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Periodic and aperiodic two-dimensional nanostructures with hierarchical order have been prepared by a combined top–down/bottom–up approach. This method allows 7 nm nanoparticles to be positioned with a accuracy of 10 nm or less, with a separation distance of several micrometers. The Figure is an optical dark field microscopy image of a square arrangement of Au dots on a Si wafer.

A method is presented for generating quasiregular arrays of nanometer-sized noble metal and metal oxide clusters on flat substrates by the use of a polymer template. The approach is of general applicability to other metals and various oxides. In the first step, polymeric micelles with a polar core were generated by dissolution of poly(styrene)-block-poly(2-vinylpyridine) in toluene. These micelles were used as nanocompartments that were loaded with a defined amount of a metal precursor. The metal ions can be reduced in such a way that exactly one elemental or oxidic particle is formed in each micelle, where each particle is of equal size. By dipping a flat substrate into a dilute solution, a monolayer of the micelles was obtained whereby the embedded equally large particles became arranged in a mesoscopic quasihexagonal two-dimensional (2-D) lattice. Exposure to an oxygen plasma allowed removal of the polymer completely, leaving the naked metal particles firmly attached to the substrate in the same quasihexagonal order as in the monomicellar film. A modified procedure in which the precursor salt was not reduced before the plasma treatment yielded clusters of identical size and in the same 2-D order. The size (height) of the clusters could be varied between 1 and 15 nm depending on the concentration of the metal salt. The interparticle distance could be varied between 30 and 140 nm by using block copolymers with different lengths of the blocks. Such lattices of Au particles have been used to bind streptavidin proteins in an ordered array.

the yield of functional circuits was limited to about 80%.More robust constructions should help to circumvent thisproblem in the future.This demonstration of fabrication of a complex, electri-cally and electrochemically functional system uses self-assembly in four ways: i) in recognition of the “lock” and“key” components, by exploiting hydrophobic interactionsbetween surfaceswith complementary shapes; ii)in tailoringthe surface properties of the subunits, by forming a hydro-philic SAM on the exposed surface of gold to prevent coat-ingwith the liquid adhesive;iii) injoining the subunits,byse-lectively forming a thin film of adhesive on the hydrophobicsurfaces by interaction of these surfaces with droplets of thisadhesive suspended in water; iv) in containing the mercurydrop as a coherent structure in the copper cup. The successof this process depends on forming the surfaces of the sub-units designed to interact into precise, complementaryshapes, and on patterning these surfaces into hydrophobicand hydrophilic regions. To achieve electrical contact repro-ducibly, some degree of mechanical freedom was required.The liquid mercury provided the system with the requiredflexibility: as long as the cathode wire of the LED touchedthe mercury,electrical contact was maintained.Simple shape complementarity, in combination with flu-idic shear and gravitational forces, has been used by Smithand co-workers in an elegant demonstration of the fillingof shaped depressions in a planar substrate by small micro-electronic devices.

We have successfully used self-assembling diblock copolymers on semiconductors as nanolithographic masks in dry etching processes. Quantum structures in the range of only a few nanometers have been fabricated, far beyond the limits of conventional optical lithography processes. In a first step, diblock-copolymers in solution are used to generate micelles. These micelles are loaded by a noble metal salt. After dipping of a semiconductor wafer into this solution, a monolayer of ordered micelles is generated over an area of up to 3 x 3 cm 2 . Exposure of the surface to a hydrogen plasma removes all the organic components and only the small metal clusters remain, each 15 nm in diameter and 50-130 nm apart. These clusters can be used as a direct mask for dry etching of semiconductor quantum wells to fabricate quantum dots. With the anisotropic etching of these structures in a reactive ion-beam chlorine plasma, it is possible to create cylinders in GaAs of up to 80 nm height. After annealing and overgrowing these structures by molecular beam epitaxy it should be possible to create quantum dots embedded in barrier material with higher energy gap and to detect photoluminescece light from these quantum structures at low temperatures.

Formation and structural transformation of inverse poly(styrene)-block-poly(2-vinylpyridine) micelles whose polyvinylpyridine core was loaded with HAuCl4 or with elementary gold nanoclusters was studied by combined static and dynamic light scattering. A transformation in the morphology from spherical particles (small Rg/Rh ratio) to large anisomeric objects (large Rg/Rh ratio) was observed by decreasing the concentration of the block copolymer below the critical micelle concentration. At this point, the polymer chains are molecularly dispersed and no longer able to prevent uncontrolled growth of the gold nanoclusters.

Formation of surface-induced nanopattern (SINPAT) in ultrathin diblock copolymer films is studied by scanning force microscopy and Monte Carlo simulation. The pattern is caused by strong adsorption of one of the two blocks forming a quasi-two-dimensional coil while the other block dewets this adsorption layer. Scanning force microscopy allowed to observe an order−disorder transition for a SINPAT film of polystyrene-block-poly(2-vinylpyridine) on mica when the length of the dewetting polystyrene block was varied. The experimental data are compared with the Monte Carlo simulations which demonstrate how the pattern formation depends on the degree of polymerization of the dewetting block and the unfavorable interaction potential between the different components.

Stabilization of nanoparticles by block copolymers does allow accurate control of particle size and inter particle distance, and offers the possibility of producing thin optically transparent films and a new technique for lithography in the nanometer range. The approach is based on micelles of diblock copolymers with a polar core, which are formed in organic solution and whose core is able to bind a transition-metal compound. Chemical conversion of the inorganic species within the nanocompartment is employed to prepare sterically stabilized inorganic crystallites or clusters. The particle size and interparticle distance of these crystallites or clusters can be controlled exclusively by the film forming block copolymer. Controlled coagulation of spherical block copolymer micelles allows to agglomerate several clusters of equal size in one compartment and to prepare strings of the clusters. After film formation the polymer shell can be removed entirely by using an oxygen plasma technique resulting in the deposition of the naked clusters on different substrates without destroying the former particle organization.

Ultrasmall gold particles have been prepared inside the micelles of polystyrene-block-poly(ethylene oxide) and polystyrene-block-poly(2-vinylpyridine) in toluene. Starting point was the formation of a thermodynamically stable dispersion of HAuCl4 or LiAuCl4 in the inverse micelles of the block copolymer which were treated with hydrazine or pyrrole. Analysis of the effect of the reduction agent on the stability of the micelles yielded a simple model for the transformation process involving coagulation of the swelling micelles. Kinetic control of the different steps, i.e., reduction, mineralization, coagulation, film formation, allowed to prepare thin films in which highly uniform gold particles were arranged in yet unknown order. When pyrrole was employed for the reduction, the gold monocrystals got embedded in a shell of polypyrrole.