The utilization of poly(styrene-random-methyl methacrylate), P(S-r-MMA), random copolymer brush surfaces to control the structure of polymer films is demonstrated. Random copolymer brush layers were generated by end anchoring the copolymers onto silicon substrates. By dictating the chemical composition of the random copolymer, the resultant brush layer could be precisely tuned to have properties ranging from pure PS to pure PMMA. This was determined by experiments where PS and PMMA homopolymer films showed dewetting behavior characteristic of the interactions between the homopolymer film and the underlying brush layer. Brushes having a styrene fraction of 0.58 have balanced interactions with PS and PMMA and constitute surfaces that are nonpreferential or neutral to PS and PMMA. The influence of interactions between polymer films and random copolymer brush layers is addressed for three systems. First, the interfacial structures of dPS and dPMMA homopolymer films with the brush layer were examined with neutron reflectivity (NR). The interfacial width between the two layers strongly depended upon the interactions between them. Furthermore, it is observed that penetration of dPMMA to the silicon substrate can occur for cases where the brush layer does not provide a sufficient enthalpic or entropic barrier. Second, atomic force microscopy studies (AFM) show that PS/PMMA demixed films had morphologies that varied greatly with substrate interactions. With annealing, some of these structures rearranged significantly while others remained relatively unchanged. The third type of polymer film examined in this study, diblock copolymers constitutes the main focus of this work. Normally, preferential interactions of one block at an interface induce a parallel orientation of the block copolymer domains. By utilizing neutral random copolymers, preferential segregation of each block is eliminated resulting in a perpendicular orientation of block copolymer domains. This was shown for poly(styrene-block-methyl methacrylate), P(S-b-MMA), block copolymers having lamellar and cylindrical morphologies. Using a wide variety of techniques the structural dependence of these films with annealing time and the effects of commensurability were examined. By controlling the growth of these domains, the generation of novel film structures comprised of perpendicular lamellar and cylindrical domains was achieved.

Hierarchical assembly of materials has attracted significant interest, since it provides opportunities to fabricate novel materials. In this thesis, we investigated three different systems where polymer chains organize hierarchically. First, a semicrystalline triblock copolymer, poly(L-lactic acid- b-ethylene oxide-b-L-lactic acid) (PLLA- b-PEO-b-PLLA), was prepared and the effect of the block-wise construction on the sequential crystallization was investigated by comparison to the corresponding homopolymer blend. In the resultant spherulitic morphology, the crystallization of PEO occurred within the framework established by the PLLA crystals. The preformed PLLA crystals biased the PEO chain orientation and the effect was more significant in the block copolymer system, where PEO chains were covalently anchored to PLLA. Secondly, the influence of the microenvironment of multifunctional chains on their organization was studied. For this investigation, styrene-based linear polymers having two different pendant groups, a carboxylic acid and a neutral group, on every repeat unit were prepared. With alkyl (n-C 10H21-) groups as the neutral pendant, the linear macromolecules assembled into thermally reversible globular aggregates through non-covalent interaction with multifunctional tertiary amines. The aggregates had a structural hierarchy and remained stable without inter-particle crosslinking. In the absence of the alkyl pendant groups, control over the structure and properties of the aggregates was lost. In a third system, the coupled self-assembly of bionanoparticles and block copolymers was investigated. A simple way to incorporate bionanoparticles into a thin film of water-insoluble block copolymer was developed by combining the bionanoparticle adsorption on a polymer film and subsequent annealing under solvent vapor. Through the use of a block copolymer having a positively charged component, the loading of bionanoparticles increased significantly. When highly loaded, a hierarchical co-assembly of the block copolymer and the bionanoparticle was observed where the microphase separation of the block copolymer forced a segregation of bionanoparticles to the grain boundaries, forming a much larger scale structure.

This work studies the stable room temperature structures of metal on metal overlayers. The purpose of this study is twofold. First, the advent of the atomic imaging technique of Scanning Tunneling Microscopy (STM) makes it now possible to directly observe complicated surface structures. This was demonstrated by the success of unraveling the (7$\times$7)-Si(111) surface structure that had withstood the storm of investigation for over 20 years. We wanted to apply this technique to the study of metallic overlayer structures, a field known for its large variety of structures. The second purpose was to investigate the feasibility and to hopefully develop a simple intuitive approach to metallic overlayer structure prediction, an approach that incorporates explicitly the extended nature of the metallic electron system. The Pb and Bi systems have large numbers of valence electrons per atom. Therefore, the electronic effects are expected to be prominent. The difference between the numbers of valence electrons of the respective atoms is relatively small but significant. This provides an opportunity to observe a quantitative variation of the effects. This study constitutes the first STM investigation of the ordered Pb and Bi structures on Cu(001). Many structural features observed using this technique disagree with the existing models derived from the electron diffraction and other scattering experiments. The differences between our observation and the current structural models are qualitative ones, thus demanding a rethinking and supplementation of the basic ideas involved in the construction of the structural models. Observation of the great similarities between the adsorbed Pb and Bi systems, lead to the new modeling approach. In our discussion, the metal adsorbate layers are described as a simple quasi-two-dimensional metal weakly coupled to the host substrate. This is consistent with the familiar notion that all metals exhibits similar properties. Our detailed analysis also discusses the Brillouin zone mechanism as a new way of lowering the energy of a given structure. In the end it enabled us to justify the occurrence of all the ordered Pb and Bi structures on Cu(001). We propose this simple model as a general approach to predict stable structures of metallic overlayers.

