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At least 487 records · Page 27

All sources NASA NTRS DOE OSTI

DOE OSTI2021

Antiferromagnetic Oxide Thin Films for Spintronic Applications

Antiferromagnetic oxides have recently gained much attention because of the possibility to manipulate electrically and optically the Néel vectors in these materials. Their ultrafast spin dynamics, long spin diffusion length and immunity to large magnetic fields make them attractive candidates for spintronic applications. Additionally, there have been many studies on spin wave and magnon transport in single crystals of these oxides. However, the successful applications of the antiferromagnetic oxides will require similar spin transport properties in thin films. In this work, we systematically show the sputtering deposition method for two uniaxial antiferromagnetic oxides, namely Cr2O3 and α-Fe2O3, on A-plane sapphire substrates, and identify the optimized deposition conditions for epitaxial films with low surface roughness. We also confirm the antiferromagnetic properties of the thin films. The deposition method developed in this article will be important for studying the magnon transport in these epitaxial antiferromagnetic thin films.

36 MATERIALS SCIENCE↗

NASA NTRS1996

Measuring the Thickness and Elastic Properties of Electroactive Thin-Film Polymers Using Platewave Dispersion Data

Electroactive thin-film polymers are candidate sensors and actuators materials. They are also finding significant potential in muscle mechanisms and microelectromechanical systems (MEMS). In these applications, polymer thin films of thickness varying between 20 and 300 micrometers are utilized. The authors are currently studying the potential use of platewave dispersion curve measurements as an effective gauging tool for electroactive thin-film polymers.

sensors actuators film thickness measurements piez↗

NASA NTRS2005

Aperture-coupled thin-membrane microstrip array antenna for beam scanning application

A microstrip array using aperture-slot-coupling technique with very thin membranes has been developed at the L-band frequency for beam scanning application. This technology-demonstration array with 4 x 2 elements achieved a relatively wide bandwidth of 100 MHz (8%) and +/-45(deg) beam scan. Very narrow coupling slots were used with each having an aspect ratio of 160 (conventional slot aspect ratio is between 10 to 30) for coupling through very thin membrane (0.05mm thickness). This thin-membrane aperture-coupling technique allows the array antenna elements to be more easily integrated with transmit/receive amplifier (T/R) and phase shifter modules. This paper addresses only the radiator portion of the array. The array and active components will be presented in a separate pape.

array antenna↗

NASA NTRS2013

Coating Thin Mirror Segments for Lightweight X-ray Optics

Next generations lightweight, high resolution, high throughput optics for x-ray astronomy requires integration of very thin mirror segments into a lightweight telescope housing without distortion. Thin glass substrates with linear dimension of 200 mm and thickness as small as 0.4 mm can now be fabricated to a precision of a few arc-seconds for grazing incidence optics. Subsequent implementation requires a distortion-free deposition of metals such as iridium or platinum. These depositions, however, generally have high coating stresses that cause mirror distortion. In this paper, we discuss the coating stress on these thin glass mirrors and the effort to eliminate their induced distortion. It is shown that balancing the coating distortion either by coating films with tensile and compressive stresses, or on both sides of the mirrors is not sufficient. Heating the mirror in a moderately high temperature turns out to relax the coated films reasonably well to a precision of about a second of arc and therefore provide a practical solution to the coating problem.

Thin Mirror↗

NASA NTRS2014

Design and Operation of a Fast, Thin-Film Thermocouple Probe on a Turbine Engine

As a demonstration of technology maturation, a thin-film temperature sensor probe was fabricated and installed on a F117 turbofan engine via a borescope access port to monitor the temperature experienced in the bleed air passage of the compressor area during an engine checkout test run. To withstand the harsh conditions experienced in this environment, the sensor probe was built from high temperature materials. The thin-film thermocouple sensing elements were deposited by physical vapor deposition using pure metal elements, thus avoiding the inconsistencies of sputter-depositing particular percentages of materials to form standardized alloys commonly found in thermocouples. The sensor probe and assembly were subjected to a strict protocol of multi-axis vibrational testing as well as elevated temperature pressure testing to be qualified for this application. The thin-film thermocouple probe demonstrated a faster response than a traditional embedded thermocouple during the engine checkout run.

thermocouples↗

NASA NTRS1994

Optical and Electrical Properties of Reactively Sputtered TiN, ZrN, and HfN Thin Films

Thin films of titanium, zirconium, and hafnium nitride are prepared by DC magnetron reactive sputtering at room temperature on fused silica, optical glass, and silicon substrates. Deposition parameters are investigated in order to obtain stoichiometric films. The optical and electrical properties of the films as a function of nitrogen partial pressure are determined. The results show that an inverse correlation exists between the optical reflectance and the electrical resistivity of the films. Ellipsometer data for all three films show that their refractive index in the visible spectrum is decreased by increasing the film thickness while the extinction coefficient is unchanged. Thin films of TiN have the lowest room temperature resistivity relative to ZrN and HfN thin films.

