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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 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Temperature- and field-driven spin reorientations in triple-layer ruthenate Sr 4 Ru 3 O 10

Sr 4 Ru 3 O 10 , the n = 3 member of the Ruddlesden-Popper type ruthenate Sr n+1 Ru n O 3n+1 , is known to exhibit a peculiar metamagnetic transition in an in-plane magnetic field. However, the nature of both the temperature- and field-dependent phase transitions remains as a topic of debate. Here, we have investigated the magnetic transitions of Sr 4 Ru 3 O 10 via single-crystal neutron diffraction measurements. At zero field, we find that the system undergoes a ferromagnetic transition with both in-plane and out-of-plane magnetic components at T c ≈ 100 K. Below T * = 50 K, the magnetic moments incline continuously toward the out-of-plane direction. At T = 1.5 K, where the spins are nearly aligned along the c axis, a spin reorientation occurs above a critical field Bc, giving rise to a spin component perpendicular to the plane defined by the field direction and the c axis. We suggest that both the temperature- and field-driven spin reorientations are associated with a change in the magnetocrystalline anisotropy, which is strongly coupled to the lattice degrees of freedom. This study elucidates the long-standing puzzles on the zero-field magnetic orders of Sr 4 Ru 3 O 10 and provides new insights into the nature of the field-induced metamagnetic transition.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Iron arsenides with three-dimensional FeAs layer networks: Can(n+1)/2(Fe1-xPtx)(2+3n)Ptn(n-1)/2As(n+1)(n+2)/2 (n=2, 3)

We report the comprehensive studies between synchrotron X-ray diffraction, electrical resistivity and magnetic susceptibility experiments for the iron arsenides Can(n+1)/2(Fe1-xPtx)(2+3n)Ptn(n -1)/2As(n+1)(n+2)/2 for n=2 and 3. Both structures crystallize in the monoclinic space group P21/m (#11) with three-dimensional FeAs structures. The horizontal FeAs layers are bridged by inclined FeAs planes through edge-sharing FeAs5 square pyramids, resulting in triangular tunneling structures rather than the simple layered structures found in conventional iron arsenides. n=3 system shows a sign of superconductivity with a small volume fraction. Our first-principles calculations of these systems clearly indicate that the Fermi surfaces originate from strong Fe-3d characters and the three-dimensional nature of the electric structures for both systems, thus offering the playgrounds to study the effects of dimensionality on high Tc superconductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Electron injection study of photoexcitation effects on supported subnanometer Pt clusters for CO 2 photoreduction

In this paper, using density functional theory, we study the effect of injected electrons (simulating photoexcited electrons) on the energetics, structures, and binding sites available to CO 2 molecules on subnanometer Pt clusters decorated onto anatase TiO 2 (101) surfaces, shedding light on the first and key step of CO 2 photoreduction. Upon the addition of one, two, or three electrons, the O–C–O angles of adsorbed CO 2 become progressively smaller in binding sites that directly contact Pt clusters, while no significant change is found in the intra bond length of the adsorbed CO 2 and in the bonding distances between the adsorbed CO 2 and supported clusters. The extra electrons lead to the stabilization of adsorption sites identified on neutral slabs, including previously metastable configurations, suggesting the enhancement of accessible CO 2 binding sites. Furthermore, supported clusters are able to populate the electronic states of adsorbed CO 2 species, facilitating the formation of the CO 2 - anion. To help interpret experimentally observed frequencies, conversion factors are proposed to gain insight into the charge state and O–C–O angle of the adsorbed CO 2 . Interestingly, upon electron addition, cluster reconstruction may exist due to the bonding inclination between CO 2 and atoms in the Pt cluster, further stabilizing the intermediate complexes. In conclusion, the rate-limiting step (C–O bond cleavage) in the CO 2 dissociation to CO is slightly reduced by the introduction of an extra electron. Our results show that subnanometer metal cluster based photocatalysts are good candidates for CO 2 photoreduction.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

