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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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Confinement effects of shock waves on laser-induced plasma from a graphite target

The spatial confinement effects of shock waves on the laser-induced plasma (LIP) from a graphite target in air were studied by probe beam deflection (PBD) measurements and optical emission spectroscopy (OES). A clear relationship between the confinement of the LIP by the shock wave and the effects on the LIP emission was observed, and the underlying mechanisms are discussed. PBD monitoring revealed that the laser-ablation induced shock wave could be well analogized to the shock wave generated by a point explosion and would be reflected by a block. OES measurements indicated that the optical emission of the LIP exhibited significant variations with the block placement. A first enhancement and then a fast decay of CN molecular emission as well as a suppression of carbon atomic emission were observed in the presence of the block. The results revealed that the reflected shock wave spatially confined the expansion of the LIP and compressed the LIP after encountering it, pushing back the species of the LIP and changing the density of the LIP species including luminous carbon atoms and CN molecules. It is suggested that the change of the LIP emission is attributed to the density variation of the LIP species due to the compression of the LIP and the reactions occurring in the plasma.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Time-domain Brillouin scattering for the determination of laser-induced temperature gradients in liquids

We present an optical technique based on ultrafast photoacoustics to determine the local temperature distribution profile in liquid samples in contact with a laser heated optical transducer. This ultrafast pump-probe experiment uses time-domain Brillouin scattering (TDBS) to locally determine the light scattering frequency shift. As the temperature influences the Brillouin scattering frequency, the TDBS signal probes the local laser-induced temperature distribution in the liquid. Here, we demonstrate the relevance and the sensitivity of this technique for the measurement of the absolute laser-induced temperature gradient of a glass forming liquid prototype, glycerol, at different laser pump powers—i.e., different steady state background temperatures. Complementarily, our experiments illustrate how this TDBS technique can be applied to measure thermal diffusion in complex multilayer systems in contact with a surrounding liquid.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Accuracy of XAS theory for unraveling structural changes of adsorbates: CO on Ni(100)

Studying surface reactions using ultrafast optical pump and X-ray probe experiments relies on accurate calculations of X-ray spectra of adsorbates for correct identification of the spectral signatures and their dynamical evolution. We show that experimental XAS can be well reproduced for the different binding sites in a static prototype system CO/Ni(100) at a standard DFT (GGA) level of theory, using a plane-wave basis and pseudopotentials. This validates its utility in analyzing ultrafast X-ray probe experiments. The accuracy of computed relative core level binding energies is about 0.2 eV, representing a lower limit for which spectral features can be resolved with this method. We also show that the commonly used Z +1 approximation gives very good core binding energy shifts overall. However, we find a discrepancy for CO adsorbed in the hollow site, which we assign to the significantly stronger hybridization in hollow bonding than in on-top.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

3D velocity map imaging of electrons with TPX3CAM

In this report we demonstrate three-dimensional velocity map imaging of low energy electrons using a TPX3CAM, where the three-dimensional momentum information [$p_x, p_y, p_z$] is encoded in position and timing [x, y, t] of hits on the camera sensor. We make use of the camera sensor for the [x, y] information and a constant fraction discriminator and fast time to digital converter in the camera for the time information. We illustrate the capabilities of our apparatus by presenting above threshold ionization measurements of xenon, which produces well defined structures in the momentum resolved photoelectron yield.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

In situ spin coater for multimodal grazing incidence x-ray scattering studies

We present herein a custom-made, in situ, multimodal spin coater system with an integrated heating stage that can be programmed with spinning and heating recipes and that is coupled with synchrotron-based, grazing-incidence wide- and small-angle x-ray scattering. The spin coating system features an adaptable experimental chamber, with the ability to house multiple ancillary probes such as photoluminescence and visible optical cameras, to allow for true multimodal characterization and correlated data analysis. This system enables monitoring of structural evolutions such as perovskite crystallization and polymer self-assembly across a broad length scale (2 Å–150 nm) with millisecond temporal resolution throughout a complete thin film fabrication process. The use of this spin coating system allows scientists to gain a deeper understanding of temporal processes of a material system, to develop ideal conditions for thin film manufacturing.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

