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DOE OSTI2020

Atomic Layer Deposition Niobium Nitride Films for High-Q Resonators

Niobium nitride (NbN) is a useful material for fabricating detectors because of its high critical temperature and relatively high kinetic inductance. In particular, NbN can be used to fabricate nanowire detectors and mm-wave transmission lines. When deposited, NbN is usually sputtered, leaving room for concern about uniformity at small thicknesses. In this work, we present atomic layer deposition niobium nitride (ALD NbN) as an alternative technique that allows for precision control of deposition parameters such as film thickness, stage temperature, and nitrogen composition. Atomic-scale control over film thickness admits a high degree of uniformity for films 4–30 nm thick; control over deposition temperature gives rise to growth rate changes, which can be used to optimize film thickness and critical temperature. In order to charac- terize ALD NbN in the radio-frequency regime, we construct single-layer micro- wave resonators and test their performance as a function of stage temperature and input power. ALD processes can admit high resonator quality factors, with ≥ 43% of resonators above Q i = 10 6 , which in turn increase detector multiplexing capabilities. i Furthermore, we find critical temperatures in the range of 7.5–10.9 K that vary as a function of cycle count and deposition temperature.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2024

Diamond and SiC Detectors for Rare Event Searches

In recent years, there has been increasing interest in developing detectors which are sensitive to sub-GeV dark matter and low-energy events from coherent neutrino scattering. Due to carbon’s light atomic weight and its tendency to form crystals with high-energy, long-lived phonon modes, carbon-based crystals (including diamond and silicon carbide (SiC)) present themselves as natural target materials for scattering-based searches in this regime. Here, we present our preliminary results in adapting our TES-based detectors to these substrates, specifically 4-H SiC and polycrystalline diamond. We focus on our fabrication efforts, specifically tuning the transition temperature (T C ) of tungsten films sputtered on these materials, as well as our advancement toward fabricating and testing devices on these substrates.

47 OTHER INSTRUMENTATION↗

DOE OSTI2018

Thickness-Dependent Thermal Oxidation of Ni into NiO Thin Films

We report thickness-dependent thermal oxidation in Ni (t = 10–300 nm) thin films exposed to air annealing and the resulting vibrational, magnetic and electrical properties of Ni films deposited directly on thermally oxidized Si substrate using magnetron sputtering technique at ambient temperature. As-deposited Ni films exhibit face-centred cubic structure with fine crystals and large lattice constant (a{sub Ni}) at lower t (< 50 nm). With increasing t, a{sub Ni} decreases and approaches to bulk value. With increasing T{sub A}, a{sub Ni} not only decreases to bulk Ni due to improved crystallization but also reduces below bulk Ni for t > 50 due to formation of NiO. The relative fraction of Ni and NiO in annealed films up to 400 {sup ∘}C strongly depends on t. Annealing Ni films at 500 {sup ∘}C results into complete oxidation of Ni into granular-type NiO. X-ray reflectivity studies reveal that oxidation process occurs from surface of the films converting Ni into NiO possibly through layer by layer process, which is subtle to t. Raman spectra show that intensity ratio between one-phonon longitudinal optical (LO) and two-phonon LO bands decreases and intensity of two-magnon band increases with increasing t for films annealed at particular T{sub A}. This confirms the growth of NiO not only with increasing T{sub A}, but also with t. As-deposited films exhibit ferromagnetism at room temperature. The presence of Ni and NiO in annealed films implies coexistence of ferromagnetic and antiferromagnetic interactions, leading to tunable exchange bias (H{sub E}), whose magnitude strongly depends on the ratio between Ni and NiO. Electrical resistance (R) of the as-deposited Ni films decreases with increasing t and follows the Namba’s model. Upon annealing, R increases largely due to oxidation of Ni. The observed results are explained on the basis of thickness dependent thermal oxidation process with increasing T{sub A}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Effect of Substrate Temperature on Structural, Morphological, Magnetic, and Electrical Properties of Fe{sub 2}CoSi Heusler Alloy Thin Films for Spin-Based Device Applications

