FIB Plan View Preparation and Electron Tomography of Ga-Containing Droplets Induced by Melt-Back Etching in Si.

Melt-back etching is an effect that can occur for gallium (Ga) containing III/V semiconductors grown on Si. Since this effect influences interfaces between the two compounds and therefore the physical characteristics of the material composition, it is desirable to understand its driving forces. Therefore, we investigated Ga grown on Si (001) via metal organic chemical vapor deposition using trimethyl Ga as a precursor. As a result of the melt-back etching, Ga-containing droplets formed on the Si surface which reach into the Si wafer. The shape of these structures was analyzed by plan view investigation and cross sectional tomography in a (scanning) transmission electron microscope. For plan view preparation a focused ion beam was used to avoid damage to the Ga-containing structures, which are sensitive to the chemicals normally used during conventional plan view preparation. Combining the results of both investigation methods confirms that the Ga-containing structure within the Si exhibits a pyramid shape with facets along the Si {111} lattice planes.

Investigation of Fluorine and Nitrogen as Anionic Dopants in Nickel-Rich Cathode Materials for Lithium-Ion Batteries.

Advanced lithium-ion batteries are of great interest for consumer electronics and electric vehicle applications; however, they still suffer from drawbacks stemming from cathode active material limitations (e.g., insufficient capacities and capacity fading). One approach for alleviating such limitations and stabilizing the active material structure may be anion doping. In this work, fluorine and nitrogen are investigated as potential dopants in Li1.02(Ni0.8Co0.1Mn0.1)0.98O2 (NCM) as a prototypical nickel-rich cathode active material. Nitrogen doping is achieved by ammonia treatment of NCM in the presence of oxygen, which serves as an unconventional and new approach. The crystal structure was investigated by means of Rietveld and pair distribution function analysis of X-ray diffraction data, which provide very precise information regarding both the average and local structure, respectively. Meanwhile, time-of-flight secondary-ion mass spectroscopy was used to assess the efficacy of dopant incorporation within the NCM structure. Moreover, scanning electron microscopy and scanning transmission electron microscopy were conducted to thoroughly investigate the dopant influences on the NCM morphology. Finally, the electrochemical performance was tested via galvanostatic cycling of half- and full-cells between 0.1 and 2 C. Ultimately, a dopant-dependent modulation of the NCM structure was found to enable the enhancement of the electrochemical performance, thereby opening a route to cathode active material optimization.

Mapping nanomechanical properties of freshly grown, native, interlamellar organic sheets on flat pearl nacre.

We imaged surfaces of freshly grown flat pearl nacre (Haliotis tuberculata) in different stages of growth in seawater using an atomic force microscope (AFM). Characteristic mineral phases of nacre, such as aragonitic stacks of coins, as well as the associated organic sheets, could be detected. Apart from imaging, the acquisition of force volumes on freshly grown organic surface areas on flat pearl nacre was conducted with the AFM. The evaluation of the force volumes with the Hertz-Sneddon model resulted in Young's moduli in the MPa range. The presented values are considerably smaller than values previously determined from macroscopic tensile tests. This might reflect the anisotropy of the organic nacre layers.