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Qu, J.

Publications and source records attributed to Qu, J..

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Screening of Polar Electron-Phonon Interactions near the Surface of the Rashba Semiconductor BiTeCl

Understanding electron-phonon coupling in noncentrosymmetric materials is critical for controlling the internal fields which give rise to Rashba interactions. We apply time- and angle-resolved photoemission spectroscopy (trARPES) to study coherent phonons in the surface and bulk regions of the polar semiconductor BiTeCl. Aided by \textit{ab initio} calculations, our measurements reveal the coupling of out-of-plane $A_1$ modes and an in-plane $E_2$ mode. By considering how these modes modulate the electric dipole moment in each unit cell, we show that the polar $A_1$ modes are more effectively screened in the metallic surface region, while the non-polar $E_2$ mode couples in both regions. Finally, in addition to informing strategies to optically manipulate Rashba interactions, this work has broader implications for the behavior of electron-phonon coupling in systems characterized by inhomogeneous dielectric environments.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Reversal of spin-polarization near the Fermi level of the Rashba semiconductor BiTeCl

Abstract Spin–orbit coupling forms the physical basis for quantum materials with non-trivial topology and potential spintronics applications. The Rashba interaction is a textbook model of spin–orbit interactions, with charge carriers undergoing linear, isotropic spin-splitting in momentum space. Recently, non-centrosymmetric semiconductors in the family BiTe X ( X = Cl, Br, I) have been identified as exemplary Rashba materials due to the strong splitting of their bulk bands, yet a detailed investigation of their spin textures, and their relationships to local crystal symmetry, is currently lacking. We perform high-efficiency spin-resolved photoemission spectroscopy to directly image the spin texture of surface states of BiTeCl, and we find dramatic deviations from idealized behavior, including a reversal of the spin-polarization near the Fermi level. We show that this behavior can be described by higher-order contributions to the canonical Rashba model with the surface states localized to individual trilayers of the crystal. Due to the prominence of these effects near the Fermi level, they should have a strong impact on the spin-dependent transport of carriers.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Vaporization behavior of tetraoctylphosphonium bis(2-ethylhexyl)phosphate ionic liquid

We determined the equilibrium vapor pressures, p e , of the ionic liquid tetraoctylphosphonium bis(2-ethylhexyl)phosphate ([P 8888 ][DEHP]) over the temperature range 409–495 K using mass loss Knudsen effusion. The p e versus temperature relationship compares well to 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide ([C 8 mim][NTf 2 ]) but is lower than that of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 2 mim][NTf 2 ]) when measured using the same technique. Here, we determined the discrepancies between the p e for [C 8 mim][NTf 2 ] and [C 2 mim][NTf 2 ] with previous studies is discussed. Finally, the enthalpy and entropy of vaporization for all three fluids are estimated from the Clasius-Clapeyron relation.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Modeling of complex wear behavior associated with grid-to-rod fretting in light water nuclear reactors

One significant concern in the operation of light water nuclear reactors is the fretting wear damage to fuel cladding from flow-induced vibrations. For years, research on the grid-to-rod fretting (GTRF) phenomena has been underway in countries where nuclear power production is a significant industry. Under the auspices of the U.S. Department of Energy Consortium for Advanced Simulation of Light Water Reactors, an effort has been underway to develop and test an engineering wear model for zirconium alloy fuel rod cladding against a supporting grid. Furthermore, the multi-stage model accounts for oxide layers and wear rate transitions. Our paper describes the basis for a GTRF engineering wear model, the physical significance of the wear factor it contains, and recent progress toward model validation based on a fretting wear testing apparatus that accounts for coolant temperature, pressure, and the presence of periodic impacts (gaps) in grid/rod contact.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

Effects of compositional complexity on the ion-irradiation induced swelling and hardening in Ni-containing equiatomic alloys

The impact of compositional complexity on the ion-irradiation induced swelling and hardening is studied in Ni and six Ni-containing equiatomic alloys with face-centered cubic structure. The irradiation resistance at the temperature of 500 °C is improved by controlling the number and, especially, the type of alloying elements. Alloying with Fe and Mn has a stronger influence on swelling reduction than does alloying with Co and Cr. Lastly, the quinary alloy NiCoFeCrMn, with known excellent mechanical properties, has shown 40 times higher swelling tolerance than nickel.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Comparative validation of the D. melanogaster modENCODE transcriptome annotation

Accurate gene model annotation of reference genomes is critical for making them useful. The modENCODE project has improved the D. melanogaster genome annotation by using deep and diverse high-throughput data. Since transcriptional activity that has been evolutionarily conserved is likely to have an advantageous function, we have performed large-scale interspecific comparisons to increase confidence in predicted annotations. To support comparative genomics, we filled in divergence gaps in the Drosophila phylogeny by generating draft genomes for eight new species. For comparative transcriptome analysis, we generated mRNA expression profiles on 81 samples from multiple tissues and developmental stages of 15 Drosophila species, and we performed cap analysis of gene expression in D. melanogaster and D. pseudoobscura. We also describe conservation of four distinct core promoter structures composed of combinations of elements at three positions. Overall, each type of genomic feature shows a characteristic divergence rate relative to neutral models, highlighting the value of multispecies alignment in annotating a target genome that should prove useful in the annotation of other high priority genomes, especially human and other mammalian genomes that are rich in noncoding sequences. We report that the vast majority of elements in the annotation are evolutionarily conserved, indicating that the annotation will be an important springboard for functional genetic testing by the Drosophila community.

59 BASIC BIOLOGICAL SCIENCES↗