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Nanoscience has become an extremely popular field, where many researchers from different disciplines combine their talents and efforts. In many projects, the ability to pattern surfaces at very small (sub-100 nm) lengthscales, and to control the chemical and physical properties of surfaces at this level, is crucial. However, many lithographic techniques do not inherently allow control over the surface chemistry. Nanotechnology has a strong record in reporting breakthroughs in lithographic methods as well as physical studies of nanostructured surfaces.

In this special issue, we aim to bring together a number of authors who are leaders in the field of modifying surfaces using chemical techniques and utilizing surface chemistry to build (pseudo-)3D structures. A range of so-called soft-lithographic techniques, relying on self-assembly, self-organization, polymer chemistry, and chemical bond formation, will be introduced in this issue. We hope that an overview of the stunning progress of these methods will act as an eye-opener to many other researchers, who might be able to use some of these ideas in their projects.

Guest Editors: Wilhelm Huck and Lars Samuelson

A brief overview is provided of recent developments in the use of block copolymer self-assembly to create morphologies that may be used to template the fabrication of nanostructures in other materials. The patterning of semiconductor surfaces using block copolymer film masks and the production of high-density arrays of magnetic domains are discussed. The use of block copolymer micelles as 'nanoreactors' to prepare metal and semiconductor nanoparticles is considered, and methods to pattern nanoparticles are highlighted. A number of approaches to design nanocapsules are summarized. Finally, applications of bulk nanostructures to make mesoporous materials with controlled pore structures and sizes, or to create photonic crystals, are discussed.

This paper reports on the directed self-assembly of nanoparticles onto charged surface areas with a resolution of 200 nm from the liquid phase and 100 nm from the gas phase. The charged areas required for this type of nanoxerographic printing were fabricated using a parallel method that employs a flexible, electrically conductive, electrode to charge a thin-film electret. As electrodes, we used metal-coated polymeric stamps and 10 µm thick doped silicon wafers carrying a pattern in topography. Each electrode was brought in contact with a thin-film electret on an n-doped silicon substrate. The charge pattern was transferred into the thin-film electret by applying a voltage pulse between the conductive electrode and the silicon substrate. Areas as large as 1 cm² were patterned with charge with 100 nm scale resolution in 10 s. These charge patterns attract nanoparticles. A liquid-phase assembly process where electrostatic forces compete with disordering forces due to ultrasonication has been developed to assemble nanoparticles onto charged based receptors in 10 s from a liquid suspension. A gas-phase assembly process was developed that uses a transparent particle assembly module to direct particles towards the charged surface while monitoring the total charge of assembled particles. Nanoparticles were generated using a tube furnace by evaporation and condensation at the outlet. The electrostatically directed assembly of 10–100 nm sized metal (gold, silver) and 30 nm sized carbon particles was accomplished with a resolution 500–1000 times greater than the resolution of existing xerographic printers.

Ring-opening metathesis polymerization (ROMP) of norbornene thiol derivative 1 and bis(thioether) 2 was carried out both on monolayer-protected gold nanoclusters (MPCs) and at self-assembled monolayers (SAMs) on a gold(111) surface. Metathesis polymerization was carried out by using the Grubbs catalyst. Mixed monolayer-protected MPCs of 1 were prepared using 1 and dodecanethiol as the ligands. ROMP on the MPCs showed both inter-and intra-particle polymerization. In-plane polymerization of SAMs of 1 and 2 on flat gold was carried out. Electrochemical impedance spectroscopy (EIS) indicated that the SAMs had retained their thickness and order after polymerization. Furthermore, EIS showed that the polymerized layers were more resistant to solvent-assisted desorption. Electrochemical reductive desorption studies showed a more negative peak potential for SAMs of 1 upon polymerization, which is attributed to the formation of multiple attachment points, decreased solubility and possibly increased resistance against permeation of the electrolyte.

We report on the selective area metal–organic vapour phase epitaxial growth of an InGaAs nano-pillar array on a partially masked InP(111)B substrate. This technique is very promising as a way to form semiconductor two-dimensional photonic crystals (2DPCs) suitable for infrared optical fibre communication. We successfully formed uniform hexagonal 2DPCs having vertical (110) facet sidewalls on 400 nm-pitch masked substrates. We observed vertical growth enhancement as well as the lateral overgrowth suppression for high aspect ratio InGaAs nano-pillar array formation under high growth-rate, long growth-time, and narrow window-opening conditions. We verified infrared emission from the InGaAs nano-pillar array by low-temperature photoluminescence measurement.

