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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Effects of Aromaticity in Cations and Their Functional Groups on the Low-Frequency Spectra and Physical Properties of Ionic Liquids

We investigate the temperature dependence of low-frequency spectra in the frequency range of 0.3–200 cm -1 for ionic liquids (ILs) whose cations possess two systematically different cyclic groups, using femtosecond Raman-induced Kerr effect spectroscopy. The target ILs are bis(trifluoromethylsulfonyl)amide [NTf 2 ]– salts of 1-cyclohexylmethyl-1-methylpyrrolidinium [CHxmMPyrr] + , 1-cyclohexylmethyl-3-methylimidazolium [CHxmMIm] + , N-cyclohexylmethylpyridinium [CHxmPy]+, 1-benzyl-1-methylpyrrolidinium [BzMPyrr] + , 1-benzyl-3-methylimidazolium [BzMIm] + , and N-benzylpyridinium [BzPy] + cations. The aim of this study is to better understand the effects of aromaticity in the cations’ constituent groups on the temperature-dependent low-frequency spectral features of the ILs. The low-frequency spectra of these ILs are temperature dependent, but the temperature-dependent spectrum of [CHxmMPyrr][NTf 2 ] is different from that of other ILs. While [CHxmMPyrr][NTf 2 ] shows spectral changes with temperature in the low-frequency region below 50 cm -1 , the other ILs also show spectral changes in the high-frequency region above 80 cm -1 (above 50 cm -1 in the case of [BzMPyrr][NTf 2 ]). We conclude that the spectral change in the low-frequency region is due to both the cation and anion, while the change in the high-frequency region is attributed to the red shift of the aromatic ring librations. On the basis of the plots of the first moment of the spectra vs. temperature, we found that the first moment of the low-frequency spectrum of the IL whose cation does not have an aromatic ring is less temperature dependent than that of the other ILs. However, the intrinsic first moment, the first moment at 0 K, of the low-frequency spectrum is governed by the absence or presence of a charged aromatic group, while a neutral aromatic group does not have much influence on determining the intrinsic first moment.

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

The 2ν{sub 3} Raman overtone of sulfur hexafluoride: Absolute spectra, pressure effects, and polarizability properties

Of the six normal vibrations of SF{sub 6}, ν{sub 3} has a key role in the mechanisms of radiative forcing. This vibration, though inactive in Raman, shows up through the transition 2ν{sub 3} allowing for a complementary view on the asymmetric stretch of the molecule. Here, we look back into this topic, which has already caught some interest in the past but with some points been left out. We make a systematic incoherent-light-scattering analysis of the overtone with the use of different gas pressures and polarization orientations for the incident beam. Absolute-scale isotropic and anisotropic spectra are reported along with natural and pressure-induced widths and shifts, and other spectral features such as the peaks corresponding to the (experimentally indistinguishable) interfering channels E{sub g} and F{sub 2g} hitherto seen solely as two-photon IR-absorption features. We make the first-ever prediction of the SF{sub 6} polarizability second derivative with respect to the ν{sub 3}-mode coordinate and we develop a heuristic argument to explain why the superposition of the three degenerate stretching motions that are related to the ν{sub 3} mode cannot but generate a polarized Raman band.

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

Temperature dependent Raman scattering and far-infrared reflectance spectra of MgO modified Pb{sub 0.99}(Zr{sub 0.95}Ti{sub 0.05}){sub 0.98}Nb{sub 0.02}O{sub 3} ceramics: A composition effect

Lattice dynamics and phase transition of MgO modified Pb{sub 0.99}(Zr{sub 0.95}Ti{sub 0.05}){sub 0.98}Nb{sub 0.02}O{sub 3} (PZTN-x wt. % MgO, x = 0, 0.1, 0.2, 0.5) ceramics have been investigated by far-infrared (FIR) reflectance in the temperature range of 5.5–300 K and Raman spectra between 77 and 300 K, respectively. With the aid of above complementary methods, the structure of all ceramics was defined as low-temperature ferroelectric rhombohedral phase [F{sub R(LT)}] at room temperature. The FIR dielectric functions were extracted from the multi-Lorentz oscillator dispersion model. The lowest frequency phonon mode, which is related to Pb-BO{sub 3} (B = Zr, Ti, Nb) vibration, mainly dominates the FIR dielectric response. With increasing MgO composition, the dielectric constants ε(0) at room temperature are estimated to 85.4, 73.4, 73.9, and 41.9, respectively. The decreasing trend can be due to the doubly ionized oxygen vacancies induced by Mg substitution for B-site. The order-disorder phase transition located around 120 K can be clearly clarified from temperature evolution of phonon frequency, damping, and intensity. It decreases slightly with increasing MgO composition, which influence the distortion due to the broken correlation chains and local permanent dipoles creation. Moreover, the transformation from antiferroelectric orthorhombic A{sub O} to [ F{sub R(LT)} ] phase has been observed around 250 K, which is associated with the antiferroelectric displacement of Pb atoms along 〈 110 〉 and coupled rotations of the corner-connected oxygen octahedral. Furthermore, the transition from [ F{sub R(LT)} ] to [ F{sub R(HT)} ] (high-temperature ferroelectric rhombohedral phase) was identified around 290 K for MgO-doped PZTN ceramics. It arises from the shift of cation (Pb and Zr/Ti/Nb/Mg ions) along the 〈 111 〉 direction and the transition temperature slightly decreases compared to the pure ceramic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Gas Hydrate Film Growth in Microfluidic Channels for Carbon Dioxide Capture and Sequestration Applications