The surface chemistry of colloidal lead halide perovskite nanowires

This study explored the interplay between the ligand–surface chemistry of colloidal CsPbBr 3 nanowires (NWs) and their optical properties. The ligand equilibrium was probed using nuclear magnetic resonance spectroscopy, and by perturbing the equilibrium via dilution, the gradual removal of ligands from the CsPbBr 3 surface was observed. This removal was correlated with an increase in the surface defect density, as suggested by a broadening of the photoluminescence (PL) spectrum, a decrease in the PL quantum yield (PLQY), and quenching of the PL decay. These results highlight similar surface binding between the traditional CsPbBr 3 quantum dots and our NWs, thereby expanding the scope of well-established ligand chemistry to a relatively unexplored nanocrystal morphology. In conclusion, by controlling the dilution factor, it was revealed that CsPbBr 3 NWs achieve a PLQY of 72% ± 2% and a relatively long average PL lifetime of 400 ± 10 ns, without relying on additional surface passivation techniques, such as ligand exchange.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

A miniature multi-anvil apparatus using diamond as anvils—MDAC: Multi-axis diamond anvil cell

The diamond anvil cell (DAC) has been widely used in high-pressure research. Despite significant progress over the past five decades, the opposed anvil geometry in the DAC inevitably leads to a disk-shaped sample configuration at high pressure. This intrinsic limitation is largely responsible for the large pressure and temperature gradients in the DAC, which often compromise precise experiments and their characterizations. Here, we designed and fabricated a multi-axis diamond anvil cell (MDAC) by adopting the concept of a multi-anvil apparatus but using single crystal diamonds as the anvil material. Preliminary data show that the MDAC can generate extreme pressure conditions above 100 GPa. The advantages of the MDAC over a traditional opposed anvil DAC include thicker, voluminous samples, quasi-hydrostatic, or designed deviatoric stress conditions, and multidirectional access windows for optical applications and x-ray probes. In this article, we present the design and performance of a prototype MDAC, as well as the application prospects in high-pressure research.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Effect of trapped-ion heating on generalised Ramsey methods for suppressing frequency shifts caused by a probe field in atomic clocks

Based on a simple one-dimensional model, we consider the effect of trapped-ion heating on the efficiency of generalised Ramsey methods for the probe-induced frequency shift suppression in optical frequency standards based on single ultracold ions. It is shown that ion heating reduces the efficiency of all previously proposed one-loop generalised Ramsey methods, leading in all cases to the appearance of a linear dependence of the reference frequency shift on the residual field frequency shift. Two versions of the most heating stable generalised Ramsey schemes, for which the proportionality coefficient in this dependence is minimal, are demonstrated. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

WEAK TURBULENCE IN THE HD 163296 PROTOPLANETARY DISK REVEALED BY ALMA CO OBSERVATIONS

Turbulence can transport angular momentum in protoplanetary disks and influence the growth and evolution of planets. With spatially and spectrally resolved molecular emission line measurements provided by (sub)millimeter interferometric observations, it is possible to directly measure non-thermal motions in the disk gas that can be attributed to this turbulence. We report a new constraint on the turbulence in the disk around HD 163296, a nearby young A star, determined from Atacama Large Millimeter/submillimeter Array Science Verification observations of four CO emission lines (the CO(3-2), CO(2-1), {sup 13}CO(2-1), and C{sup 18}O(2-1) transitions). The different optical depths for these lines permit probes of non-thermal line-widths at a range of physical conditions (temperature and density) and depths into the disk interior. We derive stringent limits on the non-thermal motions in the upper layers of the outer disk such that any contribution to the line-widths from turbulence is <3% of the local sound speed. These limits are approximately an order of magnitude lower than theoretical predictions for full-blown magnetohydrodynamic turbulence driven by the magnetorotational instability, potentially suggesting that this mechanism is less efficient in the outer (R ≳ 30 AU) disk than has been previously considered.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Near total reflection x-ray photoelectron spectroscopy: quantifying chemistry at solid/liquid and solid/solid interfaces

