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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Ferroelectrics everywhere: Ferroelectricity in magnesium substituted zinc oxide thin films

We demonstrate ferroelectricity in Mg-substituted ZnO thin films with the wurtzite structure. Zn 1–x Mg x O films are grown by dual-cathode reactive magnetron sputtering on (111)-Pt // (0001)-Al 2 O 3 substrates at temperatures ranging from 26 to 200 °C for compositions spanning from x = 0 to x = 0.37. X-ray diffraction indicates a decrease in the c-lattice parameter and an increase in the a-lattice parameter with increasing Mg content, resulting in a nearly constant c/a axial ratio of 1.595 over this composition range. Transmission electron microscopy studies show abrupt interfaces between Zn 1–x Mg x O films and the Pt electrode. When prepared at pO 2 = 0.025, film surfaces are populated by abnormally oriented grains as measured by atomic force microscopy for Mg concentrations >29%. Raising pO 2 to 0.25 eliminates the misoriented grains. Optical measurements show increasing bandgap values with increasing Mg content. When prepared on a 200 °C substrate, films display ferroelectric switching with remanent polarizations exceeding 100 μC cm –2 and coercive fields below 3 MVcm –1 when the Mg content is between ~30% and ~7%. Substrate temperature can be lowered to ambient conditions, and when doing so, capacitor stacks show only minor sacrifices to crystal orientation and nearly identical remanent polarization values; however, coercive fields drop below 2 MV/cm. Using ambient temperature deposition, we demonstrate ferroelectric capacitor stacks integrated directly with polymer substrate surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Growth and structure of alpha-Ta films for quantum circuit integration

Tantalum films incorporated into superconducting circuits have exhibited low surface losses, resulting in long-lived qubit states. The remaining loss pathways originate in microscopic defects that manifest as two level systems (TLSs) at low temperatures. These defects limit performance, so careful attention to tantalum film structures is critical for optimal use in quantum devices. In this work, we investigate the growth of tantalum using magnetron sputtering on sapphire, Si, and photoresist substrates. In the case of sapphire, we present procedures for the growth of fully-oriented films with α-Ta [1 1 1]//Al2O3 [0 0 0 1] and α-Ta [1 −1 0]//Al2O3 [1 0 −1 0] orientational relationships and having residual resistivity ratio (RRR) ∼ 60 for 220 nm thick films. On Si, we find a complex grain texturing with Ta [1 1 0] normal to the substrate and RRR ∼ 30. We further demonstrate airbridge fabrication using Nb to nucleate α-Ta on photoresist surfaces. For the films on sapphire, resonators show TLS-limited quality factors of 1.3 ± 0.3 × 106 at 10 mK (for a waveguide gap and conductor width of 3 and 6 μm, respectively). Structural characterization using scanning electron microscopy, x-ray diffraction, low temperature transport, secondary ion mass spectrometry, and transmission electron microscopy reveal the dependence of residual impurities and screw dislocation density on processing conditions. The results provide practical insights into the fabrication of advanced superconducting devices including qubit arrays and guide future works on crystallographically deterministic qubit fabrication.

42 ENGINEERING↗
DOE OSTI2025

Topochemical Synthesis and Electronic Structure of High-Crystallinity Infinite-Layer Nickelates on an Orthorhombic Substrate

Superconductivity in infinite-layer nickelates has stirred much research interest, to which questions regarding the nature of superconductivity remain elusive. A critical leap forward to address these intricate questions is through the growth of high-crystallinity infinite-layer nickelates, including the “parent” phase. Here, we report the synthesis of a high-quality thin-film nickelate, NdNiO 2 . This is achieved through the growth of a perovskite precursor phase (NdNiO 3 ) of superior crystallinity on the NdGaO 3 substrate by off-axis RF magnetron sputtering and a low-temperature topochemical reduction using NaH. We observe a nonlinear Hall effect at low temperatures in this “non-doped” phase. We further study the electronic properties using advanced X-ray scattering and first-principles calculations. We observe spectroscopic indications of the enhanced two-dimensionality and a reduced hybridization of Nd 5d and Ni 3d orbitals. These findings unlock new pathways for preparing high-quality infinite-layer nickelates and provide new insights into the intrinsic features of these compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Ferroelectricity of wurtzite Al 1−x Hf x N heterovalent alloys

