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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Ni 2 P active site ensembles tune electrocatalytic nitrate reduction selectivity

Here, we demonstrate that active site ensembles on transition metal phosphides tune the selectivity of the nitrate reduction reaction. Using Ni 2 P nanocrystals as a case study, we report a mechanism involving competitive co-adsorption of H* and NO x * intermediates. A near 100% faradaic efficiency for nitrate reduction over hydrogen evolution is observed at -0.4 V, while NH 3 selectivity is maximized at -0.2 V vs. RHE.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Alternate InP synthesis with aminophosphines: solution–liquid–solid nanowire growth

Indium phosphide nanowires are important components in high-speed electronics and optoelectronics, including photodetectors and photovoltaics. However, most syntheses either use high-temperature and costly vapor-phase methodology or highly toxic and pyrophoric tris(trimethylsilyl)phosphine. To expand on the success of the aminophosphine-based InP colloidal quantum dot synthesis, we developed a synthesis for thin (~11 nm) zinc blende InP nanowires at 180 °C using indium tris(trifluoroacetate) and tris(diethylamino)phosphine. A flat nanoribbon morphology was identified by transmission electron and atomic force microscopy analysis, with the stoichiometric (110) lattice plane exposed. Nanowire growth proceeded through a solution–liquid–solid mechanism from in situ-formed indium metal nanoparticles. Molecular byproducts of tris(oleylamino)phosphine oxide and N-oleyltrifluoroacetamide observed by 31 P and 19 F NMR spectroscopy inform a proposed mechanism of indium reduction by the aminophosphine. Morphological control over the nanowire product was achieved by varying the phosphorus injection to control the aspect ratio, the In : P ratio to toggle between nanowires and multipods, and the pre-hot injection evacuation step to favor a quantum dot product. Furthermore, replacing the indium precursor with indium tris(trifluoromethanesulfonate) was found to make bulk zinc blende InP nanowires with an average diameter of >250 nm and tens of microns in length.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Precise Fermi level engineering in a topological Weyl semimetal via fast ion implantation

The precise controllability of the Fermi level is a critical aspect of quantum materials. For topological Weyl semimetals, there is a pressing need to fine-tune the Fermi level to the Weyl nodes and unlock exotic electronic and optoelectronic effects associated with the divergent Berry curvature. However, in contrast to two-dimensional materials, where the Fermi level can be controlled through various techniques, the situation for bulk crystals beyond laborious chemical doping poses significant challenges. Here, we report the milli-electron-volt (meV) level ultra-fine-tuning of the Fermi level of bulk topological Weyl semimetal tantalum phosphide using accelerator-based high-energy hydrogen implantation and theory-driven planning. By calculating the desired carrier density and controlling the accelerator profiles, the Fermi level can be experimentally fine-tuned from 5 meV below, to 3.8 meV below, to 3.2 meV above the Weyl nodes. High-resolution transmission electron microscopy reveals the crystalline structure is largely maintained under irradiation, while electrical transport indicates that Weyl nodes are preserved and carrier mobility is also largely retained. Our work demonstrates the viability of this generic approach to tune the Fermi level in semimetal systems and could serve to achieve property fine-tuning for other bulk quantum materials with ultrahigh precision.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ab initio calculation of carrier mobility in semiconductors including ionized-impurity scattering

The past decade has seen the emergence of ab initio computational methods for calculating phonon-limited carrier mobilities in semiconductors with predictive accuracy. More realistic calculations ought to take into account additional scattering mechanisms such as, for example, impurity and grain-boundary scattering. Here, in this paper, we investigate the effect of ionized-impurity scattering on the carrier mobility. We model the analytical impurity potential parameterized from first principles by a collection of randomly distributed Coulomb scattering centers, and we include this relaxation channel into the ab initio Boltzmann transport equation, as implemented in the EPW code. We demonstrate this methodology by considering silicon, silicon carbide, and gallium phosphide, for which detailed experimental data are available. Our calculations agree well with experiments over a broad range of temperatures and impurity concentrations. For each compound investigated here, we compare the relative importance of electron-phonon scattering and ionized-impurity scattering, and we critically assess the reliability of Matthiessen's rule. We also show that an accurate description of dielectric screening and carrier effective masses can improve quantitative agreement with experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Topological Singularity Induced Chiral Kohn Anomaly in a Weyl Semimetal

