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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Simple Hydrothermal Synthesis for Mesoporous Pebble-Like NiCo{sub 2}O{sub 4} Nanostructures and Their Attractive Magnetic Properties

The mesoporous pebble-like NiCo{sub 2}O{sub 4} nanostructures were smoothly obtained via a simple hydrothermal route and the succeeding annealing treatment. Various techniques, including XRD, SEM, TEM, Raman spectra, FTIR, and MH curves have been used to study the obtained products. The obtained results exhibited that the morphology of spinel NiCo{sub 2}O{sub 4} could be controlled by adjusting the content of cetyltrimethylammonium bromide (CTAB). The morphology of NiCo{sub 2}O{sub 4} nanostructures transformed from a 300-nm popcorn-like to 30–40-nm pebble-like nanostructure by changing the content of CTAB. Compared with the popcorn-like NiCo{sub 2}O{sub 4} nanostructures, the pebble-like samples showed effective blue shifting of Raman spectroscopy, which might be due to the nano-sized effect of NiCo{sub 2}O{sub 4} particles. Finally, vibration sample magnetometer (VSM) measurements indicated the samples transformed from weak ferromagnetic (popcorn-like) to paramagnetic (pebble-like) due to small particle size.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Ge/GeSn heterostructures grown on Si (100) by molecular-beam epitaxy

The growth of GeSn layers by molecular-beam epitaxy on Si (100) wafers coated with a germanium buffer layer is investigated. The properties of the fabricated structures are controlled by reflection high-energy electron diffraction, atomic-force microscopy, X-ray diffractometry, Rutherford backscattering, and Raman scattering. It is shown that GeSn layers with thicknesses up to 0.5 μm and Sn molar fractions up to 0.073 manifest no sign of plastic relaxation upon epitaxy. The lattice constant of the GeSn layers within the growth plane is precisely the same as that of Ge. The effect of rapid thermal annealing on the conversion of metastable elastically strained GeSn layers into a plastically relaxed state is examined. Ge/GeSn quantum wells with Sn molar fraction up to 0.11 are obtained.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Surprising Effects of Hydrochloric Acid on the Water Evaporation Coefficient Observed by Raman Thermometry

© 2017 American Chemical Society. The kinetics and energetics of cloud droplet and aerosol formation in the atmosphere are strongly influenced by the evaporation and condensation rates of water, yet the magnitude and mechanism of evaporation remains incompletely characterized. Of particular import (and controversy) is the nature of interfacial water pH and its potential effects on evaporation rate and environmental reactivity. We have used Raman thermometry measurements of freely evaporating microdroplets to determine evaporation coefficients (Î) for two different hydrochloric acid solutions, both of which result in a significant deviation from Îwater. At 95% confidence, we find the evaporation coefficient for 1.0 M HCl to be 0.24 ± 0.04, a â-60% decrease relative to pure water, and for 0.1 M HCl to be 0.91 ± 0.08, a â-45% increase relative to pure water. These results suggest a large perturbation in the surface structure induced by either hydronium ions adsorbing to the water surface or by the presence of a Cl-···H3O+ ion-pair moiety in the interfacial region.

Rizzuto, Anthony M↗
DOE OSTI2016

Influence of ageing on Raman spectra and the conductivity of monolayer graphene samples irradiated by heavy and light ions

The influence of long-term ageing (about one year) on the Raman scattering (RS) spectra and the temperature dependence of conductivity has been studied in two series of monolayer graphene samples irradiated by different doses of C{sup +} and Xe{sup +} ions. It is shown that the main result of ageing consists of changes in the intensity and position of D- and G- and 2D-lines in RS spectra and in an increase of the conductivity. The observed effects are explained in terms of an increase of the radius of the “activated” area around structural defects.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Topological insulator thin films starting from the amorphous phase-Bi{sub 2}Se{sub 3} as example

