Document Actions

Gallery of pictures from 2013

Since a few months transfer systems for the ToF–SIMS (Time of Flight – Secondary Ion Mass Spectrometry, top of the figure) and the ESCA machine (Electron Spectroscopy for Chemical Analysis, bottom of the figure) are in use allowing the transport of samples from a glove box to the respective machines under protective argon atmosphere. Such a transfer system is necessary for the unbiased surface analysis of reactive materials like lithium and sodium, which are used as anode materials in secondary batteries. Moreover, it is useful for experiments which require very clean surfaces, e.g. for UPS (Ultraviolet Photoelectron Spectroscopy) analysis of metal oxide semiconductors. (Picture submitted by Hauke Metelmann)

Due to their high electrical conductivity and their chemical inertness porous gold leafs are powerful cathode materials. Especially in lithium air cells they are a promising alternative to the commonly used carbon electrodes. Porous gold cathodes are synthesized by oxidative dealloying of white gold leafs. The figure shows scanning electron microscope (SEM) pictures of a synthesized gold electrode. (Picture submitted by Benjamin Bergner.)

A typical coin cell comprises of a pair of casings (one distinctly marked with positive sign) and a spacer disc (the spring can be optional). An electrochemical cell is assembled in one casing (negative pole) and the spacers are placed in between the cathode and the other casing (positive pole). Thereafter, the cell is mounted on the suitable die and hydraulically pressed. Furthermore, a hermetically sealed coin cell can be realized for further electrochemical characterization. Similarly, using another pair of specially designed die-plungers the cell can be un-crimped. Electro-active materials collected from such un-crimped cell are intact for further analysis. However coin cell casings cannot be reused. Thus, the ‘Electric crimper machine’ is highly reliable in instant fabrication and post-mortem of an electrochemical cell. (Picture submitted by Birte Jache and Dr. Amrtha Bhide.)

The picture shows the scanning electron microscope image of a microstructured silver electrode on a solid oxygen ion conductor. From left to right the dewetting of the silver electrode is illustrated, starting from a dense film and resulting in isolated particles, as proceeding in air after a few hours at a temperature of 400 °C. The inserts are detail pictures of micro crystallites which have been formed geometrically well-defined shapes on the surface during cooling of the sample. (Picture submitted by Jonas Neumeier.)

The workgroup of Prof. Janek has received a high vacuum chamber for electrochemical mass spectrometry on solid cells (Solid electrochemical mass spectrometry (SEMS)) as a loan from the workgroup of Dr. Wolfgang Harbich (EPFL Lausanne, Switzerland). This set-up provides coupling of electrochemical and mass spectrometric techniques to obtain a deeper insight into the processes of electrochemical solid cells. The left side of the picture shows schematically the core piece of the high vacuum chamber. It consists of a heatable copper reactor in which the electrochemical cell is placed. Reaction gases are fed by capillaries and analyzed by a mass spectrometer equipped with a cylindrical tube (sniffer). By this set-up electrochemical and catalytic processes of platinum and silver electrodes on solid oxygen ion conductors are investigated. The right side of the picture shows the mass spectrometry signal of the oxygen evolution during anodic polarization (I = 10 µA) of a silver electrode at different temperatures. The different characteristics at different temperatures suggesting different mechanisms of oxygen storage and evolution can be clearly seen. (Picture submitted by Christoph Bachmann)

Using vapour deposition methods small deviations of process parameters (substrate temperature, process pressure, etc.) can alter the resulting morphology of the sample significantly. Furthermore, targets used for pulsed laser deposition are exposed to high energy densities and thus can undergo structural changes. The images shown above shall illustrate these aspects. PbTe crystallizes in a rock salt structure. Therefore, trigonal patterns are characteristic of (111)- and quadratic patterns of (200)-crystallite orientation. By modifying the process pressure, different preferred orientations could be realized (independently from the substrate). The scanning electron micrographs (a) and (b) reveal preference of (111)-orientation and (c) of (200)-orientation respectively. Variations of target constitution due to impinging laser beams are exemplarily shown in (d) by a resulting columnar structure of Na0.7CoO2. (Picture submitted by Patrick Schichtel and Christian Schneider)

The pictures show fluorescence microscopic images of human mesenchymal stem cells (hMSCs) after 2 and 24 hours of cultivation. hMSCs are stem cells from human tissue with the ability to differentiate into bone cells. On this picture, green-colored areas indicate the presence of actin (part of the cell wall), red-colored areas the presence of vinculin (component of cell-cell- and cell-matrix connections), yellow-colored areas the focal adhesions (existing cell anchorage and signaling pathways) and blue-colored areas the nucleus. After two hours of cultivation only individual cells are visible, while after 24 hours cell spreading and the formation of anchoring junctions can be seen. The aim of this imaging method is to get a first impression about the cell behavior and viability compared to control samples. Within the “Transregional Collaborative Research Centre 79” implant materials which are able to stimulate bone growth are developed and tested. The hMSCs on this picture were grown on a plasma-oxidized titanium niobium alloy. Implant samples were obtained from the Institute for Complex Materials at the IFW Dresden and plasma treated in the Janek group. All cell experiments were then carried out at the Institute of Physiological Chemistry at the TU Dresden. (Picture submitted by Markus Göttlicher.)

