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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Fabrication of PbS nanoparticle coated amorphous carbon nanotubes: Structural, thermal and field emission properties

Graphical abstract: Simple chemical synthesis of PbS nanoparticle coated amorphous carbon nanotubes have shown better thermal stability and enhanced electron field emission properties. Highlights: {yields} PbS nanocrystals coated amorphous carbon nanotubes have been synthesized through a simple chemical route at low temperature. {yields} The composite is thermally more stable than amorphous CNTs. {yields} Composite have shown excellent cold cathode field emission property. -- Abstract: A simple chemical route for the synthesis of PbS nanoparticle coated amorphous carbon nanotubes (aCNTs) was described. The nanocomposite was prepared from an aqueous suspension of acid functionalized aCNTs, lead acetate (PbAc), and thiourea (TU) at room temperature. The phase formation and composition of the samples were characterized by X-ray diffraction and energy dispersive analysis of X-ray studies. The Fourier transformed infrared spectra analysis revealed the attachment of PbS nanoparticles on the acid functionalized aCNT surfaces. Morphology of the samples was analyzed with a field emission scanning electron microscope. UV-Vis study also confirmed the attachment of PbS nanoparticles on the walls of aCNTs. Thermal gravimetric analysis showed that the PbS coated aCNTs are more thermally stable than functionalized aCNTs. The PbS coated aCNTs showed enhanced field emission properties with a turn-on field 3.34 V {mu}m{sup -1} and the result is comparable to that of pure crystalline CNTs.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Coalescence-Induced Spontaneous Shedding of Microdroplets on Superhydrophobic Surfaces Featuring Enclosed Micropillars with Hierarchical Roughness

This study investigated water vapor condensation on superhydrophobic surfaces (SHSs) featuring micropillars enclosed by wall lattices and having three-tier hierarchical roughness. A total of five samples were created with three (NW-J, W200-J and W400-J samples) having large micropillar depth (~6 μm) and two (NW-S and W200-S samples) having small micropillar depth (~1 μm). Two distinct condensate removal modes were observed during condensation: coalescence-induced jumping on samples with large micropillar depth and coalescence-induced shedding on samples with small micropillar depth. The results showed that the diameter of the shedding droplet on the W200-S sample having small micropillar depth could be as small as 107 μm, as compared to the theoretical critical diameter of 267 μm for gravitational shedding on the same sample. The enhanced functionality of the three-tier nanotextures on the W200-S sample could effectively suppress localized pinning of the three-phase contact line and Wenzel neck formation during the growth of condensate droplets. Consequently, during multidroplet coalescence, the released surface energy easily overcomes the solid–liquid adhesion, leading to spontaneous shedding of merged droplets. The inclusion of the wall lattice aids condensate growth by the droplet self-alignment along the walls and promoting coalescence. As a result, the W200-S sample exhibited the highest condensate collection as well. In conclusion, the proposed surface design has great potential for scaling up and implementation in heating, ventilation, and air-conditioning equipment due to the simplicity of the surface morphology and the facile spray-coating method used to achieve hierarchical roughness.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Rapid phase synthesis of nanocrystalline cobalt ferrite

Synthesis of single phase nanocrystalline Cobalt Ferrite (CoFe{sub 2}O{sub 4}) was achieved by single step autocombustion technique with the use of citric acid as a chelating agent in mono proportion with metal. Specimens prepared with this method showed significantly higher initial permeability's than with the conventional process. Single phase nanocrystalline cobalt ferrites were formed at very low temperature. Surface morphology identification were carried out by transmission electron microscopy (TEM) analysis. The average grain size and density at low temperature increased gradually with increasing the temperature. The single phase formation is confirmed through powder X-ray diffraction analysis. Magnetization measurements were obtained at room temperature by using a vibrating sample magnetometer (VSM), which showed that the calcined samples exhibited typical magnetic behaviors. Temperature dependent magnetization results showed improved behavior for the nanocrystalline form of cobalt ferrite when compared to the bulk nature of materials synthesized by other methods.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Pulse electrodeposited nickel using sulphamate electrolyte for hardness and corrosion resistance

