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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Mechanisms Underlying a Quantum Superposition Microscope Based on THz-Driven Coherent Oscillations in a Two-Level Molecular Sensor

Here we report pump-probe measurements of a hydrogen molecule (H 2 ) in the tunnel junction of a scanning tunneling microscope (STM) coupled to ultrashort terahertz (THz) pulses. The coherent oscillation of the THz induced DC tunneling current at a frequency of ~0.5 THz fingerprints the absorption by H 2 as a two-level system (TLS). Two components of the oscillatory signal are observed and point to both photon and field aspects of the THz pulses. A few loosely bound states with similar energies for the upper state of the TLS are evidenced by the coherent revival of oscillatory signal. Furthermore, the comparison of spectroscopic features of H 2 with different tips provides an understanding of the TLS for H 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Viral Fate and Transport for COVID-19 - NVBL

The NVBL Viral Fate and Transport Team includes researchers from eleven DOE national laboratories and is utilizing unique experimental facilities combined with physics-based and data-driven modeling and simulation to study the transmission, transport, and fate of SARSCoV-2. The team was focused on understanding and ultimately predicting SARS-CoV-2 viability in varied environments with the goal of rapidly informing strategies that guide the nation’s resumption of normal activities. The primary goals of this project include prioritizing administrative and engineering controls that reduce the risk of SARS-CoV-2 transmission within an enclosed environment; identifying the chemical and physical properties that influence binding of SARS-CoV-2 to common surfaces; and understanding the contribution of environmental reservoirs and conditions on transmission and resurgence of SARS-CoV-2.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Reactivity, Regioselectivity, and Synthetic Application of 2-Pyrenyl Units in Scholl Reactions

We herein report the reactivity and regioselectivity of 2-pyrenyl as a coupling unit in Scholl reactions. On the basis of the Scholl reactions of hexaarylbenzene substrates, we have found that pyrenyl units are preferably oxidized over naphthyl and phenyl units under appropriate Scholl reaction conditions, allowing divergent synthesis through a highly controllable intramolecular coupling sequence. We find that the C1 and C3 positions of the 2-pyrenyl unit are the favorable sites for intramolecular coupling while C4 is not reactive to allow further coupling. The reactivity and regioselectivity pattern can be explained by the spin density distribution, which shows that carbon–carbon bonds preferably form at sites with higher positive spin density. Guided by these findings, we successfully synthesized a double helicene and a sextuple helicene through the controlled Scholl reactions of 2-pyrenyl units.

Scholl reactions↗
NASA NTRS1993

Long-pulse-length 2-micron diode-pumped YLiF4 laser

A diode-pumped Ho:Tm:YLiF4 laser at room temperature has achieved an optical efficiency of 5.9 percent under normal-mode operation. Long pulse lengths, of the order of 1 microsec, have been obtained by use of 4-m ring resonator, with laser energy output of 15 mJ in single Q-switched pulses for an input energy of 2.078 J.

Jani, Mahendra G.↗
DOE OSTI2020

Materials Data on Ca(HoTe2)2 by Materials Project

Ca(HoTe2)2 crystallizes in the monoclinic P2/m space group. The structure is three-dimensional. Ca2+ is bonded to six Te2- atoms to form CaTe6 octahedra that share corners with six equivalent HoTe6 octahedra, edges with two equivalent CaTe6 octahedra, and edges with six HoTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–3°. There are two shorter (3.15 Å) and four longer (3.20 Å) Ca–Te bond lengths. There are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six Te2- atoms to form HoTe6 octahedra that share corners with six equivalent CaTe6 octahedra, edges with two equivalent CaTe6 octahedra, and edges with six HoTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–3°. There are two shorter (3.03 Å) and four longer (3.10 Å) Ho–Te bond lengths. In the second Ho3+ site, Ho3+ is bonded to six Te2- atoms to form HoTe6 octahedra that share edges with four equivalent CaTe6 octahedra and edges with six HoTe6 octahedra. There are four shorter (3.09 Å) and two longer (3.11 Å) Ho–Te bond lengths. There are two inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to two equivalent Ca2+ and three Ho3+ atoms to form a mixture of edge and corner-sharing TeCa2Ho3 square pyramids. In the second Te2- site, Te2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba2Zn(HO)6 by Materials Project

