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Results for “RAMAN EFFECT”

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 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Effects of processing temperature on the corrosion and tribocorrosion resistance of perhydropolysilazane-derived coatings on AISI 304 steel

Ensuring a highly corrosion and erosion resistant surface is critical to the reliability and structural integrity of steel canisters for long-term nuclear waste storage in corrosive environments. In this work, perhydropolysilazane (PHPS)-derived coating has been successfully applied to enhance the pitting and tribocorrosion resistance of 304 stainless steels in 0.6 M NaCl solution. Two types of coatings were synthesized on the stainless steel substrate by crosslinking PHPS at room temperature or 600 °C, resulting in different mechanical and corrosion performance. Further, Raman spectra revealed that Si-O bonds were generated in the coating crosslinked at room temperature after corrosion, while absent in that pyrolyzed at 600 °C. In tribocorrosion tests, both coatings were protective to the steel substrate, with the protective effect being more pronounced in the 600 °C pyrolyzed coating. Overall, the PHPS-derived coating synthesized at 600 °C exhibited better protection for steel in wear and corrosion coexisting environments than those synthesized at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Improvement of the quality of graphene-capped InAs/GaAs quantum dots

In this paper, we study the transfer of graphene onto InAs/GaAs quantum dots (QDs). The graphene is first grown on Cu foils by chemical vapor deposition and then polymer Polymethyl Methacrylate (PMMA) is deposited on the top of graphene/Cu. High quality graphene sheet has been obtained by lowering the dissolving rate of PMMA using vapor processing. Uncapped as well as capped graphene InAs/GaAs QDs have been studied using optical microscopy, scanning electron microscopy, and Raman spectroscopy. We gather from this that the average shifts Δω of QDs Raman peaks are reduced compared to those previously observed in graphene and GaAs capped QDs. The encapsulation by graphene makes the indium atomic concentration intact in the QDs by the reduction of the strain effect of graphene on QDs and the migration of In atoms towards the surface. This gives us a new hetero-structure graphene–InAs/GaAs QDs wherein the graphene plays a key role as a cap layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Structural, optical, and magnetic properties of Mn and Fe-doped Co{sub 3}O{sub 4} nanoparticles

Mn and Fe-doped Co{sub 3}O{sub 4} nanoparticles were prepared by a simple precipitation method. The synthesized particles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), UV-Vis absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and vibrating sample magnetometer (VSM) techniques. XRD analysis showed the cubic structure of Co{sub 3}O{sub 4}. SEM and TEM images confirmed the formation of interconnected nanoparticles. Mn and Fe-doped Co{sub 3}O{sub 4} showed broad absorption in the visible region compared to undoped sample and the band gap values are red shifted. Five Raman active modes were observed from the Raman spectra. FTIR spectra confirmed the spinel structure of Co{sub 3}O{sub 4} and the doping of Mn and Fe shifts the vibrational modes to lower wave number region. The magnetic measurements confirmed that Fe-doped Co{sub 3}O{sub 4} shows a little ferromagnetic behavior compared to undoped and Mn-doped Co{sub 3}O{sub 4}, which could be related to the uncompensated surface spins and the finite size effects.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Hydrotrope-enabled high concentration aqueous electrolytes for reversible and sustainable iron metal anodes

Iron metal-based energy storage devices hold great potential in stationary grid-scale sustainable energy due to the high theoretical specific capacity, ultralow cost, and abundance of iron. However, their practical deployment is limited by the poor reversibility of iron plating and stripping, as well as competitive hydrogen evolution. Here we introduce the concept of hydrotropy into iron electrolytes by developing an environmentally friendly and cost-effective high-concentration ferrous sulfate electrolyte using urea as a hydrotropic agent. The designed electrolyte increases the Coulombic efficiency of iron metal electrodes to approximately 96.5%, compared with ~84.6% for the dilute electrolyte. Molecular dynamics simulations and Raman spectroscopy illustrate that urea regulates the competitive coordination of anions and urea in the iron solvation sheath, while reconstructing the hydrogen-bond network in free water molecules. This reduces the activity of both solvated and free water, thereby alleviating hydrogen evolution. Moreover, the coordinated anions and urea molecules facilitate the in-situ formation of an organic-inorganic hybrid protective layer on the metallic iron, establishing a physical barrier against water and promoting homogeneous interfacial reactions. This work demonstrates an appealing opportunity to design cost-effective and high-performance electrolytes and propels the practical application of iron metal-based energy storage devices.

