Marianne Reibold

Solvothermal preparation of metallized titania sols for photocatalytic and antimicrobial coatings

The one-pot preparation of metal doped titania sols for coatings with photocatalytic and antimicrobial properties can be realized by using solvothermal conditions in alcoholic solvents at temperatures of 140 °C and above. Under these conditions, hydrolysis of Ti(OR)4 results in photoactive anatase modification while simultaneously added silver or palladium salts will be reduced to colloidal metals. The formation of the nanosized anatase particles is confirmed by wide-angle X-ray scattering (WAXS) and Raman measurements, and the formation of nanosized metal particles of silver and palladium is demonstrated by WAXS and high-resolution transmission electron microscopy (HRTEM). Dynamic light scattering investigations into the particle size of solvothermal TiO2 and Ag sols (compared with their mixtures) suggest that common composite agglomerates are formed due to considerable interactions between the sol particles. After being coated onto viscose fabrics the Ag/TiO2 and Pd/TiO2 composite sols show strong photocatalytic properties. These were determined via decomposition of the organic dye Acid Orange 7, and by antimicrobial effects against gram negative bacteria E. coli even in the dark. Therefore, since no annealing is required to form the photoactive anatase modification, solvothermal sols are well suited to functionalizing less thermally-stable materials such as textiles, polymer foils or paper.

Ferroelectric electron holography

Ferroelectrics are increasingly important as materials in semiconductor technology, e.g. for building non-volatile memory chips. For optimisation of the properties of such devices, there is an urgent need for methods, which analyse the ferroelectric properties at nanometer scale. Furthermore, the basic understanding of the interaction of ferroelectrics with electrons in the transmission electron microscopy is still incomplete. It is shown that electron holography offers a promising way to understand and investigate ferroelectrics in the electron microscope.

Preparation of Silver Nanoparticles Suitable for Textile Finishing Processes to Produce Textiles with Strong Antibacterial Properties against Different Bacteria Types

This study describes the development of a preparation technique for silver nanoparticles useable as antimicrobial material which is especially useful for textile treatment to realize antimicrobial fabrics. The silver particles need to be prepared by reduction of AgNO3 under moderate conditions and with a moderate and non-toxic reductive agent. Comparative investigations were carried out with silver particles prepared by a solvothermal process or with NaBH4 as reductive agent. Particularly, suitable silver solutions are obtained by stabilizing the silver particles with polyvinylpyrollidone PVP of high molecular weight (Mw ~ 360000 gmol−1) and the use of the non-toxic reductive agents ascorbic acid and fructose. Under these conditions the diameters of the silver particles are in the range of 10 to 30 nm as determined by HR-TEM. The formation of elemental silver has been verified by transmission electron microscopy (TEM), X-ray diffraction (XRD) and optical spectroscopy. The properties of silver particle-containing liquids were investigated by using UV/Vis spectroscopy and dynamic light scattering. Further information on particle size and size distribution was gained through SEM investigations. The prepared solutions of silver nanoparticles can be applied easily onto textiles as liquid coating agents. All prepared textile samples exhibited a high antimicrobial activity against Escherichia coli. However, only few solutions containing silver particles of smaller size exhibit high antimicrobial activity also against other types of bacteria such as Staphylococcus aureus and Streptococcus pneumoniae. Because of this high antimicrobial potential gained with silver solutions prepared in a simple process without usage of toxic components, the developed materials offer a broad range of potential applications. Graphical Abstract Preparation of Silver Nanoparticles Suitable for Textile Finishing Processes to Produce Textiles with Strong Antibacterial Properties against Different Bacteria Types

Microstructure of a Damascene sabre after annealing

Abstract X-ray phase analysis combined with high-resolution electron microscopy of samples taken from a genuine Damascus sabre after annealing for 24h at 400°C and 800°C followed by slow cooling down to room temperature has led to a better insight into the nature of cementite nanowires, which have been discovered recently. According to the present study, nanowires remained after 400°C annealing, but disappeared after heat treatment at 800°C and subsequent cooling down. On the other hand, perlitic cementite has been retained qualitatively after the same treatment. Knowing that the exceptional mechanical properties of Damascene blades disappear after annealing, the present results suggest a significant influence of the nanowires upon these features.

