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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Creation of quantum-degenerate gases of ytterbium in a compact 2D-/3D-magneto-optical trap setup

We report on the first experimental setup based on a 2D-/3D-magneto-optical trap (MOT) scheme to create both Bose-Einstein condensates and degenerate Fermi gases of several ytterbium isotopes. Our setup does not require a Zeeman slower and offers the flexibility to simultaneously produce ultracold samples of other atomic species. Furthermore, the extraordinary optical access favors future experiments in optical lattices. A 2D-MOT on the strong {sup 1}S{sub 0}{yields}{sup 1}P{sub 1} transition captures ytterbium directly from a dispenser of atoms and loads a 3D-MOT on the narrow {sup 1}S{sub 0}{yields}{sup 3}P{sub 1} intercombination transition. Subsequently, atoms are transferred to a crossed optical dipole trap and cooled evaporatively to quantum degeneracy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

First glimpse of the soft x-ray induced excited spin-state trapping effect dynamics on spin cross-over molecules

The dynamics of the soft x-ray induced excited spin state trapping (SOXIESST) effect of Fe(phen){sub 2}(NCS){sub 2} (Fe-phen) powder have been investigated by x-ray absorption spectroscopy (XAS) using the total electron yield method, in a wide temperature range. The low-spin (LS) state is excited into the metastable high-spin (HS) state at a rate that depends on the intensity of the x-ray illumination it receives, and both the temperature and the intensity of the x-ray illumination will affect the maximum HS proportion that is reached. We find that the SOXIESST HS spin state transforms back to the LS state at a rate that is similar to that found for the light induced excited spin state trapping (LIESST) effect. We show that it is possible to use the SOXIESST effect in combination with the LIESST effect to investigate the influence of cooperative behavior on the dynamics of both effects. To investigate the impact of molecular cooperativity, we compare our results on Fe-phen with those obtained for Fe([Me{sub 2}Pyrz]{sub 3}BH){sub 2} (Fe-pyrz) powder, which exhibits a similar thermal transition temperature but with a hysteresis. We find that, while the time constant of the dynamic is identical for both molecules, the SOXIESST effect is less efficient at exciting the HS state in Fe-pyrz than in Fe-phen.

36 MATERIALS SCIENCE↗
DOE OSTI2013

An atom trap trace analysis system for measuring krypton contamination in xenon dark matter detectors

We have developed an atom trap trace analysis (ATTA) system to measure Kr in Xe at the part per trillion (ppt) level, a prerequisite for the sensitivity achievable with liquid xenon dark matter detectors beyond the current generation. Since Ar and Kr have similar laser cooling wavelengths, the apparatus has been tested with Ar to avoid contamination prior to measuring Xe samples. A radio-frequency plasma discharge generates a beam of metastable atoms which is optically collimated, slowed, and trapped using standard magneto-optical techniques. Based on the measured overall system efficiency of 1.2 × 10{sup −8} (detection mode), we expect the ATTA system to reach the design goal sensitivity to ppt concentrations of Kr in Xe in <2 h.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

A high-speed vertical optical trap for the mechanical testing of living cells at piconewton forces

Although atomic force microscopy is often the method of choice to probe the mechanical response of (sub)micrometer sized biomaterials, the lowest force that can be reliably controlled is limited to ≈0.1 nN. For soft biological samples, like cells, such forces can already lead to a strain large enough to enter the non-elastic deformation regime. To be able to investigate the response of single cells at lower forces we developed a vertical optical trap. The force can be controlled down to single piconewtons and most of the advantages of atomic force microscopy are maintained, such as the symmetrical application of forces at a wide range of loading rates. Typical consequences of moving the focus in the vertical direction, like the interferometric effect between the bead and the coverslip and a shift of focus, were quantified and found to have negligible effects on our measurements. With a fast responding force feedback loop we can achieve deformation rates as high as 50 μm/s, which allow the investigation of the elastic and viscous components of very soft samples. The potential of the vertical optical trap is demonstrated by measuring the linearity of the response of single cells at very low forces and a high bandwidth of deformation rates.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Trapping ultracold gases near cryogenic materials with rapid reconfigurability

