Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Multilayer”

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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Anomalous Hall crystals in rhombohedral multilayer graphene. II. General mechanism and a minimal model

Here we propose a minimal "three-patch model"for the anomalous Hall crystal (AHC), a topological electronic state that spontaneously breaks both time-reversal symmetry and continuous translation symmetry. The proposal for this state is inspired by the recently observed integer and fractional quantum Hall states in rhombohedral multilayer graphene at zero magnetic field. There, interaction effects appear to amplify the effects of a weak moiré potential, leading to the formation of stable, isolated Chern bands. It has been further shown that Chern bands are stabilized in mean-field calculations even without a moiré potential, enabling a realization of the AHC state. Our model is built on the dissection of the Brillouin zone into patches centered around high-symmetry points. Within this model, the wave functions at high-symmetry points fully determine the topology and energetics of the state. We extract two quantum geometrical phases of the noninteracting wave functions that control the stability of the topologically nontrivial AHC state. The model predicts that the AHC state wins over the topological trivial Wigner crystal in a wide range of parameters, and agrees very well with the results of full self-consistent Hartree-Fock calculations of the rhombohedral multilayer graphene Hamiltonian.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Glassy dynamics in CuMn thin-film multilayers

Thin-film multilayered spin-glass CuMn/Cu structures exhibit glassy dynamics. The freezing temperature T f was measured for 40 layers of CuMn films of thickness L = 4.5 , 9.0 , and 20.0 nm, sandwiched between nonmagnetic Cu layers of thickness ≈ 60 nm. The Kenning effect, T f ∝ ln L , is shown to follow from power-law dynamics where the correlation length grows from nucleation as ξ ( t , T ) = c 1 a 0 ( t / τ 0 ) c 2 ( T / T g ) , leading to [ ( T f / T g ) c 2 ln ( t co / τ 0 ) ] + ln c 1 = ln ( L / a 0 ) . Here, T g is the bulk spin-glass temperature, c 1 and c 2 are constants determined from the spin-glass dynamics, t co is the time for the correlation length to grow to the film thickness, τ 0 is a characteristic exchange time ≈ ℏ / k B T g , and a 0 is the average Mn-Mn separation. For t ≥ t co , the magnetization dynamics are simple activated, with a single activation energy Δ max ( L ) / k B T g = ( 1 / c 2 ) [ ln ( L / a 0 ) - ln c 1 ] that does not change with time. Values for all these parameters are found for the three values of L explored in these measurements. We find experimentally Δ max ( L ) / k B = 907 , 1246, and 1650 K, respectively, for the three CuMn thin-film multilayer thicknesses, consistent with power-law dynamics. Here, we perform a similar analysis based on the activated dynamics of the droplet model and find a much larger spread for Δ max ( L ) than found experimentally.

36 MATERIALS SCIENCE↗
DOE OSTI2017

X-ray diffraction study of laser-driven solid-state diffusional mixing and new phase formation in Ni-Pt multilayers [X-ray diffraction study of laser-driven solid-state diffusional mixing and new phase formation]

An in situ optical pump and x-ray probe technique has been utilized to study photoinitiated solid-state diffusion in a Ni-Pt multilayer system. Hard x-ray diffraction has been used to follow the systematic growth of the NiPt alloy as a function of laser intensity and total energy deposited. It is observed that new phase growth can be driven in as little as one laser pulse, and that repeated photoexcitation can completely convert the entire multilayer structure into a single metallic alloy. In conclusion, the data suggest that lattice strain relaxation takes place prior to atomic diffusion and the formation of a NiPt alloy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Interface-independent sound speed and thermal conductivity of atomic-layer-deposition-grown amorphous AlN / Al 2 O 3 multilayers with varying oxygen composition

Dielectric amorphous multilayers (AMLs) play a critical role in a wide array of technologies such as optical coatings, nanoelectronics, energy harvesting, and recovery devices. However, despite their wide applications, a robust understanding of the effect of the interplay between chemical and structural disorder on the thermal properties of AMLs is still lacking. Therefore, in this paper, we experimentally and numerically investigate the effects of composition and interface density on the sound speed and thermal conductivity of a series of amorphous aluminum nitride and aluminum oxide multilayers grown via plasma-enhanced atomic layer deposition. To systematically change the composition, the oxygen content of the AMLs is proportionally varied with interface density during growth. We find that the longitudinal sound speed of these AMLs is dictated by the oxygen content instead of the number of interfaces. The thermal conductivity, in contrast, is dictated by both interface density and oxygen content. The interfaces act to decrease the thermal conductivity, whereas the oxygen content increases the thermal conductivity. Due to the competing influence of the interfaces and oxygen content, the thermal conductivity of the AMLs remains nearly constant as a function of interface density. Furthermore, our study provides crucial insights into the effect of the interplay of composition and interfaces on the sound speed and thermal conductivity of AMLs.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Soft Magnetic Multilayered FeSiCrB–Fe$_{x}$N Metallic Glass Composites Fabricated by Spark Plasma Sintering