Feng, Guangxia [Stanford Univ., CA (United States)↗
DOE OSTI2018

Tunable Optical Behaviour and Room Temperature Ferromagnetism of Cobalt-Doped BaSnO{sub 3} Nanostructures

In this work, the effect of Co doping on the structural, vibrational, morphological, optical and magnetic behaviour of BaSnO{sub 3} nanostructures is reported. Pure and Co (1,3, and 5%)-doped barium stannate (BSO) nanostructures were prepared by conventional hydrothermal technique followed by calcination at 900 °C for 5 h. The single crystalline cubic phase was identified by XRD analysis and structural distortions associated with Co doping were evidenced by variation in microstarin and crystallite size. FTIR and Raman studies further confirm the structural quality of the prepared samples. FESEM analysis revealed the mixed morphology of prepared samples, and the chemical compositions of all the samples were analysed using EDAX studies. The absorption studies revealed the incorporation of dopant ions and their effect on the bandgap subsequently in samples. The presence of defects and paramagnetic centres in the samples were confirmed by PL and EPR analyses. Magnetization studies demonstrated that pure BSO exhibits characteristic diamagnetism at room temperature and the addition of Co into Ba–Sn–O lattice drives the F-centre exchange interactions which results in the ferromagnetic behaviour. Hence, the occurrence of diamagnetic to ferromagnetic transition at room temperature with addition of Co as a dopant was identified.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Effect of interfacial interactions on the thermal conductivity and interfacial thermal conductance in tungsten–graphene layered structure

Graphene film was deposited by microwave plasma assisted deposition on polished oxygen free high conductivity copper foils. Tungsten–graphene layered film was formed by deposition of tungsten film by magnetron sputtering on the graphene covered copper foils. Tungsten film was also deposited directly on copper foil without graphene as the intermediate film. The tungsten–graphene–copper samples were heated at different temperatures up to 900 °C in argon atmosphere to form an interfacial tungsten carbide film. Tungsten film deposited on thicker graphene platelets dispersed on silicon wafer was also heated at 900 °C to identify the formation of tungsten carbide film by reaction of tungsten with graphene platelets. The films were characterized by scanning electron microscopy, Raman spectroscopy, and x-ray diffraction. It was found that tungsten carbide film formed at the interface upon heating only above 650 °C. Transient thermoreflectance signal from the tungsten film surface on the samples was collected and modeled using one-dimensional heat equation. The experimental and modeled results showed that the presence of graphene at the interface reduced the cross-plane effective thermal conductivity and the interfacial thermal conductance of the layer structure. Heating at 650 and 900 °C in argon further reduced the cross-plane thermal conductivity and interface thermal conductance as a result of formation nanocrystalline tungsten carbide at the interface leading to separation and formation of voids. The present results emphasize that interfacial interactions between graphene and carbide forming bcc and hcp elements will reduce the cross-plane effective thermal conductivity in composites.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Synthesis and characterization of three-dimensional flower-like tin dioxide-based structures

Three-dimensional flower-like SnO{sub 2}-based structures have been produced by the alkaline hydrothermal treatment of t-SnO{sub 2} powder with no additive and in the presence of aminoterephthalic acid (ATPA). The synthesis products have been characterized by a variety of physicochemical techniques (scanning electron microscopy, transmission electron microscopy, Raman and IR spectroscopies, X-ray diffraction, and others). The results demonstrate that raising the ATPA concentration in the reaction mixture changes the morphology of the materials and leads to the SnO{sub 2} → SnO{sub 2}/Sn{sub 3}O{sub 4} → Sn{sub 3}O{sub 4} phase transformation in the structures through the formation of SnO{sub x} nonstoichiometric tin oxide phases with 1 < x < 2. Hydrothermal treatment of the starting reagents in the presence of ≤75 wt % ATPA leads to the formation of hierarchical structures dominated by a nonstoichiometric tin oxide, which is thermally unstable at t ≥ 500°C. The morphology and phase composition of the synthesized structures have been shown to have a significant effect on the electronic conductivity of the material.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Fabricating Graphene Oxide/h-BN Metal Insulator Semiconductor Diodes by Nanosecond Laser Irradiation

