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DOE OSTI2020

Materials Data on ErUTe6 by Materials Project

UErTe6 crystallizes in the orthorhombic Amm2 space group. The structure is two-dimensional and consists of two UErTe6 sheets oriented in the (0, 1, 0) direction. U3+ is bonded in a 9-coordinate geometry to nine Te1- atoms. There are a spread of U–Te bond distances ranging from 3.22–3.24 Å. Er3+ is bonded in a 9-coordinate geometry to nine Te1- atoms. There are five shorter (3.23 Å) and four longer (3.25 Å) Er–Te bond lengths. There are six inequivalent Te1- sites. In the first Te1- site, Te1- is bonded in a 6-coordinate geometry to two equivalent U3+ and four equivalent Te1- atoms. All Te–Te bond lengths are 3.08 Å. In the second Te1- site, Te1- is bonded in a 6-coordinate geometry to two equivalent Er3+ and four equivalent Te1- atoms. All Te–Te bond lengths are 3.08 Å. In the third Te1- site, Te1- is bonded in a 5-coordinate geometry to one U3+ and four equivalent Er3+ atoms. In the fourth Te1- site, Te1- is bonded in a 5-coordinate geometry to four equivalent U3+ and one Er3+ atom. In the fifth Te1- site, Te1- is bonded in a 6-coordinate geometry to two equivalent Er3+ and four equivalent Te1- atoms. In the sixth Te1- site, Te1- is bonded in a 6-coordinate geometry to two equivalent U3+ and four equivalent Te1- atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on BaCu6Te6Se by Materials Project

BaCu6Te6Se crystallizes in the monoclinic P2 space group. The structure is three-dimensional. Ba2+ is bonded to twelve Te1- atoms to form BaTe12 cuboctahedra that share corners with eighteen CuTe3Se tetrahedra, edges with six equivalent BaTe12 cuboctahedra, and faces with six CuTe3Se tetrahedra. There are a spread of Ba–Te bond distances ranging from 3.76–3.83 Å. There are three inequivalent Cu1+ sites. In the first Cu1+ site, Cu1+ is bonded to three Te1- and one Se2- atom to form CuTe3Se tetrahedra that share corners with three equivalent BaTe12 cuboctahedra, corners with eight CuTe3Se tetrahedra, an edgeedge with one CuTe3Se tetrahedra, and a faceface with one BaTe12 cuboctahedra. There are a spread of Cu–Te bond distances ranging from 2.58–2.65 Å. The Cu–Se bond length is 2.42 Å. In the second Cu1+ site, Cu1+ is bonded to three Te1- and one Se2- atom to form CuTe3Se tetrahedra that share corners with three equivalent BaTe12 cuboctahedra, corners with eight CuTe3Se tetrahedra, edges with two equivalent CuTe3Se tetrahedra, and a faceface with one BaTe12 cuboctahedra. There are a spread of Cu–Te bond distances ranging from 2.59–2.68 Å. The Cu–Se bond length is 2.40 Å. In the third Cu1+ site, Cu1+ is bonded to three Te1- and one Se2- atom to form CuTe3Se tetrahedra that share corners with three equivalent BaTe12 cuboctahedra, corners with six CuTe3Se tetrahedra, edges with three CuTe3Se tetrahedra, and a faceface with one BaTe12 cuboctahedra. There are a spread of Cu–Te bond distances ranging from 2.59–2.65 Å. The Cu–Se bond length is 2.52 Å. There are four inequivalent Te1- sites. In the first Te1- site, Te1- is bonded in a distorted bent 150 degrees geometry to two equivalent Ba2+, two equivalent Cu1+, and one Te1- atom. The Te–Te bond length is 2.82 Å. In the second Te1- site, Te1- is bonded in a 7-coordinate geometry to two equivalent Ba2+, four Cu1+, and one Te1- atom. In the third Te1- site, Te1- is bonded in a 3-coordinate geometry to two equivalent Ba2+ and three Cu1+ atoms. In the fourth Te1- site, Te1- is bonded in a 3-coordinate geometry to two equivalent Ba2+ and three Cu1+ atoms. Se2- is bonded in a 6-coordinate geometry to six Cu1+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Te4Mo2Ru by Materials Project

