| Summary: | As devices and new technologies continue to shrink, nanocrystalline multi-metal
compounds are becoming increasingly important for high efficiency and
multifunctionality. However, synthetic methods to make desirable nanocrystalline
multi-metallics are not yet matured. In response to this deficiency, we have developed
several solution-based methods to synthesize nanocrystalline binary alloy and
intermetallic compounds. This dissertation describes the processes we have developed,
as well as our investigations into the use of lithographically patterned surfaces for
template-directed self-assembly of solution dispersible colloids.
We used a modified polyol process to synthesize nanocrystalline intermetallics of
late transition and main-group metals in the M-Sn, Pt-M', and Co-Sb systems. These
compounds are known to have interesting physical properties and as nanocrystalline
materials they may be useful for magnetic, thermoelectric, and catalytic applications.
While the polyol method is quite general, it is limited to metals that are somewhat easy
to reduce. Accordingly, we focused our synthetic efforts on intermetallics comprised of highly electropositive metals. We find that we can react single-metal nanoparticles with
zero-valent organometallic Zinc reagents in hot, coordinating amine solvents via a
thermal decomposition process to form several intermetallics in the M''-Zn system.
Characterization of the single-metal intermediates and final intermetallic products shows
a general retention of morphology throughout the reaction, and changes in optical
properties are also observed. Following this principle of conversion chemistry, we can
employ the high reactivity of nanocrystals to reversibly convert between intermetallic
phases within the Pt-Sn system, where PtSn2 ↔ PtSn ↔ Pt3Sn. Our conversion
chemistry occurs in solution at temperatures below 300 °C and within 1 hour,
highlighting the high reactivity of our nanocrystalline materials compared to the bulk.
Some evidence of the generality for this process is also presented.
Our nanocrystalline powders are dispersible in solution, and as such are
amenable to solution-based processing techniques developed for colloidal dispersions.
Accordingly, we have investigated the use of lithographically patterned surfaces to
control the self-assembly of colloidal particles. We find that we can rapidly crystallize
2-dimensional building blocks, as well as use epitaxial templates to direct the formation
of interesting superlattice structures comprised of a bidisperse population of particles.
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