Near total reflection regime has been widely used in x-ray science, specifically in grazing incidence small angle x-ray scattering and in hard x-ray photoelectron spectroscopy (XPS). In this work, we introduce some practical aspects of using near total reflection (NTR) in ambient pressure XPS and apply this technique to study chemical concentration gradients in a substrate/photoresist system. Experimental data are accompanied by x-ray optical and photoemission simulations to quantitatively probe the photoresist and the interface with the depth accuracy of ~1 nm. Together, our calculations and experiments confirm that NTR XPS is a suitable method to extract information from buried interfaces with highest depth-resolution, which can help address open research questions regarding our understanding of concentration profiles, electrical gradients, and charge transfer phenomena at such interfaces. Furthermore, the presented methodology is especially attractive for solid/liquid interface studies, since it provides all the strengths of a Bragg-reflection standing-wave spectroscopy without the need of an artificial multilayer mirror serving as a standing wave generator, thus dramatically simplifying the sample synthesis.

solid/solid interface↗
DOE OSTI2024

Is Ba 3 In 2 O 6 a high- T c superconductor?

It has been suggested that Ba 3 In 2 O 6 might be a high-Tc superconductor. Experimental investigation of the properties of Ba 3 In 2 O 6 was long inhibited by its instability in air. Recently epitaxial Ba 3 In 2 O 6 with a protective capping layer was demonstrated, which finally allows its electronic characterization. The optical bandgap of Ba3In2O6 is determined to be 2.99 eV in-the (001) plane and 2.83 eV along the c-axis direction by spectroscopic ellipsometry. First-principles calculations were carried out, yielding a result in good agreement with the experimental value. Various dopants were explored to induce (super-)conductivity in this otherwise insulating material. Neither A- nor B-site doping proved successful. The underlying reason is predominately the formation of oxygen interstitials as revealed by scanning transmission electron microscopy and first-principles calculations. Additional efforts to induce superconductivity were investigated, including surface alkali doping, optical pumping, and hydrogen reduction. To probe liquid-ion gating, Ba 3 In 2 O 6 was successfully grown epitaxially on an epitaxial SrRuO 3 bottom electrode. So far none of these efforts induced superconductivity in Ba 3 In 2 O 6 , leaving the answer to the initial question of whether Ba 3 In 2 O 6 is a high-T c superconductor to be 'no' thus far.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

X-ray diffraction study of laser-driven solid-state diffusional mixing and new phase formation in Ni-Pt multilayers [X-ray diffraction study of laser-driven solid-state diffusional mixing and new phase formation]

An in situ optical pump and x-ray probe technique has been utilized to study photoinitiated solid-state diffusion in a Ni-Pt multilayer system. Hard x-ray diffraction has been used to follow the systematic growth of the NiPt alloy as a function of laser intensity and total energy deposited. It is observed that new phase growth can be driven in as little as one laser pulse, and that repeated photoexcitation can completely convert the entire multilayer structure into a single metallic alloy. In conclusion, the data suggest that lattice strain relaxation takes place prior to atomic diffusion and the formation of a NiPt alloy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Nonlinear Magnetization Dynamics Driven by Strong Terahertz Fields

We present a comprehensive experimental and numerical study of magnetization dynamics in a thin metallic film triggered by single-cycle terahertz pulses of ~20 MV/m electric field amplitude and ~1 ps duration. The experimental dynamics is probed using the femtosecond magneto-optical Kerr effect, and it is reproduced numerically using macrospin simulations. The magnetization dynamics can be decomposed in three distinct processes: a coherent precession of the magnetization around the terahertz magnetic field, an ultrafast demagnetization that suddenly changes the anisotropy of the film, and a uniform precession around the equilibrium effective field that is relaxed on the nanosecond time scale, consistent with a Gilbert damping process. Macrospin simulations quantitatively reproduce the observed dynamics, and allow us to predict that novel nonlinear magnetization dynamics regimes can be attained with existing tabletop terahertz sources.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Optically Induced Anisotropy in Time-Resolved Scattering: Imaging Molecular-Scale Structure and Dynamics in Disordered Media with Experiment and Theory

