<p>  </p> <p>A staggering number of problems in materials chemistry relate to controlling the assembly of matter at <10 nm scales, including those with applications in nanoelectronics, energy harvesting, and biomedical device design. It is difficult to achieve precise chemical patterning at the short length scales required for such applications using traditional top-down fabrication methods (<em>e.g., </em>lithographic techniques). On the other hand, biological systems create high-resolution chemical patterns with remarkable efficiency, by assembling simple molecular building blocks with nm-scale features (<em>e.g.,</em> nucleotides, amino acids, lipids) into structurally complex motifs capable of carrying out the diverse functions required for life. </p> <p>Drawing inspiration from the diverse structures and functions of lipids in biological membranes, this work uses lipids to create high-resolution chemical patterns at interfaces, control the growth and self-assembly of nanocrystals, and to facilitate interactions that precisely template nanocrystals at chemically patterned surfaces.</p> <p>Functional alkanes assemble into striped phase monolayers on highly oriented pyrolytic graphite (HOPG), in which the alkyl chains are oriented parallel to the substrate, expressing both the polar and nonpolar regions of the amphiphile at the environmental interface. The same is true for diyne phosphoethanolamine (dPE), a phospholipid with a zwitterionic headgroup. When assembled into striped phases on HOPG, the headgroup zwitterions of dPE are confined in 1-nm-wide rows of functional groups with a pitch of ~7 nm, resulting in ordered arrays of orientable dipoles at the HOPG surface. The chemistry of dimensionally confined functional groups is distinct from bulk solution phase chemistry, and in this case enables powerful directing effects which can be used to template the adsorption of ultranarrow gold nanowires (AuNWs) in precise alignment with the template stripes. </p> <p>Technical grade oleylamine (<em>cis</em>-9-octadecen-1-amine, OLAm, 70% purity) serves as the capping ligand for the AuNWs used in this work, and additionally plays an important role in the assembly of AuNWs at dPE/HOPG surfaces. While technical-grade reagents enable cost-effective and scalable production of materials, variation in the composition of impurities between different batches have significant impacts on nanocrystal morphology and assembly. We show that thermal transitions of alkyl chain impurities (<em>trans</em> and saturated chains) in AuNW ligand shells can be used to regulate AuNW assembly at chemically patterned interfaces. </p> <p>Characterization of OLAm reagents by 1H NMR and mass spectrometry reveals significant and highly variable fractions elaidylamine (ELAm, <em>trans</em>-9-octadecen-1-amine) and octadecylamine (ODAm) between different batches of OLAm. To understand the phase behavior of mixtures of the C18 alkylamines commonly found in technical grade OLAm, we synthesize isomerically pure OLAm and its <em>trans</em> isomer, elaidylamine (ELAm), to generate binary and ternary mixtures with (ODAm), which is commercially available in high purity. Differential scanning calorimetry reveals limited miscibility of the C18 chains, and demonstrates the significant impact of chain composition on the physical properties of mixtures of alkyl chains (<em>e.g.,</em> tech. grade OLAm). Finally, we examine the impacts of <em>trans</em> and saturated alkyl chains on AuNW synthesis. We find that inclusion of ODAm and ELAm in the ligand blend used for AuNW synthesis each result in shorter AuNWs than those synthesized with pure OLAm. We also observe enhanced stability of surface adsorbed AuNWs conferred by <em>trans </em>and saturated chains. </p>

<p>Controlling the surface chemistry of 2D materials is critical for the development of next generation applications including nanoelectronics and organic photovoltaics (OPVs). Further, next generation nanoelectronics devices require very specific 2D patterns of conductors and insulators with prescribed connectivity and repeating patterns less than 10 nm. However, both top-down and bottom-up approaches currently used lack the ability to pattern materials with sub 10-nm precision over large scales. Nevertheless, a class of monolayer chemistry offers a way to solve this problem through controlled long-range ordering with superior sub-10 nm patterning resolution. Graphene is most often functionalized noncovalently, which preserves most of its intrinsic properties (<i>i.e.,</i> electronic conductivity) and allows spatial modulation of the surface. Phospholipids such as 1,2-bis(10,12-tricsadiynoyl)-<i>sn­</i>-glycero-3-phosphoethanolamine (diyne PE) form lying down lamellar phases on graphene where both the hydrophilic head and hydrophobic tail are exposed to the interface and resemble a repeating cross section of the cell membrane. Phospholipid is made up of a complex headgroup structure and strong headgroup dipole which allows for a diverse range of chemistry and docking of objects