Peter Lipowsky

Laminates of zinc oxide and poly(amino acid) layers with enhanced mechanical performance

In order to improve the resistance of solution-derived zinc oxide thin films against mechanical stress, nanostructured composite systems of soft organic and brittle ZnO layers were prepared by a bio-inspired process. As the organic component, polyelectrolyte multilayers were prepared by dip-coating using polystyrene sulfonate and poly(amino acids). The organic–inorganic laminates have typical properties in common with nacre: they consist of nanocrystals in a matrix of biomolecules, they exhibit a texture and they proved to be harder than the monolithic mineral.

Zinc oxide microcapsules obtained via a bio-inspired approach

Hollow zinc oxide microcapsules have been synthesized by a sacrificial template route involving the chemical bath deposition of nanostructured zinc oxide thin films on sulfonate-modified polystyrene microspheres and subsequent removal of the polymer core by dissolution in a solvent or by thermolysis. Scanning electron micrographs show that uniform coating of the templates is achieved when ZnO is deposited from a solution containing zinc acetate, the polymer polyvinylpyrrolidone, and a base in methanol, and that the ZnO shells remain intact after removal of the cores. A focused ion beam is used to cut slices from the spheres and demonstrate their inner morphology and hollowness. X-ray diffraction yields evidence that the shells consist of nanocrystalline ZnO with the zincite structure.

Aqueous solution deposition of indium hydroxide and indium oxide columnar type thin films

Abstract Crystalline In(OH)3 and UV-emitting In2O3 thin films with a unique columnar morphology have been successfully prepared for the first time via a simple aqueous solution deposition method. In the present study, sulfonate-terminated self-assembled monolayers on single-crystal Si wafers were used as substrates for the film deposition. Uniform In(OH)3 thin films formed on self-assembled monolayers in aqueous solutions of InCl3.4H2O at 60°C. These films, containing columnar In(OH)3 crystals, showed preferential growth orientation along the [100] direction. The current understanding of the film formation mechanism was discussed. After annealing in air at 400°C, these films were converted to nanocrystalline In2O3 films without modification of the morphology. Photoluminescence emission from In2O3 films was reported at approximately 3.4eV, which was ascribed to the near-band-edge emission.

Thin film formation by oriented attachment of polymer-capped nanocrystalline ZnO

Abstract Chemical bath deposition has been introduced as a means to produce films of inorganic substances with low engineering expenditure and close to ambient temperature. Organic additives have been used to control the growth of zinc oxide particles in solution and prevent the formation of the typical rod-like morphology. In the present work an attempt is made to combine these two approaches in order to produce thin films of zinc oxide. In the presence of β-cyclodextrin, spherical nano-crystalline deposits were obtained from solution; polyethylene glycol induced the formation of nano-structured thin films. With polyvinylpyrrolidone as an additive, uniform films were deposited. The structure of these films was analyzed by X-ray diffraction and transmission electron microscopy, which revealed the presence of domains of locally oriented nanocrystals. A mechanism of oriented attachment is proposed to explain the formation of domained ZnO films.

Bio-inspired evolution of zinc oxide-based materials directed by amino acids and peptides

Within this paper the suitability of amino acids and dipeptides as structure-directing agents is discussed. According to that bio-inspired approach these biomolecules were investigated with respect to the evolution of zinc oxide-based architectures. Those small molecules are able to trigger the morphology of these materials ranging from grain-like via two up to three dimensional features. Besides morphological aspects the structural characterization of these solids by means of electron and atomic force microscopy as well as by photoelectron spectroscopy and X-ray diffraction are discussed in order to extract the function of the biomolecules with regard to the formation of the inorganic phases.

Nacre-like TiO2- and ZnO-based organic/inorganic hybrid systems

A bioinspired approach combining chemical bath deposition (CVD) of oxides with layer-by-layer (LBL) assembly of organic polymers has been used to prepare two different types of organic/inorganic multilayer composite films, whose morphology resembles that of naturally occurring nacre. Both process steps allow for a precise control of the layer thickness, thus enabling to tailor the architecture of the multilayer composites. The first type of composite films comprised of TiO 2 layers, separated by organic interlayer composed of several oppositely charged polyelectrolytes, while the second type of composite films contained ZnO as the inorganic and poly (amino acids) as the organic component. AFM investigations revealed a granular structure of the inorganic layers which originates from the oxide particles. TEM investigation disclosed that the TiO 2 particles are amorphous, while the ZnO particles are crystalline. Moreover, TEM cross-sectional analysis of the composite films confirmed the presence of inorganic layers that are well-separated by organic layers, although signatures of partial interpenetration have been observed at the interfaces. The hardness and Youngs modulus of both types of composite films, as determined by nanoindentation testing, increased in comparison to the monolithic oxide films. The enhanced mechanical performance underlines the effectiveness of combining layers of different shear moduli into an alternate architecture.