Knut Urban

Toward atomic-scale bright-field electron tomography for the study of fullerene-like nanostructures.

We present the advancement of electron tomography for three-dimensional structure reconstruction of fullerene-like particles toward atomic-scale resolution. The three-dimensional reconstruction of nested molybdenum disulfide nanooctahedra is achieved by the combination of low voltage operation of the electron microscope with aberration-corrected phase contrast imaging. The method enables the study of defects and irregularities in the three-dimensional structure of individual fullerene-like particles on the scale of 2-3 A. Control over shape, size, and atomic architecture is a key issue in synthesis and design of functional nanoparticles. Transmission electron microscopy (TEM) is the primary technique to characterize materials down to the atomic level, albeit the images are two-dimensional projections of the studied objects. Recent advancements in aberration-corrected TEM have demonstrated single atom sensitivity for light elements at subångström resolution. Yet, the resolution of tomographic schemes for three-dimensional structure reconstruction has not surpassed 1 nm3, preventing it from becoming a powerful tool for characterization in the physical sciences on the atomic scale. Here we demonstrate that negative spherical aberration imaging at low acceleration voltage enables tomography down to the atomic scale at reduced radiation damage. First experimental data on the three-dimensional reconstruction of nested molybdenum disulfide nanooctahedra is presented. The method is applicable to the analysis of the atomic architecture of a wide range of nanostructures where strong electron channeling is absent, in particular to carbon fullerenes and inorganic fullerenes.

High-

Among various discussed ways of explosive detection, the techniques using electromagnetic radiation are considered as having great potential and research activities are recommended in this field. To identify new threats, like liquid explosives, with low rate of false alarms, fast spectral measurements are required in a broad frequency range from microwave to terahertz. We attract attention to a great potential of high-Tc Josephson technology in security applications and present our results in developing high-Tc Josephson junctions for Hilbert spectroscopy and detector arrays.

T_{c}

A study of nitrogen doping of graphene reveals the potential of high-resolution electron microscopy for imaging charge transfer around chemical bonds.

Josephson Square-Law Detectors and Hilbert Spectroscopy for Security Applications

Abstract Electron diffraction patterns, obtained in a high-voltage electron microscope (HVEM), of silicon containing a high density of small pores (diameter ca. 5 nm) produced by anodic etching show an enhancement of high-order Bragg reflections at the expense of low-order Bragg reflections. A theory of this effect is developed based on multiple scattering of Bloch waves at the pores. The theory allows the determination of the volume fraction of the pores from quantitative diffraction data. The results of this analysis are in good agreement with those obtained from HVEM images.

Electron microscopy: The challenges of graphene.

Abstract BaTbO 3 is a pseudocubic perovskite material and is proposed as a new insulating material for high-T c superconductor device applications due to its compatibility with YBa 2 Cu 3 O 7−x . Thin films of BaTbO 3 and SrTbO 3 were grown on (100) oriented SrTiO 3 substrates. the growth morphology of several YBa 2 Cu 3 O 7−x / BaTbO 3 / YBa 2 Cu 3 O 7−x multilayer films was investigated by high-resolution electron microscopy (HREM). We found that a BaTbO 3 layer of 4 nm thickness homogeneously and epitaxially covers a YBa 2 Cu 3 O 7−x bottom layer. The interface between both materials is atomically sharp and clean. The resistivity measured in crossover geometry was typically more than 6 × 10 6 Ωcm below 150 K even for a 20 × 20 μm 2 structure.

Electron diffraction in porous silicon

We have studied a voltage dependence of the response /spl Delta/I(V) of high-T/sub c/ Josephson detector to millimeter-wave radiation as a function of power of incident radiation. YBa/sub 2/Cu/sub 3/O/sub 7-x/ grain-boundary junctions with the resistances R/sub n/=0.5-1.5 Ohm and the I/sub c/R/sub n/-product in the range 0.16-0.25 mV at 80 K have been fabricated for this study. Gunn oscillator with the frequency f=86 GHz and a set of calibrated attenuators with total attenuation of 80 dB have been used for the measurements. The dynamic range, i.e. the range of power of electromagnetic radiation at which the response of the detector is directly proportional to radiation power, was found to be around 40 dB above the noise-equivalent power for frequency-selective response at voltages V near hf/2e and >45 dB for the broadband response at low voltages.

New insulating materials for high-Tc superconductor device applications

This chapter discusses the current state of aberration-corrected transmission electron microscopy (TEM) with an emphasis on atomic-resolution studies in materials science. Atomic-resolution aberration-corrected electron microscopy (EM) provides with new insight into atomic structures at a time when nanophysics and technology urgently need quantitative information on physical phenomena and their structural background. In addition, nanotechnology will benefit from the ability to analyze structures in quantitative detail down to the picometer range. Understanding the information offered by the electron waves about the inner structure of the specimen is a highly nontrivial task. This will be underscored with greater numbers of such ultrahigh-resolution studies within the next few years. These studies also demonstrate the enormous potential of the new electron optics and the wonderful science waiting for us “at the bottom.”