Gas or clathrate hydrates are a solid, crystalline compound composed of water and guest molecules that typically form at high pressure and low temperature conditions. Carbon dioxide (CO2) hydrates may be involved in several carbon dioxide capture and sequestration (CCS) applications, including CO2 pipeline transportation and CO2 offshore sequestration. Within these applications, the formation mechanism and kinetics must be well understood to manage the CCS processes, either by preventing or promoting hydrate formation. In this work, a high-pressure glass microfluidic reactor is used in tandem with visual microscopy and in-situ Raman spectroscopy to study both the morphological and kinetic behavior of gas hydrate crystals. Subcooling, pressure, and CO2 flow rate are investigated for their impact on the thickening behavior of pure CO2 hydrates, with flow rate being the only parameter to have a significant effect. Visual and Raman spectroscopy evidence show that both a dense hydrate layer and a porous hydrate layer form, and the latter may provide a path for mass transfer to continue hydrate crystallization. A first principles mass transfer model is developed to describe CO2 hydrate crystal thickening at the interface between gas and water. The impacts of gas impurities and channel wettability are also studied. This method is further applied to investigate the conversion of methane hydrate to CO2 hydrate for combined energy recovery and methane hydrate formation. The authors acknowledge the US Department of Energy Basic Energy Science award # DE-SC0022162.

Wadsworth, Lindsey [Colorado School of Mines, Gold↗
DOE OSTI2019

Quantum Isotope Effect in Silicon at Low Temperatures

High-precision studies of Raman scattering in isotopically pure {sup 28}Si, {sup 29}Si, {sup 30}Si single crystals have been performed in the temperature range from 8 to 300 K. It has been found that a difference of about (0.4 ± 0.1) cm{sup –1} observed at temperatures T ≤ 100 K between the normalized Raman frequencies of the {sup 28}Si and {sup 30}Si isotopes measured with an accuracy of 0.1 cm{sup –1} is certainly due to quantum effects damping with increasing temperature. The possibility of observing quantum isotope effects in germanium has been estimated using experimental data on isotope effects in diamond and silicon.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Polarization-separated double-imaging spectroscopy for weakly-ionized plasma diagnostics

Laser Thomson scattering, which provides thermal properties of electrons, has been extensively utilized in plasma diagnostics. However, being a non-resonant linear light scattering technique, it often encounters several challenges in weakly-ionized plasma diagnostics due to spectral overlap with different scatterings induced from other existing species, including Mie, Rayleigh, and rotational Raman scatterings. To address this challenge, we propose an imaging spectroscopy technique, polarization-separated double-imaging spectroscopy (PoDIS), which selectively separates specific scatterings based on their polarization characteristics. Using an atmospheric plasma jet as a plasma source for demonstration, we show that PoDIS can effectively separate rotational Raman and Thomson scatterings from a superimposed spectrum without prior knowledge or assumptions about the thermal properties of neutrals or electrons. This separation enables independent fitting of the rotational Raman and Thomson scattering spectra, allowing for precise determination of the thermal properties of neutral particles and electrons separately.