Novel multilayered FeSiCrB–Fe $_{x}$ N ( x = 2–4) metallic glass composites were fabricated using spark plasma sintering of FeSiCrB amorphous ribbons (Metglas 2605SA3 alloy) and Fe $_{x}$ N ( x = 2–4) powder. Crystalline Fe $_{x}$ N can serve as a high magnetic moment, high electrical resistance binder, and lamination material in the consolidation of amorphous and nanocrystalline ribbons, mitigating eddy currents while boosting magnetic performance and stacking factor in both wound and stacked soft magnetic cores. Stacking factors of nearly 100% can be achieved in an amorphous ribbon/iron nitride composite. FeSiCrB–Fe $_{x}$ N multilayered metallic glass composites prepared by spark plasma sintering have the potential to serve as a next-generation soft magnetic material in power electronics and electrical machines.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Deformation of multilayer flexible electronics subjected to torque

Flexibility is one of remarkable characteristics of flexible electronics. Therefore, the analysis of flexible electronics deformation caused by external torques will help its design. In this work, analytical derivation is conducted for flexible electronics treated as multilayer structures. In experiments, an electric motor under computer control exerts a torque to generate torsion, whose twist angles are obtained by using both optical encoder measurement and theoretical calculation. Comparisons are made between experimental and theoretical results for bare PEN (polyethylene naphthalate) substrates of different sizes, multilayer PET (polyethylene terephthalate) substrates, and ITO (indium tin oxide)-coated PET substrates. Finally, a laser displacement sensor is used to measure the out-of-plane deformation for validating the proposed theoretical model.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Colored hard coatings with AlN–TiN multilayer structures

AlN–TiN multilayer structures can be used to extend the color gamut of hard coatings while maintaining good hardness and corrosion resistance. This study used reactive magnetron sputtering on a glass substrate to produce coatings with a microhardness of 19 GPa as well as optical reflectance exceeding 80% and controllable saturation (chroma) for various hues of red, yellow, green, blue, and purple. The authors characterized the complex index of refraction of the TiN films using ellipsometry; the real refractive indices of the AlN films were derived from the reflectance values obtained using photometry. Finally, the colors of the samples were quantified using CIE-1931 chromaticity coordinates in the L*a*b* color space, and the microhardness of the films was measured using a nanoindenter. Simulation results using a multiple-beam-interference recursive method presented good consistency with experimental measurements with regard to the optical reflective spectra of AlN–TiN multilayer thin film samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Highly (001) oriented L1{sub 0}-CoPt/TiN multilayer films on glass substrates with perpendicular magnetic anisotropy

To obtain strong perpendicular magnetic anisotropy (PMA) based on L1{sub 0} structure for magnetic storage devices, costly single crystalline substrates are generally required to achieve (001) texture. Recently, various studies also have focused on depositing different kinds of seed layers on glass or other amorphous substrates to promote (001) preferred orientation of L1{sub 0} CoPt and FePt. TiN is a very promising seed layer material because of its cubic crystalline structure (similar to MgO) and excellent diffusion barring property even at high temperatures. In the present work, highly (001) oriented L1{sub 0}-CoPt/TiN multilayer films have been successfully deposited on glass substrates. After annealing at 700 °C, the film exhibits PMA, and a strong (001) peak is detected from the x-ray diffraction profiles, indicating the ordering transformation of CoPt layers from fcc (A1) to L1{sub 0} structure. It also is found that alternate deposition of cubic TiN and CoPt effectively improves the crystallinity and (001) preferred orientation of CoPt layers. This effect is verified by the substantial enhancement of (001) reflection and PMA with increasing the period number of the multilayer films.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Characterization of multilayer coated replicated Wolter optics for imaging x-ray emission from pulsed power

Here, we have developed a process for indirectly coating small diameter electroformed nickel replicated optics with multilayers to increase their response at high energy (i.e. >10 keV). The ability to fabricate small diameter multilayer-coated full-shell Wolter X-ray optics with narrow bandpass opens the door to several applications within astronomy and also provides a path for cross-fertilization to other fields. We report on the characterization and evaluation of the first two prototype X-ray Wolter optics to be delivered to the Z Pulsed Power Facility at Sandia National Laboratories. The intent is to develop and field several optics as part of an imaging system with targeted spectral ranges.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Dual ring multilayer ionization chamber and theory-based correction technique for scanning proton therapy

