Wright State University CORE Scholar Special Session 5: Carbon and Oxide Based Nanostructured Materials (2014) Special Session 5 6-2014 Synthesis and Characterization: Low-Dimensional Carbon Nanomaterials on 3C-SiC/Si John J. Boeckl john.boeckl@us.af.mil Weijie Lu Hong Huang Wright State University - Main Campus, hong.huang@wright.edu Casey Strope Wright State University - Main Campus, strope.5@wright.edu Li Wang See next page for additional authors Follow this and additional works at: http://corescholar.libraries.wright.edu/ss5_2014 Part of the Physics Commons Repository Citation Boeckl, J. J., Lu, W., Huang, H., Strope, C., Wang, L., Mishra, N., & Iacopi, F. (2014). Synthesis and Characterization: Low- Dimensional Carbon Nanomaterials on 3C-SiC/Si.. http://corescholar.libraries.wright.edu/ss5_2014/2 This Presentation is brought to you for free and open access by the Special Session 5 at CORE Scholar. It has been accepted for inclusion in Special Session 5: Carbon and Oxide Based Nanostructured Materials (2014) by an authorized administrator of CORE Scholar. For more information, please contact corescholar@www.libraries.wright.edu.
Authors John J. Boeckl, Weijie Lu, Hong Huang, Casey Strope, Li Wang, Neeraj Mishra, and Francesca Iacopi This presentation is available at CORE Scholar: http://corescholar.libraries.wright.edu/ss5_2014/2
John Boeckl 1, Weijie Lu 1, Hong Huang 2, Casey Strope 2, Li Wang 3, Neeraj Mishra 3, Francesca Iacopi 3 1. Materials and Manufacturing Directorate, Wright-Patterson Air Force Research Laboratory, OH, USA 2. Mechanical and Materials Engineering, Wright State University, OH, USA 3. Queensland Micro and Nanotechnology Centre, Griffith University, Nathan, QLD, Australia. john.boeckl@wpafb.af.mil
2 Outline Background on Low-D Carbon Materials Graphene Synthesis on Bulk SiC 3C-SiC on Si Epitaxial Growth Synthesis of Graphene Future Direction
3 Outline Background on Low-D Carbon Materials Graphene Synthesis on Bulk SiC 3C-SiC on Si Epitaxial Growth Synthesis of Graphene Future Direction
Low Dimensional Carbon Graphene Scientific American298(4), 68-75 (2008)
5 Material Properties Graphene/CNT Properties Ultra-high carrier mobility- µ 10 4 cm 2 /V s High saturation velocity- v = 10 8 cm/s High current carrying capacity 1000x that of Cu Excellent thermal conductivity - ~5000 W/mK Extreme strength - Young s modulus 1.0 TPa Flexible Elastic modulus ~ 0.25 TPa Ultra-thin geometry 1D Tube or 2D atomic layer Graphene Fast Facts Three million sheets of graphene on top of each other would be 1mm thick Graphene is the most impermeable material, even helium atoms cannot squeeze through Graphene is incredibly transparent, yet, you can still see this single layer of atoms with your naked eye
Key Materials Challenges Graphene Large scale production of high-quality graphene Need for a band gap Doping the material Ribbon processing Edge control Single surface of atoms Functionalizing Phys. Rev. Lett. 104, 043903 (2010). Interfaces/Interconnects/Contamination 2-D material development Beyond graphene MoS 2, WS 2, hbn, etc. Gate Dielectrics Heterostructures IEEE Electronic Dev. Letters 30, 547-49 (2009). Nature Materials, 7, 406-411 (2008).
