Biomedical subjects

Bernhard Schaffer

Publications and source records attributed to Bernhard Schaffer.

4 recordsLinked to original sources

PubMed2004

Cross-section analysis of organic light-emitting diodes.

The 'lift-out' technique using a focused ion beam microscope was applied to prepare cross-sectional specimens of organic light-emitting diodes for use in transmission electron microscopy. The focused ion beam equally thins the organic/inorganic hybrid devices despite the difference in material hardness of the compounds. This allowed to overcome preparation difficulties of conventional techniques such as ion thinning or ultra-microtomy. Two different samples were prepared and studied by both conventional transmission electron microscopy and analytical electron microscopy to display some of the investigation possibilities which become available with this sample preparation method.

Aluminum↗

PubMed2004

Automated spatial drift correction for EFTEM image series.

Energy filtering transmission electron microscopy (EFTEM) is a widely used technique in many areas of scientific research. Image contrast in energy-filtered images arises from specific scattering events such as the ionization of atoms. By combining a set of two or more images, relative sample thickness maps or elemental distribution maps can be easily created. It is also possible to acquire a whole series of energy-filtered images to do more complex data analysis. However, whenever several images are combined to extract certain information, problems are introduced due to sample drift between the exposures. In order to obtain artifact-free information, this spatial drift has to be taken care of. Manual alignment by overlaying and shifting the images to find the best overlap is usually very accurate but extremely time consuming for larger data sets. When large amounts of images are recorded in an EFTEM series, manual correction is no longer a reasonable option. Hence, automatic routines have been developed that are mostly based on the cross-correlation algorithm. Existing routines, however, sometimes fail and again make time consuming manual adjustments necessary. In this paper we describe a new approach to the drift correction problem by incorporating a statistical treatment of the data and we present our statistically determined spatial drift (SDSD) correction program. We show its improved performance by applying it to a typical EFTEM series data block.

Algorithms↗

PubMed2003

Energy-filtering TEM at high magnification: spatial resolution and detection limits.

Energy-filtering TEM (EFTEM) has turned out to be a very efficient and rapid tool for the chemical characterization of a specimen on a nanometer and even subnanometer length scale. Especially, the detection and measurement of very thin layers has become a great application of this technique in many materials science fields, e.g. semiconductors and hard disk technology. There, the reliability of compositional profiles is an important issue. However, the experimentally obtainable spatial resolution strongly influences the appearance of a thin layer in an EFTEM image, when dimensions reach subnanometer levels, which mainly leads to a broadening of the layer in the image. This fact has to be taken into account, when measuring the thickness of such a thin layer. Additionally, the convolution decreases contrast which makes the layer less visible in the image and finally determines the detection limit. In this work we present a systematic study on specifically designed Mn/PdMn multilayer test specimens to explore the practical aspects of spatial resolution and detection limits in EFTEM. Although specific to the ionization edges used, we will present general conclusions about the practical limitations in terms of EFTEM spatial resolution. Additionally, work will be shown about low energy-loss imaging of thin oxide layers, where delocalization is the main factor responsible for broadening.

Journal Article↗

PubMed2003

Width determination of SiO2-films in Si-based devices using low-loss EFTEM: image contrast as a function of sample thickness.

Energy filtering transmission electron microscopy (EFTEM) has become one of the most efficient tools for specimen characterization at nanometer length scales. EFTEM imaging is most often carried out in the core-loss region but image intensity becomes more and more a limiting factor with decreasing feature size. Alternatively, it is possible to record EFTEM images in the low-loss region, where intensities are essentially higher and where in many cases the images contain material specific contrasts. In this paper we investigate the influence of the important parameters on the material contrast between silicon and silicon dioxide, e.g. specimen thickness, specimen orientation, energy-loss and energy selecting slit width. We show that sample thickness plays an important role and present two methods to calculate material contrast as a function of energy-loss and sample thicknesses. The first method uses spectra taken from both materials at different sample thickness by electron energy-loss spectroscopy, the second calculates contrast directly from a series of energy filtered images. From the results we determine the ideal acquisition parameters for the Si/SiO(2) system and demonstrate imaging at sufficient resolution below 2nm with a test sample of thin SiO(2) layers on Si.

Journal Article↗