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Presentation Discussion

  • May 21, 2012 | 10:46 p.m.

    Very interesting study. Congratulations.

    Also, your video explanation was very informative and really supplemented your poster.

    This is not really my field, but I wonder what was the relevance of hematite in this study?

    Also, how do you envision your materials to be incorporated into a device? Can you give a real-word example?

  • May 23, 2012 | 03:13 p.m.

    Professor Shin,
    Thank you for your interest in my work.

    Q: What was the relevance of hematite in this study?
    A: Biomineralization systems such as the tooth of the chiton mollusk are known to form magnetite from a hydrated iron (III) oxide precursor (ferrihydrite). This observation coupled with the well-established solution syntheses of iron oxides reported by the colloid community lead us to believe that iron (III) oxide was suitable compound to use for these first studies of bio-inspired growth of transition metal oxides in a hydrogel. The goal is to explore this system for potential applications, but also to use this system to inform the design of hydrogel-based growth systems for other transition metal oxide systems that are currently being studied for such applications (e.g., ZnO, TiO2).

    Q: Also, how do you envision your materials to be incorporated into a device? Can you give a real-word example?
    A: As an excitonic solar cell material, the goal is to use these materials in a bulk heterojunction configuration. Assuming we can form a nanocomposite with good thermal and electrical properties, device fabrication could be undertaken. Currently, a great deal of research effort is aimed at forming bulk heterojunction structures based on ZnO as the electron acceptor material. These materials are assembled on ITO substrates for pairing with a good donor material (e.g., TiO2). Ultimately the success of this approach relies on the donor material having intimate contact with the acceptor, and having structural features that facilitate exciton dissociation, all the while maintaining single crystal character. The a-Fe2O3 phase formed in this study has n-type semiconducting properties and would thus be considered as the electron acceptor material for such a device. It may be possible to grow appropriate donor (p-type) oxides on top of the acceptor (n-type) layer using the bio-inspired crystal growth techniques that I am currently developing.
    Thank you!!

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Icon for: Emily Asenath-Smith


Cornell University
Years in Grad School: 2

Using Nature to Guide Materials Synthesis: Hierarchically Structured Inorganic-Inorganic Nanocomposites Formed in Silica Hydrogel

Alternative energy systems are currently limited by the trade-offs between mutually exclusive sets of properties. For example, more efficient solar cells require nanostructuring, which often come at a cost to the electron mobility. Single crystal materials with nanocomposite structures embody the potential to optimize such related properties independently.

Synthesis models for crystalline materials abound in Nature and include the formation of (bio)minerals by living organisms in a gel-like matrix of biopolymers. Many biominerals, such as seashells, exhibit single crystal characteristics due to hierarchical structuring, but are also composite materials due to the presence of incorporated biopolymers. In this work silica hydrogel is used as a bio-inspired growth matrix for the formation of hierarchically structured a-Fe2O3 (hematite) nanocomposites.

Polarized light microscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used to characterize the iron oxide particles. Based upon these results, the hematite phase was confirmed and the hierarchical structure was revealed in both solution and gel grown crystals. The ability to manipulate the aspect ratio of the subunits by growth in a hydrogel was demonstrated. Etching experiments revealed the gel-grown hematite particles to contain incorporated silica, qualifying them as inorganic-inorganic composites. While the solution grown crystals were stable upon exposure to etching in base, the gel grown particles underwent partial dissolution, revealing an ordered internal structured composed of bundled rods with crystallographic registry and dimensions <100 nm. These length scales, composite nature and crystallographic registry are in agreement with the design criteria for alternative energy systems.