Thin films of aluminum hafnium nitride (Al1−xHfxN) were synthesized via reactive magnetron sputtering for Hf contents up to x = 0.13. X-ray diffraction showed a single c-axis oriented wurtzite phase for all films. Hard x-ray photoelectron spectroscopy demonstrated homogeneous Al:Hf distribution through the thin films and confirmed their insulating character. A collection of complementary tests showed unambiguous polarization inversion, and thus ferroelectricity in multiple samples. Current density vs electric field hysteresis measurements showed distinct ferroelectric switching current peaks, the piezoelectric coefficient d 33,f,meas measured using a double beam laser interferometer (DBLI) showed a reversal in sign with similar magnitude, and anisotropic wet etching confirmed field-induced polarization inversion. This demonstrates the possibility of using tetravalent–and not just trivalent–alloying elements to enable ferroelectricity in AlN-based thin films, highlighting the compositional flexibility of ferroelectricity in wurtzites and greatly expanding the chemistries that can be considered for future devices.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Structural dependence of hydrogen evolution reaction on transition metal catalysts sputtered at different temperatures in alkaline media

In the present article, we studied the catalytic activity of magnetron sputtered Mo, V, Ni, and Co thin films for hydrogen evolution reaction (HER) in the alkaline electrolyte. Here, we find that the HER potentials (η 10 ) of the Mo and V thin film catalysts sputtered at 800 °C shift positive with respect to those of the film catalysts sputtered at 25°C. For Mo metal the observed shift of η 10 was 280 mV and for V metal observed shift of η 10 was 390 mV. On the other hand, minimal effect of sputtering temperature on both Ni and Co thin film catalyst activity for HER was observed. Structural analysis reveals that Mo and V prepared at 800 °C have uncommon face centered cubic (fcc, 0.74 packing density) structure as opposed to room-temperature sputtered Mo and V thin films which have common body centered cubic (bcc, 0.68 packing density) structure, resulting in significant increases of the packing densities when they are prepared at 800 °C. On the other hand, the high-temperature prepared thin films of Ni and Co retained fcc structures, resulting in no density changes compared to the room-temperature prepared fcc Ni and hexagonal close packed (hcp, 0.74 packing density) Co. Impedance spectroscopy shows that fcc Mo is a better catalyst than fcc Ni, which is considered an industry standard for non-noble pure metal-based catalysts in alkaline media. Stability tests also suggest that fcc Mo thin film catalysts prepared at 800 °C are more durable than fcc Ni thin films. Our study points out that structure phases of catalysts can be a key factor governing the activities of transition metals for HER in alkaline media.

08 HYDROGEN↗
DOE OSTI2022

Time-resolved electron energy distribution functions at the substrate during a HiPIMS discharge with cathode voltage reversal

Abstract The time-dependent plasma properties of a high-power impulse magnetron sputtering plasma are investigated which include a positive ‘kick’ pulse on the sputtering target 2 μ s after the main negative pulse, this reversing the voltage on the cathode. At a substrate 15 cm distant from the magnetron, the time-dependent electron energy distribution function (EEDF), plasma potential, potential commute time and plasma diffusion properties are measured using a single Langmuir probe. Results show that the positive pulse on the target expels plasma and raises the plasma potential across the chamber on the order of 1 to 2 μ s, which is the time scale of the electron diffusion. The EEDF at the substrate fits a Druyvesteyn distribution during the main negative pulse rising slightly in average energy over time. The distribution is still Druyvesteyn and at the very start of the positive pulse, but then loses the higher energy electrons and drops in average electron energy as the positive pulse progresses. A Boltzmann equation solver, BOLSIG+, was used to predict the EEDF at the substrate during the positive pulse and it agrees best with the measurements assuming a value of 0.2 Td for the E / N (electric field/gas number density).

