Supporting information for
Fabricating ordered functional nanostructures onto
polycrystalline substrates from the bottom-up
By M. Torres*, Lorena Pardo, J. Ricote, Luís E. Fuentes-Cobas, Brian J. Rodriguez,
and M.Lourdes Calzada*
Keywords: ferroelectricity, high-k dielectrics, perovskites, self-assembly, sol-gel
processes
The microemulsion mediated synthesis that we present in this work uses low
molecular weight simple chain surfactants that have successfully been used for the
preparation of nanopowders of different ferroelectric perovskite oxides.
[1]
When a
microemulsion is added to a sol, sol particles penetrate inside the core of the micelles
and nanopowders, with dimensions determined by that of the micelles, are obtained
after hydrolysis/condensation reactions and, in some cases, calcination.
Microemulsion
Sol
Water-micelles
Building units
Micellar
solution
Figure S1. Preparation of the micellar solution by mixing the sol with the
microemulsion. The microemulsion contains “water-micelles”, micelles with only
water in the core. The micellar solution contains water micelles and “building units”
that are micelles with water and sol drops at the core.
The deposition of an additional microemulsion layer modifies the surface tension of
the substrate as shown in Figure S2 (a) and (b). The contact angle decreases
demonstrating an improvement of wetting of the substrate by the precursor micellar
solution
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Figure S2. (a) Drops of micellar solution onto a Pt/TiO2/SiO2/(100)Si substrate and (b)
onto a water-micellar layer/Pt/TiO2/SiO2/(100)Si substrate (modified substrate). (c)
Bright field TEM image of a cross section of a nanostructure formed by the merging of
primary ones. (d) simulated primary nanostructures disposition that yield the
nanostructure in picture above it. (e) HRTEM images show the characteristic (101) and
(100) reticular planes of the PbTiO3 perovskite. The edge dislocations in have a spacing
D = 1.63 nm and Burger vector |b| = 4.9 Å, calculated using the relation |b| = D·sinθ
(relative rotation, θ, is 17.5°).
Figure S2 (c) shows a bright-field TEM image of a cross section of a nanostructure of
~175 nm of lateral size. The profile of the nanostructures presents rounded, irregular
top facets of ~20-25 nm of width, which can be attributed to the primary
nanostructures that merge to form this structure (Figure S2.(d)). The size of these
primary nanostructures seems to be ~25 nm of lateral size, in agreement with the
average lateral size of ~21 nm calculated from the AFM topography images.
Further analysis of the images show more details of the merging process of these
nanostructures. Figure S2 (e) shows two different regions where (100) planes can be
observed with a relative rotation of 17.5° (the edge of each region is marked by the
last planes, in blue). The merging region or tilt boundary presents a number of edge
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dislocations. This kind of low-angle boundary – called a “pure tilt boundary”- is related
to the boundaries found between adjoining crystallites consisting of arrays of
dislocations that are the result of the merging of these smaller crystallites.
As explained before, the formation of these agglomerates of nanostructures is
avoided by depositing the microemulsion on a surface coated with a water-micellar
layer (template layer).
Bibliography
[1]
H. Herrig, R. Hempelmann, Materials Letters 1996, 27, 287;H. Herrig, R.
Hempelmann, Nanostructured Materials 1997, 9, 241.
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