We demonstrate an atom chip trapping system that allows the placement and high-resolution imaging of ultracold atoms within microns from any ≲100 μm-thin, UHV-compatible material, while also allowing sample exchange with minimal experimental downtime. The sample is not connected to the atom chip, allowing rapid exchange without perturbing the atom chip or laser cooling apparatus. Exchange of the sample and retrapping of atoms has been performed within a week turnaround, limited only by chamber baking. Moreover, the decoupling of sample and atom chip provides the ability to independently tune the sample temperature and its position with respect to the trapped ultracold gas, which itself may remain in the focus of a high-resolution imaging system. As a first demonstration of this system, we have confined a 700-nK cloud of 8 × 10{sup 4} {sup 87}Rb atoms within 100 μm of a gold-mirrored 100-μm-thick silicon substrate. The substrate was cooled to 35 K without use of a heat shield, while the atom chip, 120 μm away, remained at room temperature. Atoms may be imaged and retrapped every 16 s, allowing rapid data collection.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

The behavior of off-state stress-induced electrons trapped at the buffer layer in AlGaN/GaN heterostructure field effect transistors

A measurement methodology involving the synchronous switching of gate to source voltage and drain to source voltage (V{sub DS}) was proposed for determining the shift of threshold voltage after an AlGaN/GaN heterostructure transistor endures high V{sub DS} off-state stress. The measurement results indicated slow electron detrapping behavior. The trap level was determined as (E{sub C} – 0.6 eV). Simulation tool was used to analyze the measurement results. The simulation results were consistent with the experimental results; and a relationship between the buffer trap and threshold voltage shift over time was observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Angular dependence of light trapping in In{sub 0.3}Ga{sub 0.7}As/GaAs quantum-well solar cells

The dependence of light trapping effects in In{sub 0.3}Ga{sub 0.7}As/GaAs quantum-well solar cells on wavelength and incident angle is experimentally characterized and analyzed. Separation of active device layers from their epitaxial growth substrate enables integration of thin-film semiconductor device layers with nanostructured metal/dielectric rear contacts to increase optical absorption via coupling to both Fabry-Perot resonances and guided lateral propagation modes in the semiconductor. The roles of Fabry-Perot resonances and coupling to guided modes are analyzed via photocurrent response measurements and numerical modeling for light incident at angles of 0° (normal incidence) to 30° off normal. Light trapping enables external quantum efficiency at long wavelengths as high as 2.9% per quantum well to be achieved experimentally, substantially exceeding the ∼1% per quantum well level typically observed. Increased long wavelength quantum efficiency is shown in experimental measurements to persist with increasing angle of incidence and is explained as a consequence of the large number of guided modes available in the device structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Trapping of electrons in troughs of self generated electromagnetic standing waves in a bounded plasma column

Observations and measurements are reported on electron trapping in troughs of self-generated electromagnetic standing waves in a bounded plasma column confined in a minimum-B field. The boundaries are smaller than the free space wavelength of the waves. Earlier work of researchers primarily focused upon electron localization effects induced by purely electrostatic perturbation. We demonstrate the possibility in the presence of electromagnetic standing waves generated in the bounded plasma column. The electron trapping is verified with electrostatic measurements of the plasma floating potential, electromagnetic measurements of the wave field profile, and optical intensity measurements of Argon ionic line at 488 nm. The experimental results show a reasonably good agreement with predictions of a Monte Carlo simulation code that takes into account all kinematical and dynamical effects in the plasma in the presence of bounded waves and external fields.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Plasma treatment effect on charge carrier concentrations and surface traps in a-InGaZnO thin-film transistors