Physics↗
DOE OSTI2020

Sputter-deposited low-stress boron carbide films

Significant challenges have been faced in the manufacturing of low-stress B 4 C films. Here, we demonstrate a set of process parameters for direct-current magnetron sputter deposition of smooth, high-purity, amorphous B 4 C films with near-zero total residual stress and with thicknesses up to 10 μm. Films are characterized by a combination of high-energy ion scattering, x-ray diffraction, electron microscopy, and stress measurements based on substrate curvature. In order to facilitate the process transfer to other sputtering geometries, the favorable deposition conditions are correlated with distributions of landing energies and incident angles of depositing species estimated by Monte Carlo simulations of ballistic collisions and gas phase atomic transport. Based on such simulations, a decrease in compressive stress with increasing Ar working gas pressure is attributed to the corresponding broadening of the angular distribution of depositing species and associated atomic shadowing effects.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Cu and Ni Co-sputtered heteroatomic thin film for enhanced nonenzymatic glucose detection

Abstract In this work, we report a wafer-scale and chemical-free fabrication of nickel (Ni) and copper (Cu) heteroatomic Cu–Ni thin films using RF magnetron sputtering technique for non-enzymatic glucose sensing application. The as-prepared wafer-scale Cu–Ni thin films exhibits excellent electrocatalytic activity toward glucose oxidation with a 1.86 μM detection limit in the range of 0.01 mM to 20 mM range. The Cu–Ni film shows 1.3- and 5.4-times higher glucose oxidation activity in comparison to the Cu and Ni electrodes, respectively. The improved electrocatalytic activity is attributed to the synergistic effect of the bimetallic catalyst and high density of grain boundaries. The Cu–Ni electrodes also possessed excellent anti-interference characteristics. These results indicate that Cu–Ni heteroatomic thin film can be a potential candidate for the development of non-enzymatic glucose biosensor because of its chemical free synthesis, excellent reproducibility, reusability, and long-term stability.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Large anisotropic magnetocaloric effect in all-sputtered epitaxial terbium thin films

We present an experimental investigation of the magnetic and magnetocaloric properties of sputtered epitaxial and amorphous Tb thin films. We grew epitaxial Nb (50-nm)/Tb (100-nm) bilayer thin films on Al 2 O 3 $(11\bar{2}0)$ substrate using DC magnetron sputtering at high temperature, with excellent crystalline quality of the hcp Tb(0001) layer. While the amorphous Tb thin film exhibits more isotropic magnetocaloric properties, we show that the epitaxial Tb thin film displays large anisotropic magnetocaloric properties, with a large maximum magnetic entropy change of 6.27 J kg -1 K -1 at the Néel temperature as well as a large relative cooling power of 225 J kg -1 with a magnetic field change ΔH = 20 kOe applied along the in-plane direction. These large and anisotropic magnetocaloric properties are much larger than those measured for the amorphous Tb thin film, or previously reported for Tb-based thin-film structures. Our findings highlight the opportunities for growing epitaxial rare-earth thin films using sputtering techniques and demonstrate the importance of crystallographic control on the magnetocaloric effect in Tb thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Microstructural and Superconducting Radiofrequency Properties of Multilayer Sequentially Sputtered Nb 3 Sn films

Nb 3 Sn is considered as a potential candidate for superconducting radiofrequency cavities for particle acceleration due to its higher transition temperature of 18.3 K and higher superheating field of 400 mT. Nb 3 Sn films can be grown inside the surface of a Nb cavity by sequentially sputtering multiple layers of Nb and Sn thin films followed by annealing at 950 °C for 3 h. We report on the properties of Nb 3 Sn films grown on Nb substrates by magnetron sputtering. The films’ crystal structure, surface morphology, and composition were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The films had a polycrystalline Nb 3 Sn structure with a fine-grain surface and an atomic Sn composition of ~23%. The RF surface resistance of the films was measured for different temperatures at 7.4 GHz to understand the feasibility of this method for the SRF application. The RF surface resistance of the films was 5 mΩ at 12 K, which is about 2 orders of magnitude higher than 60 μΩ previously measured in Nb 3 Sn films grown by Sn vapor diffusion. Finally, the sputtered film had a superconducting transition at 17.2 K, which is also lower than 17.9 K observed in Nb 3 Sn film prepared by vapor diffusion.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Nb₃Sn Coating of a 2.6 GHz SRF Cavity by Sputter Deposition Technique