This paper describes the formation of poly(methyl methacrylate)- b-poly(dimethylamino ethylmethacrylate)-b-poly(methyl methacrylate) (PMMA-b- PDAEMA-b-PMMA) and poly(methyl acrylate)-b-poly(methyl methacrylate)-b-poly(hydroxyethyl methacrylate) (PMA-b-PMMA- b-PHEMA) brushes and phase segregation by these materials upon exposure to a poor solvent for the outer block. Synthesis of the brushes employs room-temperature atom-transfer radical polymerization from a surface, and formation of multiblock copolymers simply involves changing the monomer solution that surrounds the substrate. Phase segregation by both types of triblock brushes in the presence of a poor solvent for the outer block results in surface domains that are about 50 nm in diameter. Sizes of domains are more uniform with PMMA-b-PDAEMA- b-PMMA than PMA-b-PMMA- b-PHEMA, but this may be specific to the solvent treatments employed for the two polymers. Formation of nanodomains by triblock copolymers appears to be a widespread phenomenon.

It has been long recognized that surface properties are of paramount importance for a broad range of materials and a large variety of devices. The recent development of nanoscience and nanotechnology has opened up novel fundamental and applied frontiers in surface functionalization and characterization. At the nanometre scale, the high surface-to-volume ratio characteristic of most nanomaterials has been demonstrated to have a tremendous influence of many fundamental material properties and device performance. In this paper, we present some of the important issues on the surface functionalization and characterization of polymers and carbon nanotubes for certain biomedical and optoelectronic applications and summarize our recent research activities along this line.

In searching for new and efficient mechanisms for moving or propelling nano-sized objects across a flat surface, we discuss the idea of using the periodically switchable topography of a certain class of polymer substrates. In this paper, we exploit the peculiar properties of diblock-copolymer and mixed brushes that can undergo transitions between very distinct topographical patterns and a flat state. We investigate if, during the transition process, the reshaping of the surface structure, accompanied by a microphase transition, could deliver a sufficient amount of mechanical work to move objects adsorbed on the surface. We show this by following the spatial distribution of an ensemble of silica particles adsorbed on several kinds of poly(methyl methacrylate–b-glycidyl methacrylate) diblock-copolymer brushes, when the surface topography undergoes many periods of the switching process.

The aim of this paper is to describe the possibility of achieving super-hydrophobic materials by tailoring their surface topography. Water droplets easily slip or roll down on such surfaces. However, it is found that microtextures on a solid can generate sticky surfaces as well, and the conditions for avoiding such an effect are discussed.

A dip-pen nanolithography based strategy for fabricating and functionalizing Au nanostructures on a semiconductor substrate is reported. The generation of arrays of nanoscale features functionalized with inorganic nanoparticles and proteins (rabbit IgG) is reported. In the case of rabbit IgG, the bioactivity of the array was demonstrated by monitoring its reaction with fluorophore-labelled anti-rabbit IgG. The methodology reported herein points towards ways of making raised optically active and bioactive nanostructures that could prove useful in stamping methodologies or biosensing applications.

We present a ¹³C labelling method for revealing the growth model of the carbon nanotubes and monitoring the detailed growth process of a multi-walled carbon nanotube (MWNT) array. ¹³C ethylene and ¹²C ethylene are fed into the chemical vapour deposition (CVD) reactor with pre-designed time sequences to growth MWNT arrays with ¹³C–¹²C sections, and the isotope compositions of each section in the nanotubes are detected by a micro-Raman after growth. By relating the positions of the isotope compositions to the corresponding feeding times, we can give obtain a detailed picture of the growth model of the carbon nanotubes as well as of the growth process of the nanotube arrays in CVD.

We present a method for controlled deposition of oriented polymeric nanofibres. The method uses a microfabricated scanned tip as an electrospinning source. The tip is dipped in a polymer solution to gather a droplet as a source material. A voltage applied to the tip causes the formation of a Taylor cone, and at sufficiently high voltages, a polymer jet is extracted from the droplet. By moving the source relative to a surface, acting as a counter-electrode, oriented nanofibres can be deposited and integrated with microfabricated surface structures. For example, we deposited fibres of polyethylene oxide with diameters ranging from 100 to 1800 nm, with the diameter primarily depending on the concentration of the polymeric solution. In addition to the uniform fibre deposition, the scanning tip electrospinning source can produce self-assembled composite fibres of micro-and nanoparticles aligned in a polymeric fibre. We also deposited oriented conductive polymeric fibres of polyaniline and investigated the conductivity of these fibres as components for polymeric nanoelectronics.

