Organic mineral interfaces in soil at the nanometer scale

Objective:

look at organic mineral material interfacing with the soil through a super microscope.

Obstacles:

the likelihood of encountering interfacing with such a small field of view is small (micrometer scale)
prevent changes to the mineral-organic interface like drying or crystalline ice formation
effectively preparing the thin sections of electron-transparency (200nm thick) needed for STEM-EELS.

Study Site and Sample collection:

Cryo-STEM-EELS procedures to show mineral interaction were used on subsoils with high carbon (C) and high iron (Fe) derived from volcanic parent materials (Andisols). Samples collected from Pololu Flow on Kohala, HI by hand in 1m pits.

Cryogenic thin-section prep:

its hard to get High-Res samples of carbon (C), Nitrogen (N), and other light elements using electron microscopy because of the high energy analysis techniques. these elements get damaged. EELS is not sensitive to isotope signatures at core-loss edges. after airdryingit breaks apart on the natural pore space borders, allowing for appropriately sized regions without milling. After transfer the top edge is coated with Platinum (Pt) for further thinning. Stored at room temp.

the thinned soil samples were assessed using an electron dispersive X-ray Spectroscopy. Electron Dispersive X-Ray (EDX) .

Cryogenic STEM-EELS:

Wedge thin-sections were transferred under liquid Nitrogen Gas (N2) and analyzed by a spectrometer.