We present a new method to obtain topological insulator Bi{sub 2}Se{sub 3} thin films with a centimeter large lateral length. To produce amorphous Bi{sub 2}Se{sub 3} thin films, we have used a sequential flash-evaporation method at room temperature. Transmission electron microscopy has been used to verify that the prepared samples are in a pure amorphous state. During annealing, the samples transform into the rhombohedral Bi{sub 2}Se{sub 3} crystalline structure which was confirmed using X-ray diffraction and Raman spectroscopy. Resistance measurements of the amorphous films show the expected Mott variable range hopping conduction process with a high specific resistance compared to the one obtained in the crystalline phase (metallic behavior). We have measured the magnetoresistance and the Hall effect at different temperatures between 2 K and 275 K. At temperatures T ≲ 50 K and fields B ≲ 1 T, we observe weak anti-localization in the MR; the Hall measurements confirm the n-type character of the samples. All experimental results of our films are in quantitative agreement with results from samples prepared using more sophisticated methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Structural ordering of multi-walled carbon nanotubes (MWCNTs) caused by gamma (γ)-ray irradiation

Multi-walled carbon nanotubes (MWCNTs) were irradiated by Gamma (γ)-rays in air with absorbed doses of 25 and 50 kGy. As a result of γ-ray irradiation, the inter-wall distance of MWCNTs was decreased and their graphitic order was improved. The reduction in inter-wall distance and structural ordering was improved with the increasing dosage of irradiation. Experimental evidences are provided by powder XRD and micro-Raman analyses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Structure and optical homogeneity of LiNbO{sub 3}:Zn (0.03–4.5 mol.%) crystals

Structure and optical homogeneity of LiNbO{sub 3}:Zn (0.03–4.5 mol.%) crystals were searched by photoinduced light scattering and by Raman spectroscopy. The photorefractive effect depends on Zn{sup 2+} concentration nonmonotonically. Decrease of photorefractive effect is explained by decrease of structure defects with localized electrons. The Zn{sup 2+} cations replace structure defects Nb{sub Li} and Li{sub Nb}, trapping levels appear near the bottom of the conduction band and photo electrons recombine with emission under laser radiation. By the Raman spectra the area of the high structure order is found. In this area the own alternation, the alternation of impurity cations and the vacancies along the polar axis is almost perfect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Raman Scattering in InSb Spherical Nanocrystals Ion-Synthesized in Silicon-Oxide Films

The Raman spectra of SiO{sub 2} films containing InSb spherical nanocrystals produced by ion-beam synthesis are studied. TO- and LO-like modes in the spectra of the InSb nanocrystals are detected at frequencies of 187 and 195 cm{sup –1}, respectively. The shift of these modes to high frequencies with respect to the corresponding frequencies in InSb bulk crystals is analyzed from the viewpoint of the influence of the quantum-confinement effect, strains in nanocrystals, the surface phonon frequency, and scattering at the frequency corresponding to stretched anion–cation modes at the surface of polar spherical nanocrystals. The position of the 195-cm{sup –1} mode corresponds to LO phonons in InSb nanocrystals hydrostatically compressed in the SiO{sub 2} matrix at pressures of about 10 kbar. The 187-cm{sup –1} mode corresponds to resonance at the Fröhlich frequency.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Electronic Raman scattering as an ultra-sensitive probe of strain effects in semiconductors

Semiconductor strain engineering has become a critical feature of high-performance electronics because of the significant device performance enhancements that it enables. These improvements, which emerge from strain-induced modifications to the electronic band structure, necessitate new ultra-sensitive tools to probe the strain in semiconductors. Here, we demonstrate that minute amounts of strain in thin semiconductor epilayers can be measured using electronic Raman scattering. We also applied this strain measurement technique to two different semiconductor alloy systems using coherently strained epitaxial thin films specifically designed to produce lattice-mismatch strains as small as 10 -4 . Thus, comparing our strain sensitivity and signal strength in Al x Ga 1-x As with those obtained using the industry-standard technique of phonon Raman scattering, we found that there was a sensitivity improvement of 200-fold and a signal enhancement of 4 × 10 3 , thus obviating key constraints in semiconductor strain metrology.

