Combining FIB milling and conventional Argon ion milling techniques to prepare high-quality site-specific TEM samples for quantitative EELS analysis of oxygen in molten iron

Summary This paper reports a procedure to combine the focused ion beam micro-sampling method with conventional Ar-milling to prepare high-quality site-specific transmission electron microscopy cross-section samples. The advantage is to enable chemical and structural evaluations of oxygen dissolved in a molten iron sample to be made after quenching and recovery from high-pressure experiments in a laser-heated diamond anvil cell. The evaluations were performed by using electron energy-loss spectroscopy and high-resolution transmission electron microscopy. The high signal to noise ratios of electron energy-loss spectroscopy core-loss spectra from the transmission electron microscopy thin foil, re-thinned down to 40 nm in thickness by conventional Argon ion milling, provided us with oxygen quantitative analyses of the quenched molten iron phase. In addition, we could obtain lattice-fringe images using high-resolution transmission electron microscopy. The electron energy-loss spectroscopy analysis of oxygen in Fe_0.94O has been carried out with a relative accuracy of 2%, using an analytical procedure proposed for foils thinner than 80 nm. Oxygen K-edge energy-loss near-edge structure also allows us to identify the specific phase that results from quenching and its electronic structure by the technique of fingerprinting of the spectrum with reference spectra in the Fe-O system.