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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Stress dependent oxidation of sputtered niobium and effects on superconductivity

We report on the suppression of room temperature oxidation of DC sputtered niobium films and the effects upon the superconductive transition temperature, T{sub c}. Niobium was sputter-deposited on silicon dioxide coated 150 mm wafers and permitted to oxidize at room temperature and pressure for up to two years. Resistivity and stress measurements indicate that tensile films greater than 400 MPa resist bulk oxidation with measurements using transmission electron microscope, electron dispersive X-ray spectroscopy, x-ray photoelectric spectroscopy, and secondary ion mass spectrometry confirming this result. Although a surface oxide, Nb{sub 2}O{sub 5}, consumed the top 6–10 nm, we measure less than 1 at. % oxygen and nitrogen in the bulk of the films after the oxidation period. T{sub c} measurements using a SQUID magnetometer indicate that the tensile films maintained a T{sub c} approaching the dirty superconductive limit of 8.4 K after two years of oxidation while maintaining room temperature sheet resistance. This work demonstrates that control over niobium film stress during deposition can prevent bulk oxidation by limiting the vertical grain boundaries ability to oxidize, prolonging the superconductive properties of sputtered niobium when exposed to atmosphere.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

HF treatment effect for carbon deposition on silicon (111) by DC sputtering technique

Surface modifications of Si (111) substrate by HF solution for thin film carbon deposition have been systematically studied. Thin film carbon on Si (111) has been deposited using DC Unbalanced Magnetron Sputtering with carbon pellet doped by 5% Fe as the target. EDAX characterization confirmed that the carbon fraction on Si substrate much higher by dipping a clean Si substrate by HF solution before sputtering process in comparison with carbon fraction on Si substrate just after conventional RCA. Moreover, SEM and AFM images show the uniform thin film carbon on Si with HF treatment, in contrast to the Si without HF solution treatment. These experimental results suggest that HF treatment of Si surface provide Si-H bonds on top Si surface that useful to enhance the carbon deposition during sputtering process. Furthermore, we investigate the thermal stability of thin film carbon on Si by thermal annealing process up to 900 °C. Atomic arrangements during annealing process were characterized by Raman spectroscopy. Raman spectra indicate that thin film carbon on Si is remaining unchanged until 600 °C and carbon atoms start to diffuse toward Si substrate after annealing at 900 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Structural and optical properties of CdO thin films deposited by RF magnetron sputtering technique

Cadmium oxide (CdO) thin films were deposited on glass substrate by r.f. magnetron sputtering technique using a high purity (99.99%) Cd target of 2-inch diameter and 3 mm thickness in an Argon and oxygen mixed atmosphere with sputtering power of 50W and sputtering pressure of 2×10{sup −2} mbar. The prepared films were characterized by X-ray diffraction (XRD), optical spectroscopy and scanning electron microscopy (SEM). The XRD analysis reveals that the films were polycrystalline with cubic structure. The visible range transmittance was found to be over 70%. The optical band gap increased from 2.7 eV to2.84 eV with decrease of film thickness.

36 MATERIALS SCIENCE↗
DOE OSTI2014

The impact of argon admixture on the c-axis oriented growth of direct current magnetron sputtered Sc{sub x}Al{sub 1−x}N thin films

The piezoelectric properties of wurtzite aluminium nitride (w-AlN) are enhanced by alloying with scandium (Sc), thus offering superior properties for applications in micro electro-mechanical systems devices. Sc{sub x}Al{sub 1−x}N thin films have been prepared by DC reactive magnetron sputtering on Si (100) substrates from a single target. When targeting a concentration range from x = 0 up to x = 0.15, the preparation conditions have been optimized by varying the Ar/N{sub 2} ratio in the sputtering gas. To incorporate an increasing Sc concentration, a higher Ar/N{sub 2} ratio has to be applied during the deposition process. Hence, the argon concentration in the sputtering gas becomes a crucial parameter for microstructure-related parameters. To determine phase purity, degree of c-axis orientation, lattice parameter, and grain size, the Sc{sub x}Al{sub 1−x}N thin films were investigated by techniques, such as scanning electron microscopy, transmission electron microscopy, and X-ray diffraction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Auger electron nanoscale mapping and x-ray photoelectron spectroscopy combined with gas cluster ion beam sputtering to study an organic bulk heterojunction