To employ graphene’s rapid conduction in 2D devices, a heterostructure with a broad bandgap dielectric that is free of traps is required. Within this paradigm, h-BN is a good candidate because of its graphene-like structure and ultrawide bandgap. We show how to make such a heterostructure by irradiating alternating layers of a-C and a-BN film with a nanosecond excimer laser, melting and zone-refining constituent layers in the process. With Raman spectroscopy and ToF-SIMS analyses, we demonstrate this localized zone-refining into phase-pure h-BN and rGO films with distinct Raman vibrational modes and SIMS profile flattening after laser irradiation. Furthermore, in comparing laser-irradiated rGO-Si MS and rGO/h-BN/Si MIS diodes, the MIS diodes exhibit an increased turn-on voltage (4.4 V) and low leakage current. The MIS diode I-V characteristics reveal direct tunneling conduction under low bias and Fowler-Nordheim tunneling in the high-voltage regime, turning the MIS diode ON with improved rectification and current flow. This study sheds light on the nonequilibrium approaches to engineering h-BN and graphene heterostructures for ultrathin field effect transistor device development.

2D materials↗
DOE OSTI2018

Impact of Rare Earth Gd{sup 3+} Ions on Structural and Magnetic Properties of Ni{sub 0.5}Zn{sub 0.5}Fe{sub 2−x}Gd{sub x}O{sub 4} Spinel Ferrite: Useful for Advanced Spintronic Technologies

In this article, we have synthesized the Gd{sup 3+}-doped Ni{sub 0.5}Zn{sub 0.5}Fe{sub 2−x}Gd{sub x}O{sub 4} (x = 0.05, 0.07, 1.0) ferrite samples using solid-state reaction route. The effects of Gd{sup 3+} doping on structural, vibrational, electrical and magnetic properties were studied. Structural and vibrational properties were characterized by x-ray diffraction (XRD), Raman, and FTIR spectroscopy. XRD data indicate that the Ni{sub 0.5}Zn{sub 0.5}Fe{sub 2−x}Gd{sub x}O{sub 4} ceramics crystallize in single-phase spinel cubic (Fd3m space group) structure. Infrared spectra show two strong absorption bands in the frequency range of 400–600 cm{sup −1} which were, respectively, attributed to tetrahedral and octahedral sites of the spinel ferrite. All the prepared samples show the typical dielectric dispersion having Maxwell–Wagner-type interfacial polarization. Decrease in dielectric constant and loss tangent has been observed with frequency and doping concentration. M − H plots reveal that all the samples exhibit ferrimagnetic nature at room temperature. A significant increase in the saturation magnetization has been observed upon the substitution of Gd{sup 3+} ions. All the as-prepared samples are isotropic and soft magnetic materials. These ferrite compounds are advantageous in advanced high-density data storage and high-frequency devices applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Anisotropic Electron-Photon and Electron-Phonon Interactions in Black Phosphorus

Orthorhombic black phosphorus (BP) and other layered materials, such as gallium telluride (GaTe) and tin selenide (SnSe), stand out among two-dimensional (2D) materials owing to their anisotropic in-plane structure. This anisotropy adds a new dimension to the properties of 2D materials and stimulates the development of angle-resolved photonics and electronics. However, understanding the effect of anisotropy has remained unsatisfactory to-date, as shown by a number of inconsistencies in the recent literatures. We use angle-resolved absorption and Raman spectroscopies to investigate the role of anisotropy on the electron-photon and electron-phonon interactions in BP. We highlight a non-trivial dependence between anisotropies and flake thickness, photon and phonon energies. We show that once understood, the anisotropic optical absorption appears to be a reliable and simple way to identify the crystalline orientation of BP, which cannot be determined from Raman spectroscopy without the explicit consideration of excitation wavelength and flake thickness, as commonly used previously.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Focused helium-ion beam irradiation effects on electrical transport properties of few-layer WSe 2 : Enabling nanoscale direct write homo-junctions

Atomically thin transition metal dichalcogenides (TMDs) are currently receiving significant attention due to their promising opto-electronic properties. Tuning optical and electrical properties of mono and few-layer TMDs, such as tungsten diselenide (WSe 2 ), by controlling the defects, is an intriguing opportunity to synthesize next generation two dimensional material opto-electronic devices. Here, we report the effects of focused helium ion beam irradiation on the structural, optical and electrical properties of few-layer WSe 2 , via high resolution scanning transmission electron microscopy, Raman spectroscopy, and electrical transport measurements. By controlling the ion irradiation dose, we selectively introduce precise defects in few-layer WSe 2 thereby locally tuning the resistivity and transport properties of the material. Hole transport in the few layer WSe 2 is degraded more severely relative to electron transport after helium ion irradiation. Moreover, by selectively exposing material with the ion beam, we demonstrate a simple yet highly tunable method to create lateral homo-junctions in few layer WSe 2 flakes, which constitutes an important advance towards two dimensional opto-electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2015

