Highly Efficient Uniaxial In-Plane Stretching of a 2D Material via Ion Insertion

Philipp K Muscher; Daniel A Rehn; Aditya Sood; Kipil Lim; Duan Luo; Xiaozhe Shen; Marc Zajac; Feiyu Lu; Apurva Mehta; Yiyang Li; Xijie Wang; Evan J Reed; William C Chueh; Aaron M Lindenberg

doi:10.1002/adma.202101875

Highly Efficient Uniaxial In-Plane Stretching of a 2D Material via Ion Insertion

Adv Mater. 2021 Sep;33(37):e2101875. doi: 10.1002/adma.202101875. Epub 2021 Jul 31.

Authors

Philipp K Muscher^{1

2

3}, Daniel A Rehn⁴, Aditya Sood^{1

2

3}, Kipil Lim^{1

5}, Duan Luo^{1

2

3

6}, Xiaozhe Shen⁶, Marc Zajac¹, Feiyu Lu¹, Apurva Mehta⁵, Yiyang Li^{1

2}, Xijie Wang⁶, Evan J Reed¹, William C Chueh^{1

2}, Aaron M Lindenberg^{1

2

3}

Affiliations

¹ Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA.
² Stanford Institute for Materials & Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
³ PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
⁴ Computational Physics Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
⁵ Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
⁶ SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.

PMID: 34331368
DOI: 10.1002/adma.202101875

Abstract

On-chip dynamic strain engineering requires efficient micro-actuators that can generate large in-plane strains. Inorganic electrochemical actuators are unique in that they are driven by low voltages (≈1 V) and produce considerable strains (≈1%). However, actuation speed and efficiency are limited by mass transport of ions. Minimizing the number of ions required to actuate is thus key to enabling useful "straintronic" devices. Here, it is shown that the electrochemical intercalation of exceptionally few lithium ions into WTe₂ causes large anisotropic in-plane strain: 5% in one in-plane direction and 0.1% in the other. This efficient stretching of the 2D WTe₂ layers contrasts to intercalation-induced strains in related materials which are predominantly in the out-of-plane direction. The unusual actuation of Li_x WTe₂ is linked to the formation of a newly discovered crystallographic phase, referred to as Td', with an exotic atomic arrangement. On-chip low-voltage (<0.2 V) control is demonstrated over the transition to the novel phase and its composition. Within the Td'-Li_0.5- _δ WTe₂ phase, a uniaxial in-plane strain of 1.4% is achieved with a change of δ of only 0.075. This makes the in-plane chemical expansion coefficient of Td'-Li_0.5-δ WTe₂ far greater than of any other single-phase material, enabling fast and efficient planar electrochemical actuation.

Keywords: 2D materials; WTe 2; actuation; electrochemistry; in situ XRD; intercalation; structural analysis.

Abstract

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