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At least 1,171 records · Page 65
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DOE OSTI2020

Materials Data on Li3Tb3(TeO6)2 by Materials Project

Li3Tb3Te2O12 crystallizes in the cubic Ia-3d space group. The structure is three-dimensional. Li1+ is bonded to four equivalent O2- atoms to form LiO4 tetrahedra that share corners with four equivalent TeO6 octahedra. The corner-sharing octahedral tilt angles are 52°. All Li–O bond lengths are 1.91 Å. Tb+3.67+ is bonded in a distorted body-centered cubic geometry to eight equivalent O2- atoms. There are four shorter (2.37 Å) and four longer (2.49 Å) Tb–O bond lengths. Te5+ is bonded to six equivalent O2- atoms to form TeO6 octahedra that share corners with six equivalent LiO4 tetrahedra. All Te–O bond lengths are 1.96 Å. O2- is bonded in a 4-coordinate geometry to one Li1+, two equivalent Tb+3.67+, and one Te5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb3Au by Materials Project

Tb3Au is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Tb is bonded in a distorted square co-planar geometry to four equivalent Au atoms. All Tb–Au bond lengths are 3.35 Å. Au is bonded to twelve equivalent Tb atoms to form a mixture of face and corner-sharing AuTb12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbCu(WO4)2 by Materials Project

TbCu(WO4)2 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are three inequivalent Tb3+ sites. In the first Tb3+ site, Tb3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Tb–O bond distances ranging from 2.29–2.84 Å. In the second Tb3+ site, Tb3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Tb–O bond distances ranging from 2.28–2.61 Å. In the third Tb3+ site, Tb3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Tb–O bond distances ranging from 2.28–2.72 Å. There are six inequivalent W6+ sites. In the first W6+ site, W6+ is bonded to six O2- atoms to form distorted edge-sharing WO6 octahedra. There are a spread of W–O bond distances ranging from 1.80–2.20 Å. In the second W6+ site, W6+ is bonded to six O2- atoms to form distorted edge-sharing WO6 octahedra. There are a spread of W–O bond distances ranging from 1.80–2.21 Å. In the third W6+ site, W6+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of W–O bond distances ranging from 1.80–2.30 Å. In the fourth W6+ site, W6+ is bonded to six O2- atoms to form distorted edge-sharing WO6 octahedra. There are a spread of W–O bond distances ranging from 1.81–2.21 Å. In the fifth W6+ site, W6+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of W–O bond distances ranging from 1.81–2.28 Å. In the sixth W6+ site, W6+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of W–O bond distances ranging from 1.80–2.26 Å. There are four inequivalent Cu1+ sites. In the first Cu1+ site, Cu1+ is bonded in a linear geometry to two equivalent O2- atoms. Both Cu–O bond lengths are 1.85 Å. In the second Cu1+ site, Cu1+ is bonded in a distorted square co-planar geometry to four O2- atoms. There are two shorter (1.87 Å) and two longer (2.46 Å) Cu–O bond lengths. In the third Cu1+ site, Cu1+ is bonded in a 4-coordinate geometry to three O2- atoms. There are a spread of Cu–O bond distances ranging from 1.85–2.58 Å. In the fourth Cu1+ site, Cu1+ is bonded in a distorted linear geometry to four O2- atoms. There are a spread of Cu–O bond distances ranging from 1.86–2.75 Å. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to one Tb3+ and two equivalent W6+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Tb3+ and two W6+ atoms. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Tb3+ and two equivalent W6+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Tb3+ and two W6+ atoms. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to one Tb3+ and two W6+ atoms. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two W6+ and one Cu1+ atom. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to one Tb3+, one W6+, and one Cu1+ atom. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to one Tb3+ and one W6+ atom. In the ninth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent Tb3+ and one W6+ atom. In the tenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Tb3+ and one W6+ atom. In the eleventh O2- site, O2- is bonded in a 2-coordinate geometry to one Tb3+, one W6+, and one Cu1+ atom. In the twelfth O2- site, O2- is bonded in a 4-coordinate geometry to one Tb3+, two W6+, and one Cu1+ atom. In the thirteenth O2- site, O2- is bonded in a 3-coordinate geometry to two W6+ and one Cu1+ atom. In the fourteenth O2- site, O2- is bonded in a 3-coordinate geometry to two W6+ and one Cu1+ atom. In the fifteenth O2- site, O2- is bonded in a bent 150 degrees geometry to one Tb3+ and one W6+ atom. In the sixteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Tb3+, one W6+, and one Cu1+ atom. In the seventeenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Tb3+ and two W6+ atoms. In the eighteenth O2- site, O2- is bonded in a 2-coordinate geometry to two Tb3+ and one W6+ atom. In the nineteenth O2- site, O2- is bonded in a 2-coordinate geometry to one Tb3+, two W6+, and one Cu1+ atom. In the twentieth O2- site, O2- is bonded in a 1-coordinate geometry to one Tb3+, one W6+, and one Cu1+ atom. In the twenty-first O2- site, O2- is bonded in a 4-coordinate geometry to one Tb3+, two W6+, and one Cu1+ atom. In the twenty-second O2- site, O2- is bonded in a bent 120 degrees geometry to one Tb3+ and one W6+ atom. In the twenty-third O2- site, O2- is bonded in a bent 150 degrees geometry to one Tb3+ and one W6+ atom. In the twenty-fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one Tb3+ and one W6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbTh3 by Materials Project

