Pressure-driven Lifshitz transition in type-II Dirac semimetal NiTe[subscript 2]
Abstract not provided
Qi, Mengyao↗
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Dimensional crossover and band topology evolution in ultrathin semimetallic NiTe 2 films
Nickel ditelluride (NiTe 2 ), a recently discovered Type-II Dirac semimetal with topological Dirac fermions near the Fermi energy, is expected to exhibit strong thickness-mediated electronic tunability and intrinsic two-gap superconductivity in the single-layer limit. Realizing such intriguing phenomena requires the fabrication of ultrathin NiTe 2 films and an understanding of the underlying physics that is still under debate. By conducting experimental band mappings of ultrathin films prepared with molecular beam epitaxy, we reveal spectroscopic evidence for the dimensionality crossover of single-crystalline ultrathin NiTe 2 films as a function of film thickness. As the film thickness increases from one to five layers, the gap in the conical topological surface states closes. Comparisons of experimental to first-principles results also highlight difficulties in fabricating atomically smooth single-layer NiTe 2 films. Our results not only provide further impetus for studying emergent phenomena in NiTe 2 but also underscore the limitations of fabricating NiTe 2 films for device applications.
36 MATERIALS SCIENCE↗
Fermi-crossing Type-II Dirac fermions and topological surface states in NiTe 2
Transition-metal dichalcogenides (TMDs) offer an ideal platform to experimentally realize Dirac fermions. However, typically these exotic quasiparticles are located far away from the Fermi level, limiting the contribution of Dirac-like carriers to the transport properties. Here we show that NiTe 2 hosts both bulk Type-II Dirac points and topological surface states. The underlying mechanism is shared with other TMDs and based on the generic topological character of the Te p-orbital manifold. However, unique to NiTe 2 , a significant contribution of Ni d orbital states shifts the energy of the Type-II Dirac point close to the Fermi level. In addition, one of the topological surface states intersects the Fermi energy and exhibits a remarkably large spin splitting of 120 meV. Our results establish NiTe 2 as an exciting candidate for next-generation spintronics devices.
36 MATERIALS SCIENCE↗
Bulk Fermi surfaces of the Dirac type-II semimetallic candidate NiTe 2
Here, we present a study on the Fermi surface of the Dirac type-II semimetallic candidate NiTe 2 via the temperature and angular dependence of the de Haas–van Alphen (dHvA) effect measured in single crystals grown through Te flux. In contrast to its isostructural compounds like PtSe 2 , band-structure calculations predict NiTe 2 to display a tilted Dirac node very close to its Fermi level that is located along the Γ to A high-symmetry direction within its first Brillouin zone. The angular dependence of the dHvA frequencies is found to be in agreement with the first-principles calculations when the electronic bands are slightly shifted with respect to the Fermi level (ε F ), and therefore provide support for the existence of a Dirac type-II node in NiTe 2 . Nevertheless, we observed mild disagreements between experimental observations and density functional theory (DFT) calculations as, for example, nearly isotropic and light experimental effective masses. This indicates that the dispersion of the bands is not well captured by DFT. Despite the coexistence of Dirac-like fermions with topologically trivial carriers, samples of the highest quality display an anomalous and large either linear or sublinear magnetoresistivity. Finally, this suggests that Lorentz invariance breaking Dirac-like quasiparticles dominate the carrier transport in this compound.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Materials Data on NiTe by Materials Project
NiTe is lead oxide-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three NiTe sheets oriented in the (0, 0, 1) direction. Ni2+ is bonded to four equivalent Te2- atoms to form a mixture of edge and corner-sharing NiTe4 tetrahedra. There are three shorter (2.50 Å) and one longer (2.54 Å) Ni–Te bond lengths. Te2- is bonded in a 4-coordinate geometry to four equivalent Ni2+ atoms.
36 MATERIALS SCIENCE↗
Materials Data on Ta(NiTe)2 by Materials Project
Ta(NiTe)2 crystallizes in the orthorhombic Pnma space group. The structure is two-dimensional and consists of two Ta(NiTe)2 sheets oriented in the (0, 0, 1) direction. Ta is bonded in a 11-coordinate geometry to eight Ni and three Te atoms. There are a spread of Ta–Ni bond distances ranging from 2.71–2.76 Å. There are two shorter (2.90 Å) and one longer (2.95 Å) Ta–Te bond lengths. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a 9-coordinate geometry to four equivalent Ta, two equivalent Ni, and three Te atoms. There are one shorter (2.41 Å) and one longer (2.53 Å) Ni–Ni bond lengths. There are one shorter (2.53 Å) and two longer (2.57 Å) Ni–Te bond lengths. In the second Ni site, Ni is bonded in a 9-coordinate geometry to four equivalent Ta, two equivalent Ni, and three Te atoms. There are one shorter (2.54 Å) and two longer (2.57 Å) Ni–Te bond lengths. There are two inequivalent Te sites. In the first Te site, Te is bonded in a 4-coordinate geometry to two equivalent Ta and two Ni atoms. In the second Te site, Te is bonded in a 5-coordinate geometry to one Ta and four Ni atoms.