The use of recent advances in resonance Raman spectroscopy studies on isolated carbon nanotubes and the scientific knowledge achieved so far from these studies is discussed in the context of advancing carbon nanotube-based technology. Changes in the Raman spectra can be used to probe and monitor structural modifications of the nanotube sidewalls that come from the introduction of defects and the attachment of different chemical species. The former effect can be probed through the analysis of the disorder-induced Raman modes and the latter through the upshifts/downshifts observed in the various Raman modes due to charge transfer effects.

Here we present an alternative, new, unconventional lithographic technique developed to create dense and multilevel nanostructure pattern transfer using a highly accurate polyurethane acrylate (PU, MINS101m, Minuta Tech.) mold and a polyelectrolyte multilayer as the adhesion promotion layer. Specifically, we demonstrate the pattern transfer of periodic 80 nm lines with 400 nm height and complex and multilevel nanostructures to a polymer layer on various substrates, such as Si or SiO₂ wafers, glass and flexible polymer films. This new, unconventional lithographic technique presented here would open the door to a variety of applications in the fields of electronic, optical and biological devices.

We report on the generation of assemblies comprising number density gradients of nanoparticles in two (2D) and three (3D) dimensions. These structures are fabricated by creating a surface-bound organic template which directs the spatial arrangement of gold nanoparticles. The 2D template is made of amine-terminated organosilane with a concentration gradient along the solid substrate. The 3D matrix comprises surface-anchored poly(acryl amide), whose molecular weight changes gradually on the specimen. In both cases, the composite is assembled at low pH, where the positively charged –NH₃⁺ groups within the organic scaffold attract negatively charged gold nanoparticles. We use a battery of experimental tools to determine the number density of particles along the gradient substrate and in the case of 3D structures also their spatial distribution. For 2D gradient assemblies, we show that gold nanoparticle coverage on the surface decreases gradually as the concentration of substrate-bound aminosilane decreases. The number of particles in the polymer brush/particle hybrid is found to increase with increasing polymer molecular weight. We show that for a given grafting density of polymer brush, larger particles predominantly stay near the brush–air interface. In contrast, smaller nanoparticles penetrate deeper into the polymer brush, thus forming a 3D structure. Finally, we discuss possible applications of these nanoparticle gradient assemblies.

Au-nanoclusters between 2 and 8 nm in diameter were deposited onto solid substrates in different pattern geometries. The basis of this approach is the self-assembly of polystyrene-b-poly[2-vinylpyridine (HAuCl₄)] diblock copolymer micelles into uniform monomicellar films on solid supports such as Si-wafers or glass cover slips. HAuCl₄ as metallic precursor or a single solid Au-nanoparticle caused by reduction of the precursor are embedded in the centre of diblock copolymer micelles. Subsequent hydrogen, oxygen or argon gas plasma treatment of the dry film causes deposition of Au-nanoparticles onto the substrate by entire removal of the polymer. The Au-dot patterns resemble the micellar patterns before the plasma treatment. Separation distances between the dots is controlled by the molecular weight of the diblock copolymers. The limitation of the separation distance between individual dots or the pattern geometry is overcome by combining self-assembly of diblock copolymer micelles with pre-structures formed by photo or e-beam lithography. Capillary forces of a retracting liquid film due to solvent evaporation on the pre-structured substrate push micelles in the corners of these defined topographies. A more direct process is demonstrated by applying monomicellar films as negative e-beam resist. Micelles that are irradiated by electrons are chemically modified and can hardly be dissolved from the substrate while non-exposed micelles can be lifted-off by suitable solvents. This process is also feasible on electrical isolating substrates such as glass cover slips if the monomicellar film is coated in addition with a 5 nm thick conductive layer of carbon before e-beam treatment. The application of cylindrical block copolymer micelles also allows for the formation of 4 nm wide lines which can be 1–50 µm long and also be organized in defined aperiodic structures.