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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Deposition and characterization of α-Fe 2 O 3 /Pd thin films for neutron reflectometry studies

Here, we report deposition of hematite/Pd thin films on silicon wafers via radio frequency (RF) magnetron sputtering and subsequent characterization for future in situ neutron reflectometry studies. Following deposition, the hematite/Pd thin films were characterized as prepared and after annealing in air for 2h at 400, 500, and 600 °C, respectively. Raman spectroscopy, grazing incidence x-ray diffraction, and neutron reflectometry (NR) were used to characterize the structure and chemical compositions of the thin films. The results indicate that pure α-Fe 2 O 3 (hematite) films were produced, free from other iron oxide phases and impurities. NR data reveal that one intermediate layer between the Pd layer and the hematite layer was formed during sputtering deposition processes. The fitted scattering length density (SLD) of the as-deposited hematite layer is 70% of the theoretical SLD value, indicating that the grains are loosely packed in the RF-deposited hematite films. After annealing at elevated temperatures, the hematite films show increased SLD values but remain comparable to that of preannealed.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Nb 3 Sn coating of SRF cavity by cosputtering from a composite target

Here, we deposited an Nb 3 Sn film on the inner surface of a 2.6 GHz Nb superconducting radio frequency cavity by cosputtering using a composite of Nb and Sn tube targets in a DC cylindrical magnetron sputtering system, followed by the thermal annealing of the coated cavity. An aluminum mockup cavity, replicating a 2.6 GHz Nb SRF cavity geometry, was utilized to optimize deposition parameters, resulting in cosputtered Nb–Sn films with an Sn content of 32–42 at. % on the beam tubes and equator positions. Several annealing conditions were investigated to improve the surface homogeneity of the Nb 3 Sn film. The best cosputtered Nb–Sn film was achieved after annealing at 600 °C for 6 h, followed by annealing at 950 °C for 1 h. The best process was applied to a Nb cavity, which was RF tested in a cryogenic dewar. RF testing of the Nb 3 Sn-coated cavity demonstrated a superconducting transition temperature of 17.78 K. The Nb 3 Sn cavity underwent light Sn recoating, followed by additional RF testing, resulting in the enhancement of the RF performance, primarily due to the improved surface homogeneity of the Nb 3 Sn coating.

Nb3Sn film↗
DOE OSTI2017

Growth of ultrathin twin-free b-oriented YBa{sub 2}Cu{sub 3}O{sub 7} {sub –} {sub x} films

Twin-free b-oriented YBa{sub 2}Cu{sub 3}O{sub 7–x} films with a thickness less than 40 nm have been epitaxially grown on (100)SrLaGaO{sub 4} crystals. Based on the temperature dependence of resistance, the onset temperature of the transition to the superconducting state is found to be 90 K; the transition width is 4 K. The film growth has been performed in two stages. A (100)PrBa{sub 2}Cu{sub 3}O{sub 7–x} buffer layer was previously grown on a (100)SrLaGaO{sub 4} substrate by rf magnetron sputtering in an Ar–O{sub 2} gas mixture at a continuous and monotonic increase in temperature from 660 to 830°C. The main YBa{sub 2}Cu{sub 3}O{sub 7–x} film was grown on the buffer layer surface by pulsed laser deposition in an oxygen medium at a fixed temperature (800°C). The above processes were implemented in different chambers, which were connected by a vacuum channel for transporting samples. Both films were grown in situ, without contacting atmosphere in all growth stages. An X-ray diffraction study has shown that the YBa{sub 2}Cu{sub 3}O{sub 7–x} films are single-crystal and free of precipitates of other phases and domains of other orientations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Experimental and Theoretical Analyses of Zinc-Vacancy-Induced Room-Temperature Ferromagnetism in ZnO Films

Room-temperature ferromagnetism (RTFM) has been observed in RF magnetron sputtered ZnO films with O{sub 2} as an auxiliary gas after annealing. The films exhibit hexagonal wurtzite structure and observable ferromagnetism. A maximum of saturation magnetization of 4.75 emu/cm{sup 3} is obtained. The zinc vacancies are believed as the RTFM origin, and oxygen vacancies are not an incentive of magnetization of the ZnO films. Theoretical study based on first principles calculation is performed for better understanding of the RTFM in substance. The intrinsic physical mechanism of regulating the ferromagnetic of the ZnO film is analyzed in detail.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electrical Properties of p-NiO/n-Si Heterostructures Based on Nanostructured Silicon