Highlights: • Nickel deposits from sulphamate solutions using pulse method are prepared. • Effect of duty cycle and frequency are studied. • XRD, SEM and AFM of the nickel deposits are characterized. • Corrosion characteristics of the nickel deposit are reported. - Abstract: Nickel deposits have been obtained on mild steel substrate by pulse current (PC) electrodeposition method using nickel sulphamate electrolyte. Micro hardness values increased with decreasing duty cycle and pulse frequency. X-ray diffraction studies revealed that (2 0 0) plane was predominant and the nickel deposit obtained at low duty cycle and low frequency has the smallest grain size. The surface morphology of the coatings was explored by scanning electron microscopy (SEM) and atomic force microscopy. These studies showed that the microstructure of the nickel coatings changed from pyramidal structure to homogeneous structure with increasing duty cycle and pulse frequencies. The corrosion resistance of coatings was evaluated by potentiodynamic polarization and electrochemical impedance studies in 3.5 wt% sodium chloride (NaCl) solutions. An enhancement of the corrosion resistance, charge-transfer resistance and wear resistance has been obtained at low duty cycle and low frequencies.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Optoelectronic and low temperature thermoelectric studies on nanostructured thin films of silver gallium selenide

Polycrystalline thin films of silver gallium selenide were deposited on ultrasonically cleaned soda lime glass substrates by multi-source vacuum co-evaporation technique. The structural analysis done by X-ray diffraction ascertained the formation of nano structured tetragonal chalcopyrite thin films. The compound formation was confirmed by X-ray photo-electron spectroscopy. Atomic force microscopic technique has been used for surface morphological analysis. Direct allowed band gap ∼1.78eV with high absorption coefficient ∼10{sup 6}/m was estimated from absorbance spectra. Low temperature thermoelectric effects has been investigated in the temperature range 80–330K which manifested an unusual increase in Seebeck coefficient with negligible phonon drag toward the very low and room temperature regime. The electrical resistivity of these n-type films was assessed to be ∼2.6Ωm and the films showed good photo response.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Amorphous indium gallium zinc oxide thin film grown by pulse laser deposition technique

Highly electrically conducting and transparent in visible light IGZO thin film were grown on glass substrate at substrate temperature of 400 C by a pulse laser deposition techniques. Structural, surface, electrical, and optical properties of IGZO thin films were investigated at room temperature. Smooth surface morphology and amorphous nature of the film has been confirmed from the AFM and GIXRD analysis. A resistivity down to 7.7×10{sup −3} V cm was reproducibly obtained while maintaining optical transmission exceeding 70% at wavelengths from 340 to 780 nm. The carrier densities of the film was obtain to the value 1.9×10{sup 18} cm{sup 3}, while the Hall mobility of the IGZO thin film was 16 cm{sup 2} V{sup −1}S{sup −1}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effects of Sintering Temperature on Structural, Morphological and Magnetic Properties of Strontium Ferrite Nanoparticles

In the present investigation, structural, morphological and magnetic properties of SrFe{sub 2}O{sub 4} ferrite nanoparticles prepared by a sol–gel method were studied. The techniques used in this investigation were thermogravimetric analysis/differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectrometry (FT-IR), vibrating sample magnetometry (VSM) and Curie temperature analysis. The average crystallite sizes of the SrFe{sub 2}O{sub 4} were calculated using the Scherrer formula and found in the range of 11–22 nm, and this can be attributed to the grain growth of the particles. The lattice parameter of SrFe{sub 2}O{sub 4} nanoparticles decreased from 6.64 to 6.51 nm as the sintering temperature was raised from 600 to 900 °C. FT-IR analysis confirmed that bands in the range 430–590 cm{sup − 1} are due to the stretching vibration of oxygen atom and metal ions (M–O) that is Fe–O confirming the formation of spinel ferrite. Surface morphology of the samples has been studied using FESEM. The elemental composition along with their relative ratios was given by EDX and was found to be in agreement with their initial calculated values. The saturation magnetization, magnetic coercivity and remanence increase with an increasing sintering temperature from 600 to 900 °C. The present study reports the Curie temperature with an amount of 551 °C of the synthesized strontium nanoferrites using the Faraday technique.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Anisotropic strain effects on the photoluminescence emission from heteroepitaxial and homoepitaxial nonpolar (Zn,Mg)O/ZnO quantum wells