36 MATERIALS SCIENCE↗
Optimized NiTe 2 /Ni back contacts via chemical deposition for high performance CdTe solar cells
The development of efficient and stable back contacts remains a major challenge in achieving high performance and long-term stability of CdTe thin-film solar cells. Here, this work revisits the formation of NiTe 2 by chemical bath deposition (CBD) as a back contact for CdTe devices. An optimized CBD recipe, based on high-purity precursors and the addition of copper chloride directly into the bath, was developed and applied to fabricate Cu-doped CdTe solar cells. A modified Cu-free methodology was also applied to Group V doped absorbers. The process included pinhole filling, ion milling, CBD, annealing, and sputtering to form a low-barrier back contact. Devices fabricated using this method achieved consistent open-circuit voltages (V oc ) above 800 mV and fill factors (FF) exceeding 70%. The best Cu-doped devices reached power conversion efficiencies (PCE) above 18 %, and preliminary results with Group V-doped material demonstrated compatibility of the method with high-efficiency, state-of-the-art CdTe devices. This study shows that NiTe 2 /Ni back contacts, formed via an optimized chemical process followed by sputtering of Ni, represent a promising pathway for achieving low-barrier and potentially stable back contacts in modern CdTe photovoltaics.
14 SOLAR ENERGY↗
Materials Data on Lu7(NiTe)2 by Materials Project
Lu7(NiTe)2 crystallizes in the orthorhombic Imm2 space group. The structure is three-dimensional. there are four inequivalent Lu sites. In the first Lu site, Lu is bonded in a 4-coordinate geometry to three equivalent Ni and one Te atom. There are two shorter (2.74 Å) and one longer (3.12 Å) Lu–Ni bond lengths. The Lu–Te bond length is 3.13 Å. In the second Lu site, Lu is bonded in a 3-coordinate geometry to three Te atoms. There are two shorter (3.15 Å) and one longer (3.19 Å) Lu–Te bond lengths. In the third Lu site, Lu is bonded in a 5-coordinate geometry to two equivalent Ni and three Te atoms. Both Lu–Ni bond lengths are 2.73 Å. There are one shorter (3.07 Å) and two longer (3.14 Å) Lu–Te bond lengths. In the fourth Lu site, Lu is bonded in a distorted rectangular see-saw-like geometry to two equivalent Ni and two equivalent Te atoms. Both Lu–Ni bond lengths are 2.76 Å. Both Lu–Te bond lengths are 3.11 Å. Ni is bonded in a 7-coordinate geometry to seven Lu atoms. There are two inequivalent Te sites. In the first Te site, Te is bonded in a 7-coordinate geometry to seven Lu atoms. In the second Te site, Te is bonded in a 8-coordinate geometry to eight Lu atoms.
36 MATERIALS SCIENCE↗
Materials Data on NiTe by Materials Project
NiTe is Tungsten Carbide-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ni2+ is bonded to six equivalent Te2- atoms to form a mixture of face, edge, and corner-sharing NiTe6 octahedra. The corner-sharing octahedral tilt angles are 52°. All Ni–Te bond lengths are 2.67 Å. Te2- is bonded in a 6-coordinate geometry to six equivalent Ni2+ atoms.
36 MATERIALS SCIENCE↗
Materials Data on Sc5(NiTe)2 by Materials Project
Sc5(NiTe)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are five inequivalent Sc sites. In the first Sc site, Sc is bonded in a 6-coordinate geometry to three Ni and three equivalent Te atoms. There are two shorter (2.60 Å) and one longer (2.65 Å) Sc–Ni bond lengths. There are one shorter (2.99 Å) and two longer (3.08 Å) Sc–Te bond lengths. In the second Sc site, Sc is bonded in a 7-coordinate geometry to six Ni and one Te atom. There are a spread of Sc–Ni bond distances ranging from 2.63–2.86 Å. The Sc–Te bond length is 3.18 Å. In the third Sc site, Sc is bonded in a 5-coordinate geometry to one Ni and four Te atoms. The Sc–Ni bond length is 2.66 Å. There are two shorter (2.93 Å) and two longer (3.00 Å) Sc–Te bond lengths. In the fourth Sc site, Sc is bonded in a 5-coordinate geometry to one Ni and four Te atoms. The Sc–Ni bond length is 2.69 Å. There are a spread of Sc–Te bond distances ranging from 2.99–3.16 Å. In the fifth Sc site, Sc is bonded in a 6-coordinate geometry to three Ni and three Te atoms. There are two shorter (2.62 Å) and one longer (2.85 Å) Sc–Ni bond lengths. There are one shorter (3.01 Å) and two longer (3.03 Å) Sc–Te bond lengths. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a 5-coordinate geometry to seven Sc and two equivalent Ni atoms. Both Ni–Ni bond lengths are 2.66 Å. In the second Ni site, Ni is bonded in a 9-coordinate geometry to seven Sc and two equivalent Ni atoms. There are two inequivalent Te sites. In the first Te site, Te is bonded to seven Sc atoms to form distorted edge-sharing TeSc7 pentagonal bipyramids. In the second Te site, Te is bonded in a 8-coordinate geometry to eight Sc atoms.
