skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Intercalation-Induced Topotactic Phase Transformation of Tungsten Disulfide Crystals
Recent research has demonstrated the potential for topological superconductivity, anisotropic Majorana bound states, optical nonlinearity, and enhanced electrochemical activity for transition metal dichalcogenides (TMDs) with a 2M structure. These unique TMD compounds exhibit metastability and, upon heating, undergo a transition to the thermodynamically stable 2H phase. The 2M phase is commonly made at high temperatures using traditional solid-state methods, and this metastability further complicates the growth of large 2M WS2 crystals. Herein, a novel synthetic method was developed, focusing on a molten salt reaction to synthesize large 2H crystals and then inducing transformation to the 2M phase through intercalation and thermal treatment. The 2H crystals were intercalated via a room-temperature sodium naphthalenide solution, producing a previously unreported Na-intercalated 2H WS2 phase. Thermal heating was required to facilitate the phase transition to the intercalated 2M crystal structure. This phase transition was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), electron dispersive X-ray spectroscopy (EDS), and Raman spectroscopy, which confirmed the synthesis of the intercalated 2M phase. Upon deintercalation, crystal and powder samples showed superconductivity with a Tc of 8.6–8.7 K, similar to previously reported values. The generality of this process was further demonstrated using alkali metal triethyl borohydride to intercalate 2H WS2 and produced the desired 2M phase. This novel synthetic method has broad implications for discovering metastable phases in other TMD families and layered materials. Separation of the intercalation and phase transition also has the potential to allow for large-scale synthesis of this technologically important phase with greater control over each step of the reaction.  more » « less
Award ID(s):
2228841
PAR ID:
10628392
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ;
Publisher / Repository:
ACS
Date Published:
Journal Name:
Chemistry of Materials
Volume:
37
Issue:
1
ISSN:
0897-4756
Page Range / eLocation ID:
129 to 138
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, 2D Materials)
    Abstract The investigation of exotic properties in two-dimensional (2D) topological superconductors has garnered increasing attention in condensed matter physics, particularly for applications in topological qubits. Despite this interest, a reliable way of fabricating topological Josephson junctions (JJs) utilizing topological superconductors has yet to be demonstrated. Controllable structural phase transition presents a unique approach to achieving topological JJs in atomically thin 2D topological superconductors. In this work, we report the pioneering demonstration of a structural phase transition from the superconducting to the semiconducting phase in the 2D topological superconductor 2M-WS2. We reveal that the metastable 2M phase of WS2remains stable in ambient conditions but transitions to the 2H phase when subjected to temperatures above 150 °C. We further locally induced the 2H phase within 2M-WS2nanolayers using laser irradiation. Notably, the 2H phase region exhibits a hexagonal shape, and scanning tunneling microscopy uncovers an atomically sharp crystal structural transition between the 2H and 2M phase regions. Moreover, the 2M to 2H phase transition can be induced at the nanometer scale by a 200 kV electron beam. The electrical transport measurements further confirmed the superconductivity of the pristine 2M-WS2and the semiconducting behavior of the laser-irradiated 2M-WS2. Our results establish a novel approach for controllable topological phase change in 2D topological superconductors, significantly impacting the development of atomically scaled planar topological JJs. 
    more » « less
  2. ; ; ; (, Angewandte Chemie International Edition)
    Abstract A modulated bi‐phase synthesis towards large‐scale manganese 1,4‐benzenedicarboxylate (MnBDC) MOFs with a precise control over their morphology (bulk vs. layered) is presented. Metal precursors and organic ligands are separated to reduce the kinetic reaction rates for better control over the crystallization process. Based on scanning electron microscopy (SEM), X‐ray diffraction (XRD), energy‐dispersive X‐ray spectroscopy (EDS), and Raman spectroscopy studies, the continuous ligand supply along with the presence of pyridine capping agent are highly effective in promoting the layer‐by‐layer growth and achieving large crystal sizes. Once layered MnBDC is stabilized, topotactic intercalation chemistry was used to demonstrate the feasibility of bromine intercalation on these layered materials. Bromine intercalation is possible between the MOFs layers for the first time. Bromine intercalation causes colossal reduction in layered MnBDC band gap while it has no observable effect on bulk MOFs. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; ; et al (, Nano Letters)
    Leveraging the reciprocal-space proximity effect between superconducting bulk and topological surface states (TSSs) offers a promising way to topological superconductivity. However, elucidating the mutual influence of bulk and TSSs on topological superconductivity remains a challenge. Here, we report pioneering transport evidence of a thickness-dependent transition from conventional to unconventional superconductivity in 2M-phase WS2 (2M-WS2). As the sample thickness reduces, we see clear changes in key superconducting metrics, including critical temperature, critical current, and carrier density. Notably, while thick 2M-WS2 samples show conventional superconductivity, with an in-plane (IP) upper critical field constrained by the Pauli limit, samples under 20 nm exhibit a pronounced IP critical field enhancement, inversely correlated with 2D carrier density. This marks a distinct crossover to unconventional superconductivity with strong spin-orbit-parity coupling. Our findings underscore the crucial role of sample thickness in accessing topological states in 2D topological superconductors, offering pivotal insights into future studies of topological superconductivity. 
    more » « less
  4. ; ; ; ; ; ; ; ; (, Energy Materials)
    A heterometallic single-source molecular precursor Li2Mn2(tbaoac)6 (1 , tbaoac = tert -butyl acetoacetato) has been specifically designed to achieve the lowest decomposition temperature and a clean conversion to mixed-metal oxides. The crystal structure of this tetranuclear molecule was determined by single crystal X-ray diffraction, and the retention of heterometallic structure in solution and in the gas phase was confirmed by nuclear magnetic resonance spectroscopy and mass spectrometry, respectively. Thermal decomposition of this precursor at the temperatures as low as 310 oC resulted in a new metastable oxide phase formulated as lithium-rich, oxygen-deficient spinel Li1.5Mn1.5O3.5. This formulation was supported by a comprehensive suite of techniques including thermogravimetric/differential thermal analysis, elemental analysis, inductively coupled mass spectrometry, iodometric titration, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy studies, and Rietveld refinement from powder X-ray diffraction data. Upon heating to about 400 oC, this new low-temperature phase disproportionates stoichiometrically, gradually converting to layered Li2MnO3 and spinel Li1+x Mn2-x O4 (x < 0.5). Further heating to 750 oC results in formation of thermodynamically stable Li2MnO3 and LiMn2O4 phases. 
    more » « less
  5. ; ; ; ; ; ; (, Nano Letters)
    Compositional tunability, an indispensable parameter to modify materials' properties, can open up new applications for the class of van der Waals (vdW) layered materials such as transition-metal dichalcogenides (TMDCs). To-date, multi-element alloy TMDC layers are obtained via exfoliation from bulk polycrystalline powders. Here, we demonstrate direct deposition of high-entropy alloy disulfide, (VNbMoTaW)S2, layers with controllable thicknesses on free-standing graphene membranes and on bare and hBN-covered Al2O3(0001) substrates via ultra-high vacuum reactive dc magnetron sputtering of VNbMoTaW target in Kr and H2S gas mixtures. Using a combination of density functional theory calculations, Raman spectroscopy, X-ray diffraction, scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, we determine that the as-deposited layers are single-phase, 2H-structured, and 0001-oriented (V0.10Nb0.16Mo0.19Ta0.28W0.27)S2.44. Our synthesis route is general and applicable for heteroepitaxial growth of a wide variety of TMDC alloys and potentially other multielement alloy vdW compounds with the desired compositions. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email