Fe{sub 2}CoSi based Heusler alloy thin films are deposited on single crystal Si (111) substrate at different substrate temperatures varying from room temperature to 600 °C using ultrahigh vacuum DC magnetron sputtering. Structural analysis of the prepared thin films is carried out using GI-XRD measurement and it conform ordered L2{sub 1} crystal structure of the films deposited at 450 °C and above. The atomic force microscopic (AFM) images of Fe{sub 2}CoSi thin films exhibiting 3D-like growth on Si (111) substrate at varying temperatures. The magnetic property of the thin films is studied using vibrating sample magnetometer (VSM). At 450 °C of substrate temperature, the prepared thin film exhibits high saturation magnetization (M{sub s} = 948 emu/cc) and low coercivity (H{sub c} = 8 Oe). The self-energy magnetization of the film and its own field is very high, when the temperature of the substrate was maintained at 450 °C and switching field ratio for this film was obtained as ~ 0.9 due to its high crystallinity and atomic ordering. The electrical property of Fe{sub 2}CoSi thin film is investigated using four-probe technique and a positive magnetoresistive behavior was observed for thin film deposited at a substrate temperature of 450 °C which indicates the possible half-metallic nature at room temperature. The enhanced magnetic and electrical properties obtained for the thin film prepared at 450 °C substrate temperature is highly suitable for spin based device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Characterizing the Josephson Effect on Ba-122 Single-Crystal Junctions

This paper presents c-direction hybrid Josephson junctions with base electrodes of Co:BaFe{sub 2}As{sub 2} single crystals. To realize Josephson junctions, it applies standard photolithography technologies and a newly developed surface polishing method that was used. As conventional isotropic s-wave superconductor counter electrodes used double layers of Pb/In. The artificial barrier for the tunneling junctions consists of a thin sputtered Ti layer or a thermally evaporated Al layer; both layers were used as an insulator barrier. For characterizing the Josephson effects with TiO{sub x} barrier, we could realize I{sub c}R{sub N} products of about 13.7 μV and unconventional I{sub c}-T dependencies. The formation of Shapiro steps under the influence of microwave irradiation and magnetic field to the junctions will be discussed as well.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Friction and Wear Properties of CrSiCN/SiC Tribopairs in Water Lubrication

CrSiCN coatings (3.4 at.% Si) were prepared on 316L stainless steels using unbalanced magnetron sputtering. According to the analysis results of x-ray diffractometer and x-ray photoelectrons spectroscopy, silicon in CrSiCN coatings mainly presented in the amorphous forms of a-SiN, a-SiCN and a-SiC. The hardness and Young’s modulus of CrSiN coatings were 19.4 ± 0.6 and 306.1 ± 5.9 GPa, respectively. In addition, the ball-on-disk sliding tests of CrSiCN/SiC tribopairs were performed in distilled water at varying velocities (0.1-0.5 m/s) and loads (2-12 N). The friction coefficient of tribopairs presented a decreasing trend with respect to velocity at low applied loads (≤ 4 N). To be specific, the low friction coefficient of 0.05-0.14 accompanied with polished wear scar was obtained at high velocities and low loads. Finally, the wear mechanism map of CrSiCN/SiC tribopairs was proposed based on a combination of friction coefficient, wear scar morphology and wear rates of tribopairs.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Structure and Tribological Properties of CrTiAlCN Coatings with Various Carbon Contents

Multi-component CrTiAlCN coatings with different carbon contents were deposited on AISI M2 high-speed steels using unbalanced magnetron sputtering via adjusting the C{sub 2}H{sub 2} flow rates, and their microstructures and mechanical properties were characterized by using SEM, EDS, XRD, Vickers hardness tester and scratch tester, respectively. The tribological properties of CrTiAlCN coatings sliding against SUS440C high carbon martensitic balls were performed using ball-on-disk tribo-tester. The results showed that CrTiAlCN coatings were mainly comprised of (111) and (200) crystal orientation. The maximum hardness of coatings was 29.4 ± 1.5 GPa as the carbon content was 22.5 at.%. With an increase in the carbon content of coatings, the friction coefficients and wear rates of CrTiAlCN/SUS440C tribo-pairs were significantly reduced, and the wear mechanism of coatings changed from adhesive wear to abrasive wear.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Influence of Substrate Bias Voltage on Corrosion and Wear Behavior of Physical Vapor Deposition CrN Coatings