7 Wide-ranging Applications Incredible Possibilities Like plastic, graphene has the potential to be used in a vast variety of materials and situations Computing All carbon electronics and computer chips Smaller, faster, lower power, electronics Structural Additive to plastics for smaller lighter composites Laminates with improved strength Energy and Optics Longer life batteries and better solar cells that are flexible, cheap and mass producible Flexible touch screens, LCDs and LEDs Flexible electronics No need for cooling Transportation vehicles become lighter and stronger improving efficiency and safety Brighter, lower voltage, and higher current robust field emitters
8 Graphene Fabrication 1. Exfoliation from HOPG on SiO 2 /Si wafers 2. CVD growth on substrates 3. Surface segregation on metal substrates 4. Epitaxial growth on SiC by Si sublimation * Our Research Focus Epitaxial Growth 1300 C - 1700 C 6 3 X 6 3 Surface reconstruction Graphene is aligned with SiC crystal structure
9 Graphene Preparation Commercial grade SiC wafer 6H and 4H-SiC, Si-face (0001) Standard chemical clean Anneal in various chambers Temperature: RT - 2100 C (TC,Pyrometer) Pressure: Ar-ATM to 10-10 Torr 2 nm W. Lu, et. al, J. Phys. D: Appl. Phys. 43, 374004, (2010) J. Boeckl, et.al, Mat. Sci, Forum, 645-648, 573-576, (2010) J. H. Park, W. C. Mitchel, S. Elhamri, and T. C. Back, APL. 100, 133107 (2012)
10 UHV- (10-8 to 10-10 Torr) Graphene LEEM, LEED, XPEEM, MBE studies Graphene formation HV- (10-5 to 10-7 Torr) Low CNT growth rate Turbo pump on LV- (10-2 to 10-4 Torr) High CNT growth rate LLV- (<10-2 Torr) No growth, burning? Growth Parameter: Pressure ATM (Argon background) graphene UHV Vacuum pressure ATM
Graphene Quality Bulk 6H-SiC 120000 Graphene C 60 : 9x10on -7 Torr bulk 1400 C 6H-SiC 30min 110000 100000 6H-SiC substrate 90000 80000 70000 Intensity 60000 50000 40000 30000 20000 10000 0 400 500 600 700 800 900 1000 1100 1200 Raman Shift (cm -1 ) Graphene starts to form at 1700 o C with highest mobility grown in the vicinity of 1700-1750 o C under vacuum. 11
12 Surface Chemistry w/oxygen SiC (s) + ½ O 2 (g) SiO (g) + C (s) Eq. 1 ½ SiC (s) + ½ CO (g) ½ SiO (g) + C (s) Eq. 2 SiC (s) + H 2 O (g) SiO (g) + C (s) + H 2 (g) Eq. 3 SiC (s) + CO 2 (g) SiO (g) + CO (g) + C (s) Eq. 4 SiC (s) Si (g) + C (s) Eq. 5 Preferential sublimation of Si from SiC surface and subsequent conversion of free carbon to graphene or CNTs Structure of the interface? Nature of chemical bonding? Transition from SiC to graphene Mechanism of the growth process?
13 Mechanism Based on Interface Chemical Reactions Graphene growth process on SiC via a defective surface layer An interface transition layer a few nm thick is formed above 1100 C The structures of this interface layer is unknown The interface layer decomposes at a lower temperature than SiC SiC (s) + O 2 (g) SiC x O y (s) SiO (g) + C (s) Surface compositional analysis of graphene/sic (0001), R. L. Barbosa, et.al., ICSCRM Proc. 2011
14 Partially Disordered Interface 1 2 3 2 nm 1100 C To form an interface layer The layer decomposes at 1400 C 1600 C Atomic Growth Model 1. A carbon rich layer on the SiC surface is formed at high temperature 2. The interaction of the residual oxygen with carbon forms thermally stable oxygen-carbon embedded structures. 3. Depending on environment such structures lead to curvature of hexagonal structures resulting in the formation of CNT nanocaps or planar graphene 3 Interface transition layer before/after graphene formation W. Lu, R. Barbosa, E. Clarke, K. Eyink, L. Grazulis, W. Mitchel, J. Boeckl, J. Phys. Chem. 116, 15342 (2012)
15 Thermally stable O-C compounds Goal to understand the thermal stable O-C compounds by TEM, TPD, and modeling Thermal desorption spectra of CO (a) and CO 2 (b) after oxygen implantation for various carbon materials. (EK98: pure graphite, and USB15: 15%B in C), Temperature region for CNT and graphene growth A. Refke,, et al. J. Nuclear Materials, 212-215, 1255 (1994).
