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Description:
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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 . |