Mo2RuTe4 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Mo3+ sites. In the first Mo3+ site, Mo3+ is bonded to five Te2- atoms to form MoTe5 square pyramids that share corners with two MoTe5 square pyramids, corners with two RuTe5 square pyramids, edges with two RuTe5 square pyramids, and edges with three MoTe5 square pyramids. There are a spread of Mo–Te bond distances ranging from 2.72–2.87 Å. In the second Mo3+ site, Mo3+ is bonded to five Te2- atoms to form MoTe5 square pyramids that share a cornercorner with one RuTe5 square pyramid, corners with three MoTe5 square pyramids, edges with two RuTe5 square pyramids, and edges with three MoTe5 square pyramids. There are a spread of Mo–Te bond distances ranging from 2.72–2.87 Å. In the third Mo3+ site, Mo3+ is bonded to five Te2- atoms to form MoTe5 square pyramids that share a cornercorner with one RuTe5 square pyramid, corners with three MoTe5 square pyramids, edges with two RuTe5 square pyramids, and edges with three MoTe5 square pyramids. There are a spread of Mo–Te bond distances ranging from 2.73–2.86 Å. In the fourth Mo3+ site, Mo3+ is bonded to five Te2- atoms to form MoTe5 square pyramids that share corners with two MoTe5 square pyramids, corners with two RuTe5 square pyramids, edges with two RuTe5 square pyramids, and edges with three MoTe5 square pyramids. There are a spread of Mo–Te bond distances ranging from 2.73–2.88 Å. There are two inequivalent Ru2+ sites. In the first Ru2+ site, Ru2+ is bonded to five Te2- atoms to form RuTe5 square pyramids that share a cornercorner with one RuTe5 square pyramid, corners with three MoTe5 square pyramids, an edgeedge with one RuTe5 square pyramid, and edges with four MoTe5 square pyramids. There are a spread of Ru–Te bond distances ranging from 2.67–2.83 Å. In the second Ru2+ site, Ru2+ is bonded to five Te2- atoms to form RuTe5 square pyramids that share a cornercorner with one RuTe5 square pyramid, corners with three MoTe5 square pyramids, an edgeedge with one RuTe5 square pyramid, and edges with four MoTe5 square pyramids. There are a spread of Ru–Te bond distances ranging from 2.65–2.83 Å. There are eight inequivalent Te2- sites. In the first Te2- site, Te2- is bonded in a 4-coordinate geometry to three Mo3+ and one Ru2+ atom. In the second Te2- site, Te2- is bonded in a distorted rectangular see-saw-like geometry to two Mo3+ and two Ru2+ atoms. In the third Te2- site, Te2- is bonded in a distorted rectangular see-saw-like geometry to three Mo3+ and one Ru2+ atom. In the fourth Te2- site, Te2- is bonded in a 4-coordinate geometry to three Mo3+ and one Ru2+ atom. In the fifth Te2- site, Te2- is bonded in a 4-coordinate geometry to three Mo3+ and one Ru2+ atom. In the sixth Te2- site, Te2- is bonded in a 4-coordinate geometry to two Mo3+ and two Ru2+ atoms. In the seventh Te2- site, Te2- is bonded in a 6-coordinate geometry to one Mo3+ and two Ru2+ atoms. In the eighth Te2- site, Te2- is bonded in a 6-coordinate geometry to three Mo3+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Na4Eu(SiTe3)2 by Materials Project

