Engineering Papers⌕ Search

SEARCH · Engineering Papers

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Laser irradiation of carbon nanotube films: Effects and heat dissipation probed by Raman spectroscopy

We investigate the thermal properties of thin films formed by single- and multi-walled carbon nanotubes submitted to laser irradiation using Raman scattering as a probe of both the tube morphology and the local temperature. The nanotubes were submitted to heating/cooling cycles attaining high laser intensities ({approx}1.4 MW/cm{sup 2}) under vacuum and in the presence of an atmosphere, with and without oxygen. We investigate the heat diffusion of the irradiated nanotubes to their surroundings and the effect of laser annealing on their properties. The presence of oxygen during laser irradiation gives rise to an irreversible increase of the Raman efficiency of the carbon nanotubes and to a remarkable increase of the thermal conductivity of multi-walled films. The second effect can be applied to design thermal conductive channels in devices based on carbon nanotube films using laser beams.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

New insight into UO 2 F 2 particulate structure by micro-Raman spectroscopy

Uranyl fluoride particles produced via hydrolysis of uranium hexafluoride have been deposited on different substrates: polished graphite disks, silver foil, stainless steel and gold-coated silicon wafer, and measured with micro-Raman spectroscopy (MRS). All three metallic substrates enhanced the Raman signal delivered by UO 2 F 2 in comparison to graphite. The fundamental stretching of the U–O band appeared at 867 cm –1 in case of the graphite substrate, while in case of the others it was shifted to lower frequencies (down to 839 cm –1 ). All applied metallic substrates showed the expected effect of Raman signal enhancement; however the gold layer appeared to be most effective. Lastly, application of new substrates provides more information on the molecular structure of uranyl fluoride precipitation, which is interesting for nuclear safeguards and nuclear environmental analysis.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Dose Dependence of Nanocrystal Formation in Helium-Implanted Silicon Layers

The possibility of nanocrystal formation in silicon layers subjected to plasma-immersion helium-ion implantation at an energy of 5 keV has been proved for the first time. The effect of the implantation dose on the microstructure of the layers has been studied by X-ray reflectometry, transmission electron microscopy and Raman scattering. It has been established that the formation of silicon nanocrystals with dimensions of 10–20 nm is accompanied by a pronounced dependence on the ion flux and occurs at a dose of 5 × 10{sup 17} cm{sup –2} with subsequent annealing at 700–800°C. The excessive dose has been shown to cause the destruction of the upper protective sublayer and the degradation of the optical properties of nanocrystals.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Electrical and photovoltaic characteristics of MoS{sub 2}/Si p-n junctions

Bulk-like molybdenum disulfide (MoS{sub 2}) thin films were deposited on the surface of p-type Si substrates using dc magnetron sputtering technique and MoS{sub 2}/Si p-n junctions were formed. The vibrating modes of E{sup 1}{sub 2g} and A{sub 1g} were observed from the Raman spectrum of the MoS{sub 2} films. The current density versus voltage (J-V) characteristics of the junction were investigated. A typical J-V rectifying effect with a turn-on voltage of 0.2 V was shown. In different voltage range, the electrical transporting of the junction was dominated by diffusion current and recombination current, respectively. Under the light illumination of 15 mW cm{sup −2}, the p-n junction exhibited obvious photovoltaic characteristics with a short-circuit current density of 3.2 mA cm{sup −2} and open-circuit voltage of 0.14 V. The fill factor and energy conversion efficiency were 42.4% and 1.3%, respectively. According to the determination of the Fermi-energy level (∼4.65 eV) and energy-band gap (∼1.45 eV) of the MoS{sub 2} films by capacitance-voltage curve and ultraviolet-visible transmission spectra, the mechanisms of the electrical and photovoltaic characteristics were discussed in terms of the energy-band structure of the MoS{sub 2}/Si p-n junctions. The results hold the promise for the integration of MoS{sub 2} thin films with commercially available Si-based electronics in high-efficient photovoltaic devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Poster - 14: Batch Effect Reduction in in-vitro Raman Microscopic Radiosensitivity Study Using Ovarian Cancer Cells