36 MATERIALS SCIENCE↗
Materials Data on Er7(NiTe)2 by Materials Project
Er7(NiTe)2 crystallizes in the orthorhombic Imm2 space group. The structure is three-dimensional. there are four inequivalent Er sites. In the first Er site, Er is bonded in a 3-coordinate geometry to three Te atoms. There are two shorter (3.17 Å) and one longer (3.21 Å) Er–Te bond lengths. In the second Er site, Er is bonded in a 4-coordinate geometry to three equivalent Ni and one Te atom. There are two shorter (2.77 Å) and one longer (3.16 Å) Er–Ni bond lengths. The Er–Te bond length is 3.17 Å. In the third Er site, Er is bonded in a distorted square co-planar geometry to two equivalent Ni and two equivalent Te atoms. Both Er–Ni bond lengths are 2.81 Å. Both Er–Te bond lengths are 3.14 Å. In the fourth Er site, Er is bonded in a 5-coordinate geometry to two equivalent Ni and three Te atoms. Both Er–Ni bond lengths are 2.77 Å. There are one shorter (3.11 Å) and two longer (3.17 Å) Er–Te bond lengths. Ni is bonded in a 7-coordinate geometry to seven Er atoms. There are two inequivalent Te sites. In the first Te site, Te is bonded in a 8-coordinate geometry to eight Er atoms. In the second Te site, Te is bonded in a 7-coordinate geometry to seven Er atoms.
36 MATERIALS SCIENCE↗
Materials Data on Y5(NiTe)2 by Materials Project
Y5(NiTe)2 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are three inequivalent Y sites. In the first Y site, Y is bonded in a 7-coordinate geometry to three Ni and four equivalent Te atoms. There are two shorter (2.86 Å) and one longer (2.91 Å) Y–Ni bond lengths. There are two shorter (3.34 Å) and two longer (3.37 Å) Y–Te bond lengths. In the second Y site, Y is bonded in a 6-coordinate geometry to three Ni and three equivalent Te atoms. There are two shorter (2.85 Å) and one longer (2.97 Å) Y–Ni bond lengths. There are one shorter (3.15 Å) and two longer (3.24 Å) Y–Te bond lengths. In the third Y site, Y is bonded in a square co-planar geometry to two Ni and two equivalent Te atoms. There are one shorter (2.91 Å) and one longer (3.17 Å) Y–Ni bond lengths. Both Y–Te bond lengths are 3.17 Å. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a 9-coordinate geometry to seven Y and two equivalent Ni atoms. Both Ni–Ni bond lengths are 2.50 Å. In the second Ni site, Ni is bonded in a 9-coordinate geometry to seven Y and two equivalent Ni atoms. Te is bonded in a 8-coordinate geometry to eight Y atoms.
