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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Microstructural Characterization of Nb$_3$Sn Thin Films Using FIB Tomography

The accelerating gradient of N b3Sn superconducting radiofrequency (SRF) cavities is currently limited, and the underlying cause remains an open question in the field. One leading hypothesis attributes this limitation to the presence of tin-deficient regions within the N b3Sn coating, which can suppress the superheating field. Due to the relatively large coherence length of N b3Sn, defects near the surface may significantly interact with the RF field. However, these subsurface defects have proven difficult to characterize. This research aims to investigate the structure and distribution of subsurface Sn deficient regions to better understand their influence on cavity performance. We employ focused ion beam (FIB) tomography to analyze the subsurface microstructure of N b3Sn thin films. This technique enables threedimensional reconstruction of both the tin distribution and the grain structure within the film. By correlating Sn content with grain structure, we find that Sn deficient regions are more prevalent that previously thought. However, the Sn deficient regions are consistently located below the surface of the film where RF fields are strongly attenuated by supercurrent screening and are likely not a limiting factor for cavity performance

Viklund, Eric [Fermilab]↗
DOE OSTI2018

High temperature oxidation behavior of a high Al-containing ferritic heat-resistant stainless steel

Highlights: • Oxidation kinetics has been analyzed by discontinuous weighing. • Microstructure and phase composition of oxide films were investigated by SEM, EDS and XRD analysis. • The oxidation resistance of 1000 °C is obviously deteriorated comparing with that at 800 °C and 900 °C. • The oxidation mechanism has been discussed. - Abstract: The high temperature oxidation behavior of a high Al-containing ferritic heat-resistant stainless steel at temperatures of 800, 900, and 1000 °C in air were studied in isothermal oxidation tests. The results showed that the isothermal oxidation kinetic curves obtained at different temperatures followed the parabolic law, and the weight gain per unit at 1000 °C was significantly higher than that at 800 and 900 °C. The oxidation rate at 1000 °C was about three times faster than that at 800 and 900 °C. Continuous and compact multicomponent oxide films mainly composed of Cr{sub 2}O{sub 3}, Al{sub 2}O{sub 3}, spinel MnFe{sub 2}O{sub 4}, and MnCr{sub 2}O{sub 4} were obtained at 800 and 900 °C. The oxide film started delaminating at 1000 °C; the outer layer was composed of Cr{sub 2}O{sub 3}, spinel MnCr{sub 2}O{sub 4}, and MnFe{sub 2}O{sub 4}, the middle layer was composed of Fe{sub 2}O{sub 3} and Fe-Cr matrix, and the inner layer was composed of Al{sub 2}O{sub 3} and SiO{sub 2}. Oxidation resistance at 1000 °C was reduced mainly because of porous Fe{sub 2}O{sub 3} and inner oxidation of Al and Si. In addition, the oxidation mechanism was discussed based on kinetic and morphological observations.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Advanced Microstructured BaTiO 3 -Embedded PVDF–HFP/PEO Film for Enhanced Triboelectric Interface in Self-Sufficient Energy Generation and Sensing

The global reliance on fossil fuels and natural gas has largely dominated the energy production field, but due to finite resource depletion and escalating greenhouse gas emissions, the immediate exploration of sustainable energy alternatives to mitigate climate change and ensure resource security has been a major concern. There has been extensive research into other more renewable methods of energy production, such as wind and hydropower. Of these current energy generation types, there are many areas of untapped potential from the mechanical movements generated ambiently not only in the large scale of power generation but also on a smaller scale. The piezoelectric and triboelectric effects are phenomena where these ambient mechanical movements can generate electrical energy. Developing a hybrid system that leverages both mechanical stress and surface charges presents an ideal opportunity to exploit these untapped energy sources. Producing a hybrid PVDF–HFP/PEO film with perovskite BaTiO 3 (BTO) enables ambient power harvesting from both mechanical movement and surface charge. The optimized cell produced a potential of up to 15 V and a current of 200 nA with a 68 kΩ resistor, a substantial increase from a base system with an average of 2.1 V and 40 nA. These hybrid TENGs offer significant potential for energy harvesting in small-scale applications, such as health monitoring devices and indicators in electric circuits.