Purpose: To improve classification by reducing batch effect in samples from the ovarian carcinoma cell lines A2780s (parental wild type) and A2780cp (cisplatin cross-radio-resistant), before, right after, and 24 hours after irradiation to 10Gy. Methods: Spectra were acquired with a home built confocal Raman microscope in 3 distinct runs of six samples: unirradiated s&cp (control pair), then 0h and 24h after irradiation. The Raman spectra were noise reduced, then background subtracted with SMIRF algorithm. ∼35 cell spectra were collected from each sample in 1024 channels from 700cm-1 to 1618cm-1. The spectra were analyzed by regularized multiclass LDA. For feature reduction the spectra were grouped into 3 overlapping group pairs: s-cp, 0Gy–10Gy0h and 0Gy10–Gy24h. The three features, the three differences of the mean spectra were mapped to the analysis sub-space by the inverse regularized covariance matrix. The batch effect noticeably confounded the dose and time effect. Results: To remove the batch effect, the 2+2=4D subspace extended by the covariance matrix of the means of the 0Gy control groups was subtracted from the spectra of each sample. Repeating the analysis on the spectra with the control group variability removed, the batch effect was dramatically reduced in the dose and time directions enabling sharp linear discrimination. The cell type classification also improved. Conclusions: We identified a efficient batch effect removal technique crucial to the applicability of Raman microscopy to radiosensitivity studies both on cell cultures and potential clinical diagnostic applications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Interaction physics for the stimulated Brillouin scattering of a laser in laser driven fusion

Energy exchange between pump wave and ion-acoustic wave during the stimulated Brillouin Scattering process in relativistic laser-plasma interactions is studied, including the effect of damping coefficient of electron-ion collision by obeying the energy and momentum conservations. The variations of plasma density and damping coefficient of electron-ion collision change the amplitudes of the interacting wave. The relativistic mass effect modifies the dispersion relations of the interacting waves and consequently, the energy exchange during the stimulated Brillouin Scattering is affected. The collisional damping of electron-ion collision in the plasma is shown to have an important effect on the evolution of the interacting waves. (author)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Kinetic description of linear wave propagation in inhomogeneous, nonstationary, anisotropic, weakly magnetized, and collisional plasma

This paper addresses the linear propagation of an electron wave in a plasma whose distribution function, at zero order in the wave amplitude, may be chosen arbitrarily, provided that it is not strongly peaked at the wave phase velocity, and that it varies very little over one wave period and one wavelength. Then, from first principles is derived an equation for the wave action density that allows for Landau damping, whose rate is calculated at first order in the variations of the wave number and frequency. Moreover, the effect of collisions is accounted for in a way that adapts to any choice for the collision operator in Boltzmann equation. The wave may also be externally driven, so that the results presented here apply to stimulated Raman scattering.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Graphitic carbon nanospheres: A Raman spectroscopic investigation of thermal conductivity and morphological evolution by pulsed laser irradiation

Graphitic carbon nanospheres (GCNSs) were prepared by a unique acidic treatment of multi-walled nanotubes. Spherical morphology with a narrow size distribution was confirmed by transmission electron microscopy studies. The room temperature Raman spectra showed a clear signature of D- and G-peaks at around 1350 and 1591 cm{sup −1}, respectively. Temperature dependent Raman scattering measurements were performed to understand the phonon dynamics and first order temperature coefficients related to the D- and G-peaks. The temperature dependent Raman spectra in a range of 83–473 K were analysed, where the D-peak was observed to show a red-shift with increasing temperature. The relative intensity ratio of D- to G-peaks also showed a significant rise with increasing temperature. Such a temperature dependent behaviour can be attributed to lengthening of the C-C bond due to thermal expansion in material. The estimated value of the thermal conductivity of GCNSs ∼0.97 W m{sup −1} K{sup −1} was calculated using Raman spectroscopy. In addition, the effect of pulsed laser treatment on the GCNSs was demonstrated by analyzing the Raman spectra of post irradiated samples.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

In-situ Raman spectroscopy and high-speed photography of a shocked triaminotrinitrobenzene based explosive

We have developed a single-shot Raman spectroscopy experiment to study at the molecular level the initiation mechanisms that can lead to sustained detonation of a triaminotrinitrobenzene-based explosive. Shocks up to 30 GPa were generated using a two-stage laser-driven flyer plate generator. The samples were confined by an optical window and shock pressure was maintained for at least 30 ns. Photon Doppler Velocimetry measurements were performed at the explosive/window interface to determine the shock pressure profile. Raman spectra were recorded as a function of shock pressure and the shifts of the principal modes were compared to static high-pressure measurements performed in a diamond anvil cell. Our shock data indicate the role of temperature effects. Our Raman spectra also show a progressive extinction of the signal which disappears around 9 GPa. High-speed photography images reveal a simultaneous progressive darkening of the sample surface up to total opacity at 9 GPa. Reflectivity measurements under shock compression show that this opacity is due to a broadening of the absorption spectrum over the entire visible region.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Generation of gamma radiation by a subterawatt ultrashort laser pulse: optimisation of preplasma and pulse duration

