A technique for the examination of polar ice using the scanning electron microscope
ABSTRACT The microstructure and location of impurities in polar ice are of great relevance to ice core studies. We describe a reliable method to examine ice in the scanning electron microscope (SEM). Specimens were cut in a cold room and could have their surfaces altered by sublimation either before (pre-etching) or after (etching) introduction to the cryo-chamber of the SEM. Pre-etching was used to smooth surfaces, whilst etching stripped away layers from the specimen surface, aiding the location of particles in situ, and allowing embedded structures to be revealed. X-ray analysis was used to determine the composition of localized impurities, which in some cases had been concentrated on the surface by etching. Examining uncoated surfaces was found to be advantageous and did not detract from qualitative X-ray analysis. Imaging uncoated was performed at low accelerating voltages and probe currents to avoid problems of surface charging.
[Show abstract] [Hide abstract]
ABSTRACT: Observation of a uranyl-salt brine layer on the ice surface using back-scattered electron detection and ice surface morphology using secondary-electron detection under equilibrium conditions was facilitated by using an environmental scanning electron microscope (ESEM) at temperatures above 250 K and pressures of hundreds of Pa. The micrographs of a brine layer over ice grains prepared by either slow or shock freezing provided a complementary picture of the contaminated ice grain boundaries. Fluorescence spectroscopy of the uranyl ions in the brine layer confirmed that the species exists predominately in the solvated state under experimental conditions of ESEM.Langmuir 04/2014; 30(19). DOI:10.1021/la500334e · 4.38 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: For many years, the microstructural characterization of ice and firn has used optical microscopy often involving observation of thin sections between crossed polarizers. However, such an approach, in addition to being of low resolution, does not provide complete information on the microstructure. In previous work (Obbard et al. 2003), we have shown how scanning electron microscopy coupled with X-ray microanalysis can be used to determine the microstructural location of impurities in ice cores. In this paper, we outline the use of scanning electron microscopy-based techniques to determine the 3-D orientation of grains and, thus, enable more complete analysis of the orientation relationships between grains in ice and firn. In addition, we show how scanning electron microscopy can be used to determine the internal surface area, porosity and grain size in firn.
Article: Making EBSD on water ice routine[Show abstract] [Hide abstract]
ABSTRACT: Electron backscatter diffraction (EBSD) on ice is a decade old. We have built upon previous work to select and develop methods of sample preparation and analysis that give >90% success rate in obtaining high-quality EBSD maps, for the whole surface area (potentially) of low porosity (<15%) water ice samples, including very fine-grained (<10 μm) and very large (up to 70 mm by 30 mm) samples. We present and explain two new methods of removing frost and providing a damage-free surface for EBSD: pressure cycle sublimation and 'ironing'. In general, the pressure cycle sublimation method is preferred as it is easier, faster and does not generate significant artefacts. We measure the thermal effects of sample preparation, transfer and storage procedures and model the likelihood of these modifying sample microstructures. We show results from laboratory ice samples, with a wide range of microstructures, to illustrate effectiveness and limitations of EBSD on ice and its potential applications. The methods we present can be implemented, with a modest investment, on any scanning electron microscope system with EBSD, a cryostage and a variable pressure capability. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.Journal of Microscopy 04/2015; DOI:10.1111/jmi.12258 · 2.15 Impact Factor