Th3Tb is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Th is bonded to eight equivalent Th and four equivalent Tb atoms to form ThTb4Th8 cuboctahedra that share corners with twelve equivalent ThTb4Th8 cuboctahedra, edges with eight equivalent TbTh12 cuboctahedra, edges with sixteen equivalent ThTb4Th8 cuboctahedra, faces with four equivalent TbTh12 cuboctahedra, and faces with fourteen equivalent ThTb4Th8 cuboctahedra. All Th–Th bond lengths are 3.57 Å. All Th–Tb bond lengths are 3.57 Å. Tb is bonded to twelve equivalent Th atoms to form TbTh12 cuboctahedra that share corners with twelve equivalent TbTh12 cuboctahedra, edges with twenty-four equivalent ThTb4Th8 cuboctahedra, faces with six equivalent TbTh12 cuboctahedra, and faces with twelve equivalent ThTb4Th8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb3InS6 by Materials Project

Tb3InS6 crystallizes in the orthorhombic P2_12_12 space group. The structure is three-dimensional. there are three inequivalent Tb3+ sites. In the first Tb3+ site, Tb3+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Tb–S bond distances ranging from 2.81–2.91 Å. In the second Tb3+ site, Tb3+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Tb–S bond distances ranging from 2.78–3.07 Å. In the third Tb3+ site, Tb3+ is bonded to seven S2- atoms to form distorted TbS7 pentagonal bipyramids that share edges with two equivalent InS6 octahedra and edges with two equivalent TbS7 pentagonal bipyramids. There are a spread of Tb–S bond distances ranging from 2.75–2.92 Å. There are two inequivalent In3+ sites. In the first In3+ site, In3+ is bonded to six S2- atoms to form InS6 octahedra that share edges with two equivalent InS6 octahedra and edges with four equivalent TbS7 pentagonal bipyramids. There are two shorter (2.62 Å) and four longer (2.63 Å) In–S bond lengths. In the second In3+ site, In3+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of In–S bond distances ranging from 2.47–3.20 Å. There are six inequivalent S2- sites. In the first S2- site, S2- is bonded in a 5-coordinate geometry to five Tb3+ atoms. In the second S2- site, S2- is bonded to three Tb3+ and two equivalent In3+ atoms to form distorted STb3In2 trigonal bipyramids that share corners with four equivalent STb3In2 trigonal bipyramids, corners with three equivalent STb3In trigonal pyramids, edges with four equivalent STb4In square pyramids, and an edgeedge with one STb3In2 trigonal bipyramid. In the third S2- site, S2- is bonded in a 5-coordinate geometry to three Tb3+ and two equivalent In3+ atoms. In the fourth S2- site, S2- is bonded to four Tb3+ and one In3+ atom to form distorted STb4In square pyramids that share a cornercorner with one STb4In square pyramid, corners with two equivalent STb3In trigonal pyramids, edges with two equivalent STb4In square pyramids, and edges with four equivalent STb3In2 trigonal bipyramids. In the fifth S2- site, S2- is bonded to three Tb3+ and one In3+ atom to form distorted STb3In trigonal pyramids that share corners with two equivalent STb4In square pyramids, corners with three equivalent STb3In2 trigonal bipyramids, and corners with three equivalent STb3In trigonal pyramids. In the sixth S2- site, S2- is bonded in a 5-coordinate geometry to five Tb3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbSnPt2 by Materials Project

TbPt2Sn crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Tb is bonded in a 8-coordinate geometry to eight equivalent Pt atoms. There are six shorter (3.01 Å) and two longer (3.13 Å) Tb–Pt bond lengths. Pt is bonded in a 7-coordinate geometry to four equivalent Tb and three equivalent Sn atoms. All Pt–Sn bond lengths are 2.76 Å. Sn is bonded to six equivalent Pt atoms to form distorted edge-sharing SnPt6 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbHoIr2 by Materials Project