We report on the properties of nonpolar a-plane (Zn,Mg)O/ZnO quantum wells (QW) grown by molecular beam epitaxy on r plane sapphire and a plane ZnO substrates. For the QWs grown on sapphire, the anisotropy of the lattice parameters of the (Zn,Mg)O barrier gives rise to an unusual in-plane strain state in the ZnO QWs, which induces a strong blue-shift of the excitonic transitions, in addition to the confinement effects. We observe this blue-shift in photoluminescence excitation experiments. The photoluminescence excitation energies of the QWs are satisfactorily simulated when taking into account the variation of the exciton binding energy with the QW width and the residual anisotropic strain. Then we compare the photoluminescence properties of homoepitaxial QWs grown on ZnO bulk substrate and heteroepitaxial QWs grown on sapphire. We show that the reduction of structural defects and the improvement of surface morphology are correlated with a strong enhancement of the photoluminescence properties: reduction of full width at half maximum, strong increase of the luminescence intensities. The comparison convincingly demonstrates the interest of homoepitaxial nonpolar QWs for bright UV emission applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

2.8 {mu}m emission from type-I quantum wells grown on InAs{sub x}P{sub 1-x}/InP metamorphic graded buffers

We report 2.8 {mu}m emission from compressively strained type-I quantum wells (QWs) grown on InP-based metamorphic InAs{sub x}P{sub 1-x} step-graded buffers. High quality metamorphic graded buffers showed smooth surface morphology and low threading dislocation densities of approximately 2.5 Multiplication-Sign 10{sup 6} cm{sup -2}. High-resolution x-ray diffraction scans showed strong satellites from multiple quantum wells grown on metamorphic buffers, and cross-sectional transmission electron microscopy revealed smooth and coherent quantum well interfaces. Room-temperature photoluminescence emission at 2.8 {mu}m with a narrow linewidth ({approx}50 meV) shows the promise of metamorphic growth for mid-infrared laser diodes on InP.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Synthesis of copper quantum dots by chemical reduction method and tailoring of its band gap

Metallic copper nano particles are synthesized with citric acid and CTAB (cetyltrimethylammonium bromide) as surfactant and chlorides as precursors. The particle size and surface morphology are analyzed by High Resolution Transmission Electron Microscopy. The average size of the nano particle is found to be 3 - 10 nm. The optical absorption characteristics are done by UV-Visible spectrophotometer. From the Tauc plots, the energy band gaps are calculated and because of their smaller size the particles have much higher band gap than the bulk material. The energy band gap is changed from 3.67 eV to 4.27 eV in citric acid coated copper quantum dots and 4.17 eV to 4.52 eV in CTAB coated copper quantum dots.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effects of Bi{sup 3+} Substitution on Structural, Morphological, and Magnetic Properties of Cobalt Ferrite Nanoparticles

In this research, the structural, morphological, and magnetic properties of Bi-doped cobalt ferrite (CoFe{sub 2-x}Bi{sub x}O{sub 4}) nanoparticles with x = 0.0, 0.05, 1, 0.15, and 0.2, prepared by the sol-gel method, were studied. In order to characterize the samples, several equipment and analyses including thermo-gravimetric and differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Fourier transform infrared spectrometer (FT-IR), and vibrating sample magnetometer (VSM) were used. The average crystallite sizes of the prepared CoFe{sub 2-x}Bi{sub x}O{sub 4} were calculated using the Scherer, UDM, SSP, and Halder-Wagner methods. The average crystallite sizes for the samples were found in the range of 26 to 44 nm, which can be attributed to the grain growth of the particles. FT-IR spectrum showed bands in the range of 430 to 590 cm{sup −1} due to the stretching vibration of an oxygen atom and metal ions (Fe-O), confirming the formation of spinel ferrite. Surface morphology of the samples was studied using FESEM. The VSM results showed that the saturation and remanence magnetizations increased by raising the doping values up to x = 0.1. The Curie temperature of the cobalt nanoferrites was determined using Faraday’s technique. The highest Curie temperature was found to be 580 °C for the undoped sample.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Characterisation of Ceramic-Coated 316LN Stainless Steel Exposed to High-Temperature Thermite Melt and Molten Sodium

