AVS2001 Session TF+BI-ThM: Bioactive and Organic/Inorganic Thin Films

Thursday, November 1, 2001 8:20 AM in Room 123

Thursday Morning

Start	Invited?	Item
8:20 AM		TF+BI-ThM-1 Self-aligned Deposition and Patterning of Biologically-active Polymer Thin Films B.H. Augustine, S.M. Ramirez, O.D. Lees (James Madison University) High-resolution patterning and microfabrication of polymeric and other soft materials is challenging since traditional photolithographic methods require organic solvents to remove photoresist. These solvents typically also dissolve or degrade biological and polymeric surfaces which one might pattern. We report selective dewetting using microcontact printing (µ-CP), micromolding in capillaries (MIMIC), and solvent assisted micromolding (SAMIM) techniques to pattern thin films of the biodegradable copolymer, poly-3-hydroxybutyrate-co-3-hydroxyvalerate [P(3HB-3HV)] onto glass, silicon, and Au coated silicon substrates. Film thicknesses range from 20 mn to over 700 nm, with minimum feature sizes as small as 3 µm. Dense 100 nm thick films with sub-10 µm features can be patterned in as few as two minutes for the entire processing resulting in potentially high throughput processing. Thin film microstructure can be dramatically changed by controlling deposition parameters such as solvent concentration, feature aspect ratio, and polarity of the solvent. While we report microfabrication techniqes for a specific biodegradable polymer system, we will also comment on extending these techniques to other polymer systems and the issues affecting the profound change in polymer microstructure using these three different patterning techniques.
9:00 AM	Invited	TF+BI-ThM-3 Desorption and Processing of Bioactive Thin Films A. Chilkoti (Duke University) I will describe methods to micro- and nano-pattern proteins and other biological ligands onto self-assembled monolayers (SAMs) and polymers for application in multianalyte biosensors, patterned biomaterials, and protein chips. These methods include: (1) Light-activated micropatterning (LAMP), which exploits spatially precise, light-activated deprotection of affinity ligands on functionalized SAMs to achieve step-and-repeat patterning of multiple biomolecules. (2) Microstamping onto activated polymer surfaces (MAPS), which involves surface-selective functionalization of polymers, followed by microcontact printing of reactive biological ligands. (3) Thermodynamically addressable reversible patterning (TRAP) which uses patterned domains with different surface energies as a thermodynamic address to direct the attachment of proteins and other biomolecules from solution. TRAP functions by the selective adsorption of nanoclusters of an elastin fusion protein above its phase transition temperature specifically on patterned hydrophobic regions, but not on a hydrophilic background. Unlike other methods for protein patterning, TRAP is reversible, and modulating the solution environment (e.g., T, ionic strength), can erase protein patterns. A theme illustrated by this talk will be the interdisciplinary convergence of surface chemistry and spectroscopic characterization (XPS, TOF-SIMS, and evanescent optical techniques) with molecular biology.
9:40 AM	Invited	TF+BI-ThM-5 Nano-scale Fabrication Using Organic Thin Films C.B. Gorman (North Carolina State University) We will show how a combination of lithographic methods on organic self-assembled monolayers (SAMs) can be used to form chemically well-defined, patterned surfaces. These surfaces can form the basis of nanometer-scale, molecular electronic devices. The talk will focus on (1)the engineering and the chemistry behind nanometer scale lithography on SAMs including an assessment of its strengths and limitations, (2) why the control of chemical functionality is so important for a true, nanometer-scale process and (3) demonstration of new, molecular electronic behaviors with potential applicability in devices.