Ybarra, Rigobert [University of Texas Rio Grande V↗
DOE OSTI2017

Ion irradiation induced structural modifications and increase in elastic modulus of silica based thin films

Ion irradiation is an alternative to heat treatment for transforming organic-inorganic thin films to a ceramic state. One major shortcoming in previous studies of ion-irradiated films is the assumption that constituent phases in ion-irradiated and heat-treated films are identical and that the ion irradiation effect is limited to changes in composition. Here, we investigate the effects of ion irradiation on both the composition and structure of constituent phases and use the results to explain the measured elastic modulus of the films. Our results indicated that the microstructure of the irradiated films consisted of carbon clusters within a silica matrix. It was found that carbon was present in a non-graphitic sp 2 -bonded configuration. It was also observed that ion irradiation caused a decrease in the Si-O-Si bond angle of silica, similar to the effects of applied pressure. A phase transformation from tetrahedrally bonded to octahedrally bonded silica was also observed. The results indicated the incorporation of carbon within the silica network. Finally, a combination of the decrease in Si-O-Si bond angle and an increase in the carbon incorporation within the silica network was found to be responsible for the increase in the elastic modulus of the films.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Gradient nanostructuring via compositional means

Nanocrystalline metals are inherently unstable against thermal and mechanical stimuli, commonly resulting in significant grain growth. Also, while these metals exhibit substantial Hall-Petch strengthening, they tend to suffer from low ductility and fracture toughness. With regard to the grain growth problem, alloying elements have been employed to stabilize the microstructure through kinetic and/or thermodynamic mechanisms. And to address the ductility challenge, spatially-graded grain size distributions have been developed to facilitate heterogeneous deformation modes: high-strength at the surface and plastic deformation in the bulk. In the present work, we combine these two strategies and present a new methodology for the fabrication of gradient nanostructured metals via compositional means. Here, we have demonstrated that annealing a compositionally stepwise Pt-Au film with a homogenous microstructure results in a film with a spatial microstructural gradient, exhibiting grains which can be twice as wide in the bulk compared to the outer surfaces. Additionally, phase-field modeling was employed for the comparison with experimental results and for further investigation of the competing mechanisms of Au diffusion and thermally induced grain growth. This fabrication method offers an alternative approach for developing the next generation of microstructurally stable gradient nanostructured films.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Correlating thermoelectric properties with microstructure in Bi 0.8 Sb 0.2 thin films

The room temperature electronic transport properties of 100 nm-thick thermoelectric Bi 0.8 Sb 0.2 films, sputter-deposited onto quartz substrates and post-annealed in an ex-situ furnace, systematically correlate with the overall microstructural quality, improving with increasing annealing temperature until close to the melting point for the alloy composition. Furthermore, the optimized films have high crystalline quality with ~99% of the grains oriented with the trigonal axis perpendicular to the substrate surface. Film resistivities and Seebeck coefficients are accurately measured by preventing deleterious surface oxide formation via a SiN capping layer and using Nd-doped Al for contacts. Our resulting values are similar to single crystals and significantly better than previous reports from films and polycrystalline bulk alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Morphological and microstructural stability of N-polar InAlN thin films grown on free-standing GaN substrates by molecular beam epitaxy

The sensitivity of the surface morphology and microstructure of N-polar-oriented InAlN to variations in composition, temperature, and layer thickness for thin films grown by plasma-assisted molecular beam epitaxy (PAMBE) has been investigated. Lateral compositional inhomogeneity is present in N-rich InAlN films grown at low temperature, and phase segregation is exacerbated with increasing InN fraction. A smooth, step-flow surface morphology and elimination of compositional inhomogeneity can be achieved at a growth temperature 50 °C above the onset of In evaporation (650 °C). A GaN/AlN/GaN/200-nm InAlN heterostructure had a sheet charge density of 1.7 × 10{sup 13 }cm{sup −2} and no degradation in mobility (1760 cm{sup 2}/V s) relative to 15-nm-thick InAlN layers. Demonstration of thick-barrier high-electron-mobility transistors with good direct-current characteristics shows that device quality, thick InAlN layers can be successfully grown by PAMBE.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Relationship between electrical properties and crystallization of indium oxide thin films using ex-situ grazing-incidence wide-angle x-ray scattering

Grazing-incidence, wide-angle x-ray scattering measurements were conducted on indium oxide thin films grown on silica substrates via pulsed laser deposition. Growth temperatures (T G ) in this study ranged from -50 °C to 600 °C, in order to investigate the thermal effects on the film structure and its spatial homogeneity, as well as their relationship to electrical properties. Films grown below room temperature were amorphous, while films prepared at T G = 25 °C and above crystallized in the cubic bixbyite structure, and their crystalline fraction increased with deposition temperature. The electrical conductivity (σ) and electrical mobility (μ) were strongly enhanced at low deposition temperatures. For T G = 25 °C and 50 °C, a strong < 100 > preferred orientation (texture) occurred, but it decreased as the deposition temperature, and consequential crystallinity, increased. Higher variations in texture coefficients and in lattice parameters were measured at the film surface compared to the interior of the film, indicating strong microstructural gradients. At low crystallinity, the in-plane lattice spacing expanded, while the out-of-plane spacing contracted, and those values merged at T G = 400 °C, where high μ was measured. This directional difference in lattice spacing, or deviatoric strain, was linear as a function of both deposition temperature and the degree of crystallinity. The crystalline sample with T G = 100 °C had the lowest mobility, as well as film diffraction peaks which split into doublets. The deviatoric strains from these doublet peaks differ by a factor of four, supporting the presence of both a microstructure and strain gradient in this film. More isotropic films exhibit larger l values, indicating that the microstructure directly correlates with electrical properties. Lastly, these results provide valuable insights that can help to improve the desirable properties of indium oxide, as well as other transparent conducting oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Mixture domain states in PbTiO 3 film with potentials for functional application

