BILAYER GRAPHENE ELECTRONICS

Transcription

1 BILAYER GRAPHENE ELECTRONICS 1 Au-Yeung Chi Ho, Joseph Department of Physics, The Chinese University of Hong Kong Supervisor: Professor Feng Wang Department of Physics, University of California at Berkeley

2 OUTLINE Graphene Bilayer Graphene Graphene Exfoliation Bilayer Graphene Electronics 2

3 GRAPHENE WHAT IS GRAPHENE? A household name in science since 2004 The Nobel-prize winning material The Nobel Prize in Physics 2010 was awarded jointly to Andre Geim and Konstantin Novoselov "for groundbreaking experiments regarding the two-dimensional material graphene" 3

4 GRAPHENE WHAT IS GRAPHENE? A single sheet of carbon arranged in honeycomb structure 4 A.K. Geim, A.H. MacDonald, Physics Today 60, (2007);

5 GRAPHENE BAND STRUCTURE Its honeycomb arrangement determines the π-electron band structure 5

6 GRAPHENE BAND STRUCTURE The touching conduction band and valence band makes it a zero-bandgap gp semiconductor Linear dispersion implies the governing equation is Dirac-like, giving exotic behaviour predicted by QED: Klein tunneling, Fractional Quantum Hall Effect 6

7 GRAPHENE IT S SO HOT Characteristic band structure was studied more than 20 years ago Started to draw physicists attention after the successful experimental isolation of single- layer graphene A hot research topic in condensed matter physics py 7

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9 BILAYER GRAPHENE BAND STRUCTURE Single Layer Graphene doesn t give a band gap Mind the GAP! Gated Bilayer Graphene can open a band gap in theory For symmetric layers, = 0 9 For asymmetric layer, E. McCann, V.I.Fal ko, Phys. Rev. Lett. 96, (2006);

10 BILAYER GRAPHENE BAND STRUCTURE Wang Group first observed the tunable bandgap produced by gated bilayer graphene in Y Zhang et al, Nature, 459, pp (2009);

11 BILAYER GRAPHENE -PRODUCTION Micromechanical Cleavage Exfoliation, Graphene Peeling Same Technique as for producing single layer 11

12 GRAPHENE EXFOLIATION Graphene bilayer flakes exfoliated from graphite Deposited onto Si/SiO2 wafers Identified by optical contrast in a microscope Number of layers confirmed by Raman spectroscopy 12

13 GRAPHENE EXFOLIATION 13

14 GRAPHENE EXFOLIATION 14

15 GRAPHENE EXFOLIATION A.C. Ferrari et al, Phys. Rev. Lett. 97, (2006) 15

16 GRAPHENE EXFOLIATION Difficulties - Extremely Low Yield and Low Efficiency - Small size - Difficult to transfer the technology Engineering Impossible Chemical vapour deposition cannot produce high quality graphene 16

17 BILAYER GRAPHENE ELECTRONICS Bilayer Graphene Field Effect Transitor (BGFET) Field Effect Transitor (FET) Using Electric Field to control the conductivity it of the charge carrier in a semiconductor Building block of modern microelectronics 17

18 BILAYER GRAPHENE ELECTRONICS A stencil mask placed over the edges of bilayer graphene Gold source and drain, and aluminum oxide deposited onto the graphene under vacuum 18

19 BILAYER GRAPHENE ELECTRONICS Transport Measurement 19

20 BILAYER GRAPHENE ELECTRONICS Exfoliated Bilayer Graphene on Hexagonal Boron Nitride subtrate (hbn) - free of dangling bonds and charge traps - atomically smooth surface - lattice constant similar to that of graphene Bilayer Graphene on hbn subtrate can enhance mobility and function of its device C.R. Dean et al, Nature Nanotechnology, 5, (2010); 20

21 BILAYER GRAPHENE ELECTRONICS Challenge: Both bilayer graphene and BN have to be exfoliated IDEA: Ask polymers to help Graphene PMMA PVA Glass Silde BN SiO2 Si Flip the glass slide, align graphene and BN using microscope, melt PVA/PMMA film 21

22 Glass Slide PVA PMMA Graphene BN SiO2 Once melt, put everything into acetone solution to PMMA film Si Graphene BN SiO2 Si 22

23 BILAYER GRAPHENE ELECTRONICS Difficulties - Interaction of PMMA and the tape is too strong - Uneven surface makes scanning process difficult 23

24 SUMMARY Gated Bilayer Graphene opens bandgap Exfoliation of graphene is a low-cost yet low yield production method. It is still being used for the high-quality graphene produced Higher mobility of bilayer graphene on hbn reported, a more efficient production method is to be worked out 24

25 ACKNOWLEDGEMENT Professor Feng Wang Dr Tsung-Ta Tang Professor Chu Ming Chung Professor Luk Kam Biu Department of Physics, CUHK 25

26 WHAT DID I LEARN IN THE PROJECT Experimental Technique Scientific Methods Multi-discipline Language 26

27 WHAT DID I LEARN IN THE OPUS PROGRAMME Language More sociable More independent American college culture 27

28 PROFESSOR CHARLES WOHL 28

29 PLACES CHECKED-IN 29