Na4Eu(SiTe3)2 crystallizes in the monoclinic C2 space group. The structure is three-dimensional. there are four inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six Te1- atoms to form NaTe6 octahedra that share corners with two equivalent NaTe6 octahedra, corners with two equivalent EuTe6 octahedra, corners with two equivalent SiSiTe3 tetrahedra, edges with two equivalent EuTe6 octahedra, edges with eight NaTe6 octahedra, and edges with two equivalent SiSiTe3 tetrahedra. The corner-sharing octahedral tilt angles are 6°. There are a spread of Na–Te bond distances ranging from 3.26–3.42 Å. In the second Na1+ site, Na1+ is bonded to six Te1- atoms to form NaTe6 octahedra that share corners with two equivalent NaTe6 octahedra, corners with two equivalent EuTe6 octahedra, corners with two equivalent SiSiTe3 tetrahedra, edges with two equivalent EuTe6 octahedra, edges with eight NaTe6 octahedra, and edges with two equivalent SiSiTe3 tetrahedra. The corner-sharing octahedral tilt angles are 6°. There are a spread of Na–Te bond distances ranging from 3.25–3.42 Å. In the third Na1+ site, Na1+ is bonded to six Te1- atoms to form NaTe6 octahedra that share corners with two equivalent NaTe6 octahedra, corners with two equivalent EuTe6 octahedra, corners with two equivalent SiSiTe3 tetrahedra, edges with two equivalent EuTe6 octahedra, edges with eight NaTe6 octahedra, and edges with two equivalent SiSiTe3 tetrahedra. The corner-sharing octahedral tilt angles are 6°. There are a spread of Na–Te bond distances ranging from 3.25–3.45 Å. In the fourth Na1+ site, Na1+ is bonded to six Te1- atoms to form NaTe6 octahedra that share corners with six NaTe6 octahedra, corners with six equivalent SiSiTe3 tetrahedra, edges with three equivalent EuTe6 octahedra, and edges with six NaTe6 octahedra. The corner-sharing octahedral tilt angles are 6°. There are a spread of Na–Te bond distances ranging from 3.30–3.32 Å. Eu2+ is bonded to six Te1- atoms to form EuTe6 octahedra that share corners with six NaTe6 octahedra, corners with six equivalent SiSiTe3 tetrahedra, and edges with nine NaTe6 octahedra. The corner-sharing octahedral tilt angles are 6°. There are a spread of Eu–Te bond distances ranging from 3.30–3.32 Å. Si is bonded to one Si and three Te1- atoms to form SiSiTe3 tetrahedra that share corners with three equivalent EuTe6 octahedra, corners with three TeNa4EuSi octahedra, corners with six NaTe6 octahedra, and edges with three NaTe6 octahedra. The corner-sharing octahedra tilt angles range from 19–77°. The Si–Si bond length is 2.37 Å. There are two shorter (2.54 Å) and one longer (2.55 Å) Si–Te bond lengths. There are three inequivalent Te1- sites. In the first Te1- site, Te1- is bonded to four Na1+, one Eu2+, and one Si atom to form TeNa4EuSi octahedra that share corners with seven TeNa4EuSi octahedra, a cornercorner with one SiSiTe3 tetrahedra, and edges with ten TeNa4EuSi octahedra. The corner-sharing octahedra tilt angles range from 0–91°. In the second Te1- site, Te1- is bonded to four Na1+, one Eu2+, and one Si atom to form TeNa4EuSi octahedra that share corners with seven TeNa4EuSi octahedra, a cornercorner with one SiSiTe3 tetrahedra, and edges with ten TeNa4EuSi octahedra. The corner-sharing octahedra tilt angles range from 0–91°. In the third Te1- site, Te1- is bonded to four Na1+, one Eu2+, and one Si atom to form TeNa4EuSi octahedra that share corners with seven TeNa4EuSi octahedra, a cornercorner with one SiSiTe3 tetrahedra, and edges with ten TeNa4EuSi octahedra. The corner-sharing octahedra tilt angles range from 0–91°.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Rb7(FeTe2)4 by Materials Project

Rb7(FeTe2)4 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are four inequivalent Rb1+ sites. In the first Rb1+ site, Rb1+ is bonded in a 8-coordinate geometry to eight Te2- atoms. There are a spread of Rb–Te bond distances ranging from 3.69–3.98 Å. In the second Rb1+ site, Rb1+ is bonded in a 8-coordinate geometry to eight Te2- atoms. There are a spread of Rb–Te bond distances ranging from 3.69–4.33 Å. In the third Rb1+ site, Rb1+ is bonded in a 7-coordinate geometry to seven Te2- atoms. There are a spread of Rb–Te bond distances ranging from 3.65–4.16 Å. In the fourth Rb1+ site, Rb1+ is bonded in a 5-coordinate geometry to five Te2- atoms. There are a spread of Rb–Te bond distances ranging from 3.70–4.17 Å. There are two inequivalent Fe+2.25+ sites. In the first Fe+2.25+ site, Fe+2.25+ is bonded to four Te2- atoms to form edge-sharing FeTe4 tetrahedra. There are a spread of Fe–Te bond distances ranging from 2.59–2.63 Å. In the second Fe+2.25+ site, Fe+2.25+ is bonded to four Te2- atoms to form edge-sharing FeTe4 tetrahedra. There are a spread of Fe–Te bond distances ranging from 2.59–2.63 Å. There are four inequivalent Te2- sites. In the first Te2- site, Te2- is bonded in a 8-coordinate geometry to five Rb1+ and three Fe+2.25+ atoms. In the second Te2- site, Te2- is bonded in a 8-coordinate geometry to five Rb1+ and three Fe+2.25+ atoms. In the third Te2- site, Te2- is bonded in a 8-coordinate geometry to seven Rb1+ and one Fe+2.25+ atom. In the fourth Te2- site, Te2- is bonded in a distorted body-centered cubic geometry to seven Rb1+ and one Fe+2.25+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on CeUTe6 by Materials Project