X-ray photoelectron spectroscopy analysis for the chemical impact of solvent addition rate on electromagnetic shielding effectiveness of HCl-doped polyaniline nanopowders

An in-depth analysis of the chemical functionality in HCl-doped polyaniline (PANI) nanopowders is discussed through interpretations of x-ray photoelectron spectra. The distinctions between three PANI sample types, produced under varied synthesis conditions, are compared on the basis correlations between newly collected electron spectra for chemical analysis (or also x-ray photoelectron spectroscopy) and electromagnetic (EM) shielding effectiveness (SE) within two frequency bands (100–1500 MHz and ∼2–14 GHz). The findings are discussed with reference to previous data analysis of electrical conductivities and Raman and UV-vis spectra analyzed from replicates of the same PANI nanopowders, where only the 8–12 GHz range for SE was tested. They further corroborate previous results for limited-solvent conditions that enhance EM shielding. The three nanopowder types show distinctive differences in polaron, bipolaron, and polar lattice contributions. The collective findings describe the chemical connections between controlling and, most importantly, limiting the available solvent for polymerization with simultaneously doping and how it is that the newly developed solvent-limited approach for HCl-PANI nanopowders provides better shielding than traditionally solvent-rich methods by having more extended and perhaps even faster polaron delocalization than other PANI-based products. The maximum oxidation (50%) and doping (49%) levels obtained in the solvent-free nanopowders also produced the highest SE values of 37.3 ± 3.7 dB (MHz band) and 68.6 ± 4.6 dB (GHz band)

36 MATERIALS SCIENCE↗
DOE OSTI2017

A facile alternative technique for large-area graphene transfer via sacrificial polymer

A novel method of transferring large-area graphene sheets onto a variety of substrates using Formvar (polyvinyl formal) is presented. Due to the ease at which formvar can be dissolved in chloroform this method allows for a consistent, a clean, and a more rapid transfer than other techniques including the PMMA assisted one. This novel transfer method is demonstrated by transferring large-area graphene onto a range of substrates including commercial TEM grids, silicon dioxide and glass. Raman spectroscopy was used to confirm the presence of graphene and characterize the morphological properties of the large-area sheets. SEM and AFM analyses demonstrated the effectiveness of our rapid transfer technique for clean crystalline large-area graphene sheets. The removal of the sacrificial polymer was found to be one to two orders of magnitude faster than PMMA methods. Ultimately this facile transfer technique offers new opportunities for a wide range of applications for large-area graphene through the utilization of a new sacrificial polymer.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Cesium intercalation of graphene: A 2D protective layer on alkali antimonide photocathode

Alkali antimonide photocathodes have wide applications in free-electron lasers and electron cooling. The short lifetime of alkali antimonide photocathodes necessitates frequent replacement of the photocathodes during a beam operation. Furthermore, exposure to mediocre vacuum causes loss of photocathode quantum efficiency due to the chemical reaction with residual gas molecules. Theoretical analyses have shown that covering an alkali antimonide photocathode with a monolayer graphene or hexagonal boron nitride protects it in a coarse vacuum environment due to the inhibition of chemical reactions with residual gas molecules. Alkali antimonide photocathodes require an ultra-high vacuum environment, and depositing a monolayer 2D material on it poses a serious challenge. In the present work, we have incorporated a novel method known as intercalation, in which alkali atoms pass through the defects of a graphene thin film to create a photocathode material underneath. Initially, Sb was deposited on a Si substrate, and a monolayer graphene was transferred on top of the Sb film. Heat cleaning around 550–600 °C effectively removed the Sb oxides, leaving metallic Sb underneath the graphene layer. Depositing Cs on top of a monolayer graphene enabled the intercalation process. Atomic force microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, low energy electron microscopy, and x-ray diffraction measurements were performed to evaluate photocathode formation underneath the monolayer graphene. Our analysis shows that Cs penetrated the graphene and reacted with Sb and formed Cs 3 Sb.

