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Results for “Nanostructured multilayers”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Multilayer Noninteracting Dielectric Metasurfaces for Multiwavelength Metaoptics

Metasurfaces provide a versatile platform for manipulating the wavefront of light using planar nanostructured surfaces. Transmissive metasurfaces, with full 2π phase control, are a particularly attractive platform for replacing conventional optical elements due to their small footprint and broad functionality. However, the operational bandwidth of metasurfaces has been a critical limitation and is directly connected to either their resonant response or the diffractive dispersion of their lattice. While multiwavelength and continuous band operation have been demonstrated, the elements suffer from either low efficiency, reduced imaging quality, or limited element size. We propose a platform that provides for multiwavelength operation by employing tightly spaced multilayer dielectric metasurfaces. As a proof of concept, we demonstrate a multiwavelength metalens doublet (NA = 0.42) with focusing efficiencies of 38% and 52% at wavelengths of 1180 and 1680 nm, respectively. We further show how this approach can be extended to three-wavelength metalenses as well as a spectral splitter. This approach could find applications in fluorescent microscopy, digital imaging, and color routing.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Optimization of La 2–x Sr x CuO 4 Single Crystal Film Growth via Molecular Beam Epitaxy

Atomic layer-by-layer molecular beam epitaxy (ALL-MBE) combined with ozone is one of the best methods to fabricate single-crystal thin films of complex oxides. Cuprate such as La 2-x Sr x CuO 4 (LSCO) is a representative complex-oxide high-temperature superconductor (HTS) material. Our group utilizes this method to produce high-quality single-crystal HTS films with atomically smooth surfaces and interfaces. In addition, ALL-MBE enables us to engineer multilayer heterostructures with atomic precision. This allows the fabrication of tunnel junctions, various nanostructures, and other HTS devices of interest for superconducting electronics. We have synthesized over three thousand LSCO thin films in the past two decades. These films’ structural and electronic properties have been studied and characterized by various methods. Here, we distill the extensive experience we accumulated into a step-by-step protocol to fabricate atomically perfect LSCO films. The recipe includes substrate preparation, ozone generation and distillation, source calibration, the in situ monitoring of the film synthesis, post-growth annealing, and ex situ characterization. It discloses a reproducible way to fabricate single-crystal LSCO films for basic research and HTS electronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Optical and Structural Properties of Ag and c-Si Nanostructures Formed During the Metal-Assisted Chemical Etching of Silicon

This study consisting of two parts is concerned with the features of the three-stage process of the metal-assisted chemical etching (MACE) of silicon. This process is used to fabricate silicon nanostructures. In the first part of this work, a layer of self-assembled Ag nanoparticles chemically deposited from a solution on the surface of single-crystal silicon (c-Si) (MACE stage 1) was studied, and the second part includes of investigation of Si nanostructures formed in stages 2 and 3. By means of spectroscopic ellipsometry (in the range of wavelengths λ = 250–900 nm), the pseudodielectric functions of the nanostructures were determined and compared for all the three stages of the MACE process. In addition, for the Si nanostructures, the parameters of layers (the thickness and void fraction) were calculated in the context of the multilayer optical model, with the use of Bruggeman’s effective-medium approximation and fitting procedures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

An Artificial Neural Network Model to Predict the Bainite Plate Thickness of Nanostructured Bainitic Steels Using an Efficient Network-Learning Algorithm

Nanostructured bainitic steel has an extraordinary ultrahigh strength of about 2.0 GPa along with good toughness of 30 MPa m{sup 1/2}. The finer thickness of plate 20-80 nm is largely responsible for achieving such a large hardness of 690-720 HV. In this work, a multilayer perceptron-based artificial neural network (ANN) model has been developed to predict the thickness of bainite plate pertaining to nanostructured bainitic steels. The inputs of the ANN model are, namely, Gibbs free energy for bainitic transformation, austenite strength, transformation temperature for bainite and carbon concentration in the steel. The model prediction revealed that the bainite plate thickness critically depends on austenite strength and Gibbs free energy. From the neural prediction, it is concluded that formation of nanostructured bainitic steel is feasible only if sufficient austenite strength (above 165 MPa) has been achieved. This can be accomplished with a minimum carbon content of 0.5 wt.% in steel and transformation temperature below 300 °C. Higher driving force (Gibbs free energy) below − 1800 J/mol is another prerequisite condition of formation of nanostructured bainite steel. The network-learning architecture has been optimized using the Broyden–Fletcher–Goldfarb–Shanno (BFGS) algorithm to minimize the network training error within eight training cycles. The algorithm facilitates a faster convergence of network training and testing errors.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Photoluminescence of Gallium Phosphide-Based Nanostructures with Germanium Quantum Dots, Grown by Liquid-Phase Epitaxy