The lateral and vertical distributions of organic p/n bulk heterojunctions for an organic solar cell device are, respectively, investigated using nanometer-scale Auger electron mapping and using X-ray photoelectron spectroscopy (XPS) with Ar gas cluster ion beam (GCIB) sputtering. The concentration of sulfur, present only in the p-type material, is traced to verify the distribution of p-type (donor) and n-type (acceptor) materials in the blended structure. In the vertical direction, a considerable change in atomic sulfur concentration is observed using XPS depth profiling with Ar GCIB sputtering. In addition, Auger electron mapping of sulfur reveals the lateral 2-dimensional distribution of p- and n-type materials. The combination of Auger electron mapping with Ar GCIB sputtering should thereby allow the construction of 3-dimensional distributions of p- and n-type materials in organic photovoltaic cells.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Simultaneous impact of neutron irradiation and sputtering on the surface structure of self–damaged ITER–grade tungsten

Simultaneous effects of neutron irradiation and long–term sputtering on the surface relief of ITER–grade tungsten were studied. The effects of neutron–induced displacement damage have been simulated by irradiation of tungsten target with W{sup 6+} ions of 20 MeV energy. Ar{sup +} ions with energy 600 eV were used as imitation of charge exchange atoms in ITER. The surface relief was studied after each sputtering act. The singularity in the WJ–IG surface relief was ascertained experimentally at the first time, which determines the law of roughness extension under sputtering. As follows from the experimental data, the neutron irradiation has not to make a decisive additional contribution in the processes developing under impact of charge exchange atoms only.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Sputtering of cobalt film with perpendicular magnetic anisotropy on disorder-free graphene

Growth of thin cobalt film with perpendicular magnetic anisotropy has been investigated on pristine graphene for spin logic and memory applications. By reduction of the kinetic energy of the sputtered atoms using indirect sputtered deposition, deposition induced defects in the graphene layer have been controlled. Cobalt film on graphene with perpendicular magnetic anisotropy has been developed. Raman spectroscopy of the graphene surface shows very little disorder induced in the graphene by the sputtering process. In addition, upon increasing the cobalt film thickness, the disorder density increases on the graphene and saturates for thicknesses of Co layers above 1 nm. The AFM image indicates a surface roughness of about 0.86 nm. In addition, the deposited film forms a granular structure with a grain size of about 40 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Influence of sputtering power on the optical properties of ITO thin films

Tin doped indium oxide films are widely used in transparent conducting coatings such as flat panel displays, crystal displays and in optical devices such as solar cells and organic light emitting diodes due to the high electrical resistivity and optical transparency in the visible region of solar spectrum. The deposition parameters have a commendable influence on the optical and electrical properties of the thin films. In this study, ITO thin films were prepared by RF magnetron sputtering. The properties of the films prepared under varying sputtering power were compared using UV- visible spectrophotometry. Effect of sputtering power on the energy band gap, absorption coefficient and refractive index are investigated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Organic field-effect transistor nonvolatile memories utilizing sputtered C nanoparticles as nano-floating-gate

High-performance organic field-effect transistor nonvolatile memories have been achieved using sputtered C nanoparticles as the nano-floating-gate. The sputtered C nano-floating-gate is prepared with low-cost material and simple process, forming uniform and discrete charge trapping sites covered by a smooth and complete polystyrene layer. The devices show large memory window, excellent retention capability, and programming/reading/erasing/reading endurance. The sputtered C nano-floating-gate can effectively trap both holes and electrons, and it is demonstrated to be suitable for not only p-type but also n-type organic field-effect transistor nonvolatile memories.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Two-dimensional X-ray diffraction and transmission electron microscopy study on the effect of magnetron sputtering atmosphere on GaN/SiC interface and gallium nitride thin film crystal structure