14 SOLAR ENERGY↗
DOE OSTI2015

Probing the Charge Storage Mechanism of a Pseudocapacitive MnO 2 Electrode Using in Operando Raman Spectroscopy

Although manganese oxide (MnO 2 ) has been extensively studied as an electrode material for pseudocapacitors, a clear understanding of its charge storage mechanism is still lacking. Here we report our findings in probing the structural changes of a thin-film model MnO 2 electrode during cycling using in operando Raman spectroscopy. The spectral features (e.g., band position, intensity, and width) are correlated quantitatively with the size (Li + , Na + , and K + ) of cations in different electrolytes and with the degree of discharge to gain better understanding of the cation-incorporation mechanism into the interlayers of pseudocapacitive MnO 2 . Also, theoretical calculations of phonon energy associated with the models of interlayer cation-incorporated MnO 2 agree with the experimental observations of cation-size effect on the positions of Raman bands. Additionally, the cation-size effects on spectral features at different potentials of MnO 2 electrode are correlated quantitatively with the amount of charge stored in the MnO 2 electrode. The understanding of the structural changes associated with charge storage gained from Raman spectroscopy provides valuable insights into the cation-size effects on the electrochemical performances of the MnO 2 electrode.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Si/ZnO nanorods/Ag/AZO structures as promising photovoltaic plasmonic cells

The test structures for photovoltaic (PV) applications based on zinc oxide nanorods (NRs) that were grown using a low-temperature hydrothermal method on p-type silicon substrates (100) covered with Ag nanoparticles (NPs) were studied. The NPs of three different diameters, i.e., 5–10 nm, 20-30 nm, and 50–60 nm, were deposited using a sputtering method. The morphology and crystallinity of the structures were confirmed by scanning electron microscopy and Raman spectroscopy. It was found that the nanorods have a hexagonal wurtzite structure. An analysis of the Raman and photoluminescence spectra permitted the identification of the surface modes at 476 cm{sup −1} and 561 cm{sup −1}. The presence of these modes is evidence of nanorods oriented along the wurtzite c-axis. The NRs with Ag NPs were covered with a ZnO:Al (AZO) layer that was grown using the low-temperature atomic layer deposition technique. The AZO layer served as a transparent ohmic contact to the ZnO nanorods. The applicability of the AZO layer for this purpose and the influence of the Ag nanoparticles on the effectiveness of light acquisition by such prepared PV cells were checked by reflectance and transmittance measurements of the AZO/glass and AZO/NPs/glass reference structures. Based on these studies, the high-energy transmittance edge was assigned to the ZnO energy gap, although it is blueshifted with respect to the bulk ZnO energy gap because of Al doping. It was also shown that the most optimal PV performance is obtained from a structure containing Ag nanoparticles with a diameter of 20–30 nm. This result is confirmed by the current-voltage measurements performed with 1-sun illumination. The structures show a plasmonic effect within the short wavelength range: the PV response for the structure with Ag nanoparticles is twice that of the structure without the nanoparticles. However, the influence of the Ag nanoparticle diameters on the plasmonic effect is ambiguous.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Study of the structures of cleaved cross sections by Raman spectroscopy

Scanning confocal Raman spectroscopy is used to study the crystal structure of GaAs irradiated with Mn{sup +} ions with subsequent pulse laser annealing. The scanning of cleaved cross sections of samples shows that the structure completely recovers over the depth of implantation after the annealing. Scattering in the coupled phonon–plasmon mode is revealed, which is indicative of electrical activation of the impurity at Mn doses above 1 × 10{sup 16} cm{sup –2}. The study shows the possibilities of using scanning confocal Raman spectroscopy in investigations of cleaved cross sections of structures. Using a test structure with a single δ-doped C layer, we show that the lateral resolution of the technique is 300 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Enhanced organic photovoltaic properties via structural modifications in PEDOT:PSS due to graphene oxide doping