10:20 AM		TF+BI-ThM-7 Hot-Filament Chemical Vapor Deposition of Fluorocarbon-Organosilicon Copolymer Thin Films S.K. Murthy, K.K. Gleason (Massachusetts Institute of Technology) Hot-filament chemical vapor deposition, a non-plasma technique, has been used to deposit copolymer thin films consisting of fluorocarbon (CF₂) groups and organosilicon groups (Si(CH₃)₂ - O) at rates of approximately 250 angstroms/min. The synthesis of such copolymers by solution chemistry techniques is difficult since one component (PTFE) is normally synthesized by free radical polymerization techniques and the other (PDMS) by ionic polymerization methods. The presence of covalent bonds between the fluorocarbon and organosilicon moieties in the thin films has been confirmed by Infrared, X-Ray Photoelectron (XPS) and solid-state ²⁹Si, ¹⁹F, and ¹³C Nuclear Magnetic Resonance (NMR) spectroscopy. These techniques also indicate retention of methyl groups from the siloxane precursor. The XPS data shows that all of the silicon present in the films is in the +2 oxidation state and that the ratio of silicon to CF₂ groups is approximately 1:0.86 based on atomic composition. Further, the NMR data suggest that the copolymer films are blocky in nature, consisting of networked chains having multiple fluorocarbon groups interspersed between siloxane groups. Atomic Force Microscopy of the films showed that the roughness of these copolymer films is in-between that of homopolymeric fluorocarbon and organosilicon films made by the same technique.
10:40 AM		TF+BI-ThM-8 Polyatomic Ion Deposition of Gradient Thin Films: A New Method for Combinatorial Materials L. Hanley, M.B.J. Wijesundara, E.R. Fuoco (University of Illinois at Chicago) Beams of gaseous ions are used for the growth and modification of interfaces in a wide variety of applications. For example, we have previously shown that mass-selected CF₃⁺, C₃F₅⁺, and Si₂O(CH₃)₃⁺ ions can be employed for the growth and modification of organic thin films on polymer and metal surfaces.footnote1We demonstrate here that polyatomic ion beams can also be employed to create chemical gradient thin films by variation of the ion fluence across the substrate. We use mass-selected C₃F₅⁺ ion deposition in vacuum to create a fluorocarbon gradient film on a polymethylmethacrylate substrate. X-ray photoelectron spectroscopy shows a continuous change in the surface chemistry from that of the native polymer to a fluorocarbon film. The contact angle varies from ~75° to ~95° across the gradient surface. We also examine the production of fluorocarbon films on polystyrene, silicon, and aluminum surfaces from C₃F₅⁺ ions. Finally, we discuss the general feasibility of producing chemical gradients surfaces from polyatomic ion beams. footnote1M.B.J. Wijesundara, Y. Ji, B. Ni, S.B. Sinnott, L. Hanley, J. Appl. Phys. 88 (2000) 5004
11:00 AM		TF+BI-ThM-9 Plasma Sputtering Deposition of Metals on PAMAM Dendrimer Monolayer A. Rar, M. Curry, F. Xu, J.A. Barnard, S.C. Street (University of Alabama) A number of nanotechnology applications require development of thin, flat surface films with well-regulated mechanical and tribological properties. A promising approach for this is metal layer deposition on PAMAM dendrimer underlayers. Previously, we demonstrated improvement in mechanical and morphological properties for Au, Co, and Cr films deposited by evaporation onto dendrimer self-assembled monolayers. In this paper we will discuss formation of metallic layers on dendrimer by plasma sputtering deposition. We will show the influence of higher incoming kinetic energy of the metal atoms on dendrimer structure and chemical changes at the interface. The evolution of the dendrimer interlayer during metal deposition was analyzed with XRR, the surface morphology of deposited films with AFM, the chemical interaction between deposited metal and dendrimers with XPS and RAIRS. Thin Cr layers obtained by plasma sputtering interact with the dendrimer interlayer in essentially the same way as films deposited by evaporation. Significant differences were found for Cu/dendrimer layers prepared by plasma sputtering deposition compared to less energetic thermal evaporation. In the first case more than 1/3 of the nitrogen atoms in the dendrimer adlayer form nitride-like chemical states. Thermal evaporation shows less pronounced influence on the N1s XPS peak.