Ba2Zn(HO)6 crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of one Ba2Zn(HO)6 sheet oriented in the (-1, 0, 2) direction. Ba2+ is bonded in a 6-coordinate geometry to two H1+ and four O2- atoms. There are one shorter (2.84 Å) and one longer (2.96 Å) Ba–H bond lengths. There are a spread of Ba–O bond distances ranging from 2.50–2.79 Å. Zn2+ is bonded in a square co-planar geometry to four O2- atoms. There are two shorter (1.82 Å) and two longer (2.57 Å) Zn–O bond lengths. There are three inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a distorted water-like geometry to one Ba2+ and one H1+ atom. The H–H bond length is 0.76 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one H1+ atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one Ba2+ and one O2- atom. The H–O bond length is 0.99 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one Ba2+, one H1+, and one O2- atom. The O–O bond length is 1.50 Å. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Ba2+, one Zn2+, and one O2- atom. In the third O2- site, O2- is bonded in a trigonal non-coplanar geometry to two equivalent Ba2+ and one Zn2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho13(Mg2Zn27)2 by Materials Project

Ho13(Mg2Zn27)2 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded in a 6-coordinate geometry to three equivalent Ho and twelve Zn atoms. All Mg–Ho bond lengths are 3.11 Å. There are six shorter (2.82 Å) and six longer (3.15 Å) Mg–Zn bond lengths. In the second Mg site, Mg is bonded in a body-centered cubic geometry to eight Zn atoms. There are a spread of Mg–Zn bond distances ranging from 2.61–2.71 Å. There are four inequivalent Ho sites. In the first Ho site, Ho is bonded in a 3-coordinate geometry to sixteen Zn atoms. There are a spread of Ho–Zn bond distances ranging from 3.01–3.22 Å. In the second Ho site, Ho is bonded in a 12-coordinate geometry to one Mg and fourteen Zn atoms. There are a spread of Ho–Zn bond distances ranging from 3.00–3.29 Å. In the third Ho site, Ho is bonded in a 11-coordinate geometry to thirteen Zn atoms. There are a spread of Ho–Zn bond distances ranging from 2.96–3.24 Å. In the fourth Ho site, Ho is bonded in a 6-coordinate geometry to fourteen Zn atoms. There are a spread of Ho–Zn bond distances ranging from 2.88–3.49 Å. There are ten inequivalent Zn sites. In the first Zn site, Zn is bonded in a 10-coordinate geometry to four Ho and six Zn atoms. There are a spread of Zn–Zn bond distances ranging from 2.60–2.90 Å. In the second Zn site, Zn is bonded in a 1-coordinate geometry to two Mg, three Ho, and three Zn atoms. There are two shorter (2.62 Å) and one longer (2.63 Å) Zn–Zn bond lengths. In the third Zn site, Zn is bonded in a 9-coordinate geometry to three Ho and six Zn atoms. There are two shorter (2.55 Å) and two longer (2.88 Å) Zn–Zn bond lengths. In the fourth Zn site, Zn is bonded to two equivalent Ho and ten Zn atoms to form face-sharing ZnHo2Zn10 cuboctahedra. There are a spread of Zn–Zn bond distances ranging from 2.59–2.77 Å. In the fifth Zn site, Zn is bonded in a 12-coordinate geometry to four Ho and eight Zn atoms. There are a spread of Zn–Zn bond distances ranging from 2.54–2.97 Å. In the sixth Zn site, Zn is bonded in a 10-coordinate geometry to one Mg, four Ho, and five Zn atoms. There are two shorter (2.57 Å) and one longer (2.59 Å) Zn–Zn bond lengths. In the seventh Zn site, Zn is bonded in a 11-coordinate geometry to five Ho and six equivalent Zn atoms. In the eighth Zn site, Zn is bonded to three equivalent Ho and nine Zn atoms to form face-sharing ZnHo3Zn9 cuboctahedra. All Zn–Zn bond lengths are 2.65 Å. In the ninth Zn site, Zn is bonded in a 1-coordinate geometry to one Mg, three Ho, and five Zn atoms. In the tenth Zn site, Zn is bonded in a 1-coordinate geometry to one Mg, four Ho, and three Zn atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1986