We have used liquid-phase epitaxy with pulsed substrate cooling using two structural designs to grow samples of nanoheteroepitaxial structures with Ge quantum dots in a GaP matrix on Si substrates. We have measured the photoluminescence spectra of the samples at temperatures of 77 K and 300 K with excitation by laser emission at λ = 4880 Å and 5145 Å. We draw conclusions concerning the factors influencing the spectrum and intensity of emission for nanostructures with quantum dots. It was found that in order to reduce nonradiative recombination in multilayer p–n structures, we need to create quantum dot arrays inside p and n regions rather than in the central portion of the depletion layer of the p–n junction. We show that the theoretical energies for Ge quantum dots of the calculated sizes are comparable with the energies of their photoluminescence maxima.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

3D Hybrid Plasmonic Framework with Au Nanopillars Embedded in Nitride Multilayers Integrated on Si

Integration of nanoscale photonic and plasmonic components on Si substrates is a critical step toward Si-based integrated nanophotonic devices. Herein, a set of unique complex 3D metamaterials with intercalated nanolayered and nanopillar structures with tunable plasmonic and optical properties on Si substrates is designed. More specifically, the 3D metamaterials combine metal (Au) nanopillars and alternating metal-nitride (Au-TiN and Au-TaN) nanolayers, epitaxially grown on Si substrates. The ultrafine Au nanopillars ( d ≈ 3 nm) continuously grow throughout all the nanolayers with high epitaxial quality. Novel optical properties, such as highly anisotropic optical property, high absorbance covering the entire visible spectrum regime, and hyperbolic property in the visible regime, are demonstrated. Furthermore, a waveguide based on a silicon nitride (Si 3 N 4 ) ridge with a multilayer structure is successfully fabricated. The demonstration of 3D nanoscale metamaterial design integrated on Si opens up a new route toward tunable metamaterials nanostructure designs with versatile material selection for various optical components in Si integrated photonics.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Enhanced Hybridization and Nanopatterning via Heated Liquid-Phase Infiltration into Self-Assembled Block Copolymer Thin Films

Organic–inorganic hybrids featuring tunable material properties can be readily generated by applying vapor- or liquid-phase infiltration (VPI or LPI) of inorganic materials into organic templates, with resulting properties controlled by type and quantity of infiltrated inorganics. While LPI offers more diverse choices of infiltratable elements, it tends to yield smaller infiltration amount than VPI, but the attempt to address the issue has been rarely reported. Here in this paper, we demonstrate a facile temperature-enhanced LPI method to control and drastically increase the quantity and kinetics of Pt infiltration into self-assembled polystyrene-block-poly(2-vinylpyridine) block copolymer (BCP) thin films. By applying LPI at mildly elevated temperatures (40–80 °C), we showcase controllable optical functionality of hybrid BCP films along with conductive three-dimensional (3D) inorganic nanostructures. Structural analysis reveals enhanced metal loading into the BCP matrix at higher LPI temperatures, suggesting multiple metal ion infiltration per monomer of P2VP. Combining temperature-enhanced LPI with hierarchical multilayer BCP self-assembly, we generate BCP-metal hybrid optical coatings featuring tunable antireflective properties as well as scalable conductive 3D Pt nanomesh structures. Enhanced material infiltration and control by temperature-enhanced LPI not only enables tunability of organic–inorganic hybrid nanostructures and properties but also expands the application of BCPs for generating uniquely functional inorganic nanostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Estimates of Equivalent Heat Conductivity Coefficients of Carbon Nanotubes

