Nanocrystalline Ni-Co alloys were synthesized using pulsed electrodeposition from a Watts-type bath, and the various plating parameters were systematically varied to examine their effect on the composition, quality, and structure of the resulting deposits. Increasing the pH of the plating bath and/or the average plating current density increased the Ni content of the deposits, but both of these parameters exhibited rather narrow processing windows for the preparation of high-quality deposits. The addition of saccharin during plating was observed both to reduce the crystallographic texture of the Ni-Co alloys and to refine the grain structure. Owing to the low stacking fault energy of Co, many of the alloy deposits exhibited a large density of nanoscale twins. The unique dual-scale grain and nano-twin structure found here caused apparent discrepancies in the grain size measured by XRD and by other microscopy techniques, and also resulted in unique trends in hardness. This thesis lays the groundwork for future tailoring of nanostructured alloys to explore how twins and stacking faults influence their strength and ductility.

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.

Intermetallic compounds are among the most important solid-state materials because of their diverse physical properties and widespread use in numerous applications. The possibility of integrating intermetallics with emerging nano-technological applications has generated renewed interest in their synthesis. Current capabilities for synthesizing nanocrystalline materials are well-established for single metals and simple binary phases, but very few processes are capable of reliably producing intermetallic nanoparticles. In this dissertation, I describe several new approaches for synthesizing intermetallic nanocrystals. The first approach involves reducing metal salts in aqueous solution using NaBH4 and precipitating a composite of metal nanoparticles. This nanocomposite can then be annealed and rapidly converted to an intermetallic phase. Using this approach, I successfully synthesized several binary and ternary compounds including known magnetic and superconducting materials. The properties of these materials were found to be comparable or superior to materials synthesized using traditional techniques. The second approach, called the polyol process, utilizes high boiling point polyalcohol solvents to heat metal salts in solution and precipitate nanocrystalline powders. Using this process, I was able to access several binary and ternary intermetallics, including two new phases: AuCuSn2 and AuNiSn2. These compounds were isolated as nanocrystals using low temperature solution synthesis techniques, which had not previously been applied to the synthesis of intermetallic compounds. Further investigation of the AuCuSn2 reaction revealed that it proceeds through a unique four step pathway: (1) galvanic reduction of Au(III) to Au(0) nanoparticles with concurrent oxidation of Sn(II) to Sn(IV) (as a SnO2 shell), (2) formation of NiAs-type AuSn along with Cu and Sn nanoparticles using NaBH4 reduction, (3) aggregation and thermal interdiffusion to form a ternary alloy, and (4) nucleation of the ordered intermetallic compound AuCuSn2. The proposed pathway was confirmed by forming AuCuSn2 via reaction of AuSn nanoparticles with Cu nanoparticles formed ex-situ. Additional investigations into the reactivity and kinetics of chemical transformations involving metal nanoparticles have revealed the idea of orthogonal reactivity in multi-component nanoparticle systems, which would allow phase (or metal) specific reactions to take place sequentially within a system of multiple metal nanoparticles.

The fabrication and characterization of a ternary nanocrystalline (NC) stabilized Ni-Cu-P alloy was reported. The complexities of fabrication a low contamination, equiaxed NC material was discussed. For comparison, elemental Ni was prepared via sputter deposition, highlighting the difficulty in fabricating an idealized structure within the confines of the parametric space. An exchange between the ideal grain size distribution and film coalescence was discussed with the ramifications of substrate heat, deposition pressure, and deposition rate considered. These results were then compared to a kinetic model to assess the validity of the model and its ability to capture the complex growth behavior noted between the Ni films.A series of ternary NC Ni-Cu-P thin films were fabricated, characterized, and loaded via in situ annealing and nanoindentation. Examination of the thermal stability behavior revealed differences in precipitation behavior as a function of Cu and P solute content. Furthermore the Ni-40Cu-0.6P (at.%) alloy was noted as the only NC stabilized composition at 550 ©2℗ʻC. The Ni-40Cu-0.3P deposit developed nanoscale precipitates upon annealing to temperatures of 550 ©2℗ʻC which ultimately resided in the matrix. It was found that the ternary Ni-Cu-P films are harder than previously studied binary Ni-1P and Ni-4P (at.%) systems. Adding Cu to the Ni-P system promoted solid solution strengthening which mitigated softening in those binary alloys previously reported.A MEMS device was then employed for in situ thermomechanical testing of the stabilized Ni-40Cu-0.6P film for comparison with a binary Ni-40Cu counterpart. Digital image correlation (DIC) was employed to data mine microstructural evolutions that occurred while the films were loaded. Increased fracture strength was reported with the P solute addition, irrespective of the loading temperature. The ramifications of adding this stabilizing solute were discussed with respect to the fracture profile and microstructural stability.