The electron-phonon interaction (EPI) is instrumental in a wide variety of phenomena in solid-state physics, such as electrical resistivity in metals, carrier mobility, optical transition, and polaron effects in semiconductors, lifetime of hot carriers, transition temperature in BCS superconductors, and even spin relaxation in diamond nitrogen-vacancy centers for quantum information processing. However, due to the weak EPI strength, most phenomena have focused on electronic properties rather than on phonon properties. One prominent exception is the Kohn anomaly, where phonon softening can emerge when the phonon wave vector nests the Fermi surface of metals. In this paper, we report a new class of Kohn anomaly in a topological Weyl semimetal (WSM), predicted by field-theoretical calculations, and experimentally observed through inelastic x-ray and neutron scattering on WSM tantalum phosphide. Compared to the conventional Kohn anomaly, the Fermi surface in a WSM exhibits multiple topological singularities of Weyl nodes, leading to a distinct nesting condition with chiral selection, a power-law divergence, and non-negligible dynamical effects. Our work brings the concept of the Kohn anomaly into WSMs and sheds light on elucidating the EPI mechanism in emergent topological materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Aging Mechanisms of Broad Area ~800 nm Laser Diodes

Here, this work presents a comprehensive study of early aging behavior (<500 hr) in ~800 nm, phosphide-based laser diodes grown by solid-source MBE with different oxygen concentration levels incorporated into the diode epitaxial layers during growth. The data indicate that lasing characteristics prior to aging are degraded by oxygen introduction, but the gradual power degradation rate after the onset of aging is not a strong function of oxygen at these concentration levels. Devices with oxygen concentrations of ~2.5 × 10 15 cm -3 showed significantly longer delay before the onset of aging (incubation time) than devices with less than 1 × 10 15 cm -3 oxygen. Generation-Recombination current and Laser Beam Induced Current measurements indicate that defect densities and aggregation are suppressed at the facets by oxygen, which can explain longer incubation times. Diagnostic data and parametric fits to diode simulation models show that increased cavity optical loss and defect density are primarily responsible for gradual power degradation during aging, rather than changes in nonradiative recombination. Mechanisms are proposed that explain this behavior, based on density functional theory (DFT) simulations and known recombination-enhanced defect generation phenomena.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Formation and evolution of carbonaceous asteroid Ryugu: Direct evidence from returned samples

Samples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed 17 Ryugu samples measuring 1 to 8 millimeters. Carbon dioxide–bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu’s parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and calcium- and aluminum-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed through aqueous alteration reactions at low temperature, high pH, and water/rock ratios of <1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite, and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate that Ryugu’s parent body formed ~2 million years after the beginning of Solar System formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Surface conduction and reduced electrical resistivity in ultrathin noncrystalline NbP semimetal

The electrical resistivity of conventional metals such as copper is known to increase in thin films as a result of electron-surface scattering, thus limiting the performance of metals in nanoscale electronics. Here, in this study, we find an unusual reduction of resistivity with decreasing film thickness in niobium phosphide (NbP) semimetal deposited at relatively low temperatures of 400°C. In films thinner than 5 nanometers, the room temperature resistivity (~34 microhm centimeters for 1.5-nanometer-thick NbP) is up to six times lower than the resistivity of our bulk NbP films, and lower than conventional metals at similar thickness (typically about 100 microhm centimeters). The NbP films are not crystalline but display local nanocrystalline, short-range order within an amorphous matrix. Our analysis suggests that the lower effective resistivity is caused by conduction through surface channels, together with high surface carrier density and sufficiently good mobility as the film thickness is reduced. These results and the fundamental insights obtained here could enable ultrathin, low-resistivity wires for nanoelectronics beyond the limitations of conventional metals.

