We present the STM investigation of four different oligopyridines at the liquid/highly oriented pyrolytic graphite interface. The heteroaromatic compounds are constitutional isomers showing the same overall shape regardless of their actual conformation. On the basis of weak intermolecular C-H...N hydrogen-bonding interactions, different nanopatterns are formed following a simple general concept for the two dimensional self-assembly. The molecules arrange either in linear or in cyclic structures. Though the oligopyridines are achiral, the formation of prochiral trimeric superstructures leads to chiral phases due to the immobilization on the surface. Some of the molecules show polymorphic structures depending on the solvent. The large variety of the presented structures formed by self-assembly of the different oligopyridines which retain the same functional heteroaromatic backbone shall open the possibility of exploiting these patterns as templates for the nanostructuring of surfaces with guests such as small molecules or metal ions for intriguing applications in, for example, catalysis.

We describe a versatile method to obtain functional hollow nanoreactors with a hydrophilic liquid core. The synthesis of hollow polyurea, polythiourea, and polyurethane nanocapsules was performed by interfacial polycondensation or cross-linking reactions in inverse miniemulsion. The miniemulsions were built upon emulsification of a solution of amines or alcohols in a polar solvent with cyclohexane as the nonpolar continuous phase. The addition of suitable hydrophobic diisocyanate or diisothiocyanate monomers to the continuous phase allows the polycondensation or the cross-linking reactions to occur at the interface of the droplets. The wall thickness of the capsules can be directly tuned by the quantity of the reactants. The nature of the monomers and the continuous phase are the critical factors for the formation of the hollow capsules, which is explained by the interfacial properties of the system. The resulting polymer nanocapsules could be subsequently dispersed in water. The capsules were found to be spherical when formamide was used as the liquid core, whereas elongated capsules were obtained with water. Finally, we used these hollow nanoreactors as a model system for the preparation of silver nanoparticles by reducing silver nitrate solutions encapsulated by the polyurea shell. These syntheses are the first that allow the encapsulation of hydrophilic compounds in miniemulsion in a hollow structure.

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The preparation of nanoparticles in a soap-free system is highly attractive, as surfactants may influence and deteriorate subsequent applications. Thereby, the assembly of solid particles on droplets/particles is well known as Pickering-type stabilization. The resulting hybrid nanocomposites offer in general a rough surface and are highly intriguing for potential drug delivery systems, coating applications, and so forth. This review highlights developments in production and application of Pickering-type nanoparticles synthesized via heterophase polymerization techniques in emulsion, miniemulsion, dispersion, and suspension. We will focus our discussion on systems, wherein stabilization of the final nanometer-sized hybrids is exclusively accomplished via particle stabilizers. In case surfactants are used during preparation, they only serve as pre-treating agents to modify the surface properties of the particle stabilizer, and not being employed for the purpose of droplet/particle stabilization.

A bisterpyridine based molecule, 3,3′-BTP, shows a variety of adlayer structures at the interface between highly oriented pyrolytic graphite (HOPG) and the liquid depending on the concentration in solution. Three closely related linear and one hexagonal 2D patterns are found. Comparison with the self-assembly at the HOPG|gas interface shows that in the absence of the solvent one of the linear and the hexagonal structures can be found. The concentration dependent order of appearance of the different surface structures is rationalized by a thermodynamic model. In the adlayer unit cell, the hexagonal phase offers a central void which is mostly filled with a seventh 3,3′-BTP molecule. In the presence of the solvent, those molecules are presumably rotating, whereas at the HOPG|gas interface no clear rotation can be observed.

