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Proceedings Paper

Correlated structural and optical properties of the MoTe2-WTe2 alloy system (Conference Presentation)
Author(s): Patrick Vora; Ryan Beams; Sean M. Oliver; Jaydeep Joshi; Sergiy Krylyuk; Irina Kalish; Alina Bruma; Iris Stone; Arunima Singh; Francesca Tavazza; Stephan J. Stranick; Albert V. Davydov

Paper Abstract

The structural polymorphism intrinsic to select transition metal dichalcogenides provides exciting opportunities for engineering novel devices. Of special interest are memory technologies that rely upon controlled changes in crystal phase, collectively known as phase change memories (PCMs). MoTe$_2$ is ideal for PCMs as the ground state energy difference between the hexagonal (2H, semiconducting) and monoclinic (1T’, metallic) phases is minimal. This energy difference can be made arbitrarily small by substituting W for Mo on the metal sublattice, thus improving PCM performance. Therefore, understanding the properties of Mo$_{1-x}$W$_x$Te$_2$ alloys across the entire compositional range is vital for the technological application of these versatile materials. We combine Raman spectroscopy with aberration-corrected scanning transmission electron microscopy and x-ray diffraction to explore the MoTe$_2$-WTe$_2$ alloy system. The results of these studies enable the construction of the complete alloy phase diagram, while polarization-resolved Raman measurements provide phonon mode and symmetry assignments for all compositions. Temperature-dependent Raman measurements indicate a transition from 1T’-MoTe$_2$ to a distorted orthorhombic phase (T$_d$) below 250 K and facilitate identification of the anharmonic contributions to the optical phonon modes in bulk MoTe$_2$ and Mo$_{1-x}W$_x$Te$_2$ alloys. We also identify a Raman-forbidden MoTe$_2$ mode that is activated by compositional disorder and find that the main WTe$_2$ Raman peak is asymmetric for x<1. This asymmetry is well-fit by the phonon confinement model and allows the determination of the phonon correlation length. Our work is foundational for future studies of Mo$_x$W${1-x}$Te$_2$ alloys and provides new insights into the impact of disorder in transition metal dichalcogenides.

Paper Details

Date Published: 21 September 2017
Proc. SPIE 10349, Low-Dimensional Materials and Devices 2017, 1034906 (21 September 2017); doi: 10.1117/12.2275340
Show Author Affiliations
Patrick Vora, George Mason Univ. (United States)
Ryan Beams, National Institute of Standards and Technology (United States)
Sean M. Oliver, George Mason Univ. (United States)
Jaydeep Joshi, George Mason Univ. (United States)
Sergiy Krylyuk, National Institute of Standards and Technology (United States)
Theiss Research (United States)
Irina Kalish, National Institute of Standards and Technology (United States)
Alina Bruma, National Institute of Standards and Technology (United States)
Iris Stone, George Mason Univ. (United States)
Arunima Singh, National Institute of Standards and Technology (United States)
Francesca Tavazza, National Institute of Standards and Technology (United States)
Stephan J. Stranick, National Institute of Standards and Technology (United States)
Albert V. Davydov, National Institute of Standards and Technology (United States)

Published in SPIE Proceedings Vol. 10349:
Low-Dimensional Materials and Devices 2017
Nobuhiko P. Kobayashi; A. Alec Talin; M. Saif Islam; Albert V. Davydov, Editor(s)

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