UCeTe6 crystallizes in the orthorhombic Amm2 space group. The structure is two-dimensional and consists of two UCeTe6 sheets oriented in the (0, 1, 0) direction. U3+ is bonded in a 9-coordinate geometry to nine Te1- atoms. There are a spread of U–Te bond distances ranging from 3.24–3.27 Å. Ce3+ is bonded in a 9-coordinate geometry to nine Te1- atoms. There are a spread of Ce–Te bond distances ranging from 3.26–3.33 Å. There are four inequivalent Te1- sites. In the first Te1- site, Te1- is bonded in a 5-coordinate geometry to one U3+ and four equivalent Ce3+ atoms. In the second Te1- site, Te1- is bonded to four equivalent U3+ and one Ce3+ atom to form a mixture of distorted corner and edge-sharing TeCeU4 trigonal bipyramids. In the third Te1- site, Te1- is bonded in a 6-coordinate geometry to two equivalent U3+ and four equivalent Te1- atoms. All Te–Te bond lengths are 3.11 Å. In the fourth Te1- site, Te1- is bonded in a 2-coordinate geometry to two equivalent Ce3+ and four equivalent Te1- atoms. All Te–Te bond lengths are 3.11 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Manipulating Spin–Lattice Coupling in Layered Magnetic Topological Insulator Heterostructure via Interface Engineering

Induced magnetic order in a topological insulator (TI) can be realized either by depositing magnetic adatoms on the surface of a TI or engineering the interface with epitaxial thin film or stacked assembly of 2D van der Waals (vdW) materials. Herein, the observation of spin-phonon coupling in the otherwise non-magnetic TI Bi 2 Te 3 is reported, due to the proximity of FePS 3 (an antiferromagnet (AFM), T N ≈ 120 K), in a vdW heterostructure framework. Temperature-dependent Raman spectroscopic studies reveal deviation from the usual phonon anharmonicity originated from spin-lattice coupling at the Bi 2 Te 3 /FePS 3 interface at/below 60 K in the peak position (self-energy) and linewidth (lifetime) of the characteristic phonon modes of Bi 2 Te 3 (106 and 138 cm –1 ) in the stacked heterostructure. The Ginzburg-Landau (GL) formalism, where the respective phonon frequencies of Bi 2 Te 3 couple to phonons of similar frequencies of FePS 3 in the AFM phase, is adopted to understand the origin of the hybrid magneto-elastic modes. At the same time, the reduction of characteristic TN of FePS 3 from 120 K in isolated flakes to 65 K in the heterostructure, possibly due to the interfacial strain, which leads to smaller Fe-S-Fe bond angles as corroborated by computational studies using density functional theory (DFT). Besides, inserting hexagonal boron nitride within Bi 2 Te 3 /FePS 3 stacking regains the anharmonicity in Bi 2 Te 3 . As a result, controlling interfacial spin-phonon coupling in stacked heterostructure can have potential application in surface code spin logic devices.