Tunable-diode laser absorption spectrometry

Tunable-diode laser absorption spectrometry (TDLAS) affords a number of advantages for atmospheric measurements. It is a universal method, applicable, in principle, to all gases of atmospheric interest. Because of its extremely high spectral resolution it provides unequivocal identification of the target species, with no interferences from other gases. It provides real-time, in situ measurements with time resolutions better than 1 minute. The sensitivity of the current TDLAS system is marginally capable of measuring HO2. This species exists in the troposphere at concentrations which are up to 2 orders of magnitude higher than those of HO and, in addition, is much less susceptible to removal by the surfaces of the instrument and its sampling system. HO2 is an important HO sub x species in its own right but can also give direct information on the HO concentration by virtue of the rapid partitioning between these two species. The addition of the high-frequency modulation technique to the TDLAS system would ensure its ability to measure HO2 under most atmospheric conditions. The ability of the TDLAS to measure hydrogen peroxide (H2O2) in the ambient atmosphere was also demonstrated. H2O2 measurements give a clear indication of HO sub x mixing ratios and are also important as a photolytic source of HO and as an important oxidant for other atmospheric consitituents such as SO2.

Schiff, H. I.↗
DOE OSTI2020

Materials Data on HoSb2 by Materials Project

HoSb2 crystallizes in the orthorhombic C222 space group. The structure is two-dimensional and consists of one HoSb2 sheet oriented in the (0, 0, 1) direction. Ho3+ is bonded in a 4-coordinate geometry to four equivalent Sb+1.50- atoms. All Ho–Sb bond lengths are 3.05 Å. Sb+1.50- is bonded in a 2-coordinate geometry to two equivalent Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Magnetic and Magnetocaloric Properties of the A 2 LnSbO 6 Lanthanide Oxides on the Frustrated fcc Lattice

Frustrated lanthanide oxides are promising candidates for cryogen-free magnetic refrigeration due to their suppressed ordering temperatures and high magnetic moments. While much attention has been paid to the garnet and pyrochlore lattices, the magnetocaloric effect in frustrated face-centered cubic (fcc) lattices remains relatively unexplored. We previously showed that the frustrated fcc double perovskite Ba 2 GdSbO 6 is a top-performing magnetocaloric material (per mol Gd) because of its small nearest-neighbor interaction between spins. Here we investigate different tuning parameters to maximize the magnetocaloric effect in the family of fcc lanthanide oxides, A 2 LnSbO 6 (A = {Ba 2+ , Sr 2+ } and Ln = {Nd 3+ , Tb 3+ , Gd 3+ , Ho 3+ , Dy 3+ , Er 3+ }), including chemical pressure via the A site cation and the magnetic ground state via the lanthanide ion. Bulk magnetic measurements indicate a possible trend between magnetic short-range fluctuations and the field-temperature phase space of the magnetocaloric effect, determined by whether an ion is a Kramers or a non-Kramers ion. We report for the first time on the synthesis and magnetic characterization of the Ca 2 LnSbO 6 series with tunable site disorder that can be used to control the deviations from Curie–Weiss behavior. Taken together, these results suggest fcc lanthanide oxides as tunable systems for magnetocaloric design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on Ho5(ReO6)2 by Materials Project

Ho5(ReO6)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.27–2.49 Å. In the second Ho3+ site, Ho3+ is bonded to six O2- atoms to form HoO6 octahedra that share corners with four equivalent ReO6 octahedra, corners with four equivalent HoO7 pentagonal bipyramids, and edges with two equivalent HoO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 38°. There are two shorter (2.20 Å) and four longer (2.31 Å) Ho–O bond lengths. In the third Ho3+ site, Ho3+ is bonded to seven O2- atoms to form distorted HoO7 pentagonal bipyramids that share corners with two equivalent HoO6 octahedra, an edgeedge with one HoO6 octahedra, edges with two equivalent ReO6 octahedra, and edges with two equivalent HoO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 56°. There are a spread of Ho–O bond distances ranging from 2.27–2.42 Å. Re+4.50+ is bonded to six O2- atoms to form ReO6 octahedra that share corners with two equivalent HoO6 octahedra, edges with two equivalent ReO6 octahedra, and edges with two equivalent HoO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 38°. There are a spread of Re–O bond distances ranging from 1.97–2.10 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to two Ho3+ and two equivalent Re+4.50+ atoms to form distorted OHo2Re2 trigonal pyramids that share corners with eight OHo3Re tetrahedra, edges with four equivalent OHo3Re tetrahedra, and an edgeedge with one OHo2Re2 trigonal pyramid. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+ and two equivalent Re+4.50+ atoms. In the third O2- site, O2- is bonded to three Ho3+ and one Re+4.50+ atom to form distorted OHo3Re tetrahedra that share corners with ten OHo3Re tetrahedra, a cornercorner with one OHo2Re2 trigonal pyramid, edges with three OHo3Re tetrahedra, and edges with two equivalent OHo2Re2 trigonal pyramids. In the fourth O2- site, O2- is bonded to four Ho3+ atoms to form OHo4 tetrahedra that share corners with ten OHo3Re tetrahedra, corners with three equivalent OHo2Re2 trigonal pyramids, and edges with four OHo3Re tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho6Mn(GeS7)2 by Materials Project