Reactive↗

NASA NTRS2025

Engineered Edge Effect Stress Redistribution in Suspended Thin Film Stacks for Flatness Control

This paper presents the systematic study of edge effect stresses and interaction between thin film stacks to achieve flat suspended thin film structures. Finite element modeling (FEM) was used for rapid analysis of support structures on microshutter array (MSA) shutter blades. The design application aims to flatten the blades to provide ultra-high contrast to optical detectors using MSAs as field masks. This is the first comprehensive study of microscopic surface feature edge effect and film-to-film stress interaction in micro electromechanical systems (MEMS). This study demonstrates flattening of thin film stacks by stress redistribution by induced shear force at the edge of strategically designed reinforcement structures.

Thin Film MEMS↗

DOE OSTI2020

Polycrystalline Thin-Film Research: Copper Indium Gallium Diselenide

Copper indium gallium diselenide (CIGS) solar cells are one of the primary focuses of research by the Thin Film Material Science and Processing Group. The group develops processes and materials related to thin-film polycrystalline photovoltaic (PV) devices as well as the equipment required for routine analysis of these devices and materials. We work closely with other groups in the Materials Science Center to achieve a deeper understanding of thin-film materials and devices.

capabilities↗

DOE OSTI2020

Synthesis and Crystallization of Atomic Layer Deposition β-Eucryptite LiAlSiO 4 Thin-Film Solid Electrolytes

Atomic layer deposition (ALD) was used to control the stoichiometry of thin lithium aluminosilicate films, thereby enabling crystallization into the ion-conducting β-eucryptite LiAlSiO 4 phase. Here, the rapid thermal annealed ALD film developed a well-defined epitaxial relationship to the silicon substrate: β-LiAlSiO4 ($1\bar{21}0$)||Si (100) and β-LiAlSiO 4 ($10\bar{10}$)||Si (001). The extrapolated room temperature ionic conductivity was found to be 1.2 × 10 –7 S/cm in the [$1\bar{21}0$] direction. Because of the unique 1-D channel along the c axis of β-LiAlSiO 4 , the epitaxial thin film has the potential to facilitate ionic transport if oriented with the c axis normal to the electrode surface, making it a promising electrolyte material for three-dimensional lithium-ion microbatteries.

25 ENERGY STORAGE↗

DOE OSTI2024

Formation and Microwave Losses of Hydrides in Superconducting Niobium Thin Films Resulting from Fluoride Chemical Processing

Abstract Superconducting niobium (Nb) thin films have recently attracted significant attention due to their utility for quantum information technologies. In the processing of Nb thin films, fluoride‐based chemical etchants are commonly used to remove surface oxides that are known to affect superconducting quantum devices adversely. However, these same etchants can also introduce hydrogen to form Nb hydrides, potentially negatively impacting microwave loss performance. Here, comprehensive materials characterization of Nb hydrides formed in Nb thin films as a function of fluoride chemical treatments is presented. In particular, secondary‐ion mass spectrometry, X‐ray scattering, and transmission electron microscopy reveal the spatial distribution and phase transformation of Nb hydrides. The rate of hydride formation is determined by the fluoride solution acidity and the etch rate of Nb 2 O 5, which acts as a diffusion barrier for hydrogen into Nb. The resulting Nb hydrides are detrimental to Nb superconducting properties and lead to increased power‐independent microwave loss in coplanar waveguide resonators. However, Nb hydrides do not correlate with two‐level system loss or device aging mechanisms. Overall, this work provides insight into the formation of Nb hydrides and their role in microwave loss, thus guiding ongoing efforts to maximize coherence time in superconducting quantum devices.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Recent Progress on Topological Structures in Ferroic Thin Films and Heterostructures

Topological spin/polarization structures in ferroic materials continue to draw great attention as a result of their fascinating physical behaviors and promising applications in the field of high-density nonvolatile memories as well as future energy-efficient nanoelectronic and spintronic devices. Such developments have been made, in part, based on recent advances in theoretical calculations, the synthesis of high-quality thin films, and the characterization of their emergent phenomena and exotic phases. Herein, progress over the last decade in the study of topological structures in ferroic thin films and heterostructures is explored, including the observation of topological structures and control of their structures and emergent physical phenomena through epitaxial strain, layer thickness, electric, magnetic fields, etc. First, the evolution of topological spin structures (e.g., magnetic skyrmions) and associated functionalities (e.g., topological Hall effect) in magnetic thin films and heterostructures is discussed. Then, the exotic polar topologies (e.g., domain walls, closure domains, polar vortices, bubble domains, and polar skyrmions) and their emergent physical properties in ferroelectric oxide films and heterostructures are explored. Lastly, a brief overview and prospectus of how the field may evolve in the coming years is provided.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Thin‐Film Ferroelectrics