The growth mechanisms of high quality GaN thin films on 6H-SiC by sputtering were investigated by X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). The XRD θ-2θ scans show that high quality (0002) oriented GaN was deposited on 6H-SiC by reactive magnetron sputtering. Pole figures obtained by 2D-XRD clarify that GaN thin films are dominated by (0002) oriented wurtzite GaN and (111) oriented zinc-blende GaN. A thin amorphous silicon oxide layer on SiC surfaces observed by STEM plays a critical role in terms of the orientation information transfer from the substrate to the GaN epilayer. The addition of H{sub 2} into Ar and/or N{sub 2} during sputtering can reduce the thickness of the amorphous layer. Moreover, adding 5% H{sub 2} into Ar can facilitate a phase transformation from amorphous to crystalline in the silicon oxide layer and eliminate the unwanted (33{sup ¯}02) orientation in the GaN thin film. Fiber texture GaN thin films can be grown by adding 10% H{sub 2} into N{sub 2} due to the complex reaction between H{sub 2} and N{sub 2}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

A compact and low-weight sputtering unit for in situ investigations of thin film growth at synchrotron radiation beamlines

In this work, we report on a highly variable, compact, and light high-vacuum sputter deposition unit designed for in situ experiments using synchrotron radiation facilities. The chamber can be mounted at various synchrotron beamlines for scattering experiments in grazing incidence geometry. The sample position and the large exit window allow to perform x-ray experiments up to large q values. The sputtering unit is easy to mount on existing experimental setups and can be remote-controlled. In this paper, we describe in detail the design and the performance of the new sputtering chamber and present the installation of the apparatus at different 3rd generation light sources. Furthermore, we describe the different measurement options and present some selected results. The unit has been successfully commissioned and is now available for users at PETRA III at DESY.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Anion formation in sputter ion sources by neutral resonant ionization

Focused Cs{sup +} beams in sputter ion sources create mm-diameter pits supporting small plasmas that control anionization efficiencies. Sputtering produces overwhelmingly neutral products that the plasma can ionize as in a charge-change vapor. Electron capture between neutral atoms rises as the inverse square of the difference between the ionization potential of the Cs state and the electron affinity of the sputtered atom, allowing resonant ionization at very low energies. A plasma collision-radiation model followed electronic excitation up to Cs(7d). High modeled Cs(7d) in a 0.5 mm recess explains the 80 μA/mm{sup 2} C{sup −} current density compared to the 20 μA/mm{sup 2} from a 1 mm recess.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Effect of sputtering pressure on microstructure and bolometric properties of Nb:TiO{sub 2−x} films for infrared image sensor applications

This study aims to investigate the influence of the sputtering pressure (P{sub S}) on Nb:TiO{sub 2−x} films to enhance the bolometric properties. A decrease in the growth rate with the sputtering pressure was perceived in amorphous Nb:TiO{sub 2−x} films. The incorporation of oxygen with P{sub S} was confirmed in an X-ray photo electron spectroscopy analysis. The electrical resistivity was increased with an increase in P{sub S} due to a decrease in the number of oxygen vacancies. The linear I-V characteristics confirmed the ohmic contact behavior between the Nb:TiO{sub 2−x} layer and the electrode material. The present investigation finds that the sample with lower resistivity has good bolometric properties with low noise and high universal bolometric parameters. Finally, the Nb:TiO{sub 2−x} sample deposited at a sputtering pressure of 2 mTorr shows better bolometric properties than other materials for infrared image sensor applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

MgAl{sub 2}O{sub 4}(001) based magnetic tunnel junctions made by direct sputtering of a sintered spinel target

We developed a fabrication process of an epitaxial MgAl{sub 2}O{sub 4} barrier for magnetic tunnel junctions (MTJs) using a direct sputtering method from an MgAl{sub 2}O{sub 4} spinel sintered target. Annealing the sputter-deposited MgAl{sub 2}O{sub 4} layer sandwiched between Fe electrodes led to the formation of a (001)-oriented cation-disorder spinel with atomically sharp interfaces and lattice-matching with the Fe electrodes. A large tunnel magnetoresistance ratio up to 245% at 297 K (436% at 3 K) was achieved in the Fe/MgAl{sub 2}O{sub 4}/Fe(001) MTJ as well as an excellent bias voltage dependence. These results indicate that the direct sputtering is an alternative method for the realization of high performance MTJs with a spinel-based tunnel barrier.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Single-crystal-like GdNdO{sub x} thin films on silicon substrates by magnetron sputtering and high-temperature annealing for crystal seed layer application