Highlights: • Graphene oxide(GO) blended with PEDOT:PSS is used as HTL for PTB7:PCBM BHJ solar cells. • Increase in conductivity due to structural alterations in PEDOT:PSS by GO addition. • The structural alterations are reaveled under Raman spectroscopy, XPS and AFM. • PEDOT:PSS changed to extended coil due to addition of GO to PEDOT:PSS. • Enhanced conductivity after GO addition to PEDOT:PSS resulted in enhanced PCE. - Abstract: Poly(3,4-thylenedioxythiophene):poly(styrene sulfonate), PEDOT:PSS is a well-known conductive polymer for hole transport in organic devices, the properties of which can be enhanced by doping. Common dopants are metal oxides and nanoparticles. In this study, addition of graphene oxide (GO) to PEDOT:PSS as a dopant is addressed in organic photovoltaics (OPVs). With GO doping, electrical conductivity and transport properties of PEDOT:PSS increases due to structural alterations in the presence of −COOH and −OH functional groups in GO. These structural alterations have been revealed under detailed study of Raman spectra, X-ray photoelectron spectroscopy (XPS) analysis, Topographical and conductive Atom force microscopy (AFM/C-AFM) mapping. OPVs fabricated using PEDOT:PSS: GO (5:1) as a hole transport layer (HTL) exhibited a power conversion efficiency (PCE) of 7.68%, which was higher than the 7.01% that was obtained for the OPVs using pristine PEDOT:PSS.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Growth and characterization of Cu3SbSe4 thin films through thermally diffusing Sb2Se3 – CuSe by chemical bath deposition (CBD)

Highlights: • Cu{sub 3}SbSe{sub 4} films were formed by chemical bath deposition followed by a heat treatment. • Prepared Cu{sub 3}SbSe{sub 4} thin films have promising properties to absorbing layer in a solar cell or thermoelectric material. • Electrical conductivity values of Cu{sub 3}SbSe{sub 4} are high, considering its manufacturing method and the previous reports in the field. - Abstract: In the present work, Cu{sub 3}SbSe{sub 4} thin films have been successfully synthesized by chemical bath deposition (CBD) involving a sequential deposition of antimony selenide (Sb{sub 2}Se{sub 3}) and copper selenide (CuSe) films and then annealing in a vacuum atmosphere. The influence of CuSe deposition time on the previously deposited Sb{sub 2}Se{sub 3} films was investigated to obtain the ternary phase. A study of the structural, morphological, optical and electrical properties of these films was carried out using appropriate characterization techniques. X-ray diffraction analysis revealed that the films show a tetragonal crystalline crystalline structure corresponding to the Permingeatite phase (Cu{sub 3}SbSe{sub 4}). The crystal size increases with the CuSe deposition time. It is identified by Raman spectroscopy that at low CuSe deposition times a low concentration of Sb{sub 2}Se{sub 3} coexists in the thin film. The optical band gap energy of these films was evaluated in the range of 0.67–1.18 eV, decreasing by increasing CuSe deposition time. By field-emission scanning electron microscopy (FESEM) a morphological study was carried out, observing that by increasing the deposition time of CuSe there is an increase of agglomerates and decrease the porosity in the samples. An elemental analysis was carried out by energy dispersive X-ray spectroscopy to observe the composition and elemental distribution in the ternary compound. The films showed a p-type electrical conductivity with values between 0.417 and 55.55 (Ω cm{sup −1}). The mobility and carrier density were performed by Hall Effect and Thermoelectric measurements observing a slight increase in the values by increasing the time of CuSe deposition. All results obtained for thin films of Cu{sub 3}SbSe{sub 4} suggest that it could be used as an absorber material in a solar cell or thermoelectric material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Extreme Spectroscopy: In situ nuclear materials behavior from optical data

