Thomas Thurn-Albrecht

Self-assembly of nanoparticles into structured spherical and networkaggregates

Multi-scale ordering of materials is central for the application of molecular systems in macroscopic devices. Self-assembly based on selective control of non-covalent interactions provides a powerful tool for the creation of structured systems at a molecular level, and application of this methodology to macromolecular systems provides a means for extending such structures to macroscopic length scale. Monolayer-functionalized nanoparticles can be made with a wide variety of metallic and non-metallic cores, providing a versatile building block for such approaches. Here we present a polymer-mediated ‘bricks and mortar’ strategy for the ordering of nanoparticles into structured assemblies. This methodology allows monolayer-protected gold particles to self-assemble into structured aggregates while thermally controlling their size and morphology. Using 2-nm gold particles as building blocks, we show that spherical aggregates of size 97 ± 17u2009nm can be produced at 23u2009°C, and that 0.5–1u2009µm spherical assemblies with (5–40) × 105 individual subunits form at -20u2009°C. Intriguingly, extended networks of ∼50-nm subunits are formed at 10u2009°C, illustrating the potential of our approach for the formation of diverse structural motifs such as wires and rods. These findings demonstrate that the assembly process provides control over the resulting aggregates, while the modularity of the ‘bricks and mortar’ approach allows combinatorial control over the constituents, providing a versatile route to new materials systems.

Electrically induced structure formation and pattern transfer

The wavelength of light represents a fundamental technological barrier to the production of increasingly smaller features on integrated circuits. New technologies that allow the replication of patterns on scales less than 100u2009nm need to be developed if increases in computing power are to continue at the present rate. Here we report a simple electrostatic technique that creates and replicates lateral structures in polymer films on a submicrometre length scale. Our method is based on the fact that dielectric media experience a force in an electric field gradient. Strong field gradients can produce forces that overcome the surface tension in thin liquid films, inducing an instability that features a characteristic hexagonal order. In our experiments, pattern formation takes place in polymer films at elevated temperatures, and is fixed by cooling the sample to room temperature. The application of a laterally varying electric field causes the instability to be focused in the direction of the highest electric field. This results in the replication of a topographically structured electrode. We report patterns with lateral dimensions of 140u2009nm, but the extension of the technique to pattern replication on scales smaller than 100u2009nm seems feasible.

Nanoscopic Templates from Oriented Block Copolymer Films

cylindrical microdomains, an orientation normal to the substrate surface is desirable. Two different approaches are used to this end. In thin films, random copolymers anchored to a substrate can be used to produce a neutral surface. [5] For entropic reasons, the microdomains orient normal to the substrate surface. [6] In a second approach, electric fields were used to orient the cylindrical microdomains parallel to the field lines. [7‐10] The approach relies on the orientation-dependent polarization energy induced when an anisotropic body is placed in an electric field. An anisotropic microphase structure will orient such that the interfaces between the two blocks are aligned parallel to the electric field. In this article it is shown that cylindrical microdomains of a copolymer film can be used to generate an array of ordered nanoscopic pores with well-controlled size, orientation, and structure. To this end, selective etching procedures and a characterization of the samples by quantitative analysis of the X-ray scattering along with electron (EM) and atomic force microscopies (AFM) are described. The processes outlined are shown to be operative over a very large range in sample thickness ranging from 40 nm up to several micrometers. The resulting nanoporous films are promising candidates as membranes with specific transport properties and as templates for electronic and magnetic nanostructured materials. Figures 1A and 1B show AFM images obtained from a

On exfoliation of montmorillonite in epoxy

Nanocomposite formation of octadecyl amine treated montmorillonite clays in epoxy was investigated by small-angle X-ray scattering and atomic force microscopy. When diglycidyl ether of bisphenol A (DGEBA) was cured with equimolar or higher amounts of meta-phenylene diamine (MPDA), only intercalated nanostructures were obtained. Exfoliated nanocomposites were formed with DGEBA cured with less than stoichiometric amounts of MPDA or with auto-polymerization of DGEBA without curing agent. Extragallery crosslinking appeared to be favored with higher curing agent concentrations. Differential scanning calorimetry analyses of the exfoliated nanocomposites indicated that the reaction need not be complete in order to attain exfoliation in the DGEBA/montmorillonite mixture.

High coercivity of ultra-high-density ordered Co nanorod arrays

Abstract We report on magnetic properties of well-ordered ultra-high density (1.25×10 12 /in 2 ) arrays of vertically oriented high-aspect-ratio Co nanorods having a 14xa0nm diameter. The arrays were fabricated by electrodeposition within the pores of a nanoscale template derived from films of diblock copolymers. We find large coercivity enhancement ( H c ≈3xa0kOe at 5xa0K and 800xa0Oe at 300xa0K) relative to a continuous Co film of comparable thickness. The high coercivity in our ordered arrays is contrasted with a distinct decrease of coercivity below ∼50xa0nm rod diameter in a randomly positioned nanorod assembly.