Nb₃Sn is of interest as a coating for SRF cavities due to its higher transition temperature Tc ~18.3 K and superheating field Hsh ~400 mT, both are twice that of Nb. Nb₃Sn coated cavities can achieve high-quality factors at 4 K and can replace the bulk Nb cavities operated at 2 K. A cylindrical magnetron sputtering system was built, commissioned, and used to deposit Nb₃Sn on the inner surface of a 2.6 GHz single-cell Nb cavity. With two identical cylindrical magnetrons, this system can coat a cavity with high symmetry and uniform thickness. Using Nb-Sn multilayer sequential sputtering followed by annealing at 950°C for 3 hours, polycrystalline Nb₃Sn films were first deposited at the equivalent positions of the cavity’s beam tubes and equator. The film’s composition, crystal structure, and morphology were characterized by energy dispersive spectroscopy, X-ray diffraction, and atomic force microscopy. The Tc of the films was measured by the four-point probe method and was 17.61 to 17.76 K. Based on these studies, ~1.2 micron thick Nb₃Sn was deposited inside a 2.6 GHz Nb cavity. We will discuss first results from samples and cavity coatings, and the status of the coating system.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Effect of substrate tilt on sputter-deposited AuTa films

Gold-tantalum alloy films are of interest for biomedical and magnetically-assisted inertial confinement fusion applications. However, growth mechanisms of such Au-Ta alloy films are not well understood. Here, we systematically study the effect of substrate tilt on properties of films deposited by direct current magnetron sputtering from a AuTa alloy target. Experimental data is correlated with distributions of landing energies and incident angles of sputtered and backscattered species calculated by Monte Carlo simulations of ballistic collisions and gas phase atomic transport. Results reveal that the deposition rate and film density monotonically decrease with increasing substrate tilt. Properties are similar for films with a tilt of 40° and below: films are amorphous, with an average compressive stress of 0.5 GPa, a density of 16 g/cm 3 , and electrical resistivity of 200 μΩ cm. The critical substrate tilt angle for the onset of porosity, a transition to a reduced stress state, and an increase in electrical resistivity lies between 40 and 60°. Based on Monte Carlo simulations, these changes in film properties are correlated with an increase in the average impact angle of the ballistic component of atomic flux. Implications of these results to deposition onto non-planar substrates are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ion-beam assisted sputtering of titanium nitride thin films

Abstract Titanium nitride is a material of interest for many superconducting devices such as nanowire microwave resonators and photon detectors. Thus, controlling the growth of TiN thin films with desirable properties is of high importance. This work aims to explore effects in ion beam-assisted sputtering (IBAS), were an observed increase in nominal critical temperature and upper critical fields are in tandem with previous work on Niobium nitride (NbN). We grow thin films of titanium nitride by both, the conventional method of DC reactive magnetron sputtering and the IBAS method, to compare their superconducting critical temperatures $$T_{c}$$ T c as functions of thickness, sheet resistance, and nitrogen flow rate. We perform electrical and structural characterizations by electric transport and x-ray diffraction measurements. Compared to the conventional method of reactive sputtering, the IBAS technique has demonstrated a 10% increase in nominal critical temperature without noticeable variation in the lattice structure. Additionally, we explore the behavior of superconducting $$T_c$$ T c in ultra-thin films. Trends in films grown at high nitrogen concentrations follow predictions of mean-field theory in disordered films and show suppression of superconducting $$T_c$$ T c due to geometric effects, while nitride films grown at low nitrogen concentrations strongly deviate from the theoretical models.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Controlled Growth of Ta Oxide With Reactive Sputtering for Overlap Josephson Junction Application

Josephson junctions $\($JJs$\)$ are indispensable elements for superconducting quantum electronics. There is a growing need to develop processes for high quality JJs. Here we explore the growth of Ta oxide as a dielectric barrier for Metal-Oxide-Metal overlap JJ implementations. We study films of Ta oxides prepared with reactive magnetron sputtering. TaOx is grown on silicon and Ta films with varying RF power and oxygen concentrations. Tuning these parameters allows us to control the rate of deposition as well as composition of polycrystalline Ta oxides needed to meet our dielectric requirements for Josephson Junctions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