Purpose: To develop a multilayer ionization chamber (MLIC) and a correction technique that suppresses differences between the MLIC and water phantom measurements in order to achieve fast and accurate depth dose measurements in pencil beam scanning proton therapy. Methods: The authors distinguish between a calibration procedure and an additional correction: 1—the calibration for variations in the air gap thickness and the electrometer gains is addressed without involving measurements in water; 2—the correction is addressed to suppress the difference between depth dose profiles in water and in the MLIC materials due to the nuclear interaction cross sections by a semiempirical model tuned by using measurements in water. In the correction technique, raw MLIC data are obtained for each energy layer and integrated after multiplying them by the correction factor because the correction factor depends on incident energy. The MLIC described here has been designed especially for pencil beam scanning proton therapy. This MLIC is called a dual ring multilayer ionization chamber (DRMLIC). The shape of the electrodes allows the DRMLIC to measure both the percentage depth dose (PDD) and integrated depth dose (IDD) because ionization electrons are collected from inner and outer air gaps independently. Results: IDDs for which the beam energies were 71.6, 120.6, 159, 180.6, and 221.4 MeV were measured and compared with water phantom results. Furthermore, the measured PDDs along the central axis of the proton field with a nominal field size of 10 × 10 cm{sup 2} were compared. The spread out Bragg peak was 20 cm for fields with a range of 30.6 and 3 cm for fields with a range of 6.9 cm. The IDDs measured with the DRMLIC using the correction technique were consistent with those that of the water phantom; except for the beam energy of 71.6 MeV, all of the points satisfied the 1% dose/1 mm distance to agreement criterion of the gamma index. The 71.6 MeV depth dose profile showed slight differences in the shallow region, but 94.5% of the points satisfied the 1%/1 mm criterion. The 90% ranges, defined at the 90% dose position in distal fall off, were in good agreement with those in the water phantom, and the range differences from the water phantom were less than ±0.3 mm. The PDDs measured with the DRMLIC were also consistent with those that of the water phantom; 97% of the points passed the 1%/1 mm criterion. Conclusions: It was demonstrated that the new correction technique suppresses the difference between the depth dose profiles obtained with the MLIC and those obtained from a water phantom, and a DRMLIC enabling fast measurements of both IDD and PDD was developed. The IDDs and PDDs measured with the DRMLIC and using the correction technique were in good agreement with those that of the water phantom, and it was concluded that the correction technique and DRMLIC are useful for depth dose profile measurements in pencil beam scanning proton therapy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Light-induced ultrafast spin transport in multilayer metallic films originates from sp-d spin exchange coupling

Ultrafast interaction between the femtosecond laser pulse and the magnetic metal provides an efficient way to manipulate the magnetic states of matter. Numerous experimental advancements have been made on multilayer metallic films in the last two decades. However, the underlying physics remains unclear. Here, relying on an efficient ab initio spin dynamics simulation algorithm, we revealed the physics that can unify the progress in different experiments. We found that light-induced ultrafast spin transport in multilayer metallic films originates from the sp - d spin-exchange interaction, which can induce an ultrafast, large, and pure spin current from ferromagnetic metal to nonmagnetic metal without charge carrier transport. The resulting trends of spin demagnetization and spin flow are consistent with most experiments. It can explain a variety of ultrafast light-spin manipulation experiments with different systems and different pump-probe technologies, covering a wide range of work in this field.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Fabrication of a terahertz quantum-cascade laser with a double metal waveguide based on multilayer GaAs/AlGaAs heterostructures

The Postgrowth processing of GaAs/AlGaAs multilayer heterostructures for terahertz quantumcascade lasers (QCLs) are studied. This procedure includes the thermocompression bonding of In–Au multilayer heterostructures with a doped n{sup +}-GaAs substrate, mechanical grinding, and selective wet etching of the substrate, and dry etching of QCL ridge mesastripes through a Ti/Au metallization mask 50 and 100 μm wide. Reactive-ion-etching modes with an inductively coupled plasma source in a BCl{sub 3}/Ar gas mixture are selected to obtain vertical walls of the QCL ridge mesastripes with minimum Ti/Au mask sputtering.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Strained multilayer structures with pseudomorphic GeSiSn layers

