ILEEMS: Methodology and Applications to Iron Oxides

Abstract

ILEEMS is the acronym for Integral Low-energy Electron Mössbauer Spectroscopy. In this variant of Mössbauer spectroscopy the low-energy electrons, E < õ15 eV, emitted by the probe nuclei in the absorber are counted as a function of source velocity. As a consequence of their low energy, the detected electrons' origin lies within a very thin surface layer with thickness of a few nanometers and consequently, ILEEMS is a useful technique to examine surfaces of Fecontaining substances. In a first part of this paper the authors briefly describe the design of a homemade ILEEMS equipment allowing the temperature of the investigated sample to be varied between 77 K and room temperature. The second part of this contribution deals with a selection of results obtained from ILEEMS spectra for various Fe oxides. In particular, the following items are covered: (1) surface versus bulk Morin transition in small-particle and near-bulk hematite, aFe 2 O 3 ; (2) bulk and thin-film magnetite, Fe 3 O 4 ; (3) ferrihydrite, 5Fe 2 O 3 I 9H 2 0, goethite, a-FeOOH, and lepidocrocite, g-FeOOH, all to some extent in relation to their morphology. Interesting and intriguing findings concerning the surface properties of these oxides were obtained and it is argued that the results encourage more systematic research in this and related fields using the surfacesensitive ILEEMS technique.

Raman spectroscopy investigation of magnetite nanoparticles in ferrofluids

“…For better analyses, the interaction between surface and core should be examined by studying the system in the pre-oxidized state if possible, which is a very difficult preparative task for such small particles, or to plot a hysteresis loop post field cooling at low temperatures (5 K). Another possibility to clarify if there is a layer with different magnetic anisotropy onto their surface is ILEEMS measurement [30]. Here, the 80 K spectrum is fitted with one sextet.…”

Influence of the borohydride concentration on the composition of the amorphous Fe–B alloy produced by chemical reduction of synthetic, nano-sized iron oxide particles

“…5). ILEEMS is a variant of conventional transmission Mössbauer spectroscopy [22] by which the low-energy electrons are counted. These electrons, with energy of ∼10 eV, are produced by after effects following the decay of the probe nuclei in the absorber.…”

Influence of Si Content on the Surface Magnetic Properties of Fe80SixB20 - xMetallic Glasses (x = 6, 10)

“…57 Fe Mössbauer spectra at room temperature (RT) were taken in scattering geometry by detecting 7.3 keV conversion electrons (CEMS, [3]) with the penetration depth of about 200 nm and by detecting 10 eV low-energy electrons (ILEEMS, [4]) the penetration depth of which is approximately 5-10 nm. Obtained spectra were analyzed using CONFIT program package [5] and calibration of velocity scale was done by a standard thin α-iron foil at RT.…”