We report an experimental and numerical study of the acceleration of electrons in a plasma interacting with a subterawatt laser pulse (intensity of ∼3 × 10{sup 18} W cm{sup −2} at a pulse duration of 50 fs). A preplasma layer on the surface of a molybdenum target is formed by an additional laser pulse with a duration of 8 ns and an intensity of ∼2 × 10{sup 12} W cm{sup −2}. It is shown that an increase in the laser pulse duration to 1700 fs at a constant energy (and a proportional decrease in intensity) leads to an increase in the yield of bremsstrahlung γ-radiation by more than an order of magnitude when the nanosecond pulse is ahead of the femtosecond one by 15 − 25 ns. Interferometry data and results of diagnostics of optical and γ-radiation of a plasma demonstrate that the collisional ionisation of atoms by electrons oscillating in the field of such a laser pulse plays an essential role in the formation of electron density profile. The sensitivity of the described effect to the level of amplified spontaneous emission is determined, despite the nanosecond pulse impact. Numerical simulations show that at a large pulse duration, the acceleration of electrons is stipulated by the beaking of plasma waves excited during stimulated Raman scattering of laser radiation. (paper)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Energy relaxation of a dissipative quantum oscillator

The dissipative harmonic oscillator is studied as a model for vibrational relaxation in a liquid environment. Continuum limit expressions are derived for the time-dependent average energy, average width of the population, and the vibrational population itself. The effect of the magnitude of the solute-solvent interaction, expressed in terms of a friction coefficient, solvent temperature, and initial energy of the oscillator on the relaxation has been studied. These results shed light on the recent femtosecond stimulated Raman scattering probe of the 1570 cm{sup −1} −C=C− stretching mode of trans-Stilbene in the first (S{sub 1}) excited electronic state. When the oscillator is initially cold with respect to the bath temperature, its average energy and width increase in time. When it is initially hot, the average energy and width decrease with time in qualitative agreement with the experimental observations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Spontaneously formed phonon frequency combs in van der Waals solid CrGeTe 3 and CrSiTe 3

Optical phonon engineering through nonlinear effects has been utilized in ultrafast control of material properties. However, nonlinear optical phonons typically exhibit rapid decay due to strong mode-mode couplings, limiting their effectiveness in temperature or frequency sensitive applications. Here we report the observation of long-lived nonlinear optical phonons through the spontaneous formation of phonon frequency combs in the van der Waals material CrXTe 3 (X=Ge, Si) using high-resolution Raman scattering. Unlike conventional optical phonons, the highest A g mode in CrGeTe 3 splits into equidistant, sharp peaks forming a frequency comb that persists for hundreds of oscillations and survives up to 200K. These modes correspond to localized oscillations of Ge 2 Te 6 clusters, isolated from Cr hexagons, behaving as independent quantum oscillators. Introducing a cubic nonlinear term to the harmonic oscillator model, we simulate the phonon time evolution and successfully replicate the observed comb structure. Similar frequency comb behavior is observed in CrSiTe 3 , demonstrating the generalizability of this phenomenon. Our findings demonstrate that Raman scattering effectively probes high-frequency nonlinear phonon modes, offering insight into the generation of long-lived, tunable phonon frequency combs with potential applications in ultrafast material control and phonon-based technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of surface potential and charge transfer mechanism in reduced graphene oxide and magnetic nanocomposites

Highlights: • Cobalt oxide/reduced graphene oxide nanocomposites were prepared by hydrothermal method. • The of cobalt oxide nanoparticles on graphene oxide sheets leads modification of surface potential of graphene oxide sheets. • Modification of surface potential causes shifting of Fermi energy level of graphene oxide sheets due to charge transfer process. • The occurrence function of graphene oxide sheets modified from 4.5 eV to 5.8 eV by decoration of cobalt oxide nanoparticles on it. • The work of charge transfer between cobalt oxide nanoparticles and graphene oxide sheets also envisaged from Raman spectra. - Abstract: In this paper, the charge transfer mechanism in hydrothermally synthesized cobalt oxide/reduced graphene oxide (Co{sub 3}O{sub 4}/RGO) nanocomposites has been established. Scanning and transmission electron microscopy results expose the decoration of Co{sub 3}O{sub 4} nanoparticles on GO sheets. Magnetic response of nanocomposites was confirmed from superconducting quantum interference device magnetometer measurement. Raman spectroscopy investigated optical properties of these nanocomposites. The Raman spectra of Co{sub 3}O{sub 4}/RGO nanocomposites shows the enhancement of D and G bands which are associated with GO due to the Surface-enhanced Raman spectroscopy effect and blue shift. Increase in the full-width half-maximum value as well as upshift in D and G peaks are strong signals of association of charge transfer process between GO sheets and decorated Co{sub 3}O{sub 4} nanoparticles. The effect of charge transfer process is measured in the expression of shifting of Fermi energy level of Co{sub 3}O{sub 4}/RGO nanocomposites. Charge transfer is correlated with observed Raman shift and scanning Kelvin probe microscopy. XRD spectra of Co{sub 3}O{sub 4}/RGO confirm the polycrystalline nature of Co{sub 3}O{sub 4} nanoparticles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Negative pressure and spallation in graphite targets under nano- and picosecond laser irradiation