36 MATERIALS SCIENCE↗

DOE OSTI2025

A Thorough Characterization of the Tellurocyanate Anion

Tellurocyanate, [TeCN] − , is the heaviest group 16 congener of the cyanate anion, [OCN] − . Due to the relative instability of the C─Te bond, tellurocyanate chemistry has seen only scarce attention. Here, we present the facile synthesis and thorough characterization of [K@crypt-222][TeCN]. The anion is essentially linear with interatomic distances C─N = 1.150(6)Å and C─Te = 2.051(4)Å, thus approximating a C≡N triple bond and for C─Te a bond order between 1 and 2. Fully 13 C and 15 N labeled [Te 13 C 15 N] − allowed for the extraction of chemical shifts and all possible coupling constants ( 13 C = 77.8 ppm, 15 N = 285.7 ppm, 125 Te = −566 ppm, 1 J 13C-15N = 8 Hz, 1 J 13C-125Te = 748 Hz, 2 J1 5N-125Te = 55 Hz), which were also determined independently by quantum chemical calculations. In the series [ChCN] − (Ch = O─Te), [TeCN] − shows the strongest spin-orbit coupling (SOC) induced heavy-atom effect on the light-atom shielding (SO-HALA-effect). In contrast, 15 N shifts are also well described without considering relativistic effects and/or SOC. Negative-ion photoelectron spectroscopy was used to extract the electron affinity (EA = 3.034 eV) and spin-orbit splitting (3807 cm −1 ) of [TeCN] • . These values continue the trends of falling EA and rising SOC in the series [ChCN] • .

Bonding analysis↗

DOE OSTI2021

MnP Films with Desired Magnetic, Magnetocaloric, and Thermoelectric Properties for a Perspective Magneto-Thermo-Electric Cooling Device

A new magneto-thermo-electric cooling device (MTECD) comprising a central magnetocaloric (MC) material (e.g., Gd) sandwiched by two thermoelectric (TE) materials (e.g., MnP) is proposed. The presence of the TE materials in the MTECD guides the heat flow direction and enhances heat pulsation. Here in this case, the usage of a ferromagnetic TE material that combines large TE with small MC properties within a similar temperature region can enhance the magnetic flux density and heat exchange efficiency. Herein, it is shown that MnP nanorod-structured films with desired magnetic, MC, and TE properties are very promising for use in MTECDs. The films are grown on Si substrates at 300, 400, and 500 °C using molecular beam epitaxy. The 400 °C sample shows a desired TE and MC combination. A large power factor of 24.06 μW m -1 K -2 is achieved at room temperature. In this temperature region, the film exhibits a small MC effect (-ΔS M ≈0.64 J kg -1 K and ΔT ad ≈0.3 K at μ 0 H = 2 T) but ferromagnetism that gives rise to the enhanced MC effect of the central MC material. These properties can enable the MTECD to operate at high frequency.

36 MATERIALS SCIENCE↗

DOE OSTI2022

High-performance and stable AgSbTe 2 -based thermoelectric materials for near room temperature applications

AgSbTe 2 -based ternary chalcogenides show excellent thermoelectric performance at low- and middle-temperature ranges, yet their practical applications are greatly limited by their intrinsic poor thermodynamic stability. In this work, we demonstrate that AgSbTe 2 -based ternary chalcogenides can be stabilized for service below their decomposition threshold. A series of Ag x Sb 2-x Te 3-x (x = 1.0, 0.9, 0.8 and 0.7) samples have been prepared by the melt-quenching method. Among them, phase pure Ag 0.9 Sb 1.1 Te 2.1 is verified by comprehensive structural characterizations from macroscale by X-ray diffraction to microscale by energy-dispersive spectroscopy and then to sub-nanometer scale by atom probe tomography. This composition is further chosen for the stability investigation. The decomposition threshold of Ag 0.9 Sb 1.1 Te 2.1 appears around 473K. Below this temperature, the chemical compositions and thermoelectric properties are barely changed even after 720 h annealing at 473 K. The figure-of-merit (zT) value of Ag 0.9 Sb 1.1 Te 2.1 below the decomposition threshold is very competitive for real applications even compared with Bi 2 Te 3 -based alloys. The average zT of Ag 0.9 Sb 1.1 Te 2.1 at 300–473 K reaches 0.84, which is higher than most other thermoelectric materials in a similar temperature range, promising applications in miniaturized refrigeration and power generation near room temperature.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Enhanced thermoelectric performance of PbSe-graphene nanocomposite manufactured with acoustic cavitation induced defects

