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SUMMARY:Determination of shear modulus and out of plane Young's modulus of
  layered materials by raman spectroscopy
DTSTART:20150424T141500
DTSTAMP:20260916T052750Z
UID:691d80bddb74bc4ad72441c8c203f75be35136023df4fedccfdd665b
CATEGORIES:Conferences - Seminars
DESCRIPTION:Silvia Milana\, Cambridge Graphene Centre\, University of Camb
 ridge\, UK\nBio: Silvia Milana is a Research Associate in Cambridge Univer
 sity Engineering Department and Pembroke College. She is in the Nanomateri
 als and Spectroscopy Group in the Electrical Engineering Division.\nThe se
 t of elastic constants of a material describes its response to applied ext
 ernal forces [1]. The elastic constants relate such external forces\, desc
 ribed by the stress tensor\, to the resulting deformation\, described by t
 he strain tensor\, and an in-depth knowledge of them is essential to gain 
 insight on the nature of crystal structure and bonding forces [1]. In crys
 tals with uniaxial hexagonal layered structure\, the elasticity matrix des
 cribing mechanical properties contains five non-vanishing\, independent te
 rms: C11\, C12\, C13\, C33\, and C44 [1]. C44 represents the shear modulus
  of the layer-layer interface\, accounting for displacement of the planes 
 with respect to each other [1]. C33 determines the Young’s modulus in th
 e normal direction\, thus describing the out-of-plane compression or expan
 sion of the layers [1]. Raman spectroscopy is the prime non-destructive ch
 aracterization tool for graphene and related layered materials (LMs) [2]. 
 The shear (C) [3] and layer breathing modes (LBMs) [4\, 5\, 6] are due to 
 relative motions of the planes\, either perpendicular or parallel to their
  normal. It is therefore possible to associate these Raman modes to their 
 respective elastic constants accounting for such displacements. Here we co
 nsider three examples of LMs\, namely NLG\, NL-MoS2 and NL-hBN (N being th
 e number of layers)\, which can be regarded as representative metallic\, s
 emiconducting and insulating templates\, respectively. Similarly to the C 
 mode of NLG and NL-hBN\, the first-order C and LBMs of MoS2 are directly a
 ccessible at room temperature\, whereas we gain insight on the LBM dynamic
 s in NLG by measuring its combinations with the D' peak. We find that the 
 positions of the observed C and LBMs in these materials depend strongly on
  N. A general linear-chain model\, based on an interlayer force constant p
 er unit area\, can account for the observed trends\, allowing a direct eva
 luation of C44 and C33\, with applicability to any layered materials. For 
 NLG we find C44 ~4.3 GPa and C33 ~37GPa. The C44 and C33 of NL- MoS2 are f
 ound to be ~18.9 GPa and ~59.6 GPa\, respectively\, whereas the C44 of NL-
 hBN is ~6.5 GPa.\n[1] G. Grimvall\, North-Holland (1986).\n[2] A. C. Ferra
 ri\, D. M. Basko\, Nat. Nanotechnol.\, 8 (2013) 235.\n[3] P. H. Tan\, W. P
 . Han\, W. J. Zhao\, Z. H. Wu\, K. Chang\, H. Wang\, T. F. Wang\, N. Bonin
 i\, N. Marzari\, N. Pugno\, G. Savini\, A. Lombardo\, A. C. Ferrari\, Nat.
  Mater. 11 (2012) 294.\n[4] X. Zhang\, W. P. Han\, J. B. Wu\, S. Milana\, 
 Y. Lu\, Q. Q. Li\, A. C. Ferrari\, P. H. Tan\, Phys. Rev. B 87 (2013) 1154
 13.\n[5] F. Bonaccorso\, P.H. Tan\, A.C. Ferrari\, 7(3) ACS Nano (2013) 18
 38.\n[6] F. Herziger\, P. May\, J. Maultzsch\, Phys. Rev. B\, 85 (2012) 23
 5447.\nHost: Oleg Yazyev
LOCATION:PH L1 503 (The aquarium )  http://plan.epfl.ch/?room=PHL1503
STATUS:CONFIRMED
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