Bak, Junhwi [Texas A&M University, College Station↗
DOE OSTI2020

Anomalous phonon-mode dependence in polarized Raman spectroscopy of the topological Weyl semimetal TaP

Topological Weyl semimetals (WSMs) have attracted widespread interest due to the chiral Weyl fermions and surface Fermi arcs that enable unique optical and transport phenomena. In this work, we present angle-resolved Raman spectroscopy of TaP, a prototypical noncentrosymmetric WSM, for five excitation wavelengths ranging from 364 to 785 nm. The Raman-active modes, $A_1$, $B^1_1$, and $B^2_1$ modes, exhibit two main unique features beyond the conventional Raman theory. First, the relative intensities of Raman-active modes change as a function of the excitation wavelength. Second, angle-resolved polarized Raman spectra show systematic deviation from the Raman tensor theory. In particular, the $B^1_1$ mode is absent for 633-nm excitation, whereas the $B^2_1$ mode shows an unusual twofold symmetry instead of a fourfold symmetry for 488-, 532-, and 633-nm excitations. Finally, these unconventional phenomena are attributed to the interference effect in the Raman process owing to the existence of multiple carrier pockets with almost the same energy but different symmetries.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Investigation into the role of silica in lithium polysulfide adsorption for lithium sulfur battery

Highlights: • Amine functionalized silica nanoparticles (AFSN) were prepared. • Polysulfide adsorption studies were carried out with silica nanoparticles and AFSN. • Sulfur cathodes were prepared with SN and AFSN for Li–S batteries. • AFSN showed excellent polysulfide adsorption. - Abstract: A new type of sulfur electrodes with the ability for polysulfide adsorption was prepared by incorporating silica nanoparticles (SN) or amine functionalized silica nanoparticles (AFSN). AFSN was synthesized by a simple and cost-effective method. The functionalization and surface morphology of silica were confirmed with Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), respectively. Polysulfide adsorption studies were carried out using UV–vis spectrometer, which confirmed the excellent adsorption of polysulfides by AFSN. Interaction of polysulfides with SN or AFSN was studied using FTIR and FT-Raman spectroscopy. The effective polysulfide adsorption by SN and AFSN leads to good and stable cycle performance of lithium sulfur cells. The results show that the incorporation of SN or AFSN with sulfur is a promising method to prepare cathode material for lithium sulfur batteries.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Effect of e-beam irradiation on graphene layer grown by chemical vapor deposition

We have grown graphene by chemical vapor deposition (CVD) and transferred it onto Si/SiO{sub 2} substrates to make tens of micron scale devices for Raman spectroscopy study. The effect of electron beam (e-beam) irradiation of various doses (600 to 12 000 {mu}C/cm{sup 2}) on CVD grown graphene has been examined by using Raman spectroscopy. It is found that the radiation exposures result in the appearance of the strong disorder D band attributed the damage to the lattice. The evolution of peak frequencies, intensities, and widths of the main Raman bands of CVD graphene is analyzed as a function of defect created by e-beam irradiation. Especially, the D and G peak evolution with increasing radiation dose follows the amorphization trajectory, which suggests transformation of graphene to the nanocrystalline and then to amorphous form. We have also estimated the strain induced by e-beam irradiation in CVD graphene. These results obtained for CVD graphene are in line with previous findings reported for the mechanically exfoliated graphene [D. Teweldebrhan and A. A. Balandin, Appl. Phys. Lett. 94, 013101 (2009)]. The results have important implications for CVD graphene characterization and device fabrication, which rely on the electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2026

The influence of iron incorporation on the microstructure and crystal chemistry of UO 2 fuel

The incorporation of dopants into UO 2 is of interest for both doped advanced fuel and nuclear forensics research. Suitable forensics dopants, or taggants, for nuclear fuels are ones that do not adversely affect the performance of the parent material while still being traceable during key stages of the fuel’s life cycle. In this paper, we present our efforts to understand the effects of doping UO 2 with Fe 2 O 3 under multiple parameters, such as Fe concentration (0–3000 wppm), sintering temperature (1673 K, 1773 K, and 1973 K), sintering time (2–12 h), and atmosphere (reducing and inert). Here, we investigated densification behavior, microstructure evolution, and lattice defects based on the geometric densities, scanning electron microscopy (SEM), X-ray diffractograms, and Raman spectra. The effect of Fe on the microstructure and crystal chemistry of UO 2 is very complex, especially at the intermediate temperature (1773 K), where we found that densification kinetics are enhanced and that lattice contraction occurs for doping concentrations greater than 1000 wppm Fe.