High thermoelectric performance in Bi 0.46 Sb 1.54 Te 3 nanostructured with ZnTe

Defect engineering and nano-structuring are the core stratagems for improving thermoelectric properties. In bismuth telluride alloys nanosizing individual crystallites has been extensively studied in efforts to reduce the thermal conductivity, but nanostructuring with second phases has been more challenging. In this study, we demonstrate a thermoelectric figure of merit ZT of 1.4 at 400 K, realized in Zn-containing BiSbTe alloys (specifically Bi 0.46 Sb 1.54 Te 3 ) by integrating defect complexity with nanostructuring. We have succeeded in creating nanostructured BiSbTe alloys containing ZnTe nanoprecipitates. We present a melt-spinning-based synthesis that forms in situ ZnTe nanoprecipitates to produce an extremely low lattice thermal conductivity of ~0.35 W m –1 K –1 at 400 K, approaching the amorphous limit in the Bi 2–x Sb x Te 3 system, while preserving the high power factor of Bi 0.46 Sb 1.54 Te 3 . These samples show excellent repeatability and thermal stability at temperatures up to 523 K. DFT calculations and experimental results show that Zn is inclined to form dual site defects, including two substitutional defects ZnBi/Sb' and a Te vacancy, to achieve full charge compensation, which was further explicitly corroborated by Positron annihilation measurement. The strong enhancement of thermoelectric properties was validated in a thermoelectric module fabricated with the melt-spun p-legs (ZnTe-nanostructured BiSbTe) and zone-melt n-legs (conventional BiTeSe) which achieved a thermoelectric conversion efficiency of 5.0% when subjected to a temperature gradient of 250 K, representing about 40% improvement compared with a commercial zone-melt-based module. Furthermore, the results presented here represent a significant step forward for applications in thermoelectric power generation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

New structural model of a chiral cubic liquid crystalline phase

A new model of a chiral cubic phase is proposed, in which the continuous lattice is embedded on a WP minimal primitive surface and chirality is related to the alternating inclination of molecules in the neighbouring segments of non-flat hexagons.

Vaupotič, Nataša↗
DOE OSTI2014

Six faint gamma-ray pulsars seen with the Fermi Large Area Telescope: Towards a sample blending into the background

Context. Here, GeV gamma-ray pulsations from over 140 pulsars have been characterized using the Fermi Large Area Telescope, enabling improved understanding of the emission regions within the neutron star magnetospheres, and the contributions of pulsars to high energy electrons and diffuse gamma rays in the Milky Way. The first gamma-ray pulsars to be detected were the most intense and/or those with narrow pulses. Aims. As the Fermi mission progresses, progressively fainter objects can be studied. In addition to more distant pulsars (thus probing a larger volume of the Galaxy), or ones in high background regions (thus improving the sampling uniformity across the Galactic plane), we detect pulsars with broader pulses or lower luminosity. Adding pulsars to our catalog with inclination angles that are rare in the observed sample, and/or with lower spindown power, will reduce the bias in the currently known gamma-ray pulsar population. Methods. We use rotation ephemerides derived from radio observations to phase-fold gamma rays recorded by the Fermi Large Area Telescope, to then determine the pulse profile properties. Spectral analysis provides the luminosities and, when the signal-to-noise ratio allows, the cutoff energies. We constrain the pulsar distances by different means in order to minimize the luminosity uncertainties. Results. We present six new gamma-ray pulsars with an eclectic mix of properties. Three are young, and three are recycled. They include the farthest, the lowest power, two of the highest duty-cycle pulsars seen, and only the fourth young gamma-ray pulsar with a radio interpulse. Finally, we discuss the biases existing in the current gamma-ray pulsar catalog, and steps to be taken to mitigate the bias.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The Close AGN Reference Survey (CARS)