We have obtained estimates of equivalent heat conductivity coefficients of nanostructured elements on the basis of the constructed mathematical model of the thermal energy transfer in a single-layer and a multilayer nanotube surrounded by a homogeneous material in the composite matrix. The values of such coefficients permit conditional replacement of nanotubes by solid anisotropic fibers, which makes it possible, in predicting the effective heat conductivity coefficient of a composite modified by carbon nanotubes, to use the known methods developed in detail to fit fibrous composites.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Three-dimensional modeling of electric-field enhancement in multilayer dielectric gratings arising from inadvertent flaws

Pulse-compression gratings for high-power, short-pulse laser systems are exposed to high electric fields that are further enhanced locally due to their 2D nanostructured surface. This makes them vulnerable to laser-induced damage. The present work considers the effect on electric-field modulation caused by an array of commonly found inadvertent flaws in gratings including fabrication defects, contamination particles, and laser-induced–damage initiation. These defects affect the laser-damage performance characteristics of the grating. To understand the local field-enhancement distribution due these imperfections, 3D modeling of the electric-field distribution is performed with a sufficiently high resolution of 1/74 of the laser wavelength ( λ ) while considering a volume of ≈489 λ 3 . The results provide estimates for the ensuing electric-field intensification and projected reduction of the laser-damage thresholds, as well as the anticipated pattern of damage growth initiation.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Sequential Infiltration Synthesis of Bilayer Porous Alumina Nanostructures for Broad-Angle, Broadband Antireflective Coatings

Antireflective coatings (ARCs) are thin films engineered to reduce light reflections. Delivering broadband, wide-angle performance is essential for photovoltaics, imaging, and sensing, yet truly omnidirectional antireflection remains difficult due to angle-dependent optical paths and a narrow palette of suitable refractive indices. Here, in this study, we systematically investigate an emerging class of multilayer inorganic ARCs based on conformally coated nanoporous alumina templated by intrinsically microporous polymers (PIMs) and block copolymers (BCPs). We establish a design framework that maps thickness reflectance relationships to identify thickness pairs minimizing reflection across wavelength and incidence angle. We show that deliberately separating the local reflectance minima of the top and bottom layers in bilayer nanostructures broadens the antireflective bandwidth and angular range. We show that 235-nm single-side bilayer porous alumina nanostructures achieves under 2 % reflectance from 380–750 nm for incidence angles up to 45° with less than 0.6% reflectance for incidence angles under 20°. The approach is readily extensible to additional layers or materials with refractive indices tuned via templated nanoporosity and composition, enabling practical, etch-free ARC fabrication without HF or fluorinated precursors and advancing straightforward design of broadband, wide-angle (quasi-omnidirectional) ARCs for next-generation optical systems.

antireflective coatings↗
DOE OSTI2025

Curvature Induced Modifications of Chirality and Magnetic Configuration in Perpendicular Films

Designing curvature in three-dimensional (3D) magnetic nanostructures enables controlled manipulation of local energy landscapes, allowing for the modification of noncollinear spin textures relevant for next-generation spintronic devices. In this study, we experimentally investigate 3D magnetization textures in a Co/Pd multilayer film, exhibiting strong perpendicular magnetic anisotropy (PMA), deposited onto curved Cu nanowire meshes with diameters as small as 50 nm and lengths of several microns. Utilizing magnetic soft X-ray nanotomography, we achieve reconstructions of 3D magnetic domain patterns at approximately 30 nm spatial resolution. This approach provides detailed information on both the orientation and magnitude of magnetization within the film. Our results reveal that interfacial anisotropy in the Co/Pd multilayers drives the magnetization toward the local surface normal. In contrast to typical labyrinth domains observed in planar films, the presence of curved nanowires significantly alters the domain structure, with domains preferentially aligning along the nanowire axis in close proximity, while adopting random orientations farther away. We report direct experimental observation of a curvature-induced Dzyaloshinskii-Moriya interaction (DMI), which is quantified to be approximately one-third of the intrinsic DMI in Co/Pd stacks. The curvature induced DMI enhances stability of Néel-type domain walls. These experimental observations are further supported by micromagnetic simulations. Altogether, our findings demonstrate that introducing curvature into magnetic nanostructures provides a powerful strategy for tailoring complex magnetic behaviors, paving the way for the design of advanced 3D racetrack memory and neuromorphic computing devices.