An order of magnitude rise in the thermoelectric (TE) performance of the PbSe, a scalable and easy-to-manufacture TE material, has been achieved by incorporating reduced graphene oxide (Gr) nanoplatelets in a PbSe/PbSeO 3 heterostructure formed by acoustic cavitation-assisted oxidation. The fabricated Gr/PbSe/PbSeO 3 nanocomposites exhibit high TE performance with an exceptionally high Seebeck coefficient coupled with low thermal conductivity. The variation in the Seebeck coefficient has been attributed to a reduction in charge carrier mobility due to the ferroelectric polarization effect. Furthermore, the increase in electrical resistivity is minimized by adding graphene. At an optimal weight fraction (0.2 wt%), graphene nano-inclusions lead to superior Seebeck coefficient values as high as ~2000 μV/K at ~500 K, providing high overall TE performance. This study shows substantial changes in the TE properties of PbSe through the incorporation of graphene and PbSeO 3 . The understanding and methodology developed in this study can be exploited for the scalable manufacturing of high-performance TE materials.

Structure-property correlations↗

DOE OSTI2025

Thermally Stable Ruthenium Contact for Robust p‑Type Tellurium Transistors

Tellurium (Te) is attractive for p-channel transistors due to its high hole mobility. Despite having a low thermal budget suitable for back-end-of-line (BEOL) monolithic integration, the practical realization of Te transistors is hindered by its thermal stability. In this work, we investigate thermal stability for Te thin films grown via scalable thermal evaporation. Our findings identify ruthenium as a more thermally stable contact for p-type Te transistors, capable of withstanding temperatures up to 250 °C. Ruthenium exhibits significantly lower diffusivity in Te compared to other contact metals commonly used such as nickel and palladium. Using the transfer-length method, we measured a contact resistance of 1.25 kΩ·μm at the ruthenium-tellurium interface. Additionally, the incorporation of high-κ ZrO2 encapsulation not only suppresses the sublimation of the Te channel at elevated temperatures but also serves as the gate dielectric in top-gate devices operating at 1 V, achieving an on/off current ratio of 105.

Rahman, I K M Reaz↗

DOE OSTI2025

Spectroscopic evidence of intra-unit-cell charge redistribution in a charge-neutral magnetic topological insulator

The magnetic topological insulator MnBi 6 Te 10 has emerged as a promising candidate for realizing the quantum anomalous Hall effect (QAHE), owing to its ability to retain ferromagnetism through precise control of anti-site defects. The next important task for realizing the QAHE is to tune the chemical potential into the energy gap formed by the broken time-reversal symmetry. Here we reveal an intra-unit-cell charge redistribution even when the overall doping suggests a near-charge-neutral condition. By performing time- and angle-resolved photoemission spectroscopy (trARPES) on the optimally 18% Sb-doped MnBi 6 Te 10 , we observe transient surface photovoltage (SPV) effects on both the MnBi 2 Te 4 and single-Bi 2 Te 3 terminations. Furthermore, we observe a time-dependent splitting of the band structure indicating multiple SPV shifts with different magnitudes. This observation suggests that adjacent plateaus with nominally the same terminating layer exhibit a strong intra-unit-cell charge redistribution, resulting in spontaneous electrical polarization. This is consistent with static micro-ARPES measurements revealing significant doping deviations from the charge-neutral configuration. Our findings underscore the challenges of engineering the family of Mn-Bi-Te materials to realize QAHE purely through chemical doping. Achieving the desired topological quantum phase requires both a uniform carrier doping and a ferromagnetic ground state. Furthermore, the light-induced polarization within each unit cell of ferromagnetic Mn(Bi 0.82 Sb 0.18 ) 6 Te 10 may open new possibilities for optoelectronic and spintronics.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2026

