Research ArticleMATERIALS SCIENCE

Ultrahigh-mobility graphene devices from chemical vapor deposition on reusable copper

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Science Advances  31 Jul 2015:
Vol. 1, no. 6, e1500222
DOI: 10.1126/sciadv.1500222
  • Fig. 1 Dry transfer of CVD-grown graphene.

    (A) Illustration of the CVD furnace with a copper enclosure inside. (B) Process schematic of the contamination-free transfer of CVD graphene from copper onto hBN. (C) Optical microscopy image of grown graphene crystals on copper foil. (D and E) Optical false-color image of graphene on copper after a first (D) and a second (E) growth cycle. The insets show close-ups of areas marked by the dashed rectangles (see also fig. S1). (F) False-color optical image of CVD graphene encapsulated in hBN. The graphene is recognizable by its fractal shape. Turquoise and yellow areas correspond to the top and bottom hBN flakes, respectively (see also fig. S2). (G) SEM image of a graphene crystal on copper.

  • Fig. 2 Raman characterization of CVD-grown graphene.

    (A) Typical Raman spectrum and microscopy image (inset) of a CVD graphene/hBN heterostructure. a.u., arbitrary units. (B) Spatially resolved map of the width of the 2D peak, Γ2D, measured in the region displayed in (A). Scale bars, 20 μm. Γ2D shows remarkably low values in the area where the graphene flake is encapsulated in hBN [marked by the dashed line, see also inset in (A)]. (C) Histogram of Γ2D measured on the encapsulated part of the graphene flake shown in (B). It exhibits a maximum at 16.8 cm–1 and a cutoff at 16 cm–1. (D) Sample-averaged Embedded Image against average strain for 29 samples. Squared and circle data points correspond to CVD-grown graphene wet-transferred to SiO2 and between hBNs, respectively. Diamond-shaped data points correspond to samples realized with the dry transfer technique starting from a new or a reused copper substrate. Different colors correspond to different growth cycles, according to the color scheme of (E). For each data point, the error bars indicate the 20th and 80th percentile of the corresponding distributions of Γ2D and strain. (E) Typical Raman spectra of samples made with the dry transfer technique performing multiple growth cycles on the same copper substrate.

  • Fig. 3 Transport characterization of dry-assembled devices.

    (A) Optical image of a Hall bar device and four-terminal resistance as a function of back-gate voltage at 1.6 K (blue) and 300 K (black). (B) Conductance σ as a function of charge carrier density n for the device shown in (A). The green curve shows data measured on another sample with carrier mobility of μ = 350,000 cm2 V–1 s–1. (C) Derivative of the Hall conductivity σxy with respect to VBG as a function of magnetic field B and VBG for the device corresponding to the green curve in (B). Landau levels (LL) at filling factors ν = …, −10, −6, −2, 0, 2, 6, 10,… are clearly visible. Several LL exhibit full degeneracy lifting already at B = 6 T, see, for example, the appearance of LL at ν = −1, 1. (D) Plot of μD = σ/ne as a function of the charge carrier density for the device shown in (A) at 1.6 K. The dashed lines represent the mobilities extracted from (B). (E) Procedure to extract n*: two lines are fitted to the double logarithmic plot of σ as a function of n. (F) Mobility as a function of temperature for the device shown in (A).

  • Fig. 4 Mobility and disorder-induced charge carrier fluctuations n* of CVD-grown graphene samples.

    Disorder-induced charge carrier density fluctuation n* and charge carrier mobility μ (averaged over both carrier types) for 10 Hall bar devices fabricated from graphene encapsulated in hBN, using the dry transfer technique (rectangles). The red data points correspond to samples from reused copper. Circle data points correspond to the transport data reported by Petrone et al. (6) for Hall bars on hBN (blue) and SiO2 (green) (39). The dashed line represents the inverse relation between the two quantities plotted and is taken from (31).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/6/e1500222/DC1

    Text

    Fig. S1. Original data corresponding to Fig. 1 (D and E).

    Fig. S2. Original data corresponding to Fig. 1F.

    Fig. S3. Magnetotransport measurements.

    Fig. S4. Wet-transferred graphene flakes.

    Fig. S5. Dry-assembled hBN/graphene/hBN heterostructures.

    Fig. S6. CVD growth of large graphene flakes.

    Fig. S7. EDX analysis of a graphene flake on copper.

    Fig. S8. EDX line scans for the oxygen K-line on three different samples.

    Fig. S9. Analysis of the strain in dry-assembled hBN/graphene/hBN heterostructure.

    Fig. S10. Linear versus Boltzmann fit of the conductance.

    Fig. S11. Carrier density–dependent mobility μD for six different samples.

    References (37, 38)

  • Supplementary Materials

    This PDF file includes:

    • Text
    • Fig. S1. Original data corresponding to Fig. 1 (D and E).
    • Fig. S2. Original data corresponding to Fig. 1F.
    • Fig. S3. Magnetotransport measurements.
    • Fig. S4. Wet-transferred graphene flakes.
    • Fig. S5. Dry-assembled hBN/graphene/hBN heterostructures.
    • Fig. S6. CVD growth of large graphene flakes.
    • Fig. S7. EDX analysis of a graphene flake on copper.
    • Fig. S8. EDX line scans for the oxygen K-line on three different samples.
    • Fig. S9. Analysis of the strain in dry-assembled hBN/graphene/hBN heterostructure.
    • Fig. S10. Linear versus Boltzmann fit of the conductance.
    • Fig. S11. Carrier density–dependent mobility μD for six different samples.
    • References (37, 38)

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