Graphene: Plane and Simple Electrical Metrology?

Transcription

1 Graphene: Plane and Simple Electrical Metrology? R. E. Elmquist, F. L. Hernandez-Marquez, M. Real, T. Shen, D. B. Newell, C. J. Jacob, and G. R. Jones, Jr. National Institute of Standards and Technology, Gaithersburg MD USA

2 Graphene mono-atomic layer of carbon - first truly 2D electronic system unique zero-band-gap semiconductor (with electronic properties of massless charge carriers) 3D 2D? 1D Graphite 0D Drawings courtesy of Gert Rietveld, VSL Graphene Carbon nanotubes Fullerenes

3 Electron in strong B-field: flux quantum = h/e R H B ne B h ( i eb ) e ie h 2

4 Theoretical graphene (beginning from 1947) (a) The first Brillouin zone of the honeycomb lattice. (b) Band structure of graphene along the lines connecting points of high symmetry. (c) Full band dispersion over the whole Brillouin zone for π (lower surface or valence band) and π * (upper surface or conduction band) bands of graphene. (Michael Fuhrer, University of Maryland) (Phys. 824 wiki, U. Delaware)

5 Graphene anomalous quantum Hall behavior Monolayer graphene: = 2, 6, 10, Separation of levels in B-field is much wider than in GaAs! Lower B Larger I QHR

6 Exfoliated Graphene from graphite crystals Devices are small and difficult to produce

7 Transferred CVD graphene Use chemical-vapor decomposition to form graphene on Ni, Cu surfaces Coat with polymer for stability Transfer to insulating substrate Pattern by lithographic methods July Q49 Q50a Q50b

8 CVD graphene device QHR temperature dependence B = 18 T, I SD = 100 na 0.55K 1.5K 4K 30K 70K xx ( ) xy ( ) Gate Voltage (V) CVD Graphene: QHE plateaus near ρ xy = 12.9 k and 4.3 k indicate that the sample is primarily monolayer graphene. The graphene material for this device was grown on Cu foil and then transferred to a SiO 2 /Si substrate at the University of Houston, and the Hall bar was fabricated at NIST.

9 Graphene on SiC Si C ºC Epitaxial Graphene growth (by sublimation of Si atoms, moderated by silicon-rich or Argon atmosphere) 1 μm (before) 1 μm (after) 0 nm 20 nm 0 nm 20 nm S. Weingart et al. / Physica E 42, (2010) ; also C. Virojanadara et al. / Physical Review B 78, (2008)

10 Atomic Force Microscope measurements H 2 - etched 6H-SiC (C-Face)

11 Planar surfaces on C-face 6H-SiC Resolved with unit-cell or ½ uc height Smoothed height profiles

12 Synthesis of graphene on SiC (Si-face) in vacuum FIG 3. AFM images of graphene on SiC(0001) surfaces prepared under various annealing conditions: (a) 1150 C for 40 min resulting in graphene thickness of 0.5 ML, (b) 1285 C for 40 min resulting in graphene thickness of 1.0 ML, (c) 1370 C for 40 min resulting in graphene thickness of 1.2 ML, and (d) 1390 C for 40 min resulting in graphene thickness of 1.9 ML. Images are displayed with gray scale ranges of 4, 3, 2 and 3 nm, respectively. Temperature-dependence of Epitaxial Graphene Formation on SiC(0001) Luxmi, et al. J. Electronic Materials, 38, 718 (2009) Images courtesy of Prof. Randall Feenstra, Carnegie-Mellon University, Pittsburgh, Pennsylvania.

13 NIST 6H-SiC sample (Si-face) H-etched 3 min 1600 C, heated in Ar 30 min 1530 C. Auger analysis: 1.8 ML graphene Image courtesy of Prof. Randall Feenstra, Carnegie-Mellon University, Pittsburgh, Pennsylvania. AFM image, 10 m x 10 m, 8 nm gray scale (line cut gives 10 nm step bunches with spacing of about 3 m, corresponding to miscut angle of 0.2 )

14 2100 C (max) Graphite element Furnace Chamber 9 cm diameter work area Argon background gas 10 6 Torr leak checked Uniformity ± 10 C ± 90 C / minute ramp Overshoot 3 C

15 RUN 06 Samples disposition. Group 1 All graphite disks had trenches that avoid samples movement during insertion in furnace. The top graphite disk in Group 1 had its polished face towards the samples. 1 Group 2 Samples FA5 and FA3 were previously processed and reused Samples A01-H6-06 and A01-H9-06 had mesas on them

16 Epitaxial Graphene growth accompanied by etching: NIST A01-20-SE-06

17 Epitaxial Graphene growth accompanied by etching: NIST A01-20-SE-06

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19 Mesa processing of polished SiC samples SF 6 Deep reactive-ion etching: 6H SiC sample (SiO2 oxidized + Ni masked)

20 Atomic terraces on Mesa-etched samples

21 Graphene grown on atomic terraces: Mesa samples

22 A01-H6-06 (left, originally with mesas) and A01-10-S-06 (right)

23 A01-10-S-06, etched imprint

24 Epitaxial Graphene on SiC Terraces NIST A01-20-SE-06 by Atomic-Force Microscopy

25 G ~1611 cm -1 G ~2760 cm -1 Raman Spectra of NIST graphene on SiC Graphene cm -1

26 Epitaxial Graphene on NIST 6H SiC sample, SEM image: Raised pleats (folds) of graphene

27 Epitaxial Graphene growth at 2000 C: NIST A01-06-S-08

28 Epitaxial Graphene on SiC Terraces NIST A01-10-N-06 by Atomic-Force Microscopy Height data

29 Epitaxial Graphene on SiC Terraces NIST A01-10-N-06 by Atomic-Force Microscopy Phase data

30 Graphene QHR Device fabrication

31 Epitaxial Graphene on SiC: Photochemical Gating ZEP 520A PMMA Graphene on SiC Photo-sensitive chemical layer for passivation and charge modulation

32 QHR Device characterization GaAs QHR device HH143e (1.40 K)

33 Co-authors and Contributors: Dr. Felipe L. Hernandez-Marquez (Centro Nacional de Metrologia, Mexico), Dr. Tian Shen (NIST), Dr. David B. Newell (NIST), Dr. George R. Jones (NIST), and Mr. Mariano A. Real (Instuto Nacional de Technologia Industrial, Argentina) NIST Quantum Conductance project. Dr. Irene G. Calizo and Dr. Angela R. Hight-Walker, NIST Optical Technology Division, for providing Raman Measurements and interpretation; Dr. Qingkai Yu, Center for Advanced Materials and ECE, University of Houston, who provided CVD graphene samples; Prof. Randall Feenstra, Carnegie-Mellon University, who provided SiC processing and LEEM results; Thank You