ICMSE Applied to Defect Engineering in Low-dimensional Compounds Objective: Integrate calculation of properties with in-situ experiments for tightly coupled iterative validation and understanding of materials behavior (Raman signatures, formation energies, ground state structures.) 5 8 5 Modeling Defects in Graphene 7 5 5 7 Experimental 5 7 7 5 5 7 7 5 5 7 7 6 5 5 7 Reconstruction via atom elimination/bond rotation Oxygen adsorbed on graphene F. Mehmood, R. Pachter et.al., J. Phys. Chem. C, 117 (20), 1036, (2013). 100 um R. Rao, B Maruyama, et al, ACS Nano 7(2), 1100, (2013) SiC pillars for graphene experiments in ARES (Pochet) 16
17 Graphene on Bulk SiC Conclusions Graphene is formed above ~1400 C Oxygen may play a role in the initial growth of graphene on SiC XPS shows oxy-carbides, sp 3 and sp 2 carbon structures Proposed growth model with oxygen SiC (s) + O 2 (g) SiCxOy (s) SiO (g) + C (s) The controlling steps: SiC SiO x C y SiO + C C sp 3 C sp 2
18 Outline Background on Low-D Carbon Materials Graphene Synthesis on Bulk SiC 3C-SiC on Si Epitaxial Growth Synthesis of Graphene Future Direction
19 Why graphene on SiC/Si? ~Holy Grail! Enables minimum effort wafer-scale devices: Reduced Cost Transfer Free Flexible membranes Self aligned patterning Combination of 2 outstanding materials Exploit existing graphene synthesis
20 3C-SiC on Si at Griffith University Epitaxial SiC on Silicon: core expertise 6 4 12 12 6 4 LPCVD reactor Large area June 2013: ANFF launch @ Griffith of the 300mm epitaxial reactor
21 3C-SiC epitaxial sequence Alternating-Supply/Atomic-Layer Epitaxy (ASE/ ALE) Si substrate SiC Surface clean Si substrate Carbonization 0.61 nm/cycle SiC Si substrate Epitaxial growth L. Wang et al., J. Cryst. Growth, 329 (2011)
22 Stacking faults in 3C-SiC SiC(111) more defective than SiC(100): different relaxation kinetics
23 Quality of the 3C-SiC Films As-deposited thin films (<100nm) 2000 Intensity (a.u.) 1800 1600 1400 1200 1000 800 600 400 #5 on (100): 6.1nm #7 on (111): 6.1nm #16 on(100): 93.0nm #14 on (111): 90.4nm 200 The as-grown thin SiC films are yet fully crystallized with predominant stacking fault throughout the film thicknesses. 0 600 700 800 900 1000 1400 1500 1600 1700 1800 Raman Shift (cm -1 ) As-deposited thick films (>400nm) Single crystalline 3C- SiC is observed and the film quality improves as thickness increases. L.Wang, et al, Thin Solid Films, 519(2011)6443-6446
24 Outline Background on Low-D Carbon Materials Graphene Synthesis on Bulk SiC 3C-SiC on Si Epitaxial Growth Synthesis of Graphene Future Direction
25 Outline Background on Low-D Carbon Materials Graphene Synthesis on Bulk SiC 3C-SiC on Si Epitaxial Growth Synthesis of Graphene Metal Catalyst (not reported in this talk) Thermal Decomposition (UHV/Anneal Furnace)
26 Sublimation from SiC/Si 2 nm Ultra High Vacuum P~ 5 10-11 Torr, 1300 C, in situ STM 1.5 nm 1.5 nm 1.5 nm B.Gupta et al, Carbon, 2014
27 Sublimation from SiC/Si Need for T>1300 C to obtain acceptable quality epitaxial graphene UHV system low residual gas Oxygen effect in low vacuum furnace?
