A Novel Method of Mounting Microsamples for Manipulation and Analysis

Johnson, Diane; Landsberg, Peter and Grady, Monica (2017). A Novel Method of Mounting Microsamples for Manipulation and Analysis. In: Lunar and Planetary Science Conference 2017, 20-24 Mar 2017, The Woodlands, TX.

URL: http://www.hou.usra.edu/meetings/lpsc2017/pdf/2693...


The micromanipulation and mounting of micron-sized grains is a specialist skill that re-quires training and patience. Over the years, as new instrumentation has enabled analysis of ever smaller particles, it has been recognised that there is a need to develop new and different methods for the manipulation of individual grains, methods that are keyed specifically to the types of analyses that are to be carried out.
Methods frequently used to manipulate micron-sized grains include use of electrostatic forces to keep the sample in position, mounting in epoxy resin or glue or crushing of the sample into a soft metallic substrate, but all have their drawbacks. Electrostatic forces are useful to transfer very small grains for short times, for example from one glass slide to another within a clean bench. Electrostatic forces lack precision and stability, and cannot be used as a stand-alone technique, for ex-ample if sample transfer to other facilities is needed. Samples > 30 μm in diameter are also too heavy to rely on electrostatic attraction to ‘stick’ to a needle.
Epoxy resin or glue is a universally-recognised and ideal technique for mounting of samples that require polishing for quantitative analysis. Unfortunately, though, three dimensional context is lost, as is information about any material adhering to the outside of the grain. Even more problematic, though, are the levels of contamination, especially organic contamination, associated with resin. It is practically impossible to re-move all the resin from a mounted sample, so once mounted, the grain is not really suitable for trace-level studies of organic material.
If a sample is crushed into a substrate, such as indium, three-dimensional information is again lost and organic contamination levels increased. Of course, these techniques are essential for, e.g., SIMS analysis, and for spectroscopy studies if indigenous organic molecules are not the focus of the work. All of these traditional methods will invariably physically damage or contaminate small samples; if the sample is to be studied by others at a later date, then these issues are significant and undesirable.
Few, if any, modern studies have been performed specifically to develop and assess success of mounting and manipulation methods of these very small but precious materials. Yet with the forthcoming return of samples from the Hayabusa 2 and Osiris-Rex missions, as well as from missions to the Moon and Mars, a new grain handling technique may be required to enable the most science-rich analyses of the returned materials to be performed. Our study aims to mount a silicate mineral test grain of 50 – 80 μm diameter to enable the sample to be analysed by several methods, such as SEM, Raman spectroscopy and micro X-ray CT, with-out requiring separate mounts for each technique. Our method uses liquid sulfur as an adhesive, which has been used as an encasing medium for IDPs [1].

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