Scanning electron microscopy images of silver sulfide structures: The images show the regular arrangement of approximately 1.5 µm large silver sulfide structures, which were prepared in a cooperation with the group of Prof. Klar in the clean room of the 1. Physical Institute (JLU Giessen). The regular arrangements were fabricated by electron beam lithography followed by thermal evaporation of silver and a thin chromium layer as cover layer. Afterwards, the sample was exposed to a sulfur atmosphere in a furnace at 80 °C. The sulfurization process resulted in the growth of silver sulfide at the free surfaces of the silver squares and lead finally to the formation of the shown silver sulfide network. The aim of the research is to investigate the ionic and electronic conductivity properties of such networks. (Picture submitted by Daniela Schön and Matthias Elm.)

The figure shows ToF-SIMS images of different ion distributions in a human osteoblast-like cell cultured on strontium-enriched calciumphosphate cement. A 3D reconstruction of a depth profile for typical cell signals is shown in the upper image. The z axis is represented by the sputter time. An overlay of the cell signals (red) and the strontium signal (Sr+, green) can be seen in the appropriate cross-sections of the cell in the bottom images. More information can be found here (http://www.biointerphases.com/content/8/1/17/abstract). The newly generated biomaterials were made by our collaboration partner at the Technical University Dresden (group of M. Gelinsky). This project is part of the SFB Transregio 79 whose scientific aim are the development and improvement of new implant materials for the therapeutic use in systemically altered bone. (Picture submitted by Julia Kokesch-Himmelreich.)

In the research group of Professor Janek an infrared spectrometer and thus a new characterization method for battery materials has been established recently. Due to its small size the new device could be installed in a glove box under a protective gas atmosphere which allows the analysis of active materials of cycled batteries without contact to air or humidity. Usually, all samples are measured using the technique of attenuated total reflection. The infrared radiation penetrates a few micrometers into the sample, excites molecular vibration and is attenuated thereby. This wavelength-dependent attenuation is registered at the detector and converted into a spectrum. As an example, spectra of typical battery electrolytes are shown in the figure. While propylene carbonate significantly differs from the three ethers, these show at first glance, not much difference. By using a database, it is possible to distinguish and identify even these three. In the background of the spectra, you can see the device with sample-stage and fixation for solid samples. (Picture submitted by Conrad L. Bender.)

The technical equipment of the working group has been complemented with a lab calender. The calender is a system of at least two rollers for compressing and smoothing electrodes. Calendering is already being applied as a standard procedure in battery manufacturing to improve energy and power densities as well as mechanical, physical and electrochemical properties of electrode materials. The figure shows the calender with two heatable rollers and SEM images of a calendered and a non-calendered CuO electrode. Compressing the electrode with a pressure of about 1300 bar reduces the volume and the porosity. By doing so, the density increases and the conductivity and connectivity between the active material, additives and the current collector improve with the result that the cycle life is prolonged. The calender runs with an operating gas pressure of 2 bar to 8.25 bar. Furthermore, the rollers can be heated up to 120 °C and rotated with a velocity up to 8.3 rmp. (Picture submitted by Franziska Klein.)

The “solid electrolyte interphase” (SEI) is a growing passivation layer on anodes in lithium ion battery systems. The composition of this lithium ion conducting surface film is experimentally not easy to analyse. An appropriate method for its analytical examination are the electron spectroscopy for chemical analysis (XPS/ESCA) and the secondary ion mass spectrometry (SIMS), for example. In the picture above the XPS depth profiles of a few characteristic elements are shown for a lithium foil, which was stored in a 1 M LiTFSI (Lithium Bis(Trifluoromethansulfonyl)Imide) solution in DOL (1,3-Dioxolane) for 24 h. Extracting the binding energies from the XPS spectra we can establish a model of the SEI layer structure (lower part of the picture). As a main part of the SEI lithium hydroxide can be identified followed by a lithium fluoride layer. In direct contact with the electrolyte, we find organic compounds consisting mainly of alkoxides, carbonates, and carbides. (Picture submitted by Carsten Fiedler.)