HoTbIr2 is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ho is bonded in a body-centered cubic geometry to eight equivalent Ir atoms. All Ho–Ir bond lengths are 2.97 Å. Tb is bonded in a body-centered cubic geometry to eight equivalent Ir atoms. All Tb–Ir bond lengths are 2.97 Å. Ir is bonded in a body-centered cubic geometry to four equivalent Ho and four equivalent Tb atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbBi3 by Materials Project

TbBi3 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Tb is bonded to twelve equivalent Bi atoms to form a mixture of face and corner-sharing TbBi12 cuboctahedra. There are six shorter (3.42 Å) and six longer (3.58 Å) Tb–Bi bond lengths. Bi is bonded in a 4-coordinate geometry to four equivalent Tb atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbLuIr2 by Materials Project

LuTbIr2 is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Lu is bonded in a body-centered cubic geometry to eight equivalent Ir atoms. All Lu–Ir bond lengths are 2.95 Å. Tb is bonded in a body-centered cubic geometry to eight equivalent Ir atoms. All Tb–Ir bond lengths are 2.95 Å. Ir is bonded in a body-centered cubic geometry to four equivalent Lu and four equivalent Tb atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbEuRh2 by Materials Project

TbEuRh2 is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Tb is bonded in a body-centered cubic geometry to eight equivalent Rh atoms. All Tb–Rh bond lengths are 2.96 Å. Eu is bonded in a body-centered cubic geometry to eight equivalent Rh atoms. All Eu–Rh bond lengths are 2.96 Å. Rh is bonded in a body-centered cubic geometry to four equivalent Tb and four equivalent Eu atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb3S by Materials Project

Tb3S is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Tb is bonded in a distorted square co-planar geometry to four equivalent S atoms. All Tb–S bond lengths are 3.26 Å. S is bonded to twelve equivalent Tb atoms to form a mixture of corner and face-sharing STb12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Tight-binding study of beryllium

In this work, we have applied the Naval Research Laboratory Tight-binding (NRL-TB) Method to the hcp alkaline-earth metal Beryllium. This approach consists of fitting to energy band and total energy data generated by the Linearized Augmented Plane Wave (LAPW) for the fcc, bcc, sc, and hcp structures as a function of volume. First, we found that using the Generalized Gradient Approximation (GGA) for the input data secures a better agreement to experimental volumes than the LDA. Second, we found that including small volumes to the fit is needed to get TB parameters that are transferable enough to successfully predict the energies of structures that were not fitted, and to perform molecular dynamics (MD) simulations. The non-orthogonal Hamiltonian obtained, is successful in correctly predicting the hcp lattice as the ground state of Be and finding eight other structures, that were not fitted to LAPW, positioned at higher energies. In addition, the NRL-TB produces accurate energy bands, densities of states, elastic constants, the Bain path and several quantities derived from MD simulations.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nuclear Structure and Decay Data for A=149 Isobars

Here, experimental nuclear structure and decay data are evaluated for all the 17 known nuclides of mass 149 (Xe, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb). Detailed compiled and evaluated spectroscopic information is presented for each reaction and decay dataset, and recommended values are provided for level properties, α, β and γ radiations, and other spectroscopic parameters, based on an evaluation of all the available experimental data for A=149 isobaric nuclides. Although large amounts of nuclear spectroscopic data are available for nuclides of A=149, yet large gaps in knowledge exist, as described below. For the lowest atomic number nuclide 149 Xe, only the isotopic identification has been made, with no data for its ground-state half-life. For 149 Cs, 149 Tm and 149 Yb information is available for only the respective ground states. For 149 Ba, 149 La and 149 Er, limited data exist for excited states. Many of the decay schemes of radioactive nuclei of A=149 are considered as incomplete, either due to large energy differences between the highest observed excited states in daughter nuclides and the respective Q-values, or due to the lack of confirmed γ-ray data, as listed below: 149 Cs → 149 Ba, 149 Ba → 149 La, 149 La → 149 Ce, 149 Ce → 149 Pr, 149 Pr → 149 Nd, 149 Tb(4.17 min) → 149 Gd, 149 Ho(21.0 s and 56 s) → 149 Dy, 149 Er(4 s and 9.6 s) → 149 Ho, and 149 Tm → 149 Er. No data exist for the decay of 149 Yb to 149 Tm. Data for half-lives of the excited states in this mass chain are generally lacking as given below by the number of excited levels of known half-life / approximate number of known levels in a nuclide: 2/17 for 149 Ba, 0/18 for 149 La, 3/53 for 149 Ce, 3/44 for 149 Pr, 17/110 for 149 Nd, 9/90 for 149 Pm, 10/210 for 149 Sm, 2/125 for 149 Eu, 6/270 for 149 Gd, 5/200 for 149 Tb, 3/80 for 149 Dy, 3/90 for 149 Ho, and 3/14 for 149 Er. This work supersedes earlier evaluations of A=149 nuclides published by 2004Si16, 1994Si18, 1985Sz01 and 1976Ho17.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Rare-earth-doped electrospun scheelite CaWO 4 nanofibers with excitation-dependent photoluminescence and high-linearity cathodoluminescence for ratiometric UV wavelength and radiation sensors