42 ENGINEERING↗
DOE OSTI2022

Precise electron beam-based target-wavelength trimming for frequency conversion in integrated photonic resonators

We demonstrate post-fabrication target-wavelength trimming with a gallium phosphide on a silicon nitride integrated photonic platform using controlled electron-beam exposure of hydrogen silsesquioxane cladding. A linear relationship between the electron-beam exposure dose and resonant wavelength red-shift enables deterministic, individual trimming of multiple devices on the same chip to within 30 pm of a single target wavelength. Second harmonic generation from telecom to near infrared at a target wavelength is shown in multiple devices with quality factors on the order of 10 4 . Post-fabrication tuning is an essential tool for targeted wavelength applications including quantum frequency conversion.

Thiel, Lillian↗
DOE OSTI2020

Materials Data on TaP by Materials Project

TaP is alpha Niobium phosphide structured and crystallizes in the tetragonal I4_1/amd space group. The structure is two-dimensional and consists of four TaP sheets oriented in the (0, 0, 1) direction. Ta3+ is bonded in a square co-planar geometry to four equivalent P3- atoms. All Ta–P bond lengths are 2.48 Å. P3- is bonded in a square co-planar geometry to four equivalent Ta3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TaAs by Materials Project

TaAs is alpha Niobium phosphide structured and crystallizes in the tetragonal I4_1md space group. The structure is three-dimensional. Ta3+ is bonded to six equivalent As3- atoms to form a mixture of distorted face, edge, and corner-sharing TaAs6 pentagonal pyramids. There are two shorter (2.62 Å) and four longer (2.64 Å) Ta–As bond lengths. As3- is bonded to six equivalent Ta3+ atoms to form a mixture of distorted face, edge, and corner-sharing AsTa6 pentagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NbAs by Materials Project

NbAs is alpha Niobium phosphide structured and crystallizes in the tetragonal I4_1md space group. The structure is three-dimensional. Nb3+ is bonded to six equivalent As3- atoms to form a mixture of distorted corner, edge, and face-sharing NbAs6 pentagonal pyramids. All Nb–As bond lengths are 2.64 Å. As3- is bonded to six equivalent Nb3+ atoms to form a mixture of distorted corner, edge, and face-sharing AsNb6 pentagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SbI3Cl8 by Materials Project

Sb(ICl4)2I is alpha Niobium phosphide-like structured and crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of one hydriodic acid molecule and one Sb(ICl4)2 cluster. In the Sb(ICl4)2 cluster, Sb5+ is bonded in an octahedral geometry to six Cl1- atoms. There are a spread of Sb–Cl bond distances ranging from 2.38–2.51 Å. I1+ is bonded in a linear geometry to two Cl1- atoms. There are one shorter (2.39 Å) and one longer (2.82 Å) I–Cl bond lengths. There are four inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Sb5+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one I1+ atom. In the third Cl1- site, Cl1- is bonded in a distorted bent 120 degrees geometry to one Sb5+ and one I1+ atom. In the fourth Cl1- site, Cl1- is bonded in a single-bond geometry to one Sb5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ICl3 by Materials Project

ICl3 is alpha Niobium phosphide-derived structured and crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of one ICl3 cluster. I is bonded in a rectangular see-saw-like geometry to four Cl atoms. There are a spread of I–Cl bond distances ranging from 2.39–2.74 Å. There are three inequivalent Cl sites. In the first Cl site, Cl is bonded in a single-bond geometry to one I atom. In the second Cl site, Cl is bonded in an L-shaped geometry to two equivalent I atoms. In the third Cl site, Cl is bonded in a single-bond geometry to one I atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AsXeF7 by Materials Project

