Aberration correction and its automatic control in scanning electron microscopes

An automatic aberration correction method has been implemented in scanning electron microscopes (SEM). Necessity of the automatic aberration correction is discussed. The procedure of the automatic aberration correction is explained in detail, where deconvolution techniques are used in order to extract probe information from SEM images. Due to the precise digitization and the usage of proper combinations of correction fields, linearity has been found between the amplitude of each aberration and the corresponding field strength. Experimental results are shown which demonstrate that the aberrations are corrected automatically by a linear feedback control method. After the automatic aberration correction, the image quality has been improved drastically.     

Confinement of the field electron emission to atomic sites on ultra sharp tips

The spatially controlled field assisted etching method for sharpening metallic tips, in a field ion microscope (FIM), is used to study the evolution of the field emission when the tip apex radius is decreased below 1 nm. Unlike the conventional image formation in a field emission microscope (FEM), we demonstrate that at this scale the field emission is rather confined to atomic sites. A single atom apex fabricated at the end of such tips exhibits an outstanding brightness compared to other atomic tips. The measurements have been repeated for two double atom tips, with different atom-atom separations, and images of atomic field emission localization have also been obtained. We have found that the field emission intensity alternates between adjacent atoms when the applied voltage is gradually increased beyond a threshold value.     

Influence of the Particle Morphology on the Activity of Nanometer Platinum Aerosol Catalysts

For nanoparticle agglomerates, the catalytic activity may depend strongly on their structure. The influence of different parameters such as agglomerate structure, primary particle temperature history and surface preconditioning on the catalytic activity of nanoparticles was investigated. The fraction of agglomerate surface contributing to the reaction depends on the agglomerate structure and on the velocity of the reaction under investigation. For extremely fast reactions such as the oxidation of hydrogen on Pt nanoparticles, only the outermost surface (exposed surface) contributes substantially to the formation of water. For the system investigated here, the inner surface not substantially contributing to the reaction accounted for at least 70% of the total particle surface as determined from oxygen presaturation experiments of the agglomerate surface. A considerable activity loss of the platinum particles was observed on preheating the nanoparticle agglomerates. The preheating leads to an increase in the nanoparticle size by an order of magnitude due to sintering. It is unclear if this activity reduction is due to changes in the particle surface state or to a real size effect of the nanoparticles.     

Lower bounds on the localisation length of balanced random quantum walks

Letters in Mathematical Physics - We consider the dynamical properties of Quantum Walks defined on the d-dimensional cubic lattice, or the homogeneous tree of coordination number 2d, with...     

Untersuchungen von Mischvorgängen bei der Herstellung technischer Kohleprodukte unter Anwendung der Methode der radioaktiven Markierung

Es werden die Ergebnisse von Mischverfahren für Kohlepulver, Pech und andere Komponenten mitgeteilt, die unter Markierungen mit ²⁴Na-Benzoat im Laboratorium (Mischvolumen etwa 1 Liter) und im Betrieb (Mischvolumen etwa 100 Liter) durchgführt wurden. Die Experimente dienten dem Vergleich der Vergleich der Wirksamkeit verschiedener Mischmaschinen, der Ermittlung optimaler Mischzeiten und der Bestimmung des Verhaltens einzelner Komponenten beim Mischprozeβ. Dis mittels Szintillationszählung gewonnenen Meβwerte werden dabei mit einem Ergebnisdrucker registriert und mit Hilfa einer Rechenanlage mathematisch ausfewertet.     

Fano blockade by a bose-einstein condensate in an optical lattice

We study the transport of atoms across a localized Bose-Einstein condensate in a one-dimensional optical lattice. For atoms scattering off the condensate, we predict total reflection as well as full transmission for certain parameter values on the basis of an exactly solvable model. The findings of analytical and numerical calculations are interpreted by a tunable Fano-like resonance and may lead to interesting applications for blocking and filtering atom beams.     

High-order harmonic generation enhanced by XUV light

The combination of high-order harmonic generation (HHG) with resonant XUV excitation of a core electron into the transient valence vacancy that is created in the course of the HHG process is investigated theoretically. In this setup, the first electron performs a HHG three-step process, whereas the second electron Rabi flops between the core and the valence vacancy. The modified HHG spectrum due to recombination with the valence and the core is determined and analyzed for krypton on the 3d→4p resonance in the ion. We assume an 800?nm laser with an intensity of about 10(14)?W/cm2 and XUV radiation from the Free Electron Laser in Hamburg (FLASH) with an intensity in the range 10(13)-10(16)W cm2. Our prediction opens perspectives for nonlinear XUV physics, attosecond x rays, and HHG-based spectroscopy involving core orbitals.     

Utilizing inverse micelles to synthesize calcium phosphate nanoparticles as nano-carriers

The aim of this study was to investigate the feasibility of the inverse micelles (IM) technique in producing protein-loaded calcium phosphate nanoparticles (CaP NPs), and to compare this technique with the conventional co-precipitation (co-ppt) technique. In this study, bovine serum albumin and lysozyme were used as model proteins. The results show that CaP NPs produced by IM were shown to be spherical and homogenous in size of ~50 nm. Protein loading efficiency of the IM technique was shown to be much higher than CaP NPs synthesized through co-ppt technique. X-ray photoelectron spectroscopy shows that proteins were not adsorbed onto the surface of IM-synthesized CaP NPs, which suggested that the proteins were entrapped within the particle matrix. Release studies show that protein release was more rapid at lower pH conditions (pH 5 and 6) than at physiological pH of 7.4. A burst release was observed for co-ppt CaP NPs, while a continuous release of protein was observed for IM-produced CaP NPs. This study shows the superiority of the IM technique in preparing pH responsive CaP NPs as nano-carriers.