Currently, stainless steel grade 316LN is the material of construction widely used for core catcher of sodium-cooled fast reactors. Design philosophy for core catcher demands its capability to withstand corium loading from whole core melt accidents. Towards this, two ceramic coatings were investigated for its application as a layer of sacrificial material on the top of core catcher to enhance its capability. Plasma-sprayed thermal barrier layer of alumina and partially stabilised zirconia (PSZ) with an intermediate bond coat of NiCrAlY are selected as candidate material and deposited over 316LN SS substrates and were tested for their suitability as thermal barrier layer for core catcher. Coated specimens were exposed to high-temperature thermite melt to simulate impingement of molten corium. Sodium compatibility of alumina and PSZ coatings were also investigated by exposing samples to molten sodium at 400 °C for 500 h. The surface morphology of high-temperature thermite melt-exposed samples and sodium-exposed samples was examined using scanning electron microscope. Phase identification of the exposed samples was carried out by x-ray diffraction technique. Observation from sodium exposure tests indicated that alumina coating offers better protection compared to PSZ coating. However, PSZ coating provided better protection against high-temperature melt exposure, as confirmed during thermite melt exposure test.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effect of dopent on the structural and optical properties of ZnS thin film as a buffer layer in solar cell application

In order to find the suitable alternative of toxic CdS buffer layer, deposition of pure ZnS and doped with Al by chemical bath deposition method have been reported. Further as grown pure and doped thin films have been annealed at 150°C. The structural and surface morphological properties have been characterized by X-Ray diffraction (XRD) and Atomic Force Microscope (AFM).The XRD analysis shows that annealed thin film has been polycrystalline in nature with sphalerite cubic crystal structure and AFM images indicate increment in grain size as well as growth of crystals after annealing. Optical measurement data give band gap of 3.5 eV which is ideal band gap for buffer layer for solar cell suggesting that the obtained ZnS buffer layer is suitable in a low-cost solar cell.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Electronic conduction mechanism for NFO/(Pb{sub 0.80}Sr{sub 0.20}) TiO{sub 3} bi-layered nanostructure multiferroic composite thin film

Multiferroic 2-2 type bi-layered NFO/(Pb{sub 0.80}Sr{sub 0.20}) TiO{sub 3} composite thin film on Pt/TiO{sub 2}/Si substrate was prepared by novel metallo-Organic process using spin coating technique. The structural and surface morphology were confirmed by X-Ray diffraction (XRD) atomic force microscope (AFM). Significantly improved ferroelectric properties (P{sub s} ~ 17.25, P{sub r} ~ 8.02 µC/cm{sup 2} and E{sub c} ~ 404 kV/cm) and magnetic properties (M{sub s} ~ 117 emu/cc, M{sub r} ~ 0.83 emu/cc and H{sub c} ~ 20 Oe) were observed at room temperature. The leakage current densities in NFO/PST composites film have been studied. Poole–Frankel bulk limited conduction mechanism dominates of film at relatively high electric filed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Synthesis and Characterization of Nickel-Substituted Cobalt Ferrite Nanoparticles Using Sol–Gel Auto-combustion Method

In the present work, Co{sub 1−x}Ni{sub x}Fe{sub 2}O{sub 4} (x = 0.02, 0.04, and 0.06 M) is prepared by sol–gel auto-combustion method and its structural, functional, magnetic, and morphological characteristics are analyzed. The peaks corresponding to the plane observed from XRD matches with JCPDS data of CoFe{sub 2}O{sub 4} (22-1086) and NiFe{sub 2}O{sub 4} (10-0325). It is noted that the average crystallite size decreases from 31 to 27 nm when the nickel concentration increases from 0.02 to 0.06 M, indicative of the incorporation of Ni{sup 2+} ion in the cobalt ferrite lattice. FTIR analysis shows the presence of M↔O vibration at the tetrahedral and octahedral sites. Micro - Raman spectroscopy shows the stretching vibrations at 486.87 cm{sup − 1} (E{sub g}) and 696.96 cm{sup − 1} (A{sub 1g}), which are the characteristic vibrations of spinel ferrites. Magnetic studies show the variation in saturation magnetization (M{sub S} = 20.25, 9.41, 18.5 emu/g.) and coercivity (H{sub C} = 746.06, 953.03, 885.59 Oe) when the concentration of Ni{sup 2+} ion increases from 0.02 to 0.06 M. The prepared nanoparticles show a ferromagnetic nature which is attributed to the creation of an antiparallel spin and the magnetic moment created by the cation at tetrahedral and octahedral sites. The surface morphology of samples is imaged by a field emission scanning electron microscope.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Up-conversion luminescent properties of La{sub (0.80−x)}VO{sub 4}:Yb{sub x}, Er{sub 0.20} phosphors