Ho6Mn(GeS7)2 crystallizes in the trigonal P3 space group. The structure is three-dimensional. there are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Ho–S bond distances ranging from 2.71–3.26 Å. In the second Ho3+ site, Ho3+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Ho–S bond distances ranging from 2.72–3.35 Å. Mn2+ is bonded in an octahedral geometry to six S2- atoms. There are three shorter (2.53 Å) and three longer (2.59 Å) Mn–S bond lengths. There are two inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded in a tetrahedral geometry to four S2- atoms. There are one shorter (2.21 Å) and three longer (2.24 Å) Ge–S bond lengths. In the second Ge4+ site, Ge4+ is bonded in a tetrahedral geometry to four S2- atoms. There are one shorter (2.20 Å) and three longer (2.24 Å) Ge–S bond lengths. There are six inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to three Ho3+ and one Ge4+ atom. In the second S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to three Ho3+ and one Ge4+ atom. In the third S2- site, S2- is bonded in a tetrahedral geometry to three equivalent Ho3+ and one Ge4+ atom. In the fourth S2- site, S2- is bonded in a tetrahedral geometry to three equivalent Ho3+ and one Ge4+ atom. In the fifth S2- site, S2- is bonded in a 4-coordinate geometry to four Ho3+ and one Mn2+ atom. In the sixth S2- site, S2- is bonded in a 5-coordinate geometry to four Ho3+ and one Mn2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2ReC2 by Materials Project

Ho2ReC2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Ho sites. In the first Ho site, Ho is bonded in a distorted rectangular see-saw-like geometry to four C atoms. There are a spread of Ho–C bond distances ranging from 2.51–2.66 Å. In the second Ho site, Ho is bonded to five C atoms to form a mixture of edge and corner-sharing HoC5 square pyramids. There are a spread of Ho–C bond distances ranging from 2.48–2.56 Å. Re is bonded in a distorted trigonal planar geometry to three C atoms. There are a spread of Re–C bond distances ranging from 1.94–2.05 Å. There are two inequivalent C sites. In the first C site, C is bonded to five Ho and one Re atom to form a mixture of edge and corner-sharing CHo5Re octahedra. The corner-sharing octahedra tilt angles range from 2–38°. In the second C site, C is bonded to four Ho and two equivalent Re atoms to form a mixture of edge and corner-sharing CHo4Re2 octahedra. The corner-sharing octahedra tilt angles range from 12–38°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoCu(MoO4)2 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoCu(WO4)2 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CsHo(MoO4)2 by Materials Project

CsHo(MoO4)2 crystallizes in the monoclinic P2/c space group. The structure is three-dimensional. Cs1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Cs–O bond distances ranging from 3.17–3.55 Å. Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.28–2.50 Å. Mo6+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Mo–O bond distances ranging from 1.75–1.86 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Cs1+ and one Mo6+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cs1+, one Ho3+, and one Mo6+ atom. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Mo6+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cs1+, one Ho3+, and one Mo6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CsHo(MoO4)2 by Materials Project

CsHo(MoO4)2 crystallizes in the orthorhombic Pccm space group. The structure is three-dimensional. Cs1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (3.18 Å) and four longer (3.44 Å) Cs–O bond lengths. Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (2.28 Å) and four longer (2.49 Å) Ho–O bond lengths. Mo6+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Mo–O bond distances ranging from 1.75–1.86 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Mo6+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cs1+, one Ho3+, and one Mo6+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Cs1+ and one Mo6+ atom.

36 MATERIALS SCIENCE↗