Active galactic nuclei (AGN) are thought to be responsible for the suppression of star formation in massive ~10 10 M ⊙ galaxies. While this process is a key feature in numerical simulations of galaxy formation, it has not been unambiguously confirmed in observational studies yet. The characterization of the star formation rate (SFR) in AGN host galaxies is challenging as AGN light contaminates most SFR tracers. Furthermore, the various SFR tracers are sensitive to different timescales of star formation from approximately a few to 100 Myr. We aim to obtain and compare SFR estimates from different tracers for AGN host galaxies in the Close AGN Reference Survey (CARS) to provide new observational insights into the recent SFR history of those systems. We constructed integrated panchromatic spectral energy distributions to measure the far infrared (FIR) luminosity as a tracer for the recent (< 100 Myr) SFR. In addition we used the integral-field unit observation of the CARS targets to employ the Hα luminosity decontaminated by AGN excitation as a proxy for the current (< 5 Myr) SFR. We find that significant differences in specific SFR of the AGN host galaxies as compared with the larger galaxy population disappear once cold gas mass, in addition to stellar mass, is used to predict the SFR for a specific AGN host. Only a tentative trend with the inclination of the host galaxy remains, such that SFR appears slightly lower than expected when the galaxies of unobscured AGN appear more edge-on along our line-of-sight, particular for dust-insensitive FIR-based SFRs. We identify individual galaxies with a significant difference in their SFR which can be related to a recent enhancement or decline in their SFR history that might be related to various processes including interactions, gas consumption, outflows, and AGN feedback. AGN can be present in various stages of galaxy evolution which makes it difficult to relate the SFR solely to the impact of the AGN. Our study shows that stellar mass alone is an insufficient parameter to estimate the expected SFR of an AGN host galaxy compared to the underlying non-AGN galaxy population. We do not find any strong evidence for a global positive or negative AGN feedback in the CARS sample. However, there is tentative evidence that (1) the relative orientation of the AGN engine with respect to the host galaxies might alter the efficiency of AGN feedback and that (2) the recent SFH is an additional tool to identify rapid changes in galaxy growth driven by the AGN or other processes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Star formation and AGN feedback in the local Universe: Combining LOFAR and MaNGA

The effect of active galactic nuclei (AGN) on their host galaxies – in particular their levels of star formation – remains one of the key outstanding questions of galaxy evolution. Successful cosmological models of galaxy evolution require a fraction of energy released by an AGN to be redistributed into the interstellar medium to reproduce the observed stellar mass and luminosity function and to prevent the formation of over-massive galaxies. Observations have confirmed that the radio-AGN population is energetically capable of heating and redistributing gas at all phases, however, direct evidence of AGN enhancing or quenching star formation remains rare. With modern, deep radio surveys and large integral field spectroscopy (IFS) surveys, we can detect fainter synchrotron emission from AGN jets and accurately probe the star-forming properties of galaxies, respectively. Here, in this paper, we combine data from the LOw Frequency ARray Two-meter Sky Survey (LoTSS) with data from one of the largest optical IFS surveys, Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), to probe the star-forming properties of 307 local (z < 0.15) galaxies that host radio-detected AGN (RDAGN). We compare our results to a robust control sample of non-active galaxies that each match the stellar mass, redshift, visual morphology, and inclination of a RDAGN host. We find that RDAGN and control galaxies have broad star-formation rate (SFR) distributions, typically lie below the SFMS, and have negative stellar light-weighted age gradients. These results indicate that AGN selected based on their current activity are not responsible for suppressing their host galaxies’ star formation. Rather, our results support the maintenance mode role that radio AGN are expected to have in the local Universe.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The edges of galaxies: Tracing the limits of star formation

The outskirts of galaxies have been studied from multiple perspectives for the past few decades. However, it is still unknown if all galaxies have clear-cut edges similar to everyday objects. We address this question by developing physically motivated criteria to define the edges of galaxies. Based on the gas density threshold required for star formation, we define the edge of a galaxy as the outermost radial location associated with a significant drop in either past or ongoing in situ star formation. We explore ~1000 low-inclination galaxies with a wide range in morphology (dwarfs to ellipticals) and stellar mass (10 7 M ⊙ < M * < 10 12 M ⊙ ). The location of the edges of these galaxies (R edge ) were visually identified as the outermost cutoff or truncation in their radial profiles using deep multi-band optical imaging from the IAC Stripe82 Legacy Project. We find this characteristic feature at the following mean stellar mass density, which varies with galaxy morphology: 2.9 ± 0.10 M ⊙ pc -2 for ellipticals, 1.1 ± 0.04 M ⊙ pc -2 for spirals, and 0.6 ± 0.03 M ⊙ pc -2 for present-day star-forming dwarfs. Additionally, we find that R edge depends on its age (colour) where bluer galaxies have larger R edge at a fixed stellar mass. The resulting stellar mass–size plane using R edge as a physically motivated galaxy size measure has a very narrow intrinsic scatter (≲0.06 dex). These results highlight the importance of new deep imaging surveys to explore the growth of galaxies and trace the limits of star formation in their outskirts.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Asteroids seen by JWST-MIRI: Radiometric size, distance, and orbit constraints