to occur at the nonpolar membrane, these principals are equally as important at the nonpolar interface of 2D materials. A key component in the development of nanoelectronics is the integration of inorganic nanocrystals such as nanowires into materials at the wafer scale. Nanocrystals can be integrated into materials through templated growth on to surface of interest as well as through assembly processes (i.e. interfacial adsorption). </p> <p>In this work, I have demonstrated that gold nanowires (AuNWs) can be templated on striped phospholipid monolayers, which have an orientable headgroup dipoles that can order and straighten flexible 2-nm diameter AuNWs with wire lengths of ~1 µm. While AuNWs in solution experience bundling effects due to depletion attraction interactions, wires adsorb to the surface in a well separated fashion with wire-wire distances (e.g. 14 or 21 nm) matching multiples of the PE template pitch. This suggests repulsive interactions between wires upon interaction with dipole arrays on the surface. Although the reaction and templating of AuNWs is completed in a nonpolar environment (cyclohexane), the ordering of wires varies based on the hydration of the PE template in the presence of excess oleylamine, which forms hemicylindrical micelles around the hydrated headgroups protecting the polar environment. Results suggest that PE template experience membrane-mimetic dipole orientation behaviors, which in turn influences the orientation and ordering of objects in a nonpolar environment.</p> <p>Another promising material for bottom-up device applications is MoS₂substrates due to their useful electronic properties. However, being able to control the surface chemistry of different materials, like MoS₂, is relatively understudied, resulting in very limited examples of MoS₂substrates used in bottom-up approaches for nanoelectronics devices. Diyne PE templates adsorb on to MoS₂­in an edge-on conformation in which the alkyl tails stack on top of each other increasing the overall stability of the monolayer. A decrease in lateral spacing results in high local concentrations of orientable headgroups dipoles along with stacked tails which could affect the interactions and adsorption of inorganic materials (i.e. AuNW) at the interface. </p> <p>Here, I show that both diyne PE/HOPG and diyne PE/MoS₂ substrates can template AuNW of various lengths with long range ordering over areas up to 100 µm². Wires on both substrates experience repulsive interactions upon contact with the headgroup dipole arrays resulting in wire-wire distances greater than the template pitch (7 nm). As the wire length is shortened the measured distance between wires become smaller eventually resulting in tight packed ribbon phases. Wires within these ribbon phases have wire-wire distances equal to the template. Ribbon phases occur on diyne PE/HOPG substrates when the wire length is ~50 nm, whereas wire below ~600 nm produce ribbon phases on diyne PE/MoS_2­substrates. </p> <p>Another important aspect to future scientific development is the catalysis of organic reactions, specifically oxygenation of organic sulfides. Sulfide oxygenation is important for applications such as medicinal chemistry, petroleum desulfurization, and nerve agent detoxification. Both reaction rates and the use of inexpensive oxidants and catalysts are important for practical applications. Hydrogen peroxide and <i>tert</i>-butyl hydroperoxide are ideal oxidants due to being cost efficient and environmentally friendly. Hydrogen peroxide can be activated through transition metal base homogeneous catalysts. Some of the most common catalysts are homo- and hetero-polyoxometalates (POMs) due their chemical robustness. Heptamolybdate [Mo₇O₂₄]^6-is a member of the isopolymolybdate family and its ammonium salt is commercially available and low in cost.²² Heteropolyoxometalates have been widely studied as a catalyst for oxygenation reactions whereas heptamolybdate has been rarely studied in oxygenation reactions. </p> <p> Here I report sulfide oxygenation activity of both heptamolybdate and its peroxo derivate [Mo₇O₂₂(O₂)₂]^6-. Sulfide oxygenation of methyl phenyl sulfide (MPS) by H₂O₂to sulfoxide and sulfone occurs rapidly with 100 % utility of H₂O₂ in the presence of [Mo₇O₂₂(O₂)₂]^6-, suggesting the peroxo adduct is an efficient catalyst. However, heptamolybdate is a faster catalyst compared to [Mo₇O₂₂(O₂)₂]^6- for MPS oxygenation and all other sulfides tested under identical conditions. Pseudo-first order <i>k</i>_cat constants from initial rate kinetics show that [Mo₇O₂₄]^6-catalyzes sulfide oxygenation faster. The significant difference in the <i>k</i>_cat suggests differences in the active catalytic species, which was characterized by both UV-Vis and electrospray ionization mass spectrometry. ESI-MS suggest that the active intermediate of [Mo₇O₂₄]^6-under catalytic reaction conditions for sulfide oxygenation by H₂O₂ is [Mo₂O₁₁]^2-. These results show that heptamolybdate is a highly efficient catalyst for H₂O₂oxygenation of organic sulfides.</p>