We present the results of experiments on the spallation phenomena in graphite targets under shock-wave nano- and picosecond irradiation, which have been performed on Kamerton-T (GPI, Moscow, Russia) and PHELIX (GSI, Darmstadt, Germany) laser facilities. In the range of the strain rates of 10{sup 6} – 10{sup 7} s{sup -1}, the data on the dynamic mechanical strength of the material at rapure (spallation) have been for the first time obtained. With a maximal strain rate of 1.4 × 10{sup 7} s{sup -1}, the spall strength of 2.1 GPa is obtained, which constitutes 64% of the theoretical ultimate tensile strength of graphite. The effect of spallation is observed not only on the rear side of the target, but also on its irradiated (front) surface. With the use of optical and scanning electron microscopes, the morphology of the front and rear surfaces of the targets is studied. By means of Raman scattering of light, the graphite structure both on the target front surface under laser exposure and on its rear side in the spall zone is investigated. A comparison of the dynamic strength of graphite and synthetic diamond is performed. (extreme light fields and their applications)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Role of Ho Doping in Magnetization Mechanism of BiFeO{sub 3} Thin Films

BiFeO{sub 3} (BFO) as one of the considerable interesting multiferroic materials has been widely investigated for its fantastic science and potential application. Herein, effects of Ho doping on the structure, morphology, and magnetic properties of BFO thin films were systematically studied. X-ray diffraction (XRD) indicates a successful substitution of Ho at Bi site and a transition in crystal structure of Bi{sub 0.9}Ho{sub 0.1}FeO{sub 3} (BHFO) thin film. Raman scattering spectrum is further evidence of XRD analysis results. The Ho-doped BFO thin films possess uniform morphology. X-ray photoelectron spectroscopy (XPS) confirms that the substitution of Bi{sup 3+} ions with Ho{sup 3+} ions is beneficial. The remanent magnetization of BHFO thin films is about three times than that of the BFO thin films under a maximum magnetic field of 15,000 Oe. And we systematically discussed several possible reasons for the enhancement of magnetization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Structural, electrical and magnetic properties of Bi{sub 0.825}Pb{sub 0.175}FeO{sub 3}, and Bi{sub 0.725}La{sub 0.1}Pb{sub 0.175}FeO{sub 3} multiferroics

Graphical abstract: - Highlights: • Samples synthesized by solid state reaction route successfully. • La and Pb substitutions significantly change the BiFeO{sub 3} crystal symmetry. • The presence of E(TO9) and E(LO9) modes indicates ferroelectric domain of BiFeO{sub 3}. • Doped ions and crystal structure affect the dielectric properties of the samples. • The observed value of conductivity for BPFO sample is 3.1 × 10{sup −9} σ{sup −1} cm{sup −1}. - Abstract: Single-phase BiFeO{sub 3}, Bi{sub 0.825}Pb{sub 0.175}FeO{sub 3} and Bi{sub 0.725}La{sub 0.1}Pb{sub 0.175}FeO{sub 3} ceramic samples were prepared via solid state reaction route to study the effects of co-doping (La/Pb) on their crystal structure and ferroelectromagnetic behaviour. X-ray diffraction data accompanied by Rietveld refinement showed that BiFeO{sub 3} crystallize in rhombohedral distorted perovskite structure (space group-R3c) while to that BPFO and BLPFO crystallize in tetragonal (P4/mmm) symmetry. Presence of E(TO9) and E(LO9) modes in Raman scattering spectra for BiFeO{sub 3} and Bi{sub 0.725}La{sub 0.1}Pb{sub 0.175}FeO{sub 3} infers ferroelectric nature. However, absence of both modes in Bi{sub 0.875}Pb{sub 0.175}FeO{sub 3} indicates the paraelectric nature. The room temperature dielectric constant (10 Hz–1 MHz) of BiFeO{sub 3}, Bi{sub 0.825}Pb{sub 0.175}FeO{sub 3} and Bi{sub 0.725}La{sub 0.1}Pb{sub 0.175}FeO{sub 3} is about 100, 60, and 200. Ferroelectromagnetic measurements revealed the existence of ferroelectricity with remnant polarization of 0.24 μC/cm{sup 2} in Bi{sub 0.725}La{sub 0.1}Pb{sub 0.175}FeO{sub 3}, paraelectricity in Bi{sub 0.875}Pb{sub 0.175}FeO{sub 3}, and weak (strong) ferromagnetism with remnant magnetizations of 0.25 (1.57) emu/g in Bi{sub 0.725}La{sub 0.1}Pb{sub 0.175}FeO{sub 3} (Bi{sub 0.825}Pb{sub 0.175}FeO{sub 3})