Abstract Over the last 30 years, the study of ferroelectric oxides has been revolutionized by the implementation of epitaxial‐thin‐film‐based studies, which have driven many advances in the understanding of ferroelectric physics and the realization of novel polar structures and functionalities. New questions have motivated the development of advanced synthesis, characterization, and simulations of epitaxial thin films and, in turn, have provided new insights and applications across the micro‐, meso‐, and macroscopic length scales. This review traces the evolution of ferroelectric thin‐film research through the early days developing understanding of the roles of size and strain on ferroelectrics to the present day, where such understanding is used to create complex hierarchical domain structures, novel polar topologies, and controlled chemical and defect profiles. The extension of epitaxial techniques, coupled with advances in high‐throughput simulations, now stands to accelerate the discovery and study of new ferroelectric materials. Coming hand‐in‐hand with these new materials is new understanding and control of ferroelectric functionalities. Today, researchers are actively working to apply these lessons in a number of applications, including novel memory and logic architectures, as well as a host of energy conversion devices.

Fernandez, Abel↗

DOE OSTI2022

Strain‐Driven Mixed‐Phase Domain Architectures and Topological Transitions in Pb 1− x Sr x TiO 3 Thin Films

Abstract The potential for creating hierarchical domain structures, or mixtures of energetically degenerate phases with distinct patterns that can be modified continually, in ferroelectric thin films offers a pathway to control their mesoscale structure beyond lattice‐mismatch strain with a substrate. Here, it is demonstrated that varying the strontium content provides deterministic strain‐driven control of hierarchical domain structures in Pb 1− x Sr x TiO 3 solid‐solution thin films wherein two types, c / a and a 1 / a 2 , of nanodomains can coexist. Combining phase‐field simulations, epitaxial thin‐film growth, detailed structural, domain, and physical‐property characterization, it is observed that the system undergoes a gradual transformation (with increasing strontium content) from droplet‐like a 1 / a 2 domains in a c / a domain matrix, to a connected‐labyrinth geometry of c / a domains, to a disconnected labyrinth structure of the same, and, finally, to droplet‐like c / a domains in an a 1 / a 2 domain matrix. A relationship between the different mixed‐phase modulation patterns and its topological nature is established. Annealing the connected‐labyrinth structure leads to domain coarsening forming distinctive regions of parallel c / a and a 1 / a 2 domain stripes, offering additional design flexibility. Finally, it is found that the connected‐labyrinth domain patterns exhibit the highest dielectric permittivity.

Kavle, Pravin↗

DOE OSTI2025

Colossal Cryogenic Electro‐Optic Response Through Metastability in Strained BaTiO 3 Thin Films

The search for thin film electro-optic materials that can retain superior performance under cryogenic conditions has become critical for quantum computing. Barium titanate thin films show large linear electro-optic coefficients in the tetragonal phase at room temperature, which is severely degraded down to ≈200 pm V −1 in the rhombohedral phase at cryogenic temperatures. There is immense interest in manipulating these phase transformations and retaining superior electro-optic properties down to liquid helium temperature. Utilizing the thermodynamic theory of optical properties, a large low-temperature electro-optic response is designed by engineering the energetic competition between different ferroelectric phases, leading to a low-symmetry monoclinic phase with a massive electro-optic response. The existence of this phase is demonstrated in a strain-tuned BaTiO 3 thin film that exhibits a linear electro-optic coefficient of 2516 ± 100 pm V −1 at 5 K, which is an order of magnitude higher than the best reported performance thus far. Importantly, the electro-optic coefficient increases by 100 × during cooling, unlike the conventional films, where it degrades. Further, at the lowest temperature, significant higher order electro-optic responses also emerge. These results represent a new framework for designing materials with property enhancements by stabilizing highly tunable metastable phases with strain.

barium titanate↗

DOE OSTI2023

Oxidation Driven Thin‐Film Solid‐State Metal Dealloying Forming Bicontinuous Nanostructures

