Direct Visualization of Trimerized States in $1{T}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{TaTe}}_{2}$

Open Access

Direct Visualization of Trimerized States in $1 T^{'} − {TaTe}_{2}$

Ismail El Baggari, Nikhil Sivadas, Gregory M. Stiehl, Jacob Waelder, Daniel C. Ralph, Craig J. Fennie, and Lena F. Kourkoutis

Phys. Rev. Lett. 125, 165302 – Published 13 October 2020

Abstract

Transition-metal dichalcogenides containing tellurium anions show remarkable charge-lattice modulated structures and prominent interlayer character. Using cryogenic scanning transmission electron microscopy (STEM), we map the atomic-scale structures of the high temperature (HT) and low temperature (LT) modulated phases in $1 T^{'} − {TaTe}_{2}$ . At HT, we directly show in-plane metal distortions which form trimerized clusters and staggered, three-layer stacking. In the LT phase at 93 K, we visualize an additional trimerization of Ta sites and subtle distortions of Te sites by extracting structural information from contrast modulations in plan-view STEM data. Coupled with density functional theory calculations and image simulations, this approach opens the door for atomic-scale visualizations of low temperature phase transitions and complex displacements in a variety of layered systems.

Received 25 March 2020
Revised 3 June 2020
Accepted 26 August 2020

DOI:https://doi.org/10.1103/PhysRevLett.125.165302

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Charge density waves Charge order Structural phase transition

2-dimensional systems Transition metal dichalcogenides

Cryo-transmission electron microscopy Density functional theory Scanning transmission electron microscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Ismail El Baggari¹, Nikhil Sivadas ², Gregory M. Stiehl¹, Jacob Waelder³, Daniel C. Ralph^1,4, Craig J. Fennie², and Lena F. Kourkoutis^2,4,*

¹Department of Physics, Cornell University, Ithaca, New York 14853, USA
²School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
³Platform for the Accelerated Realization, Analysis and Discovery of Interface Materials (PARADIM), Cornell University, Ithaca, New York 14853, USA
⁴Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York 14853, USA

^*Corresponding author. lena.f.kourkoutis@cornell.edu

Article Text

Click to Expand

Supplemental Material

Click to Expand

References

Click to Expand

Issue

Vol. 125, Iss. 16 — 16 October 2020

Reuse & Permissions

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a),(b) Room temperature structural model and HAADF-STEM image of $1 T^{'} − {TaTe}_{2}$ , respectively, viewed in cross section and along the $b$ direction of the monoclinic cell. The unit cell is marked by dashed lines. The white brackets delineate trimerized clusters of Ta atoms. (c),(d) Structural model and HAADF-STEM image in plan view at 293 K. The Te atoms appear bright and round while Ta atoms appear elongated and dimmer.
Reuse & Permissions
Figure 2
(a),(b) STEM image at 293 K and 93 K, respectively. The insets show zoomed-in views of the images, over a $\sim 1 nm \times 1 nm$ field of view. (c),(d) Amplitude of the Fourier transform (FT) at 293 K and 93 K. The inset shows linecuts of the FT amplitude from (c) (red) and (d) (blue) along the $b^{*}$ direction. At low temperature, in-plane superlattice peaks (blue circles) with $q = 1 / 3$ reciprocal lattice units appear in the FT, reflecting the presence of a modulated structure.
Reuse & Permissions
Figure 3
(a) Section of the low temperature (LT) STEM image, $I (R)$ , spanning a projection of the monoclinic unit cell. (b) Generated reference image, $I_{ref} (R)$ , of the same field of view, as described in the text. Black dots represent Ta columns and crosses represent Te columns. (c) Difference map between $I (R)$ and $I_{ref} (R)$ . The map encodes the modulations in STEM contrast which are responsible for the superlattice peaks. The bracket delimits a single low temperature trimerized cluster. White crosses represent Te atomic columns that show a reduction in intensity. (d) Zoom-in on the Ta-1, Ta-2, and Ta-3 columns and their respective intensity modifications. (e) Large field of view of the difference map showing periodic intensity modulations. The LT unit cell is marked by the dashed lines.
Reuse & Permissions
Figure 4
(a) Low temperature structure obtained from DFT structural optimization. Tantalum atoms within the existing HT trimers undergo longitudinal periodic lattice displacements along the $b$ axis, forming additional trimerized clusters. More subtle tellurium displacements occur as well. The dashed box delimits the simulated field of view. (b),(c) Multislice simulation of HAADF-STEM images of the HT and LT phase, respectively. The dots represent Ta columns and the crosses represent Te columns. The dashed lines highlight distortions in the Ta columns (Ta-1 and Ta-3) at low temperature. (d) The difference image shows a periodic intensity modulation that emerges at low temperature. The bracket delimits the low temperature Ta trimers and the white crosses represent Te columns that exhibit a reduction in intensity.
Reuse & Permissions

Physical Review Letters

Direct Visualization of Trimerized States in 1T′−TaTe2

Ismail El Baggari, Nikhil Sivadas, Gregory M. Stiehl, Jacob Waelder, Daniel C. Ralph, Craig J. Fennie, and Lena F. Kourkoutis

Phys. Rev. Lett. 125, 165302 – Published 13 October 2020

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text

Supplemental Material

References

Issue

Authorization Required

Other Options

Download & Share

Images

Figure 1

Figure 2

Figure 3

Figure 4

Reuse & Permissions

Log In

Search

Article Lookup

Paste a citation or DOI

Enter a citation

Direct Visualization of Trimerized States in $1 T^{'} − {TaTe}_{2}$