Study of the pore space in mudstones by mercury intrusion porosimetry is a common but indirect technique and it is not clear which part of the pore space is actually filled with mercury. We studied samples from the Opalinus Clay, Boom Clay, Haynesville Shale, and Bossier Shale Formations using Wood's metal injection at 316 MPa, followed by novel ion beam polishing and high-resolution scanning electron microscopy. This method allowed us to analyze at high resolution which parts of a rock are intruded by the liquid alloy at mm to cm scale. Results from the Opalinus Clay and Haynesville Shale show Wood's Metal in cracks, but the majority of the pore space is not filled although mercury intrusion data suggests that this is the case. In the silt-rich Boom Clay sample, the majority of the pore space was filled Wood's metal, with unfilled islands of smaller pores. Bossier Shale shows heterogeneous impregnation with local filling of pores as small as 10 nm. We infer that mercury intrusion data from these samples is partly due to crack filling and compression of the sample. This compaction is caused by effective stress developed by mercury pressure and capillary resistance; it can close small pore throats, prevent injection of the liquid metal, and indicate an apparent porosity. Our results suggest that many published MIP data on mudstones could contain serious artifacts and reliable metal intrusion porosimetry requires a demonstration that the metal has entered the pores, for example by Wood's metal injection, broad ion beam polishing, and scanning electron microscopy.

SummaryThe contribution describes the implementation of a broad ion beam (BIB) polisher into a scanning electron microscope (SEM) functioning at cryogenic temperature (cryo). The whole system (BIB-cryo-SEM) provides a first generation of a novel multibeam electron microscope that combines broad ion beam with cryogenic facilities in a conventional SEM to produce large, high-quality cross-sections (up to 2 mm 2 ) at cryogenic temperature to be imaged at the state-of-the-art SEM resolution. Cryogenic method allows detecting fluids in their natural environment and preserves samples against desiccation and dehydration, which may damage natural microstructures. The investigation of microstructures in the third dimension is enabled by serial cross-sectioning, providing broad ion beam tomography with slices down to 350 nm thick. The functionalities of the BIB-cryo-SEM are demonstrated by the investigation of rock salts (synthetic coarse-grained sodium chloride synthesized from halite-brine mush cold pressed at 150 MPa and 4.5 GPa, and natural rock salt mylonite from a salt glacier at Qom Kuh, central Iran). In addition, results from BIB-cryo-SEM on a gas shale and Boom Clay are also presented to show that the instrument is suitable for a large range of sedimentary rocks. For the first time, g.desbois@ged.rwth-aachen.de pore and grain fabrics of preserved host and reservoir rocks can be investigated at nm-scale range over a representative elementary area. In comparison with the complementary and overlapping performances of the BIB-SEM method with focused ion beam-SEM and X-ray tomography methods, the BIB cross-sectioning enables detailed insights about morphologies of pores at greater resolution than X-ray tomography and allows the production of large representative surfaces suitable for FIB-SEM investigations of a specific representative site within the BIB cross-section.

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Experimental nanotips have shown significant improvement in the resolution performance of a cold field emission scanning electron microscope (SEM). Nanotip electron sources are very sharp electron emitter tips used as a replacement for the conventional tungsten field emission (FE) electron sources. Nanotips offer higher brightness and smaller electron source size. An electron microscope equipped with a nanotip electron gun can provide images with higher spatial resolution and with better signal-to-noise ratio. This could present a considerable advantage over the current SEM electron gun technology if the tips are sufficiently long-lasting and stable for practical use. In this study, an older field-emission critical dimension (CD) SEM was used as an experimental test platform. Substitution of tungsten nanotips for the regular cathodes required modification of the electron gun circuitry and preparation of nanotips that properly fit the electron gun assembly. In addition, this work contains the results of the modeling and theoretical calculation of the electron gun performance for regular and nanotips, the preparation of the SEM including the design and assembly of a measuring system for essential instrument parameters, design and modification of the electron gun control electronics, development of a procedure for tip exchange, and tests of regular emitter, sharp emitter and nanotips. Nanotip fabrication and characterization procedures were also developed. Using a "sharp" tip as an intermediate to the nanotip clearly demonstrated an improvement in the performance of the test SEM. This and the results of the theoretical assessment gave support for the installation of the nanotips as the next step and pointed to potentially even better performance. Images taken with experimental nanotips showed a minimum two-fold improvement in resolution performance than the specification of the test SEM. The stability of the nanotip electron gun was excellent; the tip stayed useful for high-resolution imaging for several hours during many days of tests. The tip lifetime was found to be several months in light use. This paper summarizes the current state of the work and points to future possibilities that will open when electron guns can be designed to take full advantage of the nanotip electron emitters.

Experimental nano-tips have shown significant improvements in the resolution performance of a cold field emission scanning electron microscope. Nano-tip electron sources are very sharp electron emitter tips used as a replacement for the conventional tungsten field emission (FE) electron sources. Nano-tips offer higher brightness and smaller electron source size. An electron microscope equipped with nano-tip electron gun can provide images with higher spatial resolution and with better signalto-noise ratio. This could present a considerable advantage over the current scanning electron microscope (SEM) electron gun technology if the tips are sufficiently long-lasting and stable for practical use. In this study, an older field emission critical dimension (CD) SEM (vintage1998 Hitachi S-6000**) was used as an experimental test platform. Substitution of nano-tips for the regular cathodes required modification of the electron gun circuitry and preparation of nano-tips that properly fit the electron gun assembly. In addition, this work contains the results of the modeling and theoretical calculation of the electron gun performance for regular and nano-tips, the preparation of the SEM including the design and assembly of a measuring system for essential instrument parameters, design and modification of the electron gun control electronics, development of a procedure for tip exchange, and tests of regular emitter, sharp emitter and nano-tips. Nano-tip fabrication and characterization procedures were also developed. Using a "sharp" tip as an intermediate to the nano-tip clearly demonstrated an improvement in the resolution performance of the test SEM, which has a specification of 15 nm attainable resolution. (Figure 1) This and the results of the theoretical assessment gave support for the installation of the nano-tips as the next step and pointed to potentially even better performance. Images taken with experimental nano-tips showed a minimum twofold improvement in resolution performance than the specification of the test SEM (Figure 2). The stability of the nano-tip electron gun was excellent, the tip stayed useful for highresolution imaging for several hours during many days of tests. The tip lifetime was found to be several months in light use. This paper summarizes the current state of the work and points to future possibilities that will open when electron guns can be designed to fully take the advantage of the nano-tip electron emitters. Based on the results it appears feasible that nano-tip gun technology could replace the standard electron source and thus provide increased instrument performance. The result of this work clearly demonstrated that the improvements predicted by the theoretical calculations can actually be achieved in practice. The lifetime and resolution of the nano-tip gun were surprisingly good, which opens the possibility for the development of a new higher-resolution electron gun technology. Continued work is ongoing and it is expected that the next step for the nano-tip will be a test in a more ...