Among the many phenomena revealed and provided by nanoscience, the functionalization of a surface by nanopatterning certainly holds promise for a large number of attractive applications. A prominent example is the deposition of self-assembled monolayers by microcontact printing in order to control wettability, adhesion, friction, and wear. [1,2] In this context, the well-known lotus effect should be mentioned. This effect is based on a strong reduction of the adhesion of water droplets by nanopatterning a surface with, for example, dense arrays of statistically distributed nanopillars. [3,4] A further application of such nanopillars is their use as effective electron field emitters, as has been demonstrated for Si, [5,6] a material which is also at the focus of the present work, or, more recently, for diamond. [7] Moreover, highly ordered arrays of nanopillars are extremely helpful for the characterization of individual emitters by scanning tunneling microscopy (STM) or scanning tunneling spectroscopy (STS).For an inverted pattern of nanopillars, that is, ordered arrays of cylindrical nanopores with a high aspect ratio, a similar wealth of possible applications can be thought of. For instance, they can serve as contact holes in semiconductors. According to the present semiconductor technology roadmap, they should exhibit diameters well below 80 nm for the "65 nm node generation".[8] Similarly, applications in nanooptics appear attractive; nanopores based on colloidal masks were fabricated into Si with a diameter of 60 nm. [9] Smaller diameters of the order of 30 nm should be obtainable by nanomachining a poly(methyl methacrylate) PMMA resist with an atomic force microscope and subsequent metal-coating and lift-off, thereby accepting the disadvantage of a nonparallel process. [10] Note that the recently developed technique of controlling the diameter of nanopores in ultrathin Si/SiO 2 membranes by the electron beam of a transmission electron microscope is still a nonparallel procedure.[11] Another approach to preparing nanoholes in Si is based on self-organized porous alumina masks in combination with anisotropic Cl 2 reactiveion etching (RIE). [12] In this way, holes with diameters > 13 nm and an aspect ratio of 3 could be obtained. Similar diameters are obtained by a recently reported technique based on the self-organization of inverse spherical micelles formed from diblock copolymers dissolved in an apolar solvent, such as toluene, and selectively loaded in the micellar core with a metal salt, such as HAuCl 4 .[13-16] By dip-coating such solutions onto practically any sufficiently flat substrate, hexagonally ordered arrays of Au nanodots can be prepared by an ashing process.[17] They can be used as nanomasks in a subsequent anisotropic etching step, resulting in corresponding arrays of nanopillars. In this way, hexagonally ordered pillars with a diameter of 14 nm and an aspect ratio of 5 were obtained in Si. This micellar preparation technique offers a number of impressive advantages, such as the control of the...

The influence of the substrate and the deposition conditions-vapor deposition versus deposition from solution-on the structures formed upon self-assembly of deposited bis(terpyridine) derivative (2,4'-BTP) monolayers on different hexagonal substrates, including highly oriented pyrolytic graphite (HOPG), Au(111), and (111)-oriented Ag thin films, was investigated by high-resolution scanning tunneling microscopy and by model calculations of the intermolecular energies and the lateral corrugation of the substrate-adsorbate interaction. Similar quasi-quadratic network structures with almost the same lattice constants obtained on all substrates are essentially identical to the optimum configuration expected from an optimization of the adlayer structure with C-H...N-type bridging bonds as a structure-determining factor, which underlines a key role of the intermolecular interactions in adlayer order. Slight distortions from the optimum values to form commensurate adlayer structures on the metal substrates and the preferential orientation of the adlayer with respect to the substrate are attributed to the substrate-adsorbate interactions, specifically, the lateral corrugation in the substrate-adsorbate interaction upon lateral displacement and rotation of the adsorbed BTP molecules. The fact that similar adlayer structures are obtained on HOPG under ultrahigh vacuum conditions (solid|gas interface) and on HOPG in trichlorobenzene (solid|liquid interface) indicates that the intermolecular interactions are not severely affected by the solvent.

Polymer blends in nanoparticles have been studied by transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. The TEM studies show that blend particles formed from two immiscible polymers by the miniemulsion process exhibit biphasic morphologies. The fact that no core-shell type but Janus-like structures were found indicates that the surface free energies between both polymers and the solution-water interface (including the surfactant molecules) are similar; therefore, the blend morphology and composition of the individual phases are mainly determined by the interaction between the two polymer components. Both the TEM studies and the PL experiments provide strong evidence that phase separation in these particles strictly follows the Flory-Huggins theory. This highlights the applicability of the nanoparticle approach to fabricate blend systems with well-controllable properties and to study structure-property relationships under well-defined conditions.