Synthesis and characterization of patterned surfaces and catalytically relevant binary nanocrystalline intermetallic compounds

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Title: Synthesis and characterization of patterned surfaces and catalytically relevant binary nanocrystalline intermetallic compounds
Author: Cable, Robert E.
Abstract: 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 .
URI: http : / /hdl .handle .net /1969 .1 /85793
Date: 2008-10-10

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Synthesis and characterization of patterned surfaces and catalytically relevant binary nanocrystalline intermetallic compounds. Available electronically from http : / /hdl .handle .net /1969 .1 /85793 .

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