Nitrogen p-type doping in polycrystalline zinc selenide telluride films

Nitrogen-doped zinc selenide telluride (N:ZnSe x Te 1−x ) is of interest because it is one of the widest-gap II–VI semiconductors that can still be doped p-type with reasonably high hole concentrations. We sputter deposit N:ZnSe x Te 1−x films, varying Se/(Se + Te), or x, from 0 to 0.7, N 2 flow rate from 0.25 to 0.75 sccm, and substrate temperature from 250 to 370 °C. Increasing x from 0 to 0.39 at the optimal temperature of 370 °C and N 2 flow rate of 0.5 sccm leads to 1.3 atomic % nitrogen incorporation and wurtzite phase stabilization. Such doping and alloying increases hole concentration from 3 × 10 18 cm −3 to 3 × 10 19 cm −3 , although mobility drops from 0.4 to 0.02 cm 2 V −1 s −1 . Our sputtered N:ZnSe 0.38 Te 0.62 has an absorption onset 0.1 eV greater than the ZnTe value of 1.87 eV. Increasing x from 0 to 0.51 enhances transmittance by moving absorption onset from 1.87 to 2.11 eV with diminished band gap bowing likely due to disorder, and increases the work function from 5.12 to 5.42 eV. This combination of tunable properties makes sputtered N:ZnSe x Te 1−x desirable for transparent p-type contacts in polycrystalline Cd(Se,Te) optoelectronic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

First-principles calculation of lattice distortion, electronic structure, and bonding properties of GeTe-based and PbSe-based high-entropy chalcogenides

The massive amount of wasted heat energy from industry has pushed the development of thermoelectric (TE) materials that directly convert heat into electricity to a new level of concern. Recently, multicomponent alloys such as GeTe-based and PbSe-based high-entropy (HE) chalcogenides have attracted a great deal of attention due to their potential application as TE materials. The nature of the interatomic bonding, lattice distortion (LD), and the electronic structure in this class of materials is not fully understood. Herein, we report a comprehensive computational investigation of nine GeTe-based HE alloys with eight metallic elements (Ag, Pb, Sb, Bi, Cu, Cd, Mn, and Sn) with large supercells of 1080 atoms each; seven PbSe-based HE solid solutions: Pb0.99−ySb0.012SnySe1−2xTexSx (x = 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, with y = 0) with supercells of 1000 atoms each; and five Pb0.99−ySb0.012SnySe1−2xTexSx (y = 0.05, 0.1, 0.15, 0.2, 0.25 with x = 0.25) solid solutions with supercells of 1000 atoms each. All these HE models are theoretically investigated for the first time. The electronic structure, interatomic bonding, charge transfer, and lattice distortion (LD) are investigated by first-principles calculations based on density functional theory. Multicomponent HE alloys can cause a significant LD, which affects their mechanical, thermal, and TE properties. The calculations for the GeTe-based HE chalcogenides showed that they are semiconductors with a narrow bandgap, except for m8, which has a semi-metallic characteristic, and this makes them good candidates for TE applications. For most of these models, the Fermi level shifts upward and locates deeply in the conduction bands, resulting in the enhancement of the electrical conductivity (σ). The bonding properties showed that most bonds in m5 are more dispersed, indicating highest LD and lower lattice thermal conductivity. For PbSe-based HE solid solutions, the LD calculations showed that the models Pb0.99Sb0.012Se0.5Te0.25S0.25 and Pb0.89Sb0.012Sn0.1Se0.5Te0.25S0.25 have the higher LD, and thus a lower lattice thermal conductivity. Such investigations are in high demand since it enables us to design new HE chalcogenides for TE applications. We use the novel concept of total bond order density as a single quantum mechanical metric to characterize the internal cohesion of these HE alloys and correlate with calculated properties, especially the mechanical properties. This work provides a solid database for HE chalcogenides and a road map for many potential applications. Moreover, the computational procedure we developed can be used to design new HE chalcogenides for specific TE applications.

Physics↗

DOE OSTI2021

Evolution of ELMs, pedestal profiles and fluctuations in the inter-ELM period in NBI and ECH dominated discharges in DIII-D

