by the Bridgman method from a melt. These characteristics change nonlinearly with an increase in the REE content for Sr{sub 1-x}R{sub x}F{sub 2+x} (0 < x {<=} 0.5) with R = La, Nd, Sm, Gd, and Lu; it is maximum in the range x < 0.1 for all REEs. The changes in a number of REEs have been traced for an isoconcentration series of Sr{sub 0.90}R{sub 0.10}F{sub 2.10} crystals (R = La, Nd, Sm, Gd, Ho, Er-Lu, or Y) and crystals (similar in composition) with R = Tb and Dy. The hardness of Sr{sub 1-x}R{sub x}F{sub 2+x} crystals is higher by a factor of {approx}2-3 than that of SrF2. The effect of decrease in microstresses in SrF{sub 2} crystals is confirmed by the isomorphic introduction of R{sup 3+} ions into this crystalline matrix.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Nanostructured crystals of fluorite phases Sr{sub 1-x}R{sub x}F{sub 2+x} and their ordering: 7. A procedure for cluster modeling of Sr{sub 1-x}R{sub x}F{sub 2+x} Based on the Structure of an Ordered Phase (R = Lu)

Single crystals of the Sr{sub 1-x}Lu{sub x}F{sub 2+x} nonstoichiometric phase (x = 0.095 and 0.189), which crystallizes in the CaF{sub 2} structure type (space group Fm3-barm), are studied by X-ray diffraction. A procedure for the cluster modeling of Sr{sub 1-x}Lu{sub x}F{sub 2+x} based on the fine structural features of the Sr{sub 4}Lu{sub 3}F{sub 17} stoichiometric compound with a fluorite derivative structure (one of the ordered phases in the SrF{sub 2}-LuF{sub 3} system) is proposed. The description of the structure of the Sr{sub 1-x}Lu{sub x}F{sub 2+x} solid solutions is based on the octacubic configuration of the {l_brace}M{sub 14-n}R{sub n}F{sub 64+n}{r_brace} defect cluster. Structural data on the displacements of cations and anions in the ordered Sr{sub 4}Lu{sub 3}F{sub 17} phase (in relation to the undistorted fluorite phase) allow one to identify the distortions of the crystal lattice of the disordered (nonstoichiometric) Sr{sub 1-x}Lu{sub x}F{sub 2+x} phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Ordered gold nanostructures on sapphire surfaces: Fabrication and optical investigations

The possibilities of obtaining ordered gold nanoarrays on sapphire surfaces with oriented nanorelief are demonstrated. The structures are morphologically described using atomic force microscopy data. A study of the angular dependence of the reflectivity in the visible range of electromagnetic waves has revealed some features which are likely to indicate surface plasmon-polariton excitation at the air-gold interface under exposure to p-polarized radiation. The experimental results are found to be in good agreement with the theoretical calculations.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Construction of fractal nanostructures based on Kepler-Shubnikov nets

A system of information codes for deterministic fractal lattices and sets of multifractal curves is proposed. An iterative modular design was used to obtain a series of deterministic fractal lattices with generators in the form of fragments of 2D structures and a series of multifractal curves (based on some Kepler-Shubnikov nets) having Cantor set properties. The main characteristics of fractal structures and their lacunar spectra are determined. A hierarchical principle is formulated for modules of regular fractal structures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Nanostructured crystals of fluorite phases Sr{sub 1−x}R{sub x}F{sub 2+x} and their ordering: VIII. Imperfect crystal structure of Sr{sub 0.71}Ce{sub 0.29}F{sub 2.29}

A congruently melting single crystal of nonstoichiometric phase Sr{sub 0.71}Ce{sub 0.29}F{sub 2.29} crystallizing into the CaF{sub 2} structural type (sp. gr Fm<##> } } 3 }&#x00AF;<!-- ?? --> $ /bar 3 $ 3-bar </##>m) has been studied by X-ray diffraction analysis. Vacancies in the main fluorine position 8c and interstitial anions in two 32f positions have been found. The ratio of the structural defects in the Sr{sub 0.71}Ce{sub 0.29}F{sub 2.29} solid solution corresponds to the tetrahedral configuration of the defect cluster {Sr_4_−_nCe_nF_2_6}.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Nanostructured crystals of fluorite phases Sr{sub 1−x}R{sub x}F{sub 2+x} (R Are Rare Earth Elements) and their ordering: 10. Ordering under spontaneous crystallization and annealing of Sr{sub 1−x}R{sub x}F{sub 2+x} Alloys (R = Tb-Lu, Y) with 23.8–36.1 mol % RF{sub 3}