Infrared measurements of asteroids are crucial for the determination of physical and thermal properties of individual objects, and for understanding the small-body populations in the solar system as a whole. However, standard radiometric methods can only be applied if the orbit of an object is known, hence its position at the time of the observation. With JWST-MIRI observations the situation will change and many unknown, often very small, solar system objects will be detected. Later orbit determinations are difficult due to the faintness of the objects and the lack of dedicated follow-up concepts. We present MIRI observations of the outer-belt asteroid (10920) 1998 BC1 and an unknown object, detected in all nine MIRI bands in close apparent proximity to (10920). We developed a new method called STM-ORBIT to interpret the multi-band measurements without knowing the object’s true location. The power of the new technique is that it determines the most-likely heliocentric and observer-centric distance and phase angle ranges, allowing us to make a radiometric size estimate. The application to the MIRI fluxes of (10920) was used to validate the method. It leads to a confirmation of the known radiometric size-albedo solution, and puts constraints on the asteroid’s location and orbit in agreement with its true orbit. To back up the validation of the method, we obtained additional ground-based light curve observations of (10920), combined with Gaia data, which indicate a very elongated object (a/b ≥ 1.5), with a spin-pole at (λ, β) ecl = (178°, +81°), with an estimated error of about 20°, and a rotation period of 4.861191 ± 0.000015 h. A thermophysical study of all available JWST-MIRI and WISE measurements leads to a size of 14.5–16.5 km (diameter of an equal-volume sphere), a geometric albedo pV between 0.05 and 0.10, and a thermal inertia in the range 9–35 (best value 15) J m -2 s -0.5 K -1 . For the newly discovered MIRI object, the STM-ORBIT method revealed a size of 100–230 m. The new asteroid must be on a low-inclination orbit (0.7° < i < 2.0°) and it was located in the inner main-belt region during JWST observations. A beaming parameter η larger than 1.0 would push the size even below 100 meters, a main-belt regime that has escaped IR detections so far. This kind of MIRI observations can therefore contribute to formation and evolution studies via classical size-frequency studies, which are currently limited to objects larger than about one kilometer in size. We estimate that MIRI frames with pointings close to the ecliptic and short integration times of only a few seconds will always include a few asteroids; most of them will be unknown objects.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

The occurrence rate of galaxies with polar structures may be significantly underestimated

Polar-ring galaxies are photometrically and kinematically decoupled systems that are highly inclined to the major axis of the host. These galaxies have been explored since the 1970s, but the rarity of these systems has made such systematic studies difficult. However, over 250 good candidates have been identified. In this work, we examine a sample of over 18 000 galaxies from the Sloan Digital Sky Survey (SDSS) Stripe 82 for the presence of galaxies with polar structures. Using deep SDSS Stripe 82, DESI Legacy Imaging Surveys, and Hyper Suprime-Cam Subaru Strategic Program, we selected 53 good candidate galaxies with photometrically decoupled polar rings, 9 galaxies with polar halos, 6 galaxies with polar bulges, and 34 possibly forming polar-ring galaxies, versus 13 polar-ring candidates previously selected in Stripe 82. Our results suggest that the occurrence rate of galaxies with polar structures may be significantly underestimated, as revealed by the deep observations, and may amount to 1–3% of non-dwarf galaxies.

