Vertically aligned nanocomposite (VAN) thin films have recently stimulated
significant research interest to achieve better material functionality or
multifunctionalities. In VAN thin films, both phases grow epitaxially in parallel on given
substrates and form a unique nano-checkerboard structure. Multiple strains, including
the vertical strain which along the vertical interface and the substrate induced strain
which along the film and substrate interface, exist in VAN thin films. The competition of
these strains gives a promise to tune the material lattice structure and future more the
nanocomposite film physical properties. Those two phases in the VAN thin films are
selected based on their growth kinetics, thermodynamic stability and epitaxial growth
ability on given substrates.
In the present work, we investigated unique epitaxial two-phase VAN
(BiFeO3)x:(Sm2O3)1-x and (La0.7Sr0.3MnO3)x:(Mn3O4)1-x thin film systems by pulsed laser
deposition. These VAN thin films exhibit a highly ordered vertical columnar structure
with good epitaxial quality. The strain of the two phases can be tuned by deposition
parameters, e.g. deposition frequency and film composition. Their strain tunability is found to be related directly to the systematic variation of the column widths and domain
structures. Their physical properties, such as dielectric loss and ferromagnetisms can be
tuned systematically by this variation.
The growth morphology, microstructure and material functionalities of VAN thin
films can be varied by modifying the phase ratio, substrate orientation or deposition
conditions. Systematic study has been done on growing (SrTiO3)0.5:(MgO)0.5 VAN thin
films on SrTiO3 and MgO substrates, respectively. The variation of column width
demonstrates the substrate induced strain plays another important role in the VAN thin
film growth.
The VAN thin films also hold promise in achieving porous thin films with ordered
nanopores by thermal treatment. We selected (BiFeO3)0.5:(Sm2O3)0.5 VAN thin films as a
template and get uniformly distributed bi-layered nanopores. Controllable porosity can
be achieved by adjusting the microstructure of VAN (BiFeO3):(Sm2O3) thin films and
the annealing parameters. In situ heating experiments within a transmission electron
microscope column provide direct observations into the phases transformation,
evaporation and structure reconstruction during the annealing.
Systematic study in this dissertation demonstrate that the vertically aligned
nanocomposite microstructure is a brand new architecture in thin films and an exciting
approach that promises tunable material functionalities as well as novel nanostructures.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2011-05-9297 |
| Date | 2011 May 1900 |
| Creators | Bi, Zhenxing |
| Contributors | Wang, Haiyan |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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