Search NASA⌕ Search

SEARCH · Search NASA

Results for “laser methods”

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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Growth of residual stress-free ZnO films on SiO{sub 2}/Si substrate at room temperature for MEMS devices

ZnO thick Stress relaxed films were deposited by reactive magnetron sputtering on 2”-wafer of SiO{sub 2}/Si at room temperature. The residual stress of ZnO films was measured by measuring the curvature of wafer using laser scanning method and found in the range of 0.18 x 10{sup 9} to 11.28 x 10{sup 9} dyne/cm{sup 2} with compressive in nature. Sputter pressure changes the deposition rates, which strongly affects the residual stress and surface morphologies of ZnO films. The crystalline wurtzite structure of ZnO films were confirmed by X-ray diffraction and a shift in (0002) diffraction peak of ZnO towards lower 2θ angle was observed with increasing the compressive stress in the films. The band gap of ZnO films shows a red shift from ∼3.275 eV to ∼3.23 eV as compressive stress is increased, unlike the stress for III-nitride materials. A relationship between stress and band gap of ZnO was derived and proposed. The stress-free growth of piezoelectric films is very important for functional devices applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A laserball calibration device for the SNO+ scintillator phase

Located 2 km underground in SNOLAB, Sudbury, Canada, SNO+ is a large scale liquid scintillator experiment that primarily aims to search for neutrinoless double beta decay. Whilst SNO+ has light and radioactive calibration sources external to the inner volume, an internally deployed optical source is necessary for the full characterization of the detector model. A laser diffuser ball developed for SNO has previously demonstrated to be an effective optical calibration device for both SNO and SNO+ water phase. Since the introduction of liquid scintillator for SNO+, the material compatibility, cleanliness, and radiopurity requirements of any materials in contact with the internal medium have increased. Improving on the original SNO laserball design, a new laserball calibration device has been developed for the SNO+ scintillator phase with the goal of measuring the optical properties of the detector and performing routine PMT gain and timing calibrations. Simulations have been written to model the diffusion properties to optimise optical and temporal performance for calibration. Prototype laserballs have been built and characterised, demonstrating sub-ns timing resolution and a quasi-isotropic light distribution.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Magnetic properties and microstructure of Sm-Co/α-Fe nanocomposite thick film-magnets composed of multi-layers over 700 layers

We synthesized Sm-Co/α-Fe nanocomposite film-magnets, approximately 10 μm in thickness, composed of 780 layers by the pulse laser deposition method. Transmission electron microscopic observations revealed that the synthesized film is composed of Sm-Co and α-Fe layers with the well-controlled α-Fe thickness of approximately 10–20 nm, which is suitable one predicted by the micromagnetic simulation. In spite of the enhanced interlayer diffusion of Fe and Co by annealing for crystallization, the (BH){sub max} value of 100 kJ/m{sup 3} was obtained at the averaged compositions of Sm/(Sm + Co) = 0.16 and Fe/(Sm + Co + Fe) = 0.47. The α-Fe fraction for obtaining the highest (BH){sub max} value was smaller than that expected from the micromagnetic simulation. Although the annealing for crystallization lay the easy direction of magnetization in the plane, the film is not expected to have strong crystallographic texture.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Crystal plasticity finite element simulation of lattice rotation and x-ray diffraction during laser shock compression of tantalum

Here we present a crystal plasticity model tailored for high-pressure, high-strain-rate conditions that uses a multiscale treatment of dislocation-based slip kinetics. We use this model to analyze the pronounced plasticity-induced lattice rotations observed in shock-compressed polycrystalline tantalum via in situ x-ray diffraction. By making direct comparisons between experimentally measured and simulated texture evolution, we can explain how the details of the underlying slip kinetics control the degree of lattice rotation that ensues. Specifically, we show that only the highly nonlinear kinetics caused by dislocation nucleation can explain the magnitude of the rotation observed under shock compression. We demonstrate a good fit between our crystal plasticity model and x-ray diffraction data and exploit the data to quantify the dislocation nucleation rates that are otherwise poorly constrained by experiment in the dynamic compression regime.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Two-dimensional profile measurement of plasma parameters in radio frequency-driven argon atmospheric pressure plasma jet