28 Experimental Aspects Decomposition to Graphene Argon or Vacuum (10-5 torr) 1100-1350 o C (on 3C-SiC) 50mins - 3hours ramp-up rates (3-20 o C/min) cooling rate (5-6 C/min) Material Orientation Thickness 3C-SiC Si (100) 6 nm 3C-SiC Si (100) 90 nm 3C-SiC Si (111) 6 nm 3C-SiC Si (111) 93 nm
29 3C-SiC on Si substrates Raman Characteristics Intensity 10000 8000 6000 4000 "3C-SiC" on Si (111) 6nm as-grown 1150 o C 1h 1200 o C 1h 1200 o C 3h Intensity 8000 6000 4000 "3C-SiC" on Si (111) 90 nm as-grown 1200 o C 1h, slow 1200 o C 3h, slow 1200 o C 3h, fast Intensity 16000 12000 8000 SiC(111):6nm, 1150 o C, 1h SiC(111):6nm, 1200 o C, 1h SiC(111):90nm, 1150 o C, 1h SiC(111):90nm, 1200 o C, 1h SiC(111):90nm, 1200 o C, 3h 2000 2000 4000 0 600 700 800 900 1000 1100 1200 Raman Shift (cm -1 ) 0 600 700 800 900 1000 1100 1200 Raman Shift (cm -1 ) 0 1200 1600 2000 2400 2800 3200 Raman Shift (cm -1 ) Graphene starts to form at 1150 o C after prolonged time with better quality at 1200 o C for 1h under vacuum. In-situ SiC crystallization occurs, and longer heating time result in the formation of 6H-SiC.
30 Outline Background on Low-D Carbon Materials Graphene Synthesis on Bulk SiC 3C-SiC on Si Epitaxial Growth Synthesis of Graphene Future Direction
31 Future Direction Pillars for Rapid Growth Experimentation 100 um M. Anderson et al, MRS Symp. Proc. Vol. 1693, 2014
32 Future Direction Pillars for Rapid Growth Experimentation 100 um 1. Improved etch at Griffith 2. Use SOI to improve thermal isolation M. Anderson et al, MRS Symp. Proc. Vol. 1693, 2014
. DISTRIBUTION A. Approved for public release; distribution unlimited Future Direction Pillars for Rapid Growth Experimentation 3C-SiC on Si: Bulk and surface Si micromachining! 33
34 Future Direction Self-aligned Sublimation Epitaxial SiC on Si(111) Silicon Epi SiC Photolithography SiC plasma etching Photoresist strip Release of the microbeams Self aligned graphene by sublimation Graphene SiC Silicon
35 Future Direction Membrane Etch into Higher Quality Epi-layer F.Iacopi, R.E.Brock et al, Acta Materialia, 2013 For the first time, stress gradients measured with ~10nm resolution bring new insights
36 Future Direction Membrane Etch into Higher Quality Epi-layer Graphene 3C-SiC 20nm Si
37 Future Direction Membrane Etch into Higher Quality Epi-layer Graphene 3C-SiC 20nm Si
. DISTRIBUTION A. Approved for public release; distribution unlimited Carbon Research Group AFRL Bill Mitchel Kurt Eyink Shanee Pacley Shin Mou Weijie Lu Jeongho Park (NSF) Ruth Pachter Transport Measurements MBE, SE Raman Transport/Devices/EBIC Raman, XPS, Growth MBE, XPS Modeling Larry Grazulis Gerry Landis Howard Smith Said Elhamri AFM, STM Sample Preparation SIMS, XPS Transport Measuerments Funding Air Force Office of Scientific Research Dr. Charles Lee, (PM) 38