The temperature and composition dependences of the critical thickness of the 2D–3D transition for a GeSiSn film on Si(100) have been studied. The regularities of the formation of multilayer structures with pseudomorphic GeSiSn layers directly on a Si substrate, without relaxed buffer layers, were investigated for the first time. The possibility of forming multilayer structures based on pseudomorphic GeSiSn layers has been shown and the lattice parameters have been determined using transmission electron microscopy. The grown structures demonstrate photoluminescence for Sn contents from 3.5 to 5% in GeSiSn layers.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Surface functionalization of single-layer and multilayer graphene upon ultraviolet irradiation

The process of oxidation of single-layer and multilayer graphene films upon ultraviolet irradiation of the structure in water vapor was studied. The systematic features and distinctions between changes in the topographic and optical properties of graphene films composed of different numbers of layers were established. The possibility of surface functionalization accompanied by modification of the energy structure of graphene was shown. Differences between single-layer and multilayer graphene films in the mechanisms of oxidation on ultraviolet irradiation are discussed and analyzed. Correlation of the topographic imperfections of the properties of the graphene material with its structural defects observed in Raman spectra was shown.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Formation of silicon nanocrystals in multilayer nanoperiodic a-SiO{sub x}/insulator structures from the results of synchrotron investigations

The problem of the efficiency of the controllable formation of arrays of silicon nanoparticles is studied on the basis of detailed investigations of the electronic structure of multilayer nanoperiodic a-SiO{sub x}/SiO{sub 2}, a-SiO{sub x}/Al{sub 2}O{sub 3}, and a-SiO{sub x}/ZrO{sub 2} compounds. Using synchrotron radiation and the X-ray absorption near edge structure (XANES) spectroscopy technique, a modification is revealed for the investigated structures under the effect of high-temperature annealing at the highest temperature of 1100°C; this modification is attributed to the formation of silicon nanocrystals in the layers of photoluminescent multilayer structures.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Crystallization of Amorphous Germanium Films and Multilayer a-Ge/a-Si Structures upon Exposure to Nanosecond Laser Radiation

The processes of the crystallization of amorphous germanium films and multilayer germanium/silicon structures upon exposure to nanosecond (70 ns) ruby laser radiation (λ = 694 nm) are studied. The samples are grown on silicon and glassy substrates by plasma-enhanced chemical vapor deposition. Pulsed laser annealing of the samples is conducted in the range of pulse energy densities E{sub p} from 0.07 to 0.8 J cm{sup –2}. The structure of the films after annealing is determined by analyzing the scanning electron microscopy data and Raman spectra. It is established that, after annealing, the films are completely crystallized and, in this case, contain regions of coarse crystalline grains (>100 nm), whose fraction increases, as E{sub p} is increased, and reaches 40% of the area. From analysis of the position of the Raman peaks, it is conceived that the crystalline grains, whose dimensions exceed 100 nm, either contain structural defects or stretching strains. The correlation length of optical vibrations is determined from the phonon confinement model and found to increase from 5 to 8 nm, as E{sub p} is increased. Pulsed laser annealing of multilayer Ge(10 nm)/Si(5 nm) structures induces partial intermixing of the layers with the formation of Ge–Si alloys.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Features of Magnetorefractive Effect in a [CoFe/Cu]{sub n} Multilayer Metallic Nanostructure

The features of magnetorefractive effect (MRE) in metallic multilayer film Ni{sub 48}Fe{sub 12}Cr{sub 40}(50 Å)/[Co{sub 90}Fe{sub 10}(14 Å)/Cu(22 Å)]{sub 8}/Cr(20 Å) nanostructures, which exhibit giant magnetoresistance at room temperature, are investigated experimentally and theoretically. We show that the MRE in these structures reaches 1.5% in an applied magnetic field of 3.5 kOe, in a broad part of the IR region, and can change sign for both transmission and reflection of light. The refraction and extinction coefficients that are calculated for the nanostructures in an external magnetic field are in good agreement with our experimental data. The deduced formulas can be applied to estimating the MRE in multilayer metallic nanostructures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Microstructure and Mechanical Properties of Multilayer α-AlN/α-BCN Coating as Functions of the Current Density during Sputtering of a B{sub 4}C Target

Multilayer AlN/BCN coating of nanometer scale have been prepared by magnetron sputtering of Al and B{sub 4}C targets in an argon–nitrogen atmosphere during deposition on a Si substrate. These coating have an X-ray amorphous structure and the maximum Knoop hardness of 27 GPa (at the current density 100 mA). The first-principle molecular dynamics calculations show that the B4–BN layer is dynamically unstable; thus, it will not be epitaxial and will be amorphous or have a structure different from the B4–BN structure. The thermal vacuum annealing from 600 to 800°C of samples with multilayer nanosized coating leads to the decrease in the Knoop hardness to 18 GPa; however, the coating structure is retained X-ray amorphous.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