Various plasma treatment effects such as oxygen (O{sub 2}), nitrogen (N{sub 2}), and argon (Ar) on amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) are investigated. To study oxygen stoichiometry in a-IGZO TFTs with respect to various plasma environments, X-ray photoelectron spectroscopy was employed. The results showed that oxygen vacancies were reduced by O{sub 2} and N{sub 2} plasmas while they were increased after Ar plasma treatment. Additionally, the effects of plasma treatment on trap distribution in bulk and surface channels were explored by means of low-frequency noise analysis. Details of the mechanisms used for generating and restoring traps on the surface and bulk channel are presented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Distinguishing triplet energy transfer and trap-assisted recombination in multi-color organic light-emitting diode with an ultrathin phosphorescent emissive layer

An ultrathin layer of deep-red phosphorescent emitter tris(1-phenylisoquinoline) iridium (III) (Ir(piq){sub 3}) is inserted within different positions of the electron blocking layer fac-tris (1-phenylpyrazolato-N,C{sup 2′})-iridium(III) (Ir(ppz){sub 3}) to distinguish the contribution of the emission from the triplet exciton energy transfer/diffusion from the adjacent blue phosphorescent emitter and the trap-assisted recombination from the narrow band-gap emitter itself. The charge trapping effect of the narrow band-gap deep-red emitter which forms a quantum-well-like structure also plays a role in shaping the electroluminescent characteristics of multi-color organic light-emitting diodes. By accurately controlling the position of the ultrathin sensing layer, it is considerably easy to balance the white emission which is quite challenging for full-color devices with multiple emission zones. There is nearly no energy transfer detectable if 7 nm thick Ir(ppz){sub 3} is inserted between the blue phosphorescent emitter and the ultrathin red emitter.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Independent trapping and manipulation of microparticles using dexterous acoustic tweezers

An electronically controlled acoustic tweezer was used to demonstrate two acoustic manipulation phenomena: superposition of Bessel functions to allow independent manipulation of multiple particles and the use of higher-order Bessel functions to trap particles in larger regions than is possible with first-order traps. The acoustic tweezers consist of a circular 64-element ultrasonic array operating at 2.35 MHz which generates ultrasonic pressure fields in a millimeter-scale fluid-filled chamber. The manipulation capabilities were demonstrated experimentally with 45 and 90-μm-diameter polystyrene spheres. These capabilities bring the dexterity of acoustic tweezers substantially closer to that of optical tweezers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Enhanced loss of magnetic-mirror-trapped fast electrons by a shear Alfvén wave

Laboratory observations of enhanced loss of magnetic mirror trapped fast electrons irradiated by a shear Alfvén Wave (SAW) are reported. The experiment is performed in the quiescent after-glow plasma in the Large Plasma Device [Gekelman et al., Rev. Sci. Instrum. 62(12), 2875–2883 (1991)]. A trapped energetic electron population (>100 keV) is generated in a magnetic mirror section (mirror ratio ≈ 2, length = 3.5 m) by an X-mode high power microwave pulse, and forms a hot electron ring due to the grad-B and curvature drift. SAWs of arbitrary polarization are launched externally by a Rotating Magnetic Field source (δB/B{sub 0} ≈ 0.1%, λ{sub ∥} ≈ 9 m). Irradiated by a right-handed circularly polarized SAW, the loss of electrons, in both the radial and the axial direction of the mirror field, is significantly enhanced and is modulated at f{sub Alfvén}. The periodical loss continues even after the termination of the SAW. Experimental observations suggest that a spatial distortion of the ring is formed in the SAW field and creates a collective mode of the hot electron population that degrades its confinement and leads to electron loss from the magnetic mirror. The results could have implications on techniques of radiation belt remediation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Regulation of electron temperature gradient turbulence by zonal flows driven by trapped electron modes

Turbulent transport caused by electron temperature gradient (ETG) modes was investigated by means of gyrokinetic simulations. It was found that the ETG turbulence can be regulated by meso-scale zonal flows driven by trapped electron modes (TEMs), which are excited with much smaller growth rates than those of ETG modes. The zonal flows of which radial wavelengths are in between the ion and the electron banana widths are not shielded by trapped ions nor electrons, and hence they are effectively driven by the TEMs. It was also shown that an E × B shearing rate of the TEM-driven zonal flows is larger than or comparable to the growth rates of long-wavelength ETG modes and TEMs, which make a main contribution to the turbulent transport before excitation of the zonal flows.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Study on dynamics of photoexcited charge injection and trapping in CdS quantum dots sensitized TiO{sub 2} nanowire array film electrodes

