(317b) 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.