Silicon nanowires are formed on n-Si substrates by chemical etching. p-NiO/n-Si heterostructures are fabricated by reactive magnetron sputtering. The energy diagram of anisotype p-NiO/n-Si heterostructures is constructed according to the Anderson model. The current–voltage and capacitance–voltage characteristics are measured and analyzed. The main current-transport mechanisms through the p-NiO/n-Si heterojunction under forward and reverse biases are established.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Structural, Thermal and Luminescence Properties of AlN:Tm Thin Films Deposited on Silicon Substrate and Optical Fiber

Thin films of AlN:Tm are deposited on a Si(111) and Si(100) substrates and optical fiber by rf magnetron sputtering method. 200–400 nm thick films are deposited at various temperatures to observe the effect of temperature on their structure and morphology. Liquid nitrogen is used to deposit films at low temperature of –196°C. An electric heater is used to grow films at 250–700°C range. The deposited films are analyzed for their structure and thermal stability using X-ray diffraction and thermogravimetric analysis. Films deposited at liquid nitrogen temperature are amorphous and those deposited at high temperature are crystalline. Average grain size, strain and interatomic distance of the crystalline films are calculated. The grain size and inter-atomic distance increase from 36.54 to 45.12 nm and from 0.2368 to 0.25 nm respectively. Photoluminescence of the films excited by 783 nm crystal laser shows an intense infrared emission from Tm{sup +3} at 802 nm as a result of {sup 3}H{sub 4} → {sup 3}H{sub 6} transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Technique for the Formation of Antireflection Coatings Based on ITO Films

A technique for forming transparent conducting indium-tin-oxide films for applications, which require high current densities, are considered. These films have to combine a good surface conductivity with an increased transmittance of radiation within a wide wavelength range. A two-stage process is designed to fabricate such coatings: at the first stage, a dense indium-tin-oxide film with high electrical conductivity is formed; then, an additional antireflection layer of the same material is deposited. Possible methods for optimizing these additional indium-tin-oxide films obtained by forming nanostructured self-assembled coatings on the surface of dense films are investigated. It is shown that the best light extraction over a wide wavelength range is provided by the composite film-deposition technique, which consists in the deposition of self-assembled nanostructured coatings by electron-beam evaporation on a hot substrate and the further filling of voids by magnetron sputtering at room temperature. Since the optical properties of the obtained antireflection coatings depend on the mass ratio of materials deposited at each stage, the technique makes it possible to optimize the film properties on the basis of problems specified by the area of their application. Computer simulation of the behavior of the material distribution in the structure of the studied coatings confirms the ability of the method of combined film deposition to form the smoothest character of the change in the effective refractive index of the coating structure, which leads to the most efficient extraction of optical-range light.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Laser Annealing of Thin ITO Films on Flexible Organic Substrates

Indium–tin oxide (ITO) thin films on polyethylene-terephthalate film substrates are fabricated at room temperature by reactive magnetron sputtering. The minimum of the resistivity of ITO films formed at room temperature is 4.5 × 10 -4 Ω cm. The laser annealing of ITO films from 140 to 600 nm in thickness increases their conductivity from 10 to 24% depending on the energy density to the film and irradiation dose. It is established that the laser annealing of films up to 250 nm in thickness is efficient at an energy density in the range from 12 to 35 mJ/cm 2 . Films from 390 to 600 nm in thickness should be annealed by laser radiation with an energy density of no lower than 46 mJ/cm 2 . A model problem taking into account the influence of radiative cooling and heat exchange of the film and the substrate on the variation in the film temperature over time during laser annealing is considered. A one-dimensional thermal conductivity equation for a bilayer medium is used. The maximal stresses in the ITO film under various annealing modes are calculated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Nanostructured ITO/SiO{sub 2} Coatings

The influence of a SiO{sub 2} layer deposited onto nanostructured transparent conductive films of indium and tin oxide (ITO) on their optical characteristics is investigated. For this purpose, SiO{sub 2} films of various thicknesses are deposited by magnetron sputtering on samples with ITO films containing whiskers of preferentially vertical orientation and possessing steadily decreasing reflectance. It is shown that this makes it possible to attain noticeable coating antireflection under the condition of the uniform overgrowth of ITO whiskers by the SiO{sub 2} layer. The influence of the SiO{sub 2} layer on the optical characteristics of a dense unstructured ITO film is also investigated. The results for structured and unstructured ITO/SiO{sub 2} coatings with identical material mass contents are compared. It is noted that due to the liability of ITO material to degradation during operation in the composition of transparent conductive contacts, the results can also be interesting for the formation of coatings more resistant to the effect of the environment.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Investigation of the Current–Voltage Characteristics of New MnO{sub 2}/GaAs(100) and V{sub 2}O{sub 5}/GaAs(100) Heterostructures Subjected to Heat Treatment

