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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 OSTI2016

Structural, mechanical, and magnetic properties of GaFe{sub 3}N thin films

Using the density-functional theory, the structural, mechanical, and magnetic properties were investigated for different GaFe{sub 3}N configurations: ferromagnetic, ferrimagnetic, paramagnetic, and nonmagnetic. Ferrimagnetic and high-spin ferromagnetic states exhibit the lowest energy and are the competing ground states as the total energy difference is 0.3 meV/atom only. All theoretically predicted values could be fully confirmed by experiments. For this, the authors synthesized phase pure, homogeneous, and continuous GaFe{sub 3}N films by combinatorial reactive direct current magnetron sputtering. Despite the low melting point of gallium, the authors succeeded in the growth of GaFe{sub 3}N films at a temperature of 500 °C. Those thin films exhibit a lattice parameter of 3.794 Å and an elastic modulus of 226 ± 20 GPa. Magnetic susceptibility measurements evidence a magnetic phase transitions at 8.0 ± 0.1 K. The nearly saturated magnetic moment at ±5 T is about 1.6 μB/Fe and is close to the theoretically determined magnetic moment for a ferrimagnetic ordering (1.72 μB/Fe).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Formation of homologous In{sub 2}O{sub 3}(ZnO){sub m} thin films and its thermoelectric properties

Homologous In{sub 2}O{sub 3}(ZnO){sub 5} thin films were produced on a synthetic quartz glass substrate by thermal annealing of magnetron sputtered In{sub 2}O{sub 3}-ZnO compound films. When the annealing temperature was increased to 700 °C, the sputtered In{sub 2}O{sub 3}-ZnO film with In{sub 2}O{sub 3} microcrystalline changed to a c-oriented homologous In{sub 2}O{sub 3}(ZnO){sub 5} structure, for which the crystallization is suggested to begin from the surface and proceed along with the film thickness. The annealing temperature of 700 °C to form the In{sub 2}O{sub 3}(ZnO){sub 5} structure was substantially lower than temperatures of conventional solid state synthesis from In{sub 2}O{sub 3} and ZnO powders, which is attributed to the rapid diffusional transport of In and Zn due to the mixing of In{sub 2}O{sub 3} and ZnO in the atomic level for sputtered In{sub 2}O{sub 3}-ZnO compound films. The homologous structure collapsed at temperatures above 900 °C, which is attributed to (1) zinc vaporization from the surface and (2) a gradual increase of zinc silicate phase at the interface. This c-oriented layer structure of homologous In{sub 2}O{sub 3}(ZnO){sub 5} thin films along the film thickness allowed the thin film to reach a power factor of 1.3 × 10{sup −4} W/m K{sup 2} at 670 °C, which is comparable with the reported maximum value for the textured In{sub 2}O{sub 3}(ZnO){sub 5} powder (about 1.6 × 10{sup −4} W/m K{sup 2} at 650 °C).

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of the cadmium chloride treatment on RF sputtered Cd{sub 0.6}Zn{sub 0.4}Te films for application in multijunction solar cells

Single phase Cd{sub 0.6}Zn{sub 0.4}Te (CdZnTe) films of 1 μm thickness were deposited by radio frequency planar magnetron sputter deposition on commercial soda lime glass samples coated with fluorine-doped tin oxide and cadmium sulphide (CdS). The stack was then treated with cadmium chloride (CdCl{sub 2}) at different temperatures using a constant treatment time. The effect of the CdCl{sub 2} treatment was studied using optical, materials, and electrical characterization of the samples and compared with the as-deposited CdZnTe film with the same stack configuration. The band gap deduced from Tauc plots on the as-deposited CdZnTe thin film was 1.72 eV. The deposited film had good crystalline quality with a preferred orientation along the {111} plane. After the CdCl{sub 2} treatment, the absorption edge shifted toward longer wavelength region and new peaks corresponding to cadmium telluride (CdTe) emerged in the x-ray diffraction pattern. This suggested loss of zinc after the CdCl{sub 2} treatment. The cross sectional transmission electron microscope images of the sample treated at 400 °C and the energy dispersive elemental maps revealed the absence of chlorine along the grain boundaries of CdZnTe and residual CdTe. The presence of chlorine in the CdTe devices plays a vital role in drastically improving the device performance which was not observed in CdZnTe samples treated with CdCl{sub 2}. The loss of zinc from the surface and incomplete recrystallization of the grains together with the presence of high densities of stacking faults were observed. The surface images using scanning electron microscopy showed that the morphology of the grains changed from small spherical shape to large grains formed due to the fusion of small grains with distinct grain boundaries visible at the higher CdCl{sub 2} treatment temperatures. The absence of chlorine along the grain boundaries, incomplete recrystallization and distinct grain boundaries is understood to cause the poor performance of the fabricated devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Synthesis of model sodium sulfide films

We report the direct deposition of model sodium sulfide films by RF magnetron sputtering from Na 2 S and Na 2 S 2 deposition targets. Analytical characterization and electrochemical cycling indicate that the deposited films are amorphous with stoichiometries that correspond to Na 2 S 3 and Na 2 S 2 formed from the Na 2 S and Na 2 S 2 targets, respectively. We propose that the loss of Na in the case of the Na 2 S target is due to preferential sputtering of Na resulting from the higher energy required to break the Na–S bonds in Na 2 S. Here, the development of thin film sodium sulfides opens a new route to understanding their fundamental properties, such as Na + transport, conductivity, and reactivity.

preferential sputtering↗
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 OSTI2016

Technique for forming ITO films with a controlled refractive index

A new method for fabricating transparent conducting coatings based on indium-tin oxide (ITO) with a controlled refractive index is proposed. This method implies the successive deposition of material by electron-beam evaporation and magnetron sputtering. Sputtered coatings with different densities (and, correspondingly, different refractive indices) can be obtained by varying the ratio of the mass fractions of material deposited by different methods. As an example, films with effective refractive indices of 1.2, 1.4, and 1.7 in the wavelength range of 440–460 nm are fabricated. Two-layer ITO coatings with controlled refractive indices of the layers are also formed by the proposed method. Thus, multilayer transparent conducting coatings with desired optical parameters can be produced.

36 MATERIALS SCIENCE↗
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↗