Raftrey, David↗
DOE OSTI2020

Design of 3D Oxide–Metal Hybrid Metamaterial for Tailorable Light–Matter Interactions in Visible and Near-Infrared Region

Dielectric–metallic hybrid metamaterials exhibit extraordinary optical properties due to the light–matter interactions at the dielectric–metallic interfaces. The ability in precision control of the light–matter interactions in nanoscale is key to tailor the optical properties of hybrid metamaterials. In this work, a complex 3D framework of multilayered self-assembled BaTiO 3 (BTO)-Au hybrid thin films is demonstrated with such precision control of the light–matter interaction in nanoscale. Here, unique “bamboo-like” Au nanostructures are formed via the bilayer and trilayer stacking of BTO-Au hybrid layers with interlayers of SrTiO 3 , CeO 2 , or MgO. Different film strain states introduced by the three interlayers result in variable diameter and density of Au nanopillars. Both simulated and experimental optical data demonstrate the localized surface plasmon resonance change and hyperbolic dispersion wavelength shift in visible to near-infrared because of the effective tuning of the Au nanopillar aspect ratio and free electron density. The highly tunable optical properties along with the ferroelectric behavior and thermal robustness of the 3D hybrid film enable it to be a great candidate for multifunctional applications. This study demonstrates a unique 3D approach for precision optical property tuning and combined functionalities in oxide–metal metamaterial systems toward future integrated photonic and electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Poloidal and toroidal plasmons and fields of multilayer nanorings

Composite and janus type metallodielectric nanoparticles are increasingly considered as a means to control the spatial and temporal behavior of electromagnetic fields in diverse applications such as coupling to quantum emitters, achieving invisibility cloaks, and obtaining quantum correlations between qubits. We investigate the surface modes of a toroidal nanostructure and obtain the canonical plasmon dispersion relations and resonance modes for arbitrarily layered nanorings. Unlike particle plasmon eigenmodes in other geometries, the amplitudes of the eigenmodes of tori exhibit a distinct forward and backward coupling. We present the plasmon dispersion relations for several relevant toroidal configurations in the quasistatic limit and obtain the dominant retarded dispersion relations of a single ring for comparison, discuss mode complementarity and hybridization, and introduce two new types of toroidal particles in the form of janus nanorings. The resonance frequencies for the first few dominant modes of a ring composed of plasmon supporting materials such as gold, silver, and aluminum are provided and compared to those for a silicon ring. A generalized Green's function is obtained for multilayer tori allowing for calculation of the scattering response to interacting fields. Employing the Green's function, the scalar electric potential distribution corresponding to individual poloidal and toroidal modes in response to an arbitrarily polarized external field and the field of electrons is obtained. The results are applied to obtain the local density of states and decay rate of a dipole near the center of the torus.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Exploring phase transitions and magnetoelectric coupling of epitaxial asymmetric multilayer heterostructures

Magnetoelectric (ME) heterostructures can exhibit higher magnetic and ferroelectric ordering temperatures along with large ME coupling compared to single-phase multiferroic materials. We synthesized Pb(Fe 0.5 Nb 0.5 )O 3 (PFN)/Ni 0.65 Zn 0.35 Fe 2 O 4 (NZFO)/Pb(Fe 0.5 Nb 0.5 )O 3 (PFN)/Ni 0.65 Zn 0.35 Fe 2 O 4 (NZFO)/Pb(Fe 0.5 Nb 0.5 )O 3 (PFN) multilayer heterostructures having dimensions of 40/10/40/10/40 nm. High quality epitaxial growth of these heterostructures was confirmed via X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns. These nanostructures show well saturated polarization (~52 μC cm -2 ) and magnetization (~62 emu cm -3 ) at room temperature (RT). The magnetic and ferroelectric transitions occur well above RT. These heterostructures exhibit relaxor behavior and undergo 2nd order ferroelectric phase transition. Magnetodielectric measurements show significant coupling between the magnetic and electrical order parameters at RT. These characteristics of the heterostructures make them suitable as potential candidates for ultra-low power memory, spintronics, and different multifunctional (micro)nanoscale device applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Properties of ZnSe/Al{sub 2}O{sub 3} Nanostructures Obtained by RF Magnetron Sputtering

