1. Graphene Castro-Neto, et al. Rev. Mod. Phys. 81 (2009) 109
Single atomic layer of graphite

2. Graphene Electronic Properties (isolated graphene sheets)
Graphene Formation—Growth on SiC
Graphene Growth on BN, Co3O4, etc.

3. Castro-Neto, et al. Rev. Mod. Phys. 81 (2009) 109

4. Graphene’s band structure yields unusual properties
Castro Neto EF
The velocity of an electron at the Fermi level (vF)
Is inversely related to meff
Effective mass (m*) ~ [dE2/dk2]-1
Most semiconductors, m0 < m* < 1 me
Graphene, m* < 0.01 m0 (depending on number of carriers)
Therefore, expect VERY high mobility in graphene
Both holes and electrons can be carriers

5. Castro-Neto, et al. Rev. Mod. Phys. 81 (2009) 109
Effective mass for graphene does get very small as n~ 1012

7. The Big Problem with graphene: an imagined conversation:
A. OK: Graphene is great, lots of interesting properties for devices!
B. How do you make a device?
A. You need a sheet of graphene!
B. OK, how do you get a sheet of graphene?
A. HOPG, scotch tape, and tweezers! B.

8. How do you “grow” graphene?
You can evaporate Si from SiC(0001) (either face)
Popularized by the de Heer group at Georgia Tech.

9. Can grow multilayer films of graphene on SiC (azimuthally rotated from each other—electronically decoupled!)
Anneal at 1350 C
Interfacial layer (anneal at 1150 C)
SiC
Auger, graphene growth on SiC, deHeer et al.

10. Inverse photoemission and LEED (Forbeaux, et al, PRB, 58 (1998) 16396)
Growth of graphite on SiC(0001)
π* feature

11. Angle resolved UPS (Emtsev, et al, PRB 77(2008) 155303) shows transition to graphene band structure

12. Adjacent layers on graphene /SiC are decoupled from each other,
Due to azimuthal rotation

13. Graphene on SiC(0001) Not uniform on an atomic level, different regions due to different #s of layers, orientations M B

14. Graphene/SiC photoemission: varying hv can vary the sampling depth (Emtsev, et al, PRB 77 (2008)

15. The covalently bound stretched graphene (CSG model)
Emtsev, et al., PRB 77 (2008)

16. Pertinent Questions: How do Adjacent Graphene Sheets couple electronically?
Single layer Graphene (good)
Many layerGraphite (meh!?)
Answer: On SiC, Adjacent Sheets apparently not coupled due to azimuthal rotation
When/how this transition occurs is very pertinent to devices

17. Core (left) and valence band (right) PES graphene growth on SiC (Emtsev, et al)
Explain the implications of this for graphene coupling between layers

18. Our Focus: Direct CVD, PVD or MBE
Motivation: Direct Growth on Dielectric Substrates: Toward Industrially Practical, Scalable Graphene—Based Devices
Graphene Growth: Conventional Approaches
Metal or HOPG
CVD graphene monolayer
SiO 2 Si
transfer
Result: graphene
monolayer, interfacial inhomogeneities
SiC
(0001)
> 1500 K
monolayer or multilayer on
Si evaporation
FET: Band gap
Our Focus: Direct CVD, PVD or MBE
On Dielectrics
Charge-based devices
graphene
Si(100)
MgO(111) n
Top Gate
Spintronics
graphene
Co3O4(111)
Co(111) or Si(100)-gate
Coherent-Spin FET:
Multi-functional, non-volatile devices

19. Direct Growth of Graphene on Dielectric Substrates: Summary

20. Graphene growth & characterization without ambient exposure
Auger
LEED I(V)
STM
Intro/
transfer
deposition
Gate
valves
BCl3
NH3
Turbo
Butterfly valve
Sample heating to Torr
UHV chamber, Torr
MBE
Graphene/Co3O4
Graphene/MgO(111)
LEED
Hemispherical analyzer (XPS)
Sample processing P = Torr
UHV Analysis Chamber
P ~ 5 x Torr
Free radical source
ALD or PVD
Sample Intro chamber P = 103 Torr – 10-6 Torr
Graphene growth & characterization without ambient exposure

21. Graphene/BN/Ru(0001): Bjelkevig, et al
LEED shows BN and Graphene NOT azimuthally rotated!
Orbital hybridization with Ru 3d!

22. Gr/BN/Ru(0001): Inverse photoemission. π* not observed!
BN layer does NOT screen graphene from orbital hybridization and charge transfer from Ru!

23. Graphene on Co3O4(111): Molecular Beam Epitaxy Substrate Preparation
Evaporator
P~ 10-8 Torr
750 K
Co(111)+ dissolved O
Sapphire(0001)
Sapphire(0001)
1000 K/UHV
~3 ML Co3O4(111)
Co(111)
O segregation
Sapphire(0001)

24. Graphene growth on Co3O4(111)/Co(0001) MBE (graphite source)@1000 K:
Layer-by-layer growth
1st ML
3 ML
2nd ML
0.4 ML
M. Zhou, et al., J. Phys.: Cond. Matt. 24 (2012)

25. LEED: Oxide/Carbon Interface is incommensurate:
Different than graphene on SiC or BN!
Graphene Domain Sized (from FWHM) ~1800 Å (comp. to HOPG)
(a)
(c)
65eV
(d)
(b)
graphene
0.4 ML
Co3O4(111)
65 eV beam energy
3 ML
Oxide spots attenuated with increasing Carbon coverage
2.5 Å
2.8 Å
Fig.2 LEED image of graphene/Co3O4(111)/Co(111)/Al2O3(0001) (a). after the 1st PVD carbon growth; (b). after the 1st PVD carbon growth; (c). Line scan intensity in (a); (d). Line scan intensity in (b);
M. Zhou, et al., J. Phys.: Cond. Matt. 24 (2012)
2.8 Å O-O surface repeat distance on Co3O4(111)
W. Meyer, et al. JPCM 20 (2008)

26. π→π* XPS: C(1s) Shows π system:
Binding Energy indicates graphene oxide charge transfer
XPS (separate chamber):
π→π*
Al Kα
source
284.9(±0.1) eV binding energy:
Interfacial polarization/charge transfer to oxide
No C-O bond formation
Figure 3. Core-level spectra of (a) C(1s), (b) Co(2p), and (c) O(1s). Insert in (a) magnification of ππ* transition region.
M. Zhou, et al., J. Phys.: Cond. Matt. 24 (2012)

27. Directly grown graphene/metals and dielectrics:
Inverse photoemission and charge transfer
Position of * (relative to EF) indicates direction of interfacial charge transfer
(Kong, et al., J.Phys. Chem. C. 114 (2010) 21618 Ef
charge transfer
Forbeaux, et al.
n-type
p-type
Multilayers

28. Generalization, Directly Grown Graphene and Charge Transfer: Oxides (p-type) vs. Metals (n-type)EF e-
n-type; metal to graphene charge transfer
Transition metals
(Ru, Ni, Cu, Ir…)
graphene e-
p-type; graphene to substrate charge transfer
Oxides, SiC EF

29. Suspended graphene
Graphene (few layer) on Co3O4:
Much more conductive than suspeneded graphene
Why??
Significant doping?????
High mobility (How high)?????

30. Conclusion:
Graphene:
Large area growth on practical substrates critical for device development.
Interactions with substrates and (maybe) other graphene layers are critical to device properties