36 MATERIALS SCIENCE↗
Materials Data on Y5(NiTe)2 by Materials Project
Y5(NiTe)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are five inequivalent Y sites. In the first Y site, Y is bonded in a 6-coordinate geometry to three Ni and three Te atoms. There are two shorter (2.76 Å) and one longer (3.10 Å) Y–Ni bond lengths. There are one shorter (3.20 Å) and two longer (3.25 Å) Y–Te bond lengths. In the second Y site, Y is bonded in a 6-coordinate geometry to three Ni and three Te atoms. There are two shorter (2.72 Å) and one longer (2.79 Å) Y–Ni bond lengths. There are one shorter (3.11 Å) and two longer (3.24 Å) Y–Te bond lengths. In the third Y site, Y is bonded in a 6-coordinate geometry to three Ni and three equivalent Te atoms. There are two shorter (2.76 Å) and one longer (2.84 Å) Y–Ni bond lengths. There are one shorter (3.11 Å) and two longer (3.21 Å) Y–Te bond lengths. In the fourth Y site, Y is bonded in a 5-coordinate geometry to two Ni and three Te atoms. There are one shorter (3.08 Å) and one longer (3.15 Å) Y–Ni bond lengths. There are two shorter (3.23 Å) and one longer (3.54 Å) Y–Te bond lengths. In the fifth Y site, Y is bonded in a 6-coordinate geometry to three Ni and three equivalent Te atoms. There are two shorter (2.80 Å) and one longer (3.14 Å) Y–Ni bond lengths. There are two shorter (3.19 Å) and one longer (3.35 Å) Y–Te bond lengths. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a 9-coordinate geometry to seven Y and two equivalent Ni atoms. Both Ni–Ni bond lengths are 2.69 Å. In the second Ni site, Ni is bonded in a 9-coordinate geometry to seven Y and two equivalent Ni atoms. There are two inequivalent Te sites. In the first Te site, Te is bonded in a 8-coordinate geometry to eight Y atoms. In the second Te site, Te is bonded to seven Y atoms to form distorted edge-sharing TeY7 pentagonal bipyramids.
36 MATERIALS SCIENCE↗
Neutron irradiation & thermomechanical experiment (NITE) - design
For the reliable long-term operation of fusion power plants, it is crucial to understand and predict the lifetime of materials in use. These materials include all structural and functional materials utilized at the first wall, blanket, magnets, and shielding. The key challenge is, that the harsh environment including high heat fluxes, high thermal stress and stress cycling, neutron irradiation, and sputtering on such materials should not be viewed separately. Currently, the synergistic loads cannot be evaluated experimentally because of the lack of adequate facilities. The purpose of that work is to design a synergetic Neutron Irradiation and Thermomechanical Experiment (NITE) for fusion materials. This design will leverage the existing Advanced-Test-Reactor (ATR), a fission reactor at the Idaho National Laboratory. We also acknowledge that with existing fission reactors the exact fusion condition cannot be created, and the limitations are critically discussed. The combination of neutron irradiation with a high heat flux is the focus. This is realized with an irradiation capsule design that includes a TRISO fueled region inside the capsule to enable a steady-state heat flux on one side of the specimen. In conclusion, the experimental design modeling showed that steady-state heat fluxes of 2.4 MW/m 2 with a thermal gradient of above 250°C can be achieved in a 5 mm thick specimen.
70 - PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Materials Data on Er5(NiTe)2 by Materials Project
Er5Ni2Te2 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are three inequivalent Er sites. In the first Er site, Er is bonded in a 7-coordinate geometry to three Ni and four equivalent Te atoms. There are two shorter (2.79 Å) and one longer (2.86 Å) Er–Ni bond lengths. There are two shorter (3.31 Å) and two longer (3.35 Å) Er–Te bond lengths. In the second Er site, Er is bonded in a 6-coordinate geometry to three Ni and three equivalent Te atoms. There are two shorter (2.79 Å) and one longer (2.91 Å) Er–Ni bond lengths. There are one shorter (3.12 Å) and two longer (3.21 Å) Er–Te bond lengths. In the third Er site, Er is bonded in a square co-planar geometry to two Ni and two equivalent Te atoms. There are one shorter (2.87 Å) and one longer (3.08 Å) Er–Ni bond lengths. Both Er–Te bond lengths are 3.13 Å. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a 9-coordinate geometry to seven Er and two equivalent Ni atoms. Both Ni–Ni bond lengths are 2.48 Å. In the second Ni site, Ni is bonded in a 9-coordinate geometry to seven Er and two equivalent Ni atoms. Te is bonded in a 8-coordinate geometry to eight Er atoms.
36 MATERIALS SCIENCE↗
Materials Data on NiTe(PO4)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↗
Scanning tunneling microscopy and spectroscopy of NiTe 2
Nickel ditelluride is an unusual member of the transition metal dichalcogenide family which has garnered interest due to potential valley spin-polarized surface states near the Fermi level and the presence of Dirac nodes in its electronic band structure. In this work, exfoliation of bulk nickel ditelluride is performed under ultra-high vacuum in order to generate a clean surface for scanning tunneling microscopy and spectroscopy at 4.8 K. Multiple features in the observed electronic density of states are observed in the vicinity of the Fermi level and compared to calculated band structures to elucidate their origins. Finally, our results are consistent with the presence of the spin-polarized surface states, yet indicate trivial states, which are close to the Fermi level, can interfere with their potential utility in spintronic applications.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Repeatability in Battery Abuse Testing: Sandia and NITE NLAB Collaboration
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Kurzawski, Andrew Joseph↗