Experimental data for the synthesis of ZnSe/Al{sub 2}O{sub 3} nanostructures utilizing a technology widely used in integrated circuit (IC) production are reported. It has been shown that the refractive index and size of the coherent scattering domains grow, whereas the energy bandgap decreases, with an increase in ZnSe width. It has been supposed that samples with a ZnSe width of 9 Å contain a ZnSeO{sub 3} compound and/or ZnSe ⋅ Al{sub 2}O{sub 3} complex compound. Multilayer heterostructures with a ZnSe width more than 9 Å contain cubic ZnSe nanocrystallites.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Spectral Performance of Multilayer Amorphous Selenium and Selenium–Tellurium Photodetectors

The ability to robustly and with scalability detect single photons in the visible spectrum with wavelength resolution would transform many imaging applications. Theoretical studies propose an array of carbon nanotubes (CNTs) functionalized with semiconductor quantum dots (QDs) as a physical realization of such photon sensors. In this work, we report approaches to synthesize these CNT-QD nanostructures using DNA as a smart glue to connect CNTs to QDs.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Chemically-Controlled Stacking of Inorganic Subnets in Coordination Networks: Metal–Organic Magnetic Multilayers

Coordination networks (CNs), such as, for instance, metal–organic frameworks (MOFs), can turn into remarkable magnets, with various topologies of spin carriers and unique opportunities of cross-coupling to other functionalities. Alternatively, distinct inorganic subnetworks that are spatially segregated by organic ligands can lead to coexisting magnetic systems in a single bulk material. Here, we present a system of two CNs of general formula Mn(H 2 O) x (OOC-(C 6 H 4 ) y -COO). The compound with two water molecules and one aromatic ring (x = 2; y = 1) has a single two-dimensional magnetic subnet, while the material with x = 1.5 and y = 2 shows, additionally, another type of magnetic layer. In analogy to magnetic multilayers that are deposited by physical methods, these materials can be regarded as metal–organic magnetic multilayers (MOMMs), where the stacking of different types of magnetic layers is controlled by the choice of an organic ligand during the chemical synthesis. Lastly, this work further paves the way toward organic–inorganic nanostructures with functional magnetic properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

In situ indentation and high cycle tapping deformation responses in a nanolaminate crystalline/amorphous metal composite

The incorporation of nanostructured and amorphous metals into modern applications is reliant on the understanding of deformation and failure modes in constrained conditions. To study this, a 105 nm crystalline Cu/160 nm amorphous Cu 45 Zr 55 (at.%) multilayer structure was fabricated with the two crystalline layers sputter deposited between the top-middle-bottom amorphous layers and prepared to electron transparency. The multilayer was then in situ indented either under a single load to a depth of ~ 100 nm (max load of ~ 100 μN) or held at 20 μN and then repeatedly indented with an additional 5 μN up to 20,000 cycles in a transmission electron microscope to compare the deformation responses in the nanolaminate. For the single indentation test, the multilayer showed serrated load-displacement behavior upon initial indentation inductive of shear banding. Additionally, at an indentation depth of ~ 32 nm, the multilayer exhibited perfect plastic behavior and no strain hardening. Both indented and fatigue-indented films revealed diffraction contrast changes with deformation. Subsequent Automated Crystal Orientation Mapping (ACOM) measurements confirmed and quantified global texture changes in the crystalline layers with specifically identified grains revealing rotation. Using a finite element model, the in-plane displacement vectors under the indent mapped conditions where ACOM determined grain rotation was observed, indicating the stress flow induced grain rotation. Furthermore, the single indented Cu layers also exhibited evidence of deformation induced grain growth, which was not evident in the fatigue-indented Cu based multilayer. Finally, the single indented multilayer retained a significant plastic crater in the upper most amorphous layer that directly contacted the indenter; a negligible crater impression in the same region was observed in the fatigued tested multilayer. These differences are explained by the different loading methods, applied load, and deformation mechanisms experienced in the multilayers.

36 MATERIALS SCIENCE↗