2D materials↗
NASA NTRS2017

Ultraviolet Testing of Space Suit Materials for Mars

Human missions to Mars may require radical changes in the approach to extra-vehicular (EVA) suit design. A major challenge is the balance of building a suit robust enough to complete multiple EVAs under intense ultraviolet (UV) light exposure without losing mechanical strength or compromising the suit's mobility. To study how the materials degrade on Mars in-situ, the Jet Propulsion Laboratory (JPL) invited the Advanced Space Suit team at NASA's Johnson Space Center (JSC) to place space suit materials on the Scanning Habitable Environments with Raman & Luminescence for Organics and Chemicals (SHERLOC) instrument's calibration target of the Mars 2020 rover. In order to select materials for the rover and understand the effects from Mars equivalent UV exposure, JSC conducted ground testing on both current and new space suit materials when exposed to 2500 hours of Mars mission equivalent UV. To complete this testing, JSC partnered with NASA's Marshall Space Flight Center to utilize their UV vacuum chambers. Materials tested were Orthofabric, polycarbonate, Teflon, Dacron, Vectran, spectra, bladder, nGimat coated Teflon, and nGimat coated Orthofabric. All samples were measured for mass, tensile strength, and chemical composition before and after radiation. Mass loss was insignificant (less than 0.5%) among the materials. Most materials loss tensile strength after radiation and became more brittle with a loss of elongation. Changes in chemical composition were seen in all radiated materials through Spectral Analysis. Results from this testing helped select the materials that will fly on the Mars 2020 rover. In addition, JSC can use this data to create a correlation to the chemical changes after radiation-which is what the rover will send back while on Mars-to the mechanical changes, such as tensile strength.

Larson, Kristine↗
NASA NTRS2017

Ultraviolet Testing of Space Suit Materials for Mars

Human missions to Mars may require radical changes in the approach to extra-vehicular (EVA) suit design. A major challenge is the balance of building a suit robust enough to complete multiple EVAs under intense ultraviolet (UV) light exposure without losing mechanical strength or compromising the suit's mobility. To study how the materials degrade on Mars in-situ, the Jet Propulsion Laboratory (JPL) invited the Advanced Space Suit team at NASA's Johnson Space Center (JSC) to place space suit materials on the Scanning Habitable Environments with Raman & Luminescence for Organics and Chemicals (SHERLOC) instrument's calibration target of the Mars 2020 rover. In order to select materials for the rover and understand the effects from Mars equivalent UV exposure, JSC conducted ground testing on both current and new space suit materials when exposed to 2500 hours of Mars mission equivalent UV. To complete this testing, JSC partnered with NASA's Marshall Space Flight Center to utilize their UV vacuum chambers. Materials tested were Orthofabric, polycarbonate, Teflon, Dacron, Vectran, spectra, bladder, nGimat coated Teflon, and nGimat coated Orthofabric. All samples were measured for mass, tensile strength, and chemical composition before and after radiation. Mass loss was insignificant (less than 0.5%) among the materials. Most materials loss tensile strength after radiation and became more brittle with a loss of elongation. Changes in chemical composition were seen in all radiated materials through Spectral Analysis. Results from this testing helped select the materials that will fly on the Mars 2020 rover. In addition, JSC can use this data to create a correlation to the chemical changes after radiation-which is what the rover will send back while on Mars-to the mechanical changes, such as tensile strength.

Larson, Kristine↗
DOE OSTI2018

Ion irradiation induced nucleation and growth of nanoparticles in amorphous silicon carbide at elevated temperatures

Ion irradiation induced crystallization in as-deposited amorphous SiC films is investigated using grazing-angle incidence x-ray diffraction (GIXRD), transmission electron microscopy (TEM) and Raman spectroscopy. Irradiation with 5 MeV Xe to fluence of 115 Xe/nm2 at 700 K results in a homogenous distribution of 3C-SiC grains with an average crystallite size of ~5.7 nm over the entire film thickness (~1 µm). The nucleation and growth processes exhibit a weak dependence on dose in displacements per atom (dpa) in the dose range from 6 to 20 dpa. A transformation of homonuclear C-C bonds from sp3 to sp2 hybridization is observed in the irradiated films, which may be partly responsible for the observed grain size saturation. The results from this study may have a significant impact on synthesis of nanograins in amorphous SiC and other similar materials with effective control of grain size and density by ion irradiation.

phase transformation, SiC, ion irradiation↗