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Giant secondary grain growth in Cu films on sapphirea)
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View: Figures


Image of FIG. 1.

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FIG. 1.

Giant grains in Cu films after annealing at 950 °C. (a)-(f) Optical images taken using differential interference contrast with a 50 × objective lens. The scale bar in (d) applies to images (a)-(f). Film deposition temperature is indicated in the upper right corner of each image. Dark lines in (b), (d), and (e) are thermal grooves that mark the edges of grain boundaries in the film. The region shown in (c) is a single Cu grain. (g) Conventional optical image of a larger area for = 80 °C, stitched from several smaller images, showing the absence of grain boundaries over macroscopic areas. Dark spots are areas of dewetting.

Image of FIG. 2.

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FIG. 2.

X-ray diffraction results. (a)-(c) As-deposited films. (d)-(f) Annealed films. Legends in the center panels, (b) and (e), show the deposition temperature . The θ − 2θ scans in (a) and (d) show the Cu film is predominately (111), with a small (100) component at lower that decreases with annealing. The rocking curves in (b) and (e) show the misalignment of ⟨111⟩ decreases with annealing. The inset of (e) shows the width of the rocking curve after annealing has a sharp minimum at = 80 °C. The azimuthal scans in (c) show the complex dependence of as-deposited OR with , while those in (f) show the dramatic decrease in orientational disorder for the = 80 °C film.

Image of FIG. 3.

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FIG. 3.

EBSD texture maps of Cu orientation in as-deposited films. (a)-(c) Maps using the normal direction (ND) for = 25 °C, 80 °C and 100 °C, respectively. The color scale for these maps is shown to the right of the images. Insets show the (111) pole figure for each map, using the logarithmic intensity scale shown at right. (d)-(f) Maps using both normal and and in-plane components (ND+RD). Colors for OR I and OR II are shown to the right of the images. The scale bar in (d) applies to all images in this figure. (g) EBSD geometry showing ND, RD, and TD directions.

Image of FIG. 4.

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FIG. 4.

EBSD maps of boundary between a giant grain and the neighboring matrix. (a) Map using the normal direction (ND). (b) Map of the same region using both normal and and in-plane components (ND+RD). Color scales for both maps are the same as in Fig. 3 . (c) Pole figure for the upper region of (b) shows untwinned OR I. (d) Pole figure for the lower region of (b) shows twinned OR II. The logarithmic intensity scale applies to both pole figures.

Image of FIG. 5.

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FIG. 5.

Graphene growth on giant-grain Cu(111) films. (a) Optical image using differential interference contrast of graphene on Cu after oxidation in air at 180 °C. Oxidized Cu appears darker than the unoxidized regions covered by graphene. (b) Higher magnification image of the region of (a) in the dashed box. (c) Raman spectrum of graphene after transfer to SiO substrate.


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Single crystal metal films on insulating substrates are attractive for microelectronics and other applications, but they are difficult to achieve on macroscopic length scales. The conventional approach to obtaining such films is epitaxial growth at high temperature using slow deposition in ultrahigh vacuum conditions. Here we describe a different approach that is both simpler to implement and produces superior results: sputter deposition at modest temperatures followed by annealing to induce secondary grain growth. We show that polycrystalline as-deposited Cu on α-AlO(0001) can be transformed into Cu(111) with centimeter-sized grains. Employing optical microscopy, x-ray diffraction, and electron backscatter diffraction to characterize the films before and after annealing, we find a particular as-deposited grain structure that promotes the growth of giant grains upon annealing. To demonstrate one potential application of such films, we grow graphene by chemical vapor deposition on wafers of annealed Cu and obtain epitaxial graphene grains of 0.2 mm diameter.


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Scitation: Giant secondary grain growth in Cu films on sapphirea)