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AFM images (image sizes 10 μm × 10 μm) showing the morphology of Ni-films on YSZ(111) (a)–(e) and Al2O3(0001) (f)–(j). XRD rocking curves for the Ni(111) peak for 300 nm films on the two substrates are shown in (k). All the Ni-films were post growth annealed at 800 °C for 1 h unless otherwise stated. (a)–(c) shows morphology of 15 nm, 100 nm, and 300 nm of Ni-film deposited on YSZ at 550 °C, respectively. The surface morphology of a Ni-film on YSZ grown by depositing100 nm at 300 °C plus an additional 200 nm deposited at 550 °C is shown in (d). The inset in (d) shows the LEED pattern of the Ni-film. The AFM line scan indicated by the red-line in (d) is shown in (e). The resulting surface morphology of 300 nm Ni-film deposited on Al2O3 with similar growth condition as for YSZ in (d) is shown in (f). The inset shows the LEED image of the Ni-film indicating two 30o rotated variants of the Ni-film. AFM image of 300 nm of Ni-film deposited on Al2O3 at 650 °C is shown in (g) with its LEED pattern shown in the inset. Only a single hexagonal diffraction pattern is observed. The surface morphology of a Ni-film on Al2O3 grown by depositing 50 nm at 650 °C plus 250 nm deposited at 500 °C is shown in (h). The inset shows the large scale SEM image of Ni-film. (i) shows the surface morphology of a Ni-film obtained after covering it with a Ta-foil and annealing to 900 °C. The AFM line scan indicated by the red line in (i) is shown in (j).
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SEM, AFM, and TEM images of graphene on Ni-films grown in a tube furnace. (a) SEM image of multi-layer non-uniform graphene grown on Ni-film at 900 °C in the quartz furnace using CH4 and H2 with a ratio of 11:1 and a total pressure of 6 Torr. (b) TEM image corresponding to the region 1 in the SEM image, more than 10 graphene layers are present in these regions. (c) AFM images of the graphene corresponding to the region 2 in the SEM image. (d) AFM image corresponding to the regions 2 in the SEM image. (e) TEM image corresponding to the region 2 in the SEM image, less than 5 graphene layers are present in these regions.
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AES spectra and LEED pattern of graphene grown in a tube furnace. (a) AES of the sample prepared at 900 °C (corresponding to Fig. 2 ). The large C/Ni peak ratio of 5.65 agrees with the surface being covered by regions with layers of graphene. The LEED pattern of this sample indicates a preferential orientation of the graphene with respect to the Ni(111) substrate. A preferential rotation of the graphene lattice by ∼14° is measured. (c) and (d) show data for a sample prepared at 800 °C in a tube furnace. The AES C/Ni peak ratio corresponds to mono or bilayer graphene. The LEED pattern also shows a preferential rotation of the graphene by ∼17° relative to the Ni-substrate. The AES and LEED data shown in (c) and (d) are similar to the data obtained for previously reported graphene grown in UHV at 650 °C on the same kind of Ni-film substrate.
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AFM images and line scans of a 10 nm of yttria film grown on ML graphene on Ni or HOPG. (a) shows a large scale AFM image (20 μm × 20 μm) of yttria on ML graphene on Ni-film. The yttria was deposited at room temperature and post growth annealed to 500 °C. The underlying morphology of the Ni-film is clearly visible indicating the uniform covering of the surface by the yttria film. A higher resolution AFM image (500 nm × 500 nm) of the yttria film in (a) is shown in (b). RMS roughness of the yttria film shown in (b) is 0.34 nm. An AFM image (500 nm × 500 nm) of yttria deposited at room temperature on HOPG is shown in (c). This film exhibits a RMS roughness of 0.31 nm. Yttria films deposited at 600 °C on monolayer graphene on Ni, exhibit a larger surface roughness as shown by the AFM image (500 nm × 500 nm) in (d). The RMS roughness of the yttria film in (d) is ∼1 nm.
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Characterization of yttria films on graphene/Ni(111). For thin yttria films (∼1 nm) annealed to 500 °C a diffuse LEED pattern of the yttria film can be observed. In (a) a Y2O3(111) LEED pattern taken with 30 eV beam energy is shown. The diffuse hexagonal pattern corresponds to the large Y2O3(111) unit cell. For comparison the substrate Ni(111) LEED pattern is shown in (b) for 60 eV beam energy. It is apparent that the two hexagonal patterns are rotationally aligned. X-ray photoelectron diffraction data of ∼5 nm thick Y2O3 film are shown in (c). The variation of the Y-3d5/2 core-level intensity as a function of polar emission angle along the [1–10] azimuth of the Ni-substrate is plotted. This is compared to a cross-sectional view of the yttria crystal structure in (d), with the polar angles indicated at which photoemission intensity maxima are observed. The variation of the intensity in XPD indicates the crystalline ordering of the film with a (111) surface orientation. The ordering of the yttria film is also confirmed by cross-sectional TEM shown in (e) and (f). The low-magnification bright-field TEM image of alumina/Ni-film/monolayer graphene/Y2O3 shown in (e) indicates the uniformity of the yttria film. In the high resolution image in (f) the atomic (111) planes of the yttria film are clearly visible with the (111) planes parallel to the substrate.
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