The two-dimensional profiles of the electron density, electron temperature, neutral translational temperature, and molecular rotational temperature are investigated in an argon atmospheric pressure plasma jet, which is driven by the radio frequency of 13.56 MHz by means of the laser scattering methods of Thomson, Rayleigh, and Raman. All measured parameters have maximum values at the center of the discharge and decrease toward the plasma edge. The results for the electron temperature profile are contrary to the results for the microwave-driven plasma. From our experimental results, the profiles of the plasma parameters arise from the radial contraction of plasmas and the time averaged profile of the electric field, which is obtained by a microwave simulation performed under identical conditions to the plasma jet. In the case of the neutral temperature, a higher translational temperature than the rotational temperature is measured, and its discrepancy is tentatively explained in terms of the low ion-neutral charge exchange rate and the additional degrees of freedom of the molecules. The description of our experimental results and the underlying physics are addressed in detail.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Measurements of the electron density and degree of plasma ionization in a plasma target based on a linear electric discharge in hydrogen

Laser interferometry methods were used to measure the density of free electrons and degree of plasma ionization in a hydrogen target intended for experiments on determining energy losses of heavy ion beams in an ionized matter. It is shown that the linear electron density can be varied in the range from 3.3 Multiplication-Sign 10{sup 17} to 1.3 Multiplication-Sign 10{sup 18} cm{sup -2} by varying the initial plasma parameters (the hydrogen pressure in the target and the discharge current). The error in measuring the linear electron density in the entire range of the varied plasma parameters was less than 1%. The maximum degree of plasma ionization achieved at the initial gas pressure of 1 mbar was 0.62 {+-} 0.05.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Infrared spectroscopy of jet-cooled HCCl singlet chlorocarbene diradical: CH stretching and vibrational coupling dynamics

Quantum shot noise limited laser absorption methods are used to obtain first high-resolution infrared rovibrational spectra of jet cooled chlorocarbene (HCCl) diradical in a supersonic slit-jet discharge expansion spectrometer. The rotationally resolved absorption spectra of the C–H stretch ν 1 fundamental are analyzed in the framework of a Watson non-rigid asymmetric rotor Hamiltonian model. Further analysis of the mid-infrared data reveals the additional presence of what has nominally been assigned as the $\tilde x$(012) combination band with one quantum of the H–C–Cl bend (ν 2 ) and two quanta of the C–Cl stretch (2ν 3 ). Rovibrational constants are obtained from least squares fits for each of the four excited vibrational states built on the ν 1 fundamental $\tilde x$(100) and the $\tilde x$(012) combination mode for each 35 Cl and 37 Cl atom isotopologue. The four bands occur within a narrow spectral window, requiring detailed comparison of multiple spectral properties (e.g., rotational constant dependence on vibrational excitation, band types/transition dipole moment alignment in the body-fixed frame, etc.) to aid in the vibrational assignment. Indeed, the IR transition intensities arise from strong anharmonic mixing between the “bright” ν 1 C–H stretch and “dark” $\tilde x$(012) H–C–Cl bend/C–Cl stretch combination modes, resulting in nearly equal amplitudes for the zeroth order $\tilde x$(100) and $\tilde x$(012) harmonic states. Lastly, to aid the spectral search for HCCl in the interstellar medium, ground state two-line combination differences are combined with previous laser-induced fluorescence results to predict precision microwave transitions for HC 35 Cl and HC 37 Cl.

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

Effect of substrate temperature on the microstructural properties of titanium nitride nanowires grown by pulsed laser deposition

The current work reports on the growth and microstructural characterization of titanium nitride (TiN) nanowires on single crystal silicon substrates using a pulsed laser deposition method. The physical and microstructural properties of the nanowires were characterized using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The corrosion properties of the TiN nanowires compared to TiN thin film were evaluated using Direct Current potentiodynamic and electrochemical impedance spectroscopy. The nanowires corroded faster than the TiN thin film, because the nanowires have a larger surface area which makes them more reactive in a corrosive environment. It was observed from the FESEM image analyses that as the substrate temperature increases from 600 °C to 800 °C, there was an increase in both diameter (25 nm–50 nm) and length (150 nm–250 nm) of the nanowire growth. There was also an increase in spatial density with an increase of substrate temperature. The TEM results showed that the TiN nanowires grow epitaxially with the silicon substrate via domain matching epitaxy paradigm, despite a large misfit.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Observation of low voltage driven green emission from erbium doped Ga{sub 2}O{sub 3} light-emitting devices

