structural, electronic and optical properties of ... · 1. spectral characterization 2. magnetic...

Structural, Electronic and Optical Properties of Functionalized Graphene

(NSF Grant No. DMR-0934142)

Dr. Xiao-Qian (Larry) Wang Clark Atlanta University

Partnership: Atlanta University Center Georgia Tech MRSEC

•  AUC (Clark Atlanta, Morehouse, and Spelman) Clark Atlanta: Profs. M. Williams and Wang Morehouse: Profs. L. Muldrow and J. Mendenhall Spelman: Prof. N. Ravi

•  Georgia Tech MRSEC: The Georgia Tech Laboratory for New Electronic Materials

•  Profs: D. Hess (Director, MRSEC), M. Y. Chou (Chair), E. Conrad (Facility Director), L. Conrad (Education/Outreach Director)

Research

•  Experimental characterizations of epitaxially grown graphene 1.  Spectral characterization 2.  Magnetic properties 3.  Biosmart materials

•  Simulation studies of the electronic structures of graphene-related nanodevices 1.  First-principles density-functional theory 2.  Electron correlations (many-body e-e and e-h) 3.  Molecular dynamics (multiscale modeling)

1.  Z. F. Chen, C. B. Kah, and Xiao-Qian Wang, “Electronic Shell Structures of Russian-Doll-Style Sc4C2@C80”, Chem. Phys. Lett. DOI: 10.1016/j.cplett.2011.03.010 (2011).

2.  Duminda K. Samarakoon, Zhifan Chen, Chantel Nicolas, Xiao-Qian Wang, “Structural and Electronic Properties of Fluorographene”, Small DOI: 10.1002/smll.201002058 (2011).

3.  Z. Chen and Xiao-Qian Wang, “Stacking-Dependent Optical Spectra and Many-Electron Effects in Bilayer Graphene”, Phys. Rev. B (Rapid Communication) 83, 081405 (2011).

4.  K. Suggs, D. Reuven, and X.-Q. Wang, “Electronic Properties of Cycloaddition Functionalized Graphene”, J. Phys. Chem. C DOI: 10.1021/jp111637b (2011).

5.  K. Suggs, V. Person, C. Nicolas, and X.-Q. Wang, “Multiscale Modeling of Reinforced Epoxy Resins by Carbon Nanotubes and Graphene”, 2010 Materials Research Society Fall Meeting Proceedings in press (2011).

6.  D. Samarakoon and Xiao-Qian Wang, “Twist-Boat Conformation in Graphene Oxides”, Nanoscale (Communication) 3, 192 (2011).

7.  D. Samarakoon and X. Q. Wang, “Electronic and Structural Properties of Hydrogenated Graphene”, book chapter in Physics and Applications of Graphene: Theory, ISBN: 978-953-308-114-4 (2011).

8.  Xiao-Qian Wang, “Structural and Electronic Stability of a Volleyball-Shaped B80”, Phys. Rev. B 82, 153409 (2010).

9.  D. Samarakoon and Xiao-Qian Wang, “Tunable Gap in Bilayer Hydrogenated Graphene”, ACS Nano 4, 4126 (2010).

10.  Cherno B. Kah, James Nathaniel, Kelvin Suggs and X.-Q. Wang, “Structural and Electronic Stability of Russian-Doll-Structured Sc4C2@C80”, J. Phys. Chem. C 114, 13017 (2010).

11.  O. O. Ogunro and X.-Q. Wang, “Charge Transfer in Noncovalent Functionalization of Carbon Nanotubes”, New J. Chem. (Letter) 34, 1084 (2010).

12.  O. O. Ogunro, K. Karunwi, I. M. Khan, and Xiao-Qian Wang, “Chiral Asymmetry of Helical Polymer Nanowires”, J. Phys. Chem. Lett. 1, 704 (2010).

13.  A. Nduwimana and Xiao-Qian Wang, “Core and Shell States of Silicon Nanowires under Strain”, J. Phys. Chem. C, 114, 9702 (2010).

14.  W. Yi, A. Malkovskiy, Y. Xu, X.-Q. Wang, A. P. Sokolov, M. Lebron-Colon, M. A. Meador, and Y. Pang, “Polymer Conformation-Assisted Wrapping of Single-Walled Carbon Nanotube: The Impact of cis-Vinylene Linkage”, Polymer 51,475-481 (2010).

15.  K. Suggs and Xiao-Qian Wang, “Structural and Electronic Properties of Carbon Nanotube Reinforced Epoxy Resins”, Nanoscale (Communication) 2, 385 (2010).

16.  D. Samarakoon and Xiao-Qian Wang, “Chair and Twist-Boat Membranes in Hydrogenated Graphene”, ACS Nano 3, 4017 (2009).

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Duminda K. Samarakoon and Xiao-Qian Wang, "Chair and twisted boat membranes in hydrogenated graphene", ACS Nano 3, 4017-4022 (2009).

AGNR 21 ZGNR 12  6

Graphane nanoribbons

D. Samarakoon and Xiao‐Qian Wang, “Twist‐Boat Conforma>on in Graphene Oxides”,  Nanoscale (Communica-on) 3, 192 (2011).  

wist-boat-Chair

(b) Twist-boat-armchair

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Twist-Boat Conformation in Graphene Oxides

W Γ L W S Γ D S

(a) (b)

Boat Twist-boat

Electronic Structure

Ag   B2g  

E2g  

1652 

1662 

1589 

(Ag)  

(B2g)  

(E2g)  

ν (cm-1) 

Inte

nsity

GO 

Graphene 

Raman Spectrum

a

a

b

c a

b

c

One sided Tunable Gap in Hydrogenated Bilayer Graphene

For Engineering Band Gap, Two Layers of Graphene are Better than One

In Nano ACS Nano, 2010, 4 (7), pp 3539–3540

Bilayers •  Dirac fermion (graphene) becomes a massive

fermion. •  The band gap is tunable with electric bias. •  Full hydrogenation of graphene leads to bonding

between the layers (graphane). •  Electric bias may lead to structural

transformation and hence chemical bonding between layers.

•  Hydrogenation with electric bias or desorption of one -sided hydrogen leads to a ferromagnetic semiconductor.

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Stirrup and Chair Conformations of Fluorographene

•  Local membranes have prominent paired epoxy bond patterns, which serves as paradigms for the local stirrup structure.

•  The chair and stirrup models capture the essential structural features of the randomly distributed membranes of fluorographene.

Optical Properties: GW-BSE Approach

•  The extracted optical absorption spectrum for graphane is in very good agreement with previous computational results.

•  Specifically, the optical properties of graphane are dominated by localized charge-transfer excitations governed by enhanced electron correlations.

Calculated absorption spectra using RPA (dashed lines), GW -RPA (dotted lines), and GW -BSE (solid lines) for graphane (top panel) and fluorographene (bottom panel), respectively.

Tunable Band Gap, Many-Electron Effects, Half-Metallicity of Functionalized Graphene

•  Chair, Boat, Twist-boat, and Stirrup Conformations

•  Tunable Band Gap •  Many-electronic effects: e-e and e-h •  Active Student Involvement and Publications

•  E-mail: xwang@cau.edu •  http://programs.cau.edu/prem