The objective of the present paper is to study the influence of the substrate bias voltage on the microstructure, composition, deposition rate, tribological and corrosion properties of CrN coatings obtained by DC magnetron sputtering on 90CrMoV8 steel and Si (100) substrates. The substrate bias voltage varied from 0 to − 700 V. The deposited films were characterized by SEM, XRD and potentiodynamic polarization. The wear behavior and coefficient of friction were determined and investigated after rotative tribometer tests. The results indicated that the substrate bias voltage considerably affected the intrinsic properties of the CrN films. Indeed, it significantly influenced the grain size and the root-mean-squared roughness which varied from 20 to 29 nm, and from 9 to 19 nm, respectively, when polarization changed from 0 to − 700 V. All the CrN coatings have a dense columnar structure and are well crystallized according to the XRD analyses. Nevertheless, it has been shown that the peaks intensity decreased by increasing the substrate bias voltage. By applying a substrate bias voltage, it was obvious that the friction behavior was enhanced, and the wear volume was decreased. Finally, the CrN coating obtained under a substrate bias voltage of − 500 V presented the best corrosion resistance and wear resistance probably due to its dense microstructure.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Optimization of Interlayer/CrWN Bilayer Films Fabricated and Monitored under Shewhart Control

Chromium tungsten nitride (CrWN) films were deposited onto SUS 304 stainless steel, cutter inserts and glass substrates using direct current reactive magnetron sputtering, with pure W and Cr metal targets. The deposition parameters for the interlayer (W and WN) with multiple qualities were optimized using the gray Taguchi method. The microstructure of these coatings was determined using x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy. The results showed that the mechanical properties of bilayer samples with an interlayer of WN nitride film are superior to those with a W metal interlayer. Moreover, increasing the N{sub 2}/(N{sub 2} + Ar) flow ratio and working pressure enhanced the microhardness and the elastic recovery for coatings with an interlayer/CrWN bilayer. Dry milling tests also showed that bilayer film coatings have better mechanical performance. This increase in multiple performance characteristics is attributed to a bilayer that is manufactured using the gray Taguchi method. Control charts, which are powerful tools and widely used, were employed to monitor and ensure high-quality fabrication of the interlayer/CrWN bilayer and to show the coating processes to be stable and well regulated.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Atomic Layer-Deposited Al{sub 2}O{sub 3} Interlayer for Improved Tribological and Anti-corrosion Properties of TiN Hard Coating on 316L Stainless Steel

A dense Al{sub 2}O{sub 3} interlayer was inserted into TiN to enhance the tribological and anti-corrosion properties of TiN hard coating via a hybrid process of magnetron sputtering and atomic layer deposition (ALD). The influence of the ALD-Al{sub 2}O{sub 3} layer on the microstructure, mechanical, tribological and anti-corrosion properties of TiN was examined. The TiN-Al{sub 2}O{sub 3} coating exhibits low friction coefficient and specific wear rate, due to the structure change and columnar refinement caused by the addition of amorphous ALD-Al{sub 2}O{sub 3} interlay which improves the mechanical properties of hard coating. The improved corrosion properties of TiN are attributed to the fact that the insulating ALD-Al{sub 2}O{sub 3} used as a sealing layer can prevent the corrosive chlorine ions migrating into the lower TiN layer and block the charge transport in coatings. Moreover, raising the insertion position of ALD-Al{sub 2}O{sub 3} layer away from the steel substrate results in a further increase in the anti-corrosion property of TiN-Al{sub 2}O{sub 3} composite coating.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Visualization of Kirkendall Voids at Cu-Au Interfaces by In Situ TEM Heating Studies

Gold-plated copper alloys are used extensively in electrical contacts where diffusional processes are known to cause contact degradation. An in situ transmission electron microscopy (TEM) heating study was carried out to provide fundamental understanding of the aging phenomena in reasonable timescales. Samples to visualize the interface in TEM were prepared by focused ion beam (FIB) microscopy and heated in situ up to 350°C while holding at intermediate temperatures to enable imaging. The grain boundaries in Au coatings, specifically the columnar boundaries, provided rapid pathways for diffusion of Cu all the way to the Au surface. This unequal diffusion created vacancies in Cu which coalesced into Kirkendall voids. This in situ technique has been applied to visualize the diffusion pathways in electroplated and sputtered Au films deposited directly on Cu, as well the role of Ni and NiP as barrier layers for mitigating Cu diffusion.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Microstructure and Elevated Temperature Flexure Testing of Tungsten Produced by Electron Beam Additive Manufacturing

