Wolfgang Hauffe

Lattice constant determination from Kossel patterns observed by CCD camera

The Kossel technique is known due to its precision for lattice constant determination in micro ranges by use of X-ray films. Recently we observed the Kossel interferences also by a CCD camera in a good quality. Thus, the diffraction interferences could be immediately processed and evaluated by computer permitting considerable time saving. In order to obtain the similar accuracy as for measurements with X-ray films further technical and experimental improvements were necessary, especially for a better contrast to observe intersection points of several weak reflections, for evaluating digital patterns, for optimizing of the shortest focus-screen distance and for considering the image field curvature of the objective. As a result, a precision in lattice constant determination could be achieved at a Fe-crystal coming relatively close to the one of comparable X-ray film patterns, which is still about one order of magnitude better for the time being.

New observation method for divergent beam X-ray diffraction patterns

The simultaneous observation of X-ray reflections by a high-quality charge coupled device (CCD) camera in a scanning electron microscope is presented. The possibility of immediate further processing and evaluation of the images by computer, avoiding the extensive photographic X-ray film procedure, is discussed. The divergent beam X-ray method has considerable importance for investigations in materials research. The experimental set-up is described and the advantageous application of the camera is demonstrated for different examples.

Investigation of the three-dimensional microstructure of Cu-Sn(Pb) diffusion zones by means of ion beam sputtering, scanning electron microscopy and lattice source interferences

On model substances of Cu-Sn(Pb) solders it is shown by the combined use of several physical analytical methods that the intermetallic compounds formed during the annealing process have a crystalline structure, which can be observed also three-dimensionally by ion etching. Moreover, grain boundaries as well as phases become visible, and it is possible to determine the crystallographic orientation of the individual crystals in the Cu starting material and in the diffusion zones by means of the Kossel technique. As a result of the investigations, conclusions can be drawn with respect to the diffusion process, especially also to the crystallographic structure of the diffusion zones and the dendritic growth.

Ion Beam Preparation Procedures for Three-dimensional SEM Resolved Kikuchi (EBSD) and Kossel Microdiffraction Analysis of Deformed Metals

The SEM provides information not only on the sample surface and near-surface regions concerning topography, composition, crystal orientation etc. With special preparation techniques the full 3D microstructure can be detected. The deformation-free revealing of the internal structure is not possible with mechanical cutting and grinding. Chemical and electrolytic methods allow only selected material-specific solutions. Ion beam preparation has essential advantages compared with conventional techniques. Especially for mechanically deformed metal samples with small dimensions special ion beam processing steps are required. The well established FIB technology is only useful for very small selected regions with micrometer dimensions. Here the problem will be solved to cut and to investigate samples with cross sections of typically 20 μm x 400 μm and 4 mm length after well defined deformation by microscopy and microdiffraction in the SEM over the full sample volume. The sample shape and size are shown in Fig. 1. After defined tensile tests these samples have been cut longitudinally (cut 1) and transverse (cut 2) by ion beam slope cutting and the macroarea was etched chemically (region 3). The ion beam cutting method [1] was carried out with the Gatan Precision Etching Coating System (PECS) acc. to Fig. 2. The broad ion beam is directed onto the sample mounted under a blind with a sharp edge. The ion gun allows to produce a beam of inert gas or reactive ions with energies up to 10 keV and densities up to 40 μA/mm. The processes can be observed by optical microscopy. A new stage allows sample positioning, tilting and rotation, blind mounting and adjustment with accurate sample transfer into the SEM for the final inspection. Fig. 3 shows a detail of the longitudinal ion beam cut area. In Fig. 4 the ion beam cut area of the full cross section (transversal cut) is shown. The cutting steps were carried out with 7 keV Krypton ions. The texture analysis by EBSD is shown in Fig. 5 for the cuts corresponding to Fig. 1 by Orientation Imaging Microscopy (OIM) maps of a 20 μm thin rolled Cu foil after a tensile test. More detailed discussion of the texture modified by deformation will be given in [2]. Also X-ray Kossel microdiffraction pattern have been detected of a tensile deformed Ni crystal [3]. The Kossel pattern in Fig. 6 shows an example of strong broadening and anisotropic intensity change of reflections due to the deformation process. EBSD provides information on crystallographic orientations, whereas X-ray Kossel microdiffraction pattern allow profound statements of the real microstructure. For both techniques the ion beam procedures are excellent tools to produce cut areas with high accuracy and to combine it very well with additional analysing methods.

Short circuit diffusion in CuSn6/Ni/Au planar tricouples

To investigate processes of short circuit and uphill diffusion, low-temperature diffusion experiments were carried out with sandwich samples of CuSn6/Ni/Au in the kinetic regimeB after Harrison. Two kinds of base material CuSn6 with different grain sizes were chosen. The first material was cold rolled CuSn6 with a mean grain size of 3–4 μm. The second was annealed CuSn6 with a mean grain size of 40 μm. The Ni and Au layers with thicknesses in the μm range were deposited by galvanization. The sheets were prepared by ion beam slope cutting, characterized by scanning electron microscopy and transmission electron microscopy. After annealing at 576 K up to 120 d, the samples were investigated with glow discharge spectroscopy and scanning electron microscopy. Concentration penetration plots made with glow discharge spectroscopy showed a different diffusion behaviour dependent on the CuSn6 material. The diffusion processes in the samples of cold rolled CuSn6 are more extensive than in the annealed CuSn6 samples. To find out causes of this phenomenon, a model of short circuit diffusion was developed and concentration penetration curves were calculated numerically with the finite difference method. Images of an ion beam slope cut sample show grain growth in the Au layer.

Combined use of ion beam slope cutting and scanning electron microscopy for the investigation of the 3-dimensional micro-structure of alterated mediaeval glass

Ion beam slope cutting (IBSC) has been developed as a preparation method for SEM and TEM to avoid the problems which occur using the common mechanical preparation techniques. IBSC has been practised on metals, plastic composites ceramics and alterated mediaeval glass, too. For the investigation of the 3-dimensional microstructure of the glass samples, IBSC has been the only method, which will enable a small cut without destroying the valuable cultural heritage. By SEM investigations of the ion beam cut, the alteration process of mediaeval glass has been observed starting on the surface and spreading into deeper zones of glass. Vertical and lateral cracks are only developing and spreading in the surroundings of crater erosions. The cracks cause splitting of parts near the surface of glass. Inside the cracks, harmful atmospheric gases, like SO2 and CO2, are reacting with the main glass components to alterations salts, which will build up a white and black crust on the surface and in zones near the surface.

Local damage of HT-materials by laser irradiation in the SEM

By using a pulsed Nd:YAG laser the high temperature materials zirconium oxide, fine grain graphite and silicon nitride were rapidly irradiated (heating thermal shock) and their damage behavior was investigated. The laser beam parameters at sample surface were detected by a laser beam analyzing system and correlated with the local damage mechanisms of the materials as erosion, crack formation and solid-solid phase transformation. For the investigations image analysis, localized x-ray analysis, and the ion beam slope cutting technique were applied. The temperature field in the material was simulated by using temperature dependent material parameters for different laser beam parameters. The results illustrate both the strong influence of the temporal and spatial laser energy profile and the materials properties to the material damage.