Discovery of Nanotubes in Ancient Damascus Steel

Using high-resolution electron microscopy, we have found in a sample of Damascus sabres from the 17th century both cementite nanowires and carbon nanotubes. These might be the missing link between the banding and ancient recipes to make that ultrahigh carbon steel. The sample considered belonged to the wootz-type of Damascus steel which is fundamentally different from welded Damast. The nanotubes have only been revealed after dissolution of the sample in hydrochloric acid. Some remnants showed not yet completely dissolved cementite nanowires, suggesting that these wires were encapsulated by carbon nanotubes. Only recently, considerable progress has been achieved in reproducing the process of making the characteristic pattern of wootz. We propose a connection between impurity segregation, nanotube formation, nanotube filling with cementite, cementite wire growth, and formation of large cementite particles. Needless to say that the presence of a nanostructure will have an impact upon the mechanical properties.

Mechanical properties and structure of a nanoporous sodium borosilicate glass

The nanohardness (H) and microhardness (HM) of sodium borosilicate glasses with and without nanopores were studied. From nanoindentation measurements, along with the hardness H, the Young’s modulus E was derived. While both H and HM varied between ∼10 GPa and ∼7 GPa for the bulk glass, the values for nanoporous specimens were one order of magnitude lower at about 0.5 GPa. The Young’s moduli were found to be ∼82 GPa and ∼5 GPa for bulk and porous glasses, respectively. Cracks and pileups were observed, respectively, arising from microindents and nanoindents in the bulk glass, whereas none of them could be detected in the nanoporous material. The molecular structures of both glasses studied by X-ray diffraction are similar.

Preparation of anionic clathrate-II K24-xGe136 by filling of Ge(cF136)

Abstract Metastable Ge(cF136) with empty clathrate-II crystal structure was successfully used for the preparation of otherwise hardly accessible germanium clathrate phases. On reaction of Ge(cF136) with potassium vapour at 280 °C for 6 days, the new clathrate-II phase K24Ge136 was formed, in which the cages of the germanium framework are completely filled by potassium atoms. The crystal structure of KxGe136 is discussed for different potassium contents (x=0, 8.6, 24).

Evidence of SrO(SrTiO3)n Ruddlesden-Popper Phases by High Resolution Electron Microscopy and Holography

SrTiO3 (STO) is a preferred substrate material for ferroelectric, ferromagnetic or superconducting films. Its special electrical properties strongly depend on deviations from the stoichiometric chemical composition. Due to the reluctance of introducing point defects into the perovskite lattice, a compositional excess of Sr is compensated through the formation of Ruddlesden-Popper Phases (RP) Srn+1TinO3n+1 characterized by insertion of additional SrO planes into the perovskite lattice. These phases belong to a homologous series of so-called crystallographic shear phases [1–3] (Fig.1).

Ruddlesden-Popper Phase Formation in Pb(Zr,Ti)O3 Thin Films

In this work, we give evidences of Ruddlesden-Popper (RP) phase formation in Pb(Zr,Ti)O 3 thin films deposited by multi-target reactive sputtering at a substrate temperature of 520°C onto oxidized silicon wafers comprising a ZrO 2 buffer layer. X-ray diffraction data of films deposited at 520°C revealed the appearance of a Pb 2 (Zr,Ti)O 4 RP phase. High-resolution transmission electron microscopy (HRTEM) images have proved the presence of a corresponding superstructure with a period of about 1.3 nm. It was nucleated on top of an amorphous, lead-enriched interface layer near the ZrO 2 /PZT interface. At higher substrate temperatures, when this amorphous interface layer disappears, a perovskite structure with a sharp interface was nucleated directly on the ZrO 2 buffer layer.

Nanoscratching meets nanoindentation

Abstract A specimen of high-carbon nitrogen-doped steel has been synthesized to supplement previous studies on wootz-like steels. A comparison of different states of material as well as one of distinct methods of hardness testing has been performed. Electron microscopy of the specimens’ microstructure revealed nano-structuring similar to that observed with ancient sabers. Part of them was annealed so that the nano-structures dissolved. Nano-hardness values derived under ambient conditions from indentation as well as from scratch tests were determined and related to the microstructure prior to and after annealing. The disappearance of nanostructuring led to a significant drop of hardness. The ratio of indentation to scratch hardness proved a suitable indicator of hardening. From hardness as function of penetration depth and from friction as function of time and normal load various quantitative features of the mechanical properties and of the deformation process have been evaluated. When modeling friction, sliding and plowing parts have been distinguished quantitatively. Enhanced adhesion forces were attributed to surface layers.