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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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DOE OSTI2011

Amorphous Diamond: A High-Pressure Superhard Carbon Allotrope

Compressing glassy carbon above 40 GPa, we have observed a new carbon allotrope with a fully sp{sup 3}-bonded amorphous structure and diamondlike strength. Synchrotron x-ray Raman spectroscopy revealed a continuous pressure-induced sp{sup 2}-to-sp{sup 3} bonding change, while x-ray diffraction confirmed the perseverance of noncrystallinity. The transition was reversible upon releasing pressure. Used as an indenter, the glassy carbon ball demonstrated exceptional strength by reaching 130 GPa with a confining pressure of 60 GPa. Such an extremely large stress difference of >70 GPa has never been observed in any material besides diamond, indicating the high hardness of this high-pressure carbon allotrope.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Imaging Nonequilibrium Atomic Vibrations with X-ray Diffuse Scattering

We use picosecond x-ray diffuse scattering to image the nonequilibrium vibrations of the lattice following ultrafast laser excitation. We present images of nonequilibrium phonons in InP and InSb throughout the Brillouin-zone which remain out of equilibrium up to nanoseconds. The results are analyzed using a Born model that helps identify the phonon branches contributing to the observed features in the time-resolved diffuse scattering. In InP this analysis shows a delayed increase in the transverse acoustic (TA) phonon population along high-symmetry directions accompanied by a decrease in the longitudinal acoustic (LA) phonons. In InSb the increase in TA phonon population is less directional.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Massive Dirac Fermion on the Surface of a Magnetically Doped Topological Insulator

Topological insulators are characterized by a massless Dirac surface state and a bulk energy gap. An insulating massive Dirac fermion state is predicted to occur if the breaking of the time reversal symmetry opens an energy gap at the Dirac point, provided that the Fermi-energy resides inside both the surface and bulk gaps. By introducing magnetic dopants into the three dimensional topological insulator Bi{sub 2}Se{sub 3} to break the time reversal symmetry, we observed the formation of a massive Dirac fermion on the surface; simultaneous magnetic and charge doping furthermore positioned the Fermi-energy inside the Dirac gap. The insulating massive Dirac Fermion state thus obtained may provide a tool for studying a range of topological phenomena relevant to both condensed matter and particle physics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

What Coexists with the Ferromagnetic Metallic Phase in Manganites?

Colossal magnetoresistance, whereby the application of a magnetic field reduces the resistivity of a manganite by orders of magnitude, is generally believed to occur because of coexisting phases. Development of a complete theory to explain the phenomenon requires that the exact nature of these phases be known. We used resonant elastic soft x-ray scattering to examine the superlattice order that exists in La{sub 0.35}Pr{sub 0.275}Ca{sub 0.375}MnO{sub 3} above and below the Curie temperature. By measuring the resonance profile of the scattered x-rays at different values of q, we disentangle the contributions of orbital order and antiferromagnetism to the scattering signal above the Curie temperature. Below the Curie temperature, we see no signal from orbital order, and only antiferromagnetism coexists with the dominant ferromagnetic metallic phase.

36 MATERIALS SCIENCE↗
DOE OSTI2015

SLAC Laboratory Directed Research and Development Program: FY2014 Annual Report

The Department of Energy (DOE) and the SLAC National Accelerator Laboratory (SLAC) encourage innovation, creativity, originality and quality to maintain the Laboratory’s research activities and staff at the forefront of science and technology. To further advance the Laboratory’s scientific research capabilities, the Laboratory allocates a portion of its funds for the Laboratory Directed Research and Development (LDRD) program. With DOE guidance, the LDRD program enables SLAC scientists to make rapid and significant contributions to seeding new strategies for solving important national science and technology problems. The LDRD program is conducted using existing research facilities. The project proposals can be characterized as: Small-scale research and development activities or pilot projects; Bench-scale research projects; and Information gathering, computer modeling, conceptual design and feasibility studies. In addition to building new core competencies that support the DOE missions, the LDRD project proposals may also conduct scientific research and development that support the missions of other federal agencies and/or non-federal sponsors. In FY2014, SLAC continued to see some of the previously funded LDRD programs transition to follow on funding with the Office of Science, (including an Early Career Award), EERE and other agencies such as DARPA and NIH. This external validation shows that the projects selected were important to continuing forefront science and use-inspired applications with mission relevance and demonstrates they were delivering significant results. Annual reports for the FY14 project activities are included in this report.

25 ENERGY STORAGE↗
DOE OSTI2016

Laboratory Directed Research and Development Program: FY 2015 Annual Report

The Department of Energy (DOE) and the SLAC National Accelerator Laboratory (SLAC) encourage innovation, creativity, originality and quality to maintain the Laboratory’s research activities and staff at the forefront of science and technology. To further advance its scientific research capabilities, the Laboratory allocates a portion of its funds for the Laboratory Directed Research and Development (LDRD) program. With DOE guidance, the LDRD program enables SLAC scientists to make rapid and significant contributions that seed new strategies for solving important national science and technology problems. The LDRD program is conducted using existing research facilities.

99 GENERAL AND MISCELLANEOUS↗