Crystallography↗
DOE OSTI2015

Direct transfer and Raman characterization of twisted graphene bilayer

Twisted bilayer graphene (tBLG) is constituted of a two-graphene layer with a mismatch angle θ between the two hexagonal structures. It has recently attracted much attention—thanks to its diverse electronic and optical properties. Here, we study the tBLG fabricated by the direct transfer of graphene monolayer prepared by chemical vapor deposition (CVD) onto another CVD graphene layer remaining attached to the copper foil. We show that high quality and homogeneous tBLG can be obtained by the direct transfer which prevents interface contamination. In this situation, the top graphene layer plays a supporting mechanical role to the bottom graphene layer as confirmed by optical microscopy, scanning electron microscopy, and Raman spectroscopy measurements. The effect of annealing tBLG was also investigated using micro-Raman spectroscopy. The Raman spectra exhibit a splitting of the G peak as well as a change in the 2D band shape indicating a possible decoupling of the two monolayers. We attribute these changes to the different interactions of the top and bottom layers with the substrate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Vertically Resolved Retrievals of Aerosol Concentrations and Effective Radii from the DOE Combined HSRL and Raman lidar Measurement Study (CHARMS) Merged High-Spectral-Resolution Lidar-Raman Lidar Data Set

The Department of Energy’s (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility is a key component of DOE’s research strategy to address global climate change. The objective of the ARM Facility is to provide an experimental testbed for studying important atmospheric effects, particularly cloud and aerosol processes, and testing parameterizations of these processes for use in climate change models. ARM observational sites include a broad array of instruments to characterize cloud and aerosol properties, atmospheric state variables, and incoming and outgoing radiation. Advanced lidar systems provide valuable and unique information about the atmospheric column. We examine the potential for providing vertically resolved information about aerosol size and concentration with a combination of two such lidar systems, the Raman lidar and the High-Spectral-Resolution Lidar (HSRL). Currently ARM has a limited ability to remotely measure profiles of aerosol optical and microphysical properties on an operational basis. Although the Southern Great Plains (SGP), Eastern North Atlantic (ENA), and North Slope of Alaska (NSA, Oliktok Point location only) Raman lidars provide profiles of aerosol backscatter and extinction at 355 nm, additional information is required to better characterize the impacts of aerosols on radiation and clouds. Recent advances in lidar retrieval theory and algorithm development (Müller et al. 1999, 2014; Chemyakin et al. 2014) demonstrate that multi-wavelength lidar retrieval algorithms that use measurements of aerosol extinction at both 355 and 532 nm and backscatter at 355, 532, and 1064 nm have the potential to constrain both the aerosol optical (e.g., complex index of refraction, scattering, etc.) and microphysical properties (e.g., effective radius, concentration). This advancement greatly increases the utility of the remote-sensed aerosol observations. Based on this work, the HSRL group at the National Aeronautics and Space Administration (NASA)’s Langley Research Center (LaRC) developed automated algorithms for retrieving aerosol optical and microphysical properties, demonstrated these retrievals using data from the unique NASA/LaRC airborne multi-wavelength HSRL-2 system, and validated these retrievals using coincident airborne in situ data (Müller et al. 2014; Sawamura et al. 2017). We report here on the use of ARM instrumentation to gather a multi-wavelength ground-based lidar data set to test such retrievals. Continuous (24/7) operation of the co-located SGP Raman lidar and University of Wisconsin (UW) HSRL during the 10-week Combined HSRL and Raman lidar Measurement Study (CHARMS) (mid-July through September 2015) allowed the acquisition of a unique, multi-wavelength ground-based lidar data set. The ARM SGP Raman lidar (RLID) measured profiles of aerosol backscatter, extinction, and depolarization at 355 nm and profiles of water vapor mixing ratio and temperature. The UW HSRL simultaneously measured profiles of aerosol backscatter, extinction and depolarization at 532 nm and aerosol backscatter at 1064 nm. This RLID+HSRL combination provided a test data set to investigate these more advanced aerosol retrieval techniques with the potential to greatly improve aerosol characterization in the lower atmosphere.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Micro-Raman study on the softening and stiffening of phonons in rutile titanium dioxide film: Competing effects of structural defects, crystallite size, and lattice strain

Softening and stiffening of phonons in rutile titanium dioxide films are investigated by in situ micro-Raman studies during energetic ion irradiation. The in situ study minimized other possible mechanisms of phonon dynamics. Initial softening and broadening of Raman shift are attributed to the phonon confinement by structural defects and loss of stoichiometry. The stiffening of A{sub 1g} mode is ascribed to large distortion of TiO{sub 6} octahedra under the influence of lattice strain in the (110) plane, which gives rise to lengthening of equatorial Ti-O bond and shortening of apical Ti-O bond. The shortening of apical Ti-O bond induces stiffening of A{sub 1g} mode in the framework of the bond-order-length-strength correlation mechanism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

An Optothermal Raman Model Accounting for Convection, Radiation, and Substrate Effects for Evaluation of the Thermal Conductivity of Two‐Dimensional Coatings