XeAsF7 is alpha Niobium phosphide-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four XeAsF7 clusters. Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.00 Å) and one longer (2.22 Å) Xe–F bond lengths. As is bonded in an octahedral geometry to six F atoms. There are a spread of As–F bond distances ranging from 1.74–1.97 Å. There are seven inequivalent F sites. In the first F site, F is bonded in a single-bond geometry to one As atom. In the second F site, F is bonded in a single-bond geometry to one Xe atom. In the third F site, F is bonded in a bent 120 degrees geometry to one Xe and one As atom. In the fourth F site, F is bonded in a single-bond geometry to one As atom. In the fifth F site, F is bonded in a single-bond geometry to one As atom. In the sixth F site, F is bonded in a single-bond geometry to one As atom. In the seventh F site, F is bonded in a single-bond geometry to one As atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on I2(OF2)3 by Materials Project

I2(OF2)3 is alpha Niobium phosphide-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of two I2(OF2)3 clusters. there are three inequivalent O sites. In the first O site, O is bonded in a distorted bent 120 degrees geometry to two I atoms. There are one shorter (1.82 Å) and one longer (2.32 Å) O–I bond lengths. In the second O site, O is bonded in a distorted bent 120 degrees geometry to two I atoms. There are one shorter (1.83 Å) and one longer (2.28 Å) O–I bond lengths. In the third O site, O is bonded in a single-bond geometry to one I atom. The O–I bond length is 1.76 Å. There are two inequivalent I sites. In the first I site, I is bonded to three O and two F atoms to form distorted corner-sharing IO3F2 square pyramids. The corner-sharing octahedral tilt angles are 47°. There is one shorter (1.90 Å) and one longer (1.91 Å) I–F bond length. In the second I site, I is bonded to two O and four F atoms to form corner-sharing IO2F4 octahedra. There is one shorter (1.87 Å) and three longer (1.88 Å) I–F bond length. There are six inequivalent F sites. In the first F site, F is bonded in a single-bond geometry to one I atom. In the second F site, F is bonded in a single-bond geometry to one I atom. In the third F site, F is bonded in a single-bond geometry to one I atom. In the fourth F site, F is bonded in a single-bond geometry to one I atom. In the fifth F site, F is bonded in a single-bond geometry to one I atom. In the sixth F site, F is bonded in a single-bond geometry to one I atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZrI4 by Materials Project

ZrI4 is alpha Niobium phosphide-derived structured and crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of one ZrI4 cluster. there are two inequivalent Zr4+ sites. In the first Zr4+ site, Zr4+ is bonded to six I1- atoms to form ZrI6 octahedra that share an edgeedge with one ZrI6 octahedra and an edgeedge with one ZrI5 trigonal bipyramid. There are a spread of Zr–I bond distances ranging from 2.73–3.08 Å. In the second Zr4+ site, Zr4+ is bonded to five I1- atoms to form edge-sharing ZrI5 trigonal bipyramids. There are a spread of Zr–I bond distances ranging from 2.71–3.07 Å. There are eight inequivalent I1- sites. In the first I1- site, I1- is bonded in a water-like geometry to two equivalent Zr4+ atoms. In the second I1- site, I1- is bonded in a water-like geometry to two Zr4+ atoms. In the third I1- site, I1- is bonded in a water-like geometry to two Zr4+ atoms. In the fourth I1- site, I1- is bonded in a single-bond geometry to one Zr4+ atom. In the fifth I1- site, I1- is bonded in a single-bond geometry to one Zr4+ atom. In the sixth I1- site, I1- is bonded in a single-bond geometry to one Zr4+ atom. In the seventh I1- site, I1- is bonded in a single-bond geometry to one Zr4+ atom. In the eighth I1- site, I1- is bonded in a single-bond geometry to one Zr4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoS by Materials Project

HoS is alpha Niobium phosphide-like structured and crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of two HoS sheets oriented in the (0, 0, 1) direction. Ho is bonded in a square co-planar geometry to four equivalent S atoms. There are three shorter (2.66 Å) and one longer (2.67 Å) Ho–S bond lengths. S is bonded in a square co-planar geometry to four equivalent Ho atoms.

36 MATERIALS SCIENCE↗