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synthesis of black TiO2 with efficient visible-light photocatalytic activity by ultraviolet light irradiation and low temperature annealing

Highlights: • In this work, we have prepared black titanium dioxide (B-TiO{sub 2}) nanoparticals in combination with ultraviolet light and low temperature annealing. This method is simple, efficient and environmentally friendly. • The synthesis mechanism of the black B-TiO{sub 2} nanomaterials was analyzed by combining the different characterization data with the first-principles calculation results. • The Ti-O lattice and structure of the B-TiO{sub 2} sample did not change after low-temperature annealing. • The process of H-doping results in a reduction of the localized Ti{sup 3+} states, that are also the recombination centers of excited electrons and holes. • These nanoparticles can absorb a amount of visible light and degrade the organic pollution. - Abstract: Herein, a simple, efficient, and environmentally friendly strategy to prepare black TiO{sub 2} nanoparticles has been reported; the procedure combines the ultraviolet light irradiation and low-temperature annealing (300 °C) with continuous N{sub 2} flow under atmospheric pressure. The samples were characterized by the various techniques, such as X-ray diffraction, high resolution transmission electron microcopy, Raman spectroscopy, X-ray photoelectron spectroscopy. The photocatalytic degradation of the organic contaminant Rhodamine B was investigated when black TiO{sub 2} nanoparticles was irradiaed with ultraviolet light and visible light. The black TiO{sub 2} material possesses an anatase phase and is able to absorb a high amount of photon energy in the visible light region, effectively driving photochemical degradation reactions. The enhancement of the photocatalytic activity can be attributed to the following: first, the hydrogen ions decrease the localized Ti{sup 3+} states (which are also the e{sup −}-h{sup +} recombination centers) leading to a more efficient separation of the electron-hole pairs; secondly, the conduction band electrons in black TiO{sub 2} nanoparticles are responsible for strong absorption of visible light. Consequently, the photocatalytic degradation of Rhodamine B can be significantly enhanced using black TiO{sub 2} nanoparticles. This work proves that hydrogenated black TiO{sub 2} promotes the absorption of the entire electromagnetic spectrum and exhibits high photocatalytic activity under solar light irradiation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

On the Mechanism of Absorption and Restoration of Radiation Transmission in the Channel of Small-Scale Self-Focusing of a Short Laser Pulse in Neodymium Glass

When diagnosing a small-scale self-focusing (SSSF) channel of a 0.5-ns laser pulse with an intensity of 3–5 GW/cm{sup 2} in neodymium glasses, an absorption jump was detected (with a front of ≈0.5 ns) at wavelengths of 1.06 and 0.66 μm in addition to filament-like damage typical of SSSF, spectral broadening, and laser radiation scattering. The absorption coefficient reached 0.15 cm{sup –1}, and transmission in the medium was restored during 15–35 ns for phosphate glass and 5–10 ns for silicate glass. The physical bases of this effect of the appearance and relaxation of absorption in glasses have not been previously presented. An analysis of the experimental data showed that the absorption jump is due to the fast population of the {sup 4}I{sub 11/2} level of Nd{sup 3+} ions in glasses when nonlinear processes occur in the SSSF channel such as stimulated Raman scattering and broadening of the laser pulse spectrum. The relaxation time of the population at the {sup 4}I{sub 11/2} level and the restoration of transmission in glasses after the termination of the laser pulse are determined by the characteristic sizes of the Nd{sup 3+} ions excitation regions arising in the samples upon interference of the laser and scattered radiation, as well as the thermophysical characteristics of the glasses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