We investigated the microstructure of PbTiO 3 films epitaxially grown on DyScO 3 (110) substrates using synchrotron-based 3D reciprocal space mapping and X-ray reflection interface microscopy. The results show that an in-plane anisotropic mixture domain state ( a * + a/c ) exists in the PbTiO 3 films, where a * domains reside between a/c twin stripe domains. Furthermore, when compared with traditional a domains in a/c twins, the a * domain is found to possess a similar in-plane lattice parameter but a much smaller out-of-plane lattice (~0.5%). Here, we also discovered a temperature-driven transition between a * and a/c pointing to potential applications in functional devices due to the huge mechanical response (4.85%) and polarization rotation between the a * and c domains.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Double Hard Axes of Hysteresis Loop in Wide-Angle Obliquely Sputtered CoFeB Amorphous Films

Soft magnetic Co{sub 40}Fe{sub 40}B{sub 20} films with different tilt angle were successfully deposited on silicon substrates by using oblique sputtering technique. Different oblique angles are achieved by controlling the position of samples. The corresponding static magnetic properties of these samples were then systematically investigated. Interestingly, with the oblique angle increasing from 38° to 55°, the MOKE hysteresis loop of the thin films displays a unique and special performance with double hard axes. Meanwhile, despite of the measurement magnetic field along PR or AR direction, both of the hysteresis loops have two-stage magnetization reversal that means there are two comparably strong anisotropies in the CoFeB films. Moreover, rotating samples from in-plane to out-of-plane, the hysteresis loops demonstrate the perpendicular anisotropy exist in CoFeB films. The cross-section SEM characterizations further verify that the residual field from the magnetic cylinder will strongly impact the microstructures of thin film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Microstructural evolution and electrical resistivity of nanocrystalline W thin films grown by sputtering

Highlights: • W thin films with thicknesses of 5–40 nm were deposited by sputtering and annealed up to 400°C. • Grain size of the beta (β)-W was about 5 nm, whereas that of the alpha (α)-W was about 130 nm. • Thickness dependent electrical resistivity variations as a function of annealing temperature were presented. - Abstract: Tungsten (W) thin films and nanostructures, particularly those having a beta (β)-phase, have attracted a large amount of attention lately because an ultrathin β-phase W film attached to a ferromagnetic layer can reverse the direction of magnetization upon current injection. However, in-depth microstructural studies including the phase transformation in W films as a function of thickness and post-deposition heat treatment temperature are rare. Here, we report the microstructural evolution and the change in the electrical resistivity of W films with thicknesses of 5–40 nm. Microstructural analyses indicate that the β-W is nanocrystalline with a small grain size of about 5 nm, while the alpha (α)-W has a grain size larger than 130 nm with random crystal orientation. We present a state diagram showing the phase of the W film as functions of film thickness and annealing temperature.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Properties of Nb3Sn films fabricated by magnetron sputtering from a single target

Superconducting Nb3Sn films were fabricated on sapphire and fine grain Nb substrates by magnetron sputtering from a single stoichiometric Nb3Sn target. The structural, morphological and superconducting properties of the films annealed for 24 h at temperatures of 800-1000 {\deg}C were investigated. The effect of the annealing time at 1000 {\deg}C was examined for 1, 12, and 24 h. The film properties were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, energy dispersive X-ray spectroscopy, and Raman spectroscopy. The DC superconducting properties of the films were characterized by a four-point probe measurement down to cryogenic temperatures. The RF surface resistance of films was measured over a temperature range of 6-23 K using a 7.4 GHz sapphire-loaded Nb cavity. As-deposited Nb3Sn films on sapphire had a superconducting critical temperature of 17.21 K, which improved to 17.83 K when the film was annealed at 800 {\deg}C for 24 h. For the films annealed at 1000 {\deg}C, the surface Sn content was reduced to ~11.3 % for an annealing time of 12 h and to ~4.1 % for an annealing time of 24 h. The Raman spectra of the films confirmed the microstructural evolution after annealing. The RF superconducting critical temperature of the as-deposited Nb3Sn films on Nb was 16.02 K, which increased to 17.44 K when the film was annealed at 800 {\deg}C for 24 h.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Effect of sputtering power on the growth of Ru films deposited by magnetron sputtering

