Robert C. Cieslinski

X-ray microscopy in polymer science: prospects of a ‘new’ imaging technique☆

Abstract A relatively non-invasive imaging technique, which employs highly focused, tunable X-rays, is described. This technique—scanning transmission X-ray microscopy—can be used to investigate the bulk characteristics of polymeric materials with chemical sensitivity at a spatial resolution of about 50nm. We present examples ranging from unoriented multiplase polymers to highly oriented Kevlar fibres. In the case of oriented samples, a dichroism technique is used to determine the orientation of specific chemical bonds. Extension of the technique to investigate surfaces of bulk samples is discussed.

Instrumental requirements for the detection of electron beam-induced object excitations at the single atom level in high-resolution transmission electron microscopy.

This contribution touches on essential requirements for instrument stability and resolution that allows operating advanced electron microscopes at the edge to technological capabilities. They enable the detection of single atoms and their dynamic behavior on a length scale of picometers in real time. It is understood that the observed atom dynamic is intimately linked to the relaxation and thermalization of electron beam-induced sample excitation. Resulting contrast fluctuations are beam current dependent and largely contribute to a contrast mismatch between experiments and theory if not considered. If explored, they open the possibility to study functional behavior of nanocrystals and single molecules at the atomic level in real time.

Real-time cryo-deformation of polypropylene and impact-modified polypropylene in the transmission electron microscope☆

Abstract Dynamic plane-stress failure has been observed directly in the transmission electron microscope as a function of temperature using a commercially available cooling/straining holder in conjunction with a copper deformation cartridge. The low-temperature cooling stage permits studies of the ductile-brittle transition when the transition is between + 23 and − 170°C. A change in deformation mode was observed on the submicrometre level for polypropylene and impact-modified polypropylene. At room temperature, polypropylene and impact-modified polypropylene deform by shear yielding. Below the ductile-brittle transition the polymer chain mobility is curtailed and crazing dominates. The stage allows observation of the deformation at varying temperature, and events occurring during the deformation can be recorded in real time using a CCD camera.

Quantitative Contrast Evaluation of an Industry‐Style Rhodium Nanocatalyst with Single Atom Sensitivity

Aberration‐corrected electron microscopy opens new ways for material characterization. In catalyst research it will enable the observation of single atom arrangements, such as the location of promoter atoms on catalyst particles. However, quantitative procedures must be developed to account for dynamic contrast changes resulting from beam‐sample interactions and incoherent instrument aberrations. We demonstrate that at low acceleration voltage (80 kV), for which knock‐on damage is suppressed, the residual intensity fluctuations can be attributed to the presence of phonons resulting in 3D low frequency atom displacements. For rhodium [110] oriented particles it was found that the catalysts are platelets with an aspect ratio of about 0.2 and a surface roughness of ±1 atom. Observation of single surface atoms requires minimization of phonon‐induced motion.

Electron Tomography of Nanostructured Materials – Towards a Quantitative 3D Analysis with Nanometer Resolution

Electron tomography has developed into a powerful technique to image the 3D structure of complex materials with nanometer resolution. Both, TEM and HAADF-STEM tomography exhibit tremendous possibilities to visualize nanostructured materials for a wide range of applications. Electron tomography is not only a qualitative tool to visualize nano¬structures, but recently electron tomographic results are also exploited to obtain quantitative measurements in 3D. We evaluated the reconstruction and segmentation process for a heterogeneous catalyst and, in particular, tried to assess the reliability and accuracy of the quantification process. Furthermore, a quantitative analysis of electron tomographic results was compared to macroscopic measurements.

Direct Imaging of Rhodium Crystal Surface Structures with Signal Recovery by Low Dose Microscopy

Aberration-corrected TEM as well as the development of monochromators and high brightness guns have advanced transmission electron microscopy to a point where resolution is no longer a limiting process in imaging atomic structures. Instead, beam-sample interactions become increasingly important, particularly for nano-structures and light elements. Recently it was found that phononinduced atom vibrations significantly change the image of a rhodium nano-cluster under electron beam illumination [1]. A characteristic intensity fluctuation could be described by this phenomenon. Following, a low dose phase contrast imaging technique is applied which minimizes beam-sample interactions including phonon-induced atom vibrations and therefore results in more complete data acquisition with improved signal strength.