In DIII-D, it has been observed that ELM frequency decreases by 40% and ELM spacing becomes more regular in time when heating is changed from pure neutral beam injection (NBI) to predominantly electron cyclotron heating (ECH) in ITER Similar Shape plasmas. In comparison with pure the NBI discharges, pedestal fluctuations in magnetics and density increase in the ECH dominated discharges. Recovery of the pedestal profiles like electron density (ne), temperature (Te) and pressure (pe) shows marked differences for these two heating schemes. Average profiles in the last 30% of the ELM cycle shows higher Te, lower ne, and similar pe at the pedestal top for the ECH discharge when compared to the NBI discharge. Here, the gradient of Te (∇Te) is also steeper at the pedestal in the ECH discharge. Magnetic fluctuations show 3 distinct modes in 13~116 kHz in the ECH discharges only. ne fluctuations show two modes evolving in the inter-ELM period of the ECH discharge, a low frequency (400 kHz) quasi-coherent mode (LFQC) and high frequency (~2 MHz) broadband (HFB) fluctuations. Evolution of these modes has marked correspondence with the inter-ELM ∇Te recovery. A sharp decrease in the Dα baseline is observed whenever the LFQC weakens and the HFB grows, prior to each large ELM. Transport coefficients obtained from TRANSP shows that MTM and/or TEM are plausible candidates for the observed fluctuations. Linear gyrofluid simulation (TGLF) corroborates this characterization. TGLF shows that the linear growth rate of the most dominant mode peaks at ion-scale (kθρs ~ 0.4) at the pedestal steep gradient and the frequency is in the electron diamagnetic direction. It is proposed that increased fluctuations in the ECH dominated case, due to increased ∇Te, caused an increase in fluctuation-driven transport in the pedestal and slowed the pedestal recovery between ELMs, leading to a reduction in the ELM frequency.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2021

The role of electron-scale turbulence in the JET tokamak: experiments and modelling

Dedicated electron heat transport experiments have been carried out in L- and H-mode Deuterium plasmas of the JET-ILW tokamak to identify the amount of electron heat carried by electron-scale electron temperature gradient (ETG) modes. Ion cyclotron resonance heating at different positions has been used to probe the response of the electron temperature inverse gradient length R/L Te to changes in electron heat flux qe, while different amounts of neutral beam heating allowed to scan the ratio of ion to electron temperature T e /T i , which is a key parameter for the onset of ETGs. Results indicate a steepening of the normalized qe vs R/L Te curve above R/LT e ~ 8 for T e /T i ≤ 1, suggestive of the ETG onset. Ion-scale gyro-kinetic (GK) simulations match the ion heat flux and the low-R/L Te part of the qe curve, but do not reproduce such steepening at high R/L Te . Multi-scale GK simulations covering both ion and electron scales and including one impurity bundling light and heavy species indicate an ETG contribution only for R/L Te values larger than the experimental ones. Sensitivity studies of such result are difficult to achieve due to limitation in numerical resources. The quasi-linear TGLF model has been used for sensitivity studies. With the same bundled impurity as the GK multi-scale, TGLF shows the qe steepening at much larger R/L Te values than in experiment, but when using the real mix of light impurities neglecting the heavy impurities, TGLF gets closer to the experimental results. Profile simulations with TGLF including both light and heavy impurities show over-prediction of T e profiles and in some cases also of density, but good T i predictions, confirming issues with the model electron stiffness for these plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2023

Understanding palladium–tellurium cluster formation on WTe2: From a kinetically hindered distribution to thermodynamically controlled monodispersity

Abstract A fundamental understanding of the transition metal dichalcogenide (TMDC)–metal interface is critical for their utilization in a broad range of applications. We investigate how the deposition of palladium (Pd), as a model metal, on WTe2(001), leads to the assembly of Pd into clusters and nanoparticles. Using X-ray photoemission spectroscopy, scanning tunneling microscopy imaging, and ab initio simulations, we find that Pd nucleation is driven by the interaction with and the availability of mobile excess tellurium (Te) leading to the formation of Pd-Te clusters at room temperature. Surprisingly, the nucleation of Pd-Te clusters is not affected by intrinsic surface defects, even at elevated temperatures. Upon annealing, the Pd-Te nanoclusters adopt an identical nanostructure and are stable up to ∼523 K. Density functional theory calculations provide a foundation for our understanding of the mobility of Pd and Te atoms, preferential nucleation of Pd-Te clusters, and the origin of their annealing-induced monodispersity. These results highlight the role the excess chalcogenide atoms may play in the metal deposition process. More broadly, the discoveries of synthetic pathways yielding thermally robust monodispersed nanostructures on TMDCs are critical to the manufacturing of novel quantum and microelectronics devices and catalytically active nano-alloy centers.

36 MATERIALS SCIENCE↗