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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Phonon and magnon scattering of Bi{sub 2}Fe{sub 4}O{sub 9} ceramic

We report the phonon structure of Bi{sub 2}Fe{sub 4}O{sub 9} ceramics as synthesized by solid-state reaction route. Rietveld refined X-ray diffraction patterns confirmed the formation of single-phase perovskite structure and all the peaks of Bi{sub 2}Fe{sub 4}O{sub 9} perfectly indexed to the orthorhombic (space group Pbam). Raman scattering measurements identifies 12A{sub g}+1B{sub 2g}+1B{sub 3g} Raman active optical phonon modes. Apart from phonon scattering, mode at 470 cm{sup −1} is observed which is due to magnon scattering. The P-E loop infers paraelectric nature of Bi{sub 2}Fe{sub 4}O{sub 9}.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Structural and Raman scattering study of Ni-doped CoFe{sub 2}O{sub 4}

Raman scattering measurements were made on polycrystalline CoFe{sub 2}O{sub 4} and Co{sub 0.5}Ni{sub 0.5}Fe{sub 2}O{sub 4} ferrites as prepared by solid-state reaction route. Rietveld refined X-ray diffraction pattern confirmed the formation of single-phase and both of the samples perfectly indexed in cubic spinel structure with Fd3m space group. Slight reduction in the lattice parameter of Co{sub 0.5}Ni{sub 0.5}Fe{sub 2}O{sub 4} has been observed as compared to CoFe{sub 2}O{sub 4}. From Raman scattering spectra, a shoulder like feature has been observed in both of the compounds reveals that octahedral site is occupied by Co, Ni and Fe ions and tetrahedral site is occupied by only Fe ion.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Polarization controlled deep sub-wavelength periodic features written by femtosecond laser on nanodiamond thin film surface

Deep sub-wavelength (Λ/λ = ∼0.22) periodic features are induced uniformly on a nanodiamond (ND) thin film surface using femtosecond (fs) laser irradiation (pulse duration = ∼110 fs and central wavelength of ∼800 nm). The topography of the surface features is controlled by the laser polarization. Orientation of features is perpendicular to laser polarization. Periodicity (spatial periodicity of < λ/4) of the surface features is less than the laser wavelength. This work gives an experimental proof of polarization controlled surface plasmon-fs laser coupling mechanism prompting the interaction between fs laser and solid matter (here ND thin film) which in turn is resulting in the periodic surface features. Scanning electron microscopy in conjunction with micro Raman scattering, X-ray diffraction, and atomic force microscopy are carried out to extract surface morphology and phase information of the laser irradiated regions. This work demonstrates an easy and efficient surface fabrication technique.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Multiple-beam laser–plasma interactions in inertial confinement fusion

The experimental evidence for multiple-beam laser-plasma instabilities of relevance to laser driven inertial confinement fusion at the ignition scale is reviewed, in both the indirect and direct-drive approaches. The instabilities described are cross-beam energy transfer (in both indirectly driven targets on the NIF and in direct-drive targets), multiple-beam stimulated Raman scattering (for indirect-drive), and multiple-beam two-plasmon decay instability (in direct drive). Advances in theoretical understanding and in the numerical modeling of these multiple beam instabilities are presented.

Myatt, J. F.↗
DOE OSTI2014

The application of Raman laser in gravity measurement and metrology

Atom Interferometry is proved to be a potential method for measuring the acceleration of atoms due to Gravity, we are now building a feasible system of cold atom gravimeter, it is based on the atom interferometry technology by coherently manipulating the cold atoms in a fountain (with a height of 1m) with specific Raman lasers, the cold atom wave packet is splitted, combined, and then re-splitted in the process. Then the atomic wave packet will acquire different phase because of the different evolution path. The precise acceleration can be deduced through the precision measurement of atomic interference fringes phase, and this will be a high precision standard of acceleration. At present, the preparation of Raman laser and the precise control of the laser Frequency have been finished, and they have been proved to meet the requirements of the experiment.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Diamond micro-Raman thermometers for accurate gate temperature measurements

Determining the peak channel temperature in AlGaN/GaN high electron mobility transistors and other devices with high accuracy is an important and challenging issue. A surface-sensitive thermometric technique is demonstrated, utilizing Raman thermography and diamond microparticles to measure the gate temperature. This technique enhances peak channel temperature estimation, especially when it is applied in combination with standard micro-Raman thermography. Its application to other metal-covered areas of devices, such as field plates is demonstrated. Furthermore, this technique can be readily applied to other material/device systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Optical properties of strain-free AlN nanowires grown by molecular beam epitaxy on Si substrates

The optical properties of catalyst-free AlN nanowires grown on Si substrates by molecular beam epitaxy were investigated. Such nanowires are nearly free of strain, with strong free exciton emission measured at room temperature. The photoluminescence intensity is significantly enhanced, compared to previously reported AlN epilayer. Moreover, the presence of phonon replicas with an energy separation of ∼100 meV was identified to be associated with the surface-optical phonon rather than the commonly reported longitudinal-optical phonon, which is further supported by the micro-Raman scattering experiments.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Intermittent laser-plasma interactions and hot electron generation in shock ignition

