SUPPLEMENTARY INFORMATION
Direct fabrication of graphene on SiO2enabled by thin film stress engineering
Daniel Q. McNerny1, B. Viswanath2, Davor Copic1, Fabrice R. Laye1, Christophor Prohoda2, Anna C. Brieland-Shoultz1, Erik S. Polsen1, Nicholas T. Dee2, Vijayen S. Veerasamy3, A. John Hart1,2
1Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109
2Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
3Guardian Industries, Carleton, Michigan 48117
Corresponding author:
Supplementary Figure 1: Custom built cold-wall furnace used for graphene growth.
Supplementary Figure 2: Temperature and gas flow rate profiles for typical processing conditions, with He annealing followed by C2H2 exposure for graphene growth. During the annealing stage, 400 sccm He is flowed for 5minutes at 875 oC. Next, for graphene growth, 50 sccm C2H2 and 50 sccm H2 are introduced for short 10 seconds. Next, 200 sccm He is then introduced when the substrate power is turned off, and the substrate rapidly cools towards room temperature.
Supplementary Figure 3: XPS spectra of grapheneon SiO2 after Ni film delamination using tape. Atomic concentrations: C1s, 52.78%; O1s, 30.34%; Si2p, 15.63%; Ni2p3, 0.35%.
Supplementary Figure 4:a) Opticalimageand b) Green channel of the optical image of IGL on SiO2 after Ni delamination. Based on the contrast, we conclude that graphene domains are ~1-2 µm in diameter.
Supplementary Figure 5:2-D Raman maps of IGL on SiO2 after Ni delamination: a) I2D/IG, b) IG, c) ID, and d) I2D intensity values.
Supplementary Figure 6:Cross sectional TEM of the specimen used for characterizing interfacial graphene layersgrown on SiO2/Si substrate. The specimen was tilted to [011] zone axis of Si prior to imaging IGL. (a) HRTEM image of Si-SiO2 interface and the corresponding FFT(inset) pattern obtained
from Si. (b) SAED pattern[011] recorded from Si in cross sectional geometry.
Supplementary Figure 7: Representative TEM images showing the bi-layer and few-layer graphene grown at 875oC. (a) Bright field image shows the overlapping graphene layers of ~3 µm lateral dimension,removed from the top surface of the Ni film. Separate and overlapping graphene layers are evident from the [0001] zone axis electron diffraction patterns with 6-fold and superimposed reflections of the bilayer, respectively. (b) Dark field image shows the frequently observed moiré fringes confirming the overlapping layers of graphene grown on the top surface of Ni. Inset shows a TEM bright field image resolving few layer graphene at the edge. (c) Few layer graphene with ~2 µm lateral dimension grown at the Ni-SiO2 interface is shown here for comparison.
Supplementary Figure 8: Wrinkling of graphene.a) AFM of IGL on SiO2 after Ni removal, showing closed wrinkles matching the Ni grain size and structure.b) SEM imaging of graphene on Ni/SiO2 shows similar closed wrinkle formations, while the thermally induced wrinkles are observed c) on the top surface of the delaminated Ni film.
Supplementary Figure 9: Rare observation of fibrous carbon formations (e.g., CNTs) on SiO2after Ni delamination. CNTs are in a region with dewetted Ni nanoparticles caused by in situ delamination of Ni.
Supplementary Figure 10: Microstructural evolution of Ni film, showing the critical conditions of film cracking(tensile stress) and buckling induced delamination (compressive stress). The figures shown are the Ni film (a) as-deposited, (b) after annealing in He for 180seconds, and (c)after 300seconds using(top) optical microscopy and (middle, bottom) SEM.
Supplementary Figure 11: The residual stress of as-grown Ni thin films was estimatedby cantilever deflection. SEM micrographs of 1 µm thick Si3N4 cantilever topped with (a) 50 nm and (b) 200 nm nickel films (deposited via e-beam evaporation). Residual tensile stresses in the Ni films created by the evaporation process caused the cantilevers to curve upward. The measured radius of curvature was applied to Stoney's Equation to estimate the average film stress.
Supplementary Figure 12:Progression of average Ni grain size after annealing at different time intervals in He as determined from SEM observations.
Supplementary Figure 13: Ni film stress evolution during heating. The as-deposited Ni film relaxes its tensile stress and develops compressive stress during heating, due to the compressive thermal mismatch stress between Ni and the substrate.
Supplementary Figure 14:(a) Tensile stress evolution during Ni film grain growth. (b) The amount of tensile stress development during grain growth is estimated considering the contractive volume strain associated with grain boundary reduction and plotted versus annealing time.
Supplementary Figure 15: a) SEM imaging of the Ni film annealed in He (atmospheric pressure) show the He bubble induced pore evolution along with grain growth.
Supplementary Figure 16: a) SEM and b) TEM imaging of the Ni film annealed in He shows twin boundaries observed at during the final stage of grain growth and marked with arrow marks.
Supplementary Figure 17: Raman spectrum of graphene on bottom surface (i.e., surface that was in contact with substrate) of Ni film after delamination.
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