The photoexcited electrons transfer dynamics of the CdS quantum dots (QDs) deposited in TiO{sub 2} nanowire array films are studied using surface photovoltage (SPV) and transient photovoltage (TPV) techniques. By comparing the SPV results with different thicknesses of QDs layers, we can separate the dynamic characteristics of photoexcited electrons injection and trapping. It is found that the TPV signals of photoexcited electrons trapped in the CdS QDs occur at timescales of about 2 × 10{sup −8} s, which is faster than that of the photoexcited electrons injected from CdS into TiO{sub 2}. More than 90 nm of the thickness of the CdS QDs layer will seriously affect the photoexcited electrons transfer and injection.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Direct detection of a transport-blocking trap in a nanoscaled silicon single-electron transistor by radio-frequency reflectometry

The continuous downscaling of transistors results in nanoscale devices which require fewer and fewer charged carriers for their operation. The ultimate charge controlled device, the single-electron transistor (SET), controls the transfer of individual electrons. It is also the most sensitive electrometer, and as a result the electron transport through it can be dramatically affected by nearby charges. Standard direct-current characterization techniques, however, are often unable to unambiguously detect and resolve the origin of the observed changes in SET behavior arising from changes in the charge state of a capacitively coupled trap. Using a radio-frequency (RF) reflectometry technique, we are able to unequivocally detect this process, in very close agreement with modeling of the trap's occupation probability.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Two-dimensional and three-dimensional Coulomb clusters in parabolic traps

We consider the shell structure of Coulomb clusters in an axially symmetric parabolic trap exhibiting a confining potential U{sub c}(ρ,z)=(mω{sup 2}/2)(ρ{sup 2}+αz{sup 2}). Assuming an anisotropic parameter α = 4 (corresponding to experiments employing a cusp magnetic trap under microgravity conditions), we have calculated cluster configurations for particle numbers N = 3 to 30. We have shown that clusters with N ≤ 12 initially remain flat, transitioning to three-dimensional configurations as N increases. For N = 8, we have calculated the configurations of minimal potential energy for all values of α and found the points of configuration transitions. For N = 13 and 23, we discuss the influence of both the shielding and anisotropic parameter on potential energy, cluster size, and shell structure.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Dependence of electron trapping on bubble geometry in laser-plasma wakefield acceleration

The effect of bubble shape in laser-plasma electron acceleration was investigated. We showed the general existence of an ellipsoid bubble. The electromagnetic field in this bubble and its dependence on bubble shape were determined through theory. The electron-trapping cross-section for different bubble aspect ratios was studied in detail. When the shape of the bubble was close to spherical, the trapping cross-section reached to the maximum. When the bubble deviated from a spherical shape, the cross-section decreased until electron injection no longer occurred. These results were confirmed by particle-in-cell simulation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Analysis of carrier transport and carrier trapping in organic diodes with polyimide-6,13-Bis(triisopropylsilylethynyl)pentacene double-layer by charge modulation spectroscopy and optical second harmonic generation measurement

We studied the carrier transport and carrier trapping in indium tin oxide/polyimide (PI)/6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)/Au diodes by using charge modulation spectroscopy (CMS) and time-resolved electric field induced optical second harmonic generation (TR-EFISHG) measurements. TR-EFISHG directly probes the spatial carrier behaviors in the diodes, and CMS is useful in explaining the carrier motion with respect to energy. The results clearly indicate that the injected carriers move across TIPS-pentacene thorough the molecular energy states of TIPS-pentacene and accumulate at the PI/TIPS-pentacene interface. However, some carriers are trapped in the PI layers. These findings take into account the capacitance-voltage and current-voltage characteristics of the diodes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