We study laser-plasma interactions and hot electron generation in the ignition phase of shock ignition through 1D and 2D particle-in-cell simulations in the regime of long density scale length and moderately high laser intensity. These long-term simulations show an intermittent bursting pattern of laser-plasma instabilities, resulting from a coupling of the modes near the quarter-critical-surface and those in the lower density region via plasma waves and laser pump depletion. The majority of the hot electrons are found to be from stimulated Raman scattering and of moderate energies. However, high energy electrons of preheating threat can still be generated from the two-plasmon-decay instability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Reactive ion etching-assisted surface-enhanced Raman scattering measurements on the single nanoparticle level

Single-nanoparticle surface-enhanced Raman scattering (SERS) measurement is of essential importance for both fundamental research and practical applications. In this work, we develop a class of single-particle SERS approaches, i.e., reactive ion etching (RIE)-assisted SERS measurements correlated with scanning electron microscopy (SEM) strategy (RIE/SERS/SEM), enabling precise and high-resolution identification of single gold nanoparticle (AuNP) in facile and reliable manners. By using AuNP-coated silicon wafer and quartz glass slide as models, we further employ the developed RIE/SERS/SEM method for interrogating the relationship between SERS substrates and enhancement factor (EF) on the single particle level. Together with theoretical calculation using an established finite-difference-time-domain (FDTD) method, we demonstrate silicon wafer as superior SERS substrates, facilitating improvement of EF values.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Amorphization and recrystallization of single-crystalline hydrogen titanate nanowires by N{sup +} ion irradiation

We report on the phase transformation of hydrogen titanate (H{sub 2}Ti{sub 3}O{sub 7}) nanowires induced by 50 keV N{sup +} ion irradiation at room temperature with fluences of 1 × 10{sup 15} ions/cm{sup 2} and 1 × 10{sup 16} ions/cm{sup 2}, respectively. Using transmission electron microscopy, the internal structure of the ion irradiated nanowires is analyzed. At low fluence, a transformation from crystalline H{sub 2}Ti{sub 3}O{sub 7} to amorphous TiO{sub 2} is observed. However, at higher fluence, a remarkable crystalline-amorphous TiO{sub 2} core-shell structure is formed. At this higher fluence, the recrystallization occurs in the core of the nanowire and the outer layer remains amorphous. The phase transformation and formation of core-shell structure are explained using the thermal spike model, radiation enhanced diffusion, and classical theory of nucleation and growth under non-equilibrium thermodynamics. X-ray photoelectron spectroscopy and Raman scattering reveal further insight into the structure of the nanowires before and after ion irradiation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Experimental verification of the high pressure crystal structures in NH{sub 3}BH{sub 3}

A detailed high-pressure study on NH{sub 3}BH{sub 3} has been carried out using in situ synchrotron X-ray diffraction (XRD) and Raman scattering with a diamond anvil cell up to 20 and 33 GPa, respectively. The Rietveld refinement based on the XRD pattern and analysis of Raman data indicate two first-order phase transitions from the ambient pressure I4 mm structure (α-NH{sub 3}BH{sub 3}) to a high pressure Cmc2{sub 1} phase (β-NH{sub 3}BH{sub 3}) at 2.14 GPa, and further into a monoclinic P2{sub 1} (Z = 2) phase (γ-NH{sub 3}BH{sub 3}) at 9.67 GPa. Fitting the measured volumetric compression data to the third order Birch-Murnaghan equation of state reveals a bulk modulus of B{sub 0} = 9.9 ± 0.5 and 17.0 ± 3.0 GPa (with fixed B{sub 0}{sup ′} = 4) for the β-NH{sub 3}BH{sub 3} below and above 5 GPa, respectively. Still, with the splitting of the NBH rock mode in Raman experiment, it is concluded that a second-order isostructural phase transition occurs at 5 GPa. By analyzing the dihydrogen bonding framework, the origin of the isostructural phase transition is attributed to the number of dihydrogen bondings per molecule in the Cmc2{sub 1} phase increasing from 12 to 14 at 5 GPa.

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

First results of electron temperature measurements by the use of multi-pass Thomson scattering system in GAMMA 10

A multi-pass Thomson scattering (TS) has the advantage of enhancing scattered signals. We constructed a multi-pass TS system for a polarisation-based system and an image relaying system modelled on the GAMMA 10 TS system. We undertook Raman scattering experiments both for the multi-pass setting and for checking the optical components. Moreover, we applied the system to the electron temperature measurements in the GAMMA 10 plasma for the first time. The integrated scattering signal was magnified by approximately three times by using the multi-pass TS system with four passes. The electron temperature measurement accuracy is improved by using this multi-pass system.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Local vibrational modes competitions in Mn-doped ZnO epitaxial films with tunable ferromagnetism