Complex oxide films with a thickness of about 200 nm are formed during the thermal oxidation of GaAs with magnetron-deposited V{sub 2}O{sub 5} and MnO{sub 2} nanolayers. The electrical parameters of the films (reverse-bias breakdown voltage and current density) are determined by the method of current–voltage (I–V) characteristics at room temperature in the bias range from –5 to +5 V, and their composition and surface morphology are investigated. It is shown that V{sub 2}O{sub 5} facilitates the more intense (in comparison with MnO{sub 2}) chemical bonding of arsenic at the internal interface with the formation of As{sub 2}O{sub 5}. As a result, thermally oxidized V{sub 2}O{sub 5}/GaAs heterostructures exhibit higher breakdown voltages.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Some Physical Properties of the New Intermetallic Compound NbCd{sub 2}

Solid solutions of cadmium in niobium and NbCd{sub 2} phase are formed by magnetron sputtering and coprecipitation on substrates moving relative to the flow of Nb and Cd particles. The NbCd{sub 2} phase can be described by a tetragonal unit cell with the parameters a = 0.84357 nm, c = 0.54514 nm, and c/a = 0.6426. A very high hole concentration in NbCd{sub 2} is established by studying the coating absorption and transmission spectra corresponding to the intermetallic-compound composition near the fundamental absorption edge, determining the band gap, and measuring the carrier mobility. Such a concentration is characteristic of a strongly degenerate semiconductor or metal. The band gap is determined to be 1.26 eV. The variation in the concentration of carriers and their mobility depending on the cadmium concentration in coatings of the Nb–Cd system confirms the occurrence of the NbCd{sub 2} phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Formation of ncl-Si in the Amorphous Matrix a-SiO{sub x}:H Located near the Anode and on the Cathode, Using a Time-Modulated DC Plasma with the (SiH{sub 4}–Ar–O{sub 2}) Gas Phase (C{sub O{sub 2}} = 21.5 mol %)

The formation of ncl-Si in the amorphous matrix a-SiO{sub x}:H using a time-modulated DC plasma at an elevated oxygen content of C{sub O{sub 2}} = 21.5 mol % in a gas mixture of (SiH{sub 4}–Ar–O{sub 2}) is investigated. Plasma modulation implies the repeated (n = 180) switching on (for t{sub on} = 5, 10, 15 s) and switching off (for t{sub off} = 5, 10, 15 s) of the magnet coil of the DC magnetron. The effect of self-induction is used to enhance the processes of SiH{sub 4} dissociation, the formation of Si nanoparticles, and the ionization of oxygen and ncl-Si flows towards the electrodes. The samples are located both on an electrically isolated substrate holder near the anode and on the cathode (beyond its erosion zone). These experiments show that the shape of the dependences of the photoluminescence intensity I{sub PL}{sup ncl−Si} on the wavelength Λ are identical for all pairs of samples on the anode and cathode. When the t{sub on} value is small (t{sub on} = 5 s), the difference in the sample location only slightly affects the infrared (IR) spectra. At longer times t{sub on} (≥10 s) and a short time t{sub off} (5 s), the amorphous matrix located on the cathode is enriched with oxygen (as compared with that near the anode). The optimal plasma-modulation parameters are found to be t{sub off}/t{sub on} = 5, 10, 15/10 and t{sub off}/t{sub on} = 5, 10/15; under these conditions, the amorphous matrix has a “perfect structure” and is transparent to radiation, and the I{sub PL}{sup ncl−Si} value is the largest in the range λ ≈ 0.75–0.9 μm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Growth and Structural, Magnetic, and Magnetooptical Properties of ZnO Films Doped with a Fe{sup 57} 3d Impurity

