Anomalous frequency trends in MoS2 thin films attributed to surface effects

The layered dichalcogenide MoS2 has many unique physical properties in low dimensions. Recent experimental Raman spectroscopies report an anomalous blue shift of the in-plane E12g mode with decreasing thickness, a trend that is not understood. Here, we combine experimental Raman scattering and theor...

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Main Authors: Luo, Xin, Zhao, Yanyuan, Zhang, Jun, Xiong, Qihua, Quek, Su Ying
Other Authors: School of Electrical and Electronic Engineering
Format: Article
Language:English
Published: 2014
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Online Access:https://hdl.handle.net/10356/101642
http://hdl.handle.net/10220/18747
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Institution: Nanyang Technological University
Language: English
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spelling sg-ntu-dr.10356-1016422023-02-28T19:42:36Z Anomalous frequency trends in MoS2 thin films attributed to surface effects Luo, Xin Zhao, Yanyuan Zhang, Jun Xiong, Qihua Quek, Su Ying School of Electrical and Electronic Engineering School of Physical and Mathematical Sciences DRNTU::Science::Physics The layered dichalcogenide MoS2 has many unique physical properties in low dimensions. Recent experimental Raman spectroscopies report an anomalous blue shift of the in-plane E12g mode with decreasing thickness, a trend that is not understood. Here, we combine experimental Raman scattering and theoretical studies to clarify and explain this trend. Special attention is given to understanding the surface effect on Raman frequencies by using a force constants model based on first-principles calculations. Surface effects refer to the larger Mo-S force constants at the surface of thin film MoS2, which results from a loss of neighbours in adjacent MoS2 layers. Without surface effects, the frequencies of both out-of-plane A1g and in-plane E12g modes decrease with decreasing thickness. However, the E12g mode blue shifts while the A1g mode red shifts once the surface effect is included, in agreement with the experiment. Our results show that competition between the thickness effect and the surface effect determines the mechanical properties of two-dimensional MoS2, which we believe applies to other layered materials. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Published version 2014-01-29T03:51:10Z 2019-12-06T20:42:03Z 2014-01-29T03:51:10Z 2019-12-06T20:42:03Z 2013 2013 Journal Article Luo, X., Zhao, Y., Zhang, J., Xiong, Q., & Quek, S. Y. (2013). Anomalous frequency trends in MoS2 thin films attributed to surface effects. Physical review B, 88(7), 075320-. https://hdl.handle.net/10356/101642 http://hdl.handle.net/10220/18747 10.1103/PhysRevB.88.075320 en Physical review B © 2013 American Physical Society. This paper was published in Physical Review B - Condensed Matter and Materials Physics and is made available as an electronic reprint (preprint) with permission of American Physical Society. The paper can be found at the following official DOI: [http://dx.doi.org/10.1103/PhysRevB.88.075320].  One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law. application/pdf
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic DRNTU::Science::Physics
spellingShingle DRNTU::Science::Physics
Luo, Xin
Zhao, Yanyuan
Zhang, Jun
Xiong, Qihua
Quek, Su Ying
Anomalous frequency trends in MoS2 thin films attributed to surface effects
description The layered dichalcogenide MoS2 has many unique physical properties in low dimensions. Recent experimental Raman spectroscopies report an anomalous blue shift of the in-plane E12g mode with decreasing thickness, a trend that is not understood. Here, we combine experimental Raman scattering and theoretical studies to clarify and explain this trend. Special attention is given to understanding the surface effect on Raman frequencies by using a force constants model based on first-principles calculations. Surface effects refer to the larger Mo-S force constants at the surface of thin film MoS2, which results from a loss of neighbours in adjacent MoS2 layers. Without surface effects, the frequencies of both out-of-plane A1g and in-plane E12g modes decrease with decreasing thickness. However, the E12g mode blue shifts while the A1g mode red shifts once the surface effect is included, in agreement with the experiment. Our results show that competition between the thickness effect and the surface effect determines the mechanical properties of two-dimensional MoS2, which we believe applies to other layered materials.
author2 School of Electrical and Electronic Engineering
author_facet School of Electrical and Electronic Engineering
Luo, Xin
Zhao, Yanyuan
Zhang, Jun
Xiong, Qihua
Quek, Su Ying
format Article
author Luo, Xin
Zhao, Yanyuan
Zhang, Jun
Xiong, Qihua
Quek, Su Ying
author_sort Luo, Xin
title Anomalous frequency trends in MoS2 thin films attributed to surface effects
title_short Anomalous frequency trends in MoS2 thin films attributed to surface effects
title_full Anomalous frequency trends in MoS2 thin films attributed to surface effects
title_fullStr Anomalous frequency trends in MoS2 thin films attributed to surface effects
title_full_unstemmed Anomalous frequency trends in MoS2 thin films attributed to surface effects
title_sort anomalous frequency trends in mos2 thin films attributed to surface effects
publishDate 2014
url https://hdl.handle.net/10356/101642
http://hdl.handle.net/10220/18747
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