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First Principles Insights into 2D Materials: A Story on Interlayer, Surface and Edge Effects

Speaker: 
Su Ying Quek
Date: 
Wed, 18/09/2013 - 11:00am to 12:00pm
Location: 
S13-M01-11 (Physics Conference Room)
Event Type: 
Seminars

Two-dimensional materials such as graphene and layered transition metal dichalcogenides (TMDs) have many interesting and often surprising physical properties.  In this talk, I present an account of some of my group’s most recent findings on 2D materials, focusing on interlayer, surface and edge effects.  Our results are obtained using a combination of theoretical modeling and first principles calculations, i.e. calculations with no empirical parameters.  I shall begin with calculations of Raman spectra in 2D TMD materials, which directly probe the interlayer interactions.  We find that the effective interlayer interactions are essentially the same in 2D as in bulk, with shear force constants about 3 times smaller than compressive force constants, but 3 times larger than shear force constants in multilayer graphene.  [1] Surprisingly, despite generally weak interlayer interactions, the creation of a surface in 2D TMD materials can manifest itself as significant qualitative changes in phonon frequency trends.  [2] Our predicted results are in excellent agreement with experiment.  Finally, I show how edge effects in nanostructured armchair graphene nanoribbons can lead to interface-induced states that give rise to a magnetoresistance of ~900%.

References

1.    Y. Zhao, X. Luo, H. Li, J. Zhang, P. A. T. Araujo, C. K. Gan, H. Zhang*, S. Y. Quek*, M. S. Dresselhaus, and Q. Xiong*, “Interlayer breathing and shear modes in few-trilayer MoS2 and WSe2”, Nano Letters 13, 1007 (2013)

2.    X. Luo, Y. Zhao, J. Zhang, Q. Xiong*, S. Y. Quek*, “Anomalous Frequency     Trends in MoS2 Thin Films Attributed to Surface Effects”, submitted
 

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