Scheelite structured AWO 4 compounds (A = Ba, Ca, Pb and Sr) are efficient hosts for rare-earth dopants. In this work, high-aspect-ratio AWO 4 (A = Ba, Ca, Pb and Sr) nanofibers, doped with 5 mol.% Tb and 5 mol.% Eu on A site, were synthesized using a sol-gel electrospinning technique, and their performances as a ratiometric sensor for the detection of UV light wavelength were comparatively studied. High-resolution electron microscopy reveals the presence of nanosized grains composing the nanofibers. The AWO 4 :5Tb-5Eu nanofibers exhibit strong characteristic photoluminescence (PL) and cathodoluminescence (CL) emission from both Tb 3+ and Eu 3+ ions. In the case of CaWO 4 lattice, the emission intensity ratio of Tb 3+ /Eu 3+ is found to show a linear relationship with the excitation wavelength in the tested range of 240–330 nm, with efficient energy transfer from host lattice to rare-earth ions. However, a similar result is not observed in other scheelite structured BaWO 4 , PbWO 4 , and SrWO 4 nanofibers. Here, the unique PL emission characteristics of CaWO 4 :5Tb-5Eu under different UV excitation wavelengths are due to its unique excitation band. This study reveals a potential new application of CaWO 4 :5Tb-5Eu as a fluorescent probe for UV wavelength detection. Additionally, the CL intensities from CaWO 4 :5Tb-5Eu nanofibers exhibit highly linear dependences on the applied voltage and current without saturation, which can be utilized for radiation detection.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Influence of Compositional Complexity on Amorphization Resistance of Swift Heavy Ion Irradiated Titanate Pyrochlores

Compositionally complex oxides have garnered attention recently for their potential technological applications in harsh environments such as thermal barrier coatings and nuclear waste forms. Therefore, their response to extreme conditions, including high temperature and intense irradiation fields, must be thoroughly investigated. Here, the structural evolution of two pyrochlore oxides with comparable cation size ratio, r A /r B , (Yb 0.2 Er 0.2 Dy 0.2 Tb 0.2 Gd 0.2 ) 2 Ti 2 O 7 and Ho 2 Ti 2 O 7 , was evaluated after irradiation with 946 MeV Au ions up to a fluence of 8 × 10 12 ions/cm2 using synchrotron X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The overall radiation response is comparable for both titanate oxides and is dominated by a loss of crystallinity. When compared to a series of conventional titanate pyrochlore compositions, the amorphous track diameter of (Yb 0.2 Er 0.2 Dy 0.2 Tb 0.2 Gd 0.2 ) 2 Ti 2 O 7 is slightly larger than that of Ho2Ti2O7 and more in line with the diameter of the endmember with the maximum A-site cation size (Gd 2 Ti 2 O 7 ). Density functional theory calculations suggest that this behavior may be linked to local lattice distortions and the associated energetics of cation antisite formation. TEM and Raman analyses show that a disordered, crystalline shell surrounds the amorphous ion tracks in (Yb 0.2 Er 0.2 Dy 0.2 Tb 0.2 Gd 0.2 ) 2 Ti 2 O 7 , and the corresponding short-range structure resembles a weberite-type atomic arrangement.

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

Nature of Hyperfine Interactions in TbPc 2 Single-Molecule Magnets: Multiconfigurational Ab Initio Study