Abstract Solid‐state metal dealloying (SSMD) is a promising method for fabricating nanoscale metallic composites and nanoporous metals across a range of materials. Thin‐film SSMD is particularly attractive due to its ability to create fine features via solid‐state interfacial reactions within a thin‐film geometry, which can be integrated into devices for various applications. This work examines a new dealloying couple, namely the Nb–Al alloy with the dealloying agent Sc, as previously predicted in the machine‐learning (ML) models. Prior ML predictions aimed to guide the design of nanoarchitectured materials through dealloying, relying on intuition‐driven discovery within a large parameter space. However, this work reveals that at the nanoscale, the involvement of oxygen in thin film processing may instead drive the dealloying process, resulting in the formation of bicontinuous nanostructures similar to those formed by metal‐agent dealloying. The phase evolution, as well as chemical and morphological changes, are closely analyzed using a combination of X‐ray absorption spectroscopy, diffraction, and scanning transmission electron microscopy to understand the mechanisms behind nanostructure formation. The findings suggest a potential pathway for utilizing oxygen to drive the formation of bicontinuous metal–metal oxide nanocomposites, paving the way for further development of functional nanoporous materials in diverse fields.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Atomic‐Scale Mechanisms of Nucleation and Stabilization in CuCrO 2 and CuFeO 2 Delafossite Thin Films on Al 2 O 3

Abstract Delafossite thin films exhibit a range of intriguing physical properties derived from their layered structure, which consists of alternating noble metal ( A + ) and ( B O 2 − ) sublayers in an AB O 2 stoichiometry. The integration of these properties into functional devices requires the successful epitaxial growth of delafossites as thin films on appropriate substrates. Unfortunately, their unique lattice geometry complicates growth, as different delafossites display variable behavior on the same substrate, often unrelated to lattice mismatch. This suggests the presence of yet unidentified stabilization mechanisms that enable the selective growth of certain delafossites, allowing them to be grown either as films themselves or to be used as buffer layers for subsequent deposition. In this study, advanced scanning transmission electron microscopy (STEM) is employed to investigate the nucleation mechanisms governing the stable growth of Cu‐based delafossites on Al 2 O 3 , specifically CuCrO 2 and CuFeO 2 thin films synthesized via molecular‐beam epitaxy. These findings reveal that a combination of a misfit dislocation network at the interface and monolayer‐deep chemical intermixing effectively relieves lattice mismatch strain. This mechanism, which differs fundamentally from that observed in Pd‐based delafossites, provides key insights into the controlled epitaxy of delafossite materials.

Scheid, Anna [Max Planck Institute for Solid State↗

DOE OSTI2021

Nanocomposite‐Seeded Epitaxial Growth of Single‐Domain Lithium Niobate Thin Films for Surface Acoustic Wave Devices

Epitaxial lithium niobate (LNO) thin films are an attractive material for devices across a broad range of fields, including optics, acoustics, and electronics. These applications demand high‐quality thin films without in‐plane growth domains to reduce the optical/acoustical losses and optimize efficiency. Twin‐free single‐domain‐like growth has been achieved previously, but it requires specific growth conditions that might be hard to replicate. In this work, a versatile nanocomposite‐seeded approach is demonstrated as an effective approach to grow single‐domain epitaxial lithium niobate thin films. Films are grown through a pulsed laser deposition method and growth conditions are optimized to achieve high‐quality epitaxial film. A comprehensive microstructure characterization is performed and optical properties are measured. A piezoelectric acoustic resonator device is developed to demonstrate the future potential of the nanocomposite‐seeded approach for high‐quality LNO growth for radio frequency (RF) applications.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Real‐Time Observation of Slowed Charge Density Wave Dynamics in Thinned 1T‐TaS 2

Abstract Transient electrical pulsing is used to investigate the slowed charge density wave (CDW) kinetics of 1T‐TaS 2 . These measurements distinguish a fast response of the material, consistent with the onset of self‐heating, from much slower transients that occur on timescales orders of magnitude longer than this. The latter variations appear consistent with slow configurational changes in the CDW, which, due to the thin nature of the 1T‐TaS 2 , can be distinguished from the much faster dynamics of Joule heating. Experiments in which the cooling of the material is interrupted, demonstrate the possibility of “programming” it in different, strongly nonequilibrium, CDW phases. Collectively, the results point to the existence of a complex free‐energy space for the thinned material, whose multi‐valley structure and hidden metastable states govern the resulting thermal and field‐driven dynamics. Crucially, this work demonstrates that while the CDW dynamics in this material may have a thermal character, the timescales associated with these motions can be very different from those on which self‐heating occurs. This discovery will be important for efforts to implement active devices that utilize the CDW states of thinned 1T‐TaS 2 .

Yin, Shenchu↗