Astronomy & Astrophysics↗
DOE OSTI2026

Delving into the depths of NGC 3783 with XRISM

Using XRISM/Resolve 439 ks time-averaged spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC 3783, we investigated the nature of the Fe Kα emission line at 6.4 keV, the strongest and most common X-ray line observed in AGNs. Even the narrow component of the line is resolved with evident Fe Kα 1 (6.404 keV) and Kα 2 (6.391 keV) contributions with a 2:1 flux ratio, fully consistent with a neutral gas with negligible bulk velocity. The narrow and intermediate-width components have a full width at half maximum of 350 ± 50 km/s and 3510 ± 470 km/s, respectively, suggesting that they arise in the outer disk/torus and/or broad line region. We detect a 10% excess flux around 4–7 keV that is not described well by a symmetric Gaussian line but is consistent with a relativistically broadened emission line. In this study we took the simplest approach, modelling the asymmetric line as a single emission line (assuming neutral, He-like, or H-like iron) convolved with a relativistic disk line model. As expected, the inferred inclination angle (i) is highly sensitive to the assumed ionisation state and ranges between 17 and 44°. This model also constrains the black hole spin via the extent of the red wing: the required gravitational redshift in the fitted disk-line profile disfavours a non-spinning (Schwarzschild) black hole. The derived inner radius is close to the radius of the innermost stable circular orbit (rISCO) and is strongly correlated with the black hole spin. To better constrain the spin, we fixed the inner radius to r ISCO and derived a lower limit on the spin of a ≥ 0.29 at the 3σ confidence level. A Compton shoulder is detected in our data as well as a 2–3σ detection of the Cr Kα and Ni Kα lines.

Astronomy and AstroPhysics↗
DOE OSTI2012

The effect of step geometry in copper oxidation by hyperthermal O{sub 2} molecular beam: Cu(511) vs Cu(410)

Steps are known to be often the active sites for the dissociation of O{sub 2} molecules and the nucleation sites of oxide films since they provide paths for subsurface migration and oxygen incorporation. In order to unravel the effect of their morphology on the oxidation of Cu surfaces, we present here a detailed investigation of the O{sub 2} interaction with Cu(511) and compare it with previous results for Cu(410), a surface exhibiting terraces of similar size and geometry but different step morphology. As for Cu(410) we find, by x-ray photoemission spectroscopy performed with synchrotron radiation, that Cu{sub 2}O formation gradually starts above half a monolayer oxygen coverage and that the ignition of oxidation can be lowered to room temperature by dosing O{sub 2} via a supersonic molecular beam at hyperthermal energy. The oxidation rate for Cu(511) comes out to be lower than for Cu(410) at normal incidence, about the same when the O{sub 2} molecules impinge towards the ascending step rise, but higher when they hit the surface along trajectories even slightly inclined towards the descending step rise. These findings can be rationalized by a collision induced absorption mechanism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Electron scattering mechanisms in GZO films grown on a-sapphire substrates by plasma-enhanced molecular beam epitaxy

We report on the mechanisms governing electron transport using a comprehensive set of ZnO layers heavily doped with Ga (GZO) grown by plasma-enhanced molecular-beam epitaxy on a-plane sapphire substrates with varying oxygen-to-metal ratios and Ga fluxes. The analyses were conducted by temperature dependent Hall measurements which were supported by microstructural investigations as well. Highly degenerate GZO layers with n > 5 x 10{sup 20} cm{sup -3} grown under metal-rich conditions (reactive oxygen-to-metal ratio <1) show relatively larger grains ({approx}20-25 nm by x-ray diffraction) with low-angle boundaries parallel to the polar c-direction. For highly conductive GZO layers, ionized-impurity scattering with almost no compensation is the dominant mechanism limiting the mobility in the temperature range from 15 to 330 K and the grain-boundary scattering governed by quantum-mechanical tunnelling is negligible. However, due to the polar nature of ZnO having high crystalline quality, polar optical phonon scattering cannot be neglected for temperatures above 150 K, because it further reduces mobility although its effect is still substantially weaker than the ionized impurity scattering even at room temperature (RT). Analysis of transport measurements and sample microstructures by x-ray diffraction and transmission electron microscopy led to a correlation between the grain sizes in these layers and mobility even for samples with a carrier concentration in the upper 10{sup 20} cm{sup -3} range. In contrast, electron transport in GZO layers grown under oxygen-rich conditions (reactive oxygen-to-metal ratio >1), which have inclined grain boundaries and relatively smaller grain sizes of 10-20 nm by x-ray diffraction, is mainly limited by compensation caused by acceptor-type point-defect complexes, presumably (Ga{sub Zn}-V{sub Zn}), and scattering on grain boundaries. The GZO layers with n <10{sup 20} cm{sup -3} grown under metal-rich conditions with reduced Ga fluxes show a clear signature of grain-boundary scattering governed by the thermionic effect in the temperature-dependent mobility but with much higher RT mobility values compared to the samples grown under oxygen-rich conditions [34 vs. 7.5 cm{sup 2}/V{center_dot}s]. Properties of GZO layers grown under different conditions clearly indicate that to achieve highly conductive GZO, metal-rich conditions instead of oxygen-rich conditions have to be used.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Kinetic models of two-dimensional plane and axially symmetric current sheets: Group theory approach