In the nuclear industry, materials are regularly exposed to high temperature or/and irradiation and a better knowledge and understanding of their behavior under such extreme conditions is a key-point for improvements and further developments. Nowadays, Raman spectroscopy begins to be well known as a promising technique in the post mortem and remote characterization of nuclear materials exposed to extreme conditions. On this topic, at ANIMMA 2013 conference, we have presented some results about its implementation in the study of model or real nuclear fuel. However, the strength of Raman spectroscopy as in situ characterization tool is mainly its ability to be implemented remotely through optical fibers. Aware of this, implementation of other optical techniques can be considered in order to gain information not only on the structural dynamics of materials but also on the electronic charge carrier populations. In this paper, we propose to present our last advances in Raman characterization of nuclear materials and enlarge to the in situ use of complementary optical spectroscopies. Emphasis will be made on the information that can be gained to the behavior of the model fuel depleted UO{sub 2} under extreme conditions of high temperature and ionic irradiation: - In Situ Raman identification of the radiolysis alteration products of UO{sub 2} in contact with water under ionic irradiation. - In Situ Raman recording of the damaged dynamic of UO{sub 2} under inert atmosphere. - In Situ Raman and photo-luminescence study of virgin and damaged UO2 at high temperature. - In Situ study of electronic charge carriers' behavior in U{sub x}Th{sub 1-x}O{sub 2} solid solutions by mean of Iono- and Thermo- luminescence under and post- ionic irradiation. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2018

DOE ASR Final Report on “Use of ARM Observations to Investigate the Role of Tropical Radiative Processes and Cloud Radiative Effects in Climate Simulations”

The overall objective of this ASR funded project is to investigate the role of cloud radiative effects, especially those associated with tropical thin cirrus clouds in the tropical tropopause layer, by analyzing the ARM observations combined with numerical models. In particular, we have processed and analyzed the observations from the Raman lidar at the ARM SGP and TWP sites. In the tenure of the project (8/15/2013 – 8/14/2016 and with a no-cost extension to 8/14/2017), we have been concentrating on (i) developing an automated feature detection scheme of clouds and aerosols for the ARM Raman lidar; (ii) developing an automated retrieval of cloud and aerosol extinctions for the ARM Raman lidar; (iii) investigating cloud radiative effects based on the observations on the simulated temperatures in the tropical tropopause layer using a radiative-convective model; and (iv) examining the effect of changes of atmospheric composition on the tropical lower-stratospheric temperatures. In addition, we have examined the biases in the CALIPSO-inferred aerosol direct radiative effects using ground-based Raman lidars at the ARM SGP and TWP sites, and estimated the impact of lidar detection sensitivity on assessing global aerosol direct radiative effects. We have also investigated the diurnal cycle of clouds and precipitation at the ARM site using the cloud radar observations along with simulations from the multiscale modeling framework. The main results of our research efforts are reported in the six referred journal publications that acknowledge the DOE Grant DE-SC0010557.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Imposed magnetic field and hot electron propagation in inertial fusion hohlraums

The effects of an imposed, axial magnetic field $B_{z0}$ on hydrodynamics and energetic electrons in inertial confinement fusion indirect-drive hohlraums are studied. We present simulations from the radiation-hydrodynamics code HYDRA of a low-adiabat ignition design for the National Ignition Facility, with and without $B_{z0}=70~\text{T}$. The field’s main hydrodynamic effect is to significantly reduce electron thermal conduction perpendicular to the field. This results in hotter and less dense plasma on the equator between the capsule and hohlraum wall. The inner laser beams experience less inverse bremsstrahlung absorption before reaching the wall. The X-ray drive is thus stronger from the equator with the imposed field. We study superthermal, or ‘hot’, electron dynamics with the particle-in-cell code ZUMA, using plasma conditions from HYDRA. During the early-time laser picket, hot electrons based on two-plasmon decay in the laser entrance hole (Regan et al., Phys. Plasmas, vol. 17(2), 2010, 020703) are guided to the capsule by a 70 T field. Twelve times more energy deposits in the deuterium–tritium fuel. For plasma conditions early in peak laser power, we present mono-energetic test-case studies with ZUMA as well as sources based on inner-beam stimulated Raman scattering. Furthermore, the effect of the field on deuterium–tritium deposition depends strongly on the source location, namely whether hot electrons are generated on field lines that connect to the capsule.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