Cable, Robert E. (2007-12). Synthesis and characterization of patterned surfaces and catalytically relevant binary nanocrystalline intermetallic compounds. Doctoral Dissertation. Thesis uri icon

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.
  • 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.

publication date

  • December 2007