We reported spectroscopic investigations of high quality Mn-doped ZnO (ZnMnO) films grown by oxygen plasma-assisted molecular beam epitaxy. Raman scattering spectra revealed two local vibrational modes (LVMs) associated with Mn dopants at 523 and 712 cm{sup −1}. The LVMs and magnetic properties of ZnMnO films can be synchronously modulated by post annealing processing or by introducing tiny Co. The relative intensity of two LVMs clearly shows competitions arising from uncompensated acceptor and donor defects competition for ferromagnetic and nonmagnetic films. The experimental results indicated that LVM at 523 cm{sup −1} is attributed to Mn—(Zinc-vacancy) complexes, while LVM at 712 cm{sup −1} is attributed to Mn—(Oxygen-vacancy) complexes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Growth and characterization of horizontal GaN wires on silicon

We report the growth of in-plane GaN wires on silicon by metalorganic chemical vapor deposition. Triangular-shaped GaN microwires with semi-polar sidewalls are observed to grow on top of a GaN/Si template patterned with nano-porous SiO{sub 2}. With a length-to-thickness ratio ∼200, the GaN wires are well aligned along the three equivalent 〈 112{sup ¯}0 〉 directions. Micro-Raman measurements indicate negligible stress and a low defect density inside the wires. Stacking faults were found to be the only defect type in the GaN wire by cross-sectional transmission electron microscopy. The GaN wires exhibited high conductivity, and the resistivity was 20–30 mΩ cm, regardless of the wire thickness. With proper heterostructure and doping design, these highly aligned GaN wires are promising for photonic and electronic applications monolithically integrated on silicon.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Raman scattering in Si/SiGe nanostructures: Revealing chemical composition, strain, intermixing, and heat dissipation

We present a quantitative analysis of Raman scattering in various Si/Si{sub 1-x}Ge{sub x} multilayered nanostructures with well-defined Ge composition (x) and layer thicknesses. Using Raman and transmission electron microscopy data, we discuss and model Si/SiGe intermixing and strain. By analyzing Stokes and anti-Stokes Raman signals, we calculate temperature and discuss heat dissipation in the samples under intense laser illumination.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

An active metallic nanomatryushka with two similar super-resonances

The optical properties of a simple metallic nanomatryushka (nanosphere-in-a-nanoshell) with gain have been investigated theoretically. The spaser (surface plasmon amplification by stimulated emission of radiation) phenomena can be observed at two critical wavelengths in the active metallic nanomatryushkas. With increasing the gain coefficient of the middle layer, a similar super surface plasmon (SP) resonance is first found at the ω₋⁺|₁ mode of the active nanoparticles and then breaks down. With further increasing the gain coefficient, another similar super-resonance occurs at the ω₋⁻|₁ mode. The near-field enhancements in the active nanomatryushkas also have been greatly amplified at the critical wavelengths for ω₋⁺|₊ and ω₋⁻|₁ modes. It is further found that the amplifications of SPs in the active Ag–SiO₂–Au nanoshell are strongest in four kinds of nanoshells and hence the largest near fields. The giant near-field enhancement can greatly enhance the Raman excitation and emission.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Interactions between silver nanoparticles and polyvinyl alcohol nanofibers

The interaction of polyvinylalcohol (PVA) nanofibers with silver (Ag) nanoparticles (mean diameter 8nm) has been modeled using density functional theory (DFT) calculations. The physical adsorption of PVA through the hydroxyl group, to the Ag, and its corresponding molecular orientation was compared with experimental results obtained from surface-enhanced Raman scattering (SERS) studies of the same material. A good agreement was found between the computational model of the vibrational spectrum of the adsorbate and the experimentally observed SERS. In general, aliphatic capping molecules are used to passivate the surface of Ag{sub 55} nanocrystals (55 = atomic number of Ag). In this study, a DFT simulation was employed to show binding energies and electron contour map analyses of Ag{sub 55} with PVA. Here we show that the PVA interacts with the Ag nanoparticle's surface, through the OH group, thereby contributing significantly to the increase in SERS activity.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Argon-ion-induced formation of nanoporous GaSb layer: Microstructure, infrared luminescence, and vibrational properties

Room temperature implantation of 60 keV Ar{sup +}-ions in GaSb to the fluences of 7 × 10{sup 16} to 3 × 10{sup 18} ions cm{sup −2} is carried out at two incidence angles, viz 0° and 60°, leading to formation of a nanoporous layer. As the ion fluence increases, patches grow on the porous layer under normal ion implantation, whereas the porous layer gradually becomes embedded under a rough top surface for oblique incidence of ions. Grazing incidence x-ray diffraction and cross-sectional transmission electron microscopy studies reveal the existence of nanocrystallites embedded in the ion-beam amorphized GaSb matrix up to the highest fluence used in our experiment. Oxidation of the nanoporous layers becomes obvious from x-ray photoelectron spectroscopy and Raman mapping. The correlation of ion-beam induced structural modification with photoluminescence signals in the infrared region has further been studied, showing defect induced emission of additional peaks near the band edge of GaSb.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