Abstract Due to their superior high-temperature thermomechanical capabilities, sputter erosion durability, and excellent resistance to hydrogen isotopes, tungsten materials have garnered significant interest in fusion nuclear applications. However, low room-temperature ductility and complex machining strategies present significant challenges for traditional fabrication. Electron beam powder bed fusion (EB-PBF) shows promise in manufacturing pure tungsten via high thermal energy input, elevated build temperature, and a tightly controlled high-vacuum environment. This work explores the process, structure, and property relationship of pure tungsten fabricated by EB-PBF, where 99.8% relative density was achieved with reduced cracking by isolating the build substrate and optimizing the print parameter suite. Optical and electron imaging revealed that the microstructure contained equiaxed grains along the build direction, with subgrains present in all inspected grains. Flexural testing at ambient and elevated temperatures demonstrated high ductility at 900°C and flexural strength of 470 MPa at room temperature of additively manufactured tungsten.

Zhang, Haozhi↗

DOE OSTI2018

E-beam manipulation of Si atoms on graphene edges with an aberration-corrected scanning transmission electron microscope

The burgeoning field of atomic-level material control holds great promise for future breakthroughs in quantum and memristive device manufacture and fundamental studies of atomic-scale chemistry. Realization of atom-by-atom control of matter represents a complex and ongoing challenge. Here, we explore the feasibility of controllable motion of dopant Si atoms at the edges of graphene via the sub-atomically focused electron beam in a scanning transmission electron microscope. Furthermore, we demonstrate that the graphene edges can be cleaned of Si atoms and then subsequently replenished from nearby source material. It is also shown how Si edge atoms may be “pushed” from the edge of a small hole into the bulk of the graphene lattice and from the bulk of the lattice back to the edge. This is accomplished through sputtering of the edge of the graphene lattice to bury or uncover Si dopant atoms. Finally, we demonstrate e-beam mediated hole healing and incorporation of dopant atoms. These experiments form an initial step toward general atomic-scale material control.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2019

Electron Attachment and Electron Ionization of Formic Acid Clusters Embedded in Helium Nanodroplets

We report the results of an experimental study of electron ionization of large helium nanodroplets doped with formic acid (FA). Several homologous series of cluster anions are observed, including [FA{sub n}-H]{sup −}, undissociated FA{sub n}{sup −}, and these ions complexed with one or more H{sub 2}O. Some major features resemble those observed upon sputtering of frozen FA films but they differ significantly from results obtained by electron attachment to bare FA clusters in the gas phase. The FA{sub n}{sup −} and (H{sub 2}O)[FA{sub n}-H]{sup −} series show abrupt onsets above n = 2 and 5, respectively. A prominent resonance in the anion yield occurs at 22.5 eV due to the formation of an intermediate He{sup −*}. Also observed are homologous series of [FA-H]{sup −} or [FA{sub 2}-H]{sup −} complexed with helium. The cation chemistry is dominated by the production of protonated formic acid clusters, [FA{sub n}H]{sup +}, but various other homologous cluster ion series are observed as well. .

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2019

MeV-SIMS TOF Imaging of Organic Tissue with Continuous Primary Beam

MeV-SIMS is an emerging mass spectrometry imaging method, which utilizes fast, heavy ions to desorb secondary molecules. High yields and low fragmentation rates of large molecules, associated with the electronic sputtering process, make it particularly useful in biomedical research, where insight into distribution of organic molecules is needed. Since the implementation of MeV-SIMS in to the micro-beam line at the tandem accelerator of Jožef Stefan Institute, MeV-SIMS provided some valuable observations on the distribution of biomolecules in plant tissue, as discussed by Jenčič et al. (Nucl. Inst. Methods Phys. Res. B. 371, 205–210, 2016; Nucl. Inst. Methods Phys. Res. B. 404, 140–145, 2017). However, limited focusing ability of the chlorine ion beam only allowed imaging at the tissue level. In order to surpass shortcomings of the existing method, we introduced a new approach, where we employ a continuous, low-current primary beam. In this mode, we bombard thin samples with a steady chlorine ion flux of approx. 5000 ions/s. After desorbing molecules, chlorine ions penetrate through the thinly cut sample and trigger the time-of-flight “start” signal on a continuous electron multiplier detector, positioned behind the sample. Such bombardment is more effective than previously used pulsing-beam mode, which demanded several orders of magnitude higher primary ion beam currents. Sub-micrometer focusing of low-current primary ion beam allows imaging of biological tissue on a subcellular scale. Simultaneously, new time-of-flight acquisition approach also improves mass resolution by a factor of 5. Within the article, we compare the performance of both methods and demonstrate the application of continuous mode on biological tissue. We also describe the thin sample preparation protocol, necessary for measurements with low primary ion currents. .