Highlights: • A novel green and red emitting LaVO{sub 4}:Yb{sub x}{sup 3+}, Er{sub 0.20}{sup 3+} phosphors were synthesized. • Their structures, luminescent properties have also been investigated. • Major laser transition for Er{sup 3+} ion is {sup 2}H{sub 11/2} → {sup 4}I{sub 15/2} (525 nm). • These results suggest the possibility as photonic devices. - Abstract: Yb{sup 3+}, Er{sup 3+} co-doped LaVO{sub 4} phosphors were synthesized by solid state reaction method. Yb{sup 3+} concentrations were changed from 0.01 to 0.20 mol for the fixed Er{sup 3+} concentration at 0.2 mol. The crystalline structure of samples was investigated by X-ray diffraction (XRD). The composition was investigated by X-ray photoelectron spectroscopy (XPS) analysis. The surface morphology was observed by scanning electron microscope (SEM). The red and green up-conversion emissions were observed in Yb{sup 3+}, Er{sup 3+} co-doped LaVO{sub 4} phosphors under the excitation of 980 nm laser diode. Several emissions in green and red regions of the spectrum were observed near 525 nm, 553 nm and 659 nm radiated by {sup 2}H{sub 11/2} → {sup 4}I{sub 15/2}, {sup 4}S{sub 3/2} → {sup 4}I{sub 15/2}, and {sup 4}F{sub 3/2} → {sup 4}I{sub 15/2} transitions, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Optical and structural properties of sputtered CdS films for thin film solar cell applications

Graphical abstract: Photo current–voltage curves (a) and the quantum efficiency (QE) (b) for the solar cell with CdS film grown at 300 °C. - Highlights: • CdS thin films were grown by a RF magnetron sputtering method. • Influence of growth temperature on the properties of CdS films was investigated. • At higher T{sub g}, the crystallinity of the films improved and the grains enlarged. • CdS/CdTe solar cells with efficiencies of 9.41% were prepared at 300 °C. - Abstract: CdS thin films were prepared by radio frequency magnetron sputtering at various temperatures. The effects of growth temperature on crystallinity, surface morphology and optical properties of the films were characterized with X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectra, UV–visible spectrophotometry, and photoluminescence (PL) spectra. As the growth temperature was increased, the crystallinity of the sputtered CdS films was improved and the grains were enlarged. The characteristics of CdS/CdTe thin film solar cell appeared to be significantly influenced by the growth temperature of the CdS films. Thin film CdS/CdTe solar cells with efficiencies of 9.41% were prepared at a growth temperature of 300 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Anti-adhesive characteristics of CHF{sub 3}/O{sub 2} and C{sub 4}F{sub 8}/O{sub 2} plasma-modified silicon molds for nanoimprint lithography

The anti-adhesive characteristics of a plasma-modified silicon mold surface for nanoimprint lithography are presented. Both CHF{sub 3}/O{sub 2} and C{sub 4}F{sub 8}/O{sub 2} plasma were used to form an anti-adhesive layer on silicon mold surfaces. The gas mixing ratios of CHF{sub 3}/O{sub 2} and C{sub 4}F{sub 8}/O{sub 2} were experimentally changed between 0% and 80% to optimize the plasma conditions to obtain a low surface energy of the silicon mold. The plasma characteristics were examined by optical emission spectroscopy (OES). In order to investigate the changes in surface energy and surface chemistry of the anti-adhesive layer during repeated demolding cycles, contact angle measurements and X-ray photoelectron spectroscopy (XPS) were performed on the plasma-modified silicon mold surface. Simultaneously, the surface morphology of the demolded resists was evaluated by field-emission scanning electron microscope (FE-SEM) in order to examine the effect of the anti-adhesive layers on the duplicated patterns of the resists. It was observed that the anti-adhesive layer formed by CHF{sub 3}/O{sub 2} plasma treatment was worn out more easily during repeated demolding cycles than the film formed by C{sub 4}F{sub 8}/O{sub 2} plasma treatment, because CHF{sub 3}/O{sub 2} gas plasma formed a thinner plasma-polymerized film over the same plasma treatment time.

36 MATERIALS SCIENCE↗