ZnO films obtained by high-frequency magnetron sputtering and doped with a Fe{sup 57} metallic 3d impurity by the diffusion method are studied. The type of local environment of Fe{sup 57} impurity atoms on varying the deposition parameters of ZnO films is determined by Mössbauer spectroscopy. It is established that the ground state of Fe{sup 57} impurity atoms corresponds to metallic iron in the magnetically ordered state and there is a small fraction of Fe{sup 57} atoms with a local environment corresponding to the complex oxide Fe{sub 3}O{sub 4}, having the magnetically ordered state; there is also a fraction of iron atoms in the paramagnetic state. The magnetic and magnetooptical parameters of the films were measured using magnetooptic Kerr effect. The spectral dependences of the polar magnetooptic Kerr effect in ZnO(Fe{sup 57}) films are measured in a photon energy range of 1.5–4.5 eV and simulated by the effective-medium method. It is established that ZnO(Fe{sup 57}) possess an easy-plane magnetic anisotropy with a magnetization lying in the film plane.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Microstructure and Mechanical Properties of Multilayer α-AlN/α-BCN Coating as Functions of the Current Density during Sputtering of a B{sub 4}C Target

Multilayer AlN/BCN coating of nanometer scale have been prepared by magnetron sputtering of Al and B{sub 4}C targets in an argon–nitrogen atmosphere during deposition on a Si substrate. These coating have an X-ray amorphous structure and the maximum Knoop hardness of 27 GPa (at the current density 100 mA). The first-principle molecular dynamics calculations show that the B4–BN layer is dynamically unstable; thus, it will not be epitaxial and will be amorphous or have a structure different from the B4–BN structure. The thermal vacuum annealing from 600 to 800°C of samples with multilayer nanosized coating leads to the decrease in the Knoop hardness to 18 GPa; however, the coating structure is retained X-ray amorphous.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The Element Composition Variation in Lead Zirconate Titanate upon the Ion-Plasma Deposition: Experiment and Simulation

The element composition modification is experimentally studied in PZT thin films obtained via the RF magnetron sputtering with variable working gas pressure. The experimental data were interpreted through the statistic simulation of thermalization and diffusion of sprayed Pb, Zr, and Ti atoms during the ion-plasma deposition of PZT thin films. The simulation data are shown to adequately describe (within the limits of 5%) the change in element composition at various pressures of the gas environment. The study conducted enables one to produce PZT thin films with a set element composition, which is essential for optimizing the electric and physical properties of solid solutions at the morphotropic phase boundary.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Photoluminescence of Cu{sub 2}O Crystals of Different Origins

Low-temperature luminescence spectra of Cu{sub 2}O crystals grown by different methods (copper oxidation, induction charge melting, magnetron sputtering, and hydrothermal), as well as natural crystals, have been compared. It is suggested that the high quality of natural crystals and crystals grown by the hydrothermal method is due to the fact that they grow for a long time at relatively low temperatures, which facilitates the minimization of stress.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Influence of Silver and Gold Nanoparticles and Thin Layers on Charge Carrier Generation in InGaN/GaN Multiple Quantum Well Structures and Crystalline Zinc Oxide Films

It has been shown that Ag and Au nanoparticles and thin layers influence charge carrier generation in InGaN/GaN multiple quantum well structures and crystalline ZnO films owing to the surface morphology heterogeneity of the semiconductors. When nanoparticles 10 < d < 20 nm in size are applied on InGaN/GaN multiple quantum well structures with surface morphology less nonuniform than that of ZnO films, the radiation intensity has turned out to grow considerably because of a plasmon resonance with the participation of localized plasmons. The application of Ag or Au layers on the surface of the structures strongly attenuates the radiation. When Ag and Au nanoparticles are applied on crystalline ZnO films obtained by rf magnetron sputtering, the radiation intensity in the short-wavelength part of the spectrum increases insignificantly because of their highly heterogeneous surface morphology.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Condensation Surface Temperature as a Means for Studying Film Formation Mechanisms

A rise in the condensation surface temperature during film growth is a result of energy dissipation on the condensation surface. An example of energy dissipation is the dissipation of chemical reaction heat, which releases during film deposition by reactive magnetron sputtering. The monitoring of the surface temperature during TiN film deposition by reactive (Ti–in–N{sub 2}) and nonreactive (TiN–in–Ar or TiN–in–N{sub 2}) sputtering methods has shown that this temperature is higher in the reactive case and decreases in the (TiN–in–Ar)–(TiN–in–N{sub 2}) sequence of nonreactive sputtering modifications. It has been found that the composition and crystal structure of TiN films do not depend on the growth method and are identical to those of bulk titanium nitride. Based on these results, a formation mechanism of films obtained by the above methods has been suggested. In the case of reactive sputtering, the film was supposed to grow on the condensation surface through a reaction between titanium and nitrogen atoms. In the cases of nonreactive sputtering, the film forms from TiN molecules.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