The products of spontaneous crystallization (at a cooling rate of ∼200 K/min) of Sr{sub 1−x}R{sub x}F{sub 2+x} melts in the homogeneity range of the fluorite phase have been investigated. Thirty-two irrational compositions with 23.8–36.1 mol % RF{sub 3} and eight rational Sr{sub 2}RF{sub 7} compositions are obtained. With respect to the RF{sub 3} content, these compositions form five groups: (1) Sr{sub 0.762}R{sub 0.238}F{sub 2.238} (23.8% RF{sub 3}), (2) Sr{sub 0.744}R{sub 0.256}F{sub 2.256} (25.6%), (3) Sr{sub 0.718}R{sub 0.282}F{sub 2.282} (28.2%), (4) Sr{sub 2}RF{sub 7} (33.3%), and (5) Sr{sub 0.639}R{sub 0.361}F{sub 2.361} (36.1%). R = Tb-Lu, Y for all groups. Quenching melts of group 5 with R = Tb, Dy, and Ho leads to the formation of ordered phases with the trigonal distortion of the rhβ-Na{sub 7}Zr{sub 6}F{sub 31} type, while for melts of group 5 with R = Lu, quenching yields a phase of the trigonal rhα′-Sr{sub 4}Lu{sub 3}F{sub 17} type. In group 5 with R = Y, Er, Tm, or Yb and in groups 1–4 with all REEs, fluorite phases are formed. Annealing at 900 ± 20°C for 96 h with subsequent cooling at a rate of ∼200 K/min expands the variety of ordered phases: a phase with a new r type of orthorhombic distortion is formed in group 1 with R = Lu, in group 2 with R = Tm or Lu, and in group 3 with R = Ho-Lu, Y; a t-Sr{sub 2}RF{sub 7} phase with tetragonal distortion is formed in group 4 with R = Tb-Er, Y; and a phase of trigonal rhα′ type is formed in group 5 with R = Y, Yb, or Lu. A fluorite phase arises in group 1 with R = Tb-Lu, Y as a result of quenching and annealing. The tendency to ordering becomes more pronounced with an increase in the RF{sub 3} content and REE atomic number. The annealing conditions do not provide equilibrium or the completely ordered state of all alloys.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Analysis of the applicability of the modified kinematic approximation to describe the off-specular neutron scattering from the surface of micro- and nanostructured objects

The applicability of the modified kinematic approximation to describe the off-specular neutron scattering from interfaces between media is analyzed. It is demonstrated that in some cases one can expect not only a qualitative but also a quantitative agreement between the data and the results of experiments and calculations based on more accurate techniques. Diffuse scattering from rough surfaces and thin films with correlated and noncorrelated roughness of the upper and lower interfaces and the neutron diffraction by stripe magnetic domains and magnetic domains with a random size distribution (magnetic roughness) are considered as examples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Nanostructured Crystals of Fluorite Phases Sr{sub 1–x}R{sub x}F{sub 2+x} and Their Ordering: 12. Influence of Structural Ordering on the Fluorine-Ion Conductivity of Sr{sub 0.667}R{sub 0.333}F{sub 2.333} Alloys (R = Tb or Tm) at Their Annealing

The ionic conductivity of Sr{sub 0.667}R{sub 0.333}F{sub 2.333} alloys (rational Sr{sub 2}RF{sub 7} compositions) in SrF{sub 2}–RF{sub 3} systems (R = Tb or Tm), prepared by spontaneous crystallization, has been investigated for the “as-grown” state and after annealing in CF{sub 4} at 900 ± 20°C for 96 h. As-grown samples of both compositions, prepared by fast (200°C/min) melt crystallization, exhibit partial (nonequilibrium) ordering, which increases from Tb to Tm. Annealing of Sr{sub 0.667}R{sub 0.333}F{sub 2.333} alloys yields strong ordering (equilibrium for the annealing temperatures) of the fluorite structure (CaF{sub 2} type, sp. gr. Fm3̅m, Z = 4) at the formation of t-Sr{sub 2}RF{sub 7} tetragonal compound (sp. gr. I4/m, Z = 30). It is established that ordering of the alloy fluorite structure reduces the fluorine-ion conductivity. After the annealing, the conductivity of Sr{sub 0.667}R{sub 0.333}F{sub 2.333} alloys with the initial (nonequilibrium) ordering stage of t-Sr{sub 2}RF{sub 7} phases with almost complete (equilibrium) ordering decreases by a factor of 3–4.5.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Computer simulation of surface-enhanced Raman scattering in nanostructured metamaterials

The simulation of local field fluctuations and surface-enhanced Raman scattering in percolation systems at the percolation threshold is described. An approximate real-space renormalization group method was used in the simulation. It allows one to radically reduce the computation time compared to an exact calculation and to obtain detailed information about the electromagnetic field. The local fields in real macroscopic systems can be calculated by using this approximation. A computer simulation of the local fields in metal island (percolation) films has been performed by the developed method. The calculation has confirmed the existence of giant local field fluctuations. In turn, the local electric field excites Raman scattering. The local fields of surface-enhanced Raman scattering have been calculated for the first time. The dependence of the Raman scattering enhancement factor on the reference frequency and Stokes shift has been derived. An experimental observation of this dependence could be considered as a confirmation of the electromagnetic nature of the enhancement.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