Single-crystal-like rare earth oxide thin films on silicon (Si) substrates were fabricated by magnetron sputtering and high-temperature annealing processes. A 30-nm-thick high-quality GdNdO{sub x} (GNO) film was deposited using a high-temperature sputtering process at 500°C. A Gd{sub 2}O{sub 3} and Nd{sub 2}O{sub 3} mixture was used as the sputtering target, in which the proportions of Gd{sub 2}O{sub 3} and Nd{sub 2}O{sub 3} were controlled to make the GNO’s lattice parameter match that of the Si substrate. To further improve the quality of the GNO film, a post-deposition annealing process was performed at a temperature of 1000°C. The GNO films exhibited a strong preferred orientation on the Si substrate. In addition, an Al/GNO/Si capacitor was fabricated to evaluate the dielectric constant and leakage current of the GNO films. It was determined that the single-crystal-like GNO films on the Si substrates have potential for use as an insulator layer for semiconductor-on-insulator and semiconductor/insulator multilayer applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Synthesis and x-ray characterization of sputtered bi-alkali antimonide photocathodes

Advanced photoinjectors, which are critical to many next generation accelerators, open the door to new ways of material probing, both as injectors for free electron lasers and for ultra-fast electron diffraction. For these applications, the nonuniformity of the electric field near the cathode caused by surface roughness can be the dominant source of beam emittance. Therefore, improving the photocathode roughness while maintaining quantum efficiency is essential to the improvement of beam brightness. Here in this article, we report the demonstration of a bi-alkali antimonide photocathode with an order of magnitude improved roughness by sputter deposition from a K 2 CsSb sputter target, using in situ and operando X-ray characterizations. We found that a surface roughness of 0.5 nm for a sputtered photocathode with a final thickness of 42 nm can be achieved while still yielding a quantum efficiency of 3.3% at 530 nm wavelength.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Room temperature deposition of superconducting niobium nitride films by ion beam assisted sputtering

We use room temperature ion beam assisted sputtering to deposit niobium nitride thin films. Electrical and structural characterizations were performed by electric transport and magnetization measurements at variable temperatures, X-ray diffraction, and atomic force microscopy. Compared to reactive sputtering of niobium nitride, films sputtered in the presence of an ion beam show a remarkable increase in the superconducting critical temperature T c , while exhibiting lower sensitivity to nitrogen concentration during deposition. Thickness dependence of the superconducting critical temperature is comparable to films prepared by conventional methods at high substrate temperatures and is consistent with behavior driven by quantum size effects or weak localization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Sputtered ferroelectric aluminum scandium boron nitride (Al 1−x−y B x Sc y N)/ n -GaN heterostructures

This work demonstrates ferroelectric switching in magnetron sputtered Al 1−x−y B x Sc y N/ n -GaN heterostructures. Using high power impulse magnetron sputtering, a silicon doped n -GaN bottom electrode with an electron concentration of 6.0 × 10 19 cm −3 is grown on c-plane sapphire. Al 1−x−y B x Sc y N films are prepared on the GaN surface with Al:B:Sc ratios that produce tensile, lattice matched, or compressive epitaxial strains. X-ray diffraction shows that lattice matched and compressively strained Al 1−x−y B x Sc y N compositions are pseudomorphic, while partial relaxation is observed for tensilely strained Al 1−x−y B x Sc y N/ n -GaN heterostructures. Electrically, the Al 1−x−y B x Sc y N/ n -GaN stacks show robust hysteresis; the P–E loops are fully saturated with both lattice matched and compressively strained Al 1−x−y B x Sc y N compositions exhibiting remanent polarization values of 135 μC/cm 2 . For comparison, Al 1−x−y B x Sc y N films are also prepared on metal organic chemical vapor deposition and single crystal GaN substrates to extend strain and morphology trends to more common substrate types. This report validates that sputter deposition is a feasible technique for fabricating strain-tunable ferroelectric III–N heterostructures with high crystalline fidelity and smooth surface morphologies.

42 ENGINEERING↗