Controlled Molecular Assembly via Dynamic Confinement of Solvent.

Assembly from ultrasmall solution droplets follows a different dynamic from that of larger scales. Using an independently controlled microfluidic probe in an atomic force microscope, subfemtoliter aqueous droplets containing polymers produce well-defined features with dimensions as small as tens of nanometers. The initial shape of the droplet and the concentration of solute within the droplet play significant roles in the final assembly of polymers due to the ultrafast evaporation rate and spatial confinement by the small droplets.

Three-Dimensional Nanoprinting via Direct Delivery.

Direct writing methods are a generic and simple means to produce designed structures in three dimensions (3D). The printing is achieved by extruding printing materials through a nozzle, which provides a platform to deliver a wide range of materials. Although this method has been routinely used for 3D printing at macroscopic scales, miniaturization to micrometer and nanometer scales and building hierarchical structures at multidimensional scales represent new challenges in research and development.

Three-Dimensional Nanoprinting via Scanning Probe Lithography-Delivered Layer-by-Layer Deposition.

Three-dimensional (3D) printing has been a very active area of research and development due to its capability to produce 3D objects by design. Miniaturization and improvement of spatial resolution are major challenges in current 3D printing technology development. This work reports advances in miniaturizing 3D printing to the nanometer scale using scanning probe microscopy in conjunction with local material delivery.

Nanoscale chemical imaging by photoinduced force microscopy.

Correlating spatial chemical information with the morphology of closely packed nanostructures remains a challenge for the scientific community. For example, supramolecular self-assembly, which provides a powerful and low-cost way to create nanoscale patterns and engineered nanostructures, is not easily interrogated in real space via existing nondestructive techniques based on optics or electrons. A novel scanning probe technique called infrared photoinduced force microscopy (IR PiFM) directly measures the photoinduced polarizability of the sample in the near field by detecting the time-integrated force between the tip and the sample.

High-throughput directed self-assembly of core-shell ferrimagnetic nanoparticle arrays.

Magnetic nanoparticles (MNPs) provide a set of building blocks for constructing stimuli-responsive nanoscale materials with properties that are unique to this scale. The size and the composition of MNPs are tunable to meet the requirements for a range of applications including biosensors and data storage. Although many of these technologies would significantly benefit from the organization of nanoparticles into higher-order architectures, the precise placement and arrangement of nanoparticles over large areas of a surface remain a challenge.

Broad-spectrum antimicrobial supramolecular assemblies with distinctive size and shape.

With the increased prevalence of antibiotic-resistant infections, there is an urgent need for innovative antimicrobial treatments. One such area being actively explored is the use of self-assembling cationic polymers. This relatively new class of materials was inspired by biologically pervasive cationic host defense peptides.

Self-assembled ferrimagnet--polymer composites for magnetic recording media.

A self-assembled magnetic recording medium was created using colloidal ferrimagnetic building blocks. Monodisperse cobalt ferrite nanoparticles (CoFe(2)O(4)) were synthesized using solution-based methods and then stabilized in solution using the amphiphilic diblock copolymer, poly(acrylic acid)-b-poly(styrene) (PAA-PS). The acid groups of the acrylate block bound the polymer to the nanoparticle surface via multivalent interactions, while the styrene block afforded the magnetic nanoparticle--polymer complex solubility in organic solvents.

Nanoscale three-dimensional patterning of molecular resists by scanning probes.

For patterning organic resists, optical and electron beam lithography are the most established methods; however, at resolutions below 30 nanometers, inherent problems result from unwanted exposure of the resist in nearby areas. We present a scanning probe lithography method based on the local desorption of a glassy organic resist by a heatable probe. We demonstrate patterning at a half pitch down to 15 nanometers without proximity corrections and with throughputs approaching those of Gaussian electron beam lithography at similar resolution.

Placement and orientation of individual DNA shapes on lithographically patterned surfaces.

Artificial DNA nanostructures show promise for the organization of functional materials to create nanoelectronic or nano-optical devices. DNA origami, in which a long single strand of DNA is folded into a shape using shorter 'staple strands', can display 6-nm-resolution patterns of binding sites, in principle allowing complex arrangements of carbon nanotubes, silicon nanowires, or quantum dots. However, DNA origami are synthesized in solution and uncontrolled deposition results in random arrangements; this makes it difficult to measure the properties of attached nanodevices or to integrate them with conventionally fabricated microcircuitry.

Monolayered organosilicate toroids and related structures: A phase diagram for templating from block copolymers.

Here we report the controlled generation of micelle-templated organosilicate nanostructures resulting from self-assembly of a block copolymer/organosilicate mixture followed by organosilicate vitrification and copolymer thermolysis. Variation of solution condition and the copolymer/organosilicate mixture composition generates widely different film morphologies ranging from toroids to linear features to contiguous nanoporous monolayers. The use of reactive organosilicates for block copolymer templation generates functional inorganic nanostructures with thermal and mechanical stability.

Atomically flat gold on elastomeric substrate.

We present a procedure to fabricate extremely smooth Au films supported on thin elastomeric (PDMS) substrates. Minimum rms roughness and largest grain size are obtained using Si wafers, coated with native oxide and release layers, as templates for the growth of thermally evaporated Au films. The wafers are held at a temperature of 300 degrees C during deposition.

Patterned polyfluorene surfaces by functionalization of nanoimprinted polymeric features.

A new procedure is described for surface grafting polymer brushes by step-growth polymerization from initiator-embedded polymeric thin films and micron- and nanometer-scale patterns. An imprint lithographic process, nanocontact molding, was used to prepare thin patterned cross-linked polyacrylate network films on silicon wafers that incorporated 4-bromostyrene in the networks. These networks present reactive 4-bromophenyl functionality at the surface that act as attachment sites for the subsequent Ni(0)- mediated step-growth condensation polymerization of 2,7-dibromo-9,9-dihexylfluorene The step-growth polymerization medium consisted of 2,7-dibromo-9,9-dihexylfluorene, Ni(0)-catalyst, and bipyridine in a toluene/dimethylformamide solvent mixture.

Controlling nanowear in a polymer by confining segmental relaxation.

Molecular relaxation of a copolymer designed for nano-electromechanical systems was chemically confined by varying the spacing between cross-links, delta(c). A critical cross-link spacing of 1-3 nm marks a transition in the nano-mechanical properties evaluated by atomic force microscopy. The transition reveals an interplay between the cross-link spacing and the length scale for backbone relaxation, xi(alpha), in cooperatively rearranging regions.

Interfacial glass transition profiles in ultrathin, spin cast polymer films.

Interfacial glass transition temperature (T(g)) profiles in spin cast, ultrathin films of polystyrene and derivatives were investigated using shear-modulated scanning force microscopy. The transitions were measured as a function of film thickness (delta), molecular weight, and crosslinking density. The T(g)(delta) profiles were nonmonotonic and exhibited two regimes: (a) a sublayer extending about 10 nm from the substrate, with T(g) values lowered up to approximately 10 degrees C below the bulk value, and (b) an intermediate regime extending over 200 nm beyond the sublayer, with T(g) values exceeding the bulk value by up to 10 degrees C.