Erbium doped Ga{sub 2}O{sub 3} thin films were deposited on Si substrate by pulsed laser deposition method. Bright green emission (∼548 nm) can be observed by naked eye from Ga{sub 2}O{sub 3}:Er/Si light-emitting devices (LEDs). The driven voltage of this LEDs is 6.2 V which is lower than that of ZnO:Er/Si or GaN:Er/Si devices. Since the wide bandgap of Ga{sub 2}O{sub 3} contain more defect-related level which will enhance the effects of recombination between electrons in the defect-related level and the holes in the valence band, resulting in the improvement of the energy transfer to Er ions. We believe that this work paves the way for the development of Si-based green LEDs by using wide bandgap Ga{sub 2}O{sub 3} as the host materials for Er{sup 3+} ions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Transport properties and c/a ratio of V{sub 2}O{sub 3} thin films grown on C- and R-plane sapphire substrates by pulsed laser deposition

We prepared V{sub 2}O{sub 3} thin films on C- or R-plane sapphire (Al{sub 2}O{sub 3}) substrates by a pulsed laser deposition method. X-ray diffraction analyses confirmed that single-phase V{sub 2}O{sub 3} films were epitaxially grown on both C- and R-planes under an Ar gas ambient of 2 × 10{sup −2} mbar at a substrate temperature of 873 K. Depending on the deposition conditions, c/a ratios at room temperature of (0001)-oriented V{sub 2}O{sub 3} films widely ranged from 2.79 to 2.88. Among them, the films of 2.81 ≤ c/a ≤ 2.84 showed complex metal (M)–insulator (I)–M transition during cooling from 300 to 10 K, while those of larger c/a ratios were accompanied by metallic properties throughout this temperature range. All the films on R-plane substrates underwent simple M-I transition at ∼150 K, which was more abrupt than the films on C-plane, whereas their c/a ratios were narrowly distributed. The distinct difference of M-I transition properties between C- and R-plane films is explained by the intrinsic a- and c-axes evolution through the transition from M to I phases.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Growth of epitaxial orthorhombic YO{sub 1.5}-substituted HfO{sub 2} thin film

YO{sub 1.5}-substituted HfO{sub 2} thin films with various substitution amounts were grown on (100) YSZ substrates by the pulsed laser deposition method directly from the vapor phase. The epitaxial growth of film with different YO{sub 1.5} amounts was confirmed by the X-ray diffraction method. Wide-area reciprocal lattice mapping measurements were performed to clarify the crystal symmetry of films. The formed phases changed from low-symmetry monoclinic baddeleyite to high-symmetry tetragonal/cubic fluorite phases through an orthorhombic phase as the YO{sub 1.5} amount increased from 0 to 0.15. The additional annular bright-field scanning transmission electron microscopy indicates that the orthorhombic phase has polar structure. This means that the direct growth by vapor is of polar orthorhombic HfO{sub 2}-based film. Moreover, high-temperature X-ray diffraction measurements showed that the film with a YO{sub 1.5} amount of 0.07 with orthorhombic structure at room temperature only exhibited a structural phase transition to tetragonal phase above 450 °C. This temperature is much higher than the reported maximum temperature of 200 °C to obtain ferroelectricity as well as the expected temperature for real device application. The growth of epitaxial orthorhombic HfO{sub 2}-based film helps clarify the nature of ferroelectricity in HfO{sub 2}-based films (186 words/200 words)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Investigation on the Current Transport Characteristics of SrTiO{sub 3}/YBa{sub 2}Cu{sub 3}O{sub 7−x} Heterostructure

