The mixing of polymers and nanoparticles is opening pathways for engineering flexible composites that exhibit advantageous electrical, optical, or mechanical properties. Recent advances reveal routes to exploit both enthalpic and entropic interactions so as to direct the spatial distribution of nanoparticles and thereby control the macroscopic performance of the material. For example, by tailoring the particle coating and size, researchers have created self-healing materials for improved sustainability and self-corralling rods for photovoltaic applications. A challenge for future studies is to create hierarchically structured composites in which each sublayer contributes a distinct function to yield a mechanically integrated, multifunctional material.

We show a simple, robust, chemical route to the fabrication of ultrahigh-density arrays of nanopores with high aspect ratios using the equilibrium self-assembled morphology of asymmetric diblock copolymers. The dimensions and lateral density of the array are determined by segmental interactions and the copolymer molecular weight. Through direct current electrodeposition, we fabricated vertical arrays of nanowires with densities in excess of 1.9 x 10(11) wires per square centimeter. We found markedly enhanced coercivities with ferromagnetic cobalt nanowires that point toward a route to ultrahigh-density storage media. The copolymer approach described is practical, parallel, compatible with current lithographic processes, and amenable to multilayered device fabrication.

A simple technique for precisely controlling the interfacial energies and wetting behavior of polymers in contact with solid surfaces is described. End-functionalized statistical random copolymers of styrene and methylmethacrylate were synthesized, with the styrene fraction f varying from 0 to 1, and were end-grafted onto silicon substrates to create random copolymer brushes about 5 nanometers thick. For f < 0.7, polystyrene (PS) films (20 nanometers thick) rapidly dewet from the brushes when heated well above the glass transition temperature. The contact angle of the resulting polymer droplets increased monotonically with decreasing f. Similar behavior was observed for poly(methylmethacrylate) (PMMA) films but with an opposite dependence on f. The interfacial energies of the random copolymer brushes with PS and PMMA were equal when fwas about 0.6. Thus, precise control of the relative surface affinities of PS and PMMA was possible, demonstrating a way to manipulate polymer-surface interactions.

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tion of individual protein molecules or complexes than an extended, homogeneous surface. Of course, this hypothesis needs to be tested by biological activity. ExperimentalSize-selected metal (Au) clusters, with size between 1 and 100 atoms, were generated by an RF (radio-frequency) magnetron sputtering, gas condensation [20,21] cluster beam source and mass selected to within 5 % by a novel, lateral time-of-flight mass filter to control the cluster size, as described previously [22]. The energetic beam of ionized Au clusters was deposited on a graphite substrate with sufficient kinetic energy to ªpinº the clusters to their individual points of impact on the surface. The underlying mechanism of pinning is the displacement of a surface carbon atom to create a reactive binding site which prevents the characteristic diffusion and aggregation of clusters observed at lower incident energies [15,16]. In this work we found that such monodispersed cluster films were stable not only at room temperature but also at temperatures up to 200 C. They are also stable when placed in an autoclave (130 C for 2 h in high pressure steam) to sterilize the surface. The Au 17 + clusters were produced with an Ar flow of 60 sccm and a He flow of 25 sccm (total gas pressure of 0.4 mbar). Typical sputtering parameters were: RF power 25 W; self-bias voltage of the target 372 V. The cluster samples were imaged in ambient conditions with a bench-top STM (DME Rasterscope 4000). Typical imaging parameters were 0.4 V and 0.4 nA (using mechanically cut Pt/Ir tips). All AFM measurements were collected from a Digital Instruments DI3100 equipped with a Nanoscope IIIa controller and a liquid cell holder. Commercial oxide sharpened silicon nitride tips with nominal spring constant of either 0.38 or 0.60 N m ±1 were used for imaging.