Materials Science and Engineering Commons^™

Organic Materials And Organic/Inorganic Heterostructures In Atom Probe Tomography, Derk Joester, Andrew C. Hillier, Yi Zhang, Ty J. Prosa

Andrew C. Hillier

Nano-scale organic/inorganic interfaces are key to a wide range of materials. In many biominerals, for instance bone or teeth, outstanding fracture toughness and wear resistance can be attributed to buried organic/inorganic interfaces. Organic/inorganic interfaces at very small length scales are becoming increasingly important also in nano and electronic materials. For example, functionalized inorganic nanomaterials have great potential in biomedicine or sensing applications. Thin organic films are used to increase the conductivity of LiFePO4 electrodes in lithium ion batteries, and solid electrode interphases (SEI) form by uncontrolled electrolyte decomposition. Organics play a key role in dye-sensitized solar cells, organic photovoltaics, and …

The Physicochemical Origins Of Coincident Epitaxy In Molecular Overlayers: Lattice Modeling Vs Potential Energy Calculations, Julie A. Last, Daniel E. Hooks, Andrew C. Hillier, Michael D. Ward

Andrew C. Hillier

The physicochemical basis for epitaxial stabilization of coincident molecular overlayers is illustrated by comparison of optimum overlayer-substrate configurations calculated with potential energy (PE) methods and a simple geometric lattice misfit modeling algorithm (EpiCalc) that neglects molecular orientations and intermolecular potentials. Using â-bis(ethylenedithio)tetrathiafulvalene triiodide (â-ET2I3), perylenetetracarboxylic diimide (PTCDI), and perylenetetracarboxylic dianhydride (PTCDA) overlayers on a graphite substrate as examples, both methods predict identical optimum azimuthal overlayer orientations for each overlayer that also agree with experimental observations. PE calculations for three hypothetical PTCDA overlayers, with identical lattice parameters but different molecular orientations, predict coincidence at the same azimuthal orientation for all overlayers. …

Epitaxially Driven Assembly Of Crystalline Molecular Films On Ordered Substrates, Julie A. Last, Andrew C. Hillier, Daniel E. Hooks, Jeffrey B. Maxson, Michael D. Ward

Andrew C. Hillier

Crystalline, molecularly thick organic films mimicking layer motifs observed in bulk crystals of conducting (ET)2X charge-transfer salts (ET ) bis(ethylenedithiolo)tetrathiafulvalene, X ) I3, ReO4) form on highly oriented pyrolytic graphite (HOPG) electrodes upon electrochemical oxidation of ET in electrolytes containing I3 - or ReO4 - anions. The assembly of these molecular overlayers can be observed directly by in situ atomic force microscopy (AFM), and their structures can be deduced from lattice images obtained by AFM under growth conditions. AFM data reveal two different (ET)2I3 overlayers that are distinguished by the orientation of the ET molecules. One of these overlayers (type …

Epitaxial Interactions Between Molecular Overlayers And Ordered Substrates, Andrew C. Hillier, Michael D. Ward

Andrew C. Hillier

A framework for evaluating the epitaxy of crystalline organic overlayers of generic symmetry on ordered substrates is described, which combines a computationally efficient analytical method for explicit determination of the type of epitaxy ~i.e., commensurism, coincidence, or incommensurism! and overlayer azimuthal orientation with an analysis of the elastic properties of the overlayer and the overlayer-substrate interface. The azimuthal orientations predicted by the analytical method agree with values predicted by semiempirical potential-energy calculations and observed experimentally for previously reported organic overlayers which are demonstrated here to be coincident. Calculations based on this analytical approach are much less computationally intensive than potential-energy …

Nucleation And Growth Of Molecular Crystals On Molecular Interfaces Role Of Chemical Functionality And Topography, Phillip W. Carter, Lynn M. Frostman, Andrew C. Hillier, Michael D. Ward

Andrew C. Hillier

Nanoscale Surface Topography And Growth Of Molecular Crystals: The Role Of Anisotropic Intermolecular Bonding, Phillip W. Carter, Andrew C. Hillier, Michael D. Ward

Andrew C. Hillier

Atomic force microscopy (AFM) and phase measurement interferometric microscopy (PMIM) of the molecular crystals a-glycine and (TMTSF)2C104 (TMTSF = tetramethyltetraselenafulvalene) reveal that crystal topography, growth, and etching reflect the relative strengths of solid state intermolecular bonding. The (OlO), (110), and (01 1) faces of a-glycine exhibit terraces, ledges, and kinks that can be interpreted on the basis of intermolecular hydrogen bonding in these planes. A strong preference for [ 1001 ledges on the (001) face of (TMTSF)zC104 is a consequence of strong intermolecular charge transfer interactions between TMTSF molecules stacked along this direction. Dynamic in situ measurements of growth and …

Electrocrystallization Of An Ordered Organic Monolayer: Selective Epitaxial Growth Of B-(Et)213 On Graphite, Andrew C. Hillier, Jeffrey B. Maxson, Michael D. Ward

Andrew C. Hillier

The fabrication of highly ordered organic thin films has received considerable attention in attempts to develop materials for molecular-based electronic devices, sensors, displays, and logic e1ements.l Examples of twodimensional films with potentially desirable electronic properties include self-assembled mono- and multilayers with redox-active components2 and thin films of organic dyes grown by molecular beam epitaxy on van der Waals substrates such as graphite, MoS2, and SnSza3 Successful approaches to the manufacturing of devices based on organic thin films will ultimately rely on the development of convenient fabrication methods as well as rigorous control of the supramolecular structure of the thin-film assembly.

Scanning Electrochemical Mass Sensitivity Mapping Of The Quartz Crystal Microbalance In Liquid Media, Andrew C. Hillier, M. D. Ward

Andrew C. Hillier

The mass sensitivity distribution of the quartz crystal microbalance, denoted S(r,8), was determined in situ for pianopiano and plano-convex Aleut quartz resonators. The method involved measuring the frequency change associated with localized mass deposits created by electrochemical deposition using a scanning microelectrode in close proximity to the QCM eiectroded surface. Complete mathematical descriptions of S(r,8) were obtained from the measured data under conditions commonly encountered in QCM experiments. Our experimental resuits suggest that crystal contouring increases sensitivity toward the resonator center while reducing the extent of field fringing. Increaslng solution viscosity reduces the sensitivity to mass changes in the center …