By the combined use of the sol-gel and pulsed laser deposition methods, the SrTiO{sub 3}/YBa{sub 2}Cu{sub 3}O{sub 7−x} (STO/YBCO) heterostructure was prepared on a LaAlO{sub 3} substrate. XRD results and φ scanning test showed that the prepared STO/YBCO heterostructure had good biaxial texture. Moreover, a Pt electrode was sputtered on the STO/YBCO heterostructure to investigate the current density-voltage (J − V) characteristic curves of STO/YBCO in the 50–300 K temperature range. The results showed that the STO/YBCO heterostructure had good rectifying characteristics. With an applied positive bias voltage smaller than 3.7 V, the current density of the STO/YBCO heterostructure decreased with the decrease of temperature; for higher voltages, on the contrary, the current density increased with the decrease of temperature. When the YBCO experienced superconducting transition, the turn-on voltage (V{sub t}) changed suddenly due to the sudden opening of the superconducting energy gap of YBCO. The V{sub t} variation obtained from the experiment was essentially consistent with the known value of the YBCO superconducting energy gap.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Thermal Conductivity and Diffusivity for SiC Fibers for Use in ATF Cladding Composites

As part of the accident tolerant fuels (ATF) initiative, there is a need to understand the thermophysical properties of cladding for these fuels. One potential cladding material is silicon carbide (SiC) ceramic matrix composite reinforced with SiC fibers because of the corrosion resistance, resistance to hydrogen formation, high bulk thermal conductivity, and favorable mechanical properties of SiC. However, data about the thermal properties of individual SiC fibers in these composites is absent in the literature. This paper presents the measured axial thermal conductivity and thermal diffusivity of a leading SiC fiber (HiNicalon Type S) via a thermal measurement technique (transient electrothermal technique, TET) optimized for thin fibers. The results show that the measured properties are significantly lower than bulk values for SiC. Because of the low neutron absorption, as well as excellent thermal and mechanical properties, zircaloy has primarily been used for the fuel cladding in many nuclear reactors. A major drawback of the zircaloy is its hydrogen generation vulnerability. This issue has been known for some time, but the explosion of hydrogen accident in the Fukushima Daiichi nuclear disaster has motivated efforts for accident tolerant fuels (ATF) and their cladding as suitable substitutes for zircaloy. Fuel cladding made of silicon carbide (SiC) ceramic matrix composite (CMC) is an attractive alternative to the zircaloy. Investigation on the tubular monolithic a-SiC polytropes indicates that it has superior oxidation (hydrogen production) resistance (three orders of magnitude slower) than zircaloy. Additionally, it has well-documented, favorable mechanical properties, along with high temperature corrosion resistance. However, its bulk thermal properties can vary significantly depending on polytrope, the grain size, grain boundary, or impurities. At room temperature, SiC has a thermal conductivity as high as 490 Wm{sup -1}K{sup -1}, where the {sup 6}H polytrope has the highest conductivity. Thermal measurements of the SiC CMC are usually accomplished by laser flash method for thermal diffusivity (a) and thermal conductivity is indirectly calculated through the relationship k=aρcp. Depending on the manufacturing method and the reinforced fiber, the composite thermal conductivity varies from <10 Wm{sup -1}K{sup -1} to ∼70 Wm{sup -1}K{sup -1}. While the flash method is convenient for the measurement of the composite, it is difficult to apply to the measurement of individual fibers. Because of this, the thermal properties of individual SiC fibers is not present in the literature. Because the SiC fiber manufacturing process is different than that of the SiC matrix in the CMC, the properties of the bulk material might be erroneous when applied to the fiber. Being able to measure the fiber properties independently and directly allows for an understanding of the effect of the manufacturing process on the fiber and the opportunity to potentially improve or control the thermal properties of the composite. This improved accuracy can be achieved by measuring the fiber with a technique optimized for individual fiber measurement, known as the Transient Electrothermal Technique or TET. This paper presents the thermal conductivity and diffusivity of a leading SiC fiber (HiNicalon Type S). Measurements are performed with the TET, with the resulting properties being significantly lower than the bulk values of SiC, which is one possible explanation for relatively low CMC values. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

High-Performance Titanium Oxynitride Thin Films for Electrocatalytic Water Oxidation