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2024

Liquid metal walls

Here, the plasma performance of fusion devices depends strongly on the chosen wall materials. Solid plasma-facing components (PFCs) are predominantly used in present devices, and are the most investigated candidates for fusion designs. High-Z materials such as tungsten (W) are the leading solid PFC material candidates. To date, a material choice that scales to steady-state reactor conditions has not been identified. Moreover, if plasma transient events such as edge-localized modes and disruptions cannot be altogether avoided or sufficiently mitigated, the projected peak heat and particle loads far exceed the power exhaust capabilities of solids. Liquid metal (LM) PFCs represent an intrinsic self-healing boundary that are both resilient to surface damage from transients, and that could handle high steady-state heat and particle fluxes. Flowing LM PFCs can be designed to remove “slag,” the buildup of material erosion due to plasma-material interactions, including charge exchange sputtering in the main chamber. Further, LM offer the prospect to manage hydrogenic species otherwise retained in the PFCs, which is important from a safety and inventory standpoint. The two most promising LMs are lithium (Li) and tin (Sn), although Sn–Li eutectics may be considered. While Sn offers a higher temperature window with low vapor pressure and low hydrogen retention, Li offers the prospect of enhanced energy confinement and higher acceptable core contamination limits, and this section focuses on Li PFCs. An LM PFC development research program developed LM PFC concepts for a nuclear fusion device via engineering design calculations, single-effect experiments, and staged prototypical experiments. A self-consistent design window was identified with liquid Li flow speeds ~5–10 m/s; plasma contamination was negligible for predicted Li evolution rates. While these preconceptual designs hold promise, there is substantial R&D needed to advance the technical readiness levels of LM PFCs for application to fusion power plants.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2016

Unusual size dependent strengthening mechanisms of Cu/amorphous CuNb multilayers

Nanostructured crystalline/amorphous metallic multilayers have been increasingly studied due to their high strength and potential enhancement of plasticity in amorphous metals. Here we report on mechanical behaviors of Cu/amorphous CuNb multilayers that were prepared by magnetron sputtering with equal individual layer thickness (h) varying from 1 to 200 nm. A medium-range-order amorphous CuNb layer formed between Cu and amorphous CuNb layers. This intermediate layer facilitates transmission of plasticity from Cu to amorphous layers by preventing the smear of dislocation core on the interface. The maximum hardness of Cu/amorphous CuNb multilayers is achieved when h ≤ 50 nm, and is much lower than the hardness of single-layer amorphous CuNb films. Molecular dynamics simulations show that, comparing with single-layer amorphous CuNb, the pile-up of dislocations in Cu layers lowers the stress for the activation of shear transformation zones in amorphous CuNb layers in multilayers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Mechanical properties of metal-ceramic nanolaminates: Effect of constraint and temperature

Al/SiC nanolaminates with equal nominal thicknesses of the Al and SiC layers (10, 25, 50 and 100 nm) were manufactured by magnetron sputtering. The mechanical properties were measured at 25 °C and 100 °C by means of nanoindentation and micropillar compression tests and the deformation mechanisms were analyzed by in situ micropillar compression tests in the transmission electron microscope. In addition, finite element simulations of both tests were carried out to ascertain the role played by the strength of the Al layers and by the elastic constraint of the ceramic layers on the plastic flow of Al in the mechanical response. It was found that the mechanical response was mainly controlled by the constraint during nanoindentation or micropillar compression tests of very thin layered (≈10 nm) laminates, while the influence of the strength of Al layers was not as critical. This behavior was reversed, however, for thick layered laminates (100 nm). Here, these mechanisms point to the different effects of layer thickness during nanoindentation and micropillar compression, at both temperatures, and showed the critical role played by constraint on the mechanical response of nanolaminates made of materials with a very large difference in the elasto-plastic properties.

36 MATERIALS SCIENCE↗