Time-resolved scattering experiments enable imaging of materials at the molecular scale with femtosecond time resolution. However, in disordered media they provide access to just one radial dimension thus limiting the study of orientational structure and dynamics. Here we introduce a rigorous and practical theoretical framework for predicting and interpreting experiments combining optically induced anisotropy and time-resolved scattering. Using impulsive nuclear Raman and ultrafast x-ray scattering experiments of chloroform and simulations, we demonstrate that this framework can accurately predict and elucidate both the spatial and temporal features of these experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Simultaneous scanning near-field optical and X-ray diffraction microscopy for correlative nanoscale structure-property characterization

A multimodal imaging instrument has been developed that integrates scanning near-field optical microscopy with nanofocused synchrotron X-ray diffraction imaging. The instrument allows for the simultaneous nanoscale characterization of electronic/near-field optical properties of materials together with their crystallographic structure, facilitating the investigation of local structure–property relationships. The design, implementation and operating procedures of this instrument are reported. The scientific capabilities are demonstrated in a proof-of-principle study of the insulator–metal phase transition in samarium sulfide (SmS) single crystals induced by applying mechanical pressure via a scanning tip. The multimodal imaging of an in situ tip-written region shows that the near-field optical reflectivity can be correlated with the heterogeneously transformed structure of the near-surface region of the crystal.

insulator–metal transitions↗
DOE OSTI2015

Laser interferometric method for determining the carrier diffusion length in semiconductors

A new laser interferometric method for measuring the carrier diffusion length in semiconductors is proposed. The method is based on the interference–absorption interaction of two laser radiations in a semiconductor. Injected radiation generates additional carriers in a semiconductor, which causes a change in the material’s optical constants and modulation of the probing radiation passed through the sample. When changing the distance between carrier generation and probing points, a decrease in the carrier concentration, which depends on the diffusion length, is recorded. The diffusion length is determined by comparing the experimental and theoretical dependences of the probe signal on the divergence of the injector and probe beams. The method is successfully tested on semiconductor samples with different thicknesses and surface states and can be used in scientific research and the electronics industry.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Rotation and winds of exoplanet HD 189733 b measured with high-dispersion transmission spectroscopy

Giant exoplanets orbiting very close to their parent star (hot Jupiters) are subject to tidal forces expected to synchronize their rotational and orbital periods on short timescales (tidal locking). However, spin rotation has never been measured directly for hot Jupiters. Furthermore, their atmospheres can show equatorial super-rotation via strong eastward jet streams, and/or high-altitude winds flowing from the day- to the night-side hemisphere. Planet rotation and atmospheric circulation broaden and distort the planet spectral lines to an extent that is detectable with measurements at high spectral resolution. We observed a transit of the hot Jupiter HD 189733 b around 2.3 μm and at a spectral resolution of R∼10{sup 5} with CRIRES at the ESO Very Large Telescope. After correcting for the stellar absorption lines and their distortion during transit (the Rossiter–McLaughlin effect), we detect the absorption of carbon monoxide and water vapor in the planet transmission spectrum by cross-correlating with model spectra. The signal is maximized (7.6σ) for a planet rotational velocity of (3.4{sub −2.1}{sup +1.3}) km s{sup −1}, corresponding to a rotational period of (1.7{sub −0.4}{sup +2.9}) days. This is consistent with the planet orbital period of 2.2 days, and therefore with tidal locking. We find that the rotation of HD 189733 b is longer than 1 day (3σ). The data only marginally (1.5σ) prefer models with rotation versus models without rotation. We measure a small day- to night-side wind speed of (−1.7{sub −1.2}{sup +1.1}) km s{sup −1}. Compared to the recent detection of sodium blueshifted by (8±2) km s{sup −1}, this likely implies a strong vertical wind shear between the pressures probed by near-infrared and optical transmission spectroscopy.

79 ASTRONOMY AND ASTROPHYSICS↗