TiN x O y (TiNO) thin films with superior electrochemical properties have been synthesized in situ using a pulsed laser deposition method and a varied oxygen partial pressure from 5 to 25 mTorr. In this study, the electrochemical overpotential of these TiNO films for water oxidation was found to be as low as 290 mV at 10 mA/cm 2 , which is among the lowest overpotential values reported. The Tafel slopes, indicative of a rate of increase of electrode potential with respect to current, for these films are determined to be in the range of 85–57 mV/decade. These results further demonstrate the superiority of TiNO thin film as electrocatalyst for water oxidation to generate fossil-free fuels. The improvement in the electrocatalytic behavior of the semiconducting TiNO thin films is explained based on an adjustment in the valence band maximum edge and an enhancement in the number of electrochemically active sites. Both effects are realized by the substitution of N by O, forming a TiNO lattice that is isostructural with the rock-salt TiN lattice. These findings appear to assume significant importance in light of water electrolysis to produce fuels for the development of environmentally friendly power sources.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Characterizing extreme laser intensities by ponderomotive acceleration of protons from rarified gas

Abstract A new method to diagnose extreme laser intensities through measurement of angular and spectral distributions of protons directly accelerated by the laser focused into a rarefied gas is proposed. We simulated a laser pulse focused by an off-axis parabolic mirror by Stratton–Chu integrals, that enables description of laser pulse with different spatial-temporal profiles focusing in a focal spot down to the diffraction limit, that makes our theoretical predictions be a basis for experimental realization. The relationship between characteristics of the proton distributions and parameters of the laser pulse have been analyzed. The analytical and numerical results obtained justify the new method of laser diagnostics. The proposed scheme should be valuable for the commissioning of new extreme intensity laser facilities.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

An improved iteration loop for the three dimensional quasi-static particle-in-cell algorithm: QuickPIC

We present improvements to the three-dimensional (3D) quasi-static particle-in-cell (PIC) algorithm, which is used to efficiently model short-pulse laser and particle beam–plasma interactions. In this algorithm the fields including the index of refraction created by a static particle/laser beam are calculated. These fields are then used to advance the particle/laser beam forward in time (distance). For a 3D quasi-static code, calculating the wake fields is done using a two-dimensional (2D) PIC code where the time variable is ξ=ct-z and z is the propagation direction of the particle/laser beam. When calculating the wake, the fields, particle positions and momenta are not naturally time centered so an iterative predictor corrector loop is required. In the previous iterative loop in QuickPIC (currently the only 3D quasi-static PIC code), the field equations are derived using the Lorentz gauge. Here we describe a new algorithm which uses gauge independent field equations. It is found that with this new algorithm, the results converge to the results from fully explicitly PIC codes with far fewer iterations (typically 1 iteration as compared to 2–8) for a wide range of problems. In addition, we describe a new deposition scheme for directly depositing the time derivative of the current that is needed in one of the field equations. The new deposition scheme does not require message passing for the particles inside the iteration loop, which greatly improves the speed for parallelized calculations. Comparisons of results from the new and old algorithms and to fully explicit PIC codes are also presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Mechanical stability of the CMS strip tracker measured with a laser alignment system

The CMS tracker consists of 206 m(2) of silicon strip sensors assembled on carbon fibre composite structures and is designed for operation in the temperature range from −25 to +25°C. The mechanical stability of tracker components during physics operation was monitored with a few μm resolution using a dedicated laser alignment system as well as particle tracks from cosmic rays and hadron-hadron collisions. During the LHC operational period of 2011–2013 at stable temperatures, the components of the tracker were observed to experience relative movements of less than 30μm. In addition, temperature variations were found to cause displacements of tracker structures of about 2μm°C, which largely revert to their initial positions when the temperature is restored to its original value.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1976

Monitoring complex trace-gas mixtures by long-path laser absorption spectrometry

Laser-based spectrophotometric methods, which have been proposed for the detection of trace concentrations of gaseous contaminants, include Raman and passive radiometry. The paper discusses a simple long-path laser absorption method which is capable of resolving complex mixtures of closely related trace contaminants at ppm levels. A number of species were selected which are most likely to accumulate in closed environments, such as submarines or long-duration manned space flights. Absorption coefficients at CO2 laser wavelengths were measured, accurate to + 3 per cent or better, for each of these species. This data base was then used to determine the presence and concentration of the contaminants in prepared mixtures of 12 to 15 gases. Computer programs have been developed which will permit a real-time analysis of the monitored atmosphere. Minimum detectable concentrations for individual species are generally in the ppm range, and are not seriously degraded by interferences even in complex mixtures. Estimates of the dynamic range of this monitoring technique for various system configurations and comparison with other methods of analysis are discussed

Green, B. D.↗