High-throughput multimodal exploration of a nanocrystalline Cu-Ag library

Sputter-deposited, nanocrystalline Cu-Ag thin films produced across a broad compositional and deposition-parameter space were evaluated to unravel the process-structure-property relationships important for creating hard, conductive electrical contacts and coatings. Combinatorial deposition involving pulsed direct current magnetron sputtering of elemental targets enabled swift examination of nearly the full range of alloy compositions and a relevant portion of deposition atomistics. Several high-throughput characterization modalities were employed to evaluate the chemistry, structure, and properties of the films. The resultant hardness, modulus, film density, crystal texture, and resistivity were analyzed in terms of key deposition characteristics (incident atom kinetic energy and incidence angle) predicted by binary-collision, kinematic Monte Carlo simulations. The study revealed improved hardness, parabolic resistivity dependence on composition, and compositional and process dependencies of film tarnishing. The results are discussed in the context of variations in microstructure and film density. Transmission electron microscopy and X-ray diffraction demonstrate several forms of compositional variation including solute segregation to grain boundaries as well as periodic, intragranular compositional modulations. Annealing of a Cu-rich alloy film exhibiting grain boundary segregation showed that this as-deposited, compositional variation is not stable above 100 °C. Finally, the Cu-Ag system is shown to have potential for hard, conductive, tarnish-resistant and room temperature-stable nanocrystalline thin films across the composition space.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Effects of hydrogen on sputter-deposited boron carbide films

Sputter deposition of B 4 C films requires precise control over the microstructure and the nucleation and growth of nodular defects. Here, we study the properties of B 4 C films deposited with substrate holder temperatures of 250, 450, or 510 °C and different substrate tilt angles by direct-current magnetron sputtering in either pure Ar or a mixture of 4% H 2 in Ar as the working gas. Results show that the addition of H 2 reduces the impedance of the plasma discharge, resulting in larger discharge currents at constant power, which is attributed to a lower ionization potential of H 2 than Ar. More importantly, films deposited with the H 2 containing plasma exhibit lower oxygen impurity incorporation, a lower density of nodular defects, and suppressed columnar microstructure. These results demonstrate the effectiveness of such a plasma doping approach to improve the properties of B 4 C films.

Wong, M. S. [Lawrence Livermore National Laborator↗
DOE OSTI2024

Unconventional spin-orbit torques from sputtered MoTe 2 films

Materials with strong spin-orbit coupling and low crystalline symmetry are promising for generating large unconventional spin-orbit torques (SOTs), such as in-plane fieldlike (FL) torques and out-of-plane dampinglike (DL) torques, which can effectively manipulate and deterministically switch an out-of-plane magnetization without the need for additional external in-plane magnetic fields. Here, we report SOTs generated by magnetron-sputtered 1⁢T' MoTe 2 /Permalloy (Py; Ni 80 ⁢Fe 20 )/MgO heterostructures using both spin-torque ferromagnetic resonance (ST-FMR) and second harmonic Hall measurements. We observed unconventional FL and DL torques in our samples due to spins polarized normal to the interface of MoTe 2 and Py layers, and studied the influence of crystallographic order and MoTe 2 layer thickness on the SOTs. By comparing the Raman spectra of 1⁢T' MoTe 2 samples prepared in different ways, we found a tensile strain in sputtered MoTe 2 films, which might further enhance the generation of unconventional torques by reducing the symmetry of 1⁢T' MoTe 2 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Sputter deposition of Ta 1 W 1 Au 1 Bi 7 films for next generation hohlraums

Hohlraum simulation predicts a higher x-ray drive from Ta 1 W 1 Au 1 Bi 7 compared with our current Au hohlraum. Here, we study the effect of deposition process parameters including deposition rate, working pressure, target-to-substrate distance, substrate bias, and substrate temperature on the microstructure of Ta1W1Au1Bi7 films deposited by direct current magnetron sputtering onto planar substrates. We found that the substrate temperature has a pronounced effect on the film microstructure. This is attributed to the Bi low melting point (271°C) causing its adatom mobility to be strongly dependent on the substrate temperature. Additionally, we observed phase separation for films deposited with a high substrate bias. These results have important implications for the development of a robust Ta 1 W 1 Au 1 Bi 7 hohlraum fabrication process.

36 MATERIALS SCIENCE↗