Patterned polymer films via reactive silane infusion-induced wrinkling.

A method for simultaneously patterning and functionalizing thin poly(2-hydroxyethyl methacrylate) films through a reactive silane infusion based wrinkling is developed. Wrinkled patterns with tunable wavelengths on submicrometer size are easily produced over large area surfaces and can express a wide variety of chemical functional groups on the surface. The characteristic wavelength of wrinkling scales linearly with initial film thickness, in agreement with a gradationally swollen film model. Results from X-ray photoelectron spectroscopy confirm that the wrinkled film is composed of two layers: a gradient cross-linked top layer and a uniform un-cross-linked bottom layer. The surface chemical properties of wrinkles can be easily tuned by infusion of different functional silanes. Hierarchical wrinkled patterns with micro/nano structure can be achieved by combining wrinkling with other simple lithography methods. Wrinkled nanopatterns can be used as a mold to transfer the topology to a variety of other materials using nanoimprint lithography.

Poly(9,9-dihexylfluorene) layers grown via surface-directed Ni(0) condensation polymerization.

Poly(9,9-dihexyl fluorene) (PF) layers have been grown from modified silicon and quartz surfaces using Ni(0)-mediated coupling polymerization reactions. The surfaces were functionalized using a silane coupling reagent containing a dibromofluorene unit. 9,9-Diallyl-2,7-dibromo-9H-fluorene (1) was synthesized followed by a facile hydrosilylation with trichlorosilane yielding the desired coupling agent (3,3'-(2,7-dibromo-9H-fluorene-9,9-diyl)bis(propane-3,1-diyl))bis(trichlorosilane) (2). After treatment of the substrate surface with 2, a surface-directed polymerization of 2,7-dibromo-9,9-dihexylfluorene was performed from the functional siloxane surface to producing surfaces coated with a covalently grafted PF layer. The various surfaces were characterized using surface contact angle measurements, film thickness measurements, AFM studies, and fluorescence spectrometer measurements. This simple technique presents a novel and effective means of synthesizing a brush-like layer of a conjugated polymer on silicon and quartz substrates.

Patterned layers of a semiconducting polymer via imprinting and microwave-assisted grafting.

Enhancements in both the rate and extent of grafting of poly(9,9'-n-dihexyl fluorene) (PDHF) onto flat and nanopatterned crosslinked photopolymer films are described. Reactivity of the surfaces toward grafting via the Yamamoto-type Ni(0)-mediated coupling reaction is increased by synthesizing and incorporating 2,7-dibromo-9-fluorenyl methacrylate (DBFM, 2) as a new grafting agent. Varying the concentration of surface-embedded DBFM is shown to control both overall graft formation and fluorescence with a maximum thickness of up to 30 nm and peak emission at 407 nm for 40 wt% loading. In addition, microwave irradiation is introduced as an effective means to drive graft formation and thus allows fabrication of PDHF-functionalized surfaces in as little as 30 min. Both forms of improvement are extended to DBFM-embedded, nanocontact-molded features ranging in size from 100 microm to 100 nm in width and 60 nm in height. Microwave-assisted grafting from these patterned surfaces produces fluorescent features as imaged by optical microscopy and a corresponding increase in feature height as measured by atomic force microscopy.

Chain-end functionalized nanopatterned polymer brushes grown via in situ nitroxide free radical exchange.

The patterning of biologically active materials has been accomplished by the use of imprint lithography of functional photopolymer resins to create controlled nanoscale patterns of a cross-linked photopolymer containing embedded initiator groups. Functionalized polymer brushes consisting of polystyrene and poly(N,N-dimethylacrylamide) were grown from these patterned layers by nitroxide-mediated polymerization. Chain-end functionalization of the brush layer was accomplished by nitroxide radical exchange during the polymerization. Accordingly, brush layers terminated by pyrene and biotin functional groups were obtained by exchange with the appropriate alkoxyamines. The presence of pyrene functionality at the chain ends of the brushes was confirmed by fluorescent emission measurements. Fluorescently labeled streptavidin protein was selectively attached with high selectivity to the patterned biotinylated brush layer through biotin-streptavidin interactions. The functionalized polymer grafted surfaces and nanopatterns have been successfully characterized using a fluorescence spectrophotometer, AFM, SEM, confocal microscopy, and water contact angle measurements.

Disubstituted polyacetylene brushes grown via surface-directed tungsten-catalyzed polymerization.

Disubstituted polyacetylene brushes were grown from modified silicon and quartz surfaces using a transition metal-catalyzed polymerization technique employing tungsten hexachloride/tetraphenyl tin (WCl6/Ph4Sn). The substrate surfaces were initially functionalized with terminal alkyne functional groups by using an alkyne-functionalized silane, O-(propagyloxy)-N-(triethoxysilylpropyl) urethane, as a surface coupling agent. Surface polymerization of 5-decyne under microwave irradiation at 150 degrees C for 30 min was performed on the functional surfaces to produce surfaces consisting of grafted poly(1,2-dibutylacetylene) brushes. The alkyne-functionalized and polymer-coated surfaces were characterized using surface contact angle measurements, film thickness measurements, atomic force microscopy, and X-ray photoelectron spectroscopy, and fluorescence spectrometer measurements were performed to analyze the surfaces at each step of the modification process. This simple technique demonstrates a novel way of synthesizing a poly(1,2-dibutylacetylene) brush layer on silicon substrate, and it has future potential in the fabrication of selectively functionalized surfaces on the nanoscale via this new synthetic approach.

High-resolution soft lithography of thin film resists enabling nanoscopic pattern transfer.

Soft UV-imprint lithography at sub-micron dimensions was achieved in thin films of photopolymer resist. The imprinting was enabled by overcoming resist absorption by polydimethylsiloxane (PDMS) through surface treatment with a layer of (heptadecafluoro-1,1,2,2-tetrahydrodecyl)dimethylchlorosilane. Characterization of the composite molds was done by X-ray photoelectron spectroscopy, nanoindentation, and contact angle measurements. PDMS molds treated with fluoroalkylsilane layer were used to imprint into thin films (70-630 nm) of UV curable resins consisting of either polyurethanes or acrylates, replicating with high fidelity features over the surface of wafer substrates. The use of these highly conformal PDMS molds allowed the patterning of functional materials including gold and aluminium by a simple imprint lithographic technique. This is the first report of the use of modified PDMS surfaces in an imprint process that enables the transfer of sub-micron patterns to underlying layers for device structure fabrication. The patterned features were studied with atomic force microscopy, scanning electron microscopy, and optical microscopy.