In this paper, we present new class of solutions of Grad-Shafranov-like (GS-like) equations, describing kinetic plane and axially symmetric 2D current sheets. We show that these equations admit symmetry groups only for Maxwellian and {kappa}-distributions of charged particles. The admissible symmetry groups are used to reduce GS-like equations to ordinary differential equations for invariant solutions. We derive asymptotes of invariant solutions, while invariant solutions are found analytically for the {kappa}-distribution with {kappa}=7/2. We discuss the difference of obtained solutions from equilibria widely used in other studies. We show that {kappa} regulates the decrease rate of plasma characteristics along the current sheet and determines the spatial distribution of magnetic field components. The presented class of plane and axially symmetric (disk-like) current sheets includes solutions with the inclined neutral plane.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Efficient reduction of defects in (1120) non-polar and (1122) semi-polar GaN grown on nanorod templates

(1120) non-polar and (1122) semi-polar GaNs with a low defect density have been achieved by means of an overgrowth on nanorod templates, where a quick coalescence with a thickness even below 1 {mu}m occurs. On-axis and off-axis X-ray rocking curve measurements have shown a massive reduction in the linewidth for our overgrown GaN in comparison with standard GaN films grown on sapphire substrates. Transmission electron microscope observation demonstrates that the overgrowth on the nanorod templates takes advantage of an omni-directional growth around the sidewalls of the nanostructures. The dislocations redirect in basal planes during the overgrowth, leading to their annihilation and termination at voids formed due to a large lateral growth rate. In the non-polar GaN, the priority <0001> lateral growth from vertical sidewalls of nanorods allows basal plane stacking faults (BSFs) to be blocked in the nanorod gaps; while for semi-polar GaN, the propagation of BSFs starts to be impeded when the growth front is changed to be along inclined <0001> direction above the nanorods.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Analysis of laser remote fusion cutting based on a mathematical model

Laser remote fusion cutting is analyzed by the aid of a semi-analytical mathematical model of the processing front. By local calculation of the energy balance between the absorbed laser beam and the heat losses, the three-dimensional vaporization front can be calculated. Based on an empirical model for the melt flow field, from a mass balance, the melt film and the melting front can be derived, however only in a simplified manner and for quasi-steady state conditions. Front waviness and multiple reflections are not modelled. The model enables to compare the similarities, differences, and limits between laser remote fusion cutting, laser remote ablation cutting, and even laser keyhole welding. In contrast to the upper part of the vaporization front, the major part only slightly varies with respect to heat flux, laser power density, absorptivity, and angle of front inclination. Statistical analysis shows that for high cutting speed, the domains of high laser power density contribute much more to the formation of the front than for low speed. The semi-analytical modelling approach offers flexibility to simplify part of the process physics while, for example, sophisticated modelling of the complex focused fibre-guided laser beam is taken into account to enable deeper analysis of the beam interaction. Mechanisms like recast layer generation, absorptivity at a wavy processing front, and melt film formation are studied too.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Measuring contact angle and meniscus shape with a reflected laser beam

Side-view imaging of the contact angle between an extended planar solid surface and a liquid is problematic. Even when aligning the view perfectly parallel to the contact line, focusing one point of the contact line is not possible. We describe a new measurement technique for determining contact angles with the reflection of a widened laser sheet on a moving contact line. We verified this new technique measuring the contact angle on a cylinder, rotating partially immersed in a liquid. A laser sheet is inclined under an angle φ to the unperturbed liquid surface and is reflected off the meniscus. Collected on a screen, the reflection image contains information to determine the contact angle. When dividing the laser sheet into an array of laser rays by placing a mesh into the beam path, the shape of the meniscus can be reconstructed from the reflection image. We verified the method by measuring the receding contact angle versus speed for aqueous cetyltrimethyl ammonium bromide solutions on a smooth hydrophobized as well as on a rough polystyrene surface.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