Ruthenium is deposited by DC magnetron sputtering at different powers and is characterized. The effect of sputtering power on the electrical and structural properties of the film is investigated experimentally. High resolution X-ray diffraction is used to characterize the microstructure of Ru films deposited on SiO{sub 2} surface. The peak (002) is more sharp and intense with full width at half maximum (FWHM) of 0.37° at 250W. The grain size increases with increase in sputtering power improving the crystallinity of the film. The film deposited at high sputtering power also showed lower resistivity (12.40 µΩ-cm) and higher mobility (4.82 cm{sup 2}/V.s) as compared to the film deposited at low power. The surface morphology of the film is studied by atomic force microscopy (AFM).

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2002

A Statistical Analysis of Laser Ablated Ba(Sub 0.50)Sr(Sub 0.50)TiO(Sub 3)/LaAlO(Sub 3) Films for Microwave Applications

The NASA Glenn Research Center is constructing a 616 element scanning phased array antenna using thin film Ba(sub x)Sr(sub 1-x)TiO(sub 3) based phase shifters. A critical milestone is the production of 616 identical phase shifters at 19 GHz with [asymptotically equal to]4 dB insertion loss and at least 337.5 deg phase shift with 3 percent bandwidth. It is well known that there is a direct relationship between dielectric tuning and loss due to the Kramers-Kronig relationship and that film crystallinity and strain, affected by the substrate template, play an important role. Ba(sub 0.50)Sr(sub 0.50)TiO (sub 3) films, nominally 400 nm thick, were deposited on 48 0.25 mm thick, 5 cm diameter LaAlO(sub 3) wafers. Although previous results suggested that Mn-doped films on MgO were intrinsically superior in terms of phase shift per unit loss, for this application phase shift per unit length was more important. The composition was selected as a compromise between tuning and loss for room temperature operation (e.g. crystallinity progressively degrades for Ba concentrations in excess of 30 percent). As a prelude to fabricating the array, it was necessary to process, screen, and inventory a large number of samples. Variable angle ellipsometry was used to characterize refractive index and film thickness across each wafer. Microstructural properties of the thin films were characterized using high resolution X-ray diffractometry. Finally, prototype phase shifters and resonators were patterned on each wafer and RE probed to measure tuning as a function of dc bias voltage as well as peak (0 field) permittivity and unloaded Q. The relationship among film quality and uniformity and performance is analyzed. This work presents the first statistically relevant study of film quality and microwave performance and represents a milestone towards commercialization of thin ferroelectric films for microwave applications.

Ferroelectric thin films↗
DOE OSTI2025

Effect of Thermal Oxidation on the Structure, Surface Texturing, and Microstructure Evolution in Nanocrystalline Ga-O-N Films

An extensive examination of the nanoscale, crystallographic growth dynamics of the system, which is impacted by the thermal energy given to the GaN, is carried out to derive a deeper understanding of the growth kinetics, morphology and microstructure evolution, chemical bonding, and optical properties of Ga-O-N films. Thermal annealing of GaN films is performed in the temperature range of 900–1200 °C. Crystal structure, phase formation, chemical composition, surface morphology, and microstructure evolution of Ga-O-N films are investigated as a function of temperature. Increasing temperature induces surface oxidation, which results in the formation of stable β-Ga2O3 phase in the GaN matrix, where the overall film composition evolves from nitride (GaN) to oxynitride (Ga-O-N). While GaN surfaces are smooth, planar, and featureless, oxidation induced granular-to-rod shaped morphology evolution is seen with increasing temperature to 1200 °C. The considerable texturing and stability of the nanocrystalline Ga-O-N on Si substrates can be attributed to the surface and interface driven modification because of thermal treatment. Corroborating with structure and chemical changes, Raman spectroscopic analyses also indicate that the chemical bonding evolution progresses from fully Ga-N bonds to Ga-O-N. While the GaN oxidation process starts with the formation of β-Ga 2 O 3 at an annealing temperature of 1000 °C, higher annealing temperatures induce structural distortion with the potential formation of Ga-O-N bonds. The structure-phase-chemical composition correlation, which will be useful for nanocrystalline materials for selective optoelectronic applications, is established in Ga-O-N films made by thermal treatment of GaN.

36 MATERIALS SCIENCE↗