Lanthanide-based single-ion magnetic molecules can have large magnetic hyperfine interactions as well as large magnetic anisotropy. Recent experimental studies reported tunability of these properties by changes of chemical environments or by application of external stimuli for device applications. In order to provide insight onto the origin and mechanism of such tunability, here we investigate the magnetic hyperfine and nuclear quadrupole interactions for a 159 Tb nucleus in TbPc 2 (Pc = phthalocyanine) single-molecule magnets using multiconfigurational ab initio methods including spin–orbit interaction. Since the electronic ground and first-excited (quasi)doublets are well separated in energy, the microscopic Hamiltonian can be mapped onto an effective Hamiltonian with an electronic pseudospin S = 1/2. From the ab initio calculated parameters, we find that the magnetic hyperfine coupling is dominated by the interaction of the Tb nuclear spin with electronic orbital angular momentum. The asymmetric 4f-like electronic charge distribution leads to a strong nuclear quadrupole interaction with significant transverse terms for the molecule with low symmetry. The ab initio calculated electronic–nuclear spectrum including the magnetic hyperfine and quadrupole interactions is in excellent agreement with the experiment. We further find that the transverse quadrupole interactions significantly influence the avoided level crossings in magnetization dynamics and that the molecular distortions affect mostly the Fermi contact terms as well as the transverse quadrupole interactions. Synopsis Hyperfine interactions for 159 Tb nucleus in TbPc 2 single-molecule magnets are investigated from first-principles using multiconfigurational calculations. Strong nuclear quadrupole and magnetic hyperfine coupling are found, with the latter being dominated by the paramagnetic spin-orbital mechanism. Furthermore, we construct an ab initio pseudospin Hamiltonian and obtain the electronic-nuclear spectrum that is in excellent agreement with experiment. The Zeeman diagram is calculated, and the magnetization dynamics is discussed. The effects of molecular distortions are researched.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Photophysical Properties and Electronic Structure of Hydroporphyrin Dyads Exhibiting Strong Through-Space and Through-Bond Electronic Interactions

Electronic interactions between tetrapyrroles are utilized in natural photosynthetic systems to tune the light-harvesting and energy/charge-transfer processes in these assemblies. Such interactions also can be employed to tailor the electronic properties of tetrapyrrolic dyads and larger arrays for use in materials science and biomedical research. Here we have utilized static and time-resolved optical spectroscopy to characterize the optical absorption and emission properties of a set of chlorin and bacteriochlorin dyads with varied degrees of through-bond (TB) and through-space (TS) interactions between the constituent macrocycles. The dyads consist of two chlorins or two bacteriochlorins joined by a linker that utilizes a triple-double-triple bond (enediyne) motif in which the double bond portion is a ester-substituted ethylene or o-phenylene unit. The photophysical studies are coupled with density functional theory (DFT) calculations to probe the ground-state molecular orbital (MO) characteristics of the dyads and time-dependent calculations (TDDFT) to elucidate excited-state properties. The latter include electronic characteristics of the singlet excited state manifold and the absorption transitions to these states from the electronic ground state. Comparison of the MO and calculated spectral properties of each dyad with the linker present versus disrupted (by eliminating the double-bond portion) gives insight into the relative contributions of TB versus TS interactions to the electronic properties of the dyads. The results show that the TB and TS contributions are additive (constructively interfere), which is not always the case for molecular dyads. Most of the dyads have shorter lifetimes of the lowest singlet excited state compared to the parent monomer, which derives from increased S 1 → S 0 internal conversion. The enhancement is greater for the dyads in benzonitrile than in toluene. Furthermore, the studies provide insights into the nature of the electronic interactions between the constituents in the tetrapyrrole arrays and how these interactions dictate the spectral properties and excited-state decay characteristics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Strain-Induced Growth of Twisted Bilayers during the Coalescence of Monolayer MoS 2 Crystals

Tailoring the grain boundaries (GBs) and twist angles between two-dimensional (2D) crystals are two crucial synthetic challenges to deterministically enable envisioned applications such as moiré excitons, emerging magnetism, or single-photon emission. Here, we reveal how twisted 2D bilayers can be synthesized from the collision and coalescence of two growing monolayer MoS 2 crystals during chemical vapor deposition. The twisted bilayer (TB) moiré angles are found to preserve the misorientation angle (θ) of the colliding crystals. The shapes of the TB regions are rationalized by a kink propagation model that predicts the GB formed by the coalescing crystals. Optical spectroscopy measurements reveal a θ-dependent long-range strain in crystals with stitched grain boundaries and a sharp (θ > 20°) threshold for the appearance of TBs, which relieves this strain. Reactive molecular dynamics simulations explain this strain from the continued growth of the crystals during coalescence due to the insertion of atoms at unsaturated defects along the GB, a process that self-terminates when the defects become saturated. The simulations also reproduce atomic-resolution electron microscopy observations of faceting along the GB, which is shown to arise from the growth-induced long-range strain. These facets align with the axes of the colliding crystals to provide favorable nucleation sites for second-layer growth of a TB with twist angles that preserve the misorientation angle θ. This interplay between strain generation and aligned nucleation provides a synthetic pathway for the growth of TBs with deterministic angles.

2D materials↗