Creation of Highly Textured Metal Oxide Films Using Wrinkled and Crumpled Graphene As Intercalation Templates

Creation of Highly Textured Metal Oxide Films Using Wrinkled and Crumpled Graphene as Intercalation Templates

Po-Yen Chen^1,2*, Ian Y. Wong², Robert H. Hurt²

¹Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139

²School of Engineering, Brown University, Providence, RI 02912

Email: pychen@mit.edu

 

            Mismatched deformations in layered architectures of stiff coatings on soft substrates produce textured topographies. Recently this approach has been extended to create more complex, hierarchical wrinkled/crumpled textures of graphene coatings using multiple cycles of contraction, film removal, transfer, and further contraction. However, these complex multigenerational textures have only been realized in graphene-based films. We became interested in creating these complex multigenerational textures in other material systems, beyond graphene.  One possible synthetic approach would be to start with the established multigenerational textured graphene, and translate the texture to other inorganic materials (e.g., metal oxides) through sacrificial templating. In this study, a facile fabrication method is demonstrated for replicating complex, hierarchical graphene wrinkle/crumple textures in metal oxide films. The general synthesis approach is schematically illustrated in Figure 1. The fabrication involves: (1) spontaneous intercalation of metal ions into water-swollen GO multilayer films, (2) dehydration of cation-GO complexes and thermal decomposition of GO to dissociate the complexes, (3) calcination to remove the graphene template by O₂ oxidation and liberate the metal oxide. To explore the generality and versatility of this method a variety of mono- and multivalent metal ions were explored as intercalants (Ag⁺, Zn²⁺, Al³⁺, Mn²⁺, and Cu²⁺), and a range of GO templates was applied with pre-fabricated wrinkle and crumple textures.  We find that many but not all of the metal ions and synthesis conditions produce textured metal oxides, and the optimal precursors and concentration for successful replication are reported.  Remarkably, even the finest structural features in the multiscale hierarchical GO templates can be replicated with high fidelity in ZnO, Al₂O₃, Mn₂O₃, and CuO films when using the optimal ion loading (Figure 2). Overall, this intercalation templating approach has broad applicability for the creation of complex, textured metal oxide films, and provides a bridging technology that can transcribes textures already realized in highly flexible graphene sheets into other material systems.

Figure 1. Schematic illustration of general synthetic process to generate textured metal oxides via using multiscale GO structures as versatile sacrificial templates.

Figure 2. Metal oxide nanostructures templated by GO multiscale structures. The sequential deformation can generate multiscale GO films, which act as versatile templates to synthesize different metal oxide nanostructures. First row shows the SEM images of (a) G₁-1D-GO wrinkled template, (b) G₁-1D-ZnO, (b) G₁-1D-Al₂O₃, and (d) G₁-1D-Mn₃O₄ wrinkles. Second row shows the SEM images of (e) G₁-2D-GO crumpled template, (f) G₁-2D-ZnO, (g) G₁-2D-Al₂O₃, and (h) G₁-2D-Mn₃O₄ crumples. Third row shows the SEM images of (i) G₂-2D2D-GO hierarchical template, (j) G₂-2D2D-ZnO, (k) G₂-2D2D-Al₂O₃, and (l) G₂-2D2D-Mn₃O₄ structures. Fourth row shows the cross-sectional SEM images of (m) G₂-2D2D-GO hierarchical template, (n) G₂-2D2D-ZnO, (o) G₂-2D2D-Al₂O₃, and (p) G₂-2D2D-Mn₃O₄ structures. The scale bars in the first three rows are all 5 micrometers; the scale bars in the inset figures are 1 micrometer. The scale bars in the fourth row are 2 micrometers.