Herein we establish a relationship between controlled nanoscale surface interactions and subsequent macromolecular ordering. Chemically heterogeneous striped surfaces of polar silicon oxide and non polar gold are generated over large areas, via glancing angle evaporation on facetted silicon substrates. The processing conditions required for generation of stripe widths comparable to the size of a polymer molecule are outlined. Substrates with 20–30 nm metal linewidths and 40–60 rim stripe periods are prepared. Spin and solution casting of incompatible polymer mixtures of polystyrene (PS) and polymethylmethacrylate (PMMA) on heterogeneous surfaces are found to generate films with unique, substrate directed morphologies dependant on the kinetics of the casting process. Spin cast films posses a surface adsorbed layer of blended composition due to rapid polymer adsorption from solution, while solution cast films phase separate at the substrate/polymer interface on a molecular level. Preferential adsorption of PS to the non polar gold stripes and PMMA to polar silicon oxide stripes is observed at the substrate beneath the macroscopically phase separated domains of the blend components. Preferential adsorption occurs over a large molecular weight range, with a molecular weight dependence on the morphology of the adsorbed polymer lines found. Solution cast films of the symmetric copolymer poly(styrene-block-methylmethacrylate), P(S-b-MMA), on heterogeneous surfaces show lamellar microdomain orientations perpendicular to the substrate plane, parallel to the striping. Commensurability of the block copolymer and substrate stripe periods is found to be essential for producing such a surface directed morphology. The commensurability window depends inversely on the degree of confinement of the morphology, with unconfined films requiring more stringent conditions for surface directed morphology reorientation. The distance over which the orientation of the microdomains persists in thick films is found to depend on the ordering kinetics, scaling with copolymer molecular weight. Confinement effects such as tension and compression and defects in the lateral long range orientation of surface directed lamellar morphologies are observed for slightly incommensurate morphologies, with the amount of strain and defect concentration found to increase with the loss of commensurability.

Disordered materials, such as window glass, powders, gels, concentrated emulsions, differ tremendously in their microscopic detail, there is increasing evidence that they belong to a more general phenomenon known as jamming. The response of disordered materials to applied stresses is a particularly interesting but difficult problem with broad applications in many fields. Using confocal microscopy, we performed systematic and detailed measurements of inter-drop contact forces inside three-dimensional piles of frictionless liquid droplets. We found chain-like structures of contact forces called force chains and measured long-range correlations of the directions and magnitudes of large forces. These correlations arise from the tendency of two largest forces on a droplet to oppose one another. Furthermore, we found that piles whose height was comparable to the length of force chains exhibited greater strain hardening than did tall piles. Thus, we established a connection between the microscopic force network and the elastic response of meso- or macroscopic disordered materials. A statistical model that incorporates the force-balance constraint and that assumes random orientation of contacts, confirmed the tendency of two large forces on a grain to oppose each other, which leads to the formation of force chains in disordered materials. This model also provided direct insight into other issues, such as the role of friction, the effects of stress anisotropy, the difference between two-dimensional materials and three-dimensional materials. The numerical results obtained from the model are qualitatively consistent with earlier simulations and experiments.

A study of InGaAs channel heterostructure field effect transistors (HFETs) on GaAs substrates was undertaken utilizing the low pressure organometallic chemical vapor phase epitaxial (OMVPE) growth technique. Excellent quality HFET material properties were obtained for a split level donor structure, in which the Schottky gate was placed on an undoped AlGaAs layer grown on top of the doped AlGaAs donor layer. A one micron gate length fabrication process was developed to examine the device properties of these materials. A very strong correlation between material characterization results and device performance was observed in all cases. After demonstrating the consistency of the growth and fabrication processes using an $\rm In\sb{0.15}Ga\sb{0.85}As$ channel as a baseline, improvements to the device were undertaken. A delta doping technique was successfully developed and optimized using SIMS and Hall measurements to study the diffusion of the dopant spike. The sheet charge density and device transconductance increased for delta doped material. Increasing the channel indium content reduced the 2DEG mobility, but the expected improvements in transconductance and RF performance were observed. Critical layer thickness (CLT) issues were examined using $\rm In\sb{0.33}Ga\sb{0.67}As$ channel HFETs. Lightly dislocated material still exhibited superior device performance. An asymmetry in dislocation formation was observed, with dislocations forming preferentially in the (011) direction. Devices with a 50 A well width displayed a sharp drop in current in the (0-11) direction. The transconductance and RF properties were not as strongly affected. As the CLT was further exceeded the dislocation network became more symmetric and dense and device performance was severely degraded. A linear channel indium grading methodology was developed to delay the onset of misfit dislocations. Grading from 25-33% produced device properties commensurate with the ungraded 33% indium channel structure, without the asymmetry effects due to dislocation formation. Efforts at developing lattice constant engineered substrates were undertaken. Linear grading to 53% indium at a low growth temperature of 575$\sp\circ$C reduced the amount of three dimensional growth compared to other techniques.