Thermal conductivity of two‐dimensional (2D) materials is important to characterize as this will govern thermal transport physics in the various thermal and energy applications benefitting from the unique properties of these materials. Here, analytical and numerical techniques are presented to determine the thermal conductivity and interfacial conductance of a 2D material coating using confocal micro‐Raman spectroscopy as a noncontact diagnostic. While several methods have been proposed for calculating the values of thermal conductivity, interfacial conductance, and spatial temperature profile, these models often do not consider effects of radiation, convection, and substrate resistance on the temperature and heat flux profiles. We present a model to calculate the thermal conductivity and interfacial conductance which accounts for convection, radiation, and substrate effects to characterize a variety of 2D material coatings, which is demonstrated using large area graphene transferred onto copper and nickel substrates. Convection and radiation effects are found to have a negligible effect on the temperature profile of supported coatings, while the substrate effects have a considerable effect and therefore impact the quantification of thermal conductivity and interfacial conductance in addition to limiting the spatial resolution of the technique. These findings will allow for more accurate and reproducible extraction of the thermal conductivity of graphene and other 2D material coatings when employing noncontact optothermal Raman spectroscopy methods.

2D coatings↗
DOE OSTI2025

Raman spectroscopy of neutron irradiated silicon carbide

The effects of neutron irradiation on microstructural evolution and the resultant changes in physical and mechanical properties are of critical importance for the development of silicon carbide (SiC) materials for nuclear applications. This study neutron-irradiated βSiC under a wide range of conditions at temperatures between 235 and 750°C and neutron doses of 0.01–11.8 displacements per atom, and then evaluated the effects on the SiC structure using Raman spectroscopy. The SiC optical phonon lines were shifted to lower wavenumbers by irradiation. Correlations were found among the wavenumber of the longitudinal optical phonon line, irradiation-induced swelling, and irradiation temperature. The peak shift also correlated indirectly with decreasing thermal conductivity of irradiated SiC. The irradiation-induced peak shift is explained by combinations of lattice strain, reduction of the elastic modulus, and other factors including decreasing coherent domain size. These findings bridge irradiation-induced microstructural changes and property changes and illustrate how Raman spectroscopy is a useful tool for nondestructively assessing irradiated SiC materials for nuclear applications.

Koyanagi, T.↗
DOE OSTI2018

Raman Scattering of Light by Molecules of Methyl Orange Dye on the Surface of Silicon Containing Ion-Synthesized Silver Nanoparticles

The possibility of using a new composite material based on porous silicon containing silver nanoparticles and synthesized by means of a unique implantation nanotechnology as an optically sensitive material in biological and chemical sensors is tested experimentally. It is demonstrated that detection of small amounts of the studied organic substance (methyl orange dye) is possible due to the effect of surface-enhanced Raman scattering (SERS) from the molecules affected by the local electromagnetic field of the silver nanoparticles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Investigation of irradiation effects induced by self-ion in 6H-SiC combining RBS/C, Raman and XRD

Single crystals of 6H-SiC were irradiated at room temperature and 670 K with 4 MeV C ions at two fluences: 1015 and 1016 cm2 (0.16 and 1.6 dpa at the damage peak). Damage accumulation was studied by a combination of X-ray diffraction (XRD), Raman spectroscopy and Rutherford backscattering spectrometry in channelling geometry (RBS/C) along the [0001] direction. The irradiated layer is found to be composed of a low damage region up to 1.5 lm followed by a region where the disorder level is higher, consistent with SRIM predictions. At room temperature and low fluence, typically 1015 cm2, the strain depth profile follows the dpa depth distribution (with a maximum value of 2%). The disorder is most likely due to small defect clusters. When increasing the fluence up to 1016 cm2, a buried amorphous layer forms, as indicated by e.g. Raman results where the Si C bands become broader or even disappear. At a higher irradiation temperature of 670 K, amorphization is not observed at the same fluence, revealing a dynamic annealing process. However, results tend to suggest that the irradiated layer is highly heterogeneous and composed of different types of defects.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2011

Response of graphene to femtosecond high-intensity laser irradiation

We study the response of graphene to high-intensity, 50-femtosecond laser pulse excitation. We establish that graphene has a high ({approx}3 x 10{sup 12} Wcm{sup -2}) single-shot damage threshold. Above this threshold, a single laser pulse cleanly ablates graphene, leaving microscopically defined edges. Below this threshold, we observe laser-induced defect formation leading to degradation of the lattice over multiple exposures. We identify the lattice modification processes through in-situ Raman microscopy. The effective lifetime of chemical vapor deposition grown graphene under femtosecond near-infrared irradiation and its dependence on laser intensity is determined. These